Master of Science in Mechanical Engineering September 2020
FEASIBILITY STUDY: THE REDUCTION OF DEFECTIVE
HOLES IN PLASTIC FLOORING
MANUFACTURING
Anton Senbom
This thesis is submitted to the Faculty of Engineering at Blekinge Institute of Technology in partial fulfilment of the requirements for the degree of Master of Science in Mechanical Engineering. The thesis is equivalent to 20 weeks of full time studies.
The authors declare that they are the sole authors of this thesis and that they have not used any sources other than those listed in the bibliography and identified as references. They further declare that they have not submitted this thesis at any other institution to obtain a degree.
Contact Information:
Author(s):
Anton Senbom
E-mail: ansl14@student.bth.se
University advisor:
Lena Prinselaar
Department of Mechanical Engineering
A BSTRACT
Defects are a common phenomenon related to the manufacturing of products in industries and unavoidable to a full degree. Companies can manage or mitigate risks relating to manufacturing through standardization in processes, methods, and quality checks. The quality requirements ensure that a product lives up to the expectation set by the customer to satisfy their needs. Tarkett needs to be flexible to utilize all its capacity efficiently and at the same time decrease the risk of wastes during manufacturing. Many products are manufactured on the same line with various products tied to different material properties. Tarkett has several defects attracted to their products and improved with time through World Class Manufacturing, which means continuous improvements to decrease the number of losses and derives from Lean production.
This thesis investigates and analyzes data related to defective “holes” related to a manufacturing aggregate called 219 at Tarkett’s factory in Ronneby. The purpose is an attempt to learn and suggest possible reasons for the occurrence of holes in their homogeneous PVC-flooring. Methods used to facilitate the investigation are gathered from interviews with personnel, observation, the scientific framework, quality tools, and lab-scale tests linked to chosen products of interest. The framework of this thesis tries to be consistent in how the results are presented and how they tie up between cause and effect.
The results show that the main root-cause seems to be packing density between product granulates that increase the risk of hole formation because of porosity, implying air entrapment in the granulate bed during manufacturing through the feeder (dosage process). This granulate bed transports into a double belt press (DBP) that is a closed system and allows for minimum air escape some meters inside the DBP. The problem is either managed through DBP-parameters depending on the product that follows some set standards. But parameters do often require some configuration after the start of a work order of a product because the product needs can vary.
The conclusion is that the problem should be mitigated because there seems to be hard to implement a straightforward solution to the root cause. Suggested improvements or assessments are to continue to study granulate size and geometry related to the specific granulate extruder die that determines the granulate design set by various product standards. The dosage process and DBP are of most importance together with the recipe and product specifications.
Keywords: Defective, holes, double belt press, PVC-flooring
S AMMANFATTNING
Defekter är ett vanligt fenomen relaterat till tillverkning av produkter i industrier och är oundvikligt i hög grad. Företag kan hantera eller mildra risker relaterade till tillverkning genom standardisering i processer, metoder och kvalitetskontroller. Kvalitetskraven säkerställer att en produkt lever upp till de förväntningar som kunden ställer för att tillgodose dess behov. Tarkett måste vara flexibelt för att utnyttja all sin kapacitet på ett effektivt sätt samtidigt som risken för slöseriet minskar vid tillverkning.
Många produkter tillverkas på samma linje med olika produkter knutna till olika materialegenskaper.
Tarkett har flera defekter som lockas till sina produkter och förbättrats med tiden genom World Class Manufacturing, vilket innebär kontinuerliga förbättringar för att minska antalet förluster och härstammar från Lean-produktion.
Denna avhandling undersöker och analyserar datarelaterade till defekta "hål" relaterade till ett tillverkningsaggregat 219 vid Tarketts fabrik i Ronneby. Syftet är ett försök att lära sig och föreslå möjliga orsaker till hål i deras homogena PVC-golv. Metoder som används för att underlätta utredningen samlas in från intervjuer med personal, observation, den vetenskapliga metoden, kvalitetsverktyg och Lab skalade tester kopplade till utvalda produkter av intresse. Ramen för denna avhandling försöker vara konsekvent i hur resultaten presenteras och hur de binder mellan orsak och verkan.
Resultatet visar att den främsta orsaken verkar vara förpackningstätheten mellan produktgranulat som ökar risken för hålbildning på grund av porositet, vilket innebär att luften fastnar i granulatbädden vid tillverkning genom mataren (doseringsprocess). Denna granulatbädd transporteras till en Bandpress (DBP) som är ett slutet system och möjliggör minimalt luftutsläpp några meter inuti DBP. Problemet hanteras antingen via DBP-parametrar beroende på produkten som följer vissa fastställda standarder.
Men parametrar kräver ofta en viss konfiguration efter att en produkts arbetsorder har börjat eftersom produktbehovet kan variera.
Slutsatsen är att problemet bör mildras eftersom det verkar vara svårt att implementera en enkel lösning på rotorsaken. Föreslagna förbättringar eller bedömningar är att fortsätta att studera granulatstorlek och geometri relaterad till det specifika granulatsträngsprutmunstycket som bestämmer granulatdesignen enligt olika produktstandarder. Doseringsprocessen och DBP är viktigast tillsammans med recept och produktspecifikationer.
Nyckelord: Defekter, hål, bandpress, PVC-golv
A CKNOWLEDGMENTS
I would like to thank Tarkett for letting me conduct my thesis on the Ronneby facilities and especially Tommy Lund-Hansen. Then employees Daniel Pettersson, Thomas Svensson, Staffan Olin, Linus Pettersson and operators at 219 for all the help, guidance and insights throughout the work. Then Cecilia Melin and Qusey Abdelwahab for making it possible for me to conduct my laboratory tests at the R&D department.
Big gratitude to my supervisor Lena Pinselaar at Blekinge Institute of Technologies for all the help with the guidance of the thesis structure and report.
