Wire drawing is one of the varieties of the form of processing metal products. A distinctive feature of the operation is that it is performed under high pressure. It acts on the workpiece, which has a round or shaped section. Such a workpiece is pulled under pressure through openings that are initially smaller than the diameter of the product being drawn. Thus, they get the wire.
Types of operation
Today, a large number of wire drawing methods are used. If we talk about the types of operation, then it can be of two types. The first type is called dry. In this case, the pulling process is carried out through a container inside which soap powder.
Wet type surgery is performed using a soap emulsion. This operation has a purity of processing, which can also be performed in two categories. The first is draft, or preparatory. The second type is finishing. This is the final stage, which is necessary to create the desired shape and size of the wire.
Drawing also has such a stage as multiplicity. A single transition or multiple transition is possible. In the second case, it is assumed that the same workpiece passes through the machine several times. In addition, work can be performed in parallel. That is, the workpiece may be single-stranded, or may be multi-strand.
Dies can also differ in their mobility. They can be either a rotating type or a fixed one. The last element that affects the course of the operation is the heating of the workpiece. Naturally, it can be cold or hot.
The essence of drawing
At present, it is possible to draw aluminum wire, copper or steel. Equipment in which there is a hole of the desired diameter is called a die, hence the name of the procedure. The hole itself is called a die. The final result of the whole procedure will depend on its form.
In addition, if you compare the procedure for wire drawing and rolling, the first method is much more effective, since it will provide greater cleanliness, as well as the accuracy of the surface of the wire. In addition, this procedure is also characterized by the fact that in the process of carrying out it improves mechanical performance, which is due to the removal of hardening. At present, it is possible to produce a wire with a diameter of 1-2 microns to 10, and in some cases more, millimeters.
Technology and stages of drawing
It is worth noting that with the current development of technology, wire drawing on modern equipment guarantees a fairly high performance. And this is a very important point. Equipment for wire drawing can well function at a sufficiently high speed, without any disturbance. The speed that the units can develop reaches 60 m / s.
The process goes through several main stages:
- The first stage is the etching of the source. For this, a sulfate solution is usually used, which is preheated to a temperature of 50 degrees Celsius. The operation is necessary in order to increase the life by removing scale.
- The next procedure is annealing. It is necessary in order to increase such a characteristic as ductility, as well as to form fine-grained.
- The third stage is the removal of residual sulfate solution. For this, a washing and neutralization of the substance is carried out.
- With the help of a hammer, the ends of the workpiece are sharpened.
- At this stage, there is a direct drawing of steel wire or any other.
- The last stage is again annealing the finished product.
Operation Feature
Naturally, any operation has its drawbacks. According to experts, drawing has only one, but quite serious minus. It consists in the fact that the wire undergoes slight deformation during the operation. Most often, the raw material for wire drawing is continuously cast, pressed, rolled billets made of non-ferrous metals, ferrous metals or carbon, alloy steels. In other words, in order to achieve high quality wire, it is necessary to use a fairly high quality raw material.
Previously, steel billets were used for wire drawing, which after processing were processed in a way such as patenting. This is a heating process, at a certain temperature of which such a process as austenization and exposure in salt or lead melts took place. The exposure of such a product was carried out at about 500 degrees Celsius.
Equipment for work
For drawing copper wire, as well as steel, the unit is used, which is called the "mill". The main working element of this unit is the “peephole”, or else dragging. Naturally, the cross section is selected so that it is always smaller than the cross section of the workpiece.
Types of modern units
There are currently two types of equipment used in metal processing plants. They differ from each other by the type of pulling mechanism.
- In the first case, the technology of wire drawing is that the product is wound on a drum, thereby creating traction.
- The second case is the use of a device that pulls the workpiece in a straight line.
If we talk about the application, then the second type of aggregates is most often used if it is necessary to stretch a pipe billet, which does not require subsequent folding into a bay.
The bulk of the wire and pipes of small cross section is produced specifically on drum devices. These mechanisms can be either single or multiple. Naturally, the simplest design is for single equipment. The technological process of production in this case involves drawing the wire in one pass. If a multiple machine is used, the procedure can be repeated two or three times in a row.
