US3907474A

US3907474A - Compacting apparatus including steady and vibratory force means

Info

Publication number: US3907474A
Application number: US380538A
Authority: US
Inventors: Harry Blaser; Franz Stelzmuller
Original assignee: Von Roll AG
Current assignee: Von Roll AG
Priority date: 1972-07-20
Filing date: 1973-07-19
Publication date: 1975-09-23
Anticipated expiration: 1992-09-23
Also published as: IT991261B; GB1445736A; JPS4979908A; DE2334499A1; FR2193708A1; FR2193708B1

Abstract

To improve the accuracy of manufacturing processes, and to prevent damage to equipment, the actual compaction pressure applied to a compaction piston subjected to vibratory and steady state forces is measured, and the actual pressure compared with a command pressure to derive an error signal controlling application of steady force pressure. Steady force pressure, and vibratory energy can be separately applied to a single piston, by guiding a vibrating piston rod in a sleeve, which sleeve is subjected to steady state pressure forces, the reaction pressure force of which is measured and utilized to control application of feed power to the sleeve.

Description

[451 Sept. 23, 1975 United States Patent [191 Blaser et al.

20w499957 5fi454 6 343 444 55555555 27-7-2222-i 44444444 m mLM t. mmmm m .il-l .t t. mm e m w u wnmmm m KwBFCsHB 2 50 333 66677777 99999999 HHHHHHHH 009226300 98 4554 09 03445 $6 2 ,42 03 07947 50 5 0 66 33 33333 S cm Pl NE I In D m r E m6 m C n 2 R W m N SW :1 IF ZS h S n H UY me TR A0 .lm RT "m AA 6 A PR m0 1% B B I] f 0r v yo m r G ra nun mN "mm v w muA V H mm P m n. A n g E e 9 OT m S CS 1 A l l. 4 5 3 5 7 7 l l l [22] Filed: July 19, 1973 imary ExaminerFrancis S. Husar Assistant ExaminerJohn McQuade Appl. No.: 380,538

Attorney, Agent, or Firm-F1ynn & Frishauf ABSTRACT To improve the accuracy of manufacturing processes, and to prevent damage to equipment, the actual compaction pressure applied to a compaction piston sub- [30] Data Switzer1and....................... Aug. 18, 1972 Switzerland......

Foreign Application Priority July 20, 1972 [52] US. Cl. 425/149; 425/167; 425/353;

jected to vibratory and steady state forces is measured and the actual pressure compared with a command pressure to derive an error signal controlling application of steady force pressure. Steady force pressure, and vibratory energy can be separately applied to a single piston, by guiding a vibrating piston rod in 4 6 m, I 4 51L. a 2 485 4 O 28 2 4 l 3 M 2 a 4 [51] Int. [58] Field of Search..................

a sleeve, which sleeve is subjected to steady state pressure forces, the reaction pressure force of which is measured and utilized to control application of feed power to the sleeve.

References Cited UNITED STATES PATENTS 425/359 425/412 425/42l 18 Claims, 5 Drawing Figures 784,154 Gutteridge et 1,602,598 Stebbins............... 2,541,981 Babcock US Patent Sept. 23,1975 Sheet 3 of5 3,907,474

US Patent Sept. 23,1975 Sheet 5 of5 3,907,474

l I l W controlled.

COMPACTING? APPARATUS INCLUDING STEADY A NDVIBRATORY FORCE MEANS r' Cross reference to related Patent: US. Pat.. No. =-3,767-,35l; assigned to the Assignee of this invention.

'Thepresent invention relates to an apparatus for I manufacturing blocks-from.granulates, and particui larly electrodes inwhich-granulates are mixed with a =-binder.- i \1 ,lthas previously been proposed to make blocks, particularly block electrodes by mixing .granulates with a binder, charging thegmixture intoa compacting vessel or cylinder, and vibrating. the mixture, while applying pressure thereto, for example. by applying pressure against a. top,:or bottom of the vessel. Block anodes made in this manner are used, for example, in the aluminum industry. In one type of apparatus, thebottom and the cover olla vessel are formed as pistons, the vessel itself, being a cylinder,-the pistons-being connected to piston drives which are capable of being moved both with a feed movement as well as with vibratory move- ,pacted and .controlled as a function of time. It may occur, however,--that someof the .parameters are not matched to eachother. For example, feed movement or amplitude may be too great in relation to instantaneous degree of compaction of the granulate, thus re sulting in excessive, possibly dangerous loading on the compacting device. It may also occur that the compacting operation is not, carried out in its most ,efficient manner, for example, with insufficient compacting pressure. Such compacting devices were. heretofore used only for blocks of rather shallow, thickness.

