基本拧紧技术-福田剖析.ppt

基本拧紧技术 致：福田汽车 演讲人：陈佳华 联系方式：手 邮箱howard.chen@ 1.扭矩，摩擦力和夹紧力 扭矩，摩擦力和夹紧力 生产装配的几种方法 焊接 胶合 铆接 螺栓连接 为什么使用螺栓连接 50-40-10 规则 弹性松弛会影响夹紧力 软连接和硬连接 软连接、硬连接 软、硬连接 动态扭矩和静态扭矩 小结 各种力的关系 软硬连接 动静态扭矩 We do not measure the clamping force. The best would be to measure the clamping force directly. Pressure sensitive gaskets are used in, for example, nuclear power industry and manufacturers of large diesel engines. The problem is that one of those gaskets costs 10-100 USD. Instead we use the relationship between applied torque and the clamping force. The clamping force is linearly dependent on applied torque. BUT it is important that the friction stays approximately the same from bolt to bolt. (90% is friction). Why torque? The reasons for measuring the torque are mainly historical. In the past products tended to be over engineered, so the control of torque was considered sufficient. Also, most quality checks have been made separate from, and after, the assembly operation. Then torque is easy for quality people to measure. It is more difficult to use a pressure sensitive gasket afterwards... Elastic and permanent deformation – yield. Tightening too much will stretch the screw until it breaks. This means that when using torque controlled tightening the final torque allways has to be set in such a way that you never reach the yield point. Joint relaxation (creep) occurs to some extent in all joints and is caused by the parts in the joint collapsing under the clamping force. Relaxation is a particular problem on joints where gaskets or spring washers are present. On these joints it can take a long time before the joint settles and the result is that the clamping force is reduced until the conditions are stabilised. Solution: The joint can be retightened once the creep has stabilised. The fastener can be tightened to a high torque, then undone and finally retightened to the correct torque. In most joints 60-70% of the creep occurs within 30 ms. That means that you can do t