Although the screws of the fastener are small and inconspicuous to the eye, without countless screws for connection and fixation, the machine and equipment cannot form a solid whole and cannot operate.
It can be said that from being a national treasure to various daily necessities, screws are indispensable, and their role is crucial.
So, how is a qualified fastener screw made?
Many people may have a general understanding that screws require cold and heat treatment and strict testing before leaving the factory. This understanding is correct, but the process of making screws is not easily covered by cold and hot treatment.
Transforming from wire to qualified fastener screws requires six steps.
1. Treatment of wire
Fastener screws generally use wire with a diameter of 5-19 mm as the raw material, which mainly consists of three categories: carbon steel, stainless steel, and copper. Each category is divided into various different models, so we won't go into detail here.
2. Rough drawing processing
In order to remove the oxide skin generated during production and storage of the wire, rough drawing treatment is required, and the surface of the treated wire will present the original color of the metal.
Rough drawing is divided into two steps:
(1) Annealing. After selecting the wire, it should be heated and maintained for a period of time, and then slowly cooled. This can adjust the crystalline structure, reduce the hardness of the wire, eliminate particles, and improve the room temperature processability of the wire.
(2) Acid pickling and phosphating. By removing the oxide film on the surface of the wire through acid pickling and phosphating, a layer of phosphate film is formed on the metal surface, which makes the wire more easily processed and formed. This step can also reduce scratches and losses on the tool and mold during subsequent processing such as wire drawing and cold heading.
3. Fine drawing processing
This step is easy to understand, which is to draw the wire to the corresponding diameter and thickness according to different product requirements and specifications, in order to facilitate further processing and forming.
4. Forming process
This step is divided into three steps:
(1) Cold heading. Cut the wire into the required length through a cold heading machine, and mark the nuts and markings.
(2) Pinch the tail. Through this step, the wire can be made into a dovetail shape that can penetrate the steel plate.
(3) Rubbing silk, also known as grinding teeth. After each end of the screw is completed through cold heading and clamping, the semi-finished product that has already been formed is twisted out of the thread through the interaction between the movable and fixed tooth plates. This way, a screw is basically formed.
5. Heat treatment processing
This step is divided into five steps:
(1) Cleaning. Remove grease from the surface of the screw.
(2) High temperature carburization. This is the core step of heat treatment processing, which allows carbon atoms to penetrate into the surface layer of the screw and increase its hardness.
(3) Quenching. After high-temperature carburization treatment, the screws are quenched at high temperature to form a layer of crystals on the surface of the screws to meet the final hardness requirements.
(4) Clean the quenching oil. Clean the quenching oil from the surface of the screw.
(5) Low temperature tempering. Low temperature tempering can reduce the core hardness of screws, making them more resilient and avoiding the possibility of screws breaking due to high core hardness.