Anton Senbom 2020-10-11
C ONTENTS
ABSTRACT ...III SAMMANFATTNING ... IV ACKNOWLEDGMENTS ... V CONTENTS ... VI LIST OF FIGURES ... VIII LIST OF TABLES ... X TERMINOLOGY ... XI
1. INTRODUCTION ... 0
1.1 BACKGROUND ... 0
1.1.1 Company description ... 0
1.1.2 Problem area ... 0
1.2 PURPOSE AND GOAL ... 1
1.3 RESEARCH QUESTIONS ... 1
1.4 DELIMITATIONS ... 1
2. RELATED WORK ... 3
2.1 GULL WING PROJECT ... 3
2.2 INTERNAL HOLE PROJECTS AT TARKETT ... 3
3. THEORETICAL FRAMEWORK ... 7
3.1 INTRODUCTION TO PLASTICS ... 7
3.1.1 Polyvinyl chloride (PVC) ... 8
3.1.2 Viscosity ... 8
3.1.3 Additives ... 9
3.1.4 Melt flow index (MFI) ... 10
3.1.5 Thermal equilibrium ... 10
3.1.6 Ideal gas law ... 10
3.1.7 HAAKE ... 11
3.1.8 Density measurements of granulates ... 11
3.1.9 Porosity ... 11
3.1.9.1 Thermal conductivity ... 12
3.1.9.2 Packing density ... 13
3.2 MANUFACTURING PROCESSES... 15
3.3 LEAN ... 16
3.3.1 Zero loss thinking ... 16
3.4 QUALITY ... 17
3.4.1 Improvements tools ... 17
3.4.2 Improvement cycle – PDCA ... 19
4. METHOD ... 20
4.1 STUDY PURPOSE... 20
4.2 INVESTIGATION METHOD ... 20
4.3 LITERATURE STUDY ... 21
4.4 DATA COLLECTION ... 21
4.5 LABORATORY EXPERIMENTS ... 21
4.5.1 MFI and HAAKE ... 22
4.5.2 Compression test ... 23
4.6 QUALITY ... 23
4.7 LEAN ... 24
4.7.1 5 why’s and 2 how’s ... 24
4.7.2 5X Why ... 24
4.7.3 Swot-analysis ... 24
5. RESULTS AND ANALYSIS ... 25
5.1 INTERVIEW AND OBSERVATIONS ... 25
5.2 MAPPING OF PROCESS AND PRODUCT FLOW... 25
5.2.1 Master Recipes ... 26
5.2.2 Mixing ... 27
5.2.3 Extruding / GEX... 27
5.2.4 Dosing of plastic granulate bed ... 27
5.2.5 Double belt press ... 29
5.2.6 Coating and embossing... 29
5.2.7 IQ Eminent / IQ Natural / Eclipse Premium / Toro SC... 29
5.3 PROBLEM DEFINITION ... 31
5.4 OVERVIEW OF CAUSES ... 36
5.4.1 Method... 37
5.4.2 Machine ... 37
5.4.3 Material ... 37
5.4.4 Man ... 37
5.4.5 Root causes ... 38
5.5 THEORETICAL AND STATISTICAL ANALYSIS ... 38
5.5.1 Products with frequent problems ... 39
5.5.2 Light versus dark plastic flooring ... 41
5.5.3 Laboratory experiments ... 43
5.6 SUGGESTION ON IMPROVEMENTS OR FURTHER INVESTIGATION ... 45
6. DISCUSSION ... 48
6.1 MAPPING OF PROCESS FLOW ... 48
6.2 PROBLEM DEFINITION ... 48
6.3 OVERVIEW OF CAUSES ... 48
6.4 THEORETICAL AND STATISTICAL ANALYSIS ... 49
6.5 SUGGESTED IMPROVEMENTS AND EXPERIMENTS ... 50
7. CONCLUSION AND FUTURE WORK ... 51
REFERENCES ... 53
L IST OF FIGURES
Figure 1: Several holes displayed by light ... 4
Figure 2: Multicolor products with holes. ... 4
Figure 3: Holes on IQ natural from above and from a cross-section. ... 5
Figure 4: Illustration made by Tarkett to show the size of holes. ... 6
Figure 5: Branched polymer (left) and crosslinked polymer (right) . ... 7
Figure 6: Model over glass transition (Tg) and various material stiffnesses in megapascal (MPa) depending on applied temperature in Kelvin (K) . ... 8
Figure 7: Chemical model of polyvinyl chloride (PVC) . ... 8
Figure 8: Model of MFI equipment . ... 10
Figure 9: Similar machine used in the laboratory at Tarkett to measure torque of the PVC-granulates (x). ... 11
Figure 10: Difference between a high porosity (left) and lower porosity (right). ... 12
Figure 11: Y-axis show porosity and the x-axis show number of fine particles included in percentage of the overall bed of bidispersity spheres . ... 12
Figure 12: Implication of thermal conductivity because of porosity . ... 13
Figure 13: Show how the packing density increases in the y-axis to a maximum at around 30-40% fine particles included of total granular composition. ... 13
Figure 14: packing density of cylinders at different aspect ratios and pressure. In relation to aspect ratio (w) and pressure (τ) . ... 14
Figure 15: Packing density of cubical formed entities with different aspect ratios. ... 14
Figure 16: Model of a double belt press where material enters in the left side and then affected by pressure and temperature to then exit in the right side. ... 16
Figure 17: An example of a Histogram. ... 17
Figure 18: An example of a Pareto chart. ... 18
Figure 19: An example of a fishbone diagram. ... 18
Figure 20: A model of PDCA. ... 19
Figure 21: overview for the scientific method. ... 20
Figure 22: Products IQ Megalit, IQ natural, IQ Eminent displayed at Tarkett Ronneby. ... 25
Figure 23: Process flow of interest in the formation of holes. ... 26
Figure 24: Illustration of the dosage process. ... 27
Figure 25: Illustration of the DBP. ... 29
Figure 26: IQ Eminent / Primo Premium... 30
Figure 27: IQ Natural / Eclipse Premium. ... 30
Figure 28: Toro SC ... 30
Figure 29: Pareto chart for defects aggregate 219 during Q4 2019 to Q1 2020 quarter, where the y-axis shows the amount in kilograms, the red line the total percentage of the defects and the x-axis several defects. ... 31
Figure 30: Defective “holes” located on the surface of a product. ... 34
Figure 31: 4M-analysisor also called fishbone diagram. ... 37
Figure 32: Frequency of reported defective holes by personnel in the y-axis every month for almost three quarters in 2019. ... 38
Figure 33: Frequency of reported defective holes by personnel in the y-axis for four months of 2020. ... 38
Figure 34: Pareto chart to showcase the amount of material that needs to be reworked in kilograms and the percentage of holes at the y-axis for each product group in the x-axis produced from the start of 2019 to 2020-04-23. ... 39
Figure 35: Reported plastic flooring with holes in 𝑚2 during the period 2019 – 2020-06-15. ... 40
Figure 36: Show the percentage of defective holes compared to total production to the right and the flooring in m^2 to the left for the period 2019 – 2020-06-15. ... 41
Figure 37: Defective quantity of plastic flooring in kilograms for respective color group. ... 42
Figure 38: Defective quantity of plastic flooring in kilograms for respective color group. ... 42
Figure 39: Defective quantity of plastic flooring in kilograms for respective color group. ... 42
Figure 41: Parameters 2 sample on Eclipse Contrast from the compression test showcasing holes between granulates. ... 44 Figure 42: Sample made from the compression test with product Primo Premium displaying big and small holes on the surface. ... 45
L IST OF TABLES
Table 1: Compression test parameters. ... 23
Table 2: 5W & 2H. ... 31
Table 3: Show all recipes and related products. ... 39
Table 4: Show products and related granulates size, die and geometry. ... 40
Table 5: Shows laboratory values summarized from the five products investigated... 43
T ERMINOLOGY
Accents – Incorporated with plastic granulates to create a certain design.
