Basically, screws are cylindrical or conical pointed bolts with threads that have a head in various geometrical shapes at the top end. The thread is in the form of wedge or inclined plane that is wound or coiled spirally by rotation along the longer portion to get the optimal effect. Mentioned below are facts about screws.
Different Aspects of Screws
A unique characteristic of screws is that, although they connect two or more things only the screw is stressed by traction. And the connected parts are fixed or fastened together by adhesion. This phenomenon is known as assembly prestressing force.Screws are implemented in an application by screwing them inside a nut or internal thread. The effective length of the screw is diminished until the portions to be connected are pressed together. In some applications, a thread is incised into the connecting component. Also, there are sheet metal screws that cut the thread into the material while they are screwed in. In certain applications, screws are also used for bearing type connections. The head of the screw serves two very important functions viz.:
- As a contact point for turning tools such as screwdriver, screw-wrench, Allen wrench etc.
- Secondly, as a thrust face for pressing the top portion of the part to be connected on the subjacent part.
Basic Composition of ScrewsGenerally, screws are made from metals and alloys such as iron, steel, stainless steel, copper, aluminum, etc. In recent times, different types of screws and plastic fasteners made of PVC, Isoplast, PET, etc. are quickly replacing traditional stainless steel bolts in marine applications. Also, they can be produced in various sizes, forms, and surfaces to suit countless applications. When it comes to the direction of screws, it differs depending on the area of application. In most mechanical applications, a right-handed screw thread denotes a screw that turns clockwise when it is screwed in. And for screwing out, it turns anti-clockwise. Screws with left-turning screw threads are screwed in counter clockwise. Generally, they are available for specialty applications.
Procedure for Manufacturing of ScrewsUsually, screws with heads are manufactured using the cold press method. The cold heading machine can produce 100 to 500 screw blanks every minute. This procedure is carried out in several stages of production mentioned below.
- Cold Heading
- Initially, the basic material is fed as “wire” from mechanical coils.
- It is then uncoiled and straightened.
- The straightened wire then enters a machine that automatically cuts the wire at predefined lengths.
- After that, special machines die cut the head of the screw blank into a designated shape
- Thread Rolling
- After cold heading, the screw blanks are fed into thread-cutting dies.
- The blank is then cut using one of following three techniques:
- Reciprocating die, where the screw is placed between two flat dies to create the finished thread.
- In a center-less cylindrical die, the screw blank is rolled between two to three round dies.
- In the planetary rotary die process, several die-cutting machines roll around a stationary screw blank.