[China Aluminum Network] shrinking tail is on the surface of the billet oxide scale, segregation of tumors or oil and other impurities and attached to the liner lining of dirt, lubricants, etc., in the extrusion squeezed into the interior of the extrusion, Disadvantages are the internal discontinuousness, non-denseness of the metal product, and the reduction of the structure and performance. According to its location, it is divided into three types: central shrinking, ring shrinking and subcutaneous shrinking. It is a technical problem that has been plaguing the development of extrusion technology for a long time. It accounts for almost half of the amount of bar waste, which seriously affects the finished product rate of bars and reduces the production efficiency and economic efficiency of enterprises.
In practical production, certain effects are achieved by adjusting the extrusion process conditions. For example, by increasing the thickness of the extrusion press, it is generally about 60mm to 80mm, or the method of ingot casting can better solve the shrinkage problem, but it reduces the product yield, and increases the consumption of man-hours and energy consumption. Increase production costs. In order to find a way to avoid shrinkage and reduce the thickness of extrusion press, the method of avoiding the ingot ingot process is specifically studied from the perspective of the mold design structure, and a total of nine different design structures have been selected. A comparative extrusion test was performed. Trying to find a suitable mold design structure to minimize shrinkage waste and increase the yield of aluminum alloy rods.
1 Test Equipment and Test Plan The test material was 6063 aluminum alloy. After homogenization, the test piece was not carburized and cut into a finished ingot of Φ130×550 mm. The ingot is uniformly heated to 490-500°C in a heating furnace, and is used in a Φ130mm round extrusion tube of a 10MN horizontal extruder. A Φ200 (single hole) mold is used. The temperature of the mold is 430-450°C, and the positive direction is used. Lubricate and extrude Φ20mm 6063 aluminum alloy bar. λ=45.56; Extrusion speed V=23-25 ​​m/min; Extrusion press 15 mm; Extrusion length 22000 mm. A total of nine kinds of design structures were used for extrusion. Two extrusions were used for each type of die structure, and then the second long-extruded material was taken from the trailing end to the front end to cut low-magnification specimens and recorded. The length of the tail shrinking under the mold structure was compared and studied.
2 Test results and discussion 2.1 Test results The mold structures used in tests 1 to 9 are shown in Figures 1 to 9, respectively, and the tail-reduced lengths are shown in Table 1. The squeezed residual thickness under the conditions listed in the table are all 15 mm, and the reduced tail length includes the length of tailing of the first and second ends of the extrusion.
2.2 Discussion (1) The shrinking of the extruded section head is mainly due to the fact that the test extrusion pressure is too short, only 15 mm. This causes the ingot surface oxides, segregated neoplasia, or oil stains to be trapped in the mold and remain in the mold's diversion trough and aluminum storage ring when the last ingot extrusion is completed. When the next ingot is extruded , it must first squeeze the residual aluminum in the mold first, so that the formation of the first paragraph shrinkage. If the remaining pressure is long enough, it is not easy to shrink the head.
From the comparison of the design structures of the 1, 3, 4 mold design and the tail-reduced lengths of the head and tail sections, it can be seen that under the same extrusion process conditions, the inlet dimension of the mold diversion tank is 25 mm (see Fig. 4). The end of the compression tail is reduced to a length of 3,000 mm; when the inlet size is 100 mm (see Figure 2), the tail end of the extrusion is shorter and only 1200 mm. However, when the entrance size is increased from 100mm to 125mm or decreased to 85mm, the length of the tail-end shrunk will become longer. This proves that the design of the inlet dimension of the aluminum storage ring or diversion tank is one of the key elements to control the tailing shrinkage. Because the width and height of the front end dead zone formed by the aluminum storage ring or guide groove and the extrusion cylinder liner (as shown in Fig. 10) will affect the aluminum alloy ring or the end of the diversion tank to face the surface oxide of the barrier ingot. Segregation of tumors, oils and other dirt into the mold effect. Therefore, the determination of the inlet dimension of the aluminum storage ring or diversion tank must ensure that a sufficient width of the front dead zone is formed, and the height of the front dead zone should be reduced as much as possible.
The width L of the front dead zone is approximately equal to the difference between the radius of the lining of the squeezing cylinder and the radius of the outer circle of the aluminum sluice or the inlet of the diversion channel, as shown in FIG. 11 . In the same alloy and under the same extrusion process conditions, the width of the front end dead zone formed by the liner of the die and the extrusion cylinder is larger, and the dead zone height h is larger. The higher the dead-end height of the front end, the earlier the ingot's outer oxides, segregated neoplasia, or oily dirt will flow toward the center and form a longer tail-shrunk. The inlet size of the aluminum storage ring or diversion tank shown is neither as large as possible nor as small as possible. For example, the heights of the front dead zones of tests 1, 2, 3, and 4 are respectively 5mm, 17.5mm, 25mm, and 55mm. It can be seen from Table 1 that when the height of the dead zone at the current end is 17.5mm, the compression of the tail is prevented. The effect is good.
(3) The influence of the length and angle of the mold working belt on the length of tailing. From the comparison of the mold construction and tailing results of Test 1 and Test 5, and the comparison of the mold construction and shrinkage results of Test 5 and Test 6, it can be seen that the working belt length is shortened or the working belt is made to have a flow angle of 88°. The design can reduce the influence of the frictional stress on the aluminum alloy when it is squeezed through the working belt, so that the metal flow velocity in the metal deformation area and the outside tends to balance more, and the length of the tail section shrinking is reduced.
(4) The effect of the volume of the aluminum storage ring and the diversion channel on the length of the shortened tail.
The difference between the die structure of test 7 and test 8 is that the thickness of the aluminum storage ring is different, but the shrinkage of the head and tail section is not the same. The trailing end of test 7 is 0 mm, and the end of test 8 is the tail end. 150mm, the thicker aluminum storage ring is just equivalent to the extrusion of the tail ingot into the aluminum storage ring, which is equivalent to the extension of the thickness of the pressure, but it can not be cut off, but in turn it has increased the end of the tail length. This shows that the thicker tailings of the aluminum storage ring are shorter and even disappear. The comparative analysis of the results of Test 6 and Test 9 also shows that reducing the depth of the trough is equivalent to reducing the thickness of the pressure residue. The smaller the depth of the trough, the shrinkage of the extrusion head section. The smaller, but in turn increases the length of the end of the tail. In summary, the thicker the aluminum storage ring and the deeper the depth of the diversion channel, the shorter the tailing produced in the extrusion tail section, but it increases the tailing waste in the extrusion head section. The length of the tailing shrinkage waste in the extrusion head section is approximately equal to V/S (V: the volume of the aluminum storage ring and the diversion tank; S: the cross-sectional area of ​​the extruded bar).
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