Batch – The amount of a product or product processed under a fixed timeframe.
DBP – Double belt press is a manufacturing process.
Eclipse Premium – Name of a Tarkett product.
GEX – Granulate Extruder.
GEX-die – Designed plate that the plastic paste is pressed against to form specific granulate size and geometry.
Gull wings – Defective cavities on the plastic flooring appearing to the out sides of the flooring.
Holes – Defective cavity, void, pocket on the surface of the product.
HAAKE – Lab-scale method to measure torque in plastic materials.
HYDRA – Documentation program to access historical manufacturing data.
IQ Eminent – Name of a Tarkett product.
IQ Natural – Name of a Tarkett product.
MFI – Mass flow index.
Master / main recipe – Several products have the same recipe and only differ in granular size, geometry and included accents.
PVC – Polyvinyl chloride.
Quality – Deliver a product according to customers standard of expectation.
Recipe – Every ingredient involved in making a certain product.
Tg – Glass transition Tm – melt transition
Toro SC – Name of a Tarkett product.
Viscosity – Friction of fluids, parameter of how easily a medium flow.
1. I NTRODUCTION
This chapter introduces the company and the problem
1.1 Background
1.1.1 Company description
Tarkett group is an international company with 140 years of experience in flooring solutions for various customers in both the private and public sectors, with owners and headquarters located in France.
The product portfolio contains vinyl, wood, laminate, artificial grass, running tracks, and more. There are sales in over 100 countries and amount to 1.3 million square meters of floor sold every day. The company has around 13,000 employees worldwide with two factories available in Sweden, which consists of the facilities in Ronneby and Hanaskog. Ronneby emphasizes on homogenous plastic flooring consisting of one layer, then research, and distribution while Hanaskog has wooden floors in their disposal. Worldwide Tarkett manufactures flooring to vastly different demands depending on situations that constitute ordinary floors to hospitals and other institutions that can divert electricity.
Tarkett´s three main pillars that are strived by employees involve security, quality, and production capacity [1], [2].
At Tarkett Ronneby, there are three main areas which are the south factory, Fornanas, and a department for logistics. The south area factory consists of offices for management personnel at the Ronneby factory, manufacturing lines of homogeneous flooring, maintenance areas, and temporary storage areas.
A logistics building is located across the street and handles the logistics with the final rolls of the product that will reach the customer. Fornanas acts as a headquarters for the R&D department with an in-house lab where experiments are managed. It acts as a big storage facility for materials and products, the facility has historically been a space for when Tarkett had floor manufacturing with several lines [3].
1.1.2 Problem area
Tarkett manufacture and offers a broad portfolio of innovative products related to flooring for their customers through the ability to be flexible. Products have both engaging and characteristic patterns with several color choices based on personal preference. This form of flexibility in the process requires compensation to be able to handle vastly different sizes or geometry of raw materials, with different ingredient definitions in an adequate manner of quality. The customers have different preferences of design and desire specific products which only can be manufactured due to required material properties, which in turn produce the desired surface design patterns. Tarkett´s manufacturing can be described as a “jack of all trades” meaning that it is not constructed optimally for any given product composition and scenario related to a recipe or granulate compositions. It facilitates the production of many products on the same manufacturing line and suggests effective usage of space that can be modified, to give the customer what it requests in terms of their needs.
Tarkett has problems in connection to their production when plastic granulates are processed into a homogenous PVC-floor. These problems are called defects and are undesirable by the customer which can affect the function or aesthetics of the product. Tarkett’s priority is to deliver products on time to customers or else for example the order may be canceled, due to better alternatives from competitors being able to deliver the desired quantity on time. This is linked to one key pillar which is the capacity output from manufacturing. The delivered products need to hold a reasonable standard linked to quality that prevents the customer from complaining which in turn converts to “bad will” for Tarkett, implying a damaged reputation. The ability to decrease defects in manufacturing are therefore correlated to the success of the company regarding the possibility to save both money and energy on rework to live up to the wanted quality to deliver the product just in time to the customer. It exists many defects within for example color and pattern faults, holes, coating, stripes, packing and grinding. This thesis will focus on one of the common defects that have been occurring for the last 25 years, it is called
“holes” and looks like small unmolded pockets or cavities on the surface of a plastic floor.
This problem exists in the manufacturing of plastic floors at more than one manufacturing line, but this work focuses has solely on a line called 219 which is the biggest line at the factory in Ronneby.
Aggregate 219 have had problems concerning the occurrence of defective holes in plastic floors than other lines that use a calendaring process. Aggregate 219 has a pressing process to form the product rather than calendaring process in the other lines. This defect has existed since the inception of the installation of the double belt press at line 219 in 1995. These small holes in the floor make the product insufficient for customers and are therefore labeled as “waste”, it means that it will be reused through recycling and added to the following PVC-batches that will be manufactured. Tarkett has limited theoretical knowledge about the problem. Mainly empirical observation and manufacturing experience has discovered some causes and effects on how they can decrease the number of defective holes that occur during manufacturing in for example the double belt press. A solution to this problem would save Tarkett energy, raw material and at the same time allow for an increase in general knowledge about the problem.
1.2 Purpose and Goal
The purpose of this study is to apply methods and theory that can present primary reasons for the occurrence of holes in the manufacturing of plastic floors at Tarkett Ronneby. This allows for a greater overview and understanding of the problem based on processes and products that relate to factors of importance.
The goal is to suggest possible suggestions and arrangements to
improve the process and decrease faulty volumes of produced plastic floors through the elimination of a root cause.
This project shall be an attempt to use relevant tools that can present the problem in a structured manner with the implementation of a pre-study or feasibility study. The study can bring up some new ideas or point of views that can resolve any of the rot-causes to the problem. The project focus on assessing the flow and related variables by focusing on quality and improvement suggestions that Tarkett later can investigate further by themselves by studying the problem further related to the causes.
Prioritized causes and experiments will be presented that can have an impact to ease for other people to continue the work and discover future potential solutions.
1.3 Research Questions
The following research questions have been formulated to help the project reach its purpose and primary focus areas throughout the work that are fundamental to consider and answer.
● How does the current situation appear and what processes in the flow are relevant?
● Why is there a variation of defective holes in Tarkett´s products and what parameters show a difference?
● How can the root-causes be identified and then eliminated or mitigated for the formation of holes on the products?
1.4 Delimitations
The thesis was created during a 20-week period which involved the corona pandemic in the spring of 2020 which resulted in delays of field investigation and interviews with limited contact opportunities with key personnel at the factory in Ronneby, due to visit restrictions which lasted close to one month during the work.
