It is clearly very important to ensure that there is as much friction as is needed between fasteners. However, how do you go about ensuring that it&#;s actually enough? The main method of verifying this is through the use of torque. Torque is a measure of the rotational force that a material is subjected to. When you install a fastener using higher levels of torque, it&#;s likely to be exposed to more friction. This in turn means that you will benefit more from all the above.
However, you need to be careful with this, since having too much torque is also associated with a few problems. The most important one is the fact that the fastener may end up becoming damaged, and will then become loose. In addition to that, when the torque surpasses the plastic limits of the metal, it&#;s likely to lead to breaking of the shafts of fasteners such as steel socket head cap screws and Inconel hex head cap screws.
Link to TRM
Other measures you can take include making sure that you use washers during the installation of the fasteners. You may also need to pay attention to the guide holes through with the fasteners are used. When the guide holes are of the right size, it&#;s much easier to maintain the right amount of friction, which will in turn ensure that the fasteners stay in place for long.
All in all, friction is something that you should pay attention to when installing fasteners. Using the tips above, you can then get the most out of it without compromising the structural integrity of the fasteners in question.
It is worth noting in the figure that the direction of #friction FF is reversed when tightening and loosening bolts. This is a unique feature of #screw connections.
When #tightening , friction consumes most of the torque, which causes adverse effects. Still, after assembly, it is necessary to factor in to ensure that the bolted connection does not loosen. Friction F depends on the normal force FN and the coefficient of friction μ, the formula equation: FF=μ*FN.
The magnitude of the coefficient of friction u depends on many factors.
In addition to the normal force FN, the most important thing is the surface roughness (Figure 2), which serves as an arithmetic mean deviation Ra[um] to evaluate the profile. This situation exacerbates the presence of hard non-metallic impurities, corroding surfaces, and temperatures.
Roughness is essential in the interface between a real object and its environment. In tribology, rough surfaces generally wear out faster than smooth surfaces and have a higher coefficient of friction.
Depending on the surface finish technique, roughness can appear in any orientation or as an undefined projection arranged out of order (Figure 2).
You must overcome thread friction and friction under the screw head and nut when tightening the #connection . The higher the roughness, the greater the conflict, and the more energy is expended to overcome the friction (Figure 3).
The effect of friction on bolted connection tightening is also documented in Figure 4. The same 65Nm torque will generate a preload of about 18kN for the new #bolts and #nuts , while for corroded surfaces, this is only 30% left. The remaining energy is used to overcome friction and be converted into heat.
Friction after threaded connection assembly is also necessary. Without conflict, the entire structure disintegrates. It is friction that makes the screws join together. The associated, connected nodes will be destroyed without friction and eventually collapse. This is shown in Figure 5. When the correct assembly and size are selected, the screw connection usually does not require an external, i.e., additional safety measure.
The company is the world’s best Friction Bolt supplier. We are your one-stop shop for all needs. Our staff are highly-specialized and will help you find the product you need.
The effect of friction on anti-loosening
When the static load and operating temperature change are not large, the fastening thread connection will not automatically loosen, and its link is very reliable.
If the thread connection works in the environment of shock, vibration, variable load, or high temperature and temperature change, especially under the repeated action of transverse force (alternating stress), the thread will undergo elastic torsional deformation. There is a relative slip perpendicular to the direction of the thread axis between the contact surfaces of the part. The torsional displacement gradually accumulated, forcing the spiral pair to slide down in the winding order, reducing the preload or even disappearing and loosening the threaded connection.
In the case of a specific clamping force, to improve the self-locking ability, it is necessary to increase the bolt's friction capacity under limited conditions (such as the nominal diameter of the bolt, the friction coefficient of the surface of the corresponding parts has been determined). Only the friction coefficient of the thread pair and its surface can be increased, such as by replacing the hexagonal head bolt with a hexagonal flange face with teeth to increase the friction of the thread auxiliary bearing surface.
To avoid loosening the thread pair, select the appropriate preload during the design process. That is, you should choose the correct bolt.
The thread pair structure bearing lateral load is more in most of the existing product structures. And the anti-loosening method of increasing the friction torque of the thread pair is the most widely used, such as the fixing bolts of the automobile control arm and the subframe.
The test shows that increasing the radius and surface roughness of the thread pair bearing surface can increase the friction torque, and when its lateral load is less than the friction force, the thread pair will not #loosen.
However, in actual production, there are many cases of extreme dynamic loads (fig 6) where simple locking is no longer sufficient, so it must protect the bolted connection from loosening utilizing an external lock.
As shown above, friction is significant for bolted connections. It determines the tightening parameters and prevents the bolt from spontaneously loosening. However, these two functions are contradictory. Conflict is undesirable, But after tightening, we need friction. Otherwise, the screw connection will lose its position.
Increasing the friction torque of the thread pair is the most widely used anti-loosening method. It should also combine the actual production with the force analysis of the corresponding parts to determine the load mode it is subjected to, such as axial load, lateral load influence, etc., and select the appropriate anti-loosening method.
For more information, please visit Mesh Bolt.