US3892623A

US3892623A - Process for producing fibrous cement sheets

Info

Publication number: US3892623A
Application number: US353074A
Authority: US
Inventors: William C Barratt
Original assignee: Individual
Current assignee: Individual
Priority date: 1970-07-31
Filing date: 1973-04-20
Publication date: 1975-07-01
Anticipated expiration: 1992-07-01

Abstract

A process for producing cement sheets, particularly asbestos cement sheets, in which a cement mixture is fed into a rotating horizontal mould to form a soft centrifugally moulded cylinder, which is then removed from the mould on a mandrel, longitudinally divided, and laid out flat to harden. The mandrel both supports the cement cylinder during removal from the mould, and allows this to be rolled off the mandrel onto a receiving surface by rotating the mandrel and moving this transversely over the surface. Preferably, the cylinder of cement is formed within a liner in the mould, the edges of the liner being connected together during removal of the mandrel from the mould so that the liner assists in holding the cylinder on the mandrel. The invention also covers novel cement sheets produced by the process.

Description

United States Patent H Barratt *July 1, 1975 [54] PROCESS FOR PRODUCING FIBROUS 2,348.804 5/l944 GeriIty 162/[20 3,0l4,835 l2/l96l Feig ey et al. l. 162/l54 CEMENT SHEETS 3,097,080 7/!963 Weir 161/205 [76] Inventor: William C. Barratt, 595 Shepherd 3 773.44! H973 Banal: r l A H 425/86 St., Niagara Falls, Ontario, Canada 3,778,206 l2/l973 Barratt 425/86 Notice: The portion of the term of this Pat t ubs q n K0 1386- l l990, Primary ExaminerS Leon Bashore has b en dis laim d. Assistant ExaminerPeter Chin [22] Filed: Apr. 20, I973 Related US. Application Data A f d t h t f l I process or pro ucmg cemen s ee 5, par lcu ar y [63] gy ssgfggxg of asbestos cement sheets, in which a cement mixture is fed into a rotating horizontal mould to form a soft centrifugally moulded cylinder, which is then removed [30] Foreign Apphcanon Pnonty Data from the mould on a mandrel, longitudinally divided, July 3i, 1970 Canada 89700 and out flat to harden. The mandrel both pp the cement cylinder during removal from the mould, [52] 162/120; 162/127? 162/13]: and allows this to be rolled off the mandrel onto a re- I62/154 162/155 162/181 ceiving surface by rotating the mandrel and moving [62/230' 162/384 this transversely over the surface. Preferably, the cyl l5 Cl. l in of cement s f d a liner in [he mouldv {58] or Search 162/120 f the edges of the liner being connected together during 2 removal of the mandrel from the mould so that the 264,!08 425/84 86 liner assists in holding the cylinder on the mandrel.

The invention also covers novel cement sheets pro- [56] References Clted duced by the process UNITED STATES PATENTS Ledeboer 162/]20 7 Claims, 20 Drawing Figures nnnnnnnnnrmaanoaaoaa dannnnn nomaaoqagmpnnnnnnn FIG. IO

warwmux m5 SHEET FIG. l6

1 PROCESS FOR PRODUCING FIBROUS CEMENT SHEETS This application is a continuation in part of my United States Pat. Application 166,778 filed July 28, 1971 now abandoned.

The present invention relates to a method for producing cement sheets, particularly asbestos fibre reinforced cement sheets, which may be flat or curved or contoured. The invention makes use of apparatus more particularly described in co-pending US. Pat. Application Nos. 320,768 now US. Pat. No. 3,778,206 and 320,770, filed Jan. 3, 1973. These sheets may be used for example as structural members, wall panels, or roof sections, or may be cut to smaller sizes to form tiles, mill work or shingles.

In the so called wet process for manufacturing asbestos cement sheets, for example as described in US. Pat. No. 1856570 to Ledeboer, 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 a process which is suited to the economical production of small quantities of cement sheets, and which can readily be varied to produce different surface finishes or thicknesses in the sheets. The process can easily be modified, so that a wide variety of different cement sheets can be produced in a short time. The apparatus used for the invention does not require a large investment or take up much space, and is suitable for location close to where the building is taking place. Furthermore, the nature of the process gives a high strength product due to avoidance of excess water, uniformity of wall thickness, high density and predetermined directional resistance to stresses. Preferably, the cement is reinforced by fibres, and in this process additional strength is given by good orientation of fibres.

