Email LinkPOLYURETHANE O-RINGS
Polyurethane is the toughest, most abrasion-resistant, and most extrusion-resistant
of all elastomeric sealing materials. Polyurethane O-rings can handle
pressures up to 5,000 psi with a .010" extrusion gap. Polyurethane
is also very resistant to explosive decompression and has excellent thermal
properties (from -90° F to +225° F). Polyurethane O-rings are
used in a wide variety of products, including quick-disconnect hydraulic
fittings, hydraulic cylinders and valves, pneumatic tools, and CO2 firearms.
When choosing a polyurethane O-ring, keep in mind that its properties are the result of three main factors: 1) the polyol and 2) the diisocyanate used in the compound, and 3) the molding method used to form the seal. Choices made in each of these areas will determine the properties of the finished O-ring. Here's a quick look at your options:
There are nearly 200 polyols available, but three are most common. Polyester polyols resist tearing, abrasion, oil, and long-term heat, but they break down when exposed to water. Polyether polyols have increased water resistance, but their mechanical and heat properties suffer. Polycaprolactone polyols are better mechanically than the polyethers and better in water than the polyesters.
There are also three main diisocyanates used in the production of polyurethane O-rings. MDI is environmentally safer than other diisocyanates and is most widely used in millable gum polyurethanes. TODI lends outstanding thermal properties (up to 250° F) and compression set resistance but is rather costly and difficult to obtain. PPDI contributes outstanding dynamic properties, resilience, and heat resistance to over 275° F, but PPDI is very expensive and in short supply.
Polyurethane is typically processed as either a compression-molded millable gum, a compression-molded cast thermoset, or an injection-molded thermoplastic. Millable gum O-rings offer good low temperature flexibility, as well as resistance to sunlight, ozone, hydrocarbon fuels, and petroleum-based oils. RL Hudson's proprietary cast, thermoset compounds 9272 and 9292 combine polycaprolactone and TODI to provide exceptional heat, compression set, and water resistance. Injection-molded polyurethane O-rings have historically offered the least-favorable properties, but RL Hudson's PPDI-based compound 9800 offers an excellent combination of dynamic properties, resilience, heat resistance (up to 275° F), and compression set resistance.
