Piston and Molding Presses

The brothers J.W. and J.S. Hyatt in the USA patented the first piston injection mold press in 1872, when they solved the problem of plasticizing a mixture of nitrocellulose and camphor. Much later a screw-injecting molding machine was designed. Nowadays screw injection molding is the most commonly used method for thermoplastic materials. 

Scorim Process or SP (Cinpres-Scorim), Rheomolding Process or RP (Thermold s), and the Press Alpha Process or PAP (Sumitomo Heavy Industries and Sankyo Chemical Engineering of Japan) processes are examples of this method. The SP multi-live feed molding process where two packing pistons oscillate 180° out of phase and eliminate weld lines, etc. The RP system provides 3-D orientation based on the concept of melt rheology as a function of vibration frequency and amplitude as well as temperature and pressure. The equipment utilizes piston/type melt accumulators set up adjacent to the melt stream of the plasticator. Piston oscillates back and forth. The PAP system uses compression pins that are... 

While the Exter press uses a reciprocating piston and, therefore, is limited in operating speed, screw extruders do not have this problem. These machines were developed in the second quarter of the twentieth century, mostly for the extrusion of clay and of plastic powders or molding compounds. 

As is known, the low-density polyethylene molding onset temperature under pressure is about 70 °C [21]. Evidently, this mechanical action also influences the density and porosity of a polymeric sample in the course of the molding. Our experiments were performed using the piston and spring producing a pressure 2.6 X 10 N/m. A series of the nanocomposite samples were molded from the same powdered material in the muffle oven at the various temperatures (70, 90,100,110, 120,130, and 150 °C). As a result, we obtained 14 polymeric nanocomposite samples with a 10% concentration of MnO and CdS and 7 pure low-density polyethylene samples molded at the indicated temperatures. A comparison to the pure polyethylene samples revealed the influence of the nanoparticles presence in the polymeric matrix on the density and porosity of obtained nanocomposite materials. Using this technology, it was possible to obtain the flat, parallel disk samples with a thickness of 0.3-1 mm and a diameter of 12-14 mm, which could be readily extracted from the press. 

Tensile bars according to ASTM D-638 were prepared using the HAAKE mini-jet piston injection molder at a temperature of 360 C and mold temperature of 130 C. The injection pressure was 740 bars in each case. Prepared nanocomposites were compression molded into discs of 25 mm diameter and 2.2 mm thickness at 300 C using the Carver 4122 compression molding press, for the rheological measurements. The samples for electrical conductivity measurement were also compression molded into discs of 90 mm diameter and 1 mm thickness. 

Smooth surfaces of each polymer were also prepared (without additives) by pressing samples of the powdered polymers against a highly polished stainless steel surface in a Carver press at 16,000 p.s.i. Circular disks 1 inch in diameter and weighing several grams were formed in this way. PS and the PVeC copolymer were compressed at room temperature, PAM at 120° C.,and PMMA at 150° C. The pressure was maintained until smooth polymer surfaces were obtained. The mold and stainless steel piston were cleaned prior to use, so that contact angles could be measured on the polymer surfaces without further surface treatment. 

---