The work was conducted at the plant by following the manufacturing flow of interest that could have an impact on the occurrence of the defect, called “holes”. This was done by observing the
manufacturing process and interviewing personnel on spot. The personnel can have various types of knowledge and biases towards similar problems. Processes in the flow that have low impact, are too general, or hard to manipulate because of restrictions and constraints will be less investigated but considered. Processes and material variables were broken down into the most important ones to be able to deepen the knowledge. Meaning that specific products was investigated more than others because of time constraints and the ability to specialize. This problem was complex, and many variables are tied together in known and unknown ways. the implication follows that the changing of one cause to the problem may create a domino effect and affect other factors massively and therefore create other problems. Processes in the flow and related causes could be evaluated on the possibility of making a change or improvement without affecting the overall process flow too much. These improvements were judged against the potential investment costs required to implement the solution versus the defects annual cost.
Defective holes in manufacturing exist on more than one line, but aggregate 219 has a unique process flow and a higher capacity output in the ability to produce square meters of floor. This work will focus mostly on 219 with little regard to the other lines more than a basic understanding because the processes vary, and the processes consist of constraints. The constraints are that it is unreasonable to rebuild line 219 to become similar to the other lines, and it would require vastly more work to complete the thesis. The other lines do not have holes to the same extent, and the lines are not similar in making connections to rebuild or modify either line. The problems with holes was more focused on the mechanism that sparks more holes which can be compared to other methods of manufacturing, rather than how the manufacturing lines compares.
2. R ELATED W ORK
This chapter presents key take ways from related work done at Tarkett related to holes or similar problems.
2.1 Gull Wing Project
The gull-wing project was conducted around the time of 2014-2015 and was led by Dr. Mats Ericson that has a Ph.D. at the department of mechanical engineering in Linköping, and continuous experience by inhibiting leading R&D positions in various companies. He defined the problem and detected root causes of the problem which then was tested with several experiments and theoretical explanations to improve the verifications of several hypotheses. It was observed that higher pressure and lower temperature resulted in more gull wings on the surface of the plastic floor [3].
The proposed solutions were to rebuild an area in the double belt press located in the middle of the press to maintain constant pressure throughout the process. Between the heat and cold areas, there was an area in the DBP that was pressure-free against the material and caused the material to expand quickly. It caused the material to buckle which tore molecules from each other in the material. Then when the material reached the cooling zone and applied pressure again it shrank fast and it was proposed that buckling in the middle of the floor was self-healed while the defects at the side of the floor remained intact. Because the defect happened to occur mainly in the outer sides of the homogenous vinyl flooring and not closer to the middle. The problem was discovered from receiving access to a plastic floor sample that was received from inside the DBP where it was seen that the plastic floor had fluctuations of form right in the middle of the sample. These fluctuations in the appearance of the material started the investigation on how the material reacted during this area of the press. Conducting simulations with FEM and laboratory experiments resulted in a foundation of actual data that could convey the management team to proceed in rebuilding the DBP. The middle area was rebuilt to cause similar and consistent pressure as the other zones. The solution was successful, and most problems related to gull wings was removed [3], [4].
Tarkett works and handles their projects strictly through a 7-step method to solve problems. the steps are problem definition, evaluate the current situation, analyze root causes, create potential solutions through a hypothesis, then studying the results from the hypothesis, standardize improvements, and lastly the creation of a plan to complete the plan.
2.2 Internal hole projects at Tarkett
Tarkett has defined how holes look like in a microscope and how big they tend to be when the holes appear on the surface of the flooring. The holes appear to be around 0,5 mm wide and larger than 30 µm deep on the surface of the plastic flooring. Holes have various shapes that fluctuate between round like to buckle shaped on the surface. This indicates some differences in their main cause for formation [4].
Figure 1: Several holes displayed by light [4].
Figure 2: Multicolor products with holes [4].
From own initial observations the left picture in figure 2 has a cracklike look while the left look more that it has been exposed to air or bubbles.
Figure 3: Holes on IQ natural from above and from a cross-section [4].
As seen in figure 3 on the right picture, it looks like bigger porosity spots located right under the seeable hole that occurs on the surface. It almost looks like air entrapment have been located at those areas. Because the material has not melted together in the same scale as the surrounding areas as seen in the mid picture.
Since the inception of the gull-wing project, Tarkett has performed its projects and investigation related to holes. The information has been discovered through empiricism or laboratory tests. Specific parameters of importance and linked processes can be caused by the following reasons [3],[4]:
● Holes are one of the most common defects that occur at line 219 and has existed for many years in fluctuations of amount.
● Illuminated that products IQ Eminent and IQ Natural had the most problems with holes at 2015 of total production compared to the other products.
● The bigger the size of the granulate the more often the occurrence of holes.
● A higher thickness of the plastic granulates bed results in fewer holes.
● Air escape is critical the first few seconds of the DBP-process.
● The amount of air inclusions in the granulate bed may have an impact in the compression molding.
● How variation of pressure, temperature and time on the material in the DBP may affect the occurrence of holes or other defects, if they are set wrong in manufacturing.
● Applying dust at a reasonable dust to granulate ratio of 20/80 removes most holes.
● A suspicion that darker colored plastic floors result in more holes due to pigmentation effects of the material.
There is a hypothesis that the air inclusion content in the granulate bed is the major reason for the occurrence of holes. Calculations suggest that the air content in the granulate bed in uncompressed state
are around 60 % while it drops down rapidly during the initial compression state in the DBP. The material reaches thermal equilibrium around 30 seconds in the press which operates at a velocity range of 10-14 meters per minute depending on manufactured product [4].
Figure 4: Illustration made by Tarkett to show the size of holes [4].
3. T HEORETICAL FRAMEWORK
This chapter presents all the theory needed to understand the problem, methods and results presented in the report.
3.1 Introduction to plastics
Construction of products have required specifications and can be divided between metals and nonmetals. Plastics have gained in popularity last decades because of expanding competitive advantage though properties that inhibit low density, a corrosive protection, and facilitated user experience. A polymer consists many atoms constructing a molecule where the many molecules are joined in a so- called monomer. These monomers are the building block of polymers, thus adding and linking several monomer molecules create a polymer molecule and is called polymerization [5].
Polymeric materials with respective polymer molecule differentiate in size and geometry that affect the molecule weight. The high weight of polymers gives it special abilities compared to water that consist of small molecules with weak bonds. The name polymers origin from “polymeros” in Greek and means “many parts”. Most polymers have a polymeric system with a mix of small and big molecules, meaning a variation of molecule weight. Polymer weight is therefore calculated with an average molecular weight of the compound [5].
There exist two categories of plastics, that of thermo- and thermoset plastics. Thermoset plastics are strong because of cross-linked molecule chains and are therefore not possible to reform by a lessen bond between molecules through heating. Thermoset plastic maintains a rigid chemical structure which is hard to manipulate compared to thermoplastics that can resist chemical degeneration with input from heat to change its physical appearance [5].
Figure 5: Branched polymer (left) and crosslinked polymer (right) [6].
