Production equipment and production process of composite magnet

Abstract

The invention relates to the technical field of composite magnet production, in particular to production equipment and a production process of a composite magnet. The production equipment of the composite magnet comprises a rack, a magnet forming structure, a sintering structure and a driving assembly used for driving the magnet forming structure are arranged on the rack, the magnet forming structure comprises at least two sets of forming molds matched with each other, and forming cavities used for forming the composite magnet are formed in the forming molds. And the sintering structure is integrated on the forming mold and is used for enabling the composite magnet to form a compact structure. The composite magnet forming and sintering device has the following effects that the forming function and the sintering function are integrated in the same device, the production process is simplified, material transfer between procedures is reduced, the production efficiency of a composite magnet is improved, and the production cost is reduced.

Description

Technical Field

[0001] The present application relates to the technical field of composite magnet production, and in particular to a composite magnet production device and a production process thereof. Background Art

[0002] Composite magnets are widely used in electronics, energy and other fields due to their unique properties, and their production technology is developing rapidly with the continuous growth of market demand.

[0003] At present, the production of composite magnets involves multiple process links, including raw material preparation, molding, sintering, etc. These processes place high demands on the integration and efficiency of equipment. Efficient production equipment can not only improve production efficiency, but also reduce energy consumption, thereby promoting the large-scale application of composite magnets.

[0004] In the prior art, in order to realize the production of composite magnets, segmented equipment is usually used to complete each process: preliminary forming is performed through an independent mold forming device, and then the semi-finished product is transferred to a special sintering furnace for sintering.

[0005] However, there may be problems with the smooth connection of the process steps during the transfer of the semi-finished products to the sintering furnace, resulting in low production efficiency of the composite magnets and increased production costs. Summary of the Invention

[0006] In order to improve the production efficiency of composite magnets and reduce production costs, the present application provides a production device for composite magnets.

[0007] The present application provides a production device for composite magnets, which adopts the following technical solution: it includes a frame, on which is provided a magnet forming structure, a sintering structure and a driving assembly for driving the magnet forming structure; the magnet forming structure includes at least two groups of mutually cooperating forming molds, a forming cavity for forming a composite magnet is provided in the forming mold, and the sintering structure is integrated on the forming mold and is used to form a dense structure of the composite magnet.

[0008] By adopting the above technical solution and integrating the forming and sintering functions into the same equipment, the production process is simplified, the material transfer between processes is reduced, the production efficiency of the composite magnet is improved, and the production cost is reduced.

[0009] Preferably, the molding mold includes an upper mold and a lower mold, and the upper mold and the lower mold are connected by a guide member. When the upper mold and the lower mold are connected, a complete molding cavity is formed. The driving assembly is used to drive the upper mold close to the lower mold. The guide member includes at least one guide column arranged on the upper mold, and the lower mold is provided with at least one guide hole for inserting the guide column, and multiple guide columns and multiple guide holes correspond one to one.

[0010] By adopting the above technical solution, the cooperation of the guide column and the guide hole can ensure that the upper mold and the lower mold remain precisely aligned during the pressing process, avoiding confusion in the internal orientation structure of the magnet due to misalignment; the drive assembly is used to drive the upper mold close to the lower mold, thereby achieving high-pressure pressing of the mixed powder.

[0011] Preferably, a heat dissipation component is provided on the frame, and the heat dissipation component is arranged between the upper mold and the lower mold in the vertical direction. The end of the heat dissipation component away from the forming mold is connected to a heat recovery structure, and the heat recovery structure is used to recover the heat energy generated by forming and sintering.

[0012] By adopting the above technical solution and adding heat dissipation components and heat recovery structures, not only the temperature of the equipment during operation is effectively reduced, dissipating heat and cooling the sintered green body, but also heat recovery is achieved, reducing energy consumption in the production process.

[0013] Preferably, the heat dissipation assembly includes a heat dissipation head, a heat dissipation pipe and a suction pump, one end of the heat dissipation pipe is connected to the heat dissipation head, and the other end of the heat dissipation pipe is used to be connected to the heat energy recovery structure, the heat dissipation head is away from one end of the heat dissipation pipe toward the forming mold, and the suction pump is used to absorb the heat energy generated by forming and sintering into the heat energy recovery structure.

