Technical Paper Series
BLEISTAHL Prod. GmbH & Co.KG, Osterfeldstrasse 51, D-58300 Wetter (Ruhr) Tel: +49 (0) 2335 / 976 – 0 Fax: +49 (0) 2335 / 976 - 111
Valve Seat Inserts
State of the Art End of 2001
Gerd Krüger
Manager Research & Development Bleistahl Prod. GmbH & Co. KG
25. 02. 2002
Valve Seat Inserts – State of the Art End of 2001
Gerd Krüger
Bleistahl Prod. GmbH & Co.KG, D-58300 Wetter (Ruhr)
Abstract:
Within the valve train system, seat inserts have the function to seal the combustion chamber together with the valve, in order to obtain an acceptable combustion pressure.
Therefore, these components are important for clean burning with low polluting emission rates. The components have to satisfy extreme requirements. Exhaust gas temperatures up to 1050°C , increasing valve velocities, low wear rates and good machinability are the key points to take care of.
This paper summarizes the state of the art in PM – valve seat insert production. An overview of the current market situation is followed by application requirements.
Different types of material and their compositions are compared. Properties such as hot hardness, material stability at elevated temperatures, thermal expansion and conductivity, wear resistance and their mechanism and finally yet importantly the machinability are discussed and typical values are shown. The designs and their limits are discussed and recommendations will be made.
1. Introduction
Valve seat inserts (abbreviated as VSI in the following) and valve guides
(abbreviated as VG in the following) are important components in the valve train system and of essential significance for an optimised combustion process in the cylinder. Together with the valve the above mentioned components have to guarantee perfect sealing of the
combustion chamber to ensure that the required compression or combustion pressures are reached in the cylinder.
Increased wear results in variation of the combustion conditions and thus in a decrease of engine performance and emission. Figure 1 shows a tappet valve train system with overhead camshaft. VSI and VG are typical components suitable for large-scale production.
Figure 2 gives a survey on number of engines produced for passenger cars in 1998 and 1999 [1]. From this results is a requirement of 900 ... 1000 million components. 13 manufacturers worldwide are producing valve seat
Market Engines Produced For Passenger Cars
1998 1999
Europe 14.511.410 14.743.841
Nafta 7.989.249 8.185.106
Mercosur 1.607.090 1.328.285
Asia 11.335.091 12.343.175
Rest 541.321 492.295
Total 38.211.745 39.453.822
Figure 2: Production of Passenger Car Engines Worldwide [1]
Cam Tappet
Valve stem sealing Valve guide Valve stem Valve
Valve seat insert
Figure 1: Tappet Train System with Overhead Camshaft
Channe lKanal
inserts in two material groups. These are materials for casting and powder metallurgic (PM) materials holding 90% of the market share.
2. Requirements for Valve Seat Inserts
More than 99% of all aluminium cylinder heads are equipped with valve seat inserts, as aluminium and its alloys do not meet the material requirements for valve seats. Valve seat inserts and valve together form a tribological system with the task to guarantee perfect sealing even after several million load cycles. For modern engines wear rates are required ensuring maintenance-free operation of the mechanical valve train system without clearance
compensation within a kilometrage of 300.000 (< 2µm/1000km). The operating conditions, however, are extremely demanding
The following paper deals with the main factors influencing the wear of valve seat inserts.
2.1 Valve Seat Stress
The kind of stress exerted on the contact area of the valve seat depends on the type of engine used. Wear and deformation characteristics in the tribosystem valve/VSI are mainly
influenced by the fuel supply type, the compression and combustion pressures and the specific performance related to the temperature prevailing in the contact area. The wear factors caused by this may be summarized as under:
a) Mechanical Stress of the Seat Area. It is composed of the spring pre-stress force, the valve impact force and the combustion pressure force. Figure 3 gives a survey as an example of the stress proportioning percentage of a valve seat in an engine with overhead camshaft.