Specifically, the process produces a cement sheet having a mat of fibres which, although having a preferred orientation in the plane of the sheet, also extends continuously across the major part of the total thickness of the sheet. Sheets produced in accordance with the invention are thus distinguishable from sheets produced by simple moulding processes such as are described in US. Pat. No. 3,0l4,835 to Feigley et al, and US. Pat. No. 3,634,562 to Kole et al, and which have no preferred orientation of the fibres. Furthermore, the sheets of this invention are also distinguishable from sheets produced by processes in which a number of layers of material are built up for example on the surface of a cylinder, as described in the aforementioned US. Pat. No. 1,856,570, and also as described in US. Pat. No. 1,893,783 to Moeller. The sheets produced in accordance with these methods are somewhat like cardboard in that they have a number of distinct laminations each with a distinct fibre mat. In this connection, British Pat. No. 268,ll to Carnes is also of interest; this described cement sheets formed by feeding the cement mixture intermittently into a spinning cylindrical mould to form a series of layers or plies. The Carnes method would give an inferior product, since when each batch of material had been fed in this would form a layer with the light gypsum component on the inside surface of the layer, so that the final product would have layers of gypsum into which water could seep when the product is exposed, causing de-lamination.

In accordance with one aspect of the invention, a process for producing a cement sheet comprises the steps of:

a. feeding a cement mixture into a rotatable horizontal cylindrical mould,

b. spinning the mixture in the mould, distributing the mixture around the mould walls, and removing water therefrom, to form a soft, hollow cement cylinder,

c. inserting a cylindrical mandrel into the said cement cylinder to engage the inner surface of said cylinder,

d. sliding the cement cylinder from the mould without dimensional change by withdrawing the mandrel while holding the cylinder on the mandrel and supporting the inner surface of the cylinder by means of the mandrel,

e. dividing the cement cylinder longitudinally, and

f. progressively removing the cement cylinder from the mandrel as a sheet by initially placing one edge of the sheet on a receiving surface disposed beneath the mandrel and subsequently rolling the cement sheet off the mandrel by simultaneously rotating the mandrel and causing relative movement between the mandrel and the said receiving surface transverse to the mandrel axis.

The term rotatable horizontal cylindrical mould" means a cylindrical mould which is rotatable about a horizontal axis.

The term mandrel as used herein will be understood as meaning merely a cylindrical member having a diameter suitable for directly engaging the inner surface of the cylinder formed in the mould, without substantial dimensional change in the cylinder. The use of a mandrel is important for giving support to the soft cement cylinder during removal from the mould and during any slitting step.

The expression dividing the cement cylinder longitudinally" includes both slitting the cement cylinder longitudinally, while this is held on the mandrel, or alternatively merely splitting the cement cylinder along a longitudinal discontinuity previously formed in the cylinder, for example by means of an inwardly projecting member extending longitudinally of the mould. The longitudinal discontinuity may be a complete division, as will be the case where the radial dimension of the in wardly projecting member is greater than the radial thickness of the cement deposited in the mould.

The soft cement cylinder formed within the mould may have one end defined by a member movable axially of the mould, the process further including the steps of displacing the axially movable member from the one end of the cylinder prior to final positioning of the mandrel within the cylinder, and substantially expanding extracting means connected to the mandrel into the space previously occupied by the axially movable member. The extracting means are maintained in the expanded condition to prevent axial movement of the cylinder relative to the mandrel during the step of withdrawing the mandrel from the mould.

The term movable axially denotes that the member can be moved with an axial component of movement to provide a space around the whole end face of the cement cylinder; this does not however preclude the member from being pivotally mounted, as for example is the removable end plate at the other end of the mould.