It is an objection of the present invention to provide an apparatusin which the application of the parameters applied to the apparatus can beeffectively and readily SUBJECT MATTER OF THE PRESENT p INVENTION Briefly, the compacting pressure applied to thegranulate is measured and controlled as a function of feed, or compaction time, respectively. In accordance with a feature of the invention, the apparatus to carry out the method includes a pressure transducer which measures the pressure applied to the piston drive of the compaction apparatus ,the transducer delivering an output signal which controls the feed apparatus of the piston drives fln accordance with a feature of the invention, a hydraulic motor is used as the feed drive to the piston,

which is connected by means of a mechanical drive with a piston forming the bottom, or the top cover of the compaction cylinder (or both).

The invention will be described by way of example with reference to the accompanying drawings, wherein:

FIG. 1 is a general schematic illustration of an apparatus in accordance with the present invention, having a hydraulic feeddrive for the bottom, as well as for the top, of the compaction cylinders, and illustrating only those parts absolutely necessary tocarry out the pro cess, and with which the process can beexplained; FIGS. 2 onsheets indicated as 241,.a nd 2b taken. to-

illustration, partly in longitudinal section, of an apparatus to compact granulates; I

HO. 3 is a longitudinal sectional view of a drive for a pistonrod, or pistol spindle, without play; and

FIG: 415 a schematic illustration ofa compacting device with mechanical feed drive for the bottom, 'or cover of the compacting cylinder, partly in block diagram, and illustrating only the essential elements of the system, and necessary for an understanding of the method.

Referring first to FIG. 1: a compacting apparatus 1 is shown as a multi-ele'ment apparatus including a cylinder 2, a bottom piston 3, andatop or cover piston 4. The bottom piston 3 can beraised towards the top pisten. 4 by means of a-hydraulic feed drive 6. The top cover 4 is driven by a'hydraulic feed drive 7. The feed drives 6, 7, are reversible and can be moved towards and away from each other in synchronism, or indepengether,is a schematic representation, partly in block dently. The drives are secured to supports 8, 9 (shown only schematically), which in turn, are supported from a

frame

10,11. t

The piston drives 6, 7'are moved by-hydraulic force,

controlled by electrical signal transducerslZ, which-.- operate as electrical signal, hydraulic-force controllers,

to provide substantial amplification of the electrical control signal. The actual position ofthe

pistons

6,7 is determined by

means oftransducers

14, 17, which measure displacement of the piston with respect to a datum. Transducer 14 measures the movement of the bottom piston 3,- or the top cover 4, respectively; transducer l7-measures the displacement of the hydraulic elements, contained within the amplifier valve 12. The measured displacement values, so obtained, are connected over lines 30, 31 for the bottom, and 32,33 for .the top. cover to

comparators

34, 35 to be compared with a command value derived from a command source 20 and applied over respective lines 36, 37'. Thedifference between actual value and commanded value then provides an error signal which is applied to amplifiers 38, 40 (which have power supplied by a powersupply necessary pumps, sumps, check valves, and the like, as 7 well known in the hydraulic amplifier are, to supply pressure fluid, for example pressure oil through

lines

50, 51 to valves 12 and to treat the return pressure fluid received over

lines

52, 53. a I e The program source 20 includes a plurality of stored program units 21 24. The operating parameters stored in the respective units are illustratedschematieally by diagrams. Unit 21 provides output signals representative of pressure to be supplied by the

piston drive

6, 7, on pistons 3, 4; unit 22 controls the amplitude, unit 23 the frequency, and unit 24 the wave shape of commanded operating parameters which are transduced by valves 12 into movement of the respective pistons 3, 4, to effect compaction of the granulate within cylinder 2.