Depending on the seat angle used the stress is divided into one force active in vertical direction and one parallel to the seat face. The latter is primarily responsible of the wear and deformation characteristics of the seat. The strength of the forces and the stress distribution depend on the engine type and the operating state (e.g.
electromagnetic valve train system, engine brake train system in CV applications).
b) Dynamic Seat Stress by Relative Valve Motion towards the Seat Insert. This is a rotary motion of the valve depending on the engine speed. With conventionally
actuated valves it may rise to 10 rpm, and during so-called Rotocap application up to 45 rpm may be reached. This motion is appreciated as it ensures uniform valve temperature on the one hand and is cleaning the seat on the other hand. Another type of dynamic seat stress is bending of the valve head, which automatically occurs during pressurization at the valve head into the direction of the combustion chamber. This effect is even supported by a valve seat angle
increased by 0,5 – 1° in comparison to the seat insert, the so-called interference angle (figure 4).
This design allows a smaller seat width and thus increased surface pressure, resulting in an improved sealing effect at low combustion pressure. When increasing pressure, the content of the contact area is increased due to valve head
Percentage of Total Stress Spring Pre-Stress Force 1 – 3 %
Impact Force
(max. acceleration.1500 –7900 m/s²)
2 – 10 %
Combustion Force 87 – 97 %
Figure 3: Stress proportion at valve seat [2]
Figure 4: Interference angle valve / valve seat insert
bending and thus causes a reduced surface pressure to the seat.
c) Lubrication of the Seat Contact.
Wear rates of the tribosystem Valve / VSI are mainly influenced by lubricating
interlayers. Depending on the composition of the combustion gas mixture, the effect at exhaust and intake may very accordingly. In figure 5 the influence of the fuel type on the wear rate of valve and seat insert is compared. These effects are always overlapped by other phenomena. One of them is potential enrichment of the intake mixture due to introduction of the blow by into the intake pipe. Additionally, oil components reach the seat contact area via valve stem sealing along the stem. Oil leakage rates of 0,007 – 0,1 ccm/ 10 h are considered as normal parameters during practical operation.
Intake Exhaust
Petrol/Gasoline
Wear rate 1 – 5 µm/1000 km
++
-
Liquid lubrication at natural aspirated and turbo engines, at Otto DI engine, no lubrication, as only intake air reaches via intake
+ Solid lubrication by deposits of combustion gases
Diesel Fuel
Wear rate 1 – 5 µm/1000 km
- No lubrication, as only intake air reaches via intake
++ Solid lubrication by deposits of combustion gases
Alcohol Fuel
Wear rate 1 – 10 µm/1000 km
O Liquid lubrication at natural aspirated and turbo engines, but with corrosive portions. Effect varies according to alcohol content
O Low solid lubrication and increased water portion, effect varies according to alcohol content
CNG
Wear rate 2 – 50 µm/1000 km
- No lubrication, as only gas mixture reaches via intake
-- Low solid lubrication, as combustion clean
LPG
Wear rate 20 – 70 µm/1000 km
-- No lubrication, as only gas mixture reaches via intake
-- Low solid lubrication, as combustion clean
Hydrogen Fuel
Wear rate
20 – 70 µm/1000 km
-- No lubrication, as only gas mixture reaches via intake
-- No lubrication, as very clean
combustion, increased corrosive portion by vapour.
Figure 5 Influence of fuel type on wear resistance of valve /valve seat insert
d) Wear Partner – the Valve. Design of the valve train system has to consider a higher hardness for the contact area of the valve than that of the valve seat insert. Thus wear sharing of 1/3 at the valve and 2/3 at the valve seat insert is to be obtained. If the prevailing wear ratio is the other way round this may result in gradual weakening of the valve head, ending
up with valve failure and finally engine
destruction.
Typical hardness parameters have been summarized in figure 6.
In contrast to the materials used for valve seat inserts, the materials for valves have been standardized and can be looked up in the respective standard. The optimum combination of materials must in any case be matched with the application.
