US3436030A - Homogenisers - Google Patents

Description

April l, 1969 M. G. STANTON HOMOGENISERS Sheet Filed Aug. l1, 1966 Nv mw mw mw s,

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nted States Patent O U.S. Cl. 241--199 9 Claims ABSTRACT OF THE DISCLOSURE A homogeniser has a mortar bore containing a pestle and means for adjusting the clearance between the pestle yand the :bore and for keeping the pestle axially aligned in the bore. A plunger is used to move material in the bore into contact with the pestle.

The present invention concerns homogenisers, and has particular, although not exclusive, application to tissue homogenisers.

Tissue homogenisers are used for breaking organic tissue into its elementary parts, and find much application in :tields such as the study of the microstructure of living cells.

Tissue homogenisers have already been proposed which comprise a pestle usually having a bulbous cylindrical portion at one end and a shaft at the other end which is connected to a motor to rotate the pestle. The bulbous cylindrical portion is concentrically received with a small clearance in a circular bore in a mortar. Usually the axis of the pestle and mortar is vertical. In use, the tissue to be homogenised (the homogenant) is placed in the bottom of the mortar at the end of the bore and covered with a dispersive medium, which may conveniently be a buffered sucrose solution. The pestle is rotated and introduced into the mortar, and moved towards the tissue until the tissue is trapped between the bottom of the pestle and the bottom of the pestle and the bottom of the mortar. The shear forces in the tissue, occasioned by the contact of the tissue on the one hand with the rotating pestle and on the other hand with the stationary mortar, disrupt the inter-cellular structure of the tissue so that the cells or groups of cells are dispersed into the dispersive medium. The dispersive medium carries the dispersed cells into the small clearance between the bulbous portion of the pestle and the walls of the bore of the mortar where the shear stresses can be suiiiciently high to disrupt the cell structure itself and to disperse the constituent parts of the cells in the dispersive medium.

In order that the tissue may be relatively uniformly homogensied in the dispersive medium, it is initially subjected to a period of inter-cellular disruption between the end of the pestle and the bottom of the mortar in the manner previously described, following which, the mortar is moved up and down relative to the pestle so that the disrupted tissue suspended in the dispersive medium is forced through the clearance between the bulbous portion of the pestle and the walls dening the bore of the mortar.

While it is obviously a simple matter to regulate the rotational speed of the pestle relative to the mortar, in homogenisers of these known types, the minimum clearance between the pestle and the mortar cannot be accurately xed. This is because, among other reasons, the pestle is supported only in the bearings of the driving motor, and any play in these bearings, due to wear for example, is reected in a possible lateral movement of the bulbous-cylindrical portion which is greater in proportion 'ice to the distance of the bulbous portion from the motor bearings. Furthermore, the unsupported length of the pestle from these bearings to the distal end of the bulbous portion has tended to be so great that a disadvantageous amount of flexing of the pestle can take place.

Recent examinations of tissue fractionation techniques have revealed that homogenisers `of know types disrupt a large proportion of the intra-cellular particle, irrespective of their size. The larger particles such as mitochondria and lysosomes are particularly troublesome due to their lability. It is of particular importance therefore that the clearance between the pestle and the mortar should be held constant. Preferably also this clearance should be adjustable since different tissues and different classes of particles within each tissue have different optimum homogenising conditions. The said prior constructions do not meet these requirements fully, since even after accurate assembly of the motor, pestle and mortar, a tough material originating in the tissue, such as collagen, momentarily passing through the clearance at one point between the pestle and mortar, can cause exing of the pestle and movement in the motor bearings which will lead to very high shear stresses in the dispersive medium at a diametrically opposite point of the clearance due to a reduction in the local magnitude of the clearance.

