According to the appearance: the manhole cover is generally divided into ring square. The circumcision laser cutting is generally used in the traffic law enforcement level of the urban area. Because the annular manhole cover is easy to skew, it can well maintain the safety of non motor vehicles vehicles. The application of ring is mainly to fully consider the annular manhole cover. According to the diameter of the center point of the ring, the diameter of the manhole cover is slightly wider than that of the lower shaft no matter how rolled up, it is easy for the manhole cover to fall into the well bore.
If a square is selected, because the straight line of the square is obviously good at one of its perimeter, when the manhole cover is rolled up, the imported laser cutting is very easy to fall into the well along the linear direction of the wellbore, leading to safety risks. If the wellbore is annular significantly lower than the manhole cover, the square manhole cover is easy to fall into the well. Here is a problem of large use saving of raw materials. The application of the shaft lies in the size of the shaft. If it is necessary to install a square manhole cover with a total area far greater than the shaft, then the use practical significance of raw materials are immediately more reasonable, which only saves the raw materials of the manhole cover, but also ensures the safety of the shaft.