How to improve the service life of diamond wire drawing die?

Diamond wire drawing die is an important tool for the production of stainless steel wire and cable industry, especially in the fine wire and micro-wire applications are extremely widespread. But because of its very expensive, high production costs, how to effectively improve the life of diamond wire drawing die is a major important issue in the wire production industry.

Diamond wire drawing die has two kinds, one is natural diamond mold, natural diamond has high hardness, good wear resistance, pulling the wire surface finish is very high, due to natural diamond in the structure with anisotropy, resulting in its hardness is also anisotropic, so that the die hole wear is not uniform, the product is not round, coupled with expensive, rare, generally used as a high surface quality requirements of fine wire drawing die or finished products The other is artificial polycrystalline diamond mould, artificial polycrystalline diamond is non-directional polycrystal. It has the advantages of high hardness, good wear resistance and strong impact resistance. There is no anisotropy in hardness, uniform wear, long die life, and it is suitable for high speed drawing. With the improvement of the inherent quality and processing level of polycrystalline dies, there is a trend to replace the expensive natural diamond for finished die use.

2.1 Wire drawing die own processing quality factors lead to die wear

(1) Diamond die blank and die steel sleeve inlay is not symmetrical, sintered carbide steel sleeve distribution is not uniform or there are gaps, are easy to lead to produce U-shaped cracks in the process of drawing wire.

(2) Diamond die blanks in the laser punching process, sintered traces not cleaned or unevenly heated will cause the metal catalysts and bonding agents in the diamond layer to gather into a pile, which will easily lead to craters in the die during the wire drawing process.

(3) The mold hole type design is unreasonable, the entrance lubrication area opening is too small and the shaping area is too long, which will lead to poor lubrication, resulting in mold wear and even shattering.

2.2 The use of improper factors in the drawing process lead to mold wear

(1) The shrinkage of the drawing surface is too large, resulting in cracks or broken molds. The vast majority of cracks or fracture lines are produced by internal stress release. In any material structure, the existence of internal stress is inevitable, pulling the wire when the internal stress can enhance the diamond microcrystalline structure, but when the drawing surface shrinkage is too large, can not lubricate in time and thus the temperature rise is too high will lead to diamond die indicates that part of the material is removed, the microcrystalline structure of the stress is greatly increased, making it more likely to produce cracks or broken.

(2) the wire stretching axis and die hole center line is not symmetrical, resulting in uneven stress effect on the wire and wire drawing die, and mechanical vibration generated by the impact will also cause a high peak stress on the wire and wire drawing die, both will accelerate the die wear.

(3) due to uneven annealing and uneven hardness of the wire and other factors easily caused by diamond wire drawing die premature fatigue damage, the formation of ring grooves, intensify the die hole wear.

(4) wire surface roughness, surface adhesion oxidation layer, sand or other impurities, etc. will make the die too fast wear. When the wire through the die hole, hard, brittle oxide layer and other adhering impurities will be like abrasives to cause the wire die hole wear and abrasion of the wire surface very quickly.

(5) poor lubrication or lubricating oil containing metal debris impurities lead to mold wear. Poor lubrication will make pulling wire diamond die hole surface temperature rise too fast, diamond grains off, leading to mold damage. When the lubricating oil is not clean, especially contains pulling off the metal debris, very easy to scratch the surface of the mold and wire.

3.1 Try to use the high quality diamond wire drawing die produced by advanced die processing technology

At present, many manufacturers are still using backward equipment, using manual operation to grind hole type, therefore, there are the following problems: hole type parameters fluctuate greatly, it is difficult to process a flat working cone; sizing area and work area intersection is easy to grind out the transition angle, so that the wire in the sizing area to produce secondary compression, increase the external friction, shorten the length of the sizing area, shorten the service life of the die; worn grinding needle repair frequency Varies from person to person, the use of non-standard, resulting in poor consistency of the hole pattern. Detection means is also backward, can only rely on visual inspection or magnifying glass, microscope and other simple tools to detect, and focus on the die surface finish, the hole size can not be effectively detected, not to mention control. And the grinding process of our company's wire drawing dies generally adopts high-speed mechanical grinding machine, as well as metal grinding needles with diamond-plated surface. The equipment runs smoothly, and the specifications and use of grinding needles are standardized to make the products more accurate. The hole size of the die is checked by using the contour recorder and the hole diameter measuring instrument, and the surface finish is checked by using the microscope special for checking the wire drawing die.

3.2 Choose good hole type design diamond wire drawing die

Wire drawing die hole type is generally divided into curve type (i.e. R type series) and linear type (i.e. cone type series). As shown in the figure.

