Polystalling Diamond Drawing Die

The material revolution of the metal drawing industry has never stopped the material revolution of the drawing die. Metal wire drawing die, in the 1920s and 1930s, a large number of molds for steel and its alloys were used. The low wear resistance and short service life of the steel mold limit the increase of the drawing speed.

With the development of industrial technology, in 1923 West Germans invented a new wear-resistant material - cemented carbide, and used in the wire drawing industry in the forties. Due to the good wear resistance of the brushed die of the carbide alloy, the service life has been greatly improved, which has promoted the industrial revolution of the wire drawing, and the drawing speed of the international 50s and 60s has jumped to 600 meters/min or more. In order to improve efficiency and increase production, countries are still working hard to increase the speed of drawing. However, the service life of the mold is still a prominent contradiction.

Since the 1970s and 1980s, the world's advanced industrial countries have been exploring new wire drawing die materials and increasing the life of wire drawing die to solve the problem of further increasing the drawing speed. In view of this, the internationalization of the boronizing heat of the drawing die in the 1970s, various ion implantation heat, the layer heat of titanium carbide and titanium nitride in the early 1980s, their common feature is to strengthen the surface of the wire drawing die. Although they have achieved certain results, they have not left the basic material of cemented carbide. All of the above methods add a complicated "reprocessing" process to the manufacture of the wire drawing die, and thus have not been developed very quickly. Although since the 1950s, the Soviet Union, Eastern Europe, the United States, and Japan have carried out research on ceramic wire drawing dies of various compositions, but they are still in the experimental stage and are not used for industrial production.

In 1955, the United States General Electric Company successfully produced synthetic diamonds in the world's first experiment, and began to apply in the wire drawing industry in the mid-1970s. In the mid-eighties, the synthetic diamond brushed mold was used to make a large-sized wire drawing die with a diameter of 7-8 mm. Due to its excellent wear resistance, it brings new prospects to the wire drawing industry.

At present, the world's advanced industrial countries are vigorously developing and using wire drawing dies of this material. It is foreseeable that the extensive use of this new material drawing die will definitely advance the new development of the wire drawing industry.

2. Material Overview

Synthetic diamond crystals are divided into two kinds of finished products: one is to sinter fine natural diamond powder together at about 50,000 atmospheres and 1500 °C, and they are integrated into a combination of diamond and diamond. Rather than relying on other low-melting materials as binders; the second is the use of synthetic diamond fine powder, bonding of low-melting adhesives, and polycrystalline crystals after sintering. This article deals with this kind of synthetic diamond polycrystal, also known as polycrystalline diamond. The drawing die made with it is called polycrystalline drawing die.

2.1 naming

In 1955, the Americans invented the method of synthesizing polycrystalline diamond. At that time, they only produced powders, mainly used for industrial grinding. The drawing die was used in the mid-1970s until the early 1980s. It was more widely adopted by countries around the world, and its output doubled in 1985.

It is a non-directional polycrystal formed by non-directional polymerization of many synthetic diamond powders. Its name is in English. The first letter of English POLYCRYTALLINE DIAMOND is capitalized as PCD or PD drawing die.

2.2 material characteristics

The polycrystalline drawing die not only has some excellent properties of natural diamond, but also has superior wear resistance and anti-resolution. In addition, it can also be used in the drawing die of a wide range of medium and thick wire.

In China, especially for the manufacturers that have introduced some high-speed wire drawing machines, the polycrystalline wire drawing die has great practical significance for solving the stable high-speed production of equipment and obtaining benefits as soon as possible.

The polycrystalline core in the polycrystalline brushed mold is formed by randomly oriented fine powder diamond particles which are sintered by using metallic cobalt as a solvent and a catalyst.

Due to the irregular directionality of the diamond micropowder, the drawing die has uniform and high hardness, and the wear resistance is the same in all directions. There is no problem of "hard wear" and "soft wear" of natural diamond, which promotes PCD drawing. The mold life is improved.

PCD polycrystalline mold has high fracture resistance. Unlike natural single crystal diamond, it has no cleavage surface, so it does not cause delayed surface fracture.

Since the PCD polycrystalline mold contains a binder cobalt, it has electrical conductivity and can be processed by EDM technology.

Its main advantages when using PCD wire drawing die are:

1. The wear resistance of the tungsten carbide drawing die is increased by a factor of ten to 100 times;

2. The wear is uniform and isotropic, far more resistant than natural single crystal diamond;

3. There is no cleavage surface and it is not easy to break;

4. Improve the surface finish of wire products;

5. Increase the operating rate and reduce the mold inventory.

2.3 specifications

In recent years, China has also been able to produce polycrystalline brushed blanks, but it is still not very common, and it has been gradually promoted and applied in the 1980s. At present, in the ferrous metal products industry, there are many applications for drawing filaments, alloy steel wires and stainless steel wires. However, the quality of polycrystalline slabs produced in China cannot reach the level of similar foreign products, and it is far from the performance of natural diamonds. At present, the world's manufacturers that can provide a wide variety of PCD drawing die blanks are the United States, Britain, Japan, and so on. .

The specifications of the products are the most complete in the United States. The largest diamond diameter produced in the UK and Japan is 15 mm and can be used to make 7-8 mm wire drawing dies. Generally, the polycrystalline drawing die blank is composed of a synthetic diamond circular polycrystal and a cemented carbide sleeve on the outside thereof, and the hard gold plated jacket is called a tungsten carbide support sleeve.

According to the different particle size of the synthetic diamond micropowder, the support sleeve can also be made of stainless steel sleeve, and the small size can also be without the support sleeve. The maximum diameter recommended by each country also needs to be changed depending on the drawing material and the drawing conditions.

3. Modeling and use

3.1 Drawing die manufacturing

The manufacturing process of the wire drawing die is basically similar to the manufacturing process of the natural diamond wire drawing die. To insert the mold, firstly insert the core into the mold sleeve by press fitting, metal powder metallurgy material or welding method. Since the core is generally cylindrical, it is easy to install. Furthermore, the hardness and wear resistance of polycrystalline diamond are uniform in all directions, so it is not necessary to pre-determine the crystal plane and crystal orientation like single crystal natural diamond. drilling. Perforation is generally performed using laser electrospark technology. Small and medium-sized blanks with a thickness of less than 4.0 mm are laser perforated. When the thickness of the mold is more than 4.0 mm, EDM is used for perforation. In addition to this, it is also conceivable to use ultrasonic methods for perforation, but this is costly.

Form grinding. The forming and grinding method is basically the same as the general molding process, and is processed by an ultrasonic method with a steel needle and a diamond powder having a certain angle. According to the material of the drawing, the geometry of the drawing die hole type is different.

Final polishing. This procedure is similar to the forming process, but the mill size used is different. In general, the finer the diamond abrasive particles are used, the higher the polishing finish.

In addition, since the polycrystalline mold has a low wear rate and a high breaking strength, the length of the sizing belt can be reduced by 50% to 75%. This improves the drawing conditions, lubrication conditions, reduces the drawing force, and extends the life of the mold.

3.2 use effect

The use of PCD polycrystalline molds, in addition to drawing colored tints, is currently widely used in various ferrous metal products. For example: low carbon steel wire, high carbon steel wire, stainless steel wire, nickel ferrochrome wire, copper plated steel wire, galvanized steel wire, and the like. Its life expectancy is 4-8 times higher than natural diamond mold and 20-160 times higher than cemented carbide mold.

The quality of the wire after drawing is greatly improved. The batch quality of the wire is stable for a long period of time, and the shape and size control of the wire is improved; the surface finish of the wire is extremely high, and the possibility of cold work hardening is reduced.