Why should high-strength bolts be worn from bottom to top?

塔機上φ16以上的螺栓都是高強螺栓，這是因為塔機各部件的聯(lián)結(jié)都是摩擦型聯(lián)結(jié)或是銷軸聯(lián)結(jié)（軸銷聯(lián)結(jié)對鋼結(jié)構(gòu)制造精度要求很高，一般都是螺栓聯(lián)結(jié)），普通螺栓的強度不夠，只有高強螺栓才能滿足摩擦型的預(yù)緊力要求。所有的螺栓和銷軸都不得松動，因為一旦松動，就不能滿足摩擦型聯(lián)結(jié)的要求（保證少70%的接觸面），也就是僅靠螺栓自身的強度來把塔機聯(lián)成一體，傳遞力矩，不能達到強度要求，且晃動后受力更加復(fù)雜和更大，螺栓不僅要承受拉力，還要承受剪切力（螺栓的套管直徑比螺栓直徑大，有間隙。）。由于塔機工作的特性，塔機上所有結(jié)構(gòu)件和螺栓、銷軸都是受的交變力。因此，塔機螺栓的防松都是雙螺母防松。其它的防松措施都不能在交變力作用下保持防松效果。明白了這些就可以理解我們以前討論的《高強螺栓的穿裝方向》，從下往上穿。盡管沒有明文規(guī)定，但很多安裝單位都有自已的安裝規(guī)范，規(guī)定從下往上穿。

Tower crane φ More than 16 bolts are high-strength bolts, because the connection of all components of the tower crane is friction type connection or pin shaft connection (the shaft pin connection has high requirements on the manufacturing accuracy of steel structures, and is generally bolt connection). The strength of ordinary bolts is not enough, and only high-strength bolts can meet the requirements of friction type preload. All bolts and pins shall not be loosened, because once loosened, they cannot meet the requirements of friction type connection (ensuring at least 70% of the contact surface). That is to say, only the strength of the bolts themselves can connect the tower crane together and transmit torque, which cannot meet the strength requirements. Moreover, after shaking, the stress is more complex and greater. The bolts must bear not only tensile force but also shear force (the diameter of the sleeve of the bolts is larger than the diameter of the bolts, and there is a gap). Due to the working characteristics of the tower crane, all structural members, bolts and pins on the tower crane are subjected to alternating forces. Therefore, double nuts are used to prevent looseness of tower crane bolts. Other anti loosening measures can not maintain the anti loosening effect under the action of alternating force. Once you understand these, you can understand the direction of high-strength bolts we discussed earlier, from bottom to top. Although there are no explicit provisions in the country, many installation units have their own installation specifications, which stipulate that they should be worn from bottom to top.

我們先討論為什么從上往下穿不好。從上往下安裝很方便快速，但易漏上和漏擰螺母。漏上和漏擰螺母和不上螺母的危害區(qū)別不大（我們不再展開討論）。這就是很多安裝單位禁止螺栓從上往下穿的原因之一，就是您對孔時從上往下穿，上螺母時也要求卸掉重新從下往上穿再預(yù)緊緊固。漏擰螺母的危害太大了。

Let's discuss why it's not good to wear it from top to bottom. It is convenient and fast to install from top to bottom, but it is easy to miss the nuts. There is little difference between the hazards of missing nuts and missing nuts and those of missing nuts (we will not discuss them again). This is one of the reasons why many installation units prohibit bolts from being threaded from top to bottom, that is, when you align holes, you should thread them from top to bottom. When you install nuts, you also need to remove them and thread them from bottom to top again before pre tightening them. The danger of missing nuts is too great.

還有一個原因就是，從上往下穿時，當套管孔沒對好時，一敲就硬擠進去了，雖然方便但易傷螺牙和螺桿，也就是這個螺栓應(yīng)該受傷報廢禁止繼續(xù)使用。而從下往上穿，只有對好孔后才能穿進去，很少會傷到螺牙。

Another reason is that when threading from top to bottom, when the casing hole is not aligned properly, it will be forced in by knocking. Although it is convenient, it is easy to damage the screw thread and screw rod, that is, the bolt should be damaged and scrapped. It is forbidden to continue to use. And from the bottom to the top, it can only be inserted after the holes are aligned, which rarely hurts the screw teeth.