A forming device and method for permanent ferrite magnetic tiles with a large central angle

Abstract

A forming device and forming method for a permanent ferrite magnetic tile with a large central angle, comprising a hydraulic press, a magnetic tile mold, a magnetization and demagnetization device, a feeding device, a spray blank taking device and a mold cavity liquid level adjusting device. The mold cavity liquid level adjusting device is installed on the spray blank taking device. Before the slurry is injected into the mold cavity of the magnetic tile mold, a large amount of water is accumulated on the arch height surfaces on both sides of the lower punch die in the mold cavity through the mold cavity liquid level adjusting device, so as to increase the water content of the slurry on both sides of the mold cavity. The green blanks of the permanent ferrite magnetic tiles with a large central angle formed by using the device and method of the present invention have basically the same density at each part, can completely solve the problem that the two sides of the magnetic tile are easily cracked due to "low compression ratio in the middle and large compression ratio on both sides" during the forming of the permanent ferrite magnetic tile with a large central angle, greatly improve the forming qualified rate of the permanent ferrite magnetic tile with a large central angle, and reduce the production cost.

Description

Technical Field

[0001] The present invention relates to a magnetic tile forming device and method, and particularly to a large central angle permanent ferrite magnetic tile forming device and method. Background Art

[0002] Permanent ferrite magnetic tiles are the exciting components of permanent magnet motors. The production of permanent ferrite magnetic tiles generally includes the following processes:

[0003] (1) Wet-grind the raw materials into a slurry with a particle size of about 1 μm, and the water content of the slurry is in the range of 30%-38%;

[0004] (2) Inject the slurry into the die cavity. The hydraulic press presses the slurry in the die cavity under the condition of strong magnetic field orientation. Most of the water in the slurry is discharged out through the filter cloth on the upper die of the die, and the slurry is dehydrated and formed into a green body of the magnetic tile;

[0005] (3) Sinter the green body of the magnetic tile at high temperature to obtain a magnetic tile blank;

[0006] (4) The magnetic tile blank becomes a finished magnetic tile after grinding and cleaning.

[0007] For large central angle magnetic tiles, due to the uneven wall thickness in the vertical direction at each position, the compression ratio (compression ratio: depth of the slurry in the vertical direction / thickness of the green body in the vertical direction) at each position is different during the compression molding process, and it is difficult to make the density of each position of the pressed blank uniform, resulting in cracks and other defects in the product. CN202010098587.X has the following specific analysis on the difficulties of forming large central angle permanent ferrite magnetic tiles: When the magnetic tile is formed, the compression ratio at both sides of the magnetic tile is the largest (about 2.3), so the density of the green body at this place is also the largest; the compression ratio at the center of the magnetic tile is in the middle (about 2.0), and the density of the green body is in the middle; while the compression ratio at the corresponding position of the end of the inner arc of the magnetic tile is the smallest (about 1.6), and the density of the green body is the lowest. Due to the large jump of the green body density from the maximum to the minimum in a small area near both sides of the green body, due to the drastic fluctuation of the green body density distribution, cracks and other defects are likely to occur in this area. For magnetic tiles with a larger central angle, this problem is more serious.

[0008] Through long-term experiments and research, the inventor of the present invention found that if the water content of the slurry in the die cavity forms a distribution of "high water content at both sides and low water content at the center", that is, a slurry with a high water content is used in the large compression ratio area and a slurry with a low water content is used in the small compression ratio area, the density of the green body in each area can theoretically tend to be consistent at the end of the pressing, which is expected to solve the problems of cracks and other defects caused by uneven green body density distribution, thereby greatly improving the product qualification rate. Summary of the Invention

[0009] The technical problem to be solved by the present invention is to overcome the deficiencies of the prior art and provide a forming device and method for large central angle permanent magnet ferrite magnetic tiles that can improve the forming yield rate.

[0010] The technical solution adopted by the present invention to solve its technical problems is a forming device for large central angle permanent magnet ferrite magnetic tiles, including a hydraulic press, a magnetic tile mold, a magnetization demagnetization device, a feeding device, a spray blank taking device, and a mold cavity liquid level adjusting device. The mold cavity liquid level adjusting device is installed on the spray blank taking device, and the mold cavity liquid level adjusting device includes a plurality of water outlets.

