US3877860A

US3877860A - Extrusion machine for making articles of cement-like material

Info

Publication number: US3877860A
Application number: US069300A
Authority: US
Inventors: George Putti
Original assignee: Dyform Concrete (Prestressed) Ltd
Current assignee: DY-CORE SYSTEMS Inc
Priority date: 1969-12-04
Filing date: 1970-09-03
Publication date: 1975-04-15
Anticipated expiration: 1992-04-15

Abstract

An extrusion machine for continuously making articles, such as concrete slabs, by forcing the article-forming material through a mold, said machine being moved forwardly by reaction as the material is forced against the portion of the article already formed. The material is moved under pressure by one or more spiral conveyors through the mold, and a forming element of any predetermined cross-sectional shape is substantially aligned with the down-stream end of each spiral conveyor and is mounted so as not to rotate with the latter. It is perferable to provide a vibrator in each forming element.

Description

United States Patent 1 1 Putti [4 1 Apr. 15, 1975 EXTRUSION MACHINE FOR MAKING ARTICLES OF CEMENT-LIKE MATERIAL [75] Inventor: George Putti, North Vancouver,

British Columbia, Canada [73] Assignee: Dyform Concrete Prestressed Ltd.,

Vancouver, British Columbia, Canada [62] Division of Ser. No. 882,039, Dec. 4, I969,

25/32, 35, 11; 18/12 SE, 12 SM; 425/461, 427, 432, 456, 376, 380

[56] References Cited UNITED STATES PATENTS 2,938,255 5/1960 Oakden 25/32 X 8/1962 Carr 25/41 G 3,143,781 8/1964 Kalns 25/32 X 3,159,897 l2/l964 Ellis et al. 25/4I G 3,284,867 ll/l966 Booth 25/41 .I X 3,496,603 2/l970 Listner l8/I2 SM FOREIGN PATENTS OR APPLICATIONS 623,476 7/l96l Canada 25/14 208,282 3/1960 Germany 25/14 946,345 l/l964 United Kingdom l8/3O SQ Primary ExaminerR. Spencer Annear Attorney, Agent, or Firm-Fetherstonhaugh and Company [5 7 ABSTRACT An extrusion machine for continuously making articles, such as concrete slabs, by forcing the articleforming material through a mold, said machine being moved forwardly by reaction as the material is forced against the portion of the article already formed. The material is moved under pressure by one or more spiral conveyors through the mold, and a forming element of any predetermined cross-sectional shape is substantially aligned with the down-stream end of each spiral conveyor and is mounted so as not to 1'0- tate with the latter. It is perferable to provide a vibrator in each forming element.

23 Claims, 11 Drawing Figures FATENTEU 5575 '3, 877. 860

sum 2 I g INVENTOR GEORGE PU TTI ATTORN PATENTEEAPR 1 51975 ATTORNE PATENTEUAPRI 1915 3.877. 860

sum a Ii 4 INVENTOI GEORGE PU TTI ATTOR vs EXTRUSION MACHINE FOR MAKING ARTICLES OF CEMENT-LIKE MATERIAL This application is a division of co-pending application Ser. No. 882,039 filed Dec. 4, 1969 now abandoned.

This invention relates to extrusion machines for making articles, such as slabs. panels, beams, and the like from suitable moldable material such a concrete. The moldable material used is a relatively stiff mix and rapidly sets to a relatively solid state. For the sake of convenience, the invention will be described herein relative to making cored slabs of concrete.

There are many machines in use for making by extrusion concrete slabs and other concrete articles. An example of the prior art machines is illustrated and described in US. Pat. No. 3,159,897, dated Dec. 8. 1964. This patent discloses a machine having a plurality of spiral conveyors or augers each with a spiral flight fixed to the core shaft thereof. Each auger has a trowelling mandrel secured to the downstream end thereof so that it rotates with the auger. A vibrator is mounted on the machine outside the molding area thereof so that the entire machine is vibrated, and the vibrations are not where they should be for the best results, and they are also applied to the part of the finished product within the machine. As each trowelling unit is fixed to an auger and rotates with it, it is only possible to form cores in the concrete slabs of circular cross-section and no other cross-sectional shape.

