Under the action of drawing force, the wire rod or wire blank is pulled out from the die hole of the wire drawing die to produce small-section steel wire or non-ferrous metal wire. Wires of different cross-sectional shapes and sizes of various metals and alloys can be produced by drawing. The drawn wire has a precise size and smooth surface, and the drawing equipment and mold used are simple and easy to manufacture. When drawing ultra-fine metal wire with a wire diameter of less than 0.05mm, it is difficult to pass through the die. In order to improve the stability of the drawing process, reduce the number of times of breaking and die passing, and improve the drawing production efficiency, a safety factor K value greater than 2.0 can be used.
Drawing above the recrystallization temperature is a hot drawing, and drawing above room temperature and below the recrystallization temperature is a warm drawing. Cold drawing is the most common drawing method used in wire and wire production. When hot drawing, the metal wire needs to be heated before entering the die hole, which is mainly used for drawing high melting point metals such as tungsten, molybdenum, and other metal wires. During warm drawing, the metal wire also needs to be heated by a heater to a specified range of temperature before entering the die-hole for drawing. It is mainly used for drawing zinc wire and hard-to-deform alloy wire such as high-speed steel wire and bearing steel wire. According to the number of molds that the metal wire passes through at the same time during the drawing process, the drawing that only passes through one mold is a single-pass drawing, and the drawing that passes through several (2 to 25) molds in succession is a multi-pass continuous drawing.
The line speed of single-pass draw is low, the productivity and labor productivity are low, and it is often used for drawing large wire diameters, low plasticity, and special-shaped wires and wires. Multi-pass drawing has high wire speed, a high degree of mechanization and automation, high productivity, and labor productivity, and is the main method of wire and wire production. It is divided into non-sliding continuous drawing and sliding continuous drawing. According to the state of the lubricant used in drawing, the use of liquid lubricant is wet drawing, and the use of solid lubricant is dry drawing. According to the cross-sectional shape of the drawn metal wire, there are round wire drawings and special-shaped wire drawings. According to the pulling force acting on the drawn metal wire, there are positive pulling force drawing and reverse pulling force pulling. There are also special drawings, such as roller die drawing, etc.!
Process characteristics: The stress state of wire drawing is the three-way principal stress state of two-way compressive stress and one-way tensile stress. Compared with the main stress state of three-way compressive stress, the drawn metal wire is easier to achieve plasticity. deformed state. The deformation state of drawing is a three-dimensional main deformation state of two-dimensional compression deformation and one tensile deformation. This state is not conducive to the plasticity of metal materials, and it is easier to produce and expose surface defects. The amount of deformation of each pass in the wire drawing process is limited by its safety factor, and the smaller the deformation of the pass, the more the drawing passes. Therefore, multi-pass continuous high-speed drawing is often used in the production of metal wire.
Common problems and solutions in wire drawing
In metal processing, carbon steel, stainless steel, aluminum, copper, and other metals are forcibly passed through the mold by an external force, and their cross-sections are compressed into the required shape and size. This is our common wire drawing process. The drawing process is divided into dry drawing and wet drawing according to the equipment and lubricant used. This article briefly introduces common problems and solutions in the wet drawing.
First of all, the selection of the wet drawing process is generally aimed at metal drawing with a small diameter, surface finish, or special requirements for subsequent processing. The categories of wet pull lubricants mainly include pure oil, synthetic oil, emulsion, ointment, and so on. The selection of wet drawing lubricant is mainly based on the comprehensive consideration of many factors such as raw material, mold, surface quality, and downstream application. For example, stainless steel is commonly used for drawing, and pure oil with high viscosity and special extreme-pressure additives is generally selected. For carbon steel, the emulsion is generally selected. For non-ferrous metals, pure oil or synthetic oil can be selected according to the final application requirements, and emulsion can also be selected.
1. Discoloration of the wire
The surface discoloration of wire (such as copper) is mainly oxidative discoloration, which is caused by improper temperature and humidity conditions. It may be that the concentration of the emulsion is too low or the temperature is abnormal; too much oil is attached to the wire; the water quality is unqualified; foreign oil is mixed in, etc.
Once you find the reason for its discoloration, you can take corresponding solutions according to the actual situation. For example, if the concentration of the emulsion is too low, raise it to the normal standard; if the temperature is abnormal, it should be adjusted to the normal 35 ° C ~ 45 ° C; check whether there is drawing oil overflowing at the outlet; remove foreign oil mixed in the emulsion, etc.
2. The mold wears a lot
One of the reasons for the large mold loss is the improper operation of the machine, and the other is the wrong choice of lubricant. If the machine is not running properly, the operator needs to practice constantly and check the operation before each operation. In addition, the lubricant plays a key role in assisting and promoting the wire drawing process, and its selection is very important.
3. Broken wire scratches and burrs
The wire breakage scratches and burrs greatly affect the aesthetics and quality of the product. The cause of these problems may be the pollution of metal shavings caused by direct contact between the metal and the mold due to insufficient lubrication, clogging of the mold holes or the aging of the lubricant. The metal shavings can be removed through the filter equipment, the blockage can be removed, and the lubrication can be replaced. Response measures to solve them respectively.
4. Emulsion stratification/excessive precipitation on the surface
Microbial infestation, low pH, high hardness of the water used for dosing, high inorganic salts, high temperature of the emulsion, etc., may cause delamination of the emulsion or excessive precipitates on the surface of the wire, and the solution must be targeted.
If it is a microbial attack, you can add a bactericide to it, and add sodium hydroxide solution or triethylamine alcohol; if the pH is too low, you need to add sodium hydroxide solution or triethylamine alcohol; When the temperature is too high, it is necessary to replace the water used for mixing; while the temperature of the emulsion is too high, it needs to be moderately cooled before use.
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