If a thermoplastic which constitute of branched molecules is manipulated by a heating process it starts to loosen up the bonds within the material with heat energy throughout the molecule chains with movement of the molecules. This makes the material softer and then melted with time from inception.
When a plastic material is melted it enters a state which is called “plasticization”, thus meaning that its plasticizers and can be formed into a desired product. These thermo plastics can be reworked infinitive amount of times through softening and hardening without losing foundational properties. This do not include a plastic paste with additives included because additives, e.g. plasticizers can mitigate from the plastic at higher temperatures in small amounts. Amorphous plastic contains molecule chains that are disorganized and can therefore be formed easily. The bonds of the molecules are low strength because the molecules can move more freely when the material is affected by thermal processes [5], [6].
The definition of plastic derives from a polymer with the addition of additives, where the polymer is seen as the foundation of the material and the additives inflict changes in properties of the overall material. This change is needed to add desired properties and processability to make the material resist degradation from external factors, e.g. sunlight, tear, and higher temperatures processes.
Plastic has two critical points where thermal temperature affects the material in a major point which are called the glass transition temperature (Tg) and melting temperature (Tm). The stiffness can be modelled as a function of temperature to show how the material acts at specific temperatures. Tg indicates a point of time when the material transforms from a stiff material (glass) into a rubber state.
An increase in molecule weight imply an increase in Tg. Tm indicates the transition from rubber to liquid state of the material, but it only occurs in crystalline polymers. These stages are crucial to know when evaluating fitting process parameters [5].
Figure 6: Model over glass transition (Tg) and various material stiffnesses in megapascal (MPa) depending on applied temperature in Kelvin (K) [8].
3.1.1 Polyvinyl chloride (PVC)
Polyvinyl chloride (PVC) is an amorphous plastic, consisting of branched molecule chains, with wide applications which make it one of the most used and popular polymers by industries. PVC was invented in 1872 and later commercialized in 1920. PVC molecules consist of Chlorine, carbon, and hydrogen and the resin derives from the polymerization of vinyl chloride monomer molecules [6].
Figure 7: Chemical model of polyvinyl chloride (PVC) [9].
Pure PVC is not processable by itself without additives and susceptible to degradation and is manufactured as a white powder called PVC resin which is the raw material [7]. The powder can then be used by mixing of additional additives to improve the properties to suit processes and customer needs.
PVC in pure form is white-colored and can be manufactured in either a rigid or flexible state. Rigid PVC (U-PVC) can be manufactured into pipes or roof coverings, while the flexible or plasticized PVC (P- PVC) is manipulated with plasticizers. The plasticizer molecules are placed in-between the PVC chains to lower the connection of molecules and therefore more flexible which then can be seen in flooring, packaging, or wires. PVC has good flame and electrical conductivity resistance and a small carbon footprint [6].
3.1.2 Viscosity
Viscosity is a defined measurement to indicate the resistance of fluidity in materials under certain scenarios. The low viscosity of an entity implies high flow capabilities while high viscosity acts as an opponent to a change of shape of an entity. The friction between molecules of the compound affects how high the viscosity is and how much force or energy that is needed to form or move an entity into a desired shape. The SI unit for viscosity is pascal-seconds (Pa s). There are differences in how
liquids and gases act to external temperature changes, liquids flow better at a higher temperature while gases become sluggish [10],[11].
3.1.3 Additives
Additives offer a wide range of possibilities for the product to ease manufacturing and adapt the product to the expected user needs.
● Stabilizer
This additive helps the plastic material to manage the effects from a thermal and chemical perspective in the form of resistance to degeneration. Material is often processed through a thermally heated environment that manipulates the movement of atoms in the material to facilitate the shape of the product in the desired manner. When a plastic product reaches a customer, it needs to resist wear and light without losing essential properties or visual design.
There exist stabilizers that protect against ultraviolet radiation to counteract sunlight that reaches the product, and the ability to change resistance against higher manufacturing temperatures. Stabilizers are essential in the manufacturing of PVC and its toxic effects need to be evaluated to live up to requirements related to user needs or product applications [5].
● Dye
Pigments are added to dye the product and create a certain surface design wanted by the customer to give customers more options to choose from the same product model. It is often added together during the creation of a new PVC-batch. The pigments are included during the mixture process, often in powder form which later gets crushed and melted into finer pieces during the extruding process to gain an even color distribution throughout the plastic paste [5].
● Lubricant
The lubricant additives enable flexibility to the manufacturer to manage the flow and friction of the plastic material against molding surfaces. It should not include too much in a batch because it can cause problems that are affected by thermic heat and resolve onto the surface of the working material or the surrounding air and equipment [5].
● Anti-static
Anti-static additives remove the plastic material's ability to become electrostatic which otherwise could make the product charged up during manufacturing. The additive can be added in the mixture process in the creation of a batch. During a manufacturing process through surface treatment or by adding metal compounds in the product that leads away electricity [5].
● Filler
Fillers are cheap materials that companies add to the product to make the overall product cheaper to manufacture, but also change the characteristics of e.g. an increased density and stiffness. Fillers are important but not necessary from a theoretical standpoint for the integrity of the product. The filler occupies space in the mix to replace expensive PVC resin or other compounds. It does have benefits for the overall structure through added positive attributes. The percentage of total fillers usually subsists in the range of 1-50% of the total batch volume. Fillers enable companies with polymer focus to decrease the number of expensive ingredients in the complete recipe while obtaining positive properties of the material in a satisfied manner [5].
● Plasticizer
Plasticizers are important and change the stiffness of the material which makes it less hardened which in turn decreases the materials elastic modulus (stiffness). The manufacturer can change the material to fit customer needs and the capabilities to process the material depending on available production. Plasticizers decrease Tg and Tm of the material, making it susceptible to lower critical flow points. This material additive enables the product to be permanently softer in some cases, but it tends, with influence from higher temperatures to evaporate into a vapor and make the material more brittle with time [5].
3.1.4 Melt flow index (MFI)
MFI is a procedure to determine the resistance of flow through a defined quantified measurement and therefore gain the viscosity of a plastic composition. The mass flow index of a thermoplastic is calculated in 10-minute intervals with a predetermined force through an added weight, thus outputting the amount of melted test plastic in grams that cross a certain point at a temperature around 170-200 degrees Celsius. The MFI measures molecule weight indirectly, where low molecule weight corresponds with high MFI values and therefore better flow properties [12]. It is a standardized method to learn about the melt capabilities of the material and how it benchmarks with other plastic compositions.
Figure 8: Model of MFI equipment [12].
3.1.5 Thermal equilibrium
Thermal equilibrium is gathered from the zeroth law of thermodynamics where two systems transfer energy between each other at contact to change the temperature. Implying the time needed to reach the same temperature of both entities. This occurs when system A has a higher temperature than system B [13]. The DBP can exemplify system A and the granulates that are put into the process of granulates as system B. When the granulates enter the process it takes time for System B to reach the desired temperature in System A set by the operator of the DBP.