An extrusion machine in accordance with the present invention includes at least one spiral conveyor in and extending longitudinally of the mold of the machine for moving the concrete under press longitudinally thereof. A forming element of any predetermined crosssectional shape is aligned or substantially aligned with the down-stream end of the spiral conveyor and is mounted so as not to rotate with the latter. As a result of this, the forming element can have any desired crosssectional shape in order to produce cores in the finished product of corresponding cross-sectional shape. The mounting of the forming element makes it possible to rotate the forming element in the same direction as or counter to the direction of rotation of the spiral conveyor, and at the same or a different speed. If it is desired to make a slab with cores of a different crosssectional size or shape, it is only necessary to replace the forming element.

Additionally, should it be required to form solid slabs this can be achieved simply by removing the core forming element which of course is not possible with existing machines in which the spiral conveyor is formed integrally with the core forming element.

It is preferable to provide a vibrator within the forming element so that the vibrations are imparted to the concrete at the time the latter is being pressed against the formed part of the slab. This vibrator can be operated with less power than the vibrator of the prior art because it does not have'to shake or vibrate the entire machine.

The forming element can be made long enough to form or polish the inner surface of each core after the slab has been formed but while it is still within the mold, or it can include one or more finishing sections or elements fixedly or removably secured to the downstream end of the main forming element, and it is preferable to provide vibration dampeners between the forming element sections so that the vibrations within the forming element are not transferred to the finishing elements or sections and therefore are not transferred to the finished portion of the slab.

An extrusion machine according to the present invention comprises means for feeding concrete to a mold, a rotatable spiral conveyor in and extending longitudinally of the mold in the machine for moving said concrete under pressure through the mold and against the concrete that has set into the cross-sectional shape dictated by the cross-sectional shape of the mold, and a forming element of any predetermined crosssectional shape substantially aligned with the downstream end of the spiral conveyor and mounted so as not to rotate with the latter. The conveyor moves the material under pressure over the forming element so that said element forms a core of said predetermined cross-sectional shape in the article as it is being formed. The spiral conveyor has a spiral flight wound around a core shaft, said flight preferably being fixed to or formed with the shaft. Although not necessary for some purposes, it is preferable to provide a vibrator within the forming element so as to subject the concrete to high frequency vibrations at the time it is being subjected to the maximum amount of pressure and is being pressed against the portion of the slab already formed. In addition, it is preferable to provide one or more finishing elements or sections secured to the downstream end of the forming element through vibration dampeners. These finishing elements have a cross'sectional shape and size and the same as that of the forming element.

The conveyor preferably has those flights closer to the core forming element of slightly, greater diameter than the ones more remote from that element although the core shaft is conventionally of larger diameter in that region. In this way the composition of the concrete into the mold region is increased. To further increase the compression the leading face of the flights in the region of the mold may be radial to the core shaft i.e. they may be sectional as opposed to the normal helicoidal flights. In this way the tendency for the concrete to move up and over those flights is reduced.

Additionally the edges of the core forming element adjacent to the conveyor may be chamfered or relieved so that the element tapers from the desired final crosssection to a lesser cross-section adjacent the conveyor in this way to allow the concrete to be packed smoothly around the element.

Additionally or alternatively the pitch ofthe flights may be progressively decreased towards the mold or downstream end of the conveyor to such an arrangement as is possible to use a parallel sided core shaft.