[0014] By adopting the above technical solution, the heat sink is close to the forming mold to absorb the heat generated during the forming and sintering process. The suction pump is used to transfer the heat from the heat sink to the heat energy recovery structure to achieve heat energy recovery and further reduce energy consumption.

[0015] Preferably, a mixing drum is also provided on the frame, and the mixing drum is used to mix and stir the raw materials for producing composite magnets. A heating chamber is provided on the wall of the mixing drum for providing heat to the raw materials for producing composite magnets in the mixing drum, and the heating chamber is provided along the entire circumference of the mixing drum.

[0016] By adopting the above technical solution, the heating chamber is opened along the entire circle of the mixing drum to provide heat to the raw materials for producing the composite magnet in the mixing drum, so that the raw materials for producing the composite magnet are kept dry.

[0017] Preferably, the heat energy recovery structure includes a heat energy recovery pipe, which is spiral and embedded in the heating chamber. The heat energy recovery pipe is coiled around the mixing drum and coiled from bottom to top along the axial direction of the mixing drum in the heating chamber. One end of the heat energy recovery pipe is connected to the heat dissipation pipe, and the other end of the heat energy recovery pipe passes through the mixing drum.

[0018] By adopting the above technical solution, the heat recovery pipe is spirally coiled in the heating chamber. This design can increase the contact area between the raw materials for producing composite magnets in the mixing drum and the heat recovery pipe, fully utilize heat energy, and improve heat exchange efficiency.

[0019] Preferably, a rotating rod is provided in the mixing drum, the central axis of the rotating rod coincides with the central axis of the mixing drum, a stirring motor is provided at the bottom of the mixing drum, one end of the rotating rod passes through the bottom of the mixing drum and is coaxially connected to the output shaft of the stirring motor, the bottom of the rotating rod is rotatably connected to a first rod, a plurality of stirring blades are provided on the first rod, and the plurality of stirring blades are equidistantly arranged on the first rod along the axial direction of the first rod, and the angle between the first rod and the rotating rod is adjustable.

[0020] By adopting the above technical solution, the angle between the first rod and the rotating rod can be adjusted to adapt to the stirring requirements of different raw material characteristics. When the raw material particles are large or the stirring amount is large, the angle can be increased to increase the stirring force; when the raw material particles are small or the stirring amount is small, the angle can be reduced to avoid excessive stirring.

[0021] Preferably, the end of the first rod away from the rotating rod is rotatably connected to the second rod, the end of the second rod away from the first rod is rotatably connected to the rotating rod, and the end of the second rod away from the first rod is slidably connected to the top of the rotating rod along the axial direction of the rotating rod.

[0022] By adopting the above technical solution, this design allows the coverage range of the stirring blade to be flexibly adjusted to meet the stirring needs of different capacities. When the raw material particles are large or the stirring amount is large, the second rod can be slid to a position close to the top of the rotating rod to reduce the working area of the stirring blade; when the raw material particles are small or the stirring amount is small, the second rod can be slid to a position close to the bottom of the rotating rod to expand the working area of the stirring blade.

[0023] The present application also provides a production process for a composite magnet.

[0024] A production process for a composite magnet is implemented using the above-mentioned production equipment for a composite magnet, comprising the following steps: S1. Mixing permanent magnetic material powder and soft magnetic material powder in a mass ratio of (5:1) to (20:1) in the mixing drum to form a raw material mixture; S2. ball milling the raw material mixture under an inert gas protection environment to make the powder particle size reach 0.1-10 μm; S3, placing the mixed powder in the molding die, applying a pulsed magnetic field of 1-10T for directional pressing, and molding at a pressure of 500-1000MPa; S4, sintering through the sintered structure; S5. Perform surface finishing and coating treatment on the sintered green body.

[0025] By adopting the above technical solution, the raw materials are mixed evenly, and then undergo ball milling, directional pressing, sintering and surface treatment to finally obtain a composite magnet with excellent performance. The molding and sintering are completed on the same equipment, which simplifies the production process, reduces material transfer between processes, improves the production efficiency of the composite magnet, and reduces production costs.

[0026] Preferably, the following steps need to be performed before the coating treatment in step S5: S51, degreasing cleaning: cleaning in alkaline solution or ultrasonic; S52, pickling activation: dilute nitric acid or phosphoric acid to remove surface oxides; S53, pure water rinse: prevent residual acid from affecting the coating.

