Industrial Fiberglass Specialties, Inc. (IFS) has developed a hybrid steam manhole cover that includes an insulating layer of fibre reinforced polymer (FRP) composites to prevent burns. As well as making the surface safer to touch, the composite layer—made with AOC's Vipel® vinyl ester resin—is said to make the cover stronger.
The manufacturing process for the cover starts with grit-blasting a coast iron 'dish' to achieve a surface that provides excellent bonding between the composite and iron. The prepared surface is coated with Vipel impact-modified vinyl ester. Next, layers of Vipel resin-impregnated glass fibre are manually applied to build a structural composite.
Before the wet laminate cures into a solid state, the service provider's logo is moulded into the top of the cover. Finally, a skid-resistant coating is applied and a serial number is engraved into the surface. Specifications for the steam manhole cover include:
- A 0.25 in (6.4 mm) thick composite laminate that adds 35 lb (15.8 kg) to the 255 lb (115.7 kg) cast iron dish for a final hybrid cover weight of 290 lb (131.5 kg).
- Diameter of 31.2 in (79.2 cm).
- Can handle traffic loads up to 100,000 lb (45.4 tonnes)—the American Association of State Highway and Transportation Officials (AASHTO) traffic standard specification is 25,000 lb (11.3 tonnes).