US3742566A

US3742566A - Processing of finely divided particulate materials

Info

Publication number: US3742566A
Application number: US00161791A
Authority: US
Inventors: H Reinhardt; B Brandt; A Peters
Original assignee: Degussa GmbH
Current assignee: DEUTSCHE GOLD und SILBER SCHEIDEANSTALT DT; Evonik Operations GmbH
Priority date: 1968-11-08
Filing date: 1971-07-12
Publication date: 1973-07-03
Anticipated expiration: 1990-07-03
Also published as: NL163433B; GB1294338A; NL163433C; US3860682A; ES395483A1; US3738785A; ES196249Y; DE1807714C2; ES372366A1; DE1807714B1; CH497224A; JPS5111344B1; FR2024818A1; ES196249U; NL6915288A; US3762851A

Abstract

A mass of finely divided material is confined in a chamber. Two rollers are arranged for rotation in the chamber in axial parallelism with one another and define with each other a narrow longitudinally extending gap. At least one of the rollers has a circumferential wall composed of gas-permeable porous material. This one roller is hollow and arranged to communicate with a source of underpressure so that, as the roller rotates, the particulate material is attracted onto its outer surface forming a layer thereon which is subjected to substantial compaction when it passes through the gap between the two rollers. The rollers rotate in opposite direction. The compacted material is removed from the outer surface of the roller or rollers and subdivided into portions of desired size. A roller for use in the apparatus is disclosed.

Description

United States Patent 1191 Reinhardt et al.

[ July 3,1973

[ PROCESSING OF FINELY DIVIDED PARTICULATE MATERIALS [75] Inventors: Helmut Reinhardt, Weiss near Cologne; Bernd Brandt; Albert Peters, both of Wesseling-Berzdorf, all of Germany [73] Assignee: Deutsche Gold- Und Silber-Scheideanstalt vormals Roessler, Frankfurt am Main, Germany 22 Filed: July 12, 1971 21 Appl.No.: 161,791

Related U.S. Application Data [62] Division of Ser. No. 874,654, Nov. 6, 1969.

[30] Foreign Application Priority Data Nov. 8, 1968 [56] References Cited UNITED STATES PATENTS Spencer 29/130 X Germany P 18 07 714.0

Primary Examiner-Alfred R. Guest Att0rney-Michael S. Striker 5 7 1 ABSTRACT A mass of finely divided material is confined in a chamber. Two rollers are arranged for rotation in the chamber in axial parallelism with one another and define with each other a narrow longitudinally extending gap. At least one of the rollers has a circumferential wall composed of gas-permeable porous material. This one roller is hollow and arranged to communicate with a source of underpressure so that, as the roller rotates, the particulate material is attracted onto its outer surface forming a layer thereon which is subjected to substantial compaction when it passes through the gap between the two rollers. The rollers rotate in opposite direction. The compacted material is removed from the outer surface of the roller or rollers and subdivided into portions of desired size. A roller for use in the apparatus is disclosed.

12 Claims, 2 Drawing Figures PATENTEUJUL3 I975 snmmrz PI V HIIII ATTORNEY PROCESSING OF FINELY DIVIDED PARTICULATE MATERIALS CROSS-REFERENCE TO RELATED APPLICATION This application is a division of our application Ser. No. 874,654, filed Nov. 6, 1969 and entitled Processing of Finely Divided Particulate Materials.

BACKGROUND OF THE INVENTION The present invention relates generally to the processing of finely divided particulate materials, and more specifically to the processing of such materials which requires pre-condensing and subsequent compacting of such materials into desired shapes. The invention relates to an apparatus foreffecting such processing and to a roller for use in the apparatus.

In many instances the processing of finely divided particulate material, such as pulverulent or finecrystalline and organic materials, frequently depends upon the possibility of increasing the volumetric weight of such materials without destroying or adversely influencing their specific characteristics which depend upon the fine division of such materials. This is particularly true of highly dispersed surface-active'filler materials, such as silicium oxide, carbon black, aluminum oxide, aluminum silicates and calcium-silicates, all materials I which are used in very large quantities in various industries.

