Screws are used for fixation. Once they become loose, they lose their function. So, what should be done if screws keep loosening? Let’s take a look together.
I. How to deal with loose screws
It might be that the screws are damaged. Once screws are deformed or stripped, it will affect the preload force and thus cannot be tightened well. At this time, you can add an external spring washer to increase the friction force, or inject glue to fix and bond them to prevent loosening. For screws with load-bearing functions, regular checks are needed. Once they become loose, they should be tightened in time.
II. How to Remove Rusty Screws
1. Knocking
For severely rusted screws, even if you force them with a wrench, it’s very difficult to remove them and they are prone to breaking, leaving a part stuck. In such cases, you can first strike the rusted part a few times with a hammer, preferably in different directions. This will loosen the screw, and then you can remove it more easily with a wrench.
2. Oil Dripping
If the rust is not too severe, you can drip some cooking oil or lubricating oil on it. This has a good lubricating effect and reduces friction. Then use a wrench to turn it. Generally, the screw can be easily removed. For severely rusted screws, you can also try this method first. If it still cannot be turned, then use other methods.
3. Burning
If the screws are severely rusted but you don’t want to damage the surrounding area, you can try using a blowtorch to burn the rusted part. When it is heated to a certain extent, the rusted part will fall off. Then, drip some oil on it, and you can easily unscrew it.
4. Rust Remover
If the screws are only slightly rusted, you can completely solve the problem with rust remover. Rust remover has a certain rust-removing effect. Just drip it on the rust, and wait for a few minutes. The rust will gradually dissolve, and then you can use pliers to unscrew the screws.
What are the methods to prevent screws from loosening during work?
Generally, the connection between screws and nuts has self-locking properties. When subjected to static loads and with little change in working temperature, they will not loosen by themselves. However, under the influence of shock, vibration, or variable loads, or when the working temperature changes significantly, this connection may loosen, affecting work and even causing accidents.
To ensure the safety and reliability of the connection, effective anti-loosening measures must be taken for the connection of screws and nuts.
1. The correct specification and size of screws must be selected. Slightly larger or smaller screws may be usable for the time being, but over time, they will definitely loosen or become stuck.
2. Special engineering plastics can be processed on the screw threads. This allows the screw and nut to have full-tooth contact during the tightening process due to the compression and squeezing of the engineering plastic, generating a strong frictional torque and counterforce, providing absolute resistance to vibration and turning ordinary screws into permanent and powerful anti-loosening screws, completely solving the problem of loosening in screw connections.
3. Anti-loosening methods that increase friction. These methods prevent the loss of pressure between the tightened threads due to changes in external loads, thus always maintaining frictional resistance to prevent the connection from loosening. Anti-loosening methods that increase friction include installing spring washers and using double nuts, etc.
4. Mechanical anti-loosening. These methods use various stop parts to prevent the relative rotation of the threads and the parts, achieving anti-loosening. Mechanical anti-loosening is more reliable and thus is widely used. Common mechanical anti-loosening measures include cotter pins and slotted nuts, lock washers and round nuts, lock washers and nuts, and double steel wires, etc.
5. Non-detachable anti-loosening methods. By using methods such as spot welding and riveting to fix the nut on the bolt or the connected part, or fixing the screw on the connected part, the anti-loosening effect can be achieved.
Tightening and Anti-loosening of Threaded Connections
Abstract: Tightening of Threaded Connections
The vast majority of threaded connections must be tightened during installation. The purpose is to enhance the rigidity of the connection, increase tightness, and improve anti-loosening capability. For bolt connections subjected to axial tensile forces, it can also increase the fatigue strength of the bolt. For ordinary bolt connections subjected to transverse loads, it is beneficial to increase the friction force between the mating surfaces in the connection. …
1. Tightening of Threaded Connections
The vast majority of threaded connections must be tightened during installation. The purpose is to enhance the rigidity of the connection, increase tightness, and improve the anti-loosening ability. For bolt connections subjected to axial tensile forces, it can also increase the fatigue strength of the bolt; for ordinary bolt connections subjected to transverse loads, it is beneficial to increase the friction force between the mating surfaces of the connection.
There are many methods to control the tightening torque, such as using torque wrenches or preset torque wrenches, measuring the elongation of the bolt during assembly, specifying the turning angle or number of turns after tightening, and for large connections, using hydraulic or heating methods to elongate the bolt to the required deformation and then tightening the nut to make it contact the connected parts.
In recent years, a method has been developed that uses a microcomputer to obtain data through an axial force sensor and draw a curve of preload force versus applied tightening torque to control the tightening torque.
Due to the difficulty in accurately controlling the force applied to the wrench, sometimes the bolt may be overtightened and broken. Therefore, for bolt connections that require tightening, bolts smaller than M12 to M16 are not recommended.
2. Anti-loosening of Threaded Connections
When the static load and working temperature change little, the threaded connection can meet the self-locking condition.
The fundamental issue of anti-loosening lies in preventing the relative rotation of the threaded pair. There are many specific anti-loosening methods and devices, and according to their working principles, they can be classified into three types: utilizing friction, direct locking, and disrupting the threaded pair relationship. Examples are shown in the table.
Methods for preventing nuts from loosening
1. Adding flat washers
A washer is a part placed between the connected component and the nut. It is generally a flat metal ring used to protect the surface of the connected component from being scratched by the nut and to distribute the pressure of the nut on the connected component.
2. Adding flat washers and spring washers
Spring washers are widely used in load-bearing and non-load-bearing structures of general mechanical products. They are characterized by low cost and easy installation, and are suitable for frequently disassembled and assembled parts. However, the anti-loosening ability of spring washers is very low!
3. Self-locking nuts
Ordinary nuts may loosen by themselves during use due to vibration and other reasons. To prevent this phenomenon, self-locking nuts were invented. The main functions of self-locking nuts are anti-loosening and anti-vibration. They are used in special occasions.
Their working principle is generally based on frictional self-locking. Self-locking nuts are classified by function into types with embedded nylon rings, with necked mouths, and with metal anti-loosening devices. They all belong to the effective torque type of anti-loosening nuts. Due to their nature, self-locking nuts are difficult to tighten.
4. Anti-loosening liquid for nuts
Apply anti-loosening liquid to the tightened part of the bolt, then screw on the nut to achieve the anti-loosening effect.
5. Double nuts (left and right threads) anti-loosening
By using a left-hand thread nut and a right-hand thread nut in combination and tightening them, this is also a good method.
6. Drilling and pinning for screws and nuts
In machinery, pins are mainly used for assembly positioning and can also be used as connecting, loosening, and overload shear-off safety devices. Types of pins include cylindrical pins, conical pins, pins with holes, split pins, and safety pins, etc.
7. Heating and tightening
Heat the bolt through the central heating hole. After the bolt expands in the hot state, tighten the nut in the hot state. When the bolt cools down and contracts naturally, a preload force is formed.
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