The process of this invention preferably involves the use of a liner; this helps to hold the soft cement cylinder on the mandrel during its removal from the mould, and also allows an outer facing, for example an aggregate facing, to be held securely in place on the outside of the cement cylinder. The preferred process thus includes a preliminary step of inserting a cylindrically curved flexible sheet of material into the mould so that the mate rial forms a liner conforming to the mould surface and has adjacent edges extending longitudinally of the mould, and the subsequent steps of holding the edges of the liner together while withdrawing the mandrel from the mould and disconnecting the liner edges before dividing the cement cylinder longitudinally. The liner may be prevented from moving axially of the mandrel by extracting means expandible into the space between the end of the cement cylinder and the axially movable member, and which engage the end of the liner.

The use of extracting means which are expandible into the space previously occupied by an axially movable member is not however essential, since a liner similar to that disclosed herein could be provided with special means engageable by extracting means on the mandrel. For example a flange at either end of the liner, or holes or hooks at that end of the liner adjacent the end of the mould through which the cement cylinder is removed, could be engaged by extracting means carried by the mandrel; the extracting means may be hooks. Alternatively, the liner may have inwardly projecting longitudinal flanges with holes therein, which holes are engageable by hooks spaced along the mandrel. Specific apparatus of this type is shown in may copending U.S. Application No. 320,768, in FIGS. 7 to 12. in accordance with a further aspect of the invention, therefore, a process for producing a cement sheet comprises the steps of:

a. inserting a cylindrically curved flexible sheet of material into a rotatable horizontal cylindrical mould so that the material forms a liner conforming to the mould surface and has adjacent edges extending longitudinally of the mould,

b. feeding a cement mixture into said mould and spinning the mixture in the mould to form a cement cylinder having its outer surface defined by said liner,

c. inserting a cylindrical mandrel into the cement cylinder to engage the inner surface of said cylinder,

d. moving extracting means connected to the mandrel into position to engage said liner and to cause said liner to move with the mandrel when the mandrel is withdrawn,

e. sliding the cement cylinder from the mould by withdrawing said mandrel while holding said liner edges together,

f. disconnecting the adjacent edges of the liner and dividing the cement cylinder longitudinally, and laying out the resultant cement sheet on the liner.

The edges of the liner may be held together by clip means attached to the edges before the liner is inserted into the mould.

Also, it is desirable to use an expanding mandrel, described in more detail below, which is expanded into contact with the interior surface of the cylinder after insertion into the mould.

It is preferred that the step of inserting the mandrel into the mould should be performed while the mould is still spinning, since otherwise with large sizes of cement cylinders, there may be a danger of collapse of the cylinder when the mould is stopped. The mandrel may be caused to spin at the same speed as the mould before contact occurs between the mandrel and the cement surface, by use of interengaging means on the mandrel and the mould.

The centrifugal process used in accordance with the invention is particularly useful for producing laminated sheets, since a material distinct from the cement mixture may be fed into the mould at a predetermined stage in the feeding process, and tends to become evenly spread out, forming a uniform layer, and the centrifugal forces bond the successive layers strongly together. Accordingly, laminated sheets produced in accordance with the invention are characterized by layers of uniform thickness which layers are intimately and strongly bonded to each other without the need for any bonding agent. in addition, the process as described produces a product which is strong by virtue of the small amount of water used during the spinning step.

The invention preferably makes use of a cement mix which includes asbestos fibres. These fibres and other reinforcing fibres become orientated predominently parallel to the surface of the mould, and thus are predominently orientated in the plane of the finished cement sheet. In addition, depending on the speed at which the mould rotates, the fibres may become preferentially orientated circumferentially of the mould, so that in the final cement sheet the fibres have a preferred orientation in one direction. The term preferred orientation" means that a majority of the fibres are orientated at angles to one direction, that of preferred orientation, which are smaller than the angles which such fibres make with directions perpendicular to the preferred orientation.

