US3905732A

US3905732A - Extrusion press for making hollow concrete bodies

Info

Publication number: US3905732A
Application number: US433489A
Authority: US
Inventors: Maxime Jean Rouvin; Paul Fernand Rouvin; Philippe Edmond Rouvin
Original assignee: Individual
Current assignee: Individual
Priority date: 1973-01-24
Filing date: 1974-01-15
Publication date: 1975-09-16
Anticipated expiration: 1992-09-16
Also published as: DE2402044A1; GB1456722A; FR2215034A5

Abstract

An extrusion press is provided for making hollow concrete bodies comprising a casing defining a mould, a ram reciprocatingly movable along the longitudinal axis of the mould, at least one movable perforated core in communication with vacuum means, and at least one nonperforated core. The press may also advantageously include at least one scraping piston inside each perforated core to remove accumulated concrete slurry. The movements of the ram and cores are so ordered that the concrete is compressed, subjected to vacuum, and then extruded, and that the ram begins its backward movement only after each perforated core has substantially reached its rearmost position away from the extrusion outlet.

Description

United States Patent 1191 Rouvin et al.

1451 Sept. 16, 1975 1 1 EXTRUSION PRESS FOR MAKING HOLLOW CONCRETE BODIES [22] Filed: Jan. 15, 1974 121 Appl. No.: 433,489

[30] Foreign Application Priority Data Jan. 24, 1973 France N 73.02496 [52] US. Cl. 425/85; 425/227; 425/262; 425/376; 425/381 [51 Int. Cl. B28B 3/24 [58] Field of Search 264/87, 209, 176 R;

425/85, 262, 376, 377, 378, 379, 380, 381, 225, 226, 227, 63, 467, 291, DIG. 60, 64

[56] Ret'erences Cited UNITED STATES PATENTS 2,585,756 2/1952 Eschcnbrcnner 425/85 X 2,953,834 9/1960 Muttart 425/376 X 3,230,902 1/1966 Grimm et al 425/378 X 3,785,759 1/1974 Johnson et a1. 425/64 X 3,792,942 2/1974 Cole 425/63 X FOREIGN PATENTS OR APPLICATIONS 1,080,217 8/1967 United Kingdom 425/376 Primary ExaminerRobert D. Baldwin Assistant Examiner-Mark Rosenbaum Attorney, Agent, or FirmFinnegan, Henderson, Farabow & Garrett 5 7 ABSTRACT An extrusion press is provided for making hollow concrete bodies comprising a casing defining a mould, a ram reciprocatingly movable along the longitudinal axis of the mould, at least one movable perforated core in communication with vacuum means, and at least one nonperforated core. The press may also advantageously include at least one scraping piston inside each perforated core to remove accumulated concrete slurry. The movements of the ram and cores are so ordered that the concrete is compressed, subjected to vacuum, and then extruded, and that the ram begins its backward movement only after each perforated core has substantially reached its rearmost position away from the extrusion outlet.

13 Claims, 7 Drawing Figures I PATENTEDSEP 1 sms SEEIU 1 BF 5 g7lv/zr/zzz N w m w m N PATENTED SEP 1 61875 IOI PATENTEUSEP I 6 ms 3, 905 732 SHEET u, 0; a;

FIG. 6

PATENTEUSEPI 61975 SHZZT 5 U? 5 mom 1 EXTRUSION PRESS FOR MAKING HOLLOW CONCRETE BODIES l BACKGROUND OF THE INVENTION Extruding presses for concrete are known in which the mould is formed by l a stationary casing fixed to the frame of the press, including near its rear end a filling mouth and, sometimes, a series of stationary cores, (2) a movable part composed of a ram which cxtrudes the concrete when sliding forwards in a longitudinal direction inside the mould and to which are sometimes connected cores moving with the ram, and (3) a movable part composed of one ormore cores or filling blocks, the movement of which is actuated by a mecha nism different from that which actuates the ram, all cores or filling blocks moving in a longitudinal direction. I

