... the high-strength W-SMC manhole cover and water grates researched and developed by the company in 2009. ... the base material.The products are shaped like iron plates with a hard texture,and have made up ... 3. Light WeightIt weight only 1/3 of cast-iron manhole cover, more expediently transport, install, and rush ... its under. It gets over the problem of cast-iron and cement manhole cover run, jump, sound. It ...