The present invention seeks to overcome at least some of the problems encountered with the `known homogenisers, and according to one aspect of the present invention, there is provided a homogeniser comprising a mortar assembly having walls detining a bore of circular transverse cross-section, a pestle assembly having at least a portion which is of circular transverse cross-section and which is concentrically received in the bore at a selected axial disposition relative to the bore with an annular clearance, in normal operation, between the said portion of the pestle assembly and the walls of the bore, at least two axially spaced bearings each located between the pestle assembly and the mortar assembly and arranged to permit relative rotation therebetween, coupling means which can be coupled to driving means for rotating the pestle assembly relative to the mortar assembly and guiding means for directing homogenant material towards the annular clearance between the said portionV of the pestle assembly and the walls deiining the bore.

According to another aspect of this invention, there is provided a homogeniser comprising a mortar assembly having walls defining a bore of circular transverse crosssection, a pestle assembly having at least a portion of circular transverse in cross-section concentrically received in the bore at a selected axial disposition relative to the mortar assembly, with an annular clearance in normal operation, between the said portion of the pestle assembly and the walls of the bore, bearing means permitting relative rotation of the pestle assembly and the mortar assembly, the mortar assembly having constraining means serving to distribute loads on the pestle assembly substantially uniformly around the circumference of the said walls whereby to maintain the concentricity of the pestle assembly and the bore.

Preferably, the said bearing means comprises at least one thrust bearing which, in operation, is engaged in an axis direction, by the pestle assembly, the constraining means comprising a casing means serving to engage the said thrust bearing in an opposite axial direction, the casing means surrounding at least a part of the pestle assembly and at least part of the walls defining the bore and engaging the said walls in circumferential and axial directions.

The bearings serve to maintain substantially accurate alignment between the mortar assembly and the pestle, whilst allowing relative rotation therebetween.

At least one of the bores and the said portion of the pestle assembly may be tapered so that the area of the annular clearance between the said portion of the pestle assembly and the walls of the bore varies as between axially spaced transverse cross-sections through the said bore. This enables the homogenant material to be subjected to varying shear stresses, in operation ofthe homogeniser, as it passes through the annular clearance.

Both the bore and the said portion of the pestle assembly may be tapered in the same axial direction, and the angles of taper of the said portion and the bore may be substantially equal so that the radial clearance between the said portion and the walls of the bore is substantially uniform.

The said portion of the pestle assembly and the mortar assembly may be axially movable relative to each other so that the magnitude of the annular clearance may be varied.

Preferably at least one of the said bearings is a thrust bearing whereby axial loads on the pestle are resisted by the mortar assembly.

The guiding means may comprise a conduit in the mortar assembly forming an extension of the said bore, and there may be provided a plunger or like means movably disposed in the said conduit whereby any homogenant material in the conduit can be moved and directed towards the said annular clearance. There may be means for moving the plunger or like means relative to the said portion of the pestle assembly.

The tip of the said portion of the pestle assembly and the face `of the plunger or like means nearest to the tip may be so formed as to be rotatably cooperable whereby the homogeniser may be operated with homogenant material pressed between the tip of the said portion of the pestle assembly and the said face of the plunger or like means.

At least part of the said portion of the pestle assembly may be rifled so as to enhance, in operation, the shearing of homogenant in the said annular clearance.

The mortar assembly may be formed with at least one port on each axial side of the said portion of the pestle assembly respectively for the entrance of homogenant material to the annular clearance and for the exit of homogenate material therefrom.

Preferably, the previously mentioned riing of the said portion of the pestle assembly is such as to assist, in operation, the flow of material from the entrance port to the exit port.

There may be provided a jacketing wall surrounding, and spaced from, the said walls of the bore so as to dene a space outwardly of the bore for receiving a temperature regulating uid, such as water.

At least one of the said bearings may be adjustable for wear `or play whereby the said portion of the pestle assembly may be maintained substantially concentric with the walls of the bore.

'Embodiments of the invention will now be described by way of example only and with reference to the accompanying drawings in which:

FIGURE 1 is a diagrammatic cross-section of one form of tissue homogeniser in accordance with the invention,

FIGURE 2 is a partly-sectioned perspective view of part of a needle roller bearing employed in the homogeniser of FIGURE l, and

FIGURE 3 is a diagrammatic cross-section of another form of tissue homogeniser in accordance with the invention.