Examples of machines in accordance with this invention are illustrated in the accompanying drawings, in which FIG. 1 is a side elevation of this extrusion machine with the near side broken away to show a spiral conveyor and its associated forming element,

FIG. 2 is a plan view of the maching illustrated in FIG. 1,

FIG. 3 is a horizontal section taken substantially on the line 3-3 of FIG. 1, showingtwo spiral conveyors in plan,

FIG. 4 is an enlarged vertical longitudinal section taken substantially on the line 4--4 of FIG. 3 showing one of the spiral conveyorsand part of the forming element thereof in section,

FIG. Sis a cross-section take on the line 55 of FIG. 3

machine,

FIG. 7 is a longitudinal section through an alternative form of spiral conveyor,

FIGS. 8, 9, and 10 are reduced end views of slabs formed by this machine and illustrating cores of three different cross-sectional shapes by way. of example, and

FIG. 11 is an enlarged longitudinal section through the outer end of a spiral conveyor similar to but a little different than the conveyor of FIG. 4. 7

Referring to the drawings, 10 is an extrusion machine in accordance with this invention which is adapted to move over any suitable base in order to form articles of moldable material, such as. concrete slabs. The articles may be formed on the ground or any other suitable base which actually constitutes the bottom surface of the mold of the machine. In this example, the machine moves along a base 12 having

vertical sides

13 and 14 which form rails for the machine, said base being supported in any suitable manner, such as by

channels

15 and 16 upon which

sides

13 and 14 rest.

Machine 10 is made up of a main frame 19 consisting of

side members

20 and 21 interconnected by

cross members

22 and 23 at opposite ends thereof. A supporting frame 26 is mounted on side members 20 and.

21 between the ends thereof and extends across the machine. Frame 26 can be adjusted up and down relative to main frame 19 by bolts 27. Frame 19 is provided with wheels 28 that rise on

rails

13 and 14, and as it is necessary to prevent the down-streamend 30 of the machine from rising during operation of the apparatus, brackets 32 extend downwardly from frame 19, and carry wheels 33 which engage the lower surfaces of

sides

13 and 14, see FIG. 6.

If machine 10 is used to form a relatively narrow slab or beam with a single core therein, only one spiral conveyor 37 is mounted therein. However, there are usually several of these conveyors in the machine, two conveyors being shown invthe illustrated machine. As the spiral conveyors and the forming elements associated with them are the same as each other, only one will now be described in detail.

The spiral conveyor 37 is mounted at one end in suitable bearings carried by supporting frame 26 between

side member

20 and 21. This conveyor is made up of a flight 40 secured to or formed with a hollow core shaft 41. In this example, shaft 41 has a straight section 44 extending throughout part of the length of the conveyor, and a diverging section 45 extending throughout the remainder of the conveyor at the downstream end 46 thereof. Flight 40 may have a constant outer diameter as illustrated at 49 in FIGS. 1 and 4. Alternatively and as described with reference to FIG. 11 the outer diameter of the flight may be greater at the downstream end of the conveyor.

Each conveyor 37 is rotated in any suitable manner, and in this example, one conveyor is driven by a chain and sprocket arrangement 54 which is driven by a suitable source of power, such as an electric motor 55 mounted on frame 26. While the other conveyor can be driven by the drive 54, it is preferable to rotate the latter conveyor in the opposite direction by gears 56 and chain and sprocket arrangement 57.

FIG. 6 is an elevation of the downstream end of the a chain and sprocket arrangement 64 which is driven by a suitable source of power, such as an electric motor 65. Forming element 62 is fixedly or removably mounted on the end of shaft 63 beyond the outer end of conveyor 37,and in this example,said forming element is mounted on the .end of shaft 63 by bolts 66.

Forming element 62 can be of any desirable crosssection if shaft 63 is not rotated, such as oval, square, triangular, and the like or if it is desired to form slabs without a core the elemenet 62 can be removed. How ever, if shaft 63 is rotated, the forming element Will form a core of circular cross-section, in which case, the 7 element itself can be circular in section. The. forming element can be no larger in cross-section than the spiral conveyor, as shown or it can be cross-sectionally larger.

