US 3773447 A
Apparatus for producing a cement sheet, including a rotatable mould into which a cement mix is fed to form a soft, centrifugally moulded cylinder, which is then removed from the mould, divided longitudinally, and laid out flat to harden. The soft cement cylinder is removed by means of a mandrel inserted into the cylinder while in the mould. During removal from the mould, the cement cylinder is held onto the mandrel either by vacuum applied to perforations in the wall of the mandrel, or by means of a liner initially placed within the mould and which surrounds the cylinder while it is removed from the mould on the mandrel. Slitting means are provided, movable relative to the mandrel to form a longitudinal slit in the soft cylinder on the mandrel after its removal from the mould. The apparatus is particularly useful for producing small quantities of asbestos cement sheets with special laminations or surface effects. Apparatus in accordance with the invention may be used for producing sheets of flowable hardenable material other than cement.
Claims available in
Description (OCR text may contain errors)
United States Patent 11 1 Barratt 1 Nov. 20, 1973 APPARATUS FOR PRODUCING CEMENT SHEETS  Inventor: William C. Barratt, 595 Sheppard St., Niagara Falls, Ontario, Canada  Filed: Jan. 3, 1973  Appl. No.: 320,770
Related US. Application Data Continuation-impart 6r Ser. NO. 166,779, July 28,
 Foreign Application Priority Data 2 Feb. 1, 1972 Great Britain ..4712/72  US. Cl 425/86, 264/86, 425/297,
51 Int. Cl. 13286 21/08  Field of Search 425/86, 182, 297, 425/308, 324, 425, 426, 427, 436, 435, DIG.
44, DIG. 124; 249/112; 264/86, 159, 311
Primary ExaminerH. A. Kilby, Jr. Attorney-John W. Malley et a].
[57 ABSTRACT then removed from the mould, divided longitudinally,
and laid out flat to harden. The soft cement cylinder is removed by means of a mandrel inserted into the cylinder while in the mould. During removal from the mould, the cement cylinder is held onto the mandrel either by vacuum applied to perforations in the wall of the mandrel, or by means of a liner initially placed within the mould and which surrounds the cylinder while it is removed from the mould on the mandrel. Slitting means are provided, movable relative to the mandrel to form a longitudinal slit in the soft cylinder on the mandrel after its removal from the mould. The apparatus is particularly useful for producing small quantities of asbestos cement sheets with special laminations or surface effects. Apparatus in accordance with the invention may be used for producing sheets of flowable hardenable material other than cement.
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I APPARATUS FOR PRODUCING CEMENT SHEETS This application is a continuation-in-part of my United States Patent application Ser. No. 166,779, filed July 28th 1971 now abandoned.
The present invention relates to apparatus for producing sheets from a flowable hardenable material such as cement, which sheets may be flat curved or congtoured. The invention particularly relates to apparatus for performing the process of copending Patent application Ser. No. 166,778 also filed July 28th 1971. The sheets may be used either as produced or cut to smaller sizes, for example as structural members, wall panels, or roof sections, or for decorative components such as tiles, moulds, millwork or shingles.
In the known wet process for manufacturing cement sheets, and particularly asbestos cement sheets, a large plant is required which in order to be economical must operate on a high production basis, and such a process is not easily adapted for producing small quantities of special decorative materials.
The present invention provides apparatus which is 'suited to the economical production of small quantities of cement sheets, and which can readily be adapted to produce a wide variety of surface finishes, or other characteristics, in the cement sheets produced. The apparatus produces the cement sheets singly, one after the other, and it is a very simple matter to modify the operation of the apparatus between individual sheets, so that a wide variety of different cement sheets can be produced in a short time. The cement sheets can vary as to thickness, composition, colour, and the nature and shape of the surface finish. The apparatus thus is very suitable for producing a lot of different components, having different shapes and surface finishes, for a single building. The apparatus used in accordance with the invention does not require a large investment or take up a large amount of space, so that it is very suitable for location in the locality where building is taking place. Furthermore, the nature of the process used gives a high strength product due to avoidance of excess water, uniformity of wall thickness, high density and predetermined directional resistance to stresses. In
the case of cement reinforced by fibres, such as asbestos cement, additional strength is given by good orientation and formation of fibres. Also, the process operates with very little waste.