In the drawings, any item which appears in more than one of the figures is given the same reference numeral in each igure.

In the FIGURE 1, the tissue homogeniser, generally indicated by reference numeral 10, comprises a mortar assembly including a mortar tube 11 having an internal bore 12 of circular transverse cross-section, and a pestle assembly comprising a pestle 13 of circular transverse cross-section, a portion 14 of which is concentrically received in the bore 12.

The mortar tube 11 is received as a low-tolerance sliding t in two axially spaced internal annular flanges 15, 16 of an outer casing 17, forming part of the mortar assembly, the outer casing 17 surrounding the mortar tube 11 and being spaced therefrom to dene an annular space 1S which, in operation, is supplied with water at a selected temperature, to regulate the temperature in the bore 12 of the mortar tube 11. The internal flanges 15, 16 are each recessed on their inner faces, and rubber O- rings 19, 20 are received in the recesses to prevent the escape of water from the space 18. The outer casing 17 is provided with inlet and outlet ports 21, 22 for the water.

To the right (as viewed in FIGURE 1) of the O-ring 20 in ange 16, the mortar tube 11 has a feed port 23 which registers with a port 24 in the outer casing 17, and to the right of the ports 23, 24, the outer casing 17 is provided with an internal shoulder 25 which cooperates with an external shoulder 26 on the mortar tube 11 with a rubber 'O-ring 27 therebetween to prevent any leakage of homogenant fed from the ports 23, 24 between the outer surface of the mortar tube 11 and the inner surface Aof the outer casing 17.

The external shoulder 26 of the mortar tube 11 is provided with fine pitch external threads 2S which coopearte with tine pitch internal threads of the outer casing 17 so that the mortar tube 11 can be screwed into position in the outer casing 17. The right-hand end (as viewed in FIGURE 1) of the mortar tube 11 is formed with a ilange 29 which engages against the face 30 of the outer casing 17 with a spring washer 31 therebetween so that the relative axis positions of the mortar tube 11 and the outer casing 17 are accurately defined.

The other, left-hand, end of the outer casing 17 has a widened portion 17a which accommodates a driving pulley wheel 32 secured on the pestle 13 by means of a radial grub-screw 33, and is provided with internal threads 34 which cooperate with external threads of an end-cap 35 which closes the left-hand end of the homogeniser 10. The widened portion 17a has two peripherally-spaced axially-extending slots 36 (only one of which is visible in FIGURE 1) extending from the end-cap 35 so that an endless driving belt 37 can pass from the driving pulley wheel 32 to a driving motor (not shown).

The pestle 13 and pulley ywheel 32 are mounted for rotation relative to the outer casing 17 and the end-cap 35 by means of two axially spaced bearings generally indicated by 37a and 37b respectively.

The left-hand bearing 37a is a spring-loaded journal and thrust bearing which comprises an inner race 38 trapped between a shoulder 39 on the pestle 13 and a Washer 40 which is threada'bly attached on the pestle 13, and an outer race 41 in the form of an annular ring which is slidably received in the end cap 35, there being a number 'of ball bearings 42 which axially and radially separate the iner race 38 and the outer race 41. The outer race 41 is urged axially towards the inner race 38 by a compression spring 43 which is retained by a washer 44 secured to the end cap 35. The axial position of the pestle 11 and the bearing 37a relative to the outer casing 17 and the end cap 35 is determined by the axial position of an adjusting screw 45 which is threadably received in the end cap 35 and which acts on the pestle 13 in opposition to the compression spring 43 through a trapped ball bearing 46.