Although the fibres will tend to be orientated in the plane of the sheet, there is sufficient deviation from this orientation that cement sheets produced in accordance with the present invention have a continuous mat of reinforcing fibres incorporated therein which will generally extend across the thickness of the sheet. It may be, however, that asbestos is fed in only during a part of the feeding process, but in any case the cement sheet will generally have a continuous mat extending across the main part of the thickness of the sheet. As explained above, it is this characteristic which distinguishes sheets made in accordance with this invention from sheets made by the so-called wet process" having separate laminations. The product given by the process of this invention has a modulus of rupture in bending of 5,500 pounds per square inch, as compared with about 4,500 pounds per square inch for products made by the above-mentioned wet process," and a molulus of rupture in bending of at least 5,000 pounds per square inch can be expected.

The different materials which go to form the laminated sheet may be cements of difi'erent compositions, or different colours; or one of the layers may be formed of a particulate material which becomes bonded to the cement layer. In this manner, cement sheets having surfaces of exposed particles, for example of aggregate material or glass, metal, or plastics materials, may be produced. ln the case of these products, as well as the sheets having different cement laminations, the layers are intimately bonded together; i.e. held together by the cement of the layers themselves rather than by bonding agents which are otherwise used to bond particles onto cement sheets.

The process 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 cylinder and mandrel in place, caused 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. I4 is a cross section on lines l414 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. I6 is a cross-sectional view of the modified mandrel on lines 16-46 of FIG 15,

FIG. 17 is a partly sectioned view of the mould of FIG. 13 with the modified mandrel in place, and

FIGS. 18a, 18b and 18c illustrate modified apparatus for slitting, laying out and curing the cement sheets.

Referring to FIGS. 1 and 2, the apparatus includes a rotatable centrifugal mould indicated generally at I0. The mould has a cylindrical wall 12, which is of sheet metal and is perforated with l/l6 inch diameter holes I2a spaced apart on one 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 ofa 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 I7, 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 2la 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. I 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 provide a cover over a 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. I, 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 360 spaced along the pipe 36 at 1 foot spacing. Below the lower ends of pipes 360 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 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 corner 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 carried 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 of 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 man drel 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 42a projecting axially therefrom.

The mandrel wall 40a is pierced by longitudinal rows of 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 S, 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. and 6 show valve means 47 which allow one end of each channel 44 to be individually placed in communication selec tively 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 S0 and 51 and elbow connectors respectively to

flexible hoses

52 and 53. The

hoses

52 and 53 serve to connect the

header tubes

48 and 49 to sources of vacuum and pressurized air respectively, while allowing for rotation of the mandrel by at least one revolution.

The valve means 47, one of which is provided for each of the channels 44, comprises a valve body 55 in the form ofa rectangular block having its inner surface supported by the

header tubes

48, 49 and having its outer surface fixed to a channel member 45. The valve body has two radial bores 57 and 58 leading respectively from

header tubes

48 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 S8 and the valve member prevents flow of air through either bore By pulling out an extension 61 ofthe valve member, the recessed portion 60 is brought into registry with the bore 57, so that the channel 44 is put into communica tion with the source of vacuum through header 48 and hose 52', and when the valve member is pushed inwardly to bring recess portion 60 into register with bore 58 then the channel 44 is placed in communication 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 members as it rotates relative to the mandrel to 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 indicated at 70. it will be seen that the mandrel is an easy clearance fit within the cement cylinder, and that the end of the mandrel fits within the reinforcing ring 14.

The apparatus also includes mounting means for the mandrel which may be in the form of known handling means such as a small factory crane or hoist, and which supports the mandrel by its

axial shafts

42 and 42a. The mounting means must allow axial movement of the mandrel into the mould, and must also allow rotation of the mandrel 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 mandrel 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 for receiving a cement sheet removed from the mandrel, and which is then removable to another location where the cement sheet hardens. The receiving surface 72 may be a plan 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 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.

The charging head 23 is firstly advanced into the mould on rails 24a, to the position of FIG I, 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 including reinforcing fibres 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 water) and rotation of the cylinder at a peripheral speed of 1200 ft/min. for about five minutes caused 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% water is in contrast to other methods where more than 90% excess water is required.

