JP4706948B2 - Surface treatment method for light alloy castings - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention mainly relates to a surface treatment method for a light alloy casting product, and more particularly to a surface treatment method including a step for efficiently repairing surface defects by combining shot blasting and air blasting.
[0002]
[Prior art]
A surface treatment method for removing an oxide film and a release agent attached to the surface of a casting product by applying a shot accelerated by a rotary impeller is widely used. A so-called shot blasting device that accelerates shots with a rotating impeller can act on a large amount of shots over a wide range, and can efficiently perform surface treatment of large cast products and large amounts of cast products, but narrow portions Cannot be blasted intensively. The shot blasting device's projection density can be set by adjusting the bucket speed, but generally does not intentionally change the setting and is used with the default setting set to a projection density that is not too high. In such a setting, the surface of the workpiece is finished in a satin finish.
[0003]
A surface treatment method for repairing a defect generated on the surface of a cast product by applying a shot accelerated with compressed air is widely used. The so-called air blasting device that accelerates shots with compressed air can apply shots to a narrow area with high density and can concentrate surface treatment of narrow parts such as defect repairs, but large castings. The surface treatment of products and large quantities of cast products cannot be blasted efficiently. The projection density of the air blast device can be set by a mixing valve, but generally the setting is not intentionally changed, and it is used with the initial setting set to a relatively high projection density. Then, the surface of the workpiece is partially cured and finished in a glossy state.
[0004]
If a light alloy cast product is surface-treated with an iron alloy shot, the surface may turn dark and the product value may be reduced. Further, if the surface treatment is performed with an aluminum alloy shot, a dust explosion accident is likely to occur. For these reasons, the present inventors have developed and provided a zinc alloy shot (Japanese Patent No. 2887228). Zinc or zinc alloy shots are widely used for surface treatment of light alloy casting products by shot blasting equipment or air blasting equipment.
[0005]
[Problems to be solved by the present invention]
Conventionally, the surface treatment of a light alloy casting product that has been removed from the mold is performed by removing shots from the surface by applying a shot made of zinc or zinc alloy using a shot blasting device, and then inspecting the surface for defects. For light alloy cast products, the defective portion was scraped and repaired with an abrasive brush or grinder, and blasting was performed again with a shot blasting device to make the entire surface including the repaired portion uniform.
[0006]
However, the use of expensive abrasive brushes and the grinding work performed manually by skilled workers have delayed delivery and increased the cost of surface treatment. Furthermore, the entire blasting process for making the repaired portion inconspicuous involves many blasting to unnecessary portions, which reduces the efficiency of the surface treatment.
[0007]
If repair is performed with an air blasting device, repair can be done in a relatively short time without using a skilled worker, but only the repaired part has a glossy surface state as in the previous period, which impairs the overall aesthetics. was there. Furthermore, even if the entire blasting is performed to make the repaired part inconspicuous, as described above, the surface of the repaired part is hardened and the blasting effect is difficult to be exhibited. Thus, it has been difficult to perform efficient surface treatment.
[0008]
The present invention has been made in order to solve such problems, and its object is a surface treatment method for light alloy casting products, which eliminates the need for expensive abrasive-filled brushes and grinding work by skilled workers. It is an object of the present invention to provide a new and efficient surface treatment method capable of repairing a defect by good blasting and further omitting an overall blasting for making a repaired portion inconspicuous.
[0009]
[Means for Solving the Problems]
The surface treatment method for a light alloy casting product of the present invention, which has been made to solve the above problems, includes the following three characteristic steps.
[0010]
In the first step, a shot made of zinc or zinc alloy having a hardness of Hv 50 to 60 and an average particle diameter of 0.4 mm to 2.0 mm is accelerated by a rotating impeller on the demolded light alloy cast product. It acts at a projection density of 500 g / cm ² or more per minute to remove foreign matter on the surface.
