1. The quality of the drawing die itself causes the mold to wear out.

(1) The diamond mold blank and the mold steel sleeve are inlaid asymmetrically, and the sintered hard alloy steel sleeve is unevenly distributed or has voids, which easily leads to U-shaped cracks in the process of drawing the wire;

(2) During the laser drilling process, the diamond blanks are not cleaned or unevenly heated, which may cause the metal catalysts and binders in the diamond layer to aggregate into a pile, which may easily cause pits in the mold during the drawing process;

(3) The design of the die hole type is unreasonable. The opening of the inlet lubrication zone is too small, and the shape of the shaped zone is too long, which may result in poor lubrication, resulting in wear or even chipping of the die.

2, improper use of the drawing process leads to mold wear

(1) The drawing surface shrinkage rate is too large, causing cracks or breakage of the mold. Most of the cracks or broken cracks are caused by the release of internal stress. In any material structure, the presence of internal stress is inevitable, and the internal stress generated when drawing the wire can enhance the diamond microcrystalline structure. However, when the drawing surface shrinkage rate is too large, it cannot be lubricated in time, and the temperature rise is too high, which leads to diamond. The mold indicates that part of the material has been removed, and the stress on the microcrystalline structure is greatly increased, making it more prone to cracking or fracture.

(2) The tensile axis of the wire is asymmetric with the center line of the die hole, resulting in uneven stress on the wire and the wire drawing die, and the impact of mechanical vibration also causes high stress peaks on the wire and the wire drawing die, both Both will accelerate the wear of the mold.

(3) Factors such as uneven hardness of the wire due to uneven annealing tend to cause premature fatigue damage of the diamond wire drawing die, forming an annular groove and aggravating die hole wear.

(4) The surface of the wire is rough, and the surface adheres to the oxide layer, sand or other impurities, which causes the mold to wear too fast. When the wire passes through the die hole, the hard, brittle oxide layer and other adhering impurities can cause the wire die hole to wear quickly and scratch the wire surface like the abrasive.

(5) The lubrication is not smooth or the lubricating oil contains metal debris and the mold is worn. Poor lubrication will cause the surface temperature of the diamond die hole to rise too fast during drawing, and the diamond grains will fall off, resulting in damage to the mold. When the lubricating oil is unclean, especially if it contains metal scraps that fall off during drawing, it is easy to scratch the surface of the mold and wire.

3. Method for effectively improving the service life of diamond wire drawing die

3.1 High quality diamond wire drawing die produced by advanced mold processing technology

At present, the grinding process of foreign wire drawing molds generally adopts high-speed mechanical grinding machine and metal grinding needle with diamond-plated surface. The equipment runs smoothly, and the specifications and use of grinding needles make the product more precise. The hole size of the mold is detected by a contour recorder and an aperture measuring instrument, and the surface finish is checked by a microscope dedicated to the inspection of the wire drawing die. Many domestic manufacturers still use backward equipment and use manual operation to grind the hole type. Therefore, the following problems exist: the hole type parameters fluctuate greatly, it is difficult to process a straight working cone; the sizing area and the work area intersection Easy to grind out the transition angle, so that the wire will produce secondary compression in the sizing area, increase the external friction, shorten the length of the sizing area, and shorten the service life of the mold; the frequency of wear of the worn grinding needle varies from person to person. Not standardized, resulting in poor consistency of the hole type. The detection method is also backward. It can only rely on visual inspection or simple tools such as magnifying glass and microscope, and it pays attention to the internal surface finish of the mold. It cannot effectively detect the size of the hole, let alone control.

3.2 Select the diamond drawing die with good hole design

Type of wire die hole type

From the angle analysis of the linear deformation of the wire in the drawing die, it seems that the curve type is better than the straight type. This hole type is designed under the guidance of the "smooth transition" theory, and the hole structure can be divided into "population" according to the nature of work. Five parts of “zone”, “lubrication zone”, “work zone”, “sizing zone” and “export zone”. The junction of each department requires “chamfering”, smooth transition, grinding the whole hole into a large, A mold with a different curvature and such a hole type can be applied at the time of drawing speed at that time. By the end of the 1970s to the early 1980s, as the speed of the cable was increased, the service life of the cable die became a prominent problem. In order to meet the requirements of high-speed wire drawing, T.Maxwall and E.G. Kennth of the United States proposed the "straight line" theory. The theory focuses on the lubrication and wear factors during the drawing process. It is pointed out that the improved linear drawing die hole type should have the following characteristics:

