JP2630947B2 - Blasting method using zinc-based blast shot - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a blast method using a zinc-based blast shot, and a blast shot machine without a rubber lining sheet for reducing blackening of a blast product. A blast method for projecting a blast shot using the blast shot. The present invention is particularly useful for blasting a die-cast product represented by an aluminum die-cast product.

2. Description of the Related Art Conventional technology and its problems A blast method is well known as one of methods for cleaning a metal surface. The blast method is a method of removing burrs, scales, and the like adhering to the surface by projecting particles on the surface of the object. With the development of the automobile industry, the production volume of die-cast products, especially aluminum alloy die-cast products (for example, alternator frames) has been increasing, and the blasting has become very important.

Various blast shots have been used depending on the product to be processed. In general, aluminum-based cut wires, steel shots, stainless steel cut-wires, etc. were used for blasting of die-cast products, especially aluminum die-cast products. The safety measures required a great deal of expense. In the case of steel shots, rust is likely to occur due to the adhesion of powdered iron powder. When a stainless steel cut wire was used, deep cutting was performed at the edge, damaging the surface of the aluminum die-cast product and presenting a problem in terms of corrosion resistance.

Therefore, zinc-based shots have recently been spotlighted in place of these shots. Zinc-based shots have low explosive properties, exhibit a good blasting action without damaging the object to be treated due to their appropriate softness and other physical properties, and do not impair the aesthetic appearance or corrosion resistance. Examples of the zinc-based shot include a zinc shot made of the purest zinc and a zinc alloy shot such as Zn-Fe and Zn-Fe-Pb.

However, there are still problems with such zinc blast shots. One of them is die casting products,
In particular, when an aluminum die-cast product is blasted using a zinc-based shot, blackening of the product surface is observed.

Various factors seem to be related to the surface blackening. Several attempts have been made to improve the compatibility between the material to be treated and the shot hardness, but no sufficient countermeasures have been taken yet.

SUMMARY OF THE INVENTION The present inventors have continued to investigate the cause of blackening through the analysis of the black portion, and as a result, have confirmed that the main cause of blackening is due to the adhesion of metallic zinc. The zinc shot has a thin oxide film on its surface that is inevitably formed during manufacture and storage. Such a thin oxide film is brittle, and the metallic zinc portion in contact with it is also weakened. As the zinc shot is projected and impacts the blasted article, the oxide film delaminates and powders, as well as the weakened metallic zinc portions, resulting in metallic zinc powder. When the zinc oxide also becomes fine powder, it becomes black. The metallic zinc powder adheres to the blasted article together with the powdered zinc oxide, and becomes black. Therefore, by using a zinc shot without an oxide film, blackening should be able to be prevented.

However, in many cases, blackening was still observed even when a zinc shot without an oxide film was used. After examining the cause, it was surprisingly found that the blackening was caused by the rubber lining used in the blast equipment. During the flow of the zinc shot in the blasting facility, when the shot collides with or rubs against the rubber lining, shavings are generated and adhere to the shot surface.
The rubber pulverized material transfers and adheres to the blasted article and turns black. The rubbery substance sticks to the product surface and cannot be removed. Furthermore, when metallic zinc powder is present, it acts as an adhesive between the metallic zinc powder and the article to be blasted to increase blackening. Thus, another factor in the blackening was the rubber lining used in blasting equipment.

The present invention provides a blasting method for projecting a zinc-based blast shot from a blast machine based on this knowledge that has been overlooked so far, in which a blasting machine that does not use a rubber lining sheet for lining a blast machine portion that comes into contact with the blast shot. A blasting method using a zinc-based blast shot, wherein the blasting is performed using a machine. Is preferably used in Shiyotsuto of lower hardness H _V is a 30 to 35, also it is preferred to carry out projection in a low projection speed 25-34M / sec.

DETAILED DESCRIPTION OF THE INVENTION Zinc-based blast shots made of zinc or zinc alloy grains are made of high-purity zinc or Fe, Pb,
It is produced by subjecting a zinc alloy to which at least one of Cu, Al, Mg and the like is added to a shot to a granular form. Shotting is
There are various methods such as a spraying method and a collision method. Among them, a method in which the molten metal is allowed to fall naturally into water produces a suitable shot. A reservoir equipped with a bottom nozzle containing zinc or zinc alloy melt is placed on a water tank, and a melt is spontaneously dropped into the water through the nozzle to generate a shot. By controlling the shape and size, the distance from the nozzle to the water surface, the water temperature, and the like, a shot having an appropriate particle shape (particularly a spherical shape) and a particle size distribution can be produced.

As a blast machine, an air blast type and a centrifugal projection type are generally known. The air blast type is a type in which shots are continuously jetted by an air jetting method, while the centrifugal projection type performs projection by utilizing centrifugal force generated by rotation of an impeller. In any case, the projection speed can be easily controlled by adjusting the air ejection speed or the rotation speed of the impeller.

In any case, these blast machines are
A rubber lining sheet is often used in a portion that comes into contact with a shot in the machine, such as a shot storage room or a circulation line. When the shot collides with or rubs against the rubber lining sheet, the shot goes through the rubber lining sheet and generates rubber powder. When the shot is projected while these are adhered to the shot, the rubber powder is transferred and adhered to the product to be processed. The rubber powder adhering to the blasted article turns black and, when metallic zinc powder is present, acts as an adhesive between the metallic zinc powder and the blasted article to cover the metallic zinc powder. It was found to be attached to the blasted article surface. In the past, this has not been regarded as a problem, but has now become apparent as higher quality blast products are required.

