In modern production, many structural elements are used, each of which performs a certain function in the final product, most often very important. Therefore, one of the tasks in the design and manufacture of complex composite structures is the reliable fixation of the parts relative to each other.
Purpose of use of bolt
There are many options for joining two products, for example, welding, soldering, gluing, using rivets. However, they have one common and quite significant drawback - they are all inseparable. More precisely, detachable, however, to separate the parts will have to be deformed, cut, and so on.
It is much more convenient to use a threaded connection as fasteners, having previously selected the strength class of the bolt depending on the load imposed on the assembly.
Carving is used in almost all designs that are slightly more complicated than a regular teaspoon. Just imagine a car in which there is not a single screw. But what about the car - in a children's toy, the structural strength class of which is much lower, you still can not do without threaded elements.
Threaded joint benefits
Despite the fact that sometimes a large tightening torque does not allow after some time to freely unscrew the nut, the bolt still has a number of advantages over other mounting methods:
- High reliability of the connection, provided by the universality of the profile of metric or any other thread. The profile has been developed thanks to a lot of research, therefore it can withstand heavy loads and is protected from self-unscrewing (though for this you will have to choose the right tightening torque).
- Convenience of installation and dismantling of structures. It is provided by using a unified service tool - wrenches, wrenches, which cannot be said, for example, about welding or riveted joints.
- The ability to create large axial and lateral loads. The strength of the bolt is calculated both in the longitudinal and in the transverse direction. Modern materials and technologies can reduce the number of fasteners used and reduce its size.
- Low cost, especially when compared with the cost of the purchase of welding materials and work.
Among the disadvantages of the connection is the stress concentration in the region of the trough of the thread profile. Therefore, for a certain type of structure, it is necessary to choose the strength class of the bolt in accordance with the applied load. Also, to ensure the reliability of the threaded connection, it is worth remembering the use of locking means, for example, spring washers or locknuts.
Types of threaded connections
In order for the screw connection to exist, it is necessary to make an internal thread on one part, and an external thread on the second. Depending on the design features, three varieties can be used:
1. Screw connection. In this case, the part of the assembly plays the role of a nut (parts with internal thread). First, a hole is drilled in it. And then the thread is applied. Another with a smooth round hole is applied to the part, after which it is attracted by a screw.
2. Bolted. Everything is much simpler and more reliable here: smooth holes are drilled in both parts to be connected, a bolt is inserted into them, and a nut is inserted from the back.
3. On studs, one end of which is screwed into the part of the assembly, and a nut is screwed on the other.
Bolt strength class
As noted above, fasteners must be properly selected. It makes no sense to use
alloy steel parts in the usual shelf frame for service tools
. At the same time, in some
flange joints (for example, tightening the constituent parts of multi-ton metal structures), materials with improved mechanical characteristics are required.
In general, the strength class of a bolt (GOST 1759.4-87) is a whole complex of mechanical characteristics, which simultaneously includes tensile strength, yield strength, relative elongation after rupture, material hardness, and in some cases even toughness. As a rule, two digits separated by a period are used to indicate this parameter. The first of them, after multiplying by 10, shows the minimum value of the temporary resistance, and the second, also increased by 10 times, shows the proportion obtained by dividing the yield strength of the material by the temporary resistance. The product of these two digits will indicate the value of the minimum yield strength. The strength class of the bolt is contained in its marking, which is as follows: M12x1.25x60.58, where 58 is the same two-digit number.
Bolt tightening
In order for the threaded connection to reliably hold structural elements, it is worth paying close attention to the torque (torque). So, imagine a situation when an inexperienced "car mechanic" first falls under the hood of his own brand new car and tries to tighten the nut or screw as tightly as possible. All this can end in the first case with simply inconvenient work with a chisel, and in the second - with a hole in the body. This is due to incorrect tightening torque. Experienced car mechanics, and just repairmen, have a dynamometer built into the hand. But for a novice it is best to use a torque wrench or a pneumatic wrench, which can be adjusted for a specific tightening torque.
How to unscrew a "difficult" bolt
Let's say everything turned out to twist. But time passes, and the fasteners need to be unscrewed again. Due to corrosion, it is sometimes not very easy to do, and the high strength class of the bolt does not save it from destruction. Therefore, it is worth keeping in mind a few simple ways that simplify the unwinding:
1. First, you should use the VeDeshka. The composition dissolves the rust layer.
2. Gently tap the nut with a hammer to break the rust in the thread profile.
3. You can try to turn the nut a couple of degrees in the direction of twisting, and then unscrew.
It is important not to rush, as it is highly likely to stay with the nut or screw head in the key.