In these known presses, the concrete is forced through the mould by a reciprocating ram. while the concrete goes forward inside the mould, the pressure exerted by the ram causes water to be driven off. The concrete is exposed to a suction of the exuded water by a vacuum pump which causes a depression in a perforated part of the mould or cores, in such a manner that when the concrete is extruded it is dewatered and hard enough to be stripped from the mould and moved without damage. Extrusion occurs by jerks each time the ram goes forward. I I

The adherence of concrete is greater on the perforated surfaces through which vacuum is applied than on the nonperforated surfaces of the mould and cores. As a result, it sometimes happens that duringthe backward movement of the ram and cores a part of the concrete comes off and adheres to the perforated surfaces. This inconvenience occurs frequently with the concrete situated betweentwo adjacent cores. When the ram and cores moveiforward again, the separate parts of concrete are bound together, but the joining completed more or less during the extrusion. and cracks are imperfectly bound during the hardening time. The cracks decrease the strength of the products and cause the loss ofsome of them.

When submitting the concrete toga vacuum effect through a perforated: cores, the suction of liquid produces a slurry inside the cores with fine particles that obstruct some perforations causing irregularity and even the interruption of the vacuum effect. Extrusion must be stopped and the cores must be cleaned before beginning again.

Attention has beendirected to similar extruding devices which work with a very dry mixture to provide adequate resistance to the extrusion throughout the process in such a manner that the product is properly compacted. The completed setting of the moulded concrete occurs after the extrusion process when the moulded product is hydrated so that the water content is sufficient to complete setting and is then submitted to drying. Such devices are complicated and are suitable only for the production of pieces of relatively short length.

SUMMARY OF THE INVENTION vices described above. Research and experimentation led to the development of an extrusionpress with several reciprocating movements for the extrusion of hollow concrete elements such as pipes or the like, which comprises:

a. a frame;

b. a mould the exterior of which is defined by a stationary casing fixed to the frame, said mould tcrminating in an extrusion outlet;

c. inlet means for introducing concrete into the mould;

d. at least one perforated core movable in a direction parallel to the longitudinal axis of the mould..

closed at one end and open at the other end;

0. vacuum means in communication with each perforated core for imposing a vacuum on each perforated core;

f. at least one nonperforated core;

g. rcciprocatingly movable concrete compression means for pushing the concrete through the mould and the extrusion outlet; and

it. means in communication with the concrete compression means for maintaining the concrete under compression until each perforated core has substantially reached its rearmost position away from the extrusion outlet.

Preferably, means are provided for imparting movement to each perforated core in a direction parallel to the longitudinal axis of the mould.

It is also preferred that a manifold movable along the longitudinal axis of the mould be provided in communication with the opcn end of each perforated core. The vacuum means are preferably in communication with the manifold for imposing a vacuum on each perforated core through the manifold.

The concrete compression means preferably comprises a ram rcciprocatingly movable along the longitudinal axis of the mould and having openings which permit it to move along the mould and around the perforated and nonperforated cores. The ram has a crosssectional area which is the same as that of the extrudate. Preferably, means for imparting reciprocal movement to the ram independent of the manifold is provided.

In accordance with'the present invention, the extrusion press may further comprise scraper means located in each perforated core forremoving accumulated concrete slurry material from the perforated core. Preferably, the scraper means comprises at least one scraping piston which is rcciprocatingly movable within the perforated core.

According vto the invention. theextrudcr press may have other characteristics. For example, the perforated core or cores may move freely toward the front end so that they are carried forward by the concrete pushed by the ram, or they may be actuated by independent means according to movement of the ram. Moreover, the nonperforated core or cores may be free to move toward the front end so that they are carried forward by the concrete pushed by the ram.

The backward movement of the cores may be made dependent upon the nature and shape of the hollow elements to be produced. In addition, the ram amy be forced to exert pressure against concrete during the backward movement of some or all of the perforated and/or nonperforated cores according to the shape of product to be extruded.

Means utilized to actuate the different movements can be of any suitable devices already known in the art.

