Photometric control of the milling fineness of mineral filler and cement

VT notat

Titel: Photometric control of the milling fineness of mineral filler - and cement

Författare: Alexandre Akoulitch (gästforskare vid VTT, 1992-11-11 till 1993-08-10) och Alexej Busel

Avdelning: Projektnummer: Projektnamn: Uppdragsgivare: Distribution: Nr V222 1993 Vägavdelningen 47019-5

Gästforskare vid VTT från Vitryssland VTT

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A.V.Akoulitch, A.V.Busel, The Byelorussian Polytechnical Institute, Minsk

PHOTOMETRIC CONTROL OF' THE MILLING FINENESS OF MINERAL FILLER AND CEMENT

S UMMARY

This paper describes the photometric milling fineness control of minerals in mills with a continuous Operating regime. This method has been based on the dependance

between the intensity of reflected light on the material being milled and its specific surface. Two types of

mineral materials were tested: natural quartz sand and used foundry sand. The photometric equipment is described in this paper. This method can have wide applications in the production of asphalt concrete, cements, paints, etc.

AJV.AKOULITCH, AJV.BUSEL, The Byelorussian Polytechnical

Institute, Minsk

PHOTOMETRIC CONTROL OF THE.MILLING FINENESS OF MINERAL FILLER AND CEMENT

The world's production of powders at present to several

billion tons per year, and consume about 10% of all

electricity production. The major part of the powders produced consists of mineral fillers and cements. The milling fineness of these materials defines the milling energy consumed. Therefore, control of the degree of

milling fineness has become very important.

Normally, mechanical sieves of different types are used

for milling fineness control in which the sieving is performed through mechanical impact and vibration. The

sieving time is rather long.

Automation of the milling fineness control of minerals in mills with a continuous Operating regime thus requires a

new method for analyzing the milling level, in addition to new control equipment. The solution to this problem has been based on the dependence between the intensity of

reflected light on the material being milled and its specific surface. The investigation of quartz mineral

powders, performed with a UNICAM SP-7OO C

analysis of diffusivity reflection at a light wavelength of 25 cm'1 gives the most easily distinguished and stable results. Therefor, it was necessary to apply the

process of monochromatization of light, i.e. using a

filter passing light of a sharply defined wavelength. The

spectra of diffusivity reflection obtained defined the

dependences of reflectivity of milled quartz (light

material) and used foundry sand (dark material) on their

specific surface for the light wavelength of 25 cm"1 (Figure 2). Using these dependences, it is easy to define the fineness of material milled by the intensity of reflected light which is emitted from the light

source, reflected by the material being milled and passed to the photometry device, where it is registered.

An equipment plan was worked out (Figure 3), using the above method for control of the milling fineness and automation of the operation of the mill, Operating in a

continuous regime. The working principles of this

equipment are as follows. The material (6) for inspection

after milling by mill (11), goes to special tray (7), in which it passes under levelling beam (5). The levelling beam (5) makes the surface of material (6) relatively smooth. The material (6) then passed the moving conveyer belt (4) with reflective surface (3). A ray of light from source (l), reflected by the first surface (3), is

periodically sent to the surface of material (6). Part of the light beam is reflected by material (6) and passes to the next surface (3). After this, the movement of the

light beam is repeated again and again, while it is reflected by the last reflecting surface (3) and cought

by the light receiver (8). It should be noted that

repeatedly reflected light by the surface of material (6)

allows the results from different points to be totalled, thereby increasing the accuracy of measurement of the milling fineness. Dust on the reflective surface (3) is

removed by brushes (2) while the conveyer belt (4) is

moving.

The intensity of reflected light on receiver (8) thus provides information on the milling fineness of material

(6). This information is processed by the analysis system (9) for light signal (9). After processing, the

information goes to system (10), which operates the mill.

Thus the working regime of mill (ll) is regulated by the milling fineness of material (6). The process of powder

production is fully automatic under the continuous regime

of the mill equipment.

The method of photometric control of the milling fineness of mineral powders can have wide applications in the

production of asphalt concrete, cements, paints, etc. The automatic regulation of the mill by the above system

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Figure 1. The spectrums of diffusivity reflection of light for quartz fillers having a different specific surface:

C - the degree of diffusivity reflection of the light, %

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Figure 2.

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The dependence of the degree of diffusivity

reflection (C) on milling fineness of filler (K)

at light wavelenght of 25 cm"1 - - - - for quartz sand

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Figure 3. The photometry equipment for measurement of milling fineness of filler

C N U T r wa l

-J source of the light _7.

8. reflected surfaces _9. 10. 11. brushes conveyer belt levelling beam mineral material special tray light receiver

analysis system of the light

operating system of the mill ball mill