Valve Valve Seat Insert
Intake 270 – 370 HBW2,5/187,5 hardened >48 HRC
220 – 320 HBW2,5/187,5 Exhaust
(armed)
30 – 50 HRC 32 – 46 HRC
Figure 6: Comparison of hardness valve / valve seat insert (Tab. 4)
2.2 Material for Valve Seat Insert
Materials for valve seat inserts are not standardized and according to the required
specification consist of various alloying additions. This produced a highly complex variety of materials. On basis of the manufacturing process the valve seat materials can be classified into two main groups:
(1) Casting alloys. These material alloys are manufactured in two different production processes:
1.) Dead Mould or Sand Casting: The negative profiles of the valve seat inserts are copied in sand. Through combination and composition of the moulds a complex frame is formed into which the liquid melting is running in. The moulds are broken after solidification, the cast is drawn off and the insert blanks are separated. The material is submitted to secondary thermal treatment and afterwards the blanks are mechanically machined (turning and grinding) to become a finished part.
2.) Centrifugal Casting: In this process the metal melting is solidified in a rotating mould.
The pipe arising from this then is submitted to secondary thermal treatment, the mechanical machining (cutting, turning and grinding).
Materials produced in the described way are:
Cast iron [3]: Low-alloy grey cast is suitable for the intake and exhaust of low- stressed engines. The high proportion of free graphite in the material ensures good dry running operation properties. The quality may be improved by thermal treatment, e.g.
increase in ductility as it is required for the application in titanium valves. Due to its high proportion of carbides in the martensite matrix, white cast iron is qualified for intake valve seat inserts in CV applications. Austenite cast iron with a low proportion of free graphite is applied for adaptation to the thermal expansion coefficient of the aluminium cylinder head. Wear resistance of this material can be improved by increase of the carbide content.
Martensite Steel Cast [3]: These are materials based on tool steels or stainless martensite steels. In a hardened state they are usually applied for intake and exhaust valve seat inserts in CV applications with medium and high temperature of approx.
600°C. Their structure is formed of finely distributed special carbides in a martensite matrix. Addition of chrome improves resistance to corrosion.
Non-ferrous Cast Alloys [3]: In contrast to iron master alloys this material group consisting of high-alloy nickel and cobalt master alloys is much more expensive. They are mainly applied in exhaust materials used in extremely high-stress engines. A high proportion of carbides or intermetallic phases characterizes the structure. The material shows excellent resistance to high temperatures up to 875°C. Disadvantageous are high costs, low thermal conductivity and difficult machinability. Due to their high thermal conductivity Cu master alloys with beryllium addition have their right to exist in motorsports.
(2) PM Materials: Figure 7 shows an example of a production process for a PM component.
The powder mixture is pressed into a shape near to the final one at pressures of up to 900 MPa. Then the pressed parts, so-called green compacts, are sintered at high temperature (1000 – 1200°C for iron master alloys) and submitted to thermal treatment. Mechanical machining such as turning and grinding complete the production process. Additional production stages such as forging, calibrating, secondary sintering, hardening or vaporizing may be required for the individual materials. Target of modern PM engineering is the minimization of the number of production stages to achieve significant cost savings [4]. In figure 8 the relative costs of the individual PM production stages are compared.
PM materials are classified as described below:
Low-alloy steels: These are mainly applied in intake valve seat inserts at Otto engines.
Basis of these materials is the Fe-Cu-C system. Usually the structure is of a ferritic, pearlite kind with a cementite portion. Wear resistance is improved by low portions of nickel and molybdenum. Machinability is often optimised by addition of solid
lubricants (e.g. MnS, Pb, MoS2, CaF2 or graphite). The portion of alloying elements in total is below 5%.
Medium-alloy steels: Usually these materials are found in exhaust valve seat inserts of Otto engines and in the intake and exhaust area of Diesel engines. This group of materials is the most widespread one and includes a great variety of variables. In the following the three most common ones are described:
Martensite steels mainly consist of a martensite tempering structure with finely distributed carbides, solid lubricants and sometimes hard phases. Hard phases are intermetallic phases of high hardness and resistance to temperature influence (e.g.. Co-Mo-Cr-Si- Laves-phases, Co-Cr-W-C- phases [5]).
