Steel Hatches

General Information

Platen (plate shaped) lids are improved manhole covers, which are pound
per pound stronger than ribbed lids. Advantages of lighter weight, platen lids include:
- Increased load capacity
- Increased deflection resulting in increased energy absorption
- Decreased weight
- Easier to handle
Manhole frames have an inherently strong shape. In the past, metal sections had to be thicker because foundry molding equipment was imprecise. To compensate, generous tolerances were required to ensure minimum section thickness. 

Today’s molding machines are capable of holding tight tolerances, allowing specifiers to reduce weights and section
thicknesses. Technology now allows modern construction casting manufacturers to take advantage of the frame’s inherently
strong shape.

Modern frames are significantly reduced in weight and section thickness, without a reduction in relevant performance characteristics.

Lighter frames are viable because gray iron is stronger in compression than in tension. The lighter frames are still so
substantial that, under load testing, gray iron covers will fail well before failure of the frame.