[0011]
As already described, a so-called shot blasting apparatus that accelerates and acts on a shot by a rotating impeller is effective in efficiently blasting the entire surface of a large cast product or a large amount of cast product at a time. The shot to be used is a shot made of zinc or zinc alloy in order to prevent darkening of the target light alloy casting product and suppress the induction of dust explosion accidents. In order to reduce shot wear due to blasting, the hardness of the shot is Hv 50-60. Furthermore, shots having an average particle diameter of 0.4 mm or more in order to efficiently remove surface foreign matters such as oxide films, and an average particle diameter in the range of 2.0 mm or less in order to finish the surface into a uniform satin finish Is used.
[0012]
Further, as will be described in detail later, the projection density is 500 g / cm ² or more per minute, which is a projection density that can be stably realized by a general-purpose air blast device. A projection density is a value obtained by dividing the projecting reflecting surface product the weight of the shot to be projected in one minute.
[0013]
In the second step, surface defects are inspected. The defects of carefully cast light alloy casting products are cracked shallow scratches caused by shrinkage that occurs during the cooling stage, and are classified as defective products for reasons of detracting from aesthetics. Therefore, although there is room for introducing an automatic sorting device by image processing, it is sufficient to sort by visual inspection. The product in which no defect is found ends the surface treatment process and is sent to an assembly process for assembling other parts, if necessary. The product in which the defect is found is sent to the next process for repairing the defect.
[0014]
In the third step, the same shot as in the first step is applied to the defective portion at the same projection density to repair the defect of the light alloy cast product in which the defect was found in the previous step. The general-purpose air blasting device is initially set so that the projection density is about 1700 g / cm ^2, so if blasting is performed as it is, the repaired part becomes a glossy surface state, and the repaired part is conspicuous I explained earlier. Since the same shot as the first step is applied at the same projection density, the repaired part is finished in the same satin shape as the other parts, and the process of blasting the whole again and making the repaired part inconspicuous can be omitted. . Note that if the projection density is controlled to be less than 500 g / cm ^{2 in} a general-purpose air blasting apparatus, the injection becomes unstable and uniform blasting becomes difficult. Therefore, in the first step, 500 g / cm ² or more is required. It must be the projection density.
[0015]
Further, in order to efficiently crush and repair the defective part, the pressure of the compressed air for accelerating the shot must be 0.4 MPa or more, and 0.5 MPa or less to suppress shot wear. Must-have.
[0016]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
[0017]
In the figure, reference numeral 1 is a shot blasting apparatus responsible for the first process, reference numeral 2 is a visual inspection booth responsible for the second process, and reference numeral 3 is an air blasting apparatus responsible for the third process. The shot blasting device 1 is configured to scoop up the shot accumulated below the processing chamber by the bucket 1a and supply it to the rotary impeller 1c. The projection density can be changed by adjusting the speed of the bucket 1a. The projected area of the used shot blasting device (product symbol DZB manufactured by Shinto Brater Co., Ltd.) is 100 cm ² . In this embodiment, in order to set the projection density to 700 g / cm ² , the speed of the bucket 1 a was adjusted so as to supply a shot of 70 kg per minute. A shot made of a zinc alloy containing a trace amount of copper having an average particle diameter of 0.8 mm (product code AZ8, manufactured by Shinto Brater Co., Ltd.) was selected.
[0018]
In the first step, a motorcycle shock absorber case W (hereinafter simply referred to as a workpiece) having a diameter of 6 cm and a length of 30 cm, which is a molded aluminum alloy casting product, is hung on a rotating hanger 1d, and a shot accelerated by a rotating impeller 1c is taken. Let act for 2 minutes. As a result, foreign matters such as an oxide film and a release agent on the surface of the workpiece W were completely removed, and the surface of the workpiece W was finished in a satin finish.
[0019]
In the second step, the workpiece W that has finished the first step is moved to the visual inspection booth 2 and the presence or absence of defects is examined by visual inspection. As a result, defects were found in 6 of the 30 workpieces W subjected to the surface treatment. The 24 workpieces W in which no defect is found complete the surface treatment process and are transferred to the next assembly process. The six workpieces W in which defects are found are marked with oil-based magic on the defective portions and conveyed to the third step, which is the next step of the surface treatment, to repair the defects.