High Speed steels (HSS) show high wear resistance due to their martensite matrix with finely distributed special carbides of the M6C or MC type which are formed from alloying elements such as Cr, W, V, Mo or Si. The material for valve seat inserts is based on standard compositions of HS steels (e.g. M2, M4, M35- type), which have been submitted to technical alloying
modifications such as dilution with iron powder, addition of solid lubricants and other hard phases.
In contrast to the other two groups of material Bainite steels do not possess a tempering structure, but at bainite based structure of higher thermal stability.
Addition of solid lubricants, carbide forming elements and hard phases
combined with the structure provide good hot wear resistance. Co, Ni and Mo are typical alloying elements.
All medium-alloy steel groups are available in copper infiltrated quality, too. In this case the open pore volume of the sintered compact is filled with liquid copper during the sintering process. This alloy shows improved thermal conductivity and better machinability.
High-alloy steels: This group includes martensite and austenite materials. They are used in engines with demanding requirements concerning resistance to high
temperature oxidation and corrosion. Ni, Cr and Co are typical alloying elements of
0 0,5 1 1,5 2 2,5
P+S
CalibrationH-sintering
Cu-Inf. 2x(P+S) Turning Forging
relative costs
Figure 8: relative costs of individual PM production stages
optional
Tempering process Hardening process Vapourization process
Calibration process
Mechanical machining Turning process Grinding process Sintering process Pressing process Mixing process
Figure 7: PM Production Process Scheme
this group. Comparison to the other groups shows that due to the high portion of alloying elements these materials are very expensive. For this reason the materials are often used in double-layer technology, which means that, the valve seat insert consists of two different material layers – a high-alloy one facing the seat and a low-alloy one facing the port area [6].
Non-ferrous alloys. In contrast to cast iron alloys Ni- / Co- master alloys are really rare in the PM field. Thus they are not described here. Copper materials are of special interest in the field of motor sports applications. Target of modern material
engineering is to substitute the toxic alloying element beryllium. Adding of ceramic particles such as Al2O3 already resulted in wear resistance parameters equivalent to those of standard applications [9].
2.3 Characteristic Features
Valve seat inserts must possess certain material properties to fulfil the application engineering requirements. These key
characteristics are described below.
Hot Hardness [7]: Usually elevated temperature hardness indicates the wear resistance of a material when exposed to elevated temperature. Strong decline in hardness indicates the potential temperature limit of the application.
(Figure 9).
Thermal Structural Stability:
Thermal structural stability indicates modification of the material under temperature influence. The different effects have
been
summarized in figure 10.
Materials with a annealing structure are especially
expected to show diffusion related modifications under thermal stress.
Thermal Expansion Coefficient: Valve seat inserts are installed into cylinder heads by press fit. A similar thermal expansion coefficient of the materials for cylinder head and valve seat insert is of great advantage. If the
prevailing conditions differ considerably, increase in heat for example may result in reduction of pressing forces in parts with a
combination of iron based VSI and an aluminium cylinder head. The valve seat insert may fall out of the cylinder head bore and thus cause engine destruction.
For typical thermal expansion coefficients refer to figure 11.
Comparision of Elevated Temperature Hardness of Cobalt, Nickel and Iron Master Alloys
50 60 70 80 90
0 200 400 600 800
Temperature in °C
Hardness HRA
Co-Basis Ni-Basis Fe-Basis
Figure 9: Comparison of elevated temperature hardness [7]
Temperature Process Effect
-190°C ... 21°C Conversion of retained austenite into martensite
Increase in hardness Dimensional changing 250°C ... 900°C Reduction of internal stress
Diffusion processes Precipitation processes
Modifications in hardness Modification in properties Structural modifications Figure 10: Effects resulting from Thermal Stress
Thermal Expansion [x10-6K]
Cylinder Head Cast Iron 9 –11
Aluminium 23 – 27
Valve Seat Insert Fe-Basis (martensite)
9 – 13 Fe-Basis
(austenite)
17 – 19
Ni-Basis 12 – 16
Co-Basis 12 – 14
Figure 11: Typical thermal expansion coefficients
Thermal Conductivity: Reduction of the valve temperature requires a sufficient heat flow from the valve head via valve seat insert into the cylinder head. Figure 12 shows the
theoretical heat flow at the valve. 70 – 85% of the total valve heat quantity is transferred via valve seat insert and the rest of 15 – 30 % via valve guide into the cylinder head. Beside good heat
transmission from the valve seat to the
seat insert and from the seat insert to the water jacket of the cylinder head, the materials used have to show adequate thermal conductivity. Theoretical calculations done by Richmond et.al.