The de-watering stage is reached after the material has spun sufficiently to compact the solids into cylindrical 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 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 de-watering, the spreader means 86 is brought into contact with the ce' ment 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 73 so that this slits the cylinder longitudinally. The mandrel carrying the cement cylinder is then rolled along, ie., 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 (eg. channels 44a and 44b of FIG. 8) to be connected to a source of positive air pres sure 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 hav ing a relief design, the cement sheet being pressed onto the platen by the mandrel to reproduce the design.

It may be noted that the mandrel not 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.

Where the reinforcing fibres are to be asbestos fibres, the cement mix is produced by opening asbestos of desired grade to separate the fibres and mixing these fibres with Portland cement, and if desired, silica sand flour. Water is added to give a mixture which is approx imately 30% solids and 70% water. The mixing is thor ough so that the maximum number of fibres are coated with cement and water. When this mixture is fed into the rotating mould, the asbestos fibres tend to be laid more or less fiat, i.e. substantially parallel to the cylindrical surface of the mould, giving a laminated cement sheet which has greater strength than one in which the fibres are randomly oriented. As explained, the fibres form a mat which extends across the whole thickness of the cement sheet, apart from any particulate or special surface. Furthermore, the fibres also have a tendency to become orientated in the circumferential direction of the mould and thus give a cement sheet in which the fibres have a preferred orientation in this direction. Such cement sheets have enhanced properties in this direction, making it possible to design sheets which have strength properties suited for particular purposes. The circumferential orientation of the fibres can be varied somewhat by varying the speed of rotation of the mould. For example, spinning at a peripheral speed of l200 ft. per minute is suitable where it is merely required that the fibres be parallel to the surface. Faster spinning will tend to orientate the fibres circumferentially; for example at 2000 ft. per minute more than half the fibres would be orientated substantially circumferentially.

Clearly, any of the cement sheets made according to the processes described can be cut to desired forms, to give tiles or other products. If necessary, cutting can be carried out before the cement hardens.

laminated cement sheets may be produced in accordance with the invention by feeding a second material, distinct from the cement mixture, into the mould at a predetermined stage in the feeding process. The manner in which different materials are fed into the mould will vary widely according to the desired laminating effects. The material used may all be cement mixes, but of varying compositions or colours. For example, in one process, a fine coloured cement mix is first fed into the rotating mould, and the mould is spun until this cement mix has formed a layer of uniform thickness on the interior of the mould. Next, a coarser concrete mix is fed in while the mould continues to spin to form a further cylindrical layer within the layer of coloured cement, the concrete layer being thicker than the coloured cement layer. The process then proceeds through the spinning and de-watering stages as described above, and the cement cylinder is then removed from the mould, slit, and laid out in the form of Y a cement sheet. The cement sheet so formed is laminated, having an outer facing layer of fine, coloured, cement, and a thick supporting layer of concrete.

In another process in accordance with the invention, the material first fed into the mould is a particulate ma terial mixed with cement and water or any suitable bonding agent. The particulate material may be particles of stone having an average size between /2 inch and 1/64 inch, 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 cylindrical layer within the mould. 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. This process produces a product having a first layer with a continuous mat of fibres, as described above, and a second layer including a matrix of cement which is integral with the cement of the first layer and in which is embedded the particulate material. One surface of the cement sheet may then be polished to provide a flat surface in which the particulate material is exposed.

Alternatively the particulate material may be exposed, as in the so-called exposed aggregate surface, by removal of material surrounding the particles. In this case, a chemical retardant may be applied to the surface of the cement sheet on which the particulate material is concentrated. This can be done by applying the retardant to the pallet on which the cement sheet is laid out. After the main part of the cement sheet has hard ened, the layer having the retardant is still soft, so that the cement in this layer can be brushed away to expose the particulate material. Suitable chemical retardants for this purpose, which retard the setting of cement, are well known in the art. A cement sheet may be produced by this process which the surface particles are in intimate contact with the cement, i.e. are held onto this without the use of any bonding agent, which may deteriorate with agev 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 aggregate 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 the cement cylinder becomes bonded to the liner. The bond can be strengthened by chemical bonding with a vinyl acetate bonding agent such as the aforementioned Albitol, 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 form the longitudinal division in the cement cylin' der as particularly described in co-pending Pat. Application No. 320,768. 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.

