Screws are indispensable in the manufacturing industry, finding applications in a wide range of products, from small items like glasses to large-scale creations such as cars, aircraft, and rockets. In this article, we will provide valuable insights into screws and explore effective methods to prevent screws from loosening.
Basic Knowledge about Screws
Screws: These comprise a rod with an external thread and can feature various head shapes, including flat, countersunk, bugle, square, and round.
Bolts: Bolts typically have a hexagonal head and external screw threads. Stud bolts, also known as double-screw bolts, possess external threads on both ends, while the middle section is usually a polished rod.
Nuts: Nuts are usually hexagonal in shape and contain an internal hole with an inner thread that securely connects related items when paired with bolts.
Screw Thread: A screw thread refers to a uniform spiral bulge present on the external or internal surface of a product. It serves the purposes of tightening, connecting, and sealing, making it suitable for most screw applications.
Processing Methods for Screws and Screw Threads
To manufacture high-quality screws, it is crucial to employ suitable processing methods. Here are some common techniques:
Processing Methods for Screws
Turning: This method involves removing material to achieve the desired shape.
Advantages: High processing accuracy and no restrictions imposed by molds.
Disadvantages: High production costs and relatively slow processing speed.
Forging: Forging entails deforming the material using external force to achieve the desired shape.
Advantages: Fast production speed, lower costs, and suitable for large-scale production.
Disadvantages: Forming is limited by molds, and complex product molds can be expensive.
Cold Heading: Cold heading is a process that uses external forces and specialized molds to squeeze unheated metal wire, resulting in deformation. This method falls under the category of forging processes.
Processing Methods for Screw Threads
Thread Cutting: Thread cutting involves processing threads on a workpiece using forming or abrasive tools. It encompasses turning, milling, tapping, grinding, and cyclone cutting. During turning, milling, and grinding, the workpiece rotates while the tool moves along its axial direction. Tapping or threading involves relative rotation between the tool and the workpiece, with the initial thread groove guiding the axial movement of the cutter.
Thread Rolling: Thread rolling is a cold heading process that shapes screw threads through the plastic deformation of a workpiece using rolling dies. Machines used for this method include single-mode machines, multi-station machines, and mold closure machines. Screws produced through this method have faster production speeds and lower costs, but their appearance may be less angular and aesthetically pleasing compared to cut threads.
While the cutting process offers higher accuracy than cold heading, the latter boasts faster production speeds and lower costs. Cold heading, especially for small precision screws, offers better cost performance.
Preventing Screw Loosening: Effective Methods
Preventing screw loosening is particularly crucial in high-tech products such as aircraft and rockets. A loose screw can lead to severe consequences. Here are some effective methods to prevent screw loosening:
Select the correct size and specifications of screws. Using slightly larger or smaller screws may work temporarily, but over time, they may loosen or lock.
Apply engineering plastics on screws. These plastics generate substantial friction torque and reaction force, resulting in full-pitch contact and absolute resistance to vibration. This turns the screws into permanent locking screws, effectively eliminating loosening issues in connections.
Increase friction to prevent loosening. Methods such as using spring washers and employing double nuts can create frictional drag that counters loosening caused by external load changes.
Implement mechanical anti-loosening methods by utilizing motion-stopping components to prevent the relative rotation of screw threads. This approach is highly reliable and includes options like split pins and castellated nuts, floor clips and round nuts, lock washers and nuts, and more.
Adopt non-disassembly methods to prevent loosening. Techniques like positioning welding and riveting fix the nut on the bolt, ensuring the screws remain securely fastened to prevent loosening.
Summary
Screws play a critical role in various industries, including aerospace, automotive, and electronics. This article has provided valuable knowledge about screws, including their basic features, appropriate processing methods, and effective techniques to prevent loosening. By understanding these aspects, screw manufacturers can ensure reliable performance of screws in different applications.
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