Blue PET-P Polyester Piston Disc, CNC Turned and 4-Axis Milled, Food Equipment Rated

About This Part

This disc is the moving seal carrier of a piston in food processing machinery, and the blue color is deliberate: food industry tooling is colored blue because blue does not occur naturally in food, so a fragment is visible in inspection instead of passing unnoticed. The material, PET-P polyester, is chosen for the environment. It is hard and wear resistant, absorbs very little water, and holds its dimensions through the washdown and temperature cycles that swell nylon and degrade softer plastics.

The geometry is a stack of concentric precision. The outside runs 52 mm diameter by 26 mm high, with two seal diameters at 48.70 and 43.20 mm held to h7, 0/-0.03 mm, and a seal ring groove no narrower than 3.10 mm cut into the sidewall. Coaxiality between the seal surfaces is held within 0.02 mm to datums A and B, because an eccentric seal groove wears the ring unevenly and leaks. The face carries a horseshoe shaped U guide slot, 14 and 20 mm wide at +0.15/+0.05 mm, around a central stepped bore with R3, R7 and R18 transitions; the back is a deep recessed seal cavity.

Plastic machining discipline shows in two places. PET-P cuts cleanly but grabs: dull tools and slow surfaces smear it instead of shearing it, so the disc is turned and milled with high rake tooling at high speed with cold air cooling. And clamping is gentle: plastic takes a set under jaw pressure, so the disc runs in soft jaws turned to its exact diameter, and the sequence lets each operation's stress relax before the next dimension is cut.

Burrs are the other tell of plastic work. U slots and side grooves raise fine flashing at every tool exit, so edges are hand finished under magnification. The disc is then ultrasonically cleaned and dried, and verified on the CMM for the h7 seal diameters, the 0.02 mm coaxiality and the slot widths, with a surface roughness check of Ra 1.6 in the seal groove.