[0027] By adopting the above technical solutions and rationally selecting coating processes and materials, the life of magnets can be significantly extended.

[0028] In summary, this application includes at least one of the following beneficial technical effects: 1. By integrating the molding and sintering functions into the same equipment, the production process is simplified, the material transfer between processes is reduced, the production efficiency of composite magnets is improved, and the production cost is reduced; 2. By adding heat dissipation components and heat recovery structures, not only the temperature of the equipment during operation is effectively reduced, the heat dissipation and cooling of the sintered green body are also achieved, but also the heat energy is recovered, reducing the energy consumption in the production process. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 This is a schematic diagram of the overall structure of a composite magnet production device of the present application; Figure 2 yes Figure 1 A partial enlarged schematic diagram of part A; Figure 3 It is a cross-sectional schematic diagram of a partial structure of a composite magnet production device of the present application; Figure 4 It is a schematic diagram of a partial structure of a composite magnet production device of the present application; Figure 5 This is a process flow chart of a production process of a composite magnet of the present application; Figure 6 This is a process flow chart of a production process of a composite magnet of the present application.

[0030] Explanation of the accompanying reference numerals: 110, frame; 111, workbench; 112, upper beam; 113, upper column; 114, lower column; 115, driving cylinder; 116, support frame; 117, ball slot frame; 120, molding die; 121, upper mold; 122, lower mold; 123, molding cavity; 124, guide column; 125, guide hole; 130, heat dissipation assembly; 131, heat dissipation head; 132, heat dissipation pipe; 133, suction pump; 134, connecting ball; 135, heat recovery pipe; 140, mixing drum; 141, heating chamber; 142, rotating rod; 143, stirring motor; 144, first rod; 145, stirring blade; 146, second rod. DETAILED DESCRIPTION

[0031] The present application is further described in detail below with reference to the accompanying drawings.

[0032] The present application discloses a production device for composite magnets, which is used to improve the production efficiency of composite magnets and reduce production costs.

[0033] refer to Figures 1-4 A production device for composite magnets includes a frame 110, on which are provided a magnet molding structure, a sintering structure, a driving component for driving the magnet molding structure, a heat dissipation component 130 and a stirring drum 140. The magnet molding structure includes at least two sets of mutually cooperating molding molds 120, and a molding cavity 123 for forming a composite magnet is opened in the molding mold 120. The sintering structure is integrated on the molding mold 120 and is used to form a dense structure of the composite magnet. By integrating the molding and sintering functions into the same equipment, the production process is simplified, the material transfer between processes is reduced, the production efficiency of the composite magnet is improved, and the production cost is reduced.

[0034] The heat dissipation component 130 is arranged between the upper mold 121 and the lower mold 122 in the vertical direction. The end of the heat dissipation component 130 away from the forming mold 120 is connected to a heat recovery structure. The heat recovery structure is used to recover the heat energy generated by forming and sintering. The mixing drum 140 is used to mix and stir the raw materials for producing composite magnets. A heating chamber 141 is provided on the wall of the mixing drum 140 for providing heat to the raw materials for producing composite magnets in the mixing drum 140. The heating chamber 141 is opened along the circumference of the mixing drum 140. The heat recovery structure includes a heat recovery pipe 135. The heat recovery pipe 135 is used to recover the heat energy generated by forming and sintering. The recovery pipe 135 is spiral-shaped and the heat recovery pipe 135 is embedded in the heating chamber 141. The heat recovery pipe 135 is coiled around the circumference of the mixing drum 140 and coiled from bottom to top along the axial direction of the mixing drum 140 in the heating chamber 141. One end of the heat recovery pipe 135 is connected to the heat dissipation pipe 132, and the other end of the heat recovery pipe 135 passes through the mixing drum 140. By adding the heat dissipation component 130 and the heat recovery structure, not only the temperature of the equipment during operation is effectively reduced, the sintered green body is cooled and cooled, but also the heat energy is recovered, thereby reducing the energy consumption in the production process.