(1) The longitudinal section lines of each part of the hole type must be straight, and the straight working cone has the smallest pulling force;

(2) The intersection of the parts of the mold must be obvious, so that each part can fully play its role, avoiding the reduction of the actual length of the sizing area by the transition angle;

(3) Extend the height of the entrance area and the working area so that the wire enters the middle section of the working hole of the die hole, and the wedge shape formed by the inlet taper angle and the upper half of the working cone angle is used to establish a "wedge effect", and the surface of the wire material is formed more densely. A strong lubricating film that reduces wear and is 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 the wire is increased, and the wire is easily broken or broken after being pulled out of the die hole. The sizing zone is too short, and it is difficult to obtain a wire with stable shape, accurate size and good surface quality, and the die hole is also Will wear out too badly.

Through practical application, the wire drawing die designed by the linear theory has a service life of 3-5 times higher than that of the R-shaped wire drawing die.

3.3 The wire drawing machine equipment should be installed and used reasonably

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

(2) When installing, the tension axis of the wire should be symmetrical with the center line of the die hole, so that the stress of the wire and the wire drawing die is even;

(3) Avoid frequent starting of the parking during the pulling process, because the friction caused by the tensile stress at the time of pulling is much larger than the friction during the normal drawing, which is bound to increase the wear of the mold.

3.4 Wires used for drawing are subject to pretreatment

(1) Surface pretreatment: For the wire with dirty surface and more impurities, it should be cleaned and dried before drawing. For wires with more scale on the surface, it should be finely dried and dried. After drying, the drawing is carried out; for the wire having the phenomenon of peeling, pit, heavy skin, etc., it is also polished by a sanding machine and then pulled;

(2) Heat treatment: For wires with excessive hardness or uneven hardness, the hardness should be reduced by annealing or tempering, and the wire should be well drawn for good hardness uniformity.

3.5 Maintain a suitable drawing shrinkage rate

The diamond wire drawing die itself has the characteristics of hard and brittle. If it is used for the reduction of the large surface area, it is easy to cause the mold to withstand the stress and the scrapping and scrapping. Therefore, according to the mechanical properties of the wire, choose the appropriate surface. The shrinkage rate is drawn. The stainless steel wire is drawn by a diamond mold, and the single-face shrinkage rate is generally not more than 20%.

3.6 Use a lubricant with good lubrication

During the stretching process, the quality of the lubricant and the availability of the lubricant affect the service life of the wire drawing die. Therefore, the lubricant oil base is required to be stable, has good oxidation resistance, has excellent lubricity, cooling and cleaning properties, and maintains an optimum lubrication state throughout the production process so as to form a layer capable of withstanding high pressure without being damaged. The film reduces the friction of the work area and improves the life of the mold. During the use, it is necessary to constantly observe the condition of the lubricating oil. If it is found to be severely discolored or the metal powder in the lubricating oil increases, it should be replaced or filtered in time to avoid the lubrication performance of the lubricating oil being reduced due to oxidation, and avoiding the small peeling during the drawing process. Metal particles damage the mold.

3.7 Regular maintenance of the diamond grinding wire mold

During the long-term use of the wire drawing die, the mold wall is strongly rubbed and washed by the metal wire, and inevitably wears out. The most common is the occurrence of an annular groove (dent) at the entrance of the wire at the working area. The appearance of the drawing die ring groove exacerbates the wear of the die hole, because the small core material of the core material which is peeled off due to looseness on the ring groove is brought into the die hole working area and the sizing area by the metal wire, plays the role of the abrasive, and enters The wire of the die hole aggravates the wear of the die hole like a grinding pin. If it is not replaced in time for repair, the ring groove will continue to accelerate and expand, making the repair more difficult, and it is even possible to crack at the deeper part of the annular groove, so that the mold is completely broken and scrapped.

It is known from experience that it is very economical to develop a set of normative standards, strengthen daily maintenance, and often overhaul molds. Once the mold has experienced any slight wear and polishing in time, the time it takes to return the mold to its original polished state is short, and the die size of the mold does not change significantly.

4, summary

In summary, in order to extend the service life of the wire drawing die, in addition to selecting the appropriate die material, designing a 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, it is also necessary to determine a reasonable road. The secondary compression ratio improves the conditions of use of the wire drawing die. Pay attention to the daily maintenance of the mold during use, and wash it frequently, and ensure good lubrication during the stretching process.