The problems involved in the processing of these materials are not insignificant. On the one hand, in their while the space required for storage and transportation is substantially reduced, and dusting during filling, metering and processing is largely eliminated. It has been proposed to achieve this by transforming the finely divided materials into agglomerates of certain configuration and dimension by subjecting them to mechanical pressure. This has been found to be practical in a continuous operation only if the significant quantities of gases present in highly dispersed materials are first removed, because otherwise it is not possible to obtain agglomerates with sufficient adhesion under mechanical pressure. it has been found, for instance, that it is impossible to obtain the desired compaction and adhesion simply by passing such materials between two metal rollers which subject them to mechanical compression. Therefore, gas removal and pre-condensing has been resorted to, utilizing in known continuously operating apparatus of the type in question pressuretype conveyor screws, rollers or pairs of rollers provided with radial projections or provided on the surface of at least one roller with profiling. However, it has been found that the degassing or outgassing effect and compaction obtainable with such apparatus, which for the actual compaction utilizes a pair of pressure rollers,

is inadequate compared to the complexity and expense of the apparatus involved.

A further approach which has been tried is to deposit the material to be compacted onto hollow rollers, so-

called filter rollers, whose circumferential wall is gaspermeableand whose interior is subjected to underpressure. The gas is thereby withdrawn from the deposited material and the material is supplied by the filter rollers to the compacting gap between a pair of pressure rollers. Various modifications have been proposed for this basic approach but in each case the gap between the pressure rollers-4n which the material is subjected to compaction-is fixed. This approach is limited in its applicability because it permits only the production of compressed blanks, as the compacted bodies made from the compacted finely divided particulate materials will hereafter be called for the sake of convenience, without specific form and only within a rather broad range of grain sizes. A further disadvantage is that the compacted blanks obtained in this manner have a widely varying breaking resistance, a fact which is of particular disadvantage if the compacted blanks are of filler material which is intended for certain applications, for instance for use in rubber mixtures, because with the mixing procedure used in the production of rubber mixtures the compacted blanks can be broken down only partially to the original grain size. The result of this is an inadequate dispersal of the filler material and the resulting typical formation of pockets and cavities in the vulcanized goods.

In addition certain materials, for instance light reinforcing filler materials such as SiO can be compacted only to a bulk density of approximately 250 g/l in the apparatus known from the prior art and utilizing the socalled filter rollers, because the low mechanical strength of the fabrics used for the circumferential walls of the filter rollers makes it impossible to utilize higher compacting pressures. This is quite aside from the fact that even at these lowered operating pressures the fabrics must be very frequently replaced.

SUMMARY OF THE INVENTION It is, accordingly, an object of the present invention to overcome the "aforementioned disadvantages.

A more particular object of the invention is to provide an apparatus for processing finely divided particulate materials which is not subject to the disadvantages outlined before.

A concomitant object of the invention is to provide such an apparatus which enables continuous operation and the production of compacted blanks of specific desired shape and size with a defined narrow range of breaking resistance and increased bulk weight.

Still a further object of the invention is to provide a roller construction for use in 'such apparatus.

in pursuance of the above objects, and others which will become apparent hereafter, one feature of the invention resides in the novel apparatus in which, briefly stated, a mass of finely divided material is confined adjacent to the gas-permeable circumferential wall of a rotatable roller havinga hollow interior. The roller is thereupon rotated and subjected in its interior to underpressure so as 'to attract the material by suction to the same as to define with the latter a gap wherein the layer is subjected to compacting.