The extruder constructed according to the present invention extrudes elements without cracks and does not become obstructed when working because of the pressure applied by the ram against the concrete during the extrusion and during the backward movement of perforated cores, and because of the pumping out of slurries which are scraped off of the perforations. Moreover, the extruder is able to produce moulded elements of a very uniform stiffness and of any desired length, which may be changed at will after the stripping of the mould, using a fluid concrete feed which contains a very high content of water. This feature is particularly advantageous in that the mould is easily filled relying upon gravity alone, and since elements with thin walls are readily produced.

The accompanying drawings which are incorporated in and constitute a part of this specification illustrate several embodiments of the invention and, together with the description. serve to explain the structure and operation of this invention,

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a cross-sectional view of a moulded body of common shape obtained from the extrusion press shown in FIGS. and 6.

FIG. 2 is a cross sectional view of a moulded body of more complicated shape obtained from an extrusion press similar to that shown in FIGS. 5 and 6, but with three horizontal series of cores instead of a single one as shown in FIGS. 5 and 6.

FIG. 3 shows a view with partial cross-section of an extrusion press with two reciprocating movements where cores are connected to the driving piston.

FIG. 4. is atop sectional view of the moulding device shown in FIG. 3.

FIG. 5 is a schematic view showing a part of an extrusion press with three reciprocating movements.

FIG. 6 shows the general outline of the extrusion press shown in FIG. 5 adapted to produce the element shown in FIG. 1.

FIG. 7 is another type of extrusion press with three reciprocating movements.

It is to be understood that both the foregoing general descriptions and the following description are exemplary and explanatory, but are not restrictive of the invention.

Reference will now be made in detail to the presently preferred embodiments of the invention, examples of which are illustrated in the accompanying drawings.

DETAILED DESCRIPTION OF THE INVENTION end and open at the other end. Vacuum means in communication with each perforated core is provided for imposing a vacuum on each perforated core.

In the embodiment shown in FIGS. 3 and 4. there is a series of hollow cores 1, 3. 5. 7. perforated respectively at I. 3'. 5'. 7' through a part of their length and closed at their front ends, i.e.. toward the extrusion side. As shown in FIGS. 3 and '4, the perforated cores are in communication with vacuum means through their rear ends by a manifold 13 with a mouth 14 connected to a vacuum pump (not shown). As embodied herein. the manifold is fixed to a stirrup l8 actuated by a hollow piston 17 which can slide inside a cylinder 20 fixed to the frame 21 of the extrusion press.

The invention also provides at least one nonperforated core which may be closed at both ends. In the embodiment shown in FIGS. 3 and 4, there is a series of solid or hollow

nonperforated cores

2, 4, 6 which are notsubjectcd to vacuum.

In accordance with the concept of the invention, there is provided a reciprocatingly movable concrete compression means for pushing the concrete through the mould and the extrusion outlet.

As embodied and shown in FIGS. 3 and 4, the concrete compression means comprises a ram 8 which has the same cross-section as that of the desired product and which has openings which permit its movement around the different cores. As embodied herein. the

nonperforated cores

2, 4, 6 are formed integral with the ram at their rear ends 2'. 4, 6'. The ram 8 is fixed at its rear end to a stirrup 23 and a piston 24 which slides inside a hollow piston 17. The cores, ram and manifold can all'move parallel to the axis of the mould.

In accordance with a preferred embodiment of this 'invention, the extruder press further comprises scraper jacks l6 and a tie joint 22. A power unit, not shown,

imparts reciprocating movement to the ram 8, cores and scraping pistons and can actuate forward and backward movements either separately or together.

In operation, the device of the invention as embodied in FIGS. 3 and 4 works according to the following cycle:

1. At the beginning of the extrusion operation, the

ram 8 and all the cores are at their rear positions, i.e., toward the farthest side of the mould from the extrusion orifice. Stirrups l8 and 23 are in contact with each'other. The concrete inlet mouth 19 is open and concrete is introduced into the mould. The power unit actuates the forward movement of the

perforated cores

1, 3, 5, 7 by subjecting chamber 9 to pressure. Stirrup l8 drives the ram 8 and the

nonperforated cores

2, 4, 6. The concrete inlet mouth 19 is closed. The concrete which has been introduced into the mould is compressed, and the moulded product is extruded.