3.1.6 Ideal gas law
The law constitutes of pressure (P), volume (V), and temperature measured in Kelvin (T) of a gas.
There is a conjunction between the various parameters to predict the result. n is the number of gram- moles of a gas and R a constant called the universal gas constant. When pressure is increased in the entity there exists a lower number of moles of gas and vice versa [14],[15].
𝑃𝑉 = 𝑛𝑅𝑇 (3.1)
3.1.7 HAAKE
The HAAKE test is a standardized tool to measure the torque of polymer material being processed through a mixer or rotating extruder screw. It measures the torque needed to mix the material and temperature rise until the set temperature is reached of the mixture. A graph can be extracted from the polymer melt with torque and temperature depending on time from start. The curve for torque is high in the beginning before the material has had time to warm up and then stabilizes when the temperature is high. It is a quick and effective method to evaluate torque which is of importance when developing samples and testing samples of new products [3], [17].
Figure 9: Similar machine used in the laboratory at Tarkett to measure torque of the PVC-granulates [17].
3.1.8 Density measurements of granulates
3.1.8.1 Bulk Density
Bulk density is the measurement of solids that inhabits a fixed space or room together with voids. Therefore, useful for calculating all the available pores within a powder or granular material. The total mass of the particles is weighed and then divided by a fixed volume. In this case grams/mL can be converted into grams / cubic centimeters (𝑔/𝑐𝑚3) [18], [19].
In this case poured bulk density is of importance, where it will act like the dosage process of poured material on the steel conveyor. Poured bulk density is when the particles are poured into for example a cylinder without further manipulation. Vibration impact can higher the bulk density because of improved orientation between particles. It should, therefore, be measured in more samples and then averaged out to cause similar outcomes and not cause misleading values.
3.1.8.2 Particle density
Particle density measures only solid volume and not total volume occupied by a material.
Particle density is therefore a necessary parameter to calculate the void volume of the bulk density to receive porosity [20].
3.1.9 Porosity
Porosity is defined as the amount of pore space compared to solids that occupy the total volume of a material. This measurement can be used to calculate the porosity of granular material which affect the amount of air inside the granulate bed [22].
Figure 10: Difference between a high porosity (left) and lower porosity (right) [21].
All unworked granular materials have porosity to some degree if it is placed in a certain volume.
Where the size and geometry have an impact on the overall porosity with some percentage points compared to other references. Tests have shown that cubes have a higher packing density than for example spheres [22],[23].
𝑃𝑜𝑟𝑜𝑠𝑖𝑡𝑦 = 1 − ( 𝐵𝑢𝑙𝑘 𝐷𝑒𝑛𝑠𝑖𝑡𝑦
𝑃𝑎𝑟𝑡𝑖𝑐𝑙𝑒 𝐷𝑒𝑛𝑠𝑖𝑡𝑦) (3.2)
Figure 11: Y-axis show porosity and the x-axis show number of fine particles included in percentage of the overall bed of bidispersity spheres [24].
The Lambda (λ) showcase the ratio in diameters between the two spheres included by the equation λ =𝑑1
𝑑2. Where the highest porosity is created by the biggest particles and ratio differences between the spheres. The incorporation of fine particles like dust can decrease the amount of porosity together with bigger particles [24].
3.1.9.1 Thermal conductivity
Thermal conductivity measures the rate of heat transport throughout the cross-section of an object.
Air acts as an insulator because of the weaker bonds of molecules while the solid PVC granulates have much better thermal conductivity because of being solids. As seen in (figure x) below the amount of porosity should heavily correlate to the thermal conductivity properties of the granular bed [x].
Figure 12: Implication of thermal conductivity because of porosity [24].
3.1.9.2 Packing density
Packing density is the science of the ability to fill up and utilize a fixed space with entities with the densest possible formation. Packing density can be measured through various criteria of either random close packing or random loose packing. Where pressure is applied or not to the affected medium. Size ratio or aspect ratio had been simulated of spheres, cylinders, and cubic geometries. The aspect ratio on a cylinder is the length of the cylinder divided by the diameter of the cylinder. Meaning that a cylinder with aspect ratio of two it implies that a cylinder has double the length as the diameter of the cylinder [25].
Figure 13: Show how the packing density increases in the y-axis to a maximum at around 30-40% fine particles included of total granular composition [24].
This graph shows the relation between finer particles that can clog up pores in bigger granulated materials and produce an improvement at around 20-30% of the total packing volume.
Figure 14: packing density of cylinders at different aspect ratios and pressure. In relation to aspect ratio (w) and pressure (τ) [26].
In figure x above, it is simulated that an aspect ratio (w) of around 1-1,2 possesses the best packing density of similarly shaped cylinders. Disks that can be seen with an aspect ratio around 0,2 are worse than the cylinders with aspect ratio 1 [26].
Figure 15: Packing density of cubical formed entities with different aspect ratios [27].
The figure shows six different cubic shaped particles with different aspect ratios and therefore packing density.
a) Packing density (PD): 0,608 Aspect ratio (AR): 0,3 b) Packing density (PD): 0,645 Aspect ratio (AR): 0,5 c) Packing density (PD): 0,658 Aspect ratio (AR): 0,7 d) Packing density (PD): 0,657 Aspect ratio (AR): 1,5 e) Packing density (PD): 0,644 Aspect ratio (AR): 2 f) Packing density (PD): 0,600 Aspect ratio (AR): 4
Different geometry changes the overall packing density with several percentage points of material packed in a fixed space. The optimal packing density for cubes is either 0,7 or 1,5 with 1 being a local minimum [27].
3.2 Manufacturing processes
Calendaring of PVC
This manufacturing process compresses material into a continuous sheet by number of several heated rolls. The rolls are created from steel with a hardened surface. Tarkett have many smaller lines utilizing this manufacturing process with a smaller number of holes. The compression of material allows for a more open system rather than the aggregate 219 and the DBP [3].
Mixing
The mixing process enables the mixing of all ingredients involved in a complete standard recipe for every product. This constitutes the appropriate PVC resin together with various additives that create a batch for a certain product. Mixing can be done with a warm blend or cold blend depending on recipe composition [3].
Extrusion / GEX
After the mixing process, the plastic batch is sent to the extrusion to generate granulates and mix the ingredients even more. Tarkett has two main extruders and they differ in construction based on size and ingredient input, but the main features are the same. An extruder consists of a room or cylinder that fits a screw and, in this case, two screws that rotate clockwise [3].
Aggregate 219
Aggregate 219 is the name of the manufacturing line used by Tarkett during the production of PVC-flooring. This is the mainline investigated during the work and where the most allocation of focus have been made [3].
Granulate dosage
The dosage process gathers material from small containers packed with plastic granulate and distributes it smoothly on a conveyer [3].
Double belt press (DBP)
Figure 16: Model of a double belt press where material enters in the left side and then affected by pressure and temperature to then exit in the right side [28].