[0011] The spray blank taking device includes a blank taking missed inspection checking function module. The blank taking missed inspection checking function module is divided into two sub-modules, and the two sub-modules are installed staggeredly according to different installation height positions. The low-position sub-module is used to check the missed inspection of green blanks at the mold cavity opening, and the high-position sub-module is used to check the missed inspection of green blanks at other positions on the mold surface.

[0012] A forming method for a large central angle permanent magnet ferrite magnetic tile forming device includes operations such as blank taking, controlling the height of the arched surfaces on both sides of the lower punch die, spraying, injecting water into the mold cavity, closing the mold and feeding, pressing, holding pressure, demagnetizing, opening the mold, and returning. After the spray blank taking device takes the blank, then the hydraulic press controls the arched surfaces on both sides of the lower punch die to be more than 5 mm lower than the mold cavity surface, and then starts the spraying operation of the spray blank taking device and the mold cavity water injection operation of the mold cavity liquid level adjusting device. After the mold cavity liquid level adjusting device completes the mold cavity water injection operation, the accumulated water depth on the arched surfaces on both sides of the lower punch die in the mold cavity is not less than 4 mm.

[0013] The specific steps of the closing the mold and feeding process are as follows: after the upper mold descends to close the mold with the cavity body, the magnetization demagnetization device applies a magnetization magnetic field, and the feeding device injects the slurry into the mold cavity through the feeding small holes of the cavity body. Since a large amount of water has accumulated at the arched surfaces on both sides of the lower punch die, the slurry at the arched surfaces will actually be soaked in water, and the water content of the slurry at this place will be significantly increased. While the middle part of the mold cavity is the convex top, the slurry still maintains the original lower water content level, realizing the distribution of the slurry in the same mold cavity with low water content in the middle and high water content on both sides.

[0014] As a simplification of the operation, when the number of parts per mold in the magnetic mold is small, the mold cavity water injection operation can also be completed by spraying a large amount of spray through the spray blank taking device to cause the release agent to accumulate in the mold cavity.

[0015] The present invention has the following positive effects: The densities of each part of the green blank of the large central angle permanent magnet ferrite magnetic tile formed by using the device and method of the present invention are basically the same, which can completely solve the problem that the two sides of the green blank of the large central angle permanent magnet ferrite magnetic tile are prone to cracking, greatly improve the forming yield rate of the large central angle permanent magnet ferrite magnetic tile, and greatly reduce the production cost. Description of the Drawings

[0016] Figure 1It is a schematic cross-sectional view of the structure of the large central angle permanent ferrite magnetic tile mold in the embodiment of the present invention;

[0017] Figure 2 It is a schematic diagram of the forming compression ratio at each position in the mold cavity of the large central angle permanent ferrite magnetic tile mold in the embodiment of the present invention (the compression ratios on both sides are AA1 / A2A1 and EE1 / E2E1, the compression ratio in the middle is CC1 / C2C1, and the compression ratio at the end of the inner arc is BB1 / B2B1 and DD1 / D2D1);

[0018] Figure 3 It is a schematic diagram of the water flowing along the lower punch die surface and converging on the arch height planes on both sides of the lower punch die after the mold cavity is filled with water in the embodiment of the present invention;

[0019] Figure 4 It is a schematic diagram of the blank taking missed inspection checking function module of the spray blank taking device in the embodiment of the present invention (the view of the mold is the left view).