It is preferable to provide a vibrator 68 within formingelement 62. Any suitable vibrator may be used for this purpose, such as an eccentric vibrator, as shown. In this example, vibrator 68 consists of a body 70 mounted on a shaft 71 which is offset a little from the longitudinal central axis of the body. Shaft 71 is journalled in bearings 72 which are carried by a housing 73 supported within the forming element 62 and having perforations 74 therein. A drive shaft 75 is connected at one end to shaft 71, and extends longitudinally through shaft 63 to a suitable source of power, such as a small electric motor 76 carried by support 26 beyond the end of said shaft 63, see FIG. 1. The bearings, 72 are lubricated by oil 79 in forming element 62 which forms a housing or reservoir therefor. The level of this oil is normally kept above the bottom of vibrator body 70 so that the lattersplashes the oil to lubricate the bearings. In addition, during operation of vibrator 68, the eccen-. tric body 70 thereof slides over the inner surface of housing 73 and creates a suction through perforations 74 to draw oil therethrough even when the level of the oil is low. In effect there always is a mist of oil within the forming element to keep bearings 72 lubricated.

When the forming element is removed to produce slabs with no core it is apparent that if vibration is ret quired it will be necessary to apply it externally of the body. Such arrangements are well known per se and as such are not described in detail herein. Obviously even.

with a core forming element external vibration may be applied to the mold as an alternative to or additionally to the internal vibration system illustrated.

Forming'unit 62 may be relatiely long, or it may be formed in two or more interconnected sections, as shown.The forming element in this case consists of a main section 82 which is connected to and supported by the outer end of shaft 63, and to

additional sections

83 and 84. The two additional sections are the same size and shape in cross-section as main section 82, and

section 83 is connected by a dampener 86 to section example is illustrated in FIG. 4. Each of the dampeners is made up of a resilient block 88 located between the connected sections, and bolts 89 extending from said sections into the block to hold these element together.

A hopper 90 is mounted on frame 19 above the inner end of spiral conveyor 37. This hopper directs previously-mixed concrete of the desired consistency down into the area between the sides of frame 19 at the inner end of the spiral conveyor or conveyors. There are usually a plurality of these conveyors in apparatus of this type. The width of the slab to be produced is determined by side plates on edge mounted on opposite sides of the spiral conveyors. There may be one or a plurality of plates at each side. In this example, there are two substantially aligned

plates

92 and 93 on one side of the machine, and substantially aligned

plates

94 and 95 at the opposite side thereof.

Plates

92, 93, 94 and 95 are mounted for adjustment on

frame side members

21 and 22 by means of

bolts

97, 98, 99 and 100, respectively. The plates can be moved towards and away from the side members by these bolts.

Plates

92 and 94 are usually inclined slightly towards each other in the direction of the down-stream or discharge end of the machine, while

plates

92 and 93 are usually inclined towards each other in the same direction but to a lesser extent. The distance between the discharge ends of

plates

93 and 95, indicated at 102, determines the width of the finished product.

A support 105 extends across the machine above the conveyors and forming elements thereof and are mounted on

side members

20 and 21 and adjustable vertically thereto by shims and bolts 106. One or more horizontal top plates are suspended from support 105 above said conveyors and forming elements. In this example,

top plates

108 and 109 are adjustably suspended by bolts 111 and 112 respectively.

Side plates

92, 93, 94 and 95 and

top plates

108 and 109 for the sides and top of a mold 115 for forming the concrete articles or slabs, the surface on which machine operates forming the bottom of this mold, and in this example, base 12 serves this purpose.

During operation, premixed concrete of the desired consistency is fed by the hopper 90 into the space immediately therebelow. This concrete fills the mold l 15, engulfing the spiral conveyors and the associated forming elements. As the conveyors rotate, they tend to move the concrete towards the discharge end of the machine, but as this movement is resisted and stopped by the portion of the slab already formed, the concrete is subjected to pressure as it moves through the mold, and the machine moves in the opposite direction. The pressure in the concrete depends upon the force necessary to move the mass of the machine. The pressure can be regulated by changing the angles of

side plates

92, 93, 94 and 95, and/or of

top plates

108 and 109. The concrete is also moved around the

sections

82, 83 and 84 of the forming elements as it travels towards the discharge end of the machine.

