US 3770859 A
Description (OCR text may contain errors)
Nov. 6, 1973 c. G. BEVAN BUILDING MATERIALS 2 Sheets-Sheet l Filed June 29, 1971 INVENTOR E HRISTUPHER GRAHAM BEVAN Nov. 5, 1973 BEVAN 3.770359 BUILDING MATERIALS Filed June 29, 1971 2 Sheets-Sheet 2 INVENTOR CHRISTOPHER GRAHAM BEVAH United States Patent 3,770,859 BUILDING MATERIALS Christopher Graham Bevan, London, England, assignor to C. G. Bevan Associates Limited, London, England Filed June 29, 1971, Ser. No. 158,030 Claims priority, application Great Britain, July 7, 1970, 32,917/70; Nov. 2, 1970, 52,031/70 Int. Cl. 'B28b 1/08, N52
US. Cl. 264--71 18 Claims ABSTRACT OF THE DISCLOSURE This invention relates to the manufacture of building products, particularly panels such as wall panels or partition panels from a basic constituent comprising a liquid setting powder and a fibrous support constituent, the panels being of the type having at least one bore extending through the panel core from one edge of the panel to the opposite edge. The invention is primarily concerned with the manufacture of fibre reinforced partition panels .for the building industry, for example glass fibre reinforced gypsum panels but the invention may also be used for most liquid setting powders mixed with fibrous materials and may also include aggregate materials as fillers.
Existing methods of making fibre reinforced panels are based on the conventional concept of mixing liquid and powder before or during a fibre mixing stage and generally introducing a wet mixture of constituents into suitable moulds or formers to make the product. 'In this method, the fibres tend to act as a thickening agent and normally more liquid is required than is necessary for the chemical reaction which sets the powder, in order to reduce the viscosity to workable proportions. As a result, weak products may result or an additional process may be required to extract the excess liquid such as by pressing between filter papers. Where bored or hollow core panels are required, it is difiicult to exert sufiicient pressure to the material between closely spaced core formers; extrusion methods can overcome this difiiculty but adequate flow properties for extrusion can only be achieved with short fibres, resulting in brittle products. High viscosities of the mix also make it diflicult to control fibre orientation for optimum economy and with conventional methods using gypsum, residual material left in a mould from a previous operation tends to lead to flash setting when the next wet powder mixture is introduced. Hence retarding agents are normally incorporated in the mix which slow down the setting time and entire production cycle.
The present invention provides a method of producing a building product from a liquid setting powder constituent and a fibrous constituent, the product having at least one bore extending therethrough, the method comprising mixing the powder and fibrous constituents in a substantially dry state, forming the resultant substantially dry mixture into a required product shape incorporating said at least one bore and allowing liquid for setting the powder to seep through the mixture whilst supporting outer surfaces thereof and leaving inner sur- 3,770,859 Patented Nov. 6, 1973 face means thereof defining said at least one bore exposed to the liquid to provide flow path means for the liquid through the mixture, said fibrous constituent having a binding effect on the powder constituent to minimize erosion of the powder constituent at said inner surface means and collapse thereof into said at least one bore during liquid seepage.
The invention is particularly useful in the manufacture of hollow cored panels of the type comprising a pair of outer face layers interconnected by spaced webs defining bores therebetween and reinforced by long fibres orientated substantially along the panel length. The webs in such panels lying substantially at righ angles to the direction of fibre orientation, help to prevent longitudinal splitting of the panels when, for reasons of economy, highly unidirectional fibre orientation may be required. Using a method according to the invention, it has been found possible to produce lightweight panels of high strength with wall and web thicknesses to under a quarter of an inch.
Conveniently, the invention is carried into effect by introducing the constituents in a substantially dry state into a mould incorporating one or more formers for producing the or each bore, compacting the mixture before, during or after introduction to the mould (generally by vibration) removing the bore formers, and then gradually immersing the mould in liquid or otherwise allowing liquid to seep through the mould. After a suitable immersion time, the mould is removed from the liquid and the resultant product removed from the mould in a conventional manner.
The process according to the invention minimizes the usual difiiculties of fibre bunching when wet mixing and substantially eliminates the need for extracting excess liquid as when wet mixing methods are used. The process also eliminates the need to include retarding agents in the mixture to prevent premature setting during the mixing and mould filling when for example gypsum is the powder constituent, and production speed and mould utilization can therefore be substantially improved, it even being possible to include cure accelerating agents in the liquid to achieve a rapid or even near instantaneous or flash set of the material.
Fibre orientation is achieved readily by adjusting the feed rate of the powder fibre mix so that the leading part of each fibre is arrested by the already compacted surface of material in the mould and (with the absence of surface tension forces normally occurring in wet mixes) the trailing part is free to continue'to fall and slip each fibre into the approximate horizontal position leading to fibre orientation lengthwise of the panel.