[0020] Figure 1 、 Figure 3 、 Figure 4 In the figures: 1 - upper die, 2 - filter cloth and filter paper, 3 - mold cavity, 3a - arch height plane on the left side of the lower punch die, 3b - arch height plane on the right side of the lower punch die, 3C - liquid accumulation on the arch height areas on both left and right sides of the lower punch die, 4 - small injection holes in the cavity body, 5 - cavity body, 6 - lower punch die, 7 - mold cavity liquid level adjustment device, 8a - high-position function module for blank taking missed inspection checking, 8b - low-position function module for blank taking missed inspection checking, 9 - spray blank taking device, 10 - green magnetic tile blank; Figure 2 In the figures, the areas surrounded by A, B, C, D, E, E1, D1, C1, B1, A1 and A are the slurry cross-sections formed during injection; the areas surrounded by A2, B2, C2, D2, E2, E1, D1, C1, B1, A1 and A2 are the green blank cross-sections formed at the end of pressing. Detailed implementation manners

[0021] The present invention will be further described in detail below with reference to the accompanying drawings and embodiments.

[0022] Referring to the attached Figures 1 - 4 , in this embodiment, a permanent ferrite magnetic tile hydraulic press, an R34.4*r26.8*W64.6*L50 type magnetic tile mold, a magnetization and demagnetization device, an injection device, and a spray blank taking device known in the art are used. In addition, a mold cavity liquid level adjustment device 7 is installed on the spray blank taking device.

[0023] The mold used in this embodiment is a permanent magnet ferrite tile forming mold (R34.4*r26.8*W64.6*L50 model tile mold) manufactured using known technology, which mainly includes an upper mold, a cavity, and a convex lower punch. A large number of small drainage holes are opened on the lower end surface of the upper mold, and the small drainage holes are connected to the vacuum negative pressure pipeline. During molding, the lower end surface of the upper mold is wrapped with filter cloth and filter paper. The specific steps of molding include:

[0024] (1) Taking out the blank: Use the spray blank taking device to take out the finished magnetic tile blank;

[0025] (2) Control the height of the arch surfaces on both sides of the lower punch: After the lower punch 6 is lowered to below the injection hole 4 of the cavity, the arch surfaces 3a and 3b on both sides of the lower punch are about 20 mm lower than the surface of the cavity. At this time, the arch surfaces on both sides of the lower punch are ready to collect water;

[0026] (3) Spraying: The spray blank removal device 9 sprays so that the lower punch surface is covered with the demoulding liquid to prevent the green blank and the lower punch from sticking when the blank is removed;

[0027] (4) Mold cavity water injection: The mold cavity liquid level adjustment device 7 injects water into each mold cavity. The injected water flows down along the lower punch surface and gathers on the arch height surfaces on both sides of the lower punch (see attached Figure 3 As shown in 3C), the amount of water injected into the mold cavity can be controlled by adjusting the injection time or speed;

[0028] (5) Mold closing and injection: After the upper mold 1 wrapped with filter cloth and filter paper 2 moves down to close the mold with the cavity, the demagnetization device applies a magnetizing magnetic field, and the injection device injects the slurry into the mold cavity through the injection hole 4 of the mold cavity. Since a large amount of water has been collected at the arch surface on both sides of the lower punch 6, the slurry at the arch surface will actually be soaked in water, and the water content of the slurry at this place will be significantly increased. The middle part of the mold cavity is the convex top, and the slurry still maintains the original low water content level, thereby achieving the distribution of "low water content in the middle and high water content on both sides" of the slurry in the same mold cavity;

[0029] (6) Pressing: The hydraulic press slowly pressurizes the slurry in the mold cavity and is pressed and dehydrated under the condition of magnetic orientation (the water passes through the filter cloth 2 and enters the drainage hole of the upper mold and then is discharged to the outside) until the pressure of the press reaches the process requirement value;

[0030] (7) Maintaining pressure: The pressure of the press is maintained at the process requirement value for several seconds;

[0031] (8) Demagnetization: The demagnetization device applies a demagnetization magnetic field to demagnetize the green body in the mold cavity so that the green body can be demolded;

[0032] (9) Mold opening and return stroke: The upper mold moves upward and returns, and the mold ejects the green billet so that the spray billet removal device 9 can take the billet.