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% benzoyl peroxide added to the monomer as a catalyst. 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. 1 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.

The apparatus of FIGS. 13 and i4 is similar to that previously described in having a rotatable mould with a cylindrical wall 112 held by rings I15 resting on roolers 116 mounted on shafts 117 driven by a motor and gearbox combination I19. Unlike in the first embodiment, however, the mould wall 112 is not perforated. The dimensions ofthe mould are about 10 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 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 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 18] 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 /2inch to 1 inch thickness sufficiently flexible to form a cylinder lining the mould as shown. One edge portion of the liner is preferably thickened to provide an inwardly projecting lip surrounding that end of the liner adjacent the void ring 121. The liner has opposite edge portions which are adjacent while the liner is in the mould, the edge portion 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. These recesses are engageable by the inwardly directed jaws ofa 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 polytetrafluoroethylene.

The modified mandrel 140 used with this mould is an expanding mandrel as shown in FIGS. 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 44, 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 159 are welded to the inside of plate 141 at locations 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 to l20 of arc subtended at the axis of shaft 144. The two crank members 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 to an air space within the hollow shaft 144. The space within the shaft 144 is closed apart from the conduit 162 and a quick connector coupling by means of which a charge of compressed gas can be admitted into this space. The valve 163 is biased into a shut position, but is arranged to be opened by rotary movement which occurs when the valve arm 163a, extending radially from the inside end of the mandrel, is pivoted sideways by contact with an arm 164 which rotates with the mould. Admission of pressurized air into cylinder 161 is arranged to cause extension of this cylinder, with consequent outwards movement of members 155 and expansion of the plate 141 into the broken line position. The pivotal movement of valve arm 163a is limited so that after the valve 163 has been opened by arm 164 of the mould these arms continue to engage with each other causing rotation of the mandrel with the mould. The

arms

163a and 164 are so situated on the mandrel and mould respectively as to cause the mandrel to be rotated with the mould in such position that the adjacent longitudinal edges of the plate 141 forming the mandrel surface are disposed adjacent the junction in the liner (see FlG. 18b), so that after expansion of the mandrel a gap is provided in the cylindrical surface of the mandrel which gap underlies that between the flanges 172 of the liner.

The outer end of the mandrel is provided with a protruding spring loaded plunger 166, positioned to engage the void ring 121 so that this void ring is pushed away from a cement cylinder formed in the mould on positioning of the mandrel in this cylinder.

in operation, liner 170 is bent into the form of a cylinder, and its edges are connected together by clip 175, before the liner is fitted into the mould as shown in FIG. 14. The end plate 122 is then placed in the closed position, and the void ring 121 placed in the inner position shown in FIG. 13. With the shutter 38 of the charging head 123 held closed by cylinder 81, the trough formed by this shutter is filled with aggregate material. The charging head 123 is then advanced into the mould on rails 24a, to the position of FIG. 13. 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, thus dumping the aggregate material which distributes itself within the mould. A cement mix is then fed onto the liner surface via the

pipes

36 and 36a, and simulta neously the cylinder 84 is operated to raise the spreader means 86 gradually as feeding proceeds. 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 70% 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 149 of uniform wall thickness on the inside of the liner. within an outer layer of aggregate. The void ring 121 defines the end of the cylinder 149 of cement remote from plate 122. The centrifugal effect also concentrates and compacts the solid particles of the mix in the outer parts of the cement layer, and excess water is forced to the center of the mould and flows out of this during a dewatering stage.

The de-watering stage is reached after the material has spun sufficiently to compact the solids into cylindrical form and to form an inner layer of excess water. This takes about l 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.

Once a hollow cement cylinder has been formed, and the dewatering and compacting steps have also been performed as described for the first embodiment, the end plate 122 is lifted clear (as in FIG. 17), the space within the shaft 144 is charged with compressed air, and the mandrel 140 is inserted into the cylinder, while the cylindrical mandrel surface formed by plate 141 is in its relaxed, contracted state, and while the mould is still spinning, so that the cement cylinder is maintained in contact with the liner. Before insertion, the mandrel is preferably caused to spin at a speed slightly less than that of the mould.

