Mold tray

General purpose Rigid moldings. Trays, boats, tanks, boxes, luggage, seating. 

In the sheeting market, the low density polyethylenes are less important than the high density resins. The high density resins have excellent chemical resistance, stress-crack resistance, durabiUty, and low temperature properties which make them ideal for pond liners, waste treatment faciUties, and landfills. In thicker section, HMW-HDPE sheet makes good containers, trays, tmck-bed liners, disposable items, and concrete molds. The good durabiUty, abrasion resistance, and light weight are critical elements for its selection. 

Wet System Compression M olding. Wet system compression molding was the first high volume method for manufacturing reinforced plastic parts, in such appHcations as the Chevrolet Corvette, industrial trays, tote boxes, luggage, refrigerator liners, and other commercial appHcations. 

Thermoforming of extmded sheet is achieved by warming the sheet to its glass-transition poiat and coUapsiag it over a mold shape (21). The coUapse can be effected by vacuum suction or pressures appHed on the sheet above the mold. This technique is used to make trays and profiled advertisiag signs. Both single- and multilayer sheets can be used. 

Hot strength Fast rate of cure (hot), moldings easily removed from die. Containers, trays, housings. 

Expandable polystyrene EPS is a modified PS prepared as small beads containing pentane gas which, when steamed, expand to form lightweight, cohesive masses for forms used to mold cups and trays, package fragile products for shipment, etc. Similar dimensionally stable forms molded from EPS are used as cores for such products as automobile sun visors with surface overlays, etc. 

Figure 5 Temperature profile in primary drying of dobutamine HCl-mannitol (1 1), 53 mg solids/mL, 10 mL fill volume. Vials are 5304 molded glass vials (8.3 cm2 cross-sectional area) which are placed in a flat aluminum tray. The heat flux is 42 cal/(cm2 hr), and the chamber pressure is 0.1 torr. (From Ref. 5.)...

The primary crystalline polymer based on CHDM is the terephthalate, poly(1,4-cyclohexylenedimethylene terephthalate) (PCT). This polyester was originally developed for fiber applications but has since found wider utility as a reinforced polymer for injection molding and (when copolymerized with a small amount of isophthalic acid) as a material for crystallized food packaging trays. The key property of PCT which sets it apart from other thermoplastic polyesters in these latter applications is its melting point. 

A well-established application for extruded unreinforced PCT (copolymerized with isophthalate) is crystallized, thermoformed trays for foods. Crystallized PET is widely used for this application, but where higher-temperature performance is needed the PCT-based polymer may be chosen. Such trays are formed from extruded sheet, using a hot mold to promote crystallization. Isophthalate-modified PCT polymers are approved by the Food and Drug Administration for high-temperature food contact use. 

Figure 7.8 Refrigerator crisper trays molded from Eastman Eastar PETG 6763. Photograph provided by courtesy of Eastman Chemical Company...

A popular, related technique is to inject some sort of a volatile material into the polymer while it s still molten, causing it to foam immediately. Fluorocarbons are used this way in making polyurethane foams suitable for insulation. The trapped fluorocarbon is even better than air as an insulator. Fluorocarbon or air is used to expand PS foams also. The gas is injected as the molten polymer is forced through a die. The foamed PS is then immediately injected into a mold to make items like egg cartons and trays for meats, produce, or fast-food. 

Details of preparation and storage conditions for crops that last well through the winter are given here (seepanel, left). Some other crops can also be stored for shorter periods for example, carrots, parsnips, beets, rutabagas, and celeriac keep well if packed in moist sand or fine leaf mold in shallow trays or boxes. 

To dry herbs flat, strip the leaves from each stem and arrange them In a single layer on a rack or tray. Inspect the herbs regularly to be sure they are drying properly, and turn any of the larger leaves frequently to ensure that they dry evenly. Look also for anything that shows signs of mold or decay and remove it. 

Typical HDPE—blow-molded products bottles, cans, trays, drums, tanks, and pails injection-molded products housewares, toys, food containers, cases, pails, and crates films, pipes, bags, conduit, wire and cable coating, foam, insulation for coaxial and communication cables... 

Polyarylsulfones offer materials with good thermal-oxidative stability, solvent resistance, creep resistance, and good hydrolytic stability. Their low flammability and smoke evolution encourage their use in aircraft and transportation applications. They hold up to repeated steam sterilization cycles and are used in a wide variety of medical applications such as life support parts, autoclavable tray systems, and surgical and laboratory equipment. Blow-molded products include suction bottles, surgical hollow shapes, and tissue culture bottles. PPS has a number of automotive uses including as an injection-molded fuel line coimector and as part of the fuel filter system. 

Figure 7.72 Comparison of production costs per product for a polymer tray formed using (1) thermofoiming in a wooden mold, (2) thermoforming in an aluminum mold, (3) blow molding with a single mold, (4) compression molding, and (5) injection molding. Reprinted, by permission, from P. C. Powell and A. J. I. Housz, Engineering with Polymers, p. 58. Copyright 1998 by Stanley Thomed Publishers.

Pressure Molding. The polymer is mixed with the plasticizer in the required proportion and dissolved in methylene chloride to form a 10% solution. This solution is poured into a tray and allowed to evaporate at room temperature. At regular intervals the content of the tray is thoroughly mixed with a spatula. The cake obtained is dried for 24 hours at 110°C. 

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