The roller having the gas-permeable circumferential wall, hereafter for the sake of convenience called the filter roller, may rotate partially or completely in the material to be compacted, and the same is true of the other roller. The thickness of the layer may be maintained constant by removing excess attracted material from the layer before increments of the layer enter into the gap between the two rollers. In accordance with the invention, one of the two rollers is bia'ssed towards the other with a biassing force which is preferably maintained at constant level. The other roller may also be a filter roller or it my be a roller having a known gasimpermeable circumferential wall. In any case, the layer is compacted on passage of the gap between the two rollers so as to be reduced by at least one half of its original volume and is deformedby profiling provided on the circumferential wall of at least one of the rollersinto compacted blanks of desired shape and configuration and defined range of breaking strength.

It is desired and advantageous according to the present invention that the dwell time of the material of the layer, that is of the material of which each successive increment of the layer is composed which enters into the gap between the two rollers, be below approximately 5 seconds, a time value which of course depends upon the roller circumference and the speed of rotation of the rollers.

In accordance with the invention it is not necessary that two rollers be provided having a gas-permeable or porous circumferential wall, or that even two rollers of the same type be rotated oppositely one another. How ever, for granulating purposes it is desirable and preferable that one of the two rollers has a profiled surface of circumferential wall. Depending upon the profiling, compacted blanks of certain configuration are obtained, for instance granules, little rods, tablets and the like. For instance, if the profile is half-moon shaped, then the compacted blanks will be similarly configurated. These compacted blanks may then be reduced to the desired dimensions in a cutting device of known construction, for instance in a so-called rotary disc breaker. Because of the profiling on at least one of the rollers, at least two dimensions of the resulting product are already established before the cutting device acts upon the compacted blanks.

The novel features which are considered as characteristic of the invention are set forth in particular in the appended claims. The invention itself, however, both as to its construction and its method of operation, together with additional objects and advantages thereof, will be best understood from the following description of specific embodiments when read in connecting with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is'a partially sectioned diagrammatic perspective view of an apparatus according to the present invention; and

FIG. 2 isa partly sectioned somewhat diagrammatic perspective view illustrating one embodiment of a roller for use in the apparatus of FIG. 1.

DESCRIPTION OF THE PREFERRED EMBODIMENTS As shown in FIG. 1, the apparatus comprises a housing 1 having two transversely spaced walls 111. Mounted in the housing 1 is a filter roller 2, for instance of the type which will be discussed more specifically with reference to FIG. 2. The roller 2 is hollow, and arranged for rotation in axial parallelism with the roller 2 is the roller 3 rotating in the direction opposite to the roller 2, as indicated by the arrows respectively associated with the two rollers. The circumferential wall of the roller 3 is not gas-permeable, and the roller 3 is therefore not designated as a filter roller as is the case with the roller 2. Instead, the circumferential wall of the roller 3 is provided on its exterior with a half-moon shaped longitudinal profile 4, shown in cross-section.

According to the invention the dimensions of the housing 1 are so selected that the spacing between the filter roller 2 and the housing walls 1 in direction normal to the longitudinal axis of the filter roller 2 is substantially greater than the gap between the

rollers

2 and 3. v

The shaft 15 about which the filter roller 2 rotates is hollow and a suitable source of underpressure may be connected with it in order to obtain underpressure in the interior of the filter roller 2.

A measuring transducer 13a and a PI regulator which is coupled with an indicator device 13c, permit regulation of the value of underpressure applied to the interior of the filter roller 2, via a valve 13c.

Slide bearings 9 journal the shaft 15 of the filter roller 2, permitting movement of the latter in the direction towards and away from the roller 3. Biass'ing devices 7, which here are illustrated as being of hydraulic type but which could be mechanically or pneumatically operated, act upon the bearings 9 and bear upon a support structure which is located exteriorly of the wall 1a of the housing. A hydraulic pump 12a provides the necessary biassing force whose value is registered on the indicators 12b. If a pressure increase takes place in the system as a result of changes in the size of the gap between the

rollers

2 and 3, caused by increased thickness of the layer of material as it enters the gap or by other factors, the increased pressure can yield and fluid escapes into the two reservoir bulbs 120 which are provided. Two pressure relief valves 12d are provided intermediate the reservoirs 12c and the biassing devices 7 in order to assure that the applied "isodynamic pressure is so reduced only after it reaches a certain level. the manually operated hydraulic pump 12a is replaced with an electrically operated pump, then a maximum-minimum or limit switch 12c must be provided for effecting automatic regulation of the desired biassing pressure.