3. When the ram and cores approach their fully advanced positions, the power unit actuates the backward movement of the

perforated cores

1, 3, 5, 7 by subjecting chamber 10 to pressure and releasing the pressure on chamber 9.

Throughout the period of time during which the described ram and core movements are effected, the ram maintains the concrete under pressure and prevents the eventual formation of cracks in the concrete occurring when the direction of movement of the perforated cores submitted to vacuum is changed. given the high friction of concrete at the perforated surfaces.

4. When the perforated cores have reached their rear position. the power unit actuates the backward movement of the ram and nonperforated cores by subjecting chamber 11 to pressure and releasing the pressure on chamber 10. The ram 8 moves backward. opens the concrete inlet mouth 19 and stirrup 23 is stopped when brought into contact with stirrup 18. The moving parts of the apparatus thus return to their initial position. and the cycle can begin again.

After a number of cycles depending upon the shape of the hollow product and the nature of the concrete feed. the suction of exuded liquid produced by the vacuum effect causes the deposition of a slurry of fine particles inside the perforated cores that obstructs some of the perforations 1'. 3'. 5'. 7. of the perforated cores resulting in irregularity in the vacuum effect on the concrete. When that occurs. scraping pistons are actuated by means ofjacks 16. The backward movement of scraping pistons 15 throws the slurry out ofthe cores and into the manifold 13 from which it is aspirated and collected in the vacuum storage tank not shown.

The irregular dewatering of the concrete from one point of its cross-section to another, its faulty extrusion. and the collapse of the extruded hollow product are thereby all avoided. it is further within the concept of this invention to continuously actuate the scraping pistons 15 from the beginning and throughout the extrusion process.

The press embodied and shown in FIGS. 5 and 6 utilizes three reciprocating movements and its cores are not connected to the ram. In accordance with this embodiment of the invention, the device includes a stationary casing 101 fixed to the frame of the press, this easing defining the mould and the exterior shape of the finished product. There is a series of hollow cores 102 perforated at 102 through a part of their length, closed at their front ends, i.e., toward the extrusion side, and connected at their rear ends to a manifold 106 by a flexible piping 103. The manifold is connected to a vacuum pump not shown. Each of the cores 102 is connected by means of a connecting rod 115 to a crank 116 actuated by

cams

110, 110a. Also provided is a series of solid or hollow nonperforated cores 104 not subjected to vacuum effect. Each of the nonperforated cores is connected by means of a connecting rod 117 to a crank 118 actuated by cams 111, 111a.

As embodied in FIGS. 5 and 6, the concrete compression means comprises a ram 107 which has the same cross-section as the one of the desired product. The ram is connected by means of the cranks 119 to connecting rods 120 actuated by

cams

112, 112a.

1n the embodiment shown in FIGS. 5 and 6, there is provided scraper means comprising scraping pistons 108 inside each of the cores 102, which pistons are fixed at their rear ends to toothed racks 114 actuated by pinions 113. All of the pinions 113 are the same and are keyed in a single shaft 122.

At the beginning of the working cycle of the device.

the ram 107 and all the

cores

102, 104 are at their rear positions. i.e.. toward the farthest side of the mould from the extrusion orifice, the scraping pistons 108 being at the front ends of the perforated cores. The

concrete inlet mouth 121 is open and the concrete is introduced into the mould.

The power unit then actuates the forward movement of the ram 107 and cores. but the pinions 113 and the shaft 122 are loosely mounted so that the position of the scraping pistons 108 inside the cores stand unchanged. The

eams

110, 111, 112 push the ram and cores. The inlet mouth 121 is closed. the concrete which has been introduced in the mould is compressed. and the product is extruded.

When the ram and cores approach their fully advanced positions. the backward movement of the per forated cores 102 is actuated by means of cams a. The cores 102 are generally actuated backward together. but in some cases better results are obtained if they are backwardly actuated sequentially. given the different shapes of articles and nature of aggregates.