[8] proved that an increase in conductivity from 20 W/mK to 40 W/mK reduces operation temperature of the seat insert by 50°C and of the valve by 30°C. Measurements in different engines confirmed temperature reduction in the valve head. Infiltration of medium-alloy exhaust materials with copper is especially suited to ensure these characteristics. Figure13 shows typical thermal conductivities. During design of the cylinder it has to be considered that elevated heat introduction into the aluminium material of the cylinder head in case of highly heat conducting valve seat inserts may cause reduction in strength of the aluminium.
This type of thermal overload may cause cracking of the bridge area between the ports.
Density: In order keep material stress as low as possible, materials with high density should be preferred, because the high specific contact area is of advantage in case of the prevailing stress. The choice of a suitable material also helps to avoid fatigue failures, resulting in material fractures caused by the notch effect of the pores. In contrast to casted valve seat inserts those produced of PM material tend to have a certain pore percentage.
Resistance to Oxidation and Corrosion: The extreme operation conditions with hot exhaust gases require good resistance of the valve seat inserts to corrosion and oxidation. This may be achieved by either the chemical composition of the material or purposeful passivation, for example by pre-oxidation.
Wear Resistance: The following wear mechanisms may occur:
Adhesion: Local microweldings with subsequent cracking of the contact spots. The material is transferred from one friction partner to the other. Additionally, pitting may occur.
Abrasion: Material slicing on basis of grinding and cutting processes in the micro-range.
Material is transferred to a limited degree only.
Oxidation: Formation of brittle, not firmly adhering oxide layers. Under stress these layers chip off the surface.
Corrosion: Formation of reaction phases. In case of materials containing a high proportion of nickel, the formation of nickel-sulphur eutectic with a low melting point leads to weakening of the material or even release of material parts.
A number of different processes for determination of wear resistance have been developed.
For fundamental comparison tests (so-called Screening tests) pin-disc and disc-disc test rigs
Figure 12: Heat Flow at the Valve [9]
Thermal Conductivity [W/mK]
Fe-Basis 17 – 35
Fe-Basis (Cu-infiltrated)
40 – 49
Ni-Basis 16 – 18
Co-Basis 14 – 15
Cu-Basis 100 – 200
Figure 13: Typical Thermal Conductivity Values
Valve seat Sliding contact
Valve stem and guide
are sufficient. Functional interrelationship is tested at the concrete component at so-called functional test rigs. Due to the complexity of the complete tribological system, the material for the valve seat inserts is always released in-situ in the relevant engine.
Mechanical Machining: Beside wear resistance, good mechanical machinability is a very important criterion for materials to be used
for valve seat inserts. This is of essential significance, as due to the tolerances in the cylinder and at the seat insert, final seat machining has to be carried out in
assembled state. The inserts are machined in a turning process with plunging and generation cutting. Typical machining data have been listed in figure 14. The
kind of structure, the highest possible density and addition of solid lubricants may extend tool life.
2.4 Geometry and Tolerances
Conventional valve seat inserts usually have a simple ring-shaped profile. Special shapes with profiled OD areas are used for components being casted in during cylinder head production.
These profiles are expected to avoid falling out of the seat inserts by positive locking [10].
Figure 15 gives an example of a typical valve seat insert profile. In figure 16 the most common tolerance parameters have been summarized.