The device work machines
The main working element is the device that is present in any apparatus for wire drawing - dies. This mechanism is always created from a very durable cermet alloy. A distinctive feature of this metal is that it is very durable, has increased hardness, low viscosity, and high abrasion resistance. In rare cases, a technical diamond is used to produce a die. This gives a significant advantage in the processing of more complex metals.
These parts are placed in sufficiently strong and viscous steel clips. The clip itself is not capable of exerting a strong influence on the die, but at the same time its presence significantly reduces the tensile stress that inevitably arises during operation. At modern enterprises, a prefabricated die is often used, which is different in that it consumes less energy, and its efficiency (efficiency) is higher by about 30%.
Preparation of metal for work
Naturally, such a procedure cannot be carried out without preliminary metal preparation. In addition, without this procedure, it will not be possible to achieve a quality product. The essence of the preparatory work is that it is necessary to remove the scale from the workpiece. Before you begin the process of wire drawing, carry out one of three procedures:
- machining ;
- chemical treatment;
- electrochemical treatment.
Mechanical cleaning of the workpiece is the simplest and cheapest method of cleaning. Most often it is used if the product is made of carbon steel. During the processing procedure, the wire rod bends in different directions. At this time, its surface is treated with mechanical brushes.
Chemical and electrochemical processing
As for the chemical method of descaling, it is more complex and time-consuming. To do this, most often use either hydrochloric or sulfuric acid. In addition, in order to carry out such an operation, the dragger must have the necessary qualifications to work with chemicals.
However, it is important to note here that this method is indispensable if it is necessary to prepare high-alloy or stainless steel for drawing. In addition, after the chemical cleaning is completed, the metal surface must be washed with water.
The last method, electrochemical, is that the metal is etched in an electrolytic solution. This liquid can be either anodic or cathodic, based on what the conditions are, and also taking into account the characteristics of the material.
Drawing of copper billets
During the drawing of copper wire from copper billets, cast billets are always used, and the whole method is based on this. First you need to fuse together all the workpieces. Immediately after this, while they are still in a hot state, they are rolled. However, carrying out this process entails the appearance of a film of oxides on the surface of the product. To get rid of this problem, it is necessary to conduct treatment with chemical compounds. After that, you can go directly to the drawing procedure.
Obtaining copper wire can also be carried out by the principle of submersible molding. If this method is applied, the surface of the wire rod will remain clean and the cleaning procedure will be avoided. It is this method that is used to produce the thinnest wires (with a diameter of up to 10 microns). However, when using this method, it is very important to choose a composition that will have suitable properties.
Among these compounds stand out:
- complex solutions, which may include alkaline compounds, salts of fatty sulfonated oils and several other substances;
- it is possible to use various kinds of emulsions, such as anionic, antifoam, synthetic esters and others;
- synthetic substances such as organic and inorganic salts, as well as polymer solutions, are considered separately.
Processing options
Currently, there are a large variety of options for processing the workpiece.
- Bay type of processing. This is an option for working with pipes from billets that are assembled in bays. Also included here are those pipes that went through the drawing process, after which they were collected in bays.
- Wet processing requires the die to be immersed in a liquid lubricant during operation.
- The most commonly used application is drawing on fixed mandrels.
- There is a processing method in which the use of pipes that do not have a round (shaped) shape is allowed.
- The electroplastic method is used if there is a need to work with pulling a metal that is difficult to deform.
- Another of the processing methods is core. A rod is inserted into the workpiece in order to pull it together with the pipe. After the passage of the drag, the inserted rod must be removed back.
Diameter difference
The drawing process is divided into several types, depending on what was the initial diameter of the workpiece and what it turned out in the end. Rough dragging is a procedure in which the initial diameter was 8 mm, and after passing the drag it became 5 to 0.9 mm. An average drawing is considered an operation in which the workpiece had a diameter of 3.5 mm, and as a result, it decreased to 1.5-0.2 mm. In thin drawing, blanks from 2.6 to 1.6 mm are used. The result is products with a cross section from 0.5 to 0.05 mm.