It will be apperciated that any axial thrust towards the left, in FIGURE l, on the pestle 13, will cause the shoulder 39 to engage with the inner race 38 of the thrust thrust bearing 37a the spring 43 then distributing the axial load via the Washer 44 substantially uniform in a circumferential sense around the face of the end cap 35. The uniformly distributed load is then transmitted to the mortar tube 11 by the engagement of the outer casing 17 with the end cap 35 on the one hand and the mortar tube 11 on the other hand. The flanges 1S, 16 and the cooperating threads 28 between the outer casing 17 and the mortar tube 11 constrain the mortar tube 11 and maintain the concentricity of the pestle 13 and mortar tube by distributing any axial loads on the pestle 13 substantially uniformly around the circumference of the mortar tube 11.

The right-hand bearing 37b (as viewed in FIGURE 1) is a needle roller bearing of the type which is adjustable for radial clearance, and comprises, as will be seen from FIGURES l and 2, an annular inner race 47 which is retained between a shoulder 4S on the pestle 13 and a spring clip 49, and a number of needle rollers 50r disposed in a suitable retaining cage for rolling around the radially outer face of the inner race 47 and the radially inner face of an outer race 52. The needle rollers 50v in their retaining cage can move axially with respect to the inner race 47 but are prevented from such movement relative to the outer race 52 by the annular anges 53, thereon (see FIGURE 2). The outer race 52 is trapped between an internal shoulder 54 of the outer casing 17 and a threadably attached internal collar 55 on the outer casing 17. The outer race 52 is corrugated in axial crosssection so that by varying the axial spacing of the internal collar 55 and the internal shoulder 54, the radial distance between the outer race 52 and the inner race 47 can be varied to take up any wear in the needle rollers 50.

Between the bearing 37b and the adjacent end of the mortar tube 11 are provided two oppositely facing conventional rotary seals 56 which are axially urged apart into cooperation with internal shoulders 50 on the outer casing 17 by an annular spring 57. The upper side of the outer casing between the seals 56 is provided with a grease nipple 59 closed by a spring-urged ball valve 60. The lower side of the outer casing 17 between the seals 56 is provided with a grease drainage hole closed by a removable threaded plug 61. In operation, the space between the two rotary seals 56 is packed with a biologically inert grease to avoid the possibility that material in the mortar tube 11 could pass to the bearings 37b, 37a and contaminate and damage them. The outer casing 17 is provided with a discharge port 62 between the right-hand seal 56 and the adjacent end of the mortar tube 11 so that material to be homogenised (the homogenant) can be fed continuously to the feed port 23 and discharged continuously from the discharge port 62.

During operation of the homogeniser 10, the homogenant passes from the feed port 23 through the bore 12 in the mortar tube and via the annular clearance 63 between the right-hand portion 14 of the pestle 13 and the surrounding wall of the mortar tube 15 and is discharged at the discharge port 62. While the homogenant passes through the clearance 63, it is subject to shear forces caused by the rotation of the portion 14 of the pestle relative to the surrounding wall of the mortar tube 11 which disrupt the tissue to a degree dependent on the width of the clearance `63 and on the speed of rotation of the pestle 13. The provision of the two axially spaced bearings 37rz, 37b and the relatively short and thick pestle 13 ensures that the pestle 13 will not be ilexed or bent by the passage of hard tissue materials such as collagens, through the clearance 63, so that the clearance 63 will be maintained substantially uniform, in operation, in each transverse cross-section therethrough.

It will be seen that the portion 14 of the pestle 13 within the mortar tube 11 is tapered away from the end cap 35, and that the surrounding wall of the mortar tube 11 is substantially parallel, in axial cross-section, to the portion 14 so to provide a bore which tapers towards the feed port 23 at substantially the same angle as the portion 14 of the pestle 13. Accordingly, the clearance 63 will be substantially uniform at all regions between the portion 14 and the mortar 11, although the difference in the areas and the mean radii of the axially opposite ends of the clearance 63 will provide that the shear stresses set up in the homogenant will be smallest towards the tip 13a ot the pestle 13 and will increase as the homogenant passes through the clearance 63 towards the discharge port 62.