Outer Diameter OD < 45 mm +- 0,013 mm
OD > 45 mm +- 0,010 mm
Rectangularity 0,03 referred to chamfer face
Surface Roughness Ra = 1,25
Inner Diameter Cylindricity +- 0,1
Inner Diameter (Angle Area) +- 0,15 Surface Roughness Ra = 3,2
Coaxiality 0,2
Seat Angle +- 1°
Surface Roughness Ra = 3,2
Height Dimension +- 0,05
Parallelism 0,04
Surface Roughness of Faces Ra = 1,6 Assembly Chamfer Tolerance of Radius +- 0,15 - +- 0,3
Tolerance of Shape of Angle +- 2°
Figure 16: Standard Tolerances in Design of Valve Seat Inserts
Plunging Generation Cutting Cutting Speed m/min 100 – 300 60 – 160
Feed mm/rpm 0,05 – 0,1 0,05 – 0,1
Cutting Depth mm 0,3 0,5
Cutting Tool Material CBN HM K10
CBN HM K10 Figure 14: Typical Machining Parameters
Inner Diameter(ID) AssemblyChamfer
Seat Angle Interference Angle
Height
Outer Diameter (OD)
Figure 15: Conventional Valve Seat Insert Profile
Valve Seat: The concrete functional area of the component is the valve seat of the insert.
Usually the valve seat is finally machined in turning processes after assembly of the cylinder head, to make sure that an exact alignment of valve axis and valve seat insert axis is achieved (mismatch max. 0,02 ...
0,03 mm in new engines). Wear at the
seat can be reduced by design through reduction of the seat angle or increase of the seat width. By reduction of the seat angle or increase of the seat width the forces, which are effective parallel to the seat face, are reduced as shown in figure 17. Tests proved that reduction of axial stress results in reduction of wear rate. Standard parameters for seat angles and seat width are listed in figure 18.
Assembly Chamfer: The chamfer positions the valve seat insert and reduces the press-in forces during the cylinder head assembly.
Turned chamfers usually possess a simple bevel with an angle of 10° – 45°. Seat inserts with the chamfer being pressed during the PM production
process often have radia sized 0,4 – 1,4 mm with an OD bevel of 10° – 15°. On principle it can be assumed that smaller bevel angles result in lower assembly forces. Additionally, the assembly area has to be kept free of burs from machining processes during turning.
Burs can be avoided by deburring of the components.
Inner Diameter: Usually the inner diameter of valve seat inserts is not machined. For optimisation of flow pattern, seat inserts of intake valves are sporadically worked with inner profiles, such as Venturi-shapes.
For improvement of feeding conditions and
achievement of constant seat width parameters after
final machining of the seat insert in the cylinder head, the valve seat area is often provided with supplementary angles. These angles usually have
a size of 30° (figure 19).
Wall thickness: More and more compact
construction of modern engines require thin-walled valve seat inserts on the one hand. On the other hand increasing mechanical stress of the seat insert and production aspects have to be considered.
Standard wall thickness for large-scale production exceeds 1.8 mm. Figure 20 shows the recommended height/wall thickness ratios.
0 20 40 60 80 100 120 140
0 0,5 1 1,5 2 2,5
Seat Width in mm
Axial Face Stress in %
20°
30°
45°
Figure 17: Comparison of Axial Face Stress in Dependence on Seat Angle and Seat Width
Seat Width in mm Seat Angle Intake Exhaust
Otto Engine 1,2 – 1,6 1,4 – 1,8 45°
Diesel Engine
PC 1,6 – 2,2 1,6 – 2,2 45°
CV 2,0 – 3,0 2,0 – 3,0 20°-45°
Gas Engine 1,8 – 2,5 1,8 – 2,5 20°-45°
Figure 18: Standard Seat Width and Seat Angles
Figure 19: Supplementary Angle
Height of Insert H Height / Wall thickness 5 – 6 mm < = 2,5
6 – 9 mm < = 3,0
> 9 mm < = 4,0 Figure 20: H/W-Ratio
Suppl. Angle Machined
Seat Angle
Outer Diameter: Adequate press fit in the cylinder head is achieved by 0,05 – 0,13 mm overlapping over the cylinder head bore [7]. Another point of reference for the design of aluminium cylinder head assemblies is calculated as under:
) (
*
% 4 , 0 ...