In the process described in copending application Ser. No. 166,778, a cement sheet is produced by a centrifugal casting method, the cement mix (including water) being fed into a rotatable cylindrical mould and spun to distribute the mix evenly around the mould wall to shape the mix into a hollow cement cylinder. One end plate of the mould is removable to allow for axial removal of the cement cylinder, and in order to effect this removal a cylindrical mandrel is inserted into the mould to engage the inner surface of the cement cylinder, which is then withdrawn on the mandrel. After removal, and with the cement cylinder still in the soft or flaccid state, the cement cylinder is divided longitudinally and the resultant sheet is laid out onto a flat or curved surface and allowed to harden.
The present invention provides apparatus for performing this process, which comprises, firstly, a cylindrical mould mounted for rotation on a horizontal axis and having a removable end plate, the mould and end plate being such that a cylindrical body of cement or other material formed within the mould can be exgageable with the inside surface of a cylinder of the material as formed in the mould. Mounting means for the mandrel are provided which allow movement thereof axially into the mould and which also allow rotation after removal from the mould, to facilitate unrolling the final product. The mounting means may include handling means such as cranes or hoists, but preferably a special carriage is provided. Means are provided for holding the cylinder on the mandrel during removal thereof from the mould, as described more fully below. Also, slitting means are provided for forming a longitudinal slit in a cylinder of the material held on the mandrel outside the mould, although as an alternative to slitting means the mould may be provided with an inwardly projecting member arranged to form a longitudinal division in the cylinder formed in the mould. Suitable slitting means are an upwardly projecting blade, or a wire band saw, preferably applied to the underside of the soft cylinder of cement or other material while it is held on the mandrel. The apparatus also includes a surface for receiving a soft sheet of the material released from the mandrel, with means being provided to allow relative transverse movement between the mandrel and this surface with rotation of the mandrel to facilitate unrolling of the sheet from the mandrel.
The means for holding the cylinder onto the mandrel may include ports in the cylindrical surface of the mandrel, and conduit means connecting these ports to a source of vacuum, so that during removal of the cylinder this can be held onto the mandrel by vacuum. The mandrel may also be connectable to a source of compressed air to give release of the cylinder when required.
Alternatively, or additionally, the apparatus may ini clude a liner for example of sheet metal or rubber, bendable to form a cylindrical surface within the mould, and having a longitudinal division so that it may be laid out flat with the sheet of material formed in the mould. The liner may have opposed edge portions which are adjacent while the liner is in the mould, these opposed edge portions having means for connecting them together when the mandrel is inside the cylinder so that the liner can assist in holding the cylinder onto the mandrel. The liner edge portions may be directly connected together, by means of a clip. The liner may become incorporated in the final product, or may be separated from the final sheet and re-used. The adjacent edge portions of the liner may be spaced apart (while surrounding the cylinder) so as to allow the cylinder to be slit through the gap between the edge portions.
The process and apparatus will be particularly described by way of example with reference to the accompanying drawings in which:
FIG. 1 is a partly sectioned elevation of a first type of centrifugal mould for use in accordance with the invention,
FIG. 2 is a cross-section through the mould of FIG.
FIG. 3 is an elevation of a mandrel, FIG. 4 is a cross-section through the mandrel on line 4-4 of FIG. 3,
FIGS. 5 and 6 show details of the mandrel in crosssection and side elevation respectively,
FIG. 7 is a sectional elevation through the mould with the cement cylinder and mandrel in place,
FIG. 8 is a view of the mandrel in the last stage of the process,
FIGS. 9 and 10 show variations of the basic method which produce a cement sheet with an exposed particulate surface,
FIGS. 11 and 12 are edge views of special cement sheets produced in accordance with the invention;
FIG. 13 is a partly sectioned elevation of a second type of centrifugal mould for use in accordance with the invention,
FIG. 14 is a cross section on lines 14-14 of FIG. 13 showing details of liner locking means,
FIG. 15 is a partly broken away view of a modified mandrel for use with the mould of FIG. 13,
FIG. 16 is a cross-sectional view of the modified mandrel on lines 16-l6 of FIG. 15,
FIG. 17 is a partly sectioned view of the mould of FIG. 13 with the modified mandrel in place,
FIGS. 18a, 18band 18c illustrate modified apparatus for slitting, laying out and curing the cement sheets,
FIG. 19 shows a cross-sectional view of part of a further modified mandrel engaging a cement cylinder within a modified mould, and
FIG. 20 shows an end view of a mould with modified means for removing water from the cement.