As the concrete is moved around the forming elements these form cores in the finished product of the same cross-sectional shape and dimensions as the forming elements. The vibrators operate within the forming elements, and this subjects the concrete to high frequency vibrations as it is being compacted into the finished article. This improves the compaction, and if prestressing strands or cables extend through the machine so as to be incorporated into the finished slab, the vibration within the concrete mass assures a very strong bond between the strands or cables and the concrete.

The compaction is so good as a result of the vibrators within the concrete that the finished slab or article is immediately selfsupporting.

The finishing

sections

83 and 84 support the concrete within the cores formed therein while the concrete is still being subjected to external pressure. They also help to finish or smooth the surfaces of the cores within the slabs. If the complete forming elements is circular in cross-section, it can be rotated at the same or different speed from the speed of rotation of the spiral conveyors, and in the same direction as or opposite to the direction of rotation of said conveyors. This makes it possible to rotate to conveyors and the forming elements at the best speeds for their'respective purposes. The rotating finishing sections of the forming elements polish the surfaces of the cores. Dampeners 86 and 87 prevent the vibrations from the vibrators from being transferred to finishing

sections

83 and 84, and, therefore, to the finished portion of the slab.

FIG. 7 illustrates an alternative form of conveyor 37a which has a tubular core shaft which does not have a diverging outer section similar to section 45 on shaft 41. Conveyor 37a includes a spiral flight 122 wound around and secured to shaft 120. Conveyor shaft 120 is rotated in the same manner as conveyor shaft 41 described above.

ln the example of FIG. 7, forming element 62 is mounted on the end of a tubular shaft 125 which may be fixedly mounted in the machine, or it may be rotated by the same drive means as shaft 63 of conveyor 37. The remaining elements of conveyor 370 are the same as those of conveyor 37, aand the two conveyors operate in the same manner.

Machine 10 is such that suitablle reinforcing rods may extend therethrough so that the rods are incorporated in the concrete slabs as the latter is formed. Similarly, prestressing strands or cables can extend through the machine, in which case these are incorporated in the slab. By having the vibrators within the forming elements, the high frequency vibrations are applied to the concrete exactly where they are reqquired and where they will do the most good. These vibrations also cause the concrete to bond very firmly to the prestressing strands or cables.

The mounting of the forming elements so that they can remain stationary while the spiral conveyors rotate makes it possible to form cores of any desired crosssectional shape within the concrete slab. For example, these forming elements may be cylindrical, square, oval or any other suitable shape in section. FIGS. 8, 9 and 10 have been included to illustrate finished slabs 130, 131 and 132 having therein

cores

134, 135 and 136 respectively of different cross-sectional shapes. These are examples of different shapes that can be produced. lf theforming elements are cylindrical, they can be rotated in the same direction as or counter to the rotation of the conveyors, and they can be rotated at the same or different speeds. Thus, the forming elements can be rotated as desired in order to produce well honed cores in the slabs.

The provision of several finishing sections in the forming elements makes it possible to support the slab internally for a longer period after the slab has been formed around the main forming elements than would normally be possible. The dampeners between the forming element sections prevent the high frequency vibrations from being transferred to the finished slab so that the latter is dimensionally stable regardless ofthe fact that it has just been formed and has just emerged from the forming mold.

Another advantage of the present machine results from the fact that the forming elements can be easily and quickly removed from the machine without interfering with the spiral conveyors which itis desired to make solid concrete slabs. The

side plates

92, 93, 94 and 95 can easily be shifted laterally in order to produce slabs of different widths, while

top plates

108 and 109 can be adjusted vertically. This machine can be used to produce slabs of different thicknesses and with cores of the same or different sizes. Transverse frame 105 can be adjusted up and down on frame 19 when it is desired to change the thickness of the slab being formed. "Frame 26 will also be adjusted up and down to centralize the cores relative to the top and bottom of the slab. If the core size has to be changed, it is not necessary to replace the spiral conveyors but only to replace their associated forming elements. Two layers of cores may be formed in the slab by providing two layers of conveyors and forming elements within themold of the machine. 7

' In the conveyor illustrated in FIG. 11 the core shaft 140 has flights 141 fixed to it by welding or bolting or by forming them integrally.

