Screw threads can be commonly seen in many mechanical components. They have many applications. There are various objects to have them. They can be used for fastening. Screws, nut-bolts and studs having screw threads are used for temporarily fixing one part on to another part. They are used for joining such as co-axial joining of rods, and tubes, etc. They can be used for transmission of motion and power like lead screws of machine tools. Besides, they can also be applied for conveying and squeezing materials. For example, they are in screw conveyor, injection molding machine, and screw pump, etc.
Screw threads can be produced through various methods. The first one is casting. It only has a few threads over short length. It has less accuracy and poor finish. The second one is the removal process (machining). It is accomplished by various cutting tools in different machine tools like lathes, milling machines, drilling machines (with tapping attachment) and so on. This is widely used for high accuracy and finish. And it is employed for wide ranges of threads and volume of production from piece to mass production.
The third one is the forming (rolling). This method also has many characteristics. For instance, blanks of strong ductile metals like steels are rolled between threaded dies. Large threads are hot rolled followed by finishing and smaller threads are straight cold rolled to desired finish. And cold rolling attributes more strength and toughness to the threaded parts. This method is widely used for mass production of fasteners like bolts, screws etc.
In addition, the grinding is also a main approach for production of screw threads. It is usually done for finishing (accuracy and surface) after performing by machining or hot rolling but is often employed for direct threading on rods. Precision threads on hard or surface hardened components are finished or directly produced by grinding only. It is employed for wide ranges of type and size of threads and volume of production.
Screw threads can be divided into various types according to different classification methods. According to location, there are external screw thread (for example, on bolts) and internal screw thread (for example, in nuts). There are straight (helical) (e.g., bolts, studs), taper (helical), (e.g., in drill chuck), and radial (scroll) as in self centering chuck if classified according to configuration. Additionally, there are general threads (with usually wide thread spacing), pipe threads and fine threads (generally for leak proof) if divided according to compactness or fineness of threads.
There are still many other classifications. All in all, we can draw a conclusion that the screw threads have a very wide range of applications. Their functions and characteristics deserve our study.
Post time: Jun-19-2017