Screws are often referred to as the "rice of industry" — small in size, yet crucial in function. Especially on high-tech equipment like aircraft and rockets, even the smallest bolt must not be overlooked. A single loose bolt can lead to catastrophic consequences. So, how do engineers ensure that screws stay securely fastened?
In aircraft construction, anti-loosening measures are commonly used, such as safety wires, cotter pins, lock nuts, and safety screws. Some smaller nuts are self-locking, thanks to their elliptical shape. Before installation, these nuts are oval, but once tightened, they are clamped by a slot at the end, preventing them from loosening.
One common method is the use of fuse wires. These thin wires connect two or more fasteners together. If a component starts to loosen, the wire prevents it from moving further, effectively stopping any potential failure. Fuse wires are typically made from low carbon steel, stainless steel, or brass, with low carbon steel being the most common. They can be used in single-strand or double-strand forms, with double-twisted knots being the most widely used, as shown in the image below.
For tightly spaced screws or hard-to-reach areas, single-strand fuses are often preferred, as illustrated in the figure.
When multiple threaded fasteners are grouped together, interlocking fuses are usually more effective than individual ones. The number of fuses used depends on the specific situation and the level of vibration or stress involved.
Another method is the cotter pin. It's inserted through a hole in the bolt and then split open to prevent rotation. The installation process is simple and effective, as shown in the image.
Safety pins and locking screws also serve similar purposes, offering mechanical resistance against loosening. These methods are often used in critical applications where reliability is key.
Thread self-locking is another common technique. This is achieved by using specially designed threads with a smaller pitch, which increases friction between the screw and nut. However, the effectiveness of this method largely depends on the nut itself. If the nut becomes worn or damaged, the self-locking force may weaken, requiring replacement.
In addition to these traditional methods, modern engineering has introduced innovative solutions. For example, special engineering plastics are applied to screws during manufacturing. When the nut is tightened, the plastic deforms and creates strong friction, ensuring full contact between the threads and providing excellent resistance to vibration. This transforms a regular screw into a permanent anti-loose fastener, solving the issue of loosening completely.
There are also several other methods to prevent screw loosening:
1. **Proper Specification Selection**: Choosing the right size is essential. A slightly oversized or undersized screw might work temporarily, but over time, it could either become too tight or loosen, leading to failure.
2. **Plastic Coating**: As mentioned earlier, engineering plastics are used to increase friction and improve the locking performance of the screw.
3. **Friction-Based Anti-Loose Methods**: Using spring washers or double nuts increases the friction between the threads, helping to maintain the tightening force under varying loads.
4. **Mechanical Anti-Loose Methods**: This includes using cotter pins, slotted nuts, retaining washers, and safety wires. These methods physically prevent the nut from rotating, making them highly reliable.
5. **Permanent Fixation**: In some cases, the nut or screw is fixed permanently using welding or riveting. This ensures that it cannot come loose, though it makes future disassembly difficult.
By combining these methods, engineers can ensure that screws remain secure, even in the most demanding environments. Whether in aerospace, automotive, or industrial machinery, proper anti-loose measures are essential for safety and performance.
IDC connectors,ZOOKE IDC connectors,IDC connectors series
Zooke Connectors Co., Ltd. , https://www.zooke.com