The shaft 140 has a diverging section 142 and the flights 141 on that section are of progressively larger diameter towards the core forming element so that their compressure effect on the concrete at that region is increased over the effect of flights which is not so increased. Additionally, while the flights on the parallel sides section of the core shaft are of conventional helicoidal form those on the diverging section are of sec tional form having those faaces 143 towards the core forming element (i.e. the downstream side) radial and lying substantially normal to the axis of shaft 140 and those faces 144 remote from that element sloped.

This feature tends to resist the movement of the concrete up and over the faces 143 and thus further increase the compressure effect of the conveyor. To lead the concrete into the mold the end of the core forming element adjacent to the conveyor is chamfered or tapered as at 145.

Desirably the pitch of the flights becomes less towards the downstream end of the conveyor, as shown, and this characteristic may be combined with the features prescribed above or may replace them.

l claim:

1. In an extrusion machine including a mold for making elongated articles of concrete-like moldable material by forcing the material through said mold, said machine including means for feeding said moldable mate- I rial to said mold, said machine being moved forwardly by reaction as the material is forced against the molded portion of the article, said machine including means for guiding the forward motion of said machine along a path for forming the molded material as an elongate body in said path, the improvement which comprises: a rotatable spiral conveyor in and extending longitudinally of the mold for moving the material under pressure through the mold and against material that has set into the cross-sectional shape dictated by the crosssectional 'shape of the mold, said conveyor including a spiral flight along its length and a forming element of non-circular cross-sectional shape immediately following the down-stream end of the spiral conveyor at the downstream end of said spiral flight and mounted so as i not to be rotated by the conveyor, means for controlling the rotation of said forming element rela tive tothe rotation of said conveyor, said conveyor moving the.

material under pressure over the forming element whereby said element forms a core of said predeter mined cross-sectional shape in the article as it is being;

4. A machine as claimed in claim 3 in which the.

flights of the conveyor at least towards the downstream end thereof have radial faces lying substantially normal to the axis of the core shaft and facing towards said down-stream end.

5. A machine as claimed in claim 4 in which the upstream faces of said flightsare inclined relative to a radius of the core shaft.

6. A machine as claimed in claim 3 in which said core shaft has a constant diameter throughout the length thereof.

7. A machine as claimed in claim 3 in which said core shaft increases in diameter towards the down-stream end thereof.

8. A machine as claimed in claim 7 in which the flights of the conveyor progressively increase in diameter towards the downstream end of the conveyor over that portion of the core shaft of increasing diameter- 9. A machine as claimed in claim 8 in which the upstream end of the core forming element diverges towards the downstream end of the core shaft anddown to the size and cross-sectional shape of said downstream end.

10. A machine as claimed in claim 7 in which the flights of the conveyor at least towards the downstream 12. A machine as claimed in claim.3 in which said 1 core shaft is hollow, and including a supporting shaft extending through and beyond the down-stream end of the spiral conveyor, said forming element being,

mounted on and carried by said supporting shaft.

13. A machine as claimed in claim 1 including vmeans for removably mounting said forming element in position relative to the spiiral conveyor.

14. A machine as claimed in claim .12 including means for removably mounting said forming element in,

position relative to the spiral conveyor.

15. A machine as claimed in claim 1 including a .vi-

brator mounted within said forming element.

16. A machine as claimed in claim 12 including a brator mounted within said forming element. 1

17. A machine as claimed in claim 1 including means connected to the forming element to rotate said ele ment independently of the spiral conveyor.