In accordance with a feature of the invention, the compaction pressure, that is, the compressiveforce exerted by the bottom and top pistons 3, 4, is measured directly. The pressure transducer 25 is applied to the hydraulic portion of the

piston drive

6, 7, as shown; the hydraulic fluid pressure applied to the

piston

6, 7, is directly measured in the pressure transducers 25 and converted into an electrical signal. which is transmitted over

lines

27, 28, respectively to the

comperators

34, 35. The actual compacting pressure of the

piston drive

6, 7, can thus be controlled as a function of feed, and- /or compaction time, respectively. The signal derived from the pressure transducers 25 may be suitably processed by apparatus included in the

comparators

34, 3 5, or apparatus included in the

lines

27, 28, for example by averaging, or the like.

Referring now to FIGS. 2a and 2b, collectively denominated as FIG. 2; two cylinders 2 are connected by means or a rigid interconnection 102. A piston drive 103 is arranged to shift the cylinders 2 laterally. The cylinder 2 shown at the right FIG. 2 is in the position for compaction, and forms, together with the bottom piston 3 and the top piston 4 the compaction form or mold. During the time that compaction of granulate is effected in the cylinder 2-at the right, the other cylinder is beneath a charging apparatus, generally shown at 107. The charging apparatus includes a supply trough 108, a charging and measuring container 109, a scale 110, and a charge cover 112 operated by an operating device 111. The lower piston drive 113 places a bottom cover 114 against the bottom of the cylinder 2 being charged, to prevent. escape of granulate during charging, that is, when the closure mechanism ll2'is opened. An intermediate table 115 prevents escape of charged granulate from the cylinder 2, when the cylinder 2 is moved laterally as controlled by feed piston mechanism 103. Upon change of charge of the cylinders, the cylinder shown in line with the compaction apparatus is moved to the right, and a freshly charged cylinder is then placed beneath the compaction system. The block .within the piston 2 which has just been compacted, schematically shown at 106 (FIG. 2b) will thus be placed on the table 114 of the right lifting piston 113, which is lowered..to permit removal of a piston drive 116, and further transport over a transport path not shown. In an actual construction, the direction of movement of piston 116 would be at right angles to the plane of the drawing. The block 106 need not be a cube, and may have any suitable desired shape, as given by the shape of the cylinder 2, and of the bottom and top pistons 3, 4. The horizontal cross section may be round, or polygonal, and the side surfaces need not be of the same length.

Bottom piston 3 and topcover piston 4 are secured, each, to a piston rod 60 which may be termed a guide rod, since it also guides the respective piston in its movement. It is retained within a sleeve 62. Sleeve 62 is connected at its free end 119 to

piston drive

6, 7. The piston rod 121 of the

respective drive

6, 7 is connected to the guide rod 60 on the one hand, and further to a displacement-electrical signal transducer 14. The transducer 14 is fixed relative to the sleeve 62, for example by being secured to the end 119 thereof. The

piston drive

6, 7, is operated by an electro-hydraulic servo valve 12.

Sleeve 62 is journalled in a housing 124 which, in turn, is secured to a fixed portion l0, 11, for example the frame, of the apparatus. Sleeve 62 forms the spindle of a

spindle drive

62, 64. The spindle nut 64 is likewise journalled in housing 124. The spindle lower nut 64 is driven by means ofdrives 28; the upper spindle nut 64 is driven by worm drive 67, as best seen in FIG. 3.

The cover 4 is formed with a suction device 130 which includes a box 131 secured to housing 124 and an inner sheath 132, moveably retained within the box 131. The sheath 132 can be lowered to the upper end 134 of the cylinder 2 by means ofa sheathed drive 133. A connecting stub 135, secured to box l31.is con- 7 nectcd to a suction pump (not shown) from which gases and vapors emitted by the granulate during the compaction process can be sucked off.

Pressure drives 137 connect with the bottom 3 and the top cover 4, which are otherwise secured to the housing 124, or to the

frame elements

10, 11, of the apparatus. These pressure drives 137 are applied only against the bottom 3 and the cover 4, and are not secured to the bottom 3 and the top cover'4; they are utilized for a final compression and compaction of the block.

The hydraulic central station 45, as in the embodiment of FIG. 1, includes the necessary hydraulic pumps, pressure devices, control systems, and valves, as well as the necessary timing elements to provide the various hydraulic piston drives'with pressure fluid, in the propersequence. The connecting lines to the various piston drives are not described in detail and will be clear from the drawings; they have been given the same reference numerals as the connected piston-cylinder unit, with a prime mark.

