Two or three methods for optimizing the drawing process of cold heading wire rod

Two or three methods for optimizing the drawing process of cold heading wire rod

① Optimization of cold heading wire rod strength

If the cold heading wire rod has high carbon content and high strength, it can be softened and annealed before drawing, heated to 6~13 ℃ above Ac1 for heat preservation, furnace cooled to below 500 ℃ and then air cooled. (Low alloy steel spheroidizing annealing, heated to 20~30 ℃ above Ac1 for heat preservation, furnace cooled to 690~710 ℃ above Ar1 for heat preservation, the heat treatment process of re-air cooling below 550 ℃) reduces the hardness of the cold-heading coil, improves plasticity and toughness, and facilitates cold deformation processing. If there is residual stress in the finished wire due to multi-pass drawing (residual stress is the root cause of stress corrosion and cracks), recrystallization annealing can be used, which is to heat the workpiece to 600~700 ℃ for heat preservation and then slowly cool it with the furnace; (I .e. stress relief annealing, stress relief annealing is to heat the workpiece to 500~650 ℃ for heat preservation and then slowly cool it with the furnace) to eliminate or reduce the residual stress, reduce the strength and hardness of cold heading wire rod.

② Optimization of surface reduction rate and drawing passes

The surface reduction rate is directly related to the drawing process, the total surface reduction rate indicates the extent to which the wire rod is cold drawn, and the partial surface reduction rate is the basis for determining the drawing route. The same carbon content of cold heading wire rod, due to the total reduction rate of different, you can judge its performance and process difficulty.

Reducing the number of drawing passes can increase the hourly output (with the same size of the finished wire), but the wire rod is easy to break and affects the performance. Increasing the number of drawing passes consumes the mold and reduces the output. Therefore, the determination of the reduction rate, not only to ensure the smooth progress of drawing and cold heading wire rod finished quality, but also can reasonably reduce the drawing pass, increase production, improve production efficiency.

Low carbon steel has low carbon content, good plasticity, and low mechanical performance requirements. Most of the finished or semi-finished wires are softened and annealed, so the total surface reduction rate is not limited.

Medium and high carbon steel can not simply rely on increasing the total reduction rate to improve strength, otherwise it will make its plasticity, toughness matching improper, affecting the drawing forming. The partial surface reduction rate is mainly affected by carbon content, gold element content in steel, mechanical properties of finished products, drawing speed, drawing passes, etc. According to the requirements of finished products, if the equipment allows, the material can be released at one time, the surface quality is required, and the material can be released twice. The surface defects are determined by the first-pass drawing flaw detection, and a certain allowance is left for the second-pass drawing, and the finished products are drawn after treatment.

③ Optimization of drawing die

The drawing die is a tool that directly contacts the cold heading wire rod and deforms, and is one of the most critical factors affecting the drawing accuracy. Therefore, under the premise of unified mold size, semi-finished molds or finished molds should be classified and managed according to the different requirements of product drawing passes. Generally, the surface of the die after drawing of semi-finished products is easy to cause large loss. The surface of the die after drawing of semi-finished products has defects such as roughness, annular groove and cracking. If these dies are used for drawing finished products after general grinding, the surface accuracy of finished products is difficult to guarantee. The dies with such defects can be selected for drawing semi-finished products. Carefully select molds with high precision (ovality ≤ 0.005mm), surface blisters, scratches, pits and annular grooves, and polish them with special grinding paste to make the surface finish meet the mirror requirements so as to be used for drawing finished wires.

For light drawing products with a single-pass surface reduction rate of less than 5%, the taper of the die can be appropriately reduced and the length of the sizing belt can be extended to ensure the straightness of the drawing. For the alloy steel with low straightness requirement and easy to produce hair pulling, the shaking can be reduced by reducing the taper of the die and shortening the sizing belt to reduce the hair pulling.

④ Optimization of drawing speed

In the production, the drawing speed of SWRCH35K steel drawn from φ20mm wire rod to φ19.5mm and φ19mm to φ18mm is gradually increased, and the surface roughness can be seen to change slightly. When the drawing speed is greater than 50 m/min, the surface roughness of the cold heading wire rod increases. As the drawing speed continues to increase, the surface roughness basically does not change. Combined with the test and drawing speed on the mechanical properties of the factors, according to the actual production, in the drawing diameter of 6mm or more cold heading wire rod, the use of drawing speed of 35 m/min, the best surface roughness of the wire rod after drawing.

Table 1 Effect of drawing speed on surface roughness of cold heading wire rod

⑤ Optimization of other drawing conditions

In order to reduce the friction in the drawing process and improve the surface quality of the finished wire, it is of great significance to use reasonable lubricants and lubrication methods. Good lubricant adhesion, low friction coefficient, high pressure and high temperature resistance, can meet the needs of high-speed drawing.

For the alloy steel which is difficult to draw, the surface is smooth after pickling. If the lubricating oil is directly used for drawing, the surface oil film is not firm, and the drawing process is easy to break, resulting in direct contact between the die and the wire rod, causing the surface of the wire rod to fluffy and the die wear to increase. At this time, a combination of dry lubrication and wet lubrication can be used to obtain satisfactory results. The lubricating coating on the surface of the wire rod is dried, and then the lubricating oil is drawn to play a good lubrication effect, which can effectively improve the lubrication condition of the wire rod and improve the service life and production efficiency of the mold.

Source: Golden Spider Fastener Web