Referring to FIGS. 1 and 2, the apparatus includes a rotatable centrifugal mould indicated generally at 10. The mould has a cylindrical wall 12, which is of sheet metal and is perforated with 1/16 inch diameter holes spaced apart on 1 inch centres circumferentially and axially of the mould; these holes allow outflow of water during spinning. The mould wall 12 is reinforced by an end ring 14 secured within one end of the wall, and which is of a thickness greater than the cement cylinder to be spun; and also by reinforcing rings or tires 15 which rest on four rollers 16. The rollers 16 are carried by two parallel horizontal shafts 17, supported in bearings 18, and one of these shafts is driven by a motor and gearbox combination 19. When the motor is operated to drive the shaft 17, the frictional contact between rollers 16 and the tires 15 causes the mould to rotate about its horizontal axis.
The mould has a fixed end plate 21 and a removable end plate 22. The fixed end plate 21 is of annular form having a central aperture 21a which is large enough to allow fluid cement material to be fed into the mould by feeding means in the form of a charging head 23 to be described. The fixed end plate 21 is held by nuts on threaded studs 21b welded to the mould wall, and is removed only for maintenance or mould alterations.
The removable end plate 22 is mounted on an axially projecting stub shaft 26, which is carried in a bearing 27 supported at the end of a swing arm 28. The swing arm is pivoted at 30 and is rotatable from the closed position of FIG. 1 to the open position of FIG. 7 by means of a power cylinder 31. The inside of end plate 22 is provided with a central locating ring 33 having an inner surface which flares outwardly towards the other end of the mould, and which serves to support and locate one end of the charging head 23.
It will be apparent that the end plate 22 need not entirely cover the end of the mould, but may instead pro vide a cover over an annular portion only, of radial thickness greater than that of the cylinder to be spun therein.
The charging head 23, as shown in FIG. 1, is mounted on a support carriage 24 mounted on rails 24a adjacent that end of the mould with the fixed end plate. These rails allow movement of the charging head from the operative position of FIG. 1, in which the charging head extends through the fixed end plate 21, to a retracted position in which the charging head is withdrawn clear of the mould.
The charging head comprises a horizontally extending support member somewhat longer than the mould in the form of a parallel sided channel 34 open at its lower end and reinforced at its top by a horizontal plate 34b. At its outer end (remote from the carriage 24) the plate 34b carries a positioning pin 35, which, when the charging head is in the position of FIG. 1, locates in the locating ring 33 and assists in supporting the outer end of the charging head. The support member carries at one side a cement feed pipe 36, having downwardly extending distribution pipes 36a spaced along the pipe 36 at 1 foot spacing. Below the lower ends of pipes 36a there is provided a curved shutter 38 which, when in the closed position shown in broken lines, co-operates with the outside of the channel 34 to provide a trough suitable for retaining a quantity of particulate material. The shutter 38 is mounted on radial arms 39 pivoted to the support member at 80, and pivotally movable relative to the support member by fluid cylinder 81 to move this shutter into the open position shown in full lines, allowing material held in the shutter to be released onto the inside of the mould or to be fed directly into the mould from discharge pipes 36a.
The channel 34 accommodates a hollow, parallel sided member 83 vertically slidable therein under the control of hydraulic cylinder 84. The lower end of member 83 has a curved corner joining the vertical side of the member 83 with the horizontal lower edge-- thereof, this curved corner facing the direction of rotation of the mould which direction is indicated by the arrow. This curved comer and the adjacent surfaces of member 83 form spreader means 86 having a hard facing and capable of contacting the inner surface of a hollow cylinder of material being fed into the mould, to assist in evenly spreading the material within the mould. During the stage in which material is being fed into the mould via pipes 36a, the spreader means is caused to rise at a steady rate under control of fluid cylinder 84.