Double belt presses allow for large output, good working conditions and are easy to operate.
Material is put on a steel conveyor transport that enters and moves inside the DBP on one side. The material transports as a granular bed, where the material is shaped in a heating zone and then a cooling zone to solidify the material. The process has continuous pressure throughout the system before it leaves the DBP and moves to the next process [28]. There exist many variants that allow for different contact materials, in this case, the Teflon layer with contact against the material and is heated by hydraulics though oil. The length of the DBP can vary depending on the need from meter to several meters.
3.3 Lean
Lean is considered a philosophy concerning the production of goods or services. The origin of lean derives from a car company called Toyota in Japan. Wastes are to be minimized as much as possible that is of no importance for the end customer. The application of Lean should result in efficient resources for maximum output or capacity in e.g. manufacturing of goods. Long-term thinking is the foundation of Lean rather than short-term gain from the termination of personnel. People have a priority in Lean because companies depend on knowledge and experience from employees and subcontractors for long- term success. The employees need to have a purpose and be able to learn and improve the business through responsibility [29].
There are eight losses which are the following:
1. Defects – products fail to meet customer expectations 2. Overproduction – more supply than demand of products
3. Excessive processing – losses related to extra work or excessive quality than needed 4. Waiting – time waste between process steps
5. Inventory – waste of space for products and material of no demand 6. Transportation – unnecessary transportation between places.
7. Unused Talent – low utilization of people’s talent, knowledge and skills 8. Motion – unnecessary movement by personnel
3.3.1 Zero loss thinking
Zero loss thinking is a mindset or philosophy for management to minimize failure in production. It wants to remove all faults (losses) related to quality, breakdowns, delays, and wastes. Perfection is the goal and when zero losses are considered as the goal, no losses are hidden to the personnel which facilitates continuous overall improvement. All faulty activities are investigated and how they relate to
and eliminate smaller problems linked to the origin problem. These smaller problems are the main drivers for the bigger problems that occur and stand for the biggest losses [30].
3.4 Quality
Quality has been labeled and defined by many people in the field with various emphasizes.
Quality is a known definition of product excellence and the ability to satisfy customers. When a customer orders a product there are expectations of how the product work, feel, and look for its application. Quality can be subjective and up to each individual expectation on how a product should look and feel. Companies that are successful with implementation of standardization and quality development gain benefits with for example lower manufacturing costs and less claims. The Japanese companies put a heavy focus on quality in the 1970s and started to outcompete big international companies by taking additional market share. Other companies have since then understood the benefits of quality work to focus on customer needs and what they want. It is to offer the customer what it wants and even outperform the customers’ expectations of the sold product [29].
3.4.1 Improvements tools
In quality techniques, there exist tools to facilitate and reasonably present data to colleagues.
Japan was early with the implementation of easy tools to display data and involve all people in the improvement work. Seven improvement tools were established by Kaoru Ishikawa and later taught to employees called QC-tools [29].
3.4.1.1 Data intake
Data intake is the foundation in improvement projects to have facts that emphasize on the actual problem and related questions. Data can later be refined and analyzed to answer the questions necessary to decide on the appropriate course to learn about the problem. Data should be carefully selected and fairly displayed to resemble reality [29].
3.4.1.2 Histogram
Histograms allow the data to be classified into fitting sub-categories. Illustration of variations in a parameter can be displayed during hours, days, or months [x]. Useful to see if more defects occur during a specific day or under a specific condition and make a connection to probable causes [29].
Figure 17: An example of a Histogram [31].
3.4.1.3 Pareto chart
The Pareto chart was established by the Italian Vilfredo Pareto and is useful to illustrate the main problems. It is often a few products or causes that stand for most of the quality problems, called the 80-20 rule. Pareto charts present the number of defects in a desired unit while illustrating the percentage of total defects for each product. This imply that two values are presented in the y-axis, the
desired unit and the ratio in percentage shown in figure 18 below. The chart includes staples to present the number of defects and at the same time a line to show the percentage that one problem stands for of the total problems available. The relevant and prioritized defects or products will be presented on the left side of the chart and then subside to less important problems [29].
Figure 18: An example of a Pareto chart [32].
3.4.1.4 Cause-effect diagram
In a quality problem, there are reasons for the cause of the problem to occur. This tool, also called fishbone diagram acknowledges all causes by mapping of all the causes and sub-causes. The respective cause is evaluated to finally decide on specialization on one of the causes. The cause of work should be investigated with the five why method to extract possible root-causes. A root-cause is a small problem that can cause the biggest problems in the end. Causes should be investigated one by one in a systematic way and the diagram may inform about data deficiencies [29].
Figure 19: An example of a fishbone diagram [33].
3.4.2 Improvement cycle – PDCA
PDCA is a structured way of conducting improvement work and an abbreviation for plan, do, check, and act. The framework can proceed in an iterative cycle until a problem is fully solved. Planning involves an investigation of big causes that will be broken down into smaller root causes which are easier to manage. After finding important reasons for the occurrence of a problem, the next step is the
“do”-step which revolves around the possible actions that can be made through for example a small test.
Then study the effects of previous actions made to evaluate if there were any improvements [29].
Figure 20: A model of PDCA [34].
4. M ETHOD
This chapter consist of the methodology of this thesis and the rationale for the chosen methods.
4.1 Study Purpose
The purpose is to gain knowledge and understanding about why holes occur in manufacturing line 219 and propose potential improvements to the problem. To be able to understand the problem there is a need to follow the flow of processes that can have an impact on the material. By considering limitations in the flow, it will be of interest to investigate the production of plastic granulates and then how it reaches line 219 to become finished products with final packed rolls. This is done by interviewing people with extensive knowledge or experience about the processes in the flow at the factory and by observation. The current situation will be documented and regarded in terms of possible parameters of interest. Quality and improvement focus complemented with tools. Inspiration from a lean manufacturing philosophy can be applied to obtained information.
Theory and literature studies regarding the defect are used to describe how the defect occurs in the double belt press. The problem can be explained with the help of known theory in physics, thermodynamics, or chemistry. Theory or data is gathered and analyzed to facilitate understanding, in return it makes it possible to create and benchmark potential improvement proposals from a risk-averse perspective together with tests for further work.
4.2 Investigation Method
This thesis is run as a feasibility study with the incorporation of qualitative and quantitative empirical data gathering through the scientific method.The feasibility study should answer
fundamental questions on whether something is viable and plausible. A plan and scope need to be set to define the limits of the investigation by including relevant aspects. This is done by describing the current situation to suggest available or prioritized solutions which later can be benchmarked by management. Feasibility aspects to consider in this study revolve around the aspect if it is possible to improve to a reasonable investment cost [35].