Typical raw materials for use in the process are:
Liquid setting powders-plasters, gypsum, anhydrite, portland cement and high alumina cement.
Fibrous materialsglass, asbestos, sisal, ene, wood fibre (usually 1% to 5% ture).
Filler materials-pulverized fuel ash, crushed stone, ex panded clay aggregates, Perlite.
Setting liquids-usually-water containing additives such as wetting agents to accelerate seepage, additives to accelerate the cure of the powder such as potassium sulphate for gypsum or synthetic resins or other materials to improve the panel properties.
The invention will now be further explained by way of example with reference to the accompanying drawings in which:
FIG. 1a is a perspective view of a panel made by a process according to the invention;
FIG. 1b is an enlarged perspective view of one end of the panel shown in FIG. 1a, and
polypropyl- FIG. 2 is a diagrammatic view of a plant for producing fibre reinforced panels of the type shown in FIG. 1.
FIG. 1 shows a completed building panel having a pair of opposed planar surface layers a connected by integrally formed webs b, the webs defining therebetween bores extending from one edge of the panel d to its opposite edge e. Typical fibre orientation is shown by arrows g.
In FIG. 2, which shows a plant for producing panels as shown in FIG. 1, moulds 6 are circulated through a filling and compacting station where they receive a mixture of dry powder and fibre material which is compacted in the mould around bore formers 7, supported at their upper ends by a fixed support element 8, the moulds then gradually being lowered into a tank 11 containing liquid setting agent which seeps upwardly through the dry mixture in a mould, the mould after immersion and setting of the material within the tank being upwardly withdrawn and the resultant panel being removed so that the then empty moulds can be recirculated to the filling and compacting station.
At the filling and compacting station powder from a metering and feeding device 1 which may be of any form, for example a screw, a rotary valve, or a pneumatic device such as a vibrofiuidization feeder to the type disclosed in our copending United Kingdom patent application No. 3,979/ 70 is passed through a distributing chamber 2 which may include a sieve or baffies and hence showered through a fibre/mixing chamber where it is mixed with fibres received from conventional fibre feed devices such as fibre cutters 3 which may be in the form of rotating knives cutting controlled lengths of fibre from reels 4. Showering the powder and fibre through air in the mixing chamber 5 prevents the constituents from clogging (particularly with glass fibre). Components 5 and 8 normally vibrate with a mould mixing station and a base 9, and components 1, 3 and 4 may reciprocate horizontally along the length of the mould to fill same or alternatively a series of stationary feeders 1 and cutters 3 may be provided along the length of the mould.
The moulds each have a perforated base to accommodate the bore formers 7 and the mould at the filling station is clamped below a chamber 5 to a vibrating table 9 so that as the mixture enters the mould it is compacted by vibration. The bore formers 7 are withdrawable from the mould from below into a vibrating table 9, these being withdrawn when a mould is filled. Vibration is continued throughout the filling operation of the mould and it is stopped when the mould is filled. Then the bore formers are withdrawn and the next mould in line is clamped to the table 9.
A filled mould proceeds on rails downwardly into the tank 11 so that liquid in the tank which may be water (generally warm water to accelerate the cure) seeps upwardly through the compacted mixture within the mould, the bores providing fiow paths facilitating the passage of liquid through the mixture. The rate of immersion may for example be above 1 to 3 inches per minute for a typical coarse plaster mix dependent on the particle size and degree of compaction. When the mould is fully immersed in the tank it is retained therein for about minutes for setting and the mould is then lifted up through the liquid on rails, the completed panel is removed from the mould by opening the latter and the mould after cleaning is then returned to the filling station. Generally, after removal from the mould, the rough top surface of the panel will be trimmed level by conventional means. During liquid seepage, the outer surfaces of the panel are supported by the mould walls but the surfaces surrounding each bore are unsupported so that the bores provide passages for the upward seepage of liquid through the mixture. The interlocking effect of the fibres on the powder substantially prevents erosion of the powder at these unsupported walls and collapse of the powder constituent into the bores.
When glass and the like fibres are used in a system as described above, these tend to be received from the cutters 3 in relatively thick fibrous strands or bundles containing a number of fibre filaments. While such bundles of fibre or strands, when used in lengths of say 1" to 2", provide extremely effective reinforcement for the finished product, they are not as effective as well distributed very fine short fibres in substantially eliminating the erosion of the exposed bore surfaces during seepage.