The member 83 also incorporates means for removing water from within the centre of the cylinder of material being spun within the mould, in the form of a skimmer 88 which is movable by fluid cylinder 89 between a retracted position in which it does not extend below the surface of the spreader means, to an extended position as shown in broken lines in which it projects below the lower surface of the spreader means. The skimmer 88 has an opening facing the direction of rotation of the mould, and which communicates with a water discharge pipe 90 extending along the member 83.
The member 83 also incorporates a vibrator 92 mounted on the inside of the spreader means and arranged to cause'vibration of the spreader means for compacting material in the mould.
The apparatus also includes a special cylindrical mandrel 40, which is shown in FIGS. 3 to 7. The mandrel has a cylindrical outer wall 400, the diameter of which is selected so that this can be inserted into a cement cylinder which has been formed in the' mould.
The diameter of the mandrel is such that the cylindrical surface of this is engageable with the inside surface of the cement cylinder without dimensional change of the latter. An outer end of the mandrel is closed by an end plate 41 (see FIG. 7), to the centre of which is welded a guide member 42 in the form of a tubular shaft. The guide member 42 is longer than the length of the mould, so that it can be used to guide the mandrel into the mould. The other end of the mandrel has a shorter shaft 41a projecting axially therefrom.
The mandrel wall 40a is pierced by longitudinal rows or ports 43, and each row of ports communicates with a longitudinal channel-44 within the mandrel. These longitudinal channels, which are shown in cross-section in FIGS. 4 and 5, are constituted by channel members 45 having their outer edges welded to the inside of the wall 40a, each row of ports 43 being centrally positioned along a channel member. FIGS. 5 and 6 show valve means 47 which allow one end of each channel '44 to be individually placed in communication selectively with a vacuum header tube 48 or a compressed air header tube 49. These header tubes 48 and 49, which are shown in FIGS. 5 to 7, are toroidal tubes of equal dimensions positioned close together near to one end of the mandrel, and connected by radial conduits outer surface fixed to a channel member 45. The valve body has two radial bores 57 and 58 leading respectively from header tubes48 and 49 into the channel 44,
and a valve member 59 is slidable in an axial bore in the valve body to control flow of air through these radial bores. The valve member 59 has a central recessed portion 60; in the position shown in FIG. 6 this recessed portion-is between the radial bores 57 and 58 and the valve member prevents flow of air through either bore.
By pulling-out an extension'61 of the valve member, the
recessed portion 60 is brought into registry with the bore 57, so that the channel 44 is put into communication with the source of vacuum through header 48 and hose 52; and when the valve member is pushed inwardly to bring recessed portion 60 into register with bore 58 then the channel 44 is placed in communica- -tion with the source of compressed air via bore 58,
header 49, and hose 53.
A curved operating member may be rotatably mounted at the outer end of the mandrel, and arranged to engage the valve member as it rotates relative to the mandrelto move these from the vacuum position to the compressed air position.
FIG. 7 is a view of the mould with a spun cement cylinder in place, and with the mandrel inserted to contact the inner surface of the spun cement cylinder, which is mandrel into the mould, and must also allow rotation of the mandrel by at least almost 360 with relative transverse movement between the mandrel and the surface which receives the cement sheet, for releasing and unrolling the cement sheet from the mandrel in the manner to be described.
The only other essential parts of the apparatus are slitting means for forming a longitudinal slit in the cylinder of soft cement held on the mandrel, after removal from the mould; means for causing relative movement between the slitting means and the mandrel to form the longitudinal slit, and a surface onto which the cement sheet can be laid after removal from the mandrel.
In the simplest apparatus, the slitting means may be a blade, such as blade 73 of FIG. 8, projecting upwardly in fixed position, and associated with the receiving surface 72, the blade having a length at least equivalent to that of the mandrel and having a width greater than the thickest sheets to be produced. In this embodiment, the means for causing relative movement between the slitting means and the rnandrel will be the handling or mounting means of the mandrel which allow this to be lowered onto the blade 73. The receiving surface may be provided by a pallet which can be located suitably in relation to the slitting blade 73 for receiving a cement sheet removed from the mandrel, and which is then removable to another location where the cement sheet h'ardens. The receiving surface 72 may be a plain flat surface or curved, or may have a relief design thereon for producing a corresponding relief design in the cement sheet. In the latter case, the apparatus will also include a standard type of hydraulic or other press by means of which pressure can be applied to the top surface of the cement sheet to cause the lower surface 1 to assume the shape of the pallet surface.