Throughout the period of time during which the perforated cores are moving backward. the ram 107 main tains the concrete under pressure and prevents the eventual formation of cracks in the concrete which aould otherwise form when the perforated cores 102, which offer a high frictional resistance to the passage of concrete. are retracted.

When the perforated cores 102 have reached their rear position. the cam 111a. 112a actuate the backward movement of the ram and nonperforatcd cores. The inlet mouth 121 is opened and when the backward movement is ended. the moving parts of the apparatus will have returned to their initial positions. The cycle can therefore begin again.

In the embodiment shown in FIGS. 5 and 6, and in keeping with the concept of the invention. the scraping pistons 108 can. when necessary. be actuated to throw the slurry which has been deposited in the cores 102 out of the cores and into the manifold.

The press of the invention as shown in FIG. 7 utilizes three separate movements. In this embodiment. the device includes a stationary casing 201 fixed to the frame 205 of the press. the casing defining the mould and the exterior shape of the finished product. There is provided a series of hollow cores 202, perforated at 202' through a part of their length. and closed at their front ends, i.e., toward the extrusion side. These cores are connected at their rear ends to a manifold 206 by means of a flexible piping 203. The manifold is connected to a vacuum pump not shown. All the cores are connected together by means of a cross-piece 229.

Concrete compression means comprising a ram 207 which has the same cross-section as that of the desired product and which has openings which allow its movement around the different cores is provided. It is connected at the rear to a crab 223 that can move parallel to the axis of the cores upon rails fastened to the frame of the press. The crab 223 is connected by means of connecting

rods

215, 215a to the

cranks

216, 216a ac tuated by the

cams

210, 210a and by

jacks

217, 217a.

There is a series of solid or hollow nonperforated cores 204, not subjected to vacuum, connected at their rear ends to the ram (not shown in FIG. 7)

Scraper means comprising a scraping piston 208 is provided inside each perforated core 202 each of which is fixed at its rear end to a toothed rack 214 actuated by a pinion 213. All pinions 213 are the same and are keyed in a single shaft 222.

The perforated cores are connected by a cross-piece 229 to the

rods

226, 226a of two jacks 227, 22711 which are fixed to the crab 223. The ram and cores are actuated by the cams 210, 210av At the beginning of the normal cycle of the device embodied and shown in FIG. 7, the ram'207 and all the cores 202 and 204 are at their, rear positions. i.e.. toward the farthest side of the mould from the extrusion orifice. The scraping pistions 208 are at the front ends of the cores, i.e., toward the nearest side of the mould from the extrusion orifice. The inlet mouth 221 is open and concrete is introduced into the mould.

The

cams

210, 210a push the ram 207 and cores forward, but the pinions 213 and shaft 222 are mounted loosely so that the positions of the scraping pistons inside the cores stand unchanged. The jacks 227, 22711 are kept stationary as the pistons are stationary. The

inlet mouth 221 is closed, the concrete which has been introduced into the mould is compressed, and the product is extruded.

When the

cranks

216, 216a actuated by the

cams

210, 210a have completed their forward movement, the'lcngthening of the jacks 227, 227a is actuated, the ram and perforated coresare subjected to tensile stress and the perforated cores move backwards, for they need less force to retract than the ram needs to push the concrete forward. During the backward movement of the perforated cores. the ram maintains the concrete under pressure. This pressure prevents the eventual formation of cracks inthe dewatered concrete. cracks which otherwise occur frequently during this backward movement of the perforated cores, given the friction of concrete at the perforated surfaces. When the perforated cores have reached their retracted position, the backward movement of the ram and nonperforated cores is actuated by retracting the

jacks

217, 217a, 227, 227a. The inlet mouth 221 is opened and when the backward movement has been completed,the moving parts of the apparatus will have returned to their initial positions. The cycle can therefore begin again.

In the HO 7 embodiment also. when it is necessary, the scraping pistons 208 can be actuated to throw the slurry out of the cores 202 and' into the manifold 206.

It will be understood that the improvements described for the extruding presses, particularly those with sliding ram and movable cores. may be adapted to the similar known presses so that they will be able to extrude as good quality products as those extruded with presses according to the invention.