As a lining in place of the rubber lining sheet, a ceramic coating, a hard metal coating, a thick zinc plating or the like can be used.

If the hardness of the shot is too high, or if the projection speed is too high, dents in the blast product are likely to occur. This tendency is particularly strong for aluminum die-cast products. Therefore, for aluminum die-cast products, hardness H _V
= 30 to 45, preferably employs a 25～34M / sec slow projected speeds using zinc Shiyotsuto a hard H _V = 30 to 39 is preferred. This has also been found to be effective in preventing blackening of blast products. When a hard zinc-based shot is projected at a high projection speed, the shot pierces, bites, etc. into the blast product. Even with the above soft shot-low speed projection, a sufficient blasting action can be achieved.

The hardness adjustment of the zinc-based blast can be suitably performed to regulate the Fe content. Fe content of zinc or zinc alloy
By setting the content to 0.01% by weight, a soft shot can be obtained. For example, a zinc-based shot having a Fe content of 20 to 120 ppm is suitable. Currently, the purest zinc with 3-4ppm Fe content (Pb: 10-20ppm, Cd: 4-17ppm) can be obtained,
Hardness can be adjusted by adding an appropriate amount of Fe or other components to the composition. The regulation of the amount of Fe reduces the generation of Fe due to the pulverization of the shot, which also contributes to the prevention of blackening and corrosion.

It is effective to remove oxides on the surface of the shot to prevent blackening. The removal of the surface oxide film can be reduced or eliminated during the production of the shot, or can be removed by an appropriate means after the production.

In order to suppress surface oxidation during production, for example, in the case of a dropping method in water, it is preferable to add a reducing agent (deoxidizing agent) to water to eliminate dissolved oxygen in water as much as possible. As a reducing agent,
Inorganic salts such as sodium sulfite and sodium bisulfite, hydrazine, carbohydrazide, erythorbic acid, N, N
-Organic acid salts such as diethylhydroxylamine can be used. Further, it is preferable that the shots dropped into water and recovered are immediately dried sufficiently by flash drying or the like.

After the shot is formed, surface oxides adhering to the shot can be removed by washing with a dilute acid (sulfuric acid, hydrochloric acid, etc.). After washing, it is necessary to wash with water and dry quickly.

Empty projection is also an effective means for removing surface oxides. In the blank projection, a blast shot is projected without a product to be processed. At the time of idle projection, the shot particles rub against each other, so that the surface oxide film can be removed, and at the same time, the surface hardness can be increased. In addition, the fine zinc powder present on the surface can be removed.

The empty projection may be performed a plurality of times so as to exert a sufficient oxide film removing effect, and may be performed at appropriate intervals in the case of circulating the shot.

An excellent blast product can be obtained by projecting from a blast machine without a rubber lining sheet under appropriate conditions using a zinc-based blast shot without surface oxide.

Advantages of the Invention The hidden cause of the blackening of the blasted product is successfully investigated, and the blackening of the blasted product is prevented together with other measures, thereby contributing to quality improvement.

Example A zinc blast shot having the following composition was prepared by a water drop method.

This shot had an average Vickers hardness H _V = 36.
The particle size distribution was as follows.

+ 1680μ 4.2% -1680 to +1400 21.6% -1400 to +1000 62.9% -1000 to +710 11.0% -710 0.3% Since the recovered zinc shot had an oxide film on the surface, this zinc shot was washed with dilute sulfuric acid. Then, a zinc oxide having a metallic luster was formed by removing the surface oxide film. Using these zinc shots from which the surface oxide film had been removed, aluminum die-cast parts were blasted using a centrifugal blast shot machine. Since the centrifugal blast shot machine used a rubber lining sheet for its shot circulation path, peeled off the rubber lining sheet,
An improved product with hard metal plating on the inner surface was also prepared. The projection speed was 30 m / sec.

Blasting was performed under the same projection speed conditions using a rubber-lined sheet and a hard-metal-plated one, and a comparison showed that when a blast shot machine using a rubber-lined sheet was used, the aluminum die-cast parts were Although blackening was observed during repeated blasting, the improved hard metal-plated product did not have a tendency to blacken.

Inspection of the rubber-lined sheet revealed that many shots and scuffs were found when the shots hit or rubbed the rubber lining.

When the blackened part of the aluminum die-cast part was analyzed, rubber was detected.

Reference Example The following table shows the occurrence of dents, blackening prevention effects and blasting when changing the projection speed by using shots whose hardness was adjusted by adjusting the Fe content in a blasting machine that does not use rubber lining. The results of visual observations of the effects are shown for reference.

Claims (3)

(57) [Claims] 1. A blasting method for projecting a zinc-based blast shot from a blast machine, wherein the blasting is performed by using a blast machine that does not use a rubber lining sheet for lining a blast machine portion that comes into contact with the blast shot. A blasting method using a zinc-based blast shot. 2. The method according to claim 1, wherein a zinc-based blast shot having a hardness H _V = 30 to 39 is used. 3. The shooting speed of a shot from a blast machine is reduced.
3. The method according to claim 1, wherein the speed is 25 to 34 m / sec.