[0033] If the green compact adheres to the lower punch die surface and cannot be removed, there is a set of inspection function modules for missed blank picking on the blank picking spray device in the conventional forming facility, which is used to sweep the upper surface of the cavity to check for missed blank picking. However, in the present invention, when the height of the arched surfaces on both sides of the lower punch die is more than 4 mm lower than that of the cavity in step (2) of the next cycle, the green compact may be re-introduced into the die cavity by the lower punch die, and it is impossible to detect such missed blank picking by only sweeping the upper surface of the cavity. To avoid missed blank picking, two sets of inspection function modules for missed blank picking are installed on the blank picking device. The low-position function module 8b checks for missed blank picking at the die cavity opening, and the high-position function module 8a checks for missed blank picking at other positions on the die surface. If missed blank picking or blank dropping occurs at any position, the corresponding inspection function module for missed blank picking sends an alarm signal, and the press pauses pressing to remind the staff to come and troubleshoot.

[0034] After the green compact of the large central angle permanent magnet ferrite magnetic tile formed by the above method is sintered and ground, the product basically eliminates the cracks on both sides, and the yield rate reaches more than 92%, which is a significant improvement compared with the yield rate of about 80% in the conventional technology, and the production cost is greatly reduced.

[0035] The working principle of the present invention is as follows:

[0036] In the conventional forming method, the water content of the slurry injected into the die cavity of the magnetic tile is the same at each part, and the pressing stroke in the vertical direction at each part is also the same. However, after pressing, the wall thicknesses in the vertical direction at each position of the formed magnetic tile blank are different, resulting in different compression ratios at each part of the blank, which is reflected in different water contents at each part of the green compact, and different densities at each part of the blank are inevitable.

[0037] The inventor of the present invention calculated the relationship between the water content of the slurry, the compression ratio, and the water content of the green compact during the forming process through research on the forming mechanism of magnetic tiles as follows:

[0038] Assume the weight of the slurry is 1, and the water content of the slurry is x, then the content of the powder in the slurry is 1 - x;

[0039] Assume the weight of the green compact is 1, and the water content of the green compact is y, then the content of the powder in the green compact is 1 - y;

[0040] According to physical common sense, the true density of the permanent magnet ferrite powder is 4.9 g / cm3, and the density of water is 1 g / cm3;

[0041] Both the slurry and the green compact are composed of powder and water in a close-packed state. Assuming that there is no lateral displacement of the slurry particles during the forming process and only longitudinal (vertical) compression displacement, then:

[0042] The density of the slurry is ρ1 = 1 / (x / 1+(1 - x) / 4.9) = 1 / (0.204 + 0.796x);

[0043] The green body density is ρ2 = 1 / (y / 1+(1 - y) / 4.9) = 1 / (0.204 + 0.796y).

[0044] Let the volume of the slurry be V1 and the volume of the green body be V2, then:

[0045] The weight of the powder in the slurry = the weight of the slurry * (1 - x) = (1 - x) * ρ1 * V1;

[0046] The weight of the powder in the green body = the weight of the green body * (1 - y) = (1 - y) * ρ2 * V2;

[0047] Neglecting the factor of material leakage during the forming process, then: the weight of the powder in the slurry = the weight of the powder in the green body;

[0048] That is: (1 - x) * ρ1 * V1 = (1 - y) * ρ2 * V2;

[0049] Therefore, the ratio of the volume of the slurry to the volume of the green body (which is the vertical compression ratio at each position) can be calculated

[0050] V1 / V2 = ρ1 * (1 - y) / ρ2 / (1 - x)

[0051] = (1 - y) * (0.204 + 0.796x) / (1 - x) / (0.204 + 0.796y) (1)

[0052] According to the above, taking the water content of the magnetic tile forming slurry as 34% as an example, based on formula (1), the corresponding data results among the water content of the slurry, the compression ratio, and the water content of the green body under the condition that the water content of the slurry is 34% are shown in Table 1 below:

[0053] Table 1

[0054] Slurry moisture content x 34% 34% 34% 34% 34% 34% 34% 34% 34% 34% 34% Green body moisture content y 9.5% 10.5% 11.5% 12.5% 13.5% 14.5% 15.5% 16.5% 17.5% 18.5% 19.5% Corresponding compression ratio 2.33 2.24 2.15 2.07 2.00 1.92 1.86 1.79 1.73 1.67 1.61

