The Process of Making High-quality Bolts

The process of making high-quality bolts

1. To make a bolt, you need to design a bolt first, and then reflect the designed information on the design drawings or technical requirements. For example, in actual applications, the bolts are required to not be corroded for a long time in a relatively harsh corrosive environment, and it is necessary to select the appropriate surface treatment or bolt material according to the corrosive environment according to the corresponding standards to meet the requirements of the application environment.

2. To make the bolts meet the application needs, the material needs to be selected. The material is really important. Most of the bolts are ordinary carbon steel or alloy steel. This is a common situation, and the bolts may be used in highly corrosive environments or temperature changes. In relatively large environments, or extreme temperature environments, ordinary carbon steel or alloy steel is not suitable. For example, ordinary carbon steel materials will become brittle at extreme low temperatures, and it is easy to cause brittle fracture without warning. . However, if it is applied in a high temperature environment, ordinary carbon steel will have creep, that is, when the thread is not loose, the pre-tightening force of the bolt will be reduced, and it is easy to loose or fatigue failure.

3. Bolts are usually made of whole coils of wire rod, which are then straightened and cut to the required length. Some processes can be changed according to the equipment layout, but some processes cannot be adjusted. If the process is adjusted, it may affect product quality or reduce product performance.

4. The cold heading process is the preferred process for bolt head forming. The cold heading process has the characteristics of high productivity, high material utilization, high surface quality and high internal quality. When the steel rod is cut to the required length, the head can be headed. , The head can be cold formed or hot formed. Generally, the smaller bolts are formed by cold heading, and the larger bolts are formed by hot heading.

5. Heat treatment is one of the important processes in the manufacture of high-strength bolts, the purpose of which is to improve the comprehensive mechanical properties of the bolts.

6. Poor gas control will cause the screw to decarburize too poorly. In the process of cold heading of high-strength bolts, the annealing decarburization layer of the raw material not only exists, but also extrudes to the top of the threads of the high-strength bolts. At this time, the surface of the high-strength bolt that needs to be quenched does not need the pre-designed hardness, and the mechanical properties of the high-strength bolt will be greatly reduced at this time. In order to make the carbon potential have a favorable comprehensive effect on the carburizing process, the carbon potential of the furnace gas can be controlled in sections, that is, the carbon potential is increased as much as possible at the beginning, because the carbon absorption ability of the workpiece is very strong at this time, and it is not easy to produce carbon black. The high potential can make the concentration gradient on the surface of the permeable layer large, which is conducive to diffusion and increases the permeation rate. In the second stage, the carbon potential should be appropriately reduced, because the surface layer has established a higher concentration gradient and reached a certain depth of infiltration layer. At this time, the carbon absorption capacity of the workpiece surface has begun to decline, so the carbon potential should not be too high to avoid carbon production. black. The third stage is the diffusion period, the carbon potential in the furnace can be further reduced, so that the surface carbon concentration gradient and the depth of the infiltration layer meet the technological requirements.

7. Before rolling the thread, it is necessary to turn the part to be rolled to the pitch diameter of the thread. Rolling is formed by the pressure of the wire plate. The advantage of the thread formed by the rolling process is that the plastic metal fiber streamline of the thread part is not cut, so the bolt strength is increased, the precision is high, and the quality is uniform. Therefore, the rolling process is widely used.

8. Different lubricating materials coated on the same thread surface have different friction coefficients. Even if the same lubricating material is coated on thread surfaces with different surface treatments, the friction coefficient will be different. And different lubricating materials are suitable for different working temperatures. If the working temperature is exceeded, the lubricating effect will be lost.