Programming device (FIG. 2b) provides the necessary control or program for feed, amplitude, frequency, and wave shape, as schematically indicated by the respective diagrams in the subdivisions of program source 150. Of course, separate programming sources can be supplied for the bottom piston 3, or the top piston 4, or a single program source can be used, selectively, with suitable time-sharing controls.

The drives for the'bottom 3 and top cover 4 are controlled by the control loops. The transducer 14 provides the actual value, compared in comparators 151 with the command value derived from programming source 150. The error is applied over amplifier 152 to the electro-hydraulic servo valves 12. The

spindle drive

62, 64 is likewise controlled by programming source 150 by means of an electric motor drive, not shown.

The connecting lines for the control signals are indicated by short dash lines in FIG. 2, the return lines for the servo valve 12 are indicated by long'dash lines. Amplifier 152 is supplied from power supply 153.

Referring to FIG. 3, where the spindle drive, in the form of a worm gearing drive, is shown in detail: a worm 67 is journalled in housing 124; worm 67 engages with a worm wheel 66. Spindle nut 64 has threads 66' on the inside. Spindle nut 64 is engaged by means of its thread on threads 62 of the sleeve 62. Spindle nut 64 is journalled in housing'l24 by means of bearings 155, 156, 157. These bearings may for example, by roller bearings. I

Spindle nut 64 cooperates with a spindle nut portion 129. Portion 129 is guided with respect to the spindle nut 64 by means of overlapping edges 159 (FIG. 3) of the spindle nut 63, to center the portion 129. A bearing 160 rotatably holds portion 129 in housing 124. Portion 129 is also threaded on spingle'62, by means of internal threads"l 29"'.

A bolt l6'1'is 'carried bythe' end'face of spindle nut 64; Bolt 161" fits into a recess 162 of the portion 129.

with respect to a counter ring 166. The position of bolt 165 isthen secured in location by means of a counter nut 167. The counter ring 166bears'against'thrust bearing 168, which, in turn, is supported from'housing 124. The springs 163 bias the two elements 164,129 in order to eliminate play in the worm drive'connection.

The two

elements

64, 129 can'be relatively biased also by other means, for example hydraulically. In such an arrangement, bolt 161 is used to seal the space heneath cap 164 to form a pressure chamber, to which pressure fluid can be introduced, for example by a suitable bore, or flexible tubing terminating beneath the cap 164. Utilizing hydraulic pressure, for example, has the advantage that the relative bias of the

elements

64, 129 can be removed upon free movmem'ent of the spindle, so that the speed of adjustment of the spindle can be increased. r

Other release means for the spindle can be utilized, for example'a solenoid can be used t'o bias bolt 165, rather than the fixed bias arrangementby means of the nut 167, within the sleeve 166. In such an arrangement, sleeve 166 would support a solenoid coil which, when energized, applies pressure of a solenoid plunger against cap 164, and, when deenergized, releases the pressure to permit rapid movement of the spindle drive. Shaft 67 is driven by a suitable motor, not shown in FIG. 3, as explained in connection with shaft 28, FIG. 2.

The apparatus of FIG. 4 generally is similar to that of FIG. 2. The bottom 3 and top cover 4 are guided by means of rods 60 in sleeves 62 which, in turn, form the spindle of a positive spindle drive, that is, of a spindle drive without play. The spindle nut 64 is driven over a

worm gear drive

66, 67 by a hydraulic motor 70. The feed piston drives 6, 7, are located at the ends of the guide rod 60, secured to the sleeve 62, and subjected to pressure over hydraulic amplifier valve 12. A pressure transducer 25 is secured to the side of the feed piston drives 6, 7, which is remote from the cylinder 2.

The system of FIG. 4 utilizes two amplifier or servo valves l3, 13, one each associated with a hydraulic motor 70. Programming source has a programming part 21 for feed movement, and

programming parts

22, 23, 24 controlling amplitude, frequency, and wave shape of vibration for the granulate. The pressure control part 21 then controls the hydraulic motor 70 over

valves

13, 13. The position-command comparison is similarly carried out as before, that is incomperators 34, 35 as well as in additional comperators 34', 35. The connections associated with the programming part 21, and controlling only pressure versus time are illustrated in the same manner as the elements 22-24, and the elements connected thereto, however with a prime notation.

Various changes and modifications may be made within the scope of the invention concept and any embodiment may utilize features described in connection with any other embodiment, as appropriate.