It will be appreciated that if the axial position of the pestle 13 is adjusted relative to the mortar 11, by means of the adjusting screw 45, the magnitude of the clearance can be regulated. Thus, if the adjusting screw 45 is so turned that the pestle 13 is moved to the right, in FIGURE l, relative to the mortar tube 11, the clearance `63 will be reduced. Similar, if the adjusting screw 45 is so turned that the pestle 13 is moved to the left, (by the action of the spring 43) clearance 6-3 will be increased. Since the shear stresses which disrupt homogenant in the clearance 63 depend on the magnitude ofthe clearance, as well as the relative rotary speeds of the portion 1-4 of the pestle 13 and the mortar tube 11, it is possible to arrive at a selected degree of disruption of homogenant by twining the adjusting screw 45, and there may be no need to change the speed of rotation of the pestle 13 during operation.

The homogeniser 10 is further provided with a plunger 64 (partly sectioned in FIGURE 1) which is movably disposed in the parallel-sided portion 12a of bore 12 for propelling homogenant, if necessary, towards the pestle 13 from the feed ports 23, 24. The plunger 64 is moved in bore 12 by means of a guide rod `65 passing through the ange 29 and actuated by electric or mechanical means (eg. clockwork), or by hand.

The guide rod 65 is formed with a key-way 66, and a peg 67 housed in an aperture in the right hand end of the mortar tube 11 engages in the key-way 66 to the plunger 64 against rotation about its axis. Alternatively the guide rod 65 and its hole in the flange r29 may be of non-circular cross-section.

The propelling face 68 of the plunger 64 has a complementary shape to the tip 13a of the pestle 13 so that the plunger 64 and the pestle 13 can cooperate whilst there is relative motion therebetween. In this instance, the tip 13a is of conical form and the propelling face 68 is of internally coned form so that any homogenant trapped between the plunger 64 and the pestle 13 will be subjected to shearing forces over a greater area than would be the case were the pestle tip 13a and the propelling surface 68 at.

To operate the tissue homogeniser 10 the homogenant is passed into the parallel sided portion 12a of the bore 12 in the mortar tube 11 through the ports 23, 24. If the homogenant is initially a solid piece of tissue, it is Iirst sliced into suitably small pieces, and a suitable dispersive medium, such as buffered sucrose solution, is also passed into the portion 12a of the bore 12. The motor (not shown) driving the belt 37 is now started, and the plunger 64 advanced towards the tip 13a of the rotating pestle 13. The shear stresses occasioned in the tissue by contact on the one hand with the rotating pestle 13 and on the other hand with the non rotating plunger 64 disrupts the intercellular structure of the tissue so that cells and groups of cells become suspended in the dispersive medium. The dispersive medium carries the suspended cells through the annular clearance 63, where the shear stresses, which can be selected by turning the adjusting screw 45 and/ or by choosing an appropriate rotational speed of the pestle 13, disrupt the cells to the required extent. The homogenate leaving the homogeniser 10 at the exit port 62 can be recirculated through the homogeniser 10` via the feed ports 24, 23 to achieve further disruption of the tissue, if required.

For homogenants which comprise low viscosity material, such as the previously mentioned buffered sucrose solution, the homogeniser 10 may conveniently be arranged for loading with the axis vertical and the flange 29 lowermost, the low viscosity component of the homogenant being passed into the portion 12a of the bore 12 from a syringe (not shown) having a discharge nipple which can be sealingly received in port 24. The operation of the syringe will initially ll or partly ll the bore 12.

As tissue normally sinks in a buttered sucrose solution it is necessary to propel the tissue through the annular clearance 63 between the portion 14 of the pestle 13 and the surrounding tapering wall of the mortar tube 11 by advancing the plunger 64 towards the tip 13a of the pestle 13.

In a practical example of the homogeniser 10, the pestle 13 and mortar tube 11 are formed from stainless steel, whilst the outer casing 17 is of the aluminium based alloy, Dural. The cantilevered length of the pestle 13, i.e. to the right of the bearing 37b is 21/2 inches, the untapered diameter of the pestle about 3%: inch and the angle of taper of the pestle 13, relative to its axis of rotation, about 5 degrees.