Hence, in place of or in addition to mixing the powder with relatively long thick fibres as described above it is also useful to intimately premix the powder with shorter and very much finer or thinner fibres so that these become intimately and evenly distributed throughout the volume of powder. When such fine fibres are used in conjunction with the longer strands mentioned earlier, it has been found that only very small amounts of fine fibre are required to achieve a very marked stabilizing effect during liquid seepage and that these small inclusions of fine fibers have almost no practical effect on the dry flow characteristics of the powder.
With glass and like fibres reduction of the bundles length and separation of the filaments to obtain short fine fibres can be achieved by subjecting a fibre powder mixture in a mixing chamber to the action of a high speed cutter impeller. This operation also achieves the required intimate distribution of the fibres throughout the fibre volume and is carried out before the powder is introduced to the apparatus shown in FIG. 2.
The interlocking elfect achieved on the powder particles by the intimate distribution of short fine fibres throughout the powder volume improves the resistance of the mixture to erosion at the exposed bore surfaces during liquid seepage and accordingly allows the production of thin walled products (down to a wall thickness of under a quarter of an inch).
'We have found that by including the short fine fibres in a proportion of about 0.1% to 0.2% by weight of the powder it is possible almost entirely to eliminate erosion of powder at the exposed surfaces during water seepage provided that the fibres are thoroughly mixed and intimately distributed through the mixture and the powder is not too coarse grained. For glass fibres bundles containing about 200 individual fibre of 0.3 to O.l l0 in diameter strands are beat up with the powder by a high speed cutter impeller for about 1 minute to split the bundles, reduce the fibre length to an average of about an A2 of an inch, and thoroughly to disperse the short thin fibres throughout the powder. It is also possible to use fine asbestos or sawdust fibres for this purpose. Generally, after such processing, the powder grain size is also reduced and the bulk of the mixture will pass through a No. 40 British Standard Sieve. It has been found that if the powder particles are predominantly too coarse to pass a British Standard 40 Sieve, there will generally be more seepage erosion.
It is also possible to include long strings of reinforcing fibre in the mixture such fibre being obtained for example from a continuous unwinding device.
In particular it has been found that the powder itself can have a similar stabilizing effect as inclusions of short fibre if the shape of the powder particles or crystals is approximately oblong as opposed to cubic or spheroidal. With a length to breadth ratio of roughly 2:1 for powder crystals, it has been found that fine fibre inclusions may be omitted provided the long strands are present.
Numerous modifications are possible within the scope of the invention. For example, for mould filling, the moulds may 'be moved under a static filling head instead of moving the filling head over a static mould as disclosed above. In the case of moulds for making pipes instead of panels, these would be rotated under the filling head whilst in the case of panel moulds these would be reciprocated under the filling head.
The process is particularly suitable for use with a powder comprising a mixture of calcium sulphate (gypsum) ground or mixed with high alumina cement in the ratio for example of about 20 to 25% by weight of calcium sulphate, 75 to 80% by weight of high alumina cement.
Filling and compaction of the moulds may be by vibrofiuidization methods as discussed in the above copending application whereby the compaction takes place above the mould rather than in the mould and the mould itself need not be vibrated. In such cases the fibre orientation will be considerably reduced and the method is useful where a more random orientation is required.
Liquid seepage through the moulds can be effected by allowing the liquid to rise in a tank containing the moulds and then draining away excess liquid after setting. Alternatively the moulds themselves can form the tank and the liquid can be allowed to rise within each mould or in batteries of moulds.
Any suitable bore formers can be used such as bottom or top withdrawing formers and any cross-section is suitable provided only that there is sufiicient powder and fibre material around the bores to prevent collapse of the powder during liquid seepage. Any suitable form of vibration may be used during compaction of the drying material in the moulds to ensure flow in the upper sections of the filling apparatus. The various sections may vibrate separately and at different fequencies or they may vibrate in unison. Amplitudes of of an inch and frequencies of 3,000 cycles per minute have been found satisfactory but the vibrations may have frequencies up into the ultrasonic range depending on the type of powder fibre mix. Waveforms may be sinusoidal or any other configuration.
The rate of immersion times within the liquid will depend on the powder particle size, the fibre characteristics and the wall thickness, generally from 1 to 3 inches per minute for panels with A" thick walls. Course particles, e.g. commercial grade course plaster can be soaked more rapidly than fine powders without the risk of air pockets forming causing surface blemishes. Fillers and aggregates may be added and mixed to the constituents at any stage prior to entry to the mould and alternative distribution methods may be used.