[0035] Specifically, the molding mold 120 includes an upper mold 121 and a lower mold 122. The upper mold 121 and the lower mold 122 are connected by a guide member. The guide member ensures that the upper mold 121 and the lower mold 122 remain precisely aligned during the mold closing process. The guide member includes at least one guide column 124 arranged on the upper mold 121. The lower mold 122 is provided with at least one guide hole 125 for inserting the guide column 124. Multiple guide columns 124 and multiple guide holes 125 correspond one to one. In this embodiment, a total of four guide columns 124 are provided. The four guide columns 124 are distributed in a rectangular shape on the upper mold 121. Correspondingly, four guide holes 125 are provided on the lower mold 122. The inner wall of the guide hole 125 can be provided with an anti-wear layer to extend the service life.

[0036] In this embodiment, the frame 110 includes a workbench 111, an upper beam 112, four upper columns 113 and four lower columns 114. The upper beam 112 is located directly above the workbench 111, and the four lower columns 114 are distributed in a rectangular shape below the workbench 111 to provide support for the workbench 111. The four upper columns 113 are distributed in a rectangular shape between the workbench 111 and the upper beam 112. When the upper mold 121 and the lower mold 122 are connected, a complete molding cavity 123 is formed. The driving assembly is used to drive the upper mold 121 close to the lower mold 122. To complete the mold closing action, the drive assembly includes four drive cylinders 115. The drive cylinders 115 are vertically mounted on the upper beam 112 and are rectangular in shape. The piston rods of the drive cylinders 115 are connected to the upper surface of the upper mold 121. In addition, the upper mold 121 and the lower mold 122 can be designed as a detachable structure to facilitate the replacement of molding cavities 123 of different specifications. At the same time, the contact surfaces of the upper mold 121 and the lower mold 122 are precision-machined to ensure sealing during mold closing and prevent leakage of molding material.

[0037] In addition, the sintering structure is integrated on the molding mold 120, and mainly includes a heating element and a temperature control component. The heating element can be a resistance wire or an induction coil, embedded in the outer wall of the molding cavity 123. The resistance wire is suitable for lower temperature sintering processes, while the induction coil is more suitable for high temperature sintering scenarios; the temperature control device includes a thermocouple and a controller. The thermocouple is used to monitor the temperature changes in the molding cavity 123 in real time. The controller automatically adjusts the heating power according to the monitoring data to ensure the stability of the sintering process.

[0038] The heat dissipation assembly 130 includes a heat dissipation head 131, a heat dissipation pipe 132 and a suction pump 133. One end of the heat dissipation pipe 132 is connected to the heat dissipation head 131, and the other end of the heat dissipation pipe 132 is used to be connected to the heat recovery structure. The end of the heat dissipation head 131 away from the heat dissipation pipe 132 faces the forming mold 120. The suction pump 133 is used to absorb the heat energy generated by the forming sintering into the heat recovery structure. In this embodiment, a total of four heat dissipation heads 131 are provided. The four heat dissipation heads 131 are placed on the upper surface of the workbench 111 through the support frame 116. The four heat dissipation heads 131 are respectively distributed on the four sides of the forming mold 120. The heat dissipation heads 131 are close to the forming mold 120. It is used to absorb the heat generated during the molding and sintering process. Correspondingly, four heat dissipation tubes 132 are provided. The four heat dissipation tubes 132 correspond to the four heat dissipation heads 131 one by one, and a connecting ball 134 is integrated between the heat dissipation head 131 and the heat dissipation tube 132. A ball groove frame 117 is provided on the top of the support frame 116. The connecting ball 134 is embedded in the ball groove frame 117 for damped rotation. The heat dissipation head 131, the connecting ball 134 and the heat dissipation tube 132 are connected. The suction pump 133 is provided between the workbench 111 and the mixing drum 140. The suction pump 133 is used to transfer heat from the heat dissipation head 131 to the heat energy recovery structure to realize the recovery of heat energy and further reduce energy consumption.

[0039] Specifically, a rotating rod 142 is provided in the mixing drum 140, and the central axis of the rotating rod 142 coincides with the central axis of the mixing drum 140. A stirring motor 143 is provided at the bottom of the mixing drum 140. One end of the rotating rod 142 passes through the bottom of the mixing drum 140 and is coaxially connected to the output shaft of the stirring motor 143. The bottom of the rotating rod 142 is rotatably connected to the first rod 144, and a plurality of stirring blades 145 are provided on the first rod 144. The plurality of stirring blades 145 are arranged on the first rod 144 at equal distances along the axial direction of the first rod 144. The angle between the first rod 144 and the rotating rod 142 is adjustable. The angle between the first rod 144 and the rotating rod 142 is adjustable to meet the stirring requirements of different raw material characteristics. When the raw material particles are large or the stirring amount is large, the angle can be increased to increase the stirring force; when the raw material particles are small or the stirring amount is small, the angle can be reduced to avoid excessive stirring.

