Abstract: This invention relates to a process for making gypsum board comprising feeding a paper backing sheet and a fiberglass or plastic woven or non-woven scrim material in alignment to a board forming station, separating the paper and the scrim, feeding a high density calcium sulfate hemihydrate slurry into the trough formed between the paper and the scrim, and subsequently compressing the paper and the scrim into contact whereby the high density slurry is forced through the scrim, completely encapsulating the scrim in the high density slurry. As a result of this unique process, excellent bond is developed between the paper, the high density gypsum layer and the foamed gypsum core. The gypsum board has improved through-penetration strength.

Abstract: An acoustical ceiling tile having an improved sound absorption value and having a dual layer of acoustical materials. The base mat layer has either no mineral wool or a low mineral wool content. The surface layer has a high mineral wool content which provides improved sound absorption values with or without perforating or fissuring the tile. The dual layer acoustical ceiling tile has a noise reduction coefficient (NRC) value of at least about 0.50.

Abstract: A high temperature resistant glass fiber composition consists essentially of glass fibers having a nominal softening point of about 1000° F. (about 538° C.) which is capable of passing the British Standard 476 Part 4 fire test for building materials. The BS476-4 test begins at 750° C., substantially above the nominal softening point of the glass fibers. The increased temperature resistance is provided by coating the glass fibers with a halogenated resin latex binder and a calcium carbonate material. The method of making the glass fiber composition comprises depositing the resin latex and a calcium carbonate material on the glass fibers using a cationic flocculant. The preferred halogenated resin latex binder is selected from polyvinyl chloride and polyvinylidene chloride.

Abstract: This invention provides a method and apparatus for mixing calcined gypsum. The invention comprises a mixer which employs high pressure water to eliminate or substantially reduce the formation of lumps of gypsum inside the mixer which cause paper breaks when the calcined gypsum slurry containing the lumps is used to form the gypsum core in a gypsum wallboard product. High pressure water jets direct a spray of high pressure water at the surfaces within the mixer where the lumps of gypsum are formed. The method of this invention utilizes the high pressure water as part of the metered water that is continuously fed to the mixer, with the balance of the water being fed through low pressure nozzles.

Abstract: A cementitious composition of the setting type which can be kept in a ready-mixed state and which can be caused to set and harden upon introduction of an accelerator with reproducibility and set time predictability. The cementitious base composition contains calcium sulfate hemihydrate as a principal filler material and certain non-calcium bearing phosphate additives which prevent setting action in the presence of water. An accelerator, such as zinc sulfate, may be added to the ready-mixed, cementitious composition to initiate the setting action, or the ready-mixed cementitious composition can be used as a drying type joint compound without the addition of an accelerator.

Abstract: A mineral wool-free acoustical tile composition and the acoustical tile made therefrom wherein an expanded perlite is used as a substitute for granulated mineral wool to provide porosity and good sound absorption properties. It is preferred that the composition and acoustical tile also contain an inorganic filler to provide texturability during the manufacturing process. In addition, the acoustical tile composition also contains a starch gel binder and a fiber reinforcing agent selected from the group consisting of cellulosic fibers, polymeric fibers and glass fibers. It has been found that the mineral wool-free acoustical tile compositions of this invention have acoustical properties comparable to the commercially available cast mineral wool tiles. In addition, the mineral wool-free compositions can be used to cast an acoustical tile using equipment and procedures currently used to produce cast mineral wool tiles.

Abstract: A clay-free, asbestos-free and glass microbubble-free, drying type Joint compound containing an in-situ or associative thickener as a substitute for asbestos and any clay substitute therefor. In particular, these drying type joint compounds contain no attapulgus clay thereby improving viscosity stability, crack resistance and shrinkage. The lightweight joint compounds contain treated expanded perlite, treated to render it water-insensitive. The preferred in-situ thickeners are acidic acrylate copolymers. It has been found that the in-situ thickeners should be used in combination with the normal cellulosic thickeners used in joint compounds Instead of as replacements therefor. The joint compounds contain the usual fillers and latex emulsion binders, with at least about 50% by weight of the drying type joint compound being a filler selected from the group consisting of calcium carbonate and calcium sulfate dihydrate.

Abstract: An improved composite material is produced by mixing gypsum and host particles of a stronger substance, such as wood fibers, in a dilute slurry; heating the slurry, under pressure, to convert the gypsum to calcium sulfate alpha hemihydrate; and substantially dewatering the hot slurry before rehydrating the hemihydrate back to gypsum. The resulting material is a homogoneous mass comprising gypsum crystals physically interlocked with the discrete host particles.According to a further aspect of the invention, an improved wallboard, having fire resistance, dimensional stability and excellent strength properties, is produced by compressing the composite mass before hydrating it to a final set.

Abstract: The manufacture of sag-resistant, lightweight structural mineral panels on a foraminous support wire is accomplished by forming a dilute aqueous dispersion of mineral fiber and/or aggregate and an anionically stabilized latex binder, coupling the binder solids onto the mineral fiber materials by adding a small amount of a flocculant such as a cationic polyacrylamide, and passing the slurry onto a first flooded section of the support wire to form an open, entangled, structural mass having water in interstitial spaces of the entangled mass. Water is stripped from the mass and the mass dried without collapse of the open structure by passing heated dry air through the open entangled structure.