A hopper 14 communicates with the interior space 5 in thehousing 1 for introducing into the space 5 the finely divided particulate material which is to be compacted. When underpressure is applied to the interior of the rotating'filter roller 2, the particulate material is attracted to the outer surface of the circumferential predetermined thickness, in order to provide for as much thickness equalization-of the attracted layer as possible before the same enters into the gap between the

rollers

2 and 3. The compacted material, having the configuration imparted to it by the profiling 4, falls out of the gap between the

rollers

2 and 3, and downstream of the gap it is cut to desired lengths by the cutting device provided, here illustrated as a known disc breaker or rotary disc breaker 11.

FIG. 2 illustrates a specific embodiment of a filter roller for use in the apparatus according to the present invention. Reference numeral identifies the hollow shaft a portion of which is provided with bores 15a. There are provided two side walls or end walls 17 of disc-shape which are gas-tight with the hollow shaft 15 at the opposite axial sides of the region in which the bores 15a are provided. There is further provided a circumferential wall 16 of cylindrical configuration which is provided with a plurality of small bores or other apertures 16a. The wall 16 is fluid-tightly connected with the end walls 17, for instance by welding, and in the same manner the walls 17 may be connected with the shaft 15.

Provided on the exterior of the cylindrical circumferential wall, which may also be called the inner circumferential wall 16, is an outer circumferential wall composed of a plurality of plates 18 of sintered material, for instances metallic sintered material, synthetic plastic sintered material or ceramic sintered material. These plates 18 abut one another and, insofar as they are composed of weldable material, are welded to the inner circumferential wall 16 as well as to one another where they abut the welded seams 31. However, screw means 30 may also be provided for securing the plates 18 to the inner circumferential wall 16. The inner circumferential wall 16 is provided with interior radial reinforcing ribs 19 for increasing the strength and stability of the roller, but helically convoluted ribs or axially extending ribs 190 may also be provided, or any combination of the three. Reference numeral 20 identifies the inlet opening of the hollow shaft 15 at which underpressure may be applied.

It has been found that the production of compacted blanks with defined range of break resistance is facilitated by maintaining a constant level of biassing pressure of the

rollers

2 and 3 towards one another. In order to obtain only small fluctuations of this range it is advisable to mount one or both of the rollers inthe manner shown in FIG. 1, that is in such a manner that the gap width can change automaticallyin dependence upon the thickness of the layer carried by the filter roller, ,or the compaction of the material in the gap, or other factors, thereby assuring that the compacting and compression is always effected with identical mechanical pressure. Furthermore, such a construction of course reduces the possibility of breakdown of the apparatus. v

The level of this isodynamic pressure depends in each'individual case upon the particulate material to be compacted, its moisture content and the degree of compacting which is desired. in the case of white filter materials, such as silicium dioxide, the moisture content is'for instance desirably not below l percent.

The optimum break resistance of the, compacted blanks made from a given particulate material depends upon the intended use and can readily be determined by empirical means. For instance, it has been found that SiO, granulates produced in accordance with the present invention have adequate transport stability and maximum dispersion characteristics in a test rubber mixture if a break resistance to pressure between 100 and '500 pond (p) is obtained in he compacted blanks,

measured with the hardness tester, according to German Auslegeschrift 1,374,254. The term breaking pressure is intended to mean the pressure in ponds which is necessary to abruptly destroy a granulate of 2 3 mm grain size.

The dispersion characteristics of SiO compacted blanks made in accordance with the present invention compacted silicium dioxide blanks isset to between 200 and 250 ponds, the dispersion in the test mixture is substantially better than in the test mixture to which the silicium dioxide powder was added.