Prior to final positioning of the mandrel as shown in FIG, 17, the plunger 166 pushes the void ring 121 away from the end of the cement cylinder 170, to the position shown in FIG. 17. In the latter stages of this movement, the flange 142 passes beyond the end of the cement, allowing expansion of the mandrel to occur. In this latter stage also, the valve arm 163a of the nonrotating mandrel strikes the arm 164 of the rotating mould, causing the mandrel to rotate at the same speed as the mould, and also opening the valve 163 to allow pressurized air to pass via conduits 162 from the interior of shaft 144 to air cylinder 161. Air cylinder 161 then expands, causing expansion of the outer surface of the mandrel into contact with the interior of the cement cylinder 149, with consequent expansion of the flange 142 into the space between the end of the cement cylinder and the void ring 121. Rotation of the mould is then stopped, the parts being then positioned as shown in FIG. 17. The carriage 148 is then withdrawn, carrying the mandrel which in turn causes the cement cylinder 149 together with liner 170 to be slid (without dimensional change) from the mould. During this movement, flange 142 is maintained in the expanded condition and acts as extracting means engaging the thickened end of the liner and preventing the cement cylinder and liner from sliding off the mandrel, and the clip 175 holds the liner edges together.

FIGS. 18a and 18b show further means for slitting the cylinders and laying out the resultant sheets, particularly for use in connection with the apparatus of FIGS. 13 to 17. As shown, a series of similar pallets 185 is provided, each having a lug 186 extending along one edge and adapted to engage in the recesses of edge pieces 171 of the liners. As shown in FIG. 18b just outside the lug 186 and parallel thereto is situated one strand 187 of a wire band saw, which saw is vertically movable relative to the pallet.

At each side of the pallets 185 is situated a vertical wall 189, having a horizontal tapered upper edge suitably spaced to engage an annular recess in the support shafts 144, of the appropriate end of mandrel 140, as shown in FIG. 18a. The walls 189 are adjustable in height by raising means indicated at 190. When raised to their full height, the walls 189 are capable of forming a steam curing chamber when combined with the parts shown in FIG. 18c. These parts comprise a top 191 suit abie for covering the space between walls 189, and hinged end pieces 192 sized to close the ends of the chamber.

In operation of the apparatus shown in FIG. 18, a first pallet 185 is laid between the walls 189 while the walls are in a lowered position, After a cement cylinder has been removed from the mould on the mandrel 140, the mandrel is positioned directly above the band saw 187, with its

support shafts

144, 145 supported at one end of walls 189, and with the gap in the mandrel surface and the liner edge portions positioned as shown in FIG. 18b. The clip is removed from the liner, and one edge portion only of the liner is then re-attached to the mandrel by two U-clips shown at I94, which have opposed flanges engaging the inside of the mandrel and the outside of the edge piece 171, one clip being used at each end of the mandrei. The other edge portion 171 is engaged by lug 186 as shown in FIG. 18b. The wire band saw 187 is then operated and moved vertically to cut through the cement cylinder, the saw passing be tween the liner edge portions, by deflecting the edge portions where they abut, and also pasing through the gap between the longitudinal edges of plate 141. The cylinder and liner are then rolled out flat on the pallet I85, with one end of the liner remaining attached to the pallet and the other end remaining clipped to the mandrel until unrolled. During this unrolling operation, the mandrel support shafts 144 and 14S roll and slide along the top edges of walls 189, the movement of the mandrel being such as to stretch and roll the sheet of cemerit,

After a first sheet of cement has been laid out as described, a further pallet 1850 is laid thereon, and the next sheet is laid on this further pallet, this operation being repeated until a stack of pallets interposed with sheets of cement and liners of produced. As successive sheets of cement and pallets are laid down, the walls 189 are raised simultaneously by raising means 190, so as to remain at the same height as each other and so as to continue to support the mandrel during each unrolling operationv After a stack of about twenty cement sheets have been laid out in this manner, and with the walls 189 raised to their maximum height, a curing chamber is formed by arranging on these walls the top 191 and end pieces 192 as shown in FIG. 186, The stack of cement sheets is then steam cured to harden them, after which the sheets are removed and the pallets and liners recovered for re-use. It may be noted that, unlike in the first embodiment, the sheets are cured and hardened without being moved from the position in which they are laid out.