It will be apparent to those skilled in the art that various modifications of the apparatus of this invention can be made without departing from the scope or spirit of the invention. 7

What is claimed is:

1. An extrusion press suitable for the production of hollow concrete bodies comprising:

a. a frame;

b. a mould the exterior of which is defined by a stationary casing fixed to the frame, said mould terminating in an extrusion outlet;

c. inlet means for introducing concrete into themould; at least one perforated core movable in a direction parallel to the longitudinal axis of the mould,

rcciprocatingly movable concrete compression means for pushing the concrete through the mould and the extrusion outlet; and

h. means in communication with the concrete compression means for maintaining the concrete under compression until each perforated core has substantially reached its rearmost position away from the extrusion outlet.

2. An extrusion press according to claim 1 in which the concrete compression means comprises a ram reciprocatingly movable along the longitudinal axis of the mould and having openings which permit it to move along the mould and around the perforated and nonperforated cores.

3. An extrusion press according to claim 1 further comprising a manifold movable along the longitudinal axis of the mould and which is in communication with both the open end of each perforated core and the vacuum means and which connects each perforated core to said vacuum means.

4. An extrusion press according to claim 1 in which each perforated core is freely movable toward the extrusion outlet so it can be carried forward by the concrete which is pushed by the concrete compression means.

5. An extrusion press according to claim 1 further comprising perforated core movement means for imparting movement to each perforated core in a direction parallel to the longitudinal axis of the mould in response to the movements of the concrete compression means.

6. An extrusion press according to claim 1 in which each nonperforated core is stationary.

7. An extrusion press according to claim 1 in which each nonperforated core is connected to the concrete compression means.

8. An extrusion press according to claim 1 in which each nonperforated core is freely movable toward the extrusion outlet so it can be carried forward by the concrete which is pushed by the concrete compression means.

9. An extrusion press according to claim 1 further comprising nonperforated core movement means for imparting movement to the nonperforated core in response to the movements of the concrete compression means.

10. An extrusion press suitable for the production of hollow concrete bodies comprising:

a. a frame;

c. inlet means for introducing concrete into the mould;

. at least one perforated core movable in a direction parallel to the longitudinal axis of the mould, closed at the end nearest'the extrusion outlet and open at the end farthest from the extrusion outlet; e. means for imparting movement to each perforated core in a direction parallel to the longitudinal axis of the mould; f. a manifold movable along the longitudinal axis of the mould and which is in communication with the open end of each perforated core; g. vacuum means in communication with the manifold for imposing a vacuum on each perforated A core through the manifold;

h. at least one nonperforated core closed at both ends;

. a ram reciprocatingly movable along the longitudinal axis of the mould having openings which permit it to move along the mould and around the perforated and nonperforated cores, the ram having a cross-sectional area which is the same as that of the extrudate, the ram compressing the concrete and pushing the concrete through the mould and the extrusion outlet;

j. means for imparting a reciprocating movement along the longitudinal axis of the mould to the ram independent of the manifold;

k. at least one scraping piston in each perforated core for removing accumulated concrete slurry material from the perforated core; and

1. means for imparting a reciprocating movement to each scraping piston; and

mv means in communication with the concrete compression means for maintaining the concrete under compression until each perforated core has substantially reached its rearmost position away from the extrusion outlet.

1 1. An extrusion press suitable for the production of hollow concrete bodies comprising:

a. a frame; b. a mould the exterior of which is defined by a stationary casing fixed to the frame, said mould terminating in an extrusion outlct;

c. inlet means for introducing concrete into the mould;

d. at least one perforated core movable in a direction parallel to the longitudinal axis of the mould, closed at one end and open at the other end;

e. vacuum means in communication with each perforated core for imposing a vacuum on each perforated core;

f. at least one nonperforated core;

g. reciprocatingly movable concrete compression means for pushing the concrete through the mould and the extrusion outlet;

h. means in communication with the concrete compression means for maintaining the concrete under compression until each perforated core has substantially reached its rearmost position away from the extrusion outlet; and

. scraper means located in each perforated core for removing accumulated concrete slurry material from the perforated core.

l2. An extrusion press according to claim 11 in which the scraper means comprises at least one scraping piston.