[0020]
The air blasting device 3 is configured to adjust the amount of shot supplied from the pressurized tank 3a to the injection nozzle 3b by a mixing valve 3c. The projection density can be changed by adjusting the mixing valve 3c. The projection area of the used air blasting device (product symbol AB manufactured by Shinto Brater Co., Ltd.) is 12 cm ² . In this example, in order to set the projection density to 700 g / cm ² which is the same as that in the first step, the mixing valve 3c was adjusted so as to supply a shot of 8.4 kg per minute. The same shot as that selected in the first step (product symbol AZ8, manufactured by Shinto Brater Co., Ltd.) was selected.
[0021]
In the third step, the workpiece W in which a defect is found is held by hand, and a shot accelerated with compressed air for 10 to 30 seconds is applied to the marked defect portion K depending on the size of the defect. Let As a result, the defective part was crushed well and the defect could be eliminated. Furthermore, since the same shot as in the first step is applied at the same projection density, the repaired part is finished in a satin finish, and there is no need for the entire blasting again to make the repaired trace inconspicuous. The repaired six workpieces finish the surface treatment process and are transported to the next assembly process.
[0022]
【The invention's effect】
Since the present invention is configured as described above, the following effects can be obtained.
[0023]
Zinc or zinc alloy shot with a hardness of Hv 50-60 and an average particle size of 0.4 mm to 2.0 mm is accelerated by a rotary impeller to the light alloy cast product which has been removed from the mold, and the weight is 500 g / cm ² or more per minute. Since the first step of removing the foreign matter on the surface by operating at a projection density of 2 is provided, it is possible to efficiently remove the foreign matter such as the oxide film and the third step which is an efficient repairing process is possible. And
[0024]
A second step for inspecting a surface defect, and a light alloy casting product in which a defect is found on the surface, the same shot as the first step is applied to the defective portion at a pressure of 0.4 MPa to 0.5 MPa Since the third step of repairing defects by accelerating with air and acting at the same projection density is provided, even if a cast product with defects on the surface is included, it is not discarded as a defective product, but efficient Can improve the manufacturing process yield.
[0025]
Furthermore, since the repair uses the same shot as the first step, it is not necessary to prepare expensive abrasive brushes for repair, and it is possible to repair with an air blasting device with low shape transfer performance. It doesn't require skilled workers like work. Furthermore, since the entire blasting performed to make the repaired portion inconspicuous can be omitted, the manufacturing cost can be greatly reduced.
[Brief description of the drawings]
FIG. 1 is a conceptual diagram for explaining a surface treatment process of the present invention.
[Explanation of symbols]
1 Shot blasting equipment (first process)
1a Bucket 1b Processing chamber 1c Rotating impeller 1d Rotating hanger 2 Visual inspection booth (second process)
3 Air blasting device (third process)
3a Pressurized tank 3b Injection nozzle 3c Mixing valve W Work K Defect

Claims (2)

Hardness in demolding the light alloy casting product is the average particle size is accelerated by a is zinc or zinc alloy shot impeller 0.4mm~2.0mm to remove foreign matter on the front surface at Hv50~60 A first step, a second step for inspecting a surface defect, and a light alloy casting product in which a defect is found on the surface, the same shot as the first step is applied to the defect portion at a pressure of 0. 0. In the third step of repairing the defective portion by accelerating with compressed air of 4 MPa to 0.5 MPa, the projection density of the shot made of zinc or zinc alloy projected in the first step and the third step per minute the surface treatment method of the light alloy casting product characterized by repairing defects in the ^{500g / cm 2 ~700g / cm 2} . The surface treatment method for a light alloy casting product according to claim 1, wherein the projection time of the zinc or zinc alloy shot in the third step is set to 10 seconds to 30 seconds.

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