Machining parts from rods, sheets, or hollow forms provides an alternative to injection molding for producing heavy walled parts (not possible by injection molding), or to avoid mold construction costs for smaller production quantities or prototyping. Large stock shapes made from our Ryton^® PPS injection molding compounds are not available because the injection molding compounds are not suitable for producing thick forms.

Several sources supply compression molded PPS rod, plate, and tube stock (see the list of Specialty Compression Molders below), but it is important to understand that parts machined from compression molded PPS rods, sheets, or hollow forms will likely not perform the same as parts injection molded from Ryton^® PPS injection molding compounds. There are several reasons for this. First of all, since Ryton^® PPS injection molding compounds are generally not suitable for compression molding, those processors typically purchase raw PPS polymers and blend them with their own combinations of fillers and other additives, formulating compounds that are different from our injection molding compounds. Furthermore, in the compression molding process the PPS compound is subjected to an entirely different heat and stress history than is encountered in the molding of articles from injection molding compounds, and the frictional heat of machining operations can also cause development of localized stresses. Being a semi-crystalline thermoplastic, PPS is notch sensitive, so surface defects from machining operations may act as crack propagators and compromise the mechanical strength of a part. Finally, the machined surface, with fillers and reinforcements exposed, is more prone to abrasion and more susceptible to fluid penetration than a "resin rich" molded surface.

Unlike injection molded parts, the mechanical properties of compression molded PPS stock materials are generally more isotropic due to a more random filler distribution and/or glass fiber alignment. The mechanical strength of compression molded PPS stock materials will typically be no more than 50% to 80% of the strength of Ryton^® PPS injection molding compounds with similar filler systems, and the effects of machining can dramatically reduce part strength even further. But, the compressive properties, dimensional stability, thermal stability, and chemical resistance of compression molded PPS stock materials should generally be similar to Ryton^® PPS injection molding compounds with similar filler systems. The exposed fillers and reinforcements on a machined surface, however, make the part more prone to fluid penetration, so chemical exposure may tend to cause more swelling and more rapid strength deterioration. The electrical properties of compression molded PPS stock materials should typically be about the same as Ryton^® PPS injection molding compounds with similar filler systems. Bear in mind, however, that some Ryton^® PPS injection molding compounds are specially formulated to enhance certain performance characteristics such as impact resistance, electrical properties, and hydrolytic stability.

SPECIALTY COMPRESSION MOLDERS

Quadrant Engineering Plastic Products
Reading, PA, USA
TEL: 610-320-6600
FAX: 1-800-366-0310

EGC Corporation
Houston, TX, USA
TEL: 281-774-6100
FAX: 281-774-6219

Ensinger Special Polymers, Inc.
Houston, TX, USA
TEL: 713-683-1032
FAX: 713-683-9719

Hoerbiger America Rings & Packing, Inc.
Houston, TX, USA
TEL: 713-224-9015
FAX: 713-224-7527

Tetralene, Inc.
Houston, TX, USA
TEL: 713-695-4011
FAX: 713-699-0479