[0040] The end of the first rod 144 away from the rotating rod 142 is rotatably connected to the second rod 146, and the end of the second rod 146 away from the first rod 144 is rotatably connected to the rotating rod 142. The end of the second rod 146 away from the first rod 144 is slidably connected to the top of the rotating rod 142 along the axial direction of the rotating rod 142. This design allows the coverage range of the stirring blade 145 to be flexibly adjusted to meet the needs of stirring of different capacities. When the raw material particles are large or the stirring amount is large, the second rod 146 can be slid to a position close to the top of the rotating rod 142 to reduce the working area of the stirring blade 145; when the raw material particles are small or the stirring amount is small, the second rod 146 can be slid to a position close to the bottom of the rotating rod 142 to expand the working area of the stirring blade 145.

[0041] The implementation principle of the production equipment of a composite magnet in an embodiment of the present application is as follows: by integrating the forming and sintering functions into the same equipment, the production process is simplified, the material transfer between processes is reduced, the production efficiency of the composite magnet is improved, and the production cost is reduced; by adding a heat dissipation component 130 and a heat energy recovery structure, not only the temperature of the equipment during operation is effectively reduced, the sintered blank is cooled and dissipated, but also the heat energy is recovered, thereby reducing the energy consumption in the production process.

[0042] The application also discloses a production process of the composite magnet.

[0043] refer to Figure 1 、 Figure 5 and Figure 6 A production process for a composite magnet is implemented using the above-mentioned production equipment for a composite magnet, comprising the following steps: S1. Mixing permanent magnetic material powder and soft magnetic material powder in a mass ratio of (5:1) to (20:1) in a mixing drum 140 to form a raw material mixture; S2. ball milling the raw material mixture under an inert gas protection environment to make the powder particle size reach 0.1-10 μm; S3, placing the mixed powder in a forming mold 120, applying a pulsed magnetic field of 1-10T for directional pressing, and forming at a pressure of 500-1000MPa; S4, sintering by sintering the structure; S5. Perform surface finishing and coating treatment on the sintered green body.

[0044] In addition, the following steps need to be performed before the coating process in step S5: S51, degreasing cleaning: cleaning in alkaline solution or ultrasonic; S52, pickling activation: use dilute nitric acid or phosphoric acid to remove surface oxides; S53, pure water rinse: prevent residual acid from affecting the coating.

[0045] The implementation principle of a production process for a composite magnet in an embodiment of the present application is as follows: by optimizing the parameters of each process step, efficient production of the composite magnet is achieved. After the raw materials are evenly mixed, they are subjected to ball milling, directional pressing, sintering and surface treatment to finally obtain a composite magnet with excellent performance. Molding and sintering are completed on the same equipment, which simplifies the production process, reduces material transfer between processes, improves the production efficiency of the composite magnet, and reduces production costs.

[0046] The embodiments of this specific implementation method are all preferred embodiments of the present application and are not intended to limit the scope of protection of the present application. Therefore, any equivalent changes made based on the structure, shape, and principle of the present application should be included in the scope of protection of the present application.

Claims

1. A composite magnet production device, comprising a frame (110), characterized in that: The frame (110) is provided with a magnet forming structure, a sintering structure, and a driving assembly for driving the magnet forming structure. The magnet forming structure comprises at least two sets of mutually cooperating forming dies (120). A forming cavity (123) for forming a composite magnet is provided in the forming dies (120). The sintering structure is integrated with the forming dies (120) and is used to form the composite magnet into a dense structure.

2. The composite magnet production equipment according to claim 1, characterized in that: The molding die (120) includes an upper die (121) and a lower die (122), wherein the upper die (121) and the lower die (122) are connected via a guide member, and when the upper die (121) and the lower die (122) are connected, a complete molding cavity (123) is formed, and the driving assembly is used to drive the upper die (121) close to the lower die (122), and the guide member includes at least one guide post (124) provided on the upper die (121), and the lower die (122) is provided with at least one guide hole (125) for inserting the guide post (124), and a plurality of the guide posts (124) and a plurality of the guide holes (125) correspond one to one.

