Presses compression molding

When the molding cycle is complete, the press opens and the molded part is removed and, if required, trimmed. It is probably moved to a jig for post-cure. This is normally carried out in a vertical press (compression molding), which is also convenient for loading inserts into the molding tool. 

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... 

Presser, m. presser compressor pressman. Press-erzeugnis, n. pressings, -fehler, m. molding defect, -filter, n. pressure filter, press filter, -fliissigkeit, /. pressure fluid, -form, /. press(ure) mold, compression mold, -gas, n. compressed gas. -glanz, m. gloss from... 

Press-verfahren, n. pressing process molding technic, -vulkanisation, /. Rubber) press cure, -walze,/. press roll, -ziegel, tn, pressed brick, -zucker, m. compressed sugar. 

Figure 19 illustrates one type of compression mold suitable for molding lip type shaft seals with a metal outside diameter (O.D.). Figure 19a shows the compound preform resting on the shelf and the mold beginning to close. The mold continues to close until it gets to the position shown in Fig. 19b. Finally, the mold opens as shown in Fig. 19c. It can be seen that this molding technique produces a molded lip seal with the flash already removed. In general, when using a vacuum chamber on the press, to ensure that all the air and/or gases are evacuated from the mold after closure, one or...

Most of the compounds were extrusion compounded in a conical, partially intermeshing, counter rotating twin screw extruder (Haake Reomix TW-lOO). The extruder speed was set at 50 rpm and the barrel temperature profile was set to produce a melt temperature of 260°C at the die. Samples were injection molded in a 31.8 MT Battenfeld press with a 59 cc shot size. Where noted, samples were compounded in a 60 cc Brabender internal mixer and compression molded. 

Polymer Processing. Polymer films were cast in trimethylsilyl coated glass molds from membrane filtered 15% (w/v) methylene chloride or chloroform solutions. Transparent films were obtained which were dried to constant weight in high vacuum. Rectangular strips or round disks were cut from the films. For compression molding a Carver laboratory press equipped with thermostated, heated platens was used. Polymers were placed in a stainless steel mold and heated to 40 °C above their glass transition temperature. Then a load of 1-2 tons was applied for 5 min. 

Sample Preparation. Samples for mechanical studies were made by compression molding the polymers at 150°C between Teflon sheets for 15 minutes followed by rapid quenching to room temperature in air. These will be referred to as PQ (press-quenched or simply quenched) samples. The thickness of the PQ samples was around 10 mils (0.25 mm). The thermal history of all of the PQ samples (HBIB, HIBI, and LDPE) were essentially the same. They were used within one week after they were pressed. Samples for morphology, SALS and SEM studies were prepared from toluene solutions. These films were cast on a Teflon sheet at 80 C from a 1% (by weight) solution in toluene. These films were about 5 mils in thickness. When the polymer films had solidified (after 5 hrs), they were stored in a vacuum oven at 80°C for two days to remove residual solvent. These samples will be designated by TOL (solution cast from toluene). 

Compression molded (150°C for 3 minutes press chilled with cold water immediately thereafter) samples of poly(trans-l,4-hexadiene) (14) and poly(5-methyl-l,4-hexadiene) were examined with a General Electric (XRD-3) X-ray unit. Transmission Laue X-ray photographs were taken using nickel filtered copper X-radiation. Samples were stretched to four times of their original lengths to obtain oriented fibers. The fiber patterns were obtained in a flat plate film holder with the specimen to film distance standardized at 5 centimeters. X-ray diffraction patterns were similarly obtained for the hydrogenated sample of poly(5-methyl-l,4-hexadiene). 

Thermosets are processed by compression molding, transfer molding and injection molding or by extrusion, depending on their structure. The pressing temperatures are about 150 to 190°C. Corresponding requirements are placed on the pigments. Dyes are often also used to color thermosets. 

Preparation of Samples for Flammability Testing. Samples of the phosphorus containing terepolymers and of the polymer blends were converted to film by compression molding on a Carver Laboratory Press with electrically heated platens. The films were prepared at 250°C and 20,000 lb. pressure, using a 10 mil thick frame mold. Samples (2" x 1/4") were cut from this film for flammability testing. 

Tensile properties and flexural modulus were determined on 20 mil pressed films in accordance with ASTM D882 and D790, respectively. Izod (notched) impact strength was determined on compression molded plaques in accordance with ASTM D256. Water vapor transmission was determined on 5 mil pressed films in accordance with ASTM E96. 

During the press operation, which is actually a form of compression molding, the resin-treated laminate plies are heated under pressure and the resins cured. The initial heating phases cause the resin to melt and flow into voids in the reinforcing ply and bond the individual plies together. The applied heat simultaneously causes the resin to polymerize and eventually to cross-link or gel. Therefore, resin viscosity reaches a minimum during the press cycle. This is the point at which the curing process becomes dominant over the melt flow process. Dynamic mechanical and dielectric analyses (11) are excellent tools for study of this behavior. 

Before testing, the samples were compression molded, usually at 10°F above the milling temperature, using a cycle with a five-minute preheat and three minutes at a pressure of 40,000 pounds ram force. Specimens were then transferred to a cooling press and cooled under pressure. 

F.B. Wells, S-Trinitrobenzene as a Binder in Compression-Molded Explosive Compositions , PATR 4783 (1975) [It was found that the ideal HMX/TNB ratios required to provide compression-molded pellets that come close to the theoretical max d are 95/5 to 94/6 with no TNB loss at SOOOpsi compression press. It was also noted that the HMX used need not be of a very fine particle size to be successfully molded in the mixt] 54) J.R. Hendrickson F.B. Wells, Castable Composite Explosive Compositions Containing a Mixture of Trinitrobenzene (TNB) and Trinitroxylene , USP 3994756 (1976) CA 86, 75497 (1977) [A castable composite expl which meets Mil Specs is claimed which contains TNB 26.25, Trinitroxylene 3.75, and HMX 70 wt %] 55) F.B. Wells, High-... 

PS-25 PPO the mixture was heated to 300°C, maintained at this temperature for 6 minutes, compression molded into a film, and cooled slowly to room temperature in the press. 

Discoloration. When PVC, free of plasticizer or stabilizer, is compression molded in air at 200°C under adequate pressure (c.g., 500-6000 psig), thermal degradation results in discoloration to a pink to brown colored film. When the modified PVC containing as little as 3% of grafted cis-1,4-polybutadiene was pressed under the same conditions, the resultant film was essentially colorless or no more than faintly discolored. 

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. 

Latex rubber can be poured like polyurethanes, but they generally are only poured in thin sheets. Even thicker sheets such as Linatex require a very long cure time. Pouring is the method of choice for cast polyurethanes. Normally, rubbers require a compression molding press or injection molding machine to produce parts. This has high capital and mold costs. 

---