3 ,
0 Borediameter Cylinderhead ce
Interferen =
On principle, interference has to be adapted to the relating application as it depends on both the outer diameter of the seat insert and as well as the heat expansion of the seat insert and cylinder head materials. For good heat transfer into the cylinder head, the side facing the combustion chamber has to have especially good contact to the bore face of the cylinder head, as most of the heat is transferred there.
Figure 21 illustrates the heat dissipation within one exhaust valve seat insert.
For PM production of valve seat inserts it is important that the ratio of outer diameter / wall thickness is within the range of 10 – 13. This is essential for a sufficient green strength of the powder press compacts, which have not yet been sintered. Such a limit is not known for castings.
3. Cylinder Head Assembly
Functionality of the valve seat inserts is considerably influenced by the cylinder head geometry. The temperature prevailing in the seat insert is influenced to a large extent by design and assembly. It is of great importance that the outer diameter of the seat insert fits close to the bore face of the cylinder head. Roundness of the diameters and rectangularity of the outer diameter to the seat faces of bore and seat insert are as important as the distortion tendency of the cylinder head. Installation of the seat inserts into the cylinder head at room temperature may cause plastic deformation of the cylinder head material with material folding during assembly, due to overlapping of seat inserts and boring. A perfect seat with adequate contact area is thus prevented. Insertion of valve seat inserts after intense cooling in liquid nitrogen ensures low insertion forces on the one hand, but increases brittleness of seat insert material on the other hand. Exact process sequences are of vital importance as delays in time during assembly immediately result in an increase of insertion forces and the risk of a non- perfect press fit
4. Prospects
Changing engine requirements, alternative fuels, environmental regulations as well as the always present claim for cost savings will be pushing the development of new valve seat insert materials. New production techniques taking the place of the valve seat insert in its current form are already under development. Realization of these techniques is still influenced by questions of reliability, reproducibility and costs of manufacture, but the success in engines shows that realization on principle is possible.
Engineering activities, however, are still dominated by the requirement for materials fulfilling the demands of extreme engine conditions. From the present point view, a critical way of looking at the tribological system seems to be quite inevitable.
Figure 21: Temperature Dissipation within an Exhaust Valve Seat Insert
600°C
150°C
5. Literature
[1] VDA-Mitteilungen 1999, Internet: www.vda.de
[2] Dolenski, T.: Konstruktion eines Hochtemperatur-Stift-Scheibe- Verschleißprüfstandes, Diplomarbeit FH Bochum 1998
[3] SAE Valve Seat Information Report, SAE J 1692, Society for Automotive Engineers, Inc. Warrendale, PA (1993)
[4] Rodrigues H., Sintered Valve Seat Inserts and Valve Guides: Factors Affecting Design, Performance & Machinability, Proceedings of the International Symposium on Valve Train System Design and Materials, ASM (1997)
[5] Dooley D., Trudeau T., Bancroft D., Materials and Design Aspects of modern valve seat inserts, Proceedings of the International Symposium on Valve Train System Design and Materials, ASM (1997)
[6] Motooka N. et al, Double-Layer Seat inserts for Passenger Car Diesel Engines, SAE Technical Paper Series 850455 (1985)
[7] Valve seat insert information report, SAE J 1692, 30.8.1993
[8] Richmond, J., D.J.S.Barrett, and C.V.Whimpenny, ImechE, C389/057,121-128 (1992) [9] Dalal K., Krüger G., Todsen U., Nadkarni A., Dispersion strengthened copper valve
seat inserts and guides for automotive engines, SAE Technical Paper Series 980327 (1998)
[10] Rehr A., Offenlegungsschrift DE 3937402 A1, Deutsches Patentamt, (1991)
