Compression molding aluminum

Injection molding requires the barrel temperature to be about 350°C with a barrel pressure in excess of 138 MPa. The mold is maintained at 110°C to ensure uniform flow and high definition, and to discourage an uneven index of refraction, birefringence. The CD is about four one-hundredths of an inch (0.5 mm) thick. For prerecorded CDs, the PC is compression-molded on a stamper imprinted with the recorder information. This takes about 4 sec. Once the clear piece of polycarbonate is formed, a thin, reflective aluminum layer is sputtered onto the disc. Then, a thin acrylic layer is sprayed over the aluminum to protect it. The label is then printed onto the acrylic surface and the CD is complete. This process is described later in greater detail. 

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.

The thermal stability of poly(vinyl chloride) is improved greatly by the in situ polymerization of butadiene or by reaction with preformed cis-1,4-polybutadiene using a diethyl-aluminum chloride-cobalt compound catalyst system. The improved thermal stability at 3-10% add-on is manifested by greatly reduced discoloration when the modified poly-(vinyl chloride) is compression molded at 200°C in air in the absence of a stabilizer, hydrogen chloride evolution at 180°C is retarded, and the temperature for the onset of HCl evolution and the peak decomposition temperature (DTA) increase, i.e. 260°-280°C and 290°-325° C, respectively, compared with 240°-260°C and 260°-280°C for the unmodified homopolymer, in the absence of stabilizer. The grafting reaction may be carried out on suspension, emulsion, or bulk polymerized poly(vinyl chloride) with little or no change in the glass transition temperature. 

In this process, the polyurethane mix is poured into a mold that can be placed into a compression molding press with heated platens. The material is allowed to gel, and a top plate is placed on the material. The molding press is fully closed. The pressure applied is normally on the order of 1.50 to 2.0 MPa (250-300 psi) based on the projected area of the molding e.g., a parts plan area is 300 x 400 mm in size. Its area is 0.300 x 0.400 m2 = 0.12 m2 therefore, a pressure of 1.500 x 0.12 = 0.18 MPa on the mold is required. The molds must be capable of withstanding the direct heat and pressure of the press. Aluminum or steel molds are preferred for this process. 

Film Preparation. Polymer films (10 mil thick) were prepared by compression molding for one half hour at 175 °C. between evaporated gold films on glass microscope slides or sheets of 0.7 mil aluminum foil (Reynolds Aluminum Wrap) which had been chemically etched as above. 

Since the in-mold pressures in RIM are generally relatively low [50 to 150 psi (0.4 to 1.1 MPa)] a variety of tooling constructions have been used. These include machined steel or aluminum, cast aluminum or kirksite, sprayed metal or electroplated shells, and reinforced or aluminum filled epoxy (Chapter 17). With mold pressures usually below 100 psi (0.7 MPa), mold-clamp-pressure requirements can accordingly be low when compared to injection and compression molding. 

It is not only the blend morphology which is affected by filler presence filler orientation might be affected by its surface treatment, as was observed in the works on PC/ABS blends containing aluminum borate whisker. When the whisker surface was treated with epoxy silane, its reaction to flow in injection and compression molding processes changed, resulting in a different orientation even though all other parameters of process and composition were the same. ... 

The linear PE studied was Marlex 6015 obtained from Phillips Petroleum Co. The polymer powder was compression-molded between Teflon-coated aluminum foil at 170°C. Temperature was maintained for 15 min prior to compression for 5 min. The sample was then allowed to cool slowly to room temperature with no pressure while still in the platens of the press. Thin films were obtained which showed no macroscopic melt flow orientation and which were less than 0.002 in. thick. This sample preparation will be referred to as slow-crystallized. 

The use of compression molding has expanded significantly in recent years due to the development of new materials, reinforced materials in particular. Molding reinforced plastics (RPs) requires two matched dies usually made of inexpensive aluminum, plastics, or steel and used on short runs. 

Stamped steel Compression molded SMC PRIM Injection molded thermoplastics Stamped aluminum... 

Relative tooling cost, single cavity Lowest. Machined aluminum may be variable, depending on quantity required 20 percent more. Hardened-steel tooling 20 percent to 25 percent more. Compression-molding steel tools... 

MAJOR APPLICATIONS Fibers, films, barrier film, soft drink bottles (amorphous PET), film for compression molding polyethylene, pol)rpropylene, and for replacement of commodity metals such as steel and aluminum.( ... 

Eor certain analyses it may be desirable to ensure that the hot pressed compression molded film is frozen into an amorphous state. This may be achieved by melting a few milligrams between a pair of thin press plates or aluminum sheet, leaving part of the plates exposed from the press platens. This may be... 

Figure 1 Volume resistivity versus volume fraction of aluminum flakes in various polymers. Open symbols represent injection-molded composites with 50 1 aspect ratio flakes. Filled symbols represent compression-molded composites 16.7 1 aspect ratio flakes. ( , ) polypropylene, (A) polycarbonate, (O) ABS. From Li, L. and Chung, D.D.L. (1994) Composites, 25(3).

Measurement of a number of properties requires sheet stocks of PFA, from which specimens are punehed out and conditioned before testing. The sheet is prepared by using a chase in the shape of a picture frame with the adequate depth to produce a finished thickness of 1.5 0.25 mm. A fairly thick (0.13-0.18 mm) aluminum foil is sprayed with a high-temperature mold release agent before being placed smoothly over a flat steel plate (>1 mm thick). The chase is then placed over this plate-assembly. An amount of polymer sufficient to produce the sheet is placed in the middle of the chase in the form of a mound. A second sheet of aluminum foil is placed on top of the polymer granules and the top steel plate is added to the assembly, which is then put in a preheated (380 5°C) compression molding press. 

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