The process of the invention will now be particularly described with reference to FIGS. 1 to 8.
Operation of the apparatus in the simplest manner, to I produce a cement sheet without incorporation of fibres and without laminations, will now be described.
The charging head 23 is firstly advanced into the mould on rails 24a, to the position of FIG. 1, and the removable end plate 22 is closed. The cylinder 84 is actuated to bring the spreader means 86 close to the mould surface, and cylinder 81 is operated to open the shutter 38 to the position shown in full lines. A cement mix is then fed onto the mould surface via the pipes 36 and 36a, and simultaneously the cylinder 84 is operated to raise the spreader means 86 gradually, so that these maintain contact with the cement mix and ensure that this is spread evenly within the mould. The cement mix is fed in while wet (with about percent water) and rotation of the cylinder at a peripheral speed of 1200 ft/min. for about five minutes causes the wet cement to form a cylindrical layer of uniform wall thickness on the inside of the mould. The centrifugal effect also concentrates-and compacts the solid particles of the mix in the outer parts of the cement layer, and excess water which does not flow out of the perforations in the wall of the mould is forced to the center of the mould and flows out of this during a de-watering stage.
The use of a cement mix containing only 70 percent water is in contrast to other methods where more than 90 percent excess water is required.
The de-watering stage is reached after the material has spun sufficiently to compact the solids into cylindriical form and to form an inner layer of excess water. This takes about one minute. At this stage the cylinder 89 is operated to cause skimmer 88 to protrude from the lower surface of the spreader means, and cylinder 84 is operated to move the member 83 downwardly until the skimmer contacts the layer of water within the mould. The water is then skimmed off by pumping this through discharge pipe 90. In the final stages of dewatering, the spreader means 86 is brought into contact .with the cement cylinder, and the vibrator 92 is activated to cause vibration of the spreader means, and compaction of the cement, while the mould continues to spin.
At this stage rotation of the mould is stopped, and the end plate 22 is removed to the position shown in FIG.
- 7 by operation of cylinder 31. The cylindrical mandrel 40 is then positioned in the mould, by suitable handling means, into the position of FIG. 7.
When the mandrel is in place (as shown in FIG. 7) the valve members 61 are operated to connect the channels 44 to the source of vacuum so that the cement cylinder, which is already contacting or almost contacting the mandrel surface, is forced against the surface by atmospheric pressure. The mandrel is then withdrawn from the mould, and subsequently the cement cylinder is slit by being lowered, while still on the mandrel, onto the blade 72 so that this slits the cylinder longitudinally. The mandrel carrying the cement cylinder is then rolled along, i.e., moved transversely over the surface 72 while being simultaneously rotated, so that the cement sheet is laid out on the surface 72 (FIG. 8) During removal of the cement sheet the valve members 61 are operated successively to cause the lowermost channels 44 of the mandrel (e.g. channels 44a and 44b of FIG.
8) to be connected to a source of positive air pressure to assist the removal of the cement sheet from the mandrel. The valve members 61 of channels from which the cement sheet has been removed are returned to the neutral position of FIG. 6.
Preferably, the cement sheet so produced is subjected to a final pressing operation as between the platens of a press, this giving greater strength and density to the product. Subsequently, the cement sheet is hardened by curing in known manner. Also, the cement sheet may be rolled off the mandrel onto a platen having a relief design, the cement sheet being pressed onto the platen to reproduce the design.
It may be noted that the mandrel not only facilitates removal of the cement cylinder from the mould, and the slitting of this, but also enables the cement sheet to be rolled and compacted while being laid out.
In another process using the apparatus of the invention, the material first fed into the mould is a particulate material mixed with cement and water or any suitable bonding agent. The particulate material may be aggregate, or particles of glass, or metal, or of plastics material. As before, this particulate material is fed in while the mould is rotating, and rotation is continued until the material has formed a uniform layer within the mould.
The shutter 38 provides convenient means for supplying the particulate material to the inner surface of the mould. Before the charging head 23 is advanced into the mould, the shutter 38 is closed by cylinder 81, and the trough formed between shutter 38 and the side of member 34 is filled with the particulate material.