The picture shows the types of hole patterns of wire drawing dies

From the perspective of the wire in the wire drawing die deformation uniform analysis, it seems that the curve type is better than the linear type, this hole type is designed under the guidance of the theory of "smooth transition", its hole structure according to the nature of work can be divided into "population area", "lubrication area", "work area", "sizing area", "sunrise area" five parts. "lubrication area", "work area", "sizing area", "out of the day area" five parts, each junction The requirement of "chamfering", smooth transition, the entire hole type grinding into a large, with different curvature of the solitary surface of this hole type of mold in the drawing speed conditions at the time, or applicable. By the late 1970s to early 1980s, with the increase of drawing speed, the service life of the drawing die became a prominent issue. In order to adapt to the requirements of high-speed wire drawing, T. Maxwall and E.G. Kennth of the United States put forward the "linear" theory. The theory focuses on the role of lubrication and wear factors in the drawing process, pointed out that the improved linear drawing die hole type should have the following characteristics:

(1) the longitudinal profile line of each part of the hole type must be straight, straight work cone pulling force is the smallest.

(2) with each part of the intersection part must be obvious, so that each part can give full play to their respective roles, to avoid the transition angle on the actual length of the sizing area reduction.

(3) Extend the height of the entrance area and working area, so that the wire enters the middle section of the working cone of the die hole, using the wedge-shaped area formed by the entrance cone angle and the upper part of the working cone angle to establish a "wedge effect", forming a more dense and firm lubricating film on the wire surface, reducing wear, suitable for high-speed drawing.

(4) The sizing area must be straight and of reasonable length. The sizing zone is too long, the friction of drawing wire increases, the wire is easy to pull out of the die hole caused by shrinkage or broken wire, sizing zone is too short, it is difficult to obtain a stable shape, accurate size and good surface quality of the wire, while the die hole will also quickly wear super poor.

By practical application, the use of linear theory designed wire drawing die, its service life than the R-type wire drawing die increased by more than 3-5 times.

3.3 The installation of wire drawing machine equipment to use reasonable

(1) the installation base of the wire drawing machine needs to be very stable to avoid vibration phenomenon.

(2) installation to make the wire stretching axis and die hole centerline symmetry through debugging, so that the wire and wire drawing die stress effect evenly.

(3) avoid frequent starting and stopping during the wire process, because the friction caused by the tensile stress at the start of the drawing is much greater than the friction during normal drawing, which will inevitably increase the wear and tear of the mold.

3.4 The wire used for drawing should be pretreated

(1) Surface pretreatment: for the surface of the dirty, adhering more impurities of the wire, to be cleaned, dried before drawing; for the surface of the more oxidized wire, to be acid fine, dried before drawing; for the surface of the existence of skin, pits, heavy skin and other phenomena of the wire, but also through the grinding machine to repair the grinding before drawing;

(2) Heat treatment: For the wire with excessive hardness or uneven hardness, reduce the hardness by annealing or tempering first, and make the wire keep good hardness uniformity before drawing.

3.5 Maintain the appropriate drawing surface shrinkage rate

Diamond wire drawing die itself has hard, brittle characteristics, if used for large face shrinkage rate of shrinkage drawing, it is easy to lead to the mold can withstand the stress and broken scrap, therefore, according to the different mechanical properties of the wire, choose the appropriate face shrinkage rate for drawing. Pulling stainless steel wire with diamond mold, the general single-channel face shrinkage rate of no more than 20%.

3.6 The use of lubricants with good lubricating properties

In the drawing process, the quality of the lubricant and the lubricant supply is sufficient to affect the service life of the wire drawing die. Therefore, the lubricant is required to have stable oil base, good oxidation resistance, excellent lubricity, cooling and cleaning, and always keep the best lubrication in the whole production process, so as to form a layer of film that can bear high pressure without being destroyed, reduce the friction in the working area and improve the service life of the die.

In the process of use, keep observing the condition of lubricating oil, if you find serious discoloration or increase of metal powder in lubricating oil, you have to replace or filter it in time to avoid lubricating oil from oxidation and lubricating performance reduction, and at the same time avoid the fine metal particles shed in the drawing process to damage the die.

3.7 Regular maintenance repair diamond wire drawing die

Wire drawing die in the long-term use process, the die wall by the metal wire strong friction and scouring effect, will inevitably produce wear phenomenon, the most common is in the work area wire entrance ring groove (dent). The appearance of the ring groove of the wire drawing die intensifies the wear of the die hole, because the small particles of the core material peeled off from the ring groove due to loosening are brought into the working area of the die hole and the sizing area by the metal wire, playing the role of abrasive, while the wire entering the die hole is like a grinding needle to intensify the wear of the die hole. If not timely exchange for repair, then the ring groove will continue to accelerate the expansion of the repair to increase the difficulty, and may even be deeper in the ring groove cracks, so that the mold completely crumbled scrap.

We know from experience that it is very economical to develop a set of standard criteria, strengthen daily maintenance, and overhaul the die frequently. Once the die shows any slight wear, polishing it in time will take less time to restore the die to its original polished state, and there will be no significant change in the hole size of the die.

To sum up, in order to prolong the service life of the wire drawing die, in addition to choosing suitable die material, designing reasonable hole size, improving the manufacturing level of the wire drawing die and making the surface finish of the die hole meet the process requirements, we must also determine the reasonable compression rate of the road times and improve the usage conditions of the wire drawing die. Pay attention to the daily maintenance of the die in the process of use, should be diligently washed and changed, and to ensure that the stretching process has a good lubrication effect.