18. A machine as claimed in claim I in which said forming element is in a plurality of interconnected sections.

frame having side members adapted to co-operate with a base to create a forming space therebetween, said mold being positioned in and extending longitudinally of said forming space and said base being the bottom wall of the mold, said spiral conveyor being positioned in the forming spaced and extending into the mold.

23. A machine as claimed in claim 22 in which said mold includes a substantially horizontal top plate and substantially vertical spaced side plates, and including means for changing the angles of said top and side plates relative to the longitudinal axis of the mold.

Claims

1. In an extrusion machine including a mold for making elongated articles of concrete-like moldable material by forcing the material through said mold, said machine including means for feeding said moldable material to said mold, said machine being moved forwardly by reaction as the material is forced against the molded portion of the article, said machine including means for guiding the forward motion of said machine along a path for forming the molded material as an elongate body in said path, the improvement which comprises: a rotatable spiral conveyor in and extending longitudinally of the mold for moving the material under pressure through the mold and against material that has set into the cross-sectional shape dictated by the cross-sectional shape of the mold, said conveyor including a spiral flight along its length and a forming element of non-circular cross-sectional shape immediately following the down-stream end of the spiral conveyor at the downstream end of said spiral flight and mounted so as not to be rotated by the conveyor, means for controlling the rotation of said forming element relative to the rotation of said conveyor, said conveyor moving the material under pressure over the forming element whereby said element forms a core of said predetermined cross-sectional shape in the article as it is being formed.

2. A machine as claimed in claim 1 in which said forming element is substantially aligned with said spiral conveyor.

3. A machine as claimed in claim 1 in which said spiral conveyor comprises a core shaft with a spiral flight wound therearound.

4. A machine as claimed in claim 3 in which the flights of the conveyor at least towards the down-stream end thereof have radial faces lying substantially normal to the axis of the core shaft and facing towards said down-stream end.

5. A machine as claimed in claim 4 in which the upstream faces of said flights are inclined relative to a radius of the core shaft.

8. A machine as claimed in claim 7 in which the flights of the conveyor progressively increase in diameter towards the downstream end of the conveyor over that portion of the core shaft of increasing diameter.

9. A machine as claimed in claim 8 in which the upstream end of the core forming element diverges towards the downstream end of the core shaft and down to the size and cross-sectional shape of said downstream end.

10. A machine as claimed in claim 7 in which the flights of the conveyor at least towards the downstream end thereof have radial faces lying substantially normal the axis of the core shaft and facing towards said down-stream end.

11. A machine as claimed in claim 7 in which the upstream end of the core forming element diverges towards the downstream end of the core shaft and to the cross-sectional shape of said downstream end.

12. A machine as claimed in claim 3 in which said core shaft is hollow, and including a supporting shaft extending through and beyond the down-stream end of the spiral conveyor, said forming element being mounted on and carried by said supporting shaft.

13. A machine as claimed in claim 1 inCluding means for removably mounting said forming element in position relative to the spiiral conveyor.

14. A machine as claimed in claim 12 including means for removably mounting said forming element in position relative to the spiral conveyor.

15. A machine as claimed in claim 1 including a vibrator mounted within said forming element.

16. A machine as claimed in claim 12 including a vibrator mounted within said forming element.

17. A machine as claimed in claim 1 including means connected to the forming element to rotate said element independently of the spiral conveyor.

18. A machine as claimed in claim 1 in which said forming element is in a plurality of interconnected sections.

19. A machine as claimed in claim 18 in which said forming element sections are detachably connected to each other.

20. A machine as claimed in claim 1 in which said forming element is in a plurality of interconnected sections and including a vibrator in the downstream section next to the end of the spiral conveyor.

21. A machine as claimed in claim 20 including vibration dampener means forming the connection between forming element section with the vibrator therein and the section next thereto.

22. A machine as claimed in claim 1 including a frame having side members adapted to co-operate with a base to create a forming space therebetween, said mold being positioned in and extending longitudinally of said forming space and said base being the bottom wall of the mold, said spiral conveyor being positioned in the forming spaced and extending into the mold.