Welding manhole frames generally have circular and square type. In the aspect of urban road administration, is generally circular, because the manhole frame is not easy to be inclined, which can better protect the safety of pedestrians and vehicles. Round use is mainly considered that each diameter of the manhole frame is the same, so that if the manhole cover is rolled by the passing vehicle, because no matter how rolled, the diameter will be slightly wider than the manhole mout, the manhole cover will not fall into the manhole.
If the square ring is adopted, because the diagonal of the square is obviously longer than each side long, when such a square frame is rolled, it is easy to fall into the manhole along the diagonal direction of the manhole, causing safety risks.If the manhole is made round or significantly less than the manhole cover, the square manhole cover will not fall into the manhole.Here a question of the use and conservation of the material is involved.The use of manhole covers depends on the size of the manhole. If you need to install a square manhole cover with an area far greater than the manhole, then the utilization and practical value of materials are not more effective as the circular manhole cover, which not only saves the materials of the manhole cover, but also ensures the safety of the manhole.