Sheet forming

Plastic sheet heated oustide of forming area 

Spring pads allow stock to slip as mold is forced into plastic (spring tension increases as mold closes) 

Material has slipped into forming area on controlled basis 

Steel knife can be used for seal and subsequent trim if additional pressure can be exerted at this stage 

Typical Properties of Three Plastics for Structural Foam 

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Cork [61789-98-8] is an effective low cost charring ablator. In order to reduce moisture absorption and related poor performance, cork particles are often blended in a silicone or phenoHc resin. The result is a uniform ablative material in a sheet form that is easy to apply. 

The rolling operations that foUow take place first on hot (95°C) differential-speed roUs which dry and coUoid the paste and convert it iato sheet form, and then on even-speed roUs which produce smoothly surfaced propellant sheets ia which all iagredients have been uniformly iacorporated. The roU gap ia the differeatial roUs is adjustable to produce sheets of various thicknesses, and rolling is continued until the moisture is reduced to a predetermined level, usually less than 0.5%. The sheet is then cut off the roU. Differential rolling is potentially hazardous, and fires are not uncommon, although detonations are not apt to occur. Operations are conducted by remote control. 

Polyester sheet products may be produced from amorphous poly(ethylene terephalate) (PET) or partiaHy crystallized PET. Acid-modified (PETA) and glycol modified (PETG) resins are used to make ultraclear sheet for packaging. Poly(butylene terephthalate) (PBT) has also been used in sheet form. Liquid-crystal polyester resins are recent entries into the market for specialty sheet. They exhibit great strength, dimensional stabHity, and inertness at temperatures above 250°C (see Polyesters,thermoplastic). 

A common surface cartridge is the pleated paper constmction type, which allows larger filtration areas to be packed iato a small space. Oil filters ia the automobile iadustry are of this type. The paper is impregnated, for strength, with epoxy or polyurethane resia. Any other medium ia sheet form, similar to cellulose paper, such as wool, polypropylene, or glass may be used. 

Sheet Extrusion and Thermoforming. Sheet for thermoforming and analogous operations is usually formed by extmding the melt through a slot die onto a set of poHshed chill roUs. The sheet is usually approximately 150 cm wide. After rapid cooling, the web is coiled or cut into sheets. Polystyrene, PVC, polyethylene, polypropylene, and filled polypropylene are prepared in sheet form by extmsion. 

Products. Damping treatments are available from many manufacturers in sheet form, as tapes for adhering to a surface, and in bulk form for spraying or troweling onto a surface. Laminated glass is available from many glass suppHers (see Laminated materials, glass). 

In the sheet-forming process, stainless steel, bronze, nickel-base alloys, or titanium powders are mixed with a thermosetting plastic and presintered to polymerize the plastic. Sintering takes place in wide, shallow trays. The specified porosity is achieved by selecting the proper particle size of the powder. Sheet is available in a variety of thicknesses between 16 x 30 mm and as much as 60 x 150 cm. A sheet can be sheared, roUed, and welded into different configurations. 

Sheet form, composed of organic roofing felt, saturated with asphalt and coating on both sides with asphalt compound that may or may not contain mineral stabiHzer, surfaced with powdered talc, mica, or other tine mineral matter to prevent sticking. Classified, in mineral net mass per unit area of roofing, as Type I, 1943 g/m (39.8 lb/100 fC) Type II, 2666 g/m (54.6 lb/100 fC) Type III, 2495 g/m (51.1 lb/100 fC) and Type IV, 1943 g/m (39.8 Ib/lOOfC). 

Sheet form, in widths as agreed upon by purchaser and seUer, composed of asphalt-saturated organic felt coated on both sides with asphalt and surfaced on weather side with mineral granules, except for selvage. Classified, in minimum net mass of granule-surfaced portion, as Type I, 3610 gm/m (74.0 lb/100 fC) and Type II, 3490 gm/m (71.5 lb/100 fC). 

Sheet form, 914 mm (36 in.) in width, or widths agreed upon by purchaser and suppHer, composed of asphalt-saturated organic felt with approximately half the width of weather side coated with asphalt and surfaced with mineral granules, for use as cap sheet in constmction of BUR. Materials covered by this specification, in minimum mass per unit area, are Type I, 1806 g/m (37.0 lb/100 fU) Type II, 2260 g/m (46.3 lb/100 fU) Type III, 1733 g/m (35.5 lb/100 fU) and Type IV, 2090 g/m (42.8 lb/100 fU). 

