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Wear of diamond wire drawing dies
 

    Diamond Mold is an important tool for drawing stainless steel wire and cable industry production, especially in the thin and extremely broad application of actin filaments. But because of its price is very expensive, higher production costs, how to effectively improve the life of the diamond wire drawing dies is a big important issue wire production industry.

1 Introduction diamond wire drawing dies

    Diamond wire drawing dies, there are two, one is the natural diamond dies, natural diamond has a high hardness, good wear resistance characteristics, drawn wire surface finish very high, due to the natural diamond has anisotropy in the structure, leading to its hardness also showed anisotropy, so that the die hole uneven wear, products are not round, coupled with expensive, rare, usually used as a surface high quality requirements of the finished thread pull mode or pull mode; the other is a synthetic polycrystalline diamond mold, synthetic polycrystalline diamond is non-directional polycrystalline. It has high hardness, wear resistance, impact resistance and strong advantages. There is no anisotropy in hardness, wear uniform, mold long life, suitable for high-speed drawing. Due to the presence of domestic polycrystalline module blanks coarse grains, polished performance and poor quality problems, the domestic manufacturers to make more use of polycrystalline module overmold not as a finished mold. But with the intrinsic quality polycrystalline module and improve the processing level, a substituted expensive natural diamond mold used to make the finished product trends.

2 Wear of diamond wire drawing dies analysis
    2.1 drawing module itself processing quality factors leading to mold wear
    (1) The diamond die blanks and die steel sleeve inlay asymmetric, sintered carbide steel sleeve or uneven distribution of voids, are prone to produce U-shaped crack in the wire drawing process;
    (2) diamond die blanks in laser drilling process, the sintering is not clean or clean up traces of uneven heating may result in the diamond layer metal catalyst, combined together into a pile and the like, so easily lead to mold appears pits during drawing;
     (3) Mold unreasonable pass design, lubrication inlet opening area is too small, setting zone is too long, it will cause poor lubrication, resulting in die wear or chipping.

    2.2 the drawing process using improper factors leading to mold wear
    (1) drawing surface shrinkage is too large, resulting in cracks or broken the mold. Cracks or broken crack mostly generated by the release of internal stress. In any material structure, the presence of internal stress is inevitable, the internal stress generated when pulling the wire could enhance the diamond microcrystalline structure, but brushed surface shrinkage is too large, not been able to lubricate thus excessive temperature rise will lead to diamond Die show part of the material is removed, microcrystalline structure to withstand stress is greatly increased, making it more prone to cracking or breaking.
     (2) Tensile wire centerline axis of the die hole asymmetry, resulting in the wire and cable model for uneven stress, and mechanical vibration
The impact can also cause high stress peaks on the wire and cable model, both of which will accelerate mold wear.
     (3) non-uniform due to uneven annealing wire hardness caused by other factors likely to cause diamond drawing die premature fatigue damage, the formation of the annular groove, increased die bore wear.
    (4) the wire surface roughness, the surface oxide layer adhesion, sand or other impurities cause excessive wear of the mold. When the wire through the die orifice, hard, brittle oxide layer and other contaminants will adhere to the same manner as the abrasive Pull die bore quickly cause wear and abrasion wire surface.
     (5) poor lubrication or oil-containing impurities cause mold wear metal debris. Poor lubrication makes drawing diamond die hole surface temperature quickly, diamond grains fall off, leading to mold damage. When the lubricant unclean, especially when drawing containing metal debris shedding, very easy to scratch the surface of the die and wire.

     3 effectively improve the life of the diamond wire drawing dies methods
    3.1 try to use advanced mold technology to produce high quality diamond drawing dies
    Currently, foreign cable mold milling process commonly used high-speed mechanical grinding machine, as well as diamond plated metal grinding, smooth operation of the equipment, grinding and the use of standardized specifications make the product more accurate. Pass the size of the mold using contour logger and aperture measuring instrument to detect and check the cable model with a special microscope to check for surface finish. Many domestic manufacturers are still using backward equipment, use manual operation to grind pass, therefore, there is the following problem: pass parameter fluctuations, work hard to process the flat cone; sizing zone and work zone junction easy to grind out the transition angle, so that the wire is generated in the secondary compression sizing region, increase outside friction, shorten the length of the sizing zone, shortening the life of mold; worn grinding repair frequency varies, use not standardized, resulting in poor consistency pass. Detection means also behind, we can only rely on visual or magnifying glass, microscope and other simple tools to detect, but also pay attention to the mold surface finish of the hole size can not effectively detect, let alone control.