Thus, considering available stakeholders, manufacturing processes, and material properties to existing theory or technologies. Planning or execution of a potential improvement and its requirements should be presented in the results. The Possible damage management options or solutions shall be evaluated through a SWOT-analysis. Empirical data will be gathered from both interviews and investigation on- site while accessing historical statistical data through Tarkett’s data gathering system HYDRA. The empirical data is gathered on potential root causes linked to theory; it can then be evaluated through related experiments to test assumptions about how the problem may occur. The thesis must include a scientific methodology to be considered complete and will, therefore, include supervised or own experiments.
Figure 21: overview for the scientific method.
Scientific work requires information gathering to create assumptions and hypotheses related to the problem. The hypothesizes are then to be tested through experiments to see gain insights on correlations or faults. The results from the experiments can then be evaluated in the form of analysis, where the hypothesis will be compared to the experimental outcome. Thus, illuminating the hypothesis to faults or refinement which then can be documented or improved upon through further experimentation. The empirical knowledge gathered from observation is developed through rational data of numbers. A valid
observations and should, therefore, be susceptible to repetition. If it would occur variation in results, there should be errors in how either the hypothesis or experiment was constructed and require evaluation [36].
4.3 Literature Study
Searching and reading of relevant literature associated with the problem enabled theory as a basis for understanding the problem to complement empiric knowledge from the on-site investigation.
This was used to test if the actual data gathered from interviews and observations can compare from a theoretical standpoint. Information gathered from personnel was not assumed to be true because all had various degrees of knowledge and experience. Several sources of data from scientific literature were gathered and evaluated to create the theory part of the report. The literature answered questions linked to processes in the flow, the defect itself occurring inside the processes with physics, thermodynamics, and plastic material technology to explain how holes may occur on the product.
The sources were gathered from borrowed books, BTH summons, and google scholar through keyword searches to receive access to scientific literature, books related to the relevant areas.
4.4 Data collection
Data collection was gained through interviews with experienced staff and observation with guiding of the flow in the production process. The interviews were conducted with both predetermined questions and through initiative open-ended discussions. The interviews and observations had an iterative element, to continues ask and answer questions that was discovered throughout the project.
Emails were sent with staff to gain an answer in questions and access to material linked to the defect during this period. Some meetings with personnel was conducted more as a lecturer where a process engineer explained how much of the flows, processes and materials work. Then could questions be asked, and feedback be received right at the spot. This was done to gather all the fundamental knowledge available already from people with experience of the production of plastic flooring.
Historical data about specific processes and products were gathered through available data gathering systems like HYDRA and previous related work by request. The system records manufacturing data for products, all batch numbers, colors, and reported faults. Data can be hard to come by in specific scenarios because of a complex documentation. Historical statistical data is interesting to investigate to understand the basics of the problem occurring. The fundamental questions need to be answered about all available processes and products to put everything into context before a specific investigation starts. The data from HYDRA makes it possible to compare products and gain knowledge about the situation and how to move forward in the investigation. Following question marks needed to be answered and documented. How big of a problem is holes compared to other defects and how many holes do each product account for that are manufactured on aggregate 219?
The basic understanding of how the different products work, differ and why the products act accordingly in the following process steps, to the output resulting in varied numbers of defective holes.
Documents were gathered about five chosen products to compare and measure the material and process properties to benchmark the products against each other. If products have varying amounts of problems of the same defect it exposes the critical differences. Meaning that hypothesizes can be evaluated through experiments and linked to studied scientific literature theory.
4.5 Laboratory Experiments
When the holistic fundamental investigation was done it transformed into an investigation about specific product characteristics and their respective process guidelines. This was completed by gaining insights into differences between five different products with varying amounts of defective holes, through experiments together with the R&D laboratory at Fornanas. The products had to be tested to receive quantitative data that could be analyzed and not just qualitive data in this case. Before the experiments could be done it was needed to explain and rationale for the reason and time needed for the experiments to be conducted at the laboratory. Contact went through the supervisor of the R&D lab for some weeks before the tests could be done. The products and experiments were discussed with a supervisor that then ordered bags of granulates for each product. These experiments will allow for a
measurement of product material properties on how the granulate geometry act in compression at different compression parameters based on temperature, pressure, and time under compression. It will show how the product reacts under specific conditions by prediction based on packing density, recipe composition, granulate geometry, and size.
The GEX-die for IQ eminent has been changed since the latest experimentation on holes in 2015.
The size and geometry of the granulate resulted in fewer holes overall since the change and it would be interesting to further evaluate five different products depending on granular size and geometry.
Questions to consider are:
• How much did the changed GEX-die impact IQ Eminent ability to form holes and why is that the case?
• Is the bulk density for IQ Eminent different now from after the GEX-die change and is it an important parameter for the formation of holes?
• Is the decrease of holes because of mainly smaller granulate sizes? Different granulate geometry or higher packing density with better thermal conductivity and less porosity? Or a combination?
• Why do products with smaller like Primo Premium fewer holes? Is it because of smaller granulates, geometry, recipes, or processes linked to granular manufacturing?
• Has the bulk density, particle density, HAAKE, and MFI measurements since 2015 changed, and how do the values compare to the number of defective holes per product at the current moment?
The hypothesizes include properties about how viscosity and porosity affect the formation of holes.
The impacts of geometry versus material properties can be challenged. Experiments can allow for the knowledge to determine the priority of either recipe composition with flow capabilities or if the packing density matters more than flow capabilities with the manufacturing of the actual granulate size or geometry.
Bulk density allow to calculate porosity and was measured in a plastic cup with a volume of 500 ml and a weight of 24,9 grams and was excluded when weighting the granulates. One milliliter converts to one cubic centimeter. Three cups where overfilled for every product and the granulates that exceeded the top corners of the cup were removed with a ruler. The leftover granulates falls to the table to leave a plain and even filling of the cups. Lastly, all the cups were weighted by themselves and documented.
The results were then averaged from the three values to gain a final value. Bulk density in grams per cubic centimeters was then calculated by dividing the weight of the granulate with the volume of the plastic cup.
4.5.1 MFI and HAAKE
MFI And HAAKE was done because they measure the processability of a product and the ability to of the product flow in a heated state. This could be related to the scenario inside the DBP when the granulates melts together into a homogeneous floor. If granulates not melt together there will remain cavities between granulates.
Both machines had step by step instructions to perform the procedure. It consisted of a filling of the machine and appropriate parameters. The parameters were set by standard constraints related to the specific products. Granulate was weighed on a scale to ensure consistent results rather from inconsistent loading of the machine. Around 5 grams of granulate were used for every test. The machines could take around 15 minutes to complete with the material, appropriate product parameters, and the wait time during the operation of the actual test. When the tests were completed the data appeared on the computer and written down to paper. The output from HAAKE consisted of the torque (N/m) needed to mix the granulates into a paste based on the time from start. A max value and stabilization value were gathered.
From the MFI a value from grams of plastic material that flowed through a small hole in 10 minutes (g/10min) The MFI has standard weights that can be set to pressure out the material were a weight of 21,6 kg had been set.