EXAMPLE I A panel of the type shown in FIG. 1 was produced in apparatus as shown in FIG. 2 using a powder constituent comprising gypsum plaster, i.e. plaster of paris without set retarding agents, in fine plaster form and was premixed in a dry state by a cutter impeller or fluidizer mixer with 0.1% by weight of glass fibre strands chopped to quarter inch lengths. After treatment in the cutter impeller for two minutes the quarter inch fibre strands be came split into their constituent hair-like individual fibres ranging in length up to a quarter inch. The resultant powder constituent was fed into the feeder device 2 and mixed in chamber 5 with relatively long fibre strands chopped by the knives 4 to lengths of about 1 /2 inches. The resultant mixture was showered into a mould 6 and compacted therein by vibration. The bore formers 7 were then removed and the mould was immersed in a warm liquid bath with a speed of immersion of about 1 inch per minute. minutes after complete immersion within the bath, the mould was immediately removed and the resultant panel demoulded. The size of the panels were 2 feet in height, 8 feet in length and 1% inches wide with wall thickness and web thicknesses of a inch. Temperature of the water was 50 C.
EXAMPLE II The above process was repeated with a powdered constituent being a mixture of 60% by weight of high alumina cement, 30% by weight of gypsum as in Example I, and 10% by weight of fine Perlite. The process as set out in Example I was repeated except that an extra 15 minutes immersion time was allowed.
In processes according to the invention, it has been found that the resultant panels have relatively long fibres distributed substantially along the planes of the outer faces and webs as shown at f in FIG. 1b and this gives the required reinforcement to the powder constituent in the finished product.
What is claimed is: 1. A method of producing a building product from a liquid setting powder constituent and a fibrous constituent, the product having at least one bore extending therethrough, the method comprising mixing the powder and fibrous support constituents in a substantially dry state,
forming the resultant substantially dry mixture into a required product shape incorporating said at least one bore, and
allowing liquid for setting the powder to seep through the shaped mixture whilst supporting the outer surfaces thereof and leaving the inner surfaces thereof defining said at least one bore unsupported by extraneous support means whereby said inner surfaces are free and exposed to said liquid to provide a flow path for the liquid through the mixture, said fibrous constituent being present in sufiicient amount to have a binding effect on the powder Constituent to minimize erosion of the powder constituent at said inner surfaces and to minimize collapse thereof into said at least one bore during liquid seepage.
2. A method as claimed in claim 1 wherein said substantially dry mixture is formed into said required shape in a mould incorporating bore forming means said bore forming means being withdrawn before liquid seepage.
3. A method as claimed in claim 1 wherein said substantially dry mixture is compacted during its formation into said required shape.
4. A method as claimed in claim 3 wherein compaction of said substantially dry mixture is effected by vibration.
5. A method as claimed in claim 4 wherein the rate of feed of the dry mixture is such that oncoming mixture feeds onto a substantially compacted mixture surface to substantially unidirectionally orientate relatively long fibre strands contained in the fibrous constituent.
6. A method as claimed in claim 1 wherein liquid seepage is effected by immersion of said shaped mixture in liquid.
7. A method as claimed in claim 1 wherein said fibrous constituent comprises relatively long reenforcing fibres distributed through said powder constituent.
8. A method as claimed in claim 7 wherein said fibrous constituent further comprises relatively short fine fibres substantially evenly distributed through said powder constituent.
9. A method as claimed in claim 8 wherein said relatively short fine fibres are hair-like fibres having a length up to 4 inch.
10. A method as claimed in claim 9 wherein said mixture contains about 0.1% to 0.2% by Weight of said relatively short fine fibres.
11. A method as claimed in claim 1 wherein at least a part of said fibrous constituent is mixed with said powder constituent by beating up said at least part of said fibrous constituent with said powder constituent.
12. A method as claimed in claim 1 wherein the powder contains elongate powder particles.
13. A method as claimed in claim 1 wherein at least a part of said fibrous constituent is mixed with said powder constituent by showering said constituents through a mixing chamber.
14. A method as claimed in claim 1 wherein a set accelerating agent is included in the liquid.
15. A method as claimed in claim 1 wherein cure of the powder is accelerated by using warm water as the seepage liquid.
16. A method as claimed in claim 1 wherein an aggregate material is included in said mixture as a filler.
17. A method as claimed in claim 1 wherein said product is a building panel comprising a pair of spaced outer layers interconnected by a series of webs defining bores therebetween extending from one edge to the opposite edge of the panel.
18. A method as claimed in claim 17 wherein the fibres are oriented along the length of said outer layers at right angles to the direction of extent of the Webs.
References Cited UNITED STATES PATENTS Stockwell 26471 Clark 264-Dig. 43 Ross 264Dig. 43 Jaques 264-333 Halnicke 264-Dig. 43 Webb et a1 264-Dig. 43 Tarlton 264333 Warden 264Dig. 43
ROBERT F. WHITE, Primary Examiner J. R. THURLOW, Assistant Examiner US. Cl. X.R.
264-108, 122, 154, 256, 333, Big 43