'After the charging head is in position in the mould the shutter 38 is opened to release the particulate material onto the inner surface of the mould. This material is then evenly spread in the mould by operation of the spreader means 86. Subsequently, a cement mix is fed into the mould, and the mould is spun to produce a flaccid laminated cement cylinder having the particulate material bonded to the outer layer. The cement cylinder is removed from the mould on the vacuum mandrel, as described above, slit, and the cement sheet laid out to harden. The surface of the cement sheet may then be polished to provide a flat surface in which the particulate material is exposed.
Instead of being a plain flat surface, e.g., the surface of a pallet, the receiving surface may be such as to be capable of becoming bonded to the soft cement sheet. One example of this is illustrated in FIG. 9, which shows a soft cement sheet being laid out onto a bed of aggregate material. Bonding of the soft cement sheet to the granular material is achieved firstly by using the mandrel in the manner of a roller, and then by pressing the resultant product between the platens of a press. The final product is illustrated in FIG. 11. Instead of using a bed of particulate material, the soft cement sheet can be laid out on a sheet already prepared according to the process, so that a thick laminate can be built up.
In the process of FIG. 10, an asbestos cement sheet which has been produced in accordance with the invention, as described, is laid out flat on a pallet, but before the sheet hardens aggregate material is sprinkled on the sheet, and pressed in, and the sheet is then allowed to set.
FIG. 12 shows a portion of a cement sheet having a sculptured or relief design surface. This can be made by laying out a soft sheet onto a pallet having a corresponding relief design surface, and pressing the soft sheet into place by means of a press.
Also, instead of the mandrel being moved transversely over the receiving surface, the surface may be arranged on a carriage for movement underneath a stationary, but rotatable, mandrel.
Additionally, cement sheets with liners bonded thereto may be produced by inserting a liner into the mould before adding the cement, so that cement cylinder becomes bonded to the liner. The bond can be strengthened by chemical bonding with a latex product such as Albitol (registered trade mark), applied to the inner surface of the liner. A gap may be left between the adjacent edges of the liner, to allow for slitting by the blade 73. Alternatively the liner itself may forrn the longitudinal division in the cement cylinder as particularly described in co-pending Patent application Ser. No. 166,780. Liner materials may be of metal, plastics or rubber.
The liners used may be plain and imperforated, in which case a non-perforated mould would be used and all the excess water would be removed from the centre of the hollow cylinder produced. A plain liner may be used with the vacuum mandrel described or with the different types of apparatus shown in FIGS. 13 to 18.
However, one type of liner which is particularly useful with the perforated mould just described is a wire mesh liner having its surface mainly formed of a fine wire mesh of about 75 wires to the inch (both ways), and similar to the wire mesh or wire cloth used on paper-making machines of the Fourdrinier type. This wire mesh liner when used in the mould having a perforated cylindrical wall, allows a large amount of water to be removed by centrifugal action during spinning, thus resulting in a dryer, denser and stronger product than that produced with a plain liner. The liner is normally 'stripped from the cement sheet before this hardens, and is re-usable. The wire mesh may be used in conjunction with other laminating steps described for example a layer of aggregate, or exposed particles of glass or metal may also be incorporated in the cement sheet. The cement sheets produced in accordance with this invention can be further treated by drying when hard at temperatures of 105C or higher, soaking in a liquid monomer such as methyl methacrylate, and curing it to polymerize the monomer. Polymerization can be achieved by irradiating the impregnated cement or by heating the cement to 75C for 2 hours with 2 percent benzoyl peroxide added to the monomer as a catlyst. This process gives much improved physical properties to the cement sheet, and also makes it impermeable.
A different form of apparatus for performing the same basic process, but in which the mandrel is fully rotatable when inserted in the mould, will now be described with reference to FIGS. 13-18.
FIGS. 13 and 14 show moulding apparatus generally similar to that of FIGS. 1 and 2, but adapted for use with the modified form of mandrel shown in FIGS. 15
and 16. 1
The apparatus of FIGS. 13 and 14 is similar to that previously described in having a rotatable mould with a cylindrical wall 112 held by rings 115 resting on rollers 116 mounted on shafts 117 driven by a motor and gearbox combination 119. Unlike in the first embodiment, however, the mould wall 112 is not perforated.