3. The production equipment of a composite magnet according to claim 2, characterized in that: A heat dissipation assembly (130) is provided on the frame (110), and the heat dissipation assembly (130) is vertically arranged between the upper mold (121) and the lower mold (122). An end of the heat dissipation assembly (130) away from the forming mold (120) is connected to a heat recovery structure, and the heat recovery structure is used to recover heat energy generated by forming and sintering.

4. The composite magnet production equipment according to claim 3, characterized in that: The heat dissipation assembly (130) comprises a heat dissipation head (131), a heat dissipation pipe (132) and a suction pump (133); one end of the heat dissipation pipe (132) is connected to the heat dissipation head (131); the other end of the heat dissipation pipe (132) is used to be connected to the heat energy recovery structure; one end of the heat dissipation head (131) away from the heat dissipation pipe (132) is directed toward the forming mold (120); and the suction pump (133) is used to absorb heat energy generated by forming and sintering into the heat energy recovery structure.

5. The production equipment of a composite magnet according to claim 4, characterized in that: A stirring drum (140) is further provided on the frame (110). The stirring drum (140) is used for mixing and stirring raw materials for producing composite magnets. A heating chamber (141) for providing heat to the raw materials for producing composite magnets in the stirring drum (140) is provided on the drum wall of the stirring drum (140). The heating chamber (141) is provided along the entire circumference of the stirring drum (140).

6. The production equipment of a composite magnet according to claim 5, characterized in that: The heat energy recovery structure comprises a heat energy recovery pipe (135), the heat energy recovery pipe (135) is spiral-shaped and embedded in the heating chamber (141), the heat energy recovery pipe (135) is coiled along the circumference of the mixing drum (140) and coiled from bottom to top along the axial direction of the mixing drum (140) in the heating chamber (141), one end of the heat energy recovery pipe (135) is connected to the heat dissipation pipe (132), and the other end of the heat energy recovery pipe (135) is passed out of the mixing drum (140).

7. The composite magnet production equipment according to claim 6, characterized in that: A rotating rod (142) is provided in the mixing drum (140), the central axis of the rotating rod (142) coincides with the central axis of the mixing drum (140), a stirring motor (143) is provided at the bottom of the mixing drum (140), one end of the rotating rod (142) passes through the bottom of the mixing drum (140) and is coaxially connected to the output shaft of the stirring motor (143), the bottom of the rotating rod (142) is rotatably connected to a first rod (144), a plurality of stirring blades (145) are provided on the first rod (144), and the plurality of stirring blades (145) are arranged on the first rod (144) at equal intervals along the axial direction of the first rod (144), and the angle between the first rod (144) and the rotating rod (142) is adjustable.

8. The production equipment of a composite magnet according to claim 7, characterized in that: One end of the first rod (144) away from the rotating rod (142) is rotatably connected to the second rod (146), one end of the second rod (146) away from the first rod (144) is rotatably connected to the rotating rod (142), and one end of the second rod (146) away from the first rod (144) is slidably connected to the top of the rotating rod (142) along the axial direction of the rotating rod (142).

9. A production process for a composite magnet, characterized in that: The production device of a composite magnet according to any one of claims 1 to 8 is used to achieve the above-mentioned result, comprising the following steps: S1, mixing permanent magnetic material powder and soft magnetic material powder in a mass ratio of (5:1) to (20:1) in the mixing drum (140) to form a raw material mixture; S2. ball milling the raw material mixture under an inert gas protection environment to make the powder particle size reach 0.1-10 μm; S3, placing the mixed powder in the molding die (120), applying a pulsed magnetic field of 1-10 T for directional pressing, and molding at a pressure of 500-1000 MPa; S4, sintering through the sintered structure; S5. Perform surface finishing and coating treatment on the sintered green body.

10. The production process of a composite magnet according to claim 9, characterized in that: The following steps need to be performed before the coating treatment in step S5: S51, degreasing cleaning: cleaning in alkaline solution or ultrasonic; S52, pickling activation: dilute nitric acid or phosphoric acid to remove surface oxides; S53, pure water rinse: prevent residual acid from affecting the coating.

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