Everybody knows that manhole covers generally stay on roads or pavements, and thus must be strong enough with high load ability to withstand vehicles and pedestrians. Over 95% of manhole covers are made from cast iron. There are some problems associated with manhole covers,which includes the fact that cast iron material are useful material with economic value. So cast iron manhole covers are often stolen, melted down and sold on the black market. Once covers are stolen, the open holes will cause a serious accident. That’s the direct reason why plastic manhole covers are of big market.
The different materials used within the manufacturing process included rejects of thermoplastics(or recycled thermoplastics),foundry sand,and steel bards for reinforcement. In no question,recycled thermoplastics can reduce production cost and bring more profit for factories. In China,most manufacturers like to use recycled thermoplastics to create price advantage in competition.
Read below diagram of plastic rejects for manhole covers products to understand more easily.
Why do most plastic manhole covers need to use steel bar inside?
A steel mesh is incorporated in the manhole cover to enhance the mechanical properties of the manhole covers. The steel mesh included 10% reinforcement of the total volume of the manhole cover. The genuine composite manhole cover shouldn’t use steel bar inside,but most manufacturers still not master the techniques how to abandon steel bars to let it keep same high load ability.