Waterproof. Waterproofing barrier systems may be either hot- or cold-appHed. The hot-appHed generaUy involve a bituminous material such as asphalt used in conjunction with a reinforcing fabric such as roofing felt, cotton, or glass cloth. Cold-appHed can be bituminous or elastomeric materials either in Hquid or sheet form, with or without fabric reinforcement. Liquid elastomeric treatments include neoprene, polyurethanes, and blends of these or epoxies with bituminous materials. Among the commonly used precured elastomeric sheet materials are neoprene, polyisobutylene, EPDM mbber, and plasticized PVC. Polyethylene and PVC films and nonwoven plastic or glass fabric coated with bituminous materials also find use (78). Because these... 

Base-plate wax compositions are generally regarded as trade secrets. A substantial percentage of paraffin is usually present, probably 50—80 wt %. Beeswax [8012-89-3] camauba wax [8015-86-9] ceresin, microcrystalline waxes, Acrawax C (Glyco Products Co. Inc.), mastic gum, rosin [8050-09-7] and synthetic resins may make up the balance of the formulation. Base-plate waxes are generally sold in sheet form about 1.3 mm thick, 75 mm wide, and 140 mm long. 

Cylinder Heat-Transfer Units Sometimes called can dryers or drying rolls, these devices are differentiated from drum diyers in that they are used for solids in flexible continuous-sheet form, whereas drum dryers are used for liquid or paste forms. The construction of the individual cyhnders, or drums, is similar in most respec ts to that of drum diyers. Special designs are used to obtain uniform distribution of steam within large drums when uniform heating across the drum surface is critical. 

These cylinder units are applicable to almost any form of sheet material that is not injuriously affected by contact with steam-heated metal surfaces. They are used chiefly when the sheet possesses certain properties such as a tendency to shrink or lacks the mechanical strength necessary for most types of continuous-sheeting air diyers. Applications are to diy films of various sorts, paper pulp in sheet form, paper sheets, paperboard, textile piece goods and fibers, etc. In some cases, imparting a special finish to the surface of the sheet may be an objective. 

Available forms. Blanket (felt and batt), block, cements, loose fiU, foil and sheet, formed or foamed in place, flexible, rigid, and semirigid. 

This is a material produced from the impregnation of glass fibre-mat (fibreglass, which is in the form of dry sheet, is commonly known as chopped stranded mat (CSM)) or rovings, with a liquid and unsaturated polyester resin, which thickens chemically to a dry sheet form. The total mix is sandwiched between polyethylene films and then roller-pressed to impregnate and consolidate it. 

Each repeat forms a right-handed P-loop-a structure similar to those found in the two other classes of a/p structures described earlier. Sequential p-loop-a repeats are joined together in a similar way to those in the a/P-bar-rel stmctures. The P strands form a parallel p sheet, and all the a helices are on one side of the P sheet. However, the P strands do not form a closed barrel instead they form a curved open stmcture that resembles a horseshoe with a helices on the outside and a p sheet forming the inside wall of the horseshoe (Figure 4.11). One side of the P sheet faces the a helices and participates in a hydrophobic core between the a helices and the P sheet the other side of the P sheet is exposed to solvent, a characteristic other a/p structures do not have. 

The variable domains associate in a strikingly different manner. It is obvious from Figure 15.11 that if they were associated in the same way as the constant domains, via the four-stranded p sheets, the CDR loops, which are linked mainly to the five-stranded p sheet, would be too far apart on the outside of each domain to contribute jointly to the antigen-binding site. Thus in the variable domains the five-stranded p sheets form the domain-domain interaction area (Figure 15.11). Furthermore, the relative orientation of the p strands in the two domains is closer to parallel than in the constant domains and the curvature of the five-stranded p sheets is such that they do not pack... 

Copolymers of methyl methacrylate and butyl acrylate gave polymers that were somewhat tougher and slightly softer than the homopolymers. Materials believed to be of this type were marketed in sheet form by ICI as Asterite for a short while in the 1960s (the name having been recently revived for another product as described in Section 15.2.6). 

Superior heat resistanee to most rigid thermoplasties, particularly those that are available in sheet form. 

Pads of a mixture of paper pulp and asbestos fiber are used in bacteriological filtrations. In sheet form it is employed in the laboratory for all kinds of filtration. Filter papers are made in many grades of porosity for use in porcelain and glass funnels. Industrially, paper in the form of sheets is used directly or as a precoat in filter presses. 

The term thermoforming incoroporates a wide range of possibilities for sheet forming but basically there are two sub-divisions - vacuum forming and pressure forming. 

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