We claim:

1. Compacting apparatus to manufacture blocks by compacting a mixture ofa granulate and a binder, comprising 6 a compacting cylinder (2) in which the granulate to be compacted is placed; bottom and top pistons (3, 4) closing said cylinder and movable to compact granulate within the cylinr i a piston support. means (62) connected, to an d supporting at least one of the Pistons 4);

means 6, 7, 12) moving at least one piston (3, 4) in compaction ,direction, comprising A a spindle drive, the support means (62) forming the spindle element of thespindle drive and a spindle nuti,(64) forming the nut element of the spindle drivep a housing (124) for the spindle drive, and means (10,

11) supporting. the housing, the spindle element (62) being journalled in the housing and the spindle nut elements (64, 129) being supported in the k housing; v

and motor means in rotating engagement with one of the elements of the spindle drive (20);

wherein the piston support. means comprises a piston guide rod (60) connected to each of the pistons (3,

a sleeve (.62) surrounding each of the piston guide .rods (60), the sleeve forming said spindle element;

and wherein separate force means (12) are provided,

secured to the sleeve (62) and to the piston guide rod (60) respectively, to impart a force to the piston guide rod (60) and hence to the pistons (3, 4) with respect to the sleeve.

2. Apparatus according to claim 1, wherein the element of the spindle drive being rotated is the spindle nut element (64);

and means rotating the said element comprises a worm drive (28, 67) engaging the spindle nut element (64) to impart rotation thereto.

3. Apparatus according to claim 1 wherein the spindle nut element (64) is formed with an inner thread engaging the spindle element (62) and with an outer gearing (66), said outer gearing being engaged by the worm (67) of the worm drive.

4. Apparatus according to claim 1, wherein the motor means comprises a hydraulic motor (70).

5. Apparatus according to claim 1, wherein the sleeve (62) is threaded at least in part on the outside and forming the spindle element for the spindle drive.

6. Apparatus according to claim 5 including motor control means (20, 21; connected to the motor means (70) and controlling the motor means to apply a steady force on the sleeve (62) in the direction to compact granulate within the compaction cylinder (2).

7. Apparatus according to claim 6 wherein the motor means comprises a hydraulic motor;

electrohydraulic valve means (13) are provided controlling flow of hydraulic pressure fluid to the motor;

and pressure-sensing means (25) are provided to sense reaction pressure of said at least one piston, the pressure-sensing means being connected to at least one of: said piston rod (60); said sleeve (62).

8. Apparatus according to claim 1 further comprising pressure sensing means (25) connected through said at least one piston (3, 4) having pressure applied thereto and providing a pressure signal representative of actual pressure applied to the granulate, said signal controlling the pressure applied by said motor means.

9. Apparatusaccording to claim 8 wherein the motor means is a hydraulic motor (70); a

an 'electrohydraulie valve (12 is provided and means "(45 supplying hydraulic fluid under pressure to I said valve;

and v'v herein the pressure signal is connectedto said 'alve (.1 2 tofc ori'trol; the application of hydraulic pr essuie by said valve. i g I ll). 'Apparatus' accofding to claim-1, yvherein the spindle drive comprises play or backlash elimination mansklzs, 127,123). I I

ll.'Appara'tus "according to claim 10 wherein the spindle nut element 'is'fo rmedin two part s'(64,i 129) and means (163) resiliently biassing said parts with respect to each other. t i' '12. Apparatus according to'c laim' 1 1, vvhereih the means biassing' said partsfwith respect to ea'c li other comprisesspring m'eans"( 163) located to spread said parts to provide play-free engagement of o'nc'a'r said parts '(64) withthe spind-le'(62). 1

l3. 'A pparatus according to claim'll', wherein the means biassing said-parts with respect-i o each other comprises a cavity formed in one of said parts,'facing the other;

and projecting meansextending in said cavity and ,towards theother part'to provide-a cylinder-piston farrangement i and means introducingpressure-fluid in said cavity,

. a.de r s while theothepcylinder is subjected to said v\(;( ).r I 1p action-forces, 1 H

1 43 Apparatus according touclaim l wherein the apparatus ,further;comprises a suction box housing .(131' f tting against the upper portion of the cylinden (,2), and.m eans removing gases and vapors arisingduring compactionof the granulatein the cylinl 7.1App arat us according to claim I further comprising a hydraulic .ram 137) acting between the housing 120 (l lifil andatjleast one of saidpistons 2,3) tosubject the respective piston to compaction pressure separately from the force capable of being exerted by the motor means (7 0). a.

