The Tighter The Bolt, The Better?

When fixing mechanical equipment, many people will screw the bolts until they can’t be screwed. Is this a good way? Well, not really. It is also said that the bolt should be pulled back half a circle after tightening, so as to be tight. Is this statement right? Is there any science behind it? In fact, there are a lot of people in life who think so, where is the scientific basis? As a professional fastener manufacturer, Xinchi Fastener Company has more than ten years of experience in the fastener field, we are happy to answer this question.

Should the bolts be tightened as tightly as possible? Or is it better to tighten back half a turn?

A screwed bolt is acted upon by two forces, one downward and one upward. The bolt rotates down the thread, creating a downward axial force in contact with the thread.

At the same time, there is an upward force corresponding to the downward axial force, which is generated by the upward distribution of the nut in contact with the plane below. The two forces of a tightened bolt should balance each other. Because of the function of bolts, the material of bolt manufacturing has two requirements, one is rigid, and the other is toughness, both of which are indispensable.

But all ductile materials have one thing in common, that is, there is a limit to stress. In mechanics, this limit is represented by a stress-strain curve. There is no need to go too far. We just need to know that in the process of screwing the bolt, as an elastic part, the elasticity of the bolt will come into play.

As the bolt is tightened gradually, the elastic action of the bolt will approach a limit. Once this limit is broken, the bolt will enter the yield stage from the elastic stage.

Once the bolt enters the yield stage, it will cause permanent deformation, which is irreversible, that is to say, the bolt will fail. In real life, when we keep tightening the bolt, there will be a trip phenomenon, which is caused by this reason. And once the bolt snaps, it’s impossible to screw it back on because it’s permanently deformed.

So, when we screw a bolt, do we really need to tighten it and back it half a turn? No. As we said, when the bolt is screwed, once the limit is breached and the yield stage is reached, the bolt will be permanently deformed, at which point it is no longer useful to go back half a turn. On the contrary, the back bolt loses some of its toughness and is more likely to break.

If the bolt is not tightened to the limit, then a half-turn back is not necessary, as it will only loosen the bolt.

When can the bolt return half-turn after tightening?

It should be known that untightened bolts will become looser and looser during use due to vibration. So no matter whether the bolt is tightened to break the limit, it is harmful to return half a circle. The one exception, of course, is when there are washers. Sometimes the bolts are fitted with washers.

So what is the purpose of this thin, circular piece of metal? In fact, the function of the metal plate is equivalent to a spring, the purpose is also to increase the elasticity. The purpose of increasing the elasticity is to make the whole component stronger. However, as a spring component, the bearing capacity of the washer is also limited. Springs deform when squeezed and recover when the pressure is removed due to their elasticity, but there is a limit to their resilience.

When the pressure borne by the gasket is too large to exceed the limit, its role as a spring will disappear, so the existence of the gasket is redundant.

In order to maintain the elastic effect of the gasket and make the whole component stronger, after tightening the bolt, we can return it half a circle, so as to maintain the elasticity of the gasket, which is more conducive to the robustness of the whole component. The only way to do this is to make sure that the bolt is not too tight and deformed.

So how do we make sure the bolts aren’t tightened too tightly? In precision instrument manufacturing, we use torque wrenches that can measure force, but in daily life, this is unnecessary. In daily life, screwing bolts mainly depends on experience and feel. In addition, don’t be manipulated by obsessive-compulsive disorder. Don’t keep twisting.

Xinchi Fastener Company is a trustworthy fastener company, especially in furniture nuts. And we are the designated fastener supplier to“STAPLE”. As a trusted fastener supplier,  Xinchi Fastener Company can offer a wide range of high-quality fasteners, including tee nuts, screws, bolts, rivets, washers, etc. If you want to know more about fasteners or want to wholesale fasteners, please feel free to contact us. And then our experienced and expert service team will reply to you as soon as possible.