For routine cleaning, the outer casing 17 is formed in two axially discrete portions which are separable in the plane of the mating faces 69 of external ilanges 70 formed on the portions of the outer casing 17. The flanges 70 are clamped to each other by bolts 71 with a gasket 72 (or rubber O-ring) accommodated therebetween to prevent the escape of water from the annular space 18. When the bolts 71 have been undone, and the two portions of the outer casing 17 axially separated, the mortar tube 11 is removed with the right-hand portion (as viewed in FIGURE l) of the outer casing 17 leaving the portion 14 of the pestle 13 protruding from the left-hand portion of the outer casing 17 and available for cleaning. The mortar tube 11 can be cleaned either Whilst in situ in the right-hand portion of the outer casing 17 or after removal therefrom by unscrewing the threads 28 adjacent the ange 29 of the mortar tube 11.

The tissue homogeniser can ibe dismantled for more thorough servicing or overhaul by unscrewing the end cap 35 from the outer casing 17 (by means of threads 34), after which the end cap 35, the bearings 37a, the pestle 13, the pulley wheel 32 and the inner race 47 ofthe bearings 37b can be withdrawn to the left as seen in FIG. 1.

The tissue homogeniser 110 shown in FIGURE 3 is generally of similar construction to the tissue homogeniser depicted in FIGURE 1, and the difference between these designs will be highlighted below:

The tip 13a of the pestle 13 is rounded rather than conical, and is provided with spiral grooves 75 similar to the rilling of a gun and having a small angle of twist. The grooves 75 extend about a third of the length of the portion 14 of the pestle 13, from the tip 13a, and it has been found that they assist the separation of cellular tissue from more coherent materials such as collagens and also enhance the ow of homogenant through the homogeniser 110 in the Same manner as an Archimedian screw, provided the direction of twist is appropriately chosen to suit the direction of rotation of the pestle 13. The propelling face 68 of the plunger 64 is internally rounded to the same internal shape as the external shape of the tip 13a of the pestle 13 so as to be complementary in shape thereto and to permit rotational cooperation therewith.

IIn this embodiment, the mortar tube 11 has an external tapered surface 111 at its left-hand end (as viewed in FIGURE 3) which cooperates with an internal tapered surface 121 forming the radially inner face of the lefthand flange 21. At the right-hand end of the mortar tube 11, the threads 28 have been omitted, and the ilange 29 is urged towards the outer casing 17 yby bolts 77 which engage in threaded lblind bores 78 in the outer casing 17. The cooperation of the tapered surfaces 111, 121 of the mortar tube 11 and the outer casing 17 together with the provision of the bolts 77 to provide engagement between the mortar tube 11 and the casing 17 enables the pestle 13 and the mortar tube 11 to jbe accurately aligned after each disassembly. Preferably, when the homogeniser 110 is assembled, there is a small gap 80 between the adjacent faces of the outer casing 18 and the flange 29 to allow for compensation for any wear which may have taken place in the tapert surfaces 111, 121 by adjustment of the bolts 77. In a variant of this embodiment, the ange 29 is extended transversely (as shown 4by dotted lines 29a) and the external flanges 70 and flange 29a are connected by bolts 77a (shown dotted) so as to increase the rigidity of the mortar assembly.

The mortar tube 11 is further provided with an external shoulder 79 to the left (as viewed in FIGURE 3) of the shoulder 26. The shoulder 79 cooperates with a shoulder 81 to trap the rubber O-ring 20 therebetween (instead of disposing the O-ring 20 in a groove in the internal flange 16 asin the ligure/embodiment), the O- ring 20 serving to prevent seepage of water outwardly from the annular space 18. The tissue homogeniser also employs an O-ring 172 located in cooperating grooves in the flanges 70 instead of the gasket 72 employed in the homogeniser 10 of FIGURE 1.