For instance, if the original finely divided particulate material is a SiO powder with primary particle sizes smaller than-50 p. and with a bulk weight of approximately g/l, then a SiOfgranulate according to the present invention and having breaking pressure values between 200 and 250 ponds may beproduced unde approximately the following circumstances:

approximately 0.l 0.5 t/cm approximately 1 6 mm, up to approximately 4 mm play in direction normal to the roller roller pressure roller gap axes dwell time in the approximately 0.01 0.1 sec. 8 F underpressure applied to filter roller gas penneability of the filter roller surface approximately 0.3 0.95 kg/cm approximately 6 mlcm X i If the roller diameter is for instance 200 mm and the length of the rollers is 300 mm, the production amounts to approximately 250 kg/h granulate having a bulk weight of approximately 330 g/l. During the transportation of the particulate material on the surface of the filter roller into the roller gap, that is prior to the com .pacting which takes place in the roller gap itself, a precompacting or precompressing to a bulk weight of approximately 250 g/l is obtained in this case.

If for instance one of the rollers' has a half-moonshaped longitudinal profile in its outer circumferential surface with dimensions of 6 X 2 mm, then a finished granulate with approximately the following screen analysis is obtained by breaking the rod-shaped SiO compacted blanks falling out of the gap between the rollers in a conventional rotary disc breaker and subjecting them subsequently to screen removal of the fines smaller than 0.5 mm;

Particle Size Enlarged photographs of the individual sieve or screen fractions of the finished granulate show that the form obtained for the compacted blanks during compacting in the gap between the rollers is readily visible in case of the fraction 3 mm, and that it is still readily identifiable in case of the fraction 2 3 mm. This means that the identifiably shaped granulate quantity amounts to 65 percent, that is the total of the fractions 3 5 mm and 2 3 mm.

It will be appreciated that unlike the embodiment illustrated in FIG. 1, it is possible to mount the filter roller 2 for rotation but not for shifting movement, and to mount the roller 3 for such shifting movement. However, the embodiment illustrated in FIG. 1 is preferred.

It is advantageous in accordance with the present invention that the pores. of the material of which the outer circumferential wall of the filter roller is composed be so dimensioned that at a predetermined operational load of the suction device an underpressure of constant value in the interior of the filter roller, irrespective of whether the filter roller is partly or completely immersed in the material to be compacted.

If, as illustrated in the embodiment of FIG. 1, a rotary .disc breaker is arranged below the gap between the

rollers

2 and 3, then it is advantageous that the cutting edges of the rotary'discs of the breaker extend in planes transversely to the elongation of the gap. This is particularly advantageous if the apparatus according to the present invention produces compacted blanks in profiling which extends longitudinally of the rollers.

The material for the porous outer circumferential wall of the filter roller is a suitable sinter material, such as sinter metal, sintered synthetic plastic or sintered ceramic. It is of course not necessary that the outer circumferential wall consist of the plate-shaped portions illustrated in FIG. 2, but this enhances the stability.

It is advantageous, but not absolutely necessary, that the spacing of the filter roller from the bottom wall of the housing 1 be at least equal to half the roller diameter, and that the lateral spacing between the sinter roller and the housing wall be equal to at least one roller diameter. The doctor blade mentioned before may be adjustably mounted so as to movable towards and away from the circumferential wall of the filter roller, and it may also be so mounted that its angle with respect to the circumferential wall can be adjusted.

The pores of theporous material of the outer circumferential wall of the filter roller may have a diameter of approximately 0 200 [1,, preferably between 0 35 p. The thickness of 'the outer circumferential wall should be at least approximately 1 mm. At underpressures of 0.01 1.0 kg/cm the gas permeability of the outer circumferential wall of the filter roller may be in the region between approximately 0.1 and 7 m lcm X h.

