Machined plastic parts to your print

The resin and its grade, because PTFE alone covers virgin, glass-filled, carbon-filled and bronze-filled materials with very different wear and creep, and PEEK and nylon come unfilled and filled too. Add the tolerances with the temperature they are measured at, since plastics grow with heat and nylon also swells with moisture, and note any surface finish, color and certification the part needs. A STEP file for the shape and a PDF for the tolerances is the ideal pair.

PTFE for chemical inertness and low friction, but it creeps under a steady load and has hardly any elastic recovery [S1]. PEEK for strength against extrusion, in seats, back-up rings and bushings that a softer plastic would deform [S1]. UHMW polyethylene for wear resistance [S1]. Nylon and acetal cover general bushings, spacers and wear parts at everyday temperatures.

Yes. SAE AS8791 is the document for PTFE back-up rings in hydraulic and pneumatic service [S2], and Parker's O-ring handbook cross-references the military back-up ring numbers by cut style, among them MS27595, continuous, and MS28774, single turn with a scarf cut [S3]. The rings come from manufacturers that make to the part number on your print, and the backup rings page lists the families with their sources. In the groove a back-up ring adds its own thickness to the groove width, with the ring on the low-pressure side of the O-ring, and two rings where pressure comes from both directions.

Tighter than rubber, looser than metal, and always tied to temperature. Plastics expand far more than steel, PTFE creeps under sustained load, and nylon swells as it takes on moisture, so a tolerance is only meaningful with the measuring temperature and conditioning stated on the drawing. The shops we source from quote to the tolerances on your print; if a feature is tighter than the material can hold in service, the quote says so before the parts are made.

In some jobs, yes. Where an O-ring extrudes, swells or runs dry, a PTFE or PEEK seat or back-up ring takes the load the rubber cannot, and PTFE seals handle chemistry and dry running that elastomers do not. The trade is that PTFE has no elastic recovery, so a plastic seal needs a groove made for it or an elastomer energizer behind it, which is why many high-pressure and rotary seals are a plastic face with a rubber spring.

A seal ring turned from a plastic tube or rod instead of being molded, usually in PTFE, filled PTFE, PEEK or UHMW. It suits materials that are not molded to shape, sizes and profiles no maker molds as standard, small quantities and seals that are out of production; the shops we source from machine it to your drawing.

No. A machined seal is a single ring or lip cut from plastic stock, while a mechanical seal is an assembled face seal that seals a rotating pump or mixer shaft. Mechanical seals have their own page.