The liners may be re-used by being bent up around a suitable mandrel, and cleaned on their external surfaces before being inserted into the mould. After inser

Claims

1. A PROCESS FOR PRODUCING A FIBREINFORCED CEMENT SHEET COMPRISING THE STEPS OF: A. FEEDING A CEMENT MIXTURE TOGETHER WITH REINFORCEING FIBERS INTO A ROTATABLE HORIZONTAL MOULD, B. SPINNING THE MIXTURE IN THE MOULD, DISTRIBUTING THE MIXTURE AROUND THE MOULD WALLS, AND REMOVING WATER THEREFROM, TO FORM A SOFT, HOLLOW CYLINDER, C. INSERTING A CYLINDRICAL MANDREL INTO THE SAID CEMENT CYLINDER TO ENGAGE THE INNER SURFACE OF SAID CYLINDER, D. SLIDING THE CEMENT CYLINDER FROM THE MOULD WITHOUT DIMENSIONAL CHANGE BY WITHDRAWING SAID MANDREL WHILE HOLDING SAID CYLINDER ON THE MANDREL AND SUPPORTING THE INNER SURFACE OF THE SOFT CEMENT CYLINDER BY MEANS OF SAID MANDREL, E. DIVIDING SAID CEMENT CYLINDER LONGITUDINALLY, AND F. PROGRESSIVELY REMOVING THE CEMENT CYLINDER FROM THE MANDREL AS A SHEET BY INITIALLY PLACING ONE EDGE OF THE SHEET ON A RECEIVING SURFACE DISPOSED BENEATH SHEET FROM DREL AND SUBSEQUENTLY UNROLLING THE CEMENT SHEET FROM THE MANDREL BY SIMULTANEOUSLY ROTATING THE MANDREL AND CAUSING RELATIVE MOVEMENT BETWEEN TH MANDREL AND THE SAID RECEIVING SURFACE TRANSVERSE TO THE MANDREL AXIS.

2. A process according to claim 1, further including the steps of applying a vacuum to ports in the cylindrical surface of the mandrel after the mandrel has been inserted into the cylinder to cause the cylinder to cling to the surface of the mandrel, and releasing said vacuum prior to or during the step of removing the cement cylinder from the mandrel.

3. A process according to claim 1, further comprising the initial step of inserting a cylindrically curved flexible sheet of material into the mould so that the material forms a liner conforming to the mould surface and has adjacent edges extending longitudinally of the mould, said liner defining the outer surface of said cement cylinder subsequently formed in the mould, and wherein said step of holding said cylinder on the mandrel is performed by moving extracting means connected to said mandrel into position to engage the liner and to cause the liner to move with the mandrel when the mandrel is withdrawn, the said adjacent edges of the liner being connected together during the step of withdrawing the mandrel from the mould and being disconnected prior to dividing the cement cylinder longitudinally.

4. A process according to claim 1, wherein said step of dividing the cement cylinder longitudinally is performed by longitudinally slitting the cement cylinder while it is supported by the mandrel outside the mould.

5. A process according to claim 1, wherein said cement cylinder is formed in the mould with a longitudinal discontinuity caused by an inwardly projecting member extending longitudinally of the mould, and wherein the step of dividing the cement cylinder longitudinally involves splitting the cement cylinder along said discontinuity.

6. A process according to claim 1, wherein said fibres includes asbestos fibres.

7. A process according to claim 3, wherein, prior to feeding said cement mixture into the mould, particles of stone having an average size of between 1/2 inch and 1/64 inch are distributed in the mould to form a cylinder of said particles within the liner, said cement mixture being subsequently fed into the mould and distributed within the mould to form a cement cylinder within said cylinder of particles and adhering thereto.