     3.2 Selecting good pass design diamond drawing dies
    Drawing die hole is generally divided into curve (ie, R-series) and linear (ie cone series).
    Pass the cable model type from the wire in the cable model deformation uniform point of view, it seems relatively straight curved good, this pass is under "smooth transition" theory to guide the design out of its hole structure by Job Nature can be divided into "population area", "lubrication zone", "workspace", "sizing zone", "the day area" of five parts, the ministries junction requirements "chamfer" smooth transition, the entire hole ground into a large, female lone mold surface having different curvatures of this at the time of drawing speed conditions, or can be applied. To the late 1970s and early 1980s, with the increase rate of pull, pull mode of life became a prominent issue. In order to meet the requirements of high-speed cable, the United States and EGKennth T.Maxwall proposed a "linear" theory. The theory focuses on considering the drawing process lubrication and wear factor, noted by the improved linear pull mode pass should have the following characteristics:
 

    (1) a longitudinal section line pass each part must be straight, flat work force smallest cone drawing;
    (2) the transfer of part of the mold each part must be clear, so that each part can give full play their respective roles, to avoid a reduction in the angle of the actual length of the transition zone sizing;
     (3) extend the height of the entrance area and the work area, the wire into the middle section of the die hole taper work, the use of the wedge on the inlet cone angle and work half cone angle formed by the establishment of "wedge effect" in the wire surface to form a more compact solid lubricating film, reducing wear and suitable for high-speed drawing;
    (4) sizing area must be flat and reasonable length. Sizing zone too long, cable friction increases, after the wire pulled out easily cause necking die hole or break, sizing area is too short, it is difficult to obtain a stable shape, size, accuracy and good surface quality of the wire, while the die hole also will soon wear tolerance.
Through practical application, using linear theory to design a pull mode, its life than the R-type cable model increased by 3-5 times.
 

    3.3 drawing machine equipment installation must be reasonable
     Installed base (1) drawing machine needs very strong, avoid vibration phenomena;
     (2) through the wire stretching debugging installation symmetry axis and the center line of the die hole, the wire and cable model stress uniformity;
     (3) Pull the process to avoid frequent start stop, start drawing the tensile stress due to friction caused when normal ratio of friction when the drawing is much greater, which is bound to increase the mold wear.
 

    3.4 for drawing the wire to go through the pre-treatment
     (1) Surface preparation: For surface dirt, adhering more impurities wire, first after washing, drying and then be drawn; for more wire surface oxide scale, first through a fine acid, bake dry and then be drawn; for the present on the surface from the skin, dimples, heavy leather and other phenomena of the wire, but also through the grinder after grinding were conducted drawing;
     (2) Heat treatment: For the hardness is too large or uneven hardness of the wire, first reduce the hardness by annealing or tempering, and the wire holding good hardness uniformity then drawn.
 

    3.5 to maintain proper drawing surface shrinkage
     Diamond Drawing mold itself has a hard, brittle characteristics, if for Omo shrinkage of necking drawing, can easily lead to mold can withstand the stress fracture scrapped, and therefore depending on the mechanical properties of the wire, select the appropriate surface Drawing shrinkage rate. Stainless steel wire drawing diamond die, usually single-channel surface shrinkage rate does not exceed 20%.
 

    3.6 Use good lubrication performance lubricants
     In the drawing process, the supply of lubricants and lubricant quality are affecting the adequacy of pull mode of life. Thus requiring the lubricant oil base stability, good oxidation resistance, with excellent lubrication, cooling and cleaning of the entire production process has always been to maintain optimum lubrication, in order to form a layer able to withstand high pressures without being destroyed The film, the work area to reduce friction and improve mold life.

     Use of the process, we must continue to observe the condition of lubricating oil, lubricating oil, if found serious discoloration or metal powder to increase, we must promptly replace or filtered, to avoid lubricating oil lubricating performance degradation due to oxidation, while avoiding drawing process tiny shed metal particles mold damage.
 

    3.7 Regular maintenance grinding diamond wire drawing dies
     Cable model in the long-term use, the die wall friction by strong metal wire and scouring action will inevitably produce wear and tear, the most common is the emergence of an annular groove Caojing (dents) in the wire at the entrance to the work area. Pull mode ring groove appears exacerbated wear die hole, because the ring ditch because loose and flaking of the core material of small particles into the wire die hole workspace and sizing zone, acts as an abrasive, and enter Wire die hole is like grinding as increased wear die hole. If we do not fix exchange, then the ring groove will continue to accelerate the expansion, so the repair more difficult, there may even be a crack in the annular groove deeper, broken the mold completely collapse scrapped.
 

    Learn from experience, to develop a set of standards, strengthen the routine maintenance, repair mold is often very cost-effective thing. Once the mold there are any slight abrasion, timely polishing, then the mold is restored to its original state spent polishing time is shorter, and pass no significant changes in the size of the mold.

    In summary, in order to prolong the life of the cable model, in addition to select the appropriate mold material, well-designed hole size, improve the manufacturing level pull mold, the mold hole surface finish process requirements, but also must determine a reasonable track times compression ratio, improving the conditions of use of the cable model. Note that the mold in the course of routine maintenance, you should wash frequently changes, and to ensure that the stretching process has a good lubricating effect.

 
 
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