= 1 8. Apparatusaccordi ngto claim lwherein the separate force meanscomprises vibrating means-(20-24; 150) to inipart vibratory rnovementto the piston rod (60 w ith respect to the sleeve (62). a

Claims

1. Compacting apparatus to manufacture blocks by compacting a mixture of a granulate and a binder, comprising a compacting cylinder (2) in which the granulate to be compacted is placed; bottom and top pistons (3, 4) closing said cylinder and movable to compact granulate within the cylinder; a piston support means (62) connected to and supporting at least one of the pistons (3, 4); means (6, 7, 12) moving at least one piston (3, 4) in compaction direction, comprising a spindle drive, the support means (62) forming the spindle element of the spindle drive and a spindle nut (64) forming the nut element of the spindle drive; a housing (124) for the spindle drive, and means (10, 11) supporting the housing, the spindle element (62) being journalled in the housing and the spindle nut elements (64, 129) being supported in the housing; and motor means (70) in rotating engagement with one of the elements of the spindle drive (20); wherein the piston support means comprises a piston guide rod (60) connected to each of the pistons (3, 4); a sleeve (62) surrounding each of the piston guide rods (60), the sleeve forming said spindle element; and wherein separate force means (12) are provided, secured to the sleeve (62) and to the piston guide rod (60) respectively, to impart a force to the piston guide rod (60) and hence to the pistons (3, 4) with respect to the sleeve.

2. Apparatus according to claim 1, wherein the element of the spindle drive being rotated is the spindle nut element (64); and means rotating the said element comprises a worm drive (28, 67) engaging the spindle nut element (64) to impart rotation thereto.

6. Apparatus according to claim 5 including motor control means (20, 21; 150) connected to the motor means (70) and controlling the motor means to apply a steady force on the sleeve (62) in the direction to compact granulate within the compaction cylinder (2).

7. Apparatus according to claim 6 wherein the motor means comprises a hydraulic motor; electrohydraulic valve means (13) are provided controlling flow of hydraulic pressure fluid to the motor; and pressure-sensing means (25) are provided to sense reaction pressure of said at least one piston, the pressure-sensing means being connected to at least one of: said piston rod (60); said sleeve (62).

9. Apparatus according to claim 8 wherein the motor means is a hydraulic motor (70); an electrohydraulic valve (12) is provided and means (45) supplying hydraulic fluid under pressure to said valve; and wherein the pressure signal is connected to said valve (12) to control the application of hydraulic pressure by said valve.

10. Apparatus according to claim 1, wherein the spindle drive comprises play, or backlash elimination means (126, 127, 128).

11. Apparatus according to claim 10 wherein the spindle nut element is formed in two parts (64, 129) and means (163) resiliently biassing said parts with respect to each other.

12. Apparatus according to claim 11, wherein the means biassing said parts with respect to each other comprises spring means (163) located to spread said parts to provide play-free engagement of one of said parts (64) with the spindle (62).

13. Apparatus according to claim 11, wherein the means biassing said parts with respect to each other comprises a cavity formed in one of said parts, facing the other; and projecting means extending in said cavity and towards the other part to provide a cylinder-piston arrangement; and means introducing pressure fluid in said cavity, to project said projecting means and hence spread said parts to provide for play-free engagement of one of said parts (64) with respect to the spindle.

14. Apparatus according to claim 1, wherein said cylinder (2) is laterally moveable.

15. Apparatus according to claim 14, wherein two cylinders (2) are provided, coupled to each other, and both conjointly laterally shiftable; and means are provided to charge one of said cylinders while the other cylinder is subjected to said compaction forces.

16. Apparatus according to claim 1, wherein the apparatus further comprises a suction box housing (131) fitting against the upper portion of the cylinder (2), and means removing gases and vapors arising during compaction of the granulate in the cylinder (2).

17. Apparatus according to claim 1, further comprising a hydraulic ram (137) acting between the housing (124) and at least one of said pistons (2, 3) to subject the respective piston to compaction pressure separately from the force capable of being exerted by the motor means (70).

18. Apparatus according to claim 1 wherein the separate force means comprises vibrating means (20-24; 150) to impart vibratory movement to the piston rod (60) with respect to the sleeve (62).