13. An extrusion press according to claim 12 further comprising means for imparting a reciprocating move- UNITED STATES PATENT AND TRADEMARK OFFICE CERTIFICATE OF CORRECTION PATENT NO- 1 3,905,732

DATED I September 16, 1975 INVENTOR( I Maxime Jean Rouvin; Paul Fernand Rouvin and .P Edm. d v It Is certrfl (3&1YFI-HJ[JB F%DDGEHS fi t lte afiae -r rle n trfled patent and that sard Letters Patent are hereby corrected as shown below:

In column 9, claim 10, lines 1 and 2, delete "closed at both ends"; and

In column 9 claim 10, line 16, delete "and".

Signed and Scaled this A ttes t:

RUTH C. MASON C. MARSHALL DANN Arresting Officer (ummissinner oj'Patents and Trademarks

Claims

1. An extrusion press suitable for the production of hollow concrete bodies comprising: a. a frame; b. a mould the exterior of which is defined by a stationary casing fixed to the frame, said mould terminating in an extrusion outlet; c. inlet means for introducing concrete into the mould; d. at least one perforated core movable in a direction parallel to the longitudinal axis of the mould, closed at one end and open at the other end; e. vacuum means in communication with each perforated core for imposing a vacuum on each perforated core; f. at least one nonperforated core; g. reciprocatingly movable concrete compression means for pushing the concrete through the mould and the extrusion outlet; and h. means in communication with the concrete compression means for maintaining the concrete under compression until each perforated core has substantially reached its rearmost position away from the extrusion outlet.

10. An extrusion press suitable for the production of hollow concrete bodies comprising: a. a frame; b. a mould the exterior of which is defined by a stationary casing fixed to the frame, said mould terminating in an extrusion outlet; c. inlet means for introducing concrete into the mould; d. at least one perforated core movable in a direction parallel to the longitudinal axis of the mould, closed at the end nearest the extrusion outlet and open at the end farthest from the extrusion outlet; e. means for imparting movement to each perforated core in a direction parallel to the longitudinal axis of the mould; f. a manifold movable along the longitudinal axis of the mould and which is in communication with the open end of each perforated core; g. vacuum means in communication with the manifold for imposing a vacuum on each perforated core through the manifold; h. at least one nonperforated core closed at both ends; i. a ram reciprocatingly movable along the longitudinal axis of the mould having openings which permit it to move along the mould and around the perforated and nonperforated cores, the ram having a cross-sectional area which is the same as that of the extrudate, the ram compressing the concrete and pushing the concrete through the Mould and the extrusion outlet; j. means for imparting a reciprocating movement along the longitudinal axis of the mould to the ram independent of the manifold; k. at least one scraping piston in each perforated core for removing accumulated concrete slurry material from the perforated core; and l. means for imparting a reciprocating movement to each scraping piston; and m. means in communication with the concrete compression means for maintaining the concrete under compression until each perforated core has substantially reached its rearmost position away from the extrusion outlet.

11. An extrusion press suitable for the production of hollow concrete bodies comprising: a. a frame; b. a mould the exterior of which is defined by a stationary casing fixed to the frame, said mould terminating in an extrusion outlet; c. inlet means for introducing concrete into the mould; d. at least one perforated core movable in a direction parallel to the longitudinal axis of the mould, closed at one end and open at the other end; e. vacuum means in communication with each perforated core for imposing a vacuum on each perforated core; f. at least one nonperforated core; g. reciprocatingly movable concrete compression means for pushing the concrete through the mould and the extrusion outlet; h. means in communication with the concrete compression means for maintaining the concrete under compression until each perforated core has substantially reached its rearmost position away from the extrusion outlet; and i. scraper means located in each perforated core for removing accumulated concrete slurry material from the perforated core.

12. An extrusion press according to claim 11 in which the scraper means comprises at least one scraping piston.

13. An extrusion press according to claim 12 further comprising means for imparting a reciprocating movement to each scraping piston.