Bolted joint for Nuts And Screw

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Bolted joint

Screw joint

Stud joint
Bolted joints are one of the most common elements in construction and machine design. They consist of cap screws or studs that capture and join other parts, and are secured with the mating of screw threads.
There are two main types of bolted joint designs. In one method the bolt is tightened to a calculated clamp load, usually by applying a measured torque load. The joint will be designed such that the clamp load is never overcome by the forces acting on the joint (and therefore the joined parts see no relative motion).
The other type of bolted joint does not have a designed clamp load but relies on the shear strength of the bolt shaft. This may include clevis linkages, joints that can move, and joints that rely on locking mechanism (like lock washers, thread adhesives, and lock nuts).
Contents
1 Theory
1.1 Thread strength
2 Setting the torque
3 Property class
4 Failure modes
5 Locking mechanisms
6 Measurement of frictional torque of threads in bolt
7 Bolt banging
8 International standards
9 See also
10 References
10.1 Notes
10.2 Bibliography
11 External links
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Theory
The clamp load, also called preload, of a cap screw is created when a torque is applied, and is generally a percentage of the cap screw's proof strength. Cap screws are manufactured to various standards that define, among other things, their strength and clamp load. Torque charts are available that identify the required torque for cap screws based on their property class.
When a cap screw is tightened it is stretched, and the parts that are captured are compressed. The result is a spring-like assembly. External forces are designed to act on the parts that have been compressed, and not on the cap screw.
The result is a non-intuitive distribution of strain; in this engineering model, as long as the forces acting on the compressed parts do not exceed the clamp load, the cap screw doesn't see any increased load. This model is only valid when the members under compression are much stiffer than the capscrew.
This is a simplified model. In reality the bolt will see a small fraction of the external load prior to it exceeding the clamp load, depending on the compressed parts' stiffness with respect to the hardware's stiffness.
The results of this type of joint design are:
Greater preloads in bolted joints reduce the fatigue loading of the hardware.
For cyclic loads, the bolt does not see the full amplitude of the load. As a result, fatigue life can be increased or, if the material exhibits an endurance limit, extended indefinitely.
As long as the external loads on a joint don't exceed the clamp load, the hardware doesn't see any motion and will not come loose (no locking mechanisms are required).
In the case of the compressed member being less stiff than the hardware (soft, compressed gaskets for example) this analogy doesn't hold true. The load seen by the hardware is the preload plus the external load.
Thread strength
Nut threads are designed to support the rated clamp load of their respective bolts. If tapped threads are used instead of a nut, then their strength needs to be calculated. Steel hardware into tapped steel threads requires a depth of 1.5 thread diameter to support the full clamp load.
If an appropriate depth of threads is not available, or the threads are in a weaker material than the cap screw, then the clamp load (and torque) needs to be derated appropriately.
Threads are usually created on a thread rolling machine. They may also be cut with a lathe, tap or die. Rolled threads are about 40% stronger than cut threads.
Setting the torque
Engineered joints require the torque to be accurately set. Setting the torque for cap screws is commonly achieved using a torque wrench. The required torque value for a particular screw application may be quoted in the published standard document or defined by the manufacturer.
The clamp load produced during tightening is higher than 75% of the fastener's proof load. To achieve the benefits of the pre-loading, the clamping force in the screw must be higher than the joint separation load. For some joints a number of screws are required to secure the joint, these are all hand tightened before the final torque is applied to ensure an even joint seating.
The torque value is dependent on the friction between the threads and beneath the bolt or nut head, this friction can be affected by the application of a lubricant or any plating (e.g. cadmium or zinc) applied to the screw threads. The screw standard will define whether the torque value is for a dry or lubricated screw thread. If a screw is torqued rather than the nut then the torque value should be increased to compensate for the...(and so on) To get More information , you can visit some products about chi hair straightening iron, doorbell intercom, wood executive desks, multimedia car stereo, gps auto navigation system, welding hood, camera baby monitor, hydraulic pressure gauge, pda car charger, medical sterilization, . The metal brad products should be show more here!