Bolt loosening problem is increasing. Where is the fastener anti-loose way out?

Q: Why are the problems of loose bolts increasing?

A: Thread loosening is one of the main reasons for loose bolts. Thread slack can cause preload loss and can be divided into three categories: thread slack caused by settling, thread slack caused by surface slack, or thread slack (creep) caused by temperature changes.

The occurrence of settlement is related to the roughness and irregular construction of the surface. After the pre-tightening force is applied, the surface of the clamped portion will generate pressure, causing the irregular structure of the thread surface to begin to flatten. When the irregular surface is completely flattened, this part becomes loose and the pre-tightening force begins to decrease. If the preload is reduced to a sufficient extent, the bolted connection may loosen. Low preload also increases the risk of fatigue damage.

If the degree of compression of the material is increased over a period of time, slack occurs, resulting in further loss of preload. This is often the case with materials such as polymers, composites, copper and other soft metals.

Creep refers to the slow movement of solid materials or permanent deformation under the influence of external pressure. Creep occurs when the material is subjected to pressures below the yield strength of the material for extended periods of time. If the material is heated for a long time and the temperature is close to the recrystallization temperature, the creep will be more severe. The creep condition always doubles as the ambient temperature increases.

Today, more bolted connections are exposed to more extreme environments such as high speed, high temperature and high load conditions. If the parts are also produced in "old-fashioned" steel, they can be very cumbersome. In order to reduce the total weight, today's parts are made of synthetic materials, plastics and aluminum, which is the reason for the increasing problem of thread slack. Nord-Lock's X-series washers are designed to handle thread slack and help designers perfectly solve the problem of thread slack at the bolted joints.