The dimensions of the mould are about ft (3 meters) length and about 6 ft (1.8 meters) in diameter. The mould has a removable end plate 122 which again is the same as that of the first embodiment. At the end of the v mould opposite the plate 122 however the construction is different from the first embodiment, in that it incorporates an axially movable annular member 121 hereinafter referred to as a void ring, which will now be described.
The void ring 122 is of channel form, having an outwardly facing opening engaged by an annular plate 180 which is bolted to the end flange of the mould. The void ring is movable axially of the mould between the positions shown in FIGS. 13 and 17, and sealing means 181 provide a seal between the inner flange of the ring and the inner surface of the mould. The void ring 121 has a radial dimension greater than that of the thickest cylinders to be spun within the mould, and has interior dimensions large enough to allow space for entry of the charging head 123 which is identical to the charging head 23 already described with reference to the first embodiment, and which is shown in cross section in FIG. 14.
FIG. 14 also shows a special form of liner 170 used in this second embodiment. This liner is a sheet of abrasion resistant rubber of one-half inch (12 mm) thickness sufficiently flexible to form a cylinder lining the mould as shown. The liner has opposite edge portions which are adjacent while the liner is in the mould, the edge portions being bonded to sheet metal edge pieces 171. The edges of the liner extend beyond the edge pieces 171 to form a seal preventing cement or other material from passing between the edge pieces 171. The edge pieces 171 are provided with radially outwardly directed flanges 172, and the outer edges of these flanges have lips 173 bent back parallel to the liner surface and forming a recess therewith. The recesses are engageable by the inwardly directed jaws of a locking clip 175, the cross-sectional form of which is shown in FIG. 14, and which is accommodated in a suitably shaped longitudinal groove 176 in the mould surface. The clip 175 thus co-operates with the edge pieces 171 to hold the edge portions of the liner together when the cylinder and liner are removed together from the mould, as will be described, thus holding the cement cylinder on the mandrel when removed from the mould. To facilitate removal from the mould, the outside surface of the liner, and the inside surface of the mould, are coated with polytetra-fiuoroethylene.
The modified mandrel used with this mould is an expanding mandrel as shown in FIGS. 15 and 16. The mandrel includes a cylindrically curved surface formed by a slightly flexible metal plate 141, the longitudinal edges of which are close together when the plate 141 is unstressed and is at its minimum diameter as indicated in full lines in FIG. 16. The plate 141 has an annular end flange 142 at one end, and is capable of being expanded by means to be described to the condition shown in broken lines in FIG. 16, the amount of radial expansion being greater than the radial depth of flange 142.
The mandrel is mounted on a tubular shaft 144 carried at its inner end by a rail mounted carriage 148, the carriage allowing axial movement of the mandrel into the mould and also allowing free rotation of the shaft 144. The shaft 144 has an extension 145 at the outer end of the mandrel (i.e., that remote from the carriage 148), which serves a purpose to be described. The shaft 144 carries two axially spaced expanding arrangements 151 and 152 by which the plate 141 is connected to the shaft 144. Each expanding arrangement comprises two opposed pairs of gussets 154 welded to shaft 144, and two symmetrically arranged triangular crank members 155 each having a first corner pivoted at 156 to gussets 154, a second corner pivoted to gussets 157 which are welded internally to plate 141 near to the longitudinal edges thereof, and a third corner pivotally connected by links 158 to gussets 159. The crank members 155 of expanding arrangements 151 and 152 are connected for movement together by plate 155a. Also, both crank members 155 and links 158 are of channel form having parallel side plates or flanges connected by a web. The gussets 157 are welded to the inside of plate 141 at 10- cations spaced away from gussets 157, being on the opposite side of a plane through pivots 156 from these gussets 157. The spacing between adjacent gussets 157 and 159 is roughly equivalent to that between the two gussets 159, this spacing being of the order of 100 to 120 of arc subtended at the axis of shaft 144. The two crank members 155 are arranged to be urged apart by a pneumatic cylinder 161, this cylinder being connected by a flexible conduit 162 via a rotary valve 163