[0055] As can be seen from Table 1, on the premise that slurry particles do not produce lateral displacement during the assumed forming process and only have longitudinal (vertical) compression displacement, when the compression ratios are 2.33 (typical side compression ratio), 2.0 (typical middle compression ratio), and 1.61 (typical inner arc end compression ratio) respectively, the corresponding green body water contents are 9.5%, 13.5%, and 19.5%. The differences in these three green body water content data are significant, reflecting significant differences in the density of each position of the green body. In particular, the compression ratio at both sides of the magnetic tile green body is too large and the green body water content is too low. According to the principle of material forming science, when there are obvious density differences in different parts of the blank during the forming process, the particles in the blank in the large density area will produce lateral layer shift towards the small density area. There will be a large stress distribution in the lateral layer shift, and cracks are more likely to appear at the corners of the blank due to the rapid release of stress during demolding. This is the reason why the two sides of the magnetic tile with a large central angle are prone to cracking under normal forming process conditions.

[0056] If the water content of the slurry at each position in the mold cavity is adjusted to different values, it is possible to achieve the same water content in the green body under different compression ratio conditions, thereby making the density of each position of the green body tend to be the same. Based on formula (1), the data in Table 2 can be calculated as follows:

[0057] Table 2

[0058] Slurry moisture content x 38.8% 34.0% Green body moisture content y 13.5% 13.5% Corresponding compression ratio 2.33 2.00

[0059] Table 2 shows that when the water content of the slurry at both sides of the magnetic tile is adjusted to 38.8%, at a compression ratio of 2.33, the corresponding green body water content is 13.5%, thus being the same as the green body water content obtained under the condition of "the water content in the middle of the magnetic tile is 34% and the corresponding compression ratio is 2.0", and thus achieving the same density of each position of the green body.

[0060] In the above example in the theoretical analysis, the calculation example is based on a slurry water content of 34%. In fact, according to formula (1), it can be found that for various slurry water content conditions, the same conclusion can be drawn, that is: after achieving the distribution of "low water content in the middle and high water content on both sides" of the slurry in the same mold cavity, it is beneficial to improve the consistency of the water content of each part of the magnetic tile green body, and further improve the consistency of the density of each position of the green body.

[0061] Those skilled in the art can make various modifications and variations to the present invention. If these modifications and variations are within the scope of the claims of the present invention and their equivalent technologies, then these modifications and variations are still within the protection scope of the present invention patent.

[0062] The content not described in detail in the specification is the prior art well-known to those skilled in the art.

Claims

1. A method of using a forming device for large central angle permanent ferrite magnetic tiles, the device comprising a hydraulic press, a magnetic tile mold, a magnetization and demagnetization device, a feeding device, a spray and blank taking device, and a mold cavity liquid level adjusting device, characterized in that: The cavity liquid level adjusting device is installed on the billet taking and spraying device. The cavity liquid level adjusting device includes a plurality of water outlets. The process includes billet taking, controlling the height of the arch surfaces on both sides of the lower punch die, spraying, injecting water into the cavity, closing the mold and injecting material, pressing, holding pressure, demagnetizing, opening the mold, and returning. After billet taking, the height of the arch surfaces on both sides of the lower punch die needs to be ensured to be more than 5 mm lower than the cavity surface of the mold before starting the spraying and cavity water injection process operations. Before closing the mold and injecting material, the depth of the accumulated water at the bottom on both sides of the mold cavity is not less than 4 mm.

2. The method of using a forming device for large central angle permanent ferrite magnetic tiles according to claim 1, characterized in that: The billet taking and spraying device includes a billet taking missed inspection checking function module, which is divided into two sub-modules. The two sub-modules are installed in a staggered manner according to different installation height positions. The low-position sub-module is used to check for missed inspection of green billets at the cavity opening, and the high-position sub-module is used to check for missed inspection of green billets at other positions on the mold surface.

3. The method of using a forming device for large central angle permanent ferrite magnetic tiles according to claim 1, characterized in that: The cavity water injection process is completed by spraying a large amount of spray through the billet taking and spraying device to cause release agent accumulation in the cavity.

Images