JPS60190541A - Zinc alloy shot for blasting and its production - Google Patents

Abstract

PURPOSE:To produce Zn alloy shot for blasting which does not blacken the part to be blasted by dropping by gravity the melt of a Zn alloy contg. a specific small amt. of Fe into water. CONSTITUTION:The melt of a Zn alloy contg. 0.01-1.0wt% Fe at 550-610 deg.C is put into a vessel 10 and is dropped by gravity into a water tank 1 provided in the lower part from a nozzle 15 made of ceramics such as alumina, silicon nitride, carbon nitride or the like formed in the bottom. The molten Zin alloy is cooled by the water in the tank 1 to form spherical shot which glides on an inclined bottom 4 and accumulates in a recovering vessel 5 consisting of a cage formed of a stainless steel wire net. The spherical Zn alloy shot having a desired diameter is obtd. in this case by adjusting adequately the depth (a) of the molten Zn alloy in the vessel 10, the inside diameter of the nozzle 15, the spacing (b) between the bottom end of the nozzle and the surface of the cooling water