1、 High-quality carbide drawing die produced by advanced die processing technology or diamond drawing die shall be selected as far as possible
At present, high-speed mechanical grinders and metal grinding needles plated with hard alloy on the surface are commonly used for the grinding process of wire drawing dies in foreign countries. The equipment operates stably, and the specifications and use of grinding needles make the product precision higher. The hole size of the die is detected by the contour recorder and the aperture measuring instrument, and the surface finish is checked by the special microscope for checking the pull-wire die. But many domestic manufacturers are still using backward equipment, using manual operation to grind the hole pattern, therefore, there are the following problems: the fluctuation of hole pattern parameters is large, and it is difficult to process a straight working cone; The transition angle is easy to be grinded at the joint between the sizing area and the working area, so that the wire material generates secondary compression in the sizing area, increases the external friction, shortens the length of the sizing area, and shortens the service life of the mould; The repair frequency of worn grinding pin varies from person to person, and the use is not standardized, resulting in poor consistency of hole type. Inspection methods are also backward, only visual inspection or simple tools such as magnifying glass and microscope can be used for inspection. What's more, attention is paid to the smoothness of the inner surface of the mold, and the hole size cannot be effectively inspected, let alone controlled.
2、 Selection of drawing dies with good hole pattern design
The hole type of drawing die is generally divided into curve type (i.e. R series) and straight type (i.e. taper series).
Analyzing from the angle of uniform deformation of 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 theory of "smooth transition". According to the working nature, the hole structure can be divided into five parts: "population area", "lubrication area", "working area", "fixed diameter area" and "leaving day area". The joint of each part requires "chamfering" and smooth transition. The whole hole type can be grinded into a large, single surface with different curvatures. Under the condition of the drawing speed at that time, this hole type can be applicable. From the late 1970s to the early 1980s, with the increase of wire pulling speed, the service life of wire pulling die became a prominent problem. In order to meet the requirements of high-speed guy wire, T. Maxwall and E.G. Kennth of America put forward the theory of "straight line". The theory focuses on the lubrication and wear factors in the drawing process, and points out that the improved straight wire die hole type should have the following characteristics:
(1) The longitudinal section line of each part of the hole type must be straight, and the pulling force of the straight working cone surface is the minimum;
(2) The connection part of each part of the mould must be obvious, so that each part can give full play to their respective functions, avoiding the reduction of the transition angle to the actual length of the sizing area;
(3) Extend the height of the inlet area and the working area to make the wire enter the middle section of the die hole working cone. Establish the "wedge effect" by using the wedge area formed by the inlet cone angle and the upper part of the working cone angle, so as to form a denser and firm lubricating film on the wire surface, reduce abrasion and adapt to high-speed drawing;
(4) The sizing area must be straight and of reasonable length. If the sizing area is too long, the wire friction will increase, which will easily cause diameter reduction or wire break after the wire is pulled out of the die hole. If the sizing area is too short, it is difficult to obtain the wire with stable shape, accurate size and good surface quality. Meanwhile, the die hole will be quickly worn out.
Through practical application, the service life of the pull-wire die designed by linear theory is 3-5 times longer than that of R-type pull-wire die.
3、 The installation and use of wire drawing machine shall be reasonable
(1) The installation foundation of wire drawing machine shall be very stable to avoid vibration;
(2) During installation, the tensile axis of the wire material shall be symmetric with the centerline of the die hole through commissioning, so as to ensure uniform stress of the wire material and the stay wire die;
(3) Frequent start and stop shall be avoided during the pulling process, because the friction caused by the pulling stress during the pulling start is much greater than the friction during the normal pulling, which will certainly increase the wear of the die.