It will Abe seen in both of the described embodiments that since the mean radius of the annular clearance 63 between the portion 14 of the pestle 13 and the surrounding internally tapered surface of the mortar tube is smallest nearest to the feed port 23 and largest nearest to the discharge port 62, the homogenant is initially subjected to the lowest shear stresses, and as it progresses through the annular clearance 63 towards the exit port 62 the shear stresses become greater. It may from time to time be preferable that the shear stresses suffered by the hornogenant are initially greater than they are just before the homogenant reaches the exit port. Accordingly, it is contemplated that the homogenant may be loaded into the homogeniser 10 or 110 via the discharge port 62, to issue as homogenate vvia the feed ports 23, 24. Alternatively, the homogeniser 10 or 110` may be so adapted that the tapering portion 14 of the pestle 13 and the sur rounding internally tapered surface of the mortar tube 11 taper the opposite way to that shown in FIGS. 1 and 3, so that the annular clearance 163 between these surfaces decreases in mean radius in passing from the ports 23, 24 to the discharge port 62 of the homogeniser 10 (or 110). In this alternative, the homogeniser would need to be assembled in a manner dilering from the manner shown in FIGS. 1 and 3: for example, the `pestle 13 could be formed with the tapering portion threadably attached to the remainder of the pestle 13 from opposite axial ends of the homogeniser.

It is contemplated that instead of both the pestle 13 and the internal bore of the mortor tube 11 having tapered surfaces or portions, only the pestle 13 or the bore 4may have a tapered surface or portion. Furthermore, whilst in the described embodiments, the angles of taper of the portion 14 of the pestle 13 and the internally tapered surface of the mortar tube 11 are substantially equal, the angles of taper of the pestle 13 and the mortar tube 11 may diler to provide a required disrupture effect ofthe material to be hornogenised.

Various combinations of features of the described embodiment may be employed without departing from the invention.

I claim:

1. A homogeniser comprising a mortar assembly having walls defining a bore of circular transverse crosssection, a pestle assembly having at least a portion of circular transverse cross-section concentrically mounted in said bore at a selected axial disposition relative to the mortar assembly, said portion and said walls normally defining an `annular clearance, said mort-ar assembly delining a conduit communicating with said annular cleavance, plunger means movably disposed in said conduit for urging homogenant material in said conduit towards said annual clearance, and the pestle assembly and the plunger means having cooperating opposed faces adopted to permit rotation of the pestle assembly relative to the plunger means.

2. A homogeniser -as in claim 1, wherein said bore defined by said walls of said mortar assembly land said conduit are contigous and have their axes aligned.

3. A homogeniser as in claim 2, wherein said cooperating opposed faces comprise an end face of said pestle assembly and an end face of said plunger means.

4. A homogeniser as in claim 3, wherein the end face of the pestle is of general conical form.

5. A homogeniser as in claim 3, wherein the end face of the pestle is rounded.

6. A homogeniser comprising a mortar assembly having walls dening a bore of circular transverse crosssection, a pestle assembly having at least a portion of circular transverse cross-section concentrically mounted in the -bore at a selected axial disposition relative to the mortar assembly, said portion and said walls normally defining an annular clearance, and two spaced apart bearing means supporting said pestle assembly for rotation relative to said mortar assembly, one of said bearing -means being adjustable for wear whereby the said portion of the pestle assembly may be maintained substantially concentric with the walls of the bore.

7. A homogeniser 4as in claim 6, wherein said adjustable bearing means is nearer said portion of said pestle assembly than the other bearing means.

References Cited UNITED STATES PATENTS 1,985,569 12/1934 Haskell et al. 241-247 1,988,743 1/ 1935 MacKenzie 241-247 X 2,173,975 9/1939 Lyons 241-256 X 2,231,421 2/1941 Gitzendanner 241-256 2,338,198 1/1944 Pall 241-199 X 2,547,330 4/1951 Morden 241-247 X ANDREW R. JUHASZ, Primary Examiner.

F. T. YOST, Assistant Examiner.

U.S. C1. X.R. 241-247, 256

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