Abstract: A cement board having bare surfaces and a woven mesh of reinforcing fibers underlying the top, bottom, and longitudinal edge surfaces is made continuously on an improved apparatus which comprises a pair of edger rails which slidably rest on a conveyor belt and define the path of the cement board being made on the conveyor belt and a means for folding and pressing outer margins of the bottom mesh into the edge surfaces and the top surface.

Abstract: A method for comminuting plastic scrap material wherein the plastic scrap is suspended in water and an antifoam agent is added to the suspension which is then passed through a disc refiner or a Valley beater to comminute the plastic scrap. The antifoam agent is selected from defoamers having an HLB value of from about 0.5 to about 10 and a polypropylene glycol having an average molecular weight of from about 900 to about 1500. The comminuted plastic scrap is useful as an additive to the core material of a gypsum wallboard.

Abstract: A process for economically producing tabular acicular gypsum crystals in a continuously stirred reactor is disclosed. The process involves establishing a steady state atmospheric pressure reaction zone of about 20% to about 25% by weight solids of gypsum crystals in water at a temperature of about 50.degree. C. to about 60.degree. C. with continuous mild agitation. Calcium sulfate hemihydrate is fed to the reaction zone at a rate to maintain a low level of supersaturation, and a suspension of gypsum crystals in water containing crystals of a mean particle length at least greater than 45 microns is withdrawn.

Abstract: Low density mineral wool structural panels are manufactured by frothing a dilute aqueous dispersion of mineral wool, lightweight aggregate, binder and a small amount of amine-based cationic surfactant onto a non-woven scrim cover sheet, dewatering the mass and drying it. The froth is a mass of weakly resilient bubbles that rapidly dewater and burst to concentrate the solids in the mass. The bubbles are readily broken without loss of the voided structural configuration by a first application of brief pulses of high vacuum followed by further dewatering under vacuum and rapid drying by passing large volumes of air through the voided mass without collapse of the structure to result in lightweight structural mineral wool panels.

Abstract: A suspended ceiling structure adapted for unopposed intersections wherein the webs of the main grid runners adjacent the cross runner slots are provided with embossments which strengthen the web and contain the cross runner end connector against withdrawal. It is preferred that the embossments are placed at each side of the cross runner slots. The cross runner end connectors have tabs bent laterally from the longitudinal axis of the cross runners with the rearward edge of the tab bearing against the face of the main runner web, whereby upon the application of a pull out force, the tab edge bends outwardly until it presses against the ends of the embossments. This unopposed intersection structure is commonly referred to in the art as an "ashlar" condition or configuration.

Abstract: A wet pulp of mineral fibers or the like is forced between a pulp carrier and a corrugated texturing skid inclined toward the downstream end of a moving slab of the pulp. The corrugations of the skid are co-directional with the machine direction of the conveyor belt that transports the pulp under and beyond the skid.

Abstract: A method for the manufacture of very low density mineral wool structural panels on a moving foraminous support wire by frothing a dilute aqueous dispersion of mineral wool is disclosed. The forth, a mass of delicate, non-resilient and non-uniform bubbles among the entangled mineral wool fibers readily breaks, is stripped of water and dried without substantial loss of the highly open, porous structural configuration by a first controlled rate of maturation dewatering followed by brief pulses of high vacuum. Then the open structure is rapidly stripped of remaining water and dried by passing high volumes of heated dry air through the structure with continued vacuum. The drainage water may be recycled in the process to maintain a low level of binder and any frothing aid additions.

Abstract: In a method and apparatus for calcining calcium sulphate dihydrate or like heat sensitive material, in which a bed of the material is heated in a vessel (41) by the direct introduction of a hot gas through a tube (21) extending downwardly into the bed, the proportion of insoluble anhydrite (II) in the product is reduced by lowering the temperature of the hot gas before it contacts the material of the bed. This is done by indirect heat exchange through the wall of the tube 21 with a relatively cool substance, for example, powdered gypsum or recycled exhaust gases, in an outer tube (26). The cooling material in the outer tube contacts the material in the bed before the latter is contacted by the hot gas.

Abstract: A paper cover sheet particularly designed for use as the face sheet in the manufacture of gypsum wallboard, the face sheet having a base formed of a plurality of filler plies formed of recycled paper comprised of clean hard stocks such as kraft and boxboard cuttings, and being free of topliner plies containing flyleaf furnish, the base having a coating on the face surface thereof comprising a light colored mineral filler and a binder. The coating provides a light color to the face surface generally termed "manila". The elimination of the topliner plies results in a paper of excellent strength and porosity.

Abstract: This invention comprises a suspended ceiling grid system having an adjustable compression strut installed between the grid members of the system and the building or construction superstructure which lies in a plane above the suspended ceiling. The adjustable compression strut stabilizes the ceiling system and prevents upward movement of the system such as might occur during a seismic shock or earthquake tremor. The compression strut comprises two co-axial, telescoping cylindrical strut members having a spring clip attached to the inner end of the inner strut member that allows the strut to be extended but not retracted. The compression strut is installed by simply holding it in position between the suspended ceiling grid and the superstructure and then extending the strut members until they are locked in place by the action of the spring clip.