1. The goal of roof control From the current technical level, there are three reasonable roof control targets for the single hydraulic strut working face: firstly, it can eliminate the hidden dangers of pressure, leakage and pushing top to minimize the occurrence of various types of roofing accidents; It can keep the top plate bottoming amount, the step sinking amount and the end face height and other top plate state parameters within a certain limit to ensure that the top plate is in good condition; third, the required cost is the least. In order to achieve the above first goal, from the fact that the current roof accident is mainly a push-type roof, the initial support force of the single hydraulic prop should be increased as much as possible. In order to achieve the above second goal, daily support quality and roof dynamic monitoring or pressure regulation tests must be carried out in production practice. In addition, the minimum cost should be considered if the first and second goals are met. 2. Principle of roof control Starting from the goal of roof control, the principle of roof control of the single hydraulic strut working face is as follows: (1) The principle of “support†for the rock formation in the fallen belt, that is, the working resistance of the stop pillar should balance the weight of the working space and the rock formation above the goaf; the initial support force of the stop pillar should be balanced. The space and the falling zone above the goaf are directly at the top of the rock; (2) The principle of “letting†is adopted for the fractured strata, that is, the shrinkage of the stop of the stope should be able to adapt to the sinking of the fracture zone; (3) When the thickness is less than 1 times the immediate roof mining high, especially when the coal seam is not directly above the roof of the thickness, the principles can be "cut" taken off above the old headspace region; (4) When the direct top thickness is less than 1 time, the top picking height can be picked up by the principle of “pickâ€. Roof thick plate of hard, loose chipping should be taken 3 times higher layer of roof; with a drilling or working side measures before blasting or high pressure water is Weakening, or mining pick top 3 times higher in the mined-out area; These measures can also be collectively referred to as "picking"; (5) Regardless of the type of roof, the problem of "protection" should be considered for the stability of the direct roof; (6) Regardless of the type of top plate, if it is a composite top plate, the initial support force of the pillar itself should be prevented. JIS B2220 is Japanese flange standard, pressure 5K, 10K, 16K, 20K, 30K and more, flange type Plate Flange, Blind Flange , hub flange, Weld Neck Flange, sealing face raised face RF, flat face flange FF, popular using 5K FF flange, 10K FF flange, 10K RF flange, 16K SOhub Flange, 20K Hub flange, carbon steel for SS400 SS275 Q235 A105 jis 5k flanges, jis 10k flange, jis 16k flanges, jis 20k flanges, jis b2220 flanges manufacturer Jinan Hyupshin Flanges Co., Ltd , https://www.iflange.com