The roller for utilization in the apparatus according to the present invention, has certain very definite advantages over the roller used in known apparatus, namely a long life irrespective of whether it is rotated at low or high rotational speeds, resistance to much higher pressure than are possible with the known constructions, and retention of its shape, that is resistance to being deformed so it is out-of-round in cross-section.

The following examples will further aid in an understanding of the invention.

EXAMPLE 1 In an apparatus according to FIGS. 1 and 2 compacted blanks of highly dispersed surface active silicium dioxide were produced. The starting material, obtained by precipitation from an aqueous silicate solution, had the following characteristics:

Dry loss (105) approximately 6% Specific weight 1.9 2.0 Bulk weight so 1 10 g/l Vibratory weight I60 200 g/l BET-surface 240 m Primary particle 16 p. diameter The apparatus utilized an isodynamically biassed filter roller and a nonadjusted rotatable non-gas permeable counter roller having half-moon shaped longitudinal profiling. Both rollers were 300 mm long and had a diameter of 100 mm. The outer circumferential wall of the filter roller was 5 mm thick andconsisted of sinter metal Siperm R (Remanit) having a maximum pore width of 35 .4.. The profile of the counter roller had the dimensions 6 X 2. Arranged below the gap between these rollers was a rotary disc type breaker with a spacing between the disc of 3 mm.

Prior to operation of the device the housing was filled via the hopper to approximately two-thirds with the pulverulent material to be compacted, a roller pressure of 0.35 t/cm was set and an underpressure of 0.6 kg/cm was applied to the filter roller. The doctor blade arranged above the filter roller was set at a distance of 15 mm from the circumferential wall of the filter roller. Thereupon, both rollers and the disc type breaker were simultaneously started. The rotation of the rollers was so regulated that the medium dwell time of the material to be compacted in the gap between the rollers was approximately 0.15 sec. The width of the gap was approximately 1- mm. The movements of the filter roller in direction normal to the axes of the two rollers, which occurred during the compacting operation, were in the range ofbetween l 3 mm.

The bulk weight of the precompacted particulate material forming a layer on the filter roller prior to entering into the gap was 255 gl. The output obtained was approximately 260 kg/h granulate having a bulk weight of 330 g/l. The breaking pressure of the compacted blanks was between 200 and 250 pond.

After screening and classification to particle sizes between 0.5 5 mm, only a fine smaller than 0.5 mm amounting to 15 percent was left.

Sieve analysis on a laboratory sieve or screen of commercially available type showed the following values in the final product:

Particle Size The granulate portion having an identifiable shape (fractions 5, 3 5 mm and 2 3 mm) correspond to 62.6 percent of the total.

The dispersion ability of the granulates was tested in a red colored test rubber mixture free of vulcanizing additives. A Brabender-Plastograph was used as dispersion apparatus.

TEST MIXTURE AND DISPERSION CONDITIONS Vessel Utili- Mixing quantities vol. zation rpm Temp. time Components 3 ml ml C' min. Butyl rubber") 28 28 50 50 10 Iron oxide batch 5 5 Kpl40(") 1.7 1.7 Granulate 20 10 The mixtures thus obtained were subsequently passed at 95 C and at a gap setting of 1 mm three times through a laboratorytwo-roller frame and then rolled out to a thickness of 5 8 mm. The quantity of dispersion was thereupon determined under a light microscope, based upon top-lighted photographs of microtome cuts taken of the rolled-out skin. No pockets or similar irregularities were found. Surprisingly, the degree of dispersion obtained with.the SiO granulates produced according to the present invention was even distinctly better than that obtained in test mixtures which were made with pulverulent starting material.

