H1b. continuous casting of sheet - uses a pair of moving, parallel, highly-polished, and endless, stainless steel belts, between which is poured or pumped an acrylic syrup similar, but not identical, to that used for cell casting of acrylic as described above. (The material mixture may be varied in order to provide the proper viscosity for the method used. The final sheet, though a thermoplastic, will contain some cross-linked material to improve chemical and stain resistance and thermo-formability.) Flexible gaskets at the edges of the sheets prevent leakage. The stainless steel belts convey the material through a heating phase to induce polymerization, followed by a quick cooling phase to prevent bubbling of the material. Another heating phase up to about 260 ° F (125 ° C) is then used to complete the polymerization to the desired level. Then the solid product exits the belt system, the surfaces are covered with a protective film and sheets are cut to the length desired. Fig. 4H1b illustrates the process. The equipment required is rather large and expensive but output rates are high. Most acrylic sheet is produced by the continuous casting method. Sheet thicknesses can range from about 0.080 to 0.500 in (2 to 12.5 mm). Applications are the same as those for cell cast sheet except that optical properties are not as good as those from cell casting. Skylights, sign components, and glazing are all applications for continuous cast acrylic sheet.

Fig. 4H1b Schematic view of equipment used for the continuous casting of acrylic sheet. The acrylic syrup is spread and compressed between two polished stainless steel belts, which carry it through a series of ovens that polymerize the acrylic by heating, cooling, and reheating to produce a solid cast sheet. (Note: For convenience of illustration, the heating and cooling zones are shown much shorter than those in actual production equipment.)

H2. casting structural foam parts - is simply reaction injection molding (as discussed above in 4C3b) performed on a manual basis. Liquid components of thermosetting resins (usually polyurethane) are mixed and poured into a mold. Polymerization and foaming take place in the mold. Heated molds are used to accelerate polymerization. Oven curing usually takes place after casting. This process is particularly applicable to prototypes and limited quantity production, and can be used effectively for large plastic parts.

H3. casting nylon parts - Cast nylon has superior machinability, stiffness and heat deflection properties than nylon 6/6 which is injection molded or extruded. The nylon casting process involves use of the monomer; polymerization takes place in the mold. The monomer must be heated and melted before casting, and must be protected against moisture absorption during the casting sequence since it is highly hygroscopic. Sealed containers and inert atmospheres may be used to prevent moisture from coming in contact with the material. Molds can be inexpensive since the forces they are subjected to are low. Aluminum, epoxy, and silicone rubber, as well as steel, have been used as mold materials. The casting operation often takes place in heated ovens. (The monomer material is heated to 390 ° F (200 ° C). For smaller parts, centrifugal casting may be employed, i.e., the molds are spun to provide sufficient force to fully fill the mold cavities. Cooling of finished parts is slow to permit relief of internal stresses from shrinkage (15%). Large parts (up to 400 lbs − 180 Kg) can be produced with the process. Gears, sheaves, cams, various machine parts, bushings, and bearings are common applications. The casting process lends itself well to low-quantity production levels.

H4. casting acrylic parts - The same kind of monomer-polymer mixture used in cell casting of acrylic sheets (See H1a above) can produce shaped parts if a suitable mold is used. The process is useful at low production quantities when the cost of an injection mold and molding machine cannot be justified. The optical clarity of acrylic makes it useful for embedding an object or biological specimen in a clear protective or decorative block. Embedded objects are pre-positioned in the mold before casting. Molds can be made of almost any material because the operation does not require elevated temperatures. Art statuary, and marble-like kitchen and bathroom counters and sinks are other applications. When marble-like objects are cast, the acrylic is mixed with up to 60% of inorganic filler which gives the appearance of marble.

H5. encapsulation and potting - various electronic and electrical devices are encapsulated with plastics to provide insulation, and mechanical and environmental protection. Potting involves partly surrounding a device with plastic to fix it in place in some component. Both encapsulation and potting involve casting, usually with thermosets. Epoxy potting of small transformers for electronic devices is a common example of potting. High voltage transformers are frequently potted with silicone rubber. As with regular casting, simple molds can be used. Often, immediately after casting, the filled mold is placed in a vacuum chamber so that any trapped gases or air will bubble out of the liquid casting resin before it sets. This procedure eliminates or minimizes voids in the cured material.