How are screws made? This article takes you to understand the whole manufacturing process of fastener screws
From the wire into a qualified fastener screw, you need to go through 6 processes.
- Treatment of wire
Fastener screws generally use wire with a diameter of 5-19㎜ as raw materials, and its material is mainly carbon steel, stainless steel, copper three categories, each category is divided into a variety of different models, here do not go into details.
- Rough drawing processing
In order to remove the oxidized skin generated during the production and storage of the wire, it is necessary to carry out rough extraction treatment, and the surface of the wire after treatment will show the original color of the metal.
Rough drawing is divided into two steps:
(1) Annealing. After the wire is selected, it must be heated for a period of time, and then slowly cooled, which can adjust the crystalline structure, reduce the hardness of the wire, eliminate particles, and improve the workability of the wire at room temperature.
(2) pickling phosphating. The oxidized film on the surface of the wire is removed by pickling and phosphating, and a phosphate film is formed on the metal surface, so that the wire can be more easily processed and formed. This step can also reduce the abrasion and loss of the mold during subsequent processing such as wire drawing and cold forging.
- Fine drawing processing
This step is better understood, that is, according to different product needs and specifications, pull the wire to the corresponding wire diameter thickness, in order to facilitate further processing and forming.
- Molding process
This step is divided into three steps:
(1) Cold heading. The wire is cut to the required length by the cold heading machine, and the nuts and marks are printed.
(2) Clip the tail. Through this step, the wire can be made into a dovetail shape that can penetrate the steel plate.
(3) Rolling silk, that is, grinding teeth. After the end of the screw is completed by cold upsetting and clamping, the semi-finished product that has been formed is rolled out of the thread through the interaction of the movable die plate and the fixed die plate, so that a screw is basically formed.
- Heat treatment processing
This step is divided into five steps:
(1) Cleaning. Remove grease from screw surface.
(2) High temperature carburizing. This is the core step of the heat treatment process, which allows carbon atoms to penetrate the screw surface layer and increase the hardness of the screw.
(3) Quenching. The screw after high temperature carburizing treatment is quenched at high temperature to form a layer of crystal on the surface of the screw to achieve the final hardness requirements.
(4) Cleaning quenching oil. Remove the hardening oil from the screw surface.
(5) Low temperature tempering. Low temperature tempering can reduce the core hardness of the screws, make the screws more ductile, and avoid breaking the screws because the core hardness is too high.
Step 6: Plating
After the completion of the first 5 processes, the screws will be sent to the laboratory for strict testing, and then the last process: electroplating after all parameters have been tested.
The role of electroplating should be known to everyone is to prevent screws from rusting, extend the service life, and make the screws more beautiful. Electroplating is mainly through the principle of electrochemistry, which is to generate another kind of metal on the screw surface to alleviate the external corrosion of the screw body, such as our common galvanized, chromium-plated, nickel-plated, copper plated and so on.
Finally, after about 2 hours of electroplating treatment, one qualified screw will be refined.