EXAMPLE 2 (COMPARISON TEST) The starting SiO material used in the Example 1 for producing granulates was pressed with a known apparatus of comparable dimensions. Precompression took place via a vertically operated screw and compacting took place in the gap between two oppositely rotating metal rollers whose circumferential walls were provided with wave-shaped serrations. In order to be able to at all obtain a granulate break resistance on the order of 2 pond it was necessary to pass the Si0 repeatedly through the gap between the rollers. The production output was only 50 kg/h. The granulate dispersion in the test mixture produced in accordance with Example 1' was significantly poorer than that of the test mixture utilizing the pulverulent starting material. It was a particular disadvantage that the fines 0.5 mm obtained onclassification in the range between 0.5 mm was 50 percent after the first compacting, and could be reduced to approximately percent only by repeated compacting.

It will be understood that each of the elements described above, or two or more together, may also find a useful application in other types of apparatus differing from the types described above.

While .the invention has been illustrated and departing in any way from the spirit of the present invention.

Without further analysis, the foregoing will so fully reveal the gist of the present invention that others can I by applying current knowledge readily adapt it for various applications without omitting features that, from the standpoint of prior art, fairly constitute essential characteristics of the generic or specific aspects of this invention and, therefore, such adaptations should and are intended to be comprehended within the meaning and range of equivalence of the following claims.

What is claimed as new and desired to be protected by Letters Patent is set forth in the appended claims:

l.-- A roller for use in an apparatus for processing finely divided particulate materials, said roller comprising a hollow shaft having an elongated apertured portion; a 'pair of disk-shaped end walls fluid-tightly mounted on said shaft at opposite axial ends of said apertured portion; an apertured inner circumferential wall extending from one to the other of said end walls concentric with said portion of said shaft and fluidtightly connected with said end walls; and a porous outer circumferential wall mounted on and exteriorly surrounding said inner circumferential wall and at least predominantly consisting of sintered material.

2. A roller as defined in claim 1, wherein said material of said outer wall is selected from the group consisting of sintered metal, sintered synthetic plastics and sintered ceramics.

3. A roller as defined in claim 1, wherein said outer wall is composed of a plurality of abutting sections; and further comprising screw means securing said sections to said inner wall.

4. A roller as defined in claim 1, wherein said outer wall is composed of a plurality of abutting sections which are welded to one another and to said inner wall.

5. A roller as defined in claim 1; and further comprising a plurality of reinforcing ribs provided on said inner wall.

6. A roller as defined in claim 5, wherein at least some of said reinforcing ribs extend axially of said inner wall.

7. A roller as defined in claim 5, wherein at least some of said reinforcing ribs extend radially of said inner wall.

8. A roller as defined in claim 6, wherein at least some others of said reinforcing ribs extend radially of said inner wall.

9. A roller as defined in claim 1, wherein said porous material comprises pores having diameters in the range between substantially 0200 u.

10. A roller as defined in claim 10, wherein said pores have diameters in the range between substantially 0-35 p.

11. A roller as defined in claim 1, said outer circumferential wall having a thickness of at least 1 mm.

12. A roller as defined in claim 1, said outer circumferential wall having a gas-permeability of between substantially 0.1 and 7 m lcm when subjected at one side to an underpressure of between substantially 001-1 .0 kg/cm

Claims

1. A roller for use in an apparatus for processing finely divided particulate materials, said roller comprising a hollow shaft having an elongated apertured portion; a pair of diskshaped end walls fluid-tightly mounted on said shaft at opposite axial ends of said apertured portion; an apertured inner circumferential wall extending from one to the other of said end walls concentric with said portion of said shaft and fluidtightly connected with said end walls; and a porous outer circumferential wall mounted on and exteriorly surrounding said inner circumferential wall and at least predominantly consisting of sintered material.

9. A roller as defined in claim 1, wherein said porous material comprises pores having diameters in the range between substantially 0-200 Mu .

10. A roller as defined in claim 10, wherein said pores have diameters in the range between substantially 0-35 Mu .

12. A roller as defined in claim 1, said outer circumferential wall having a gas-permeability of between substantially 0.1 and 7 m3/cm2 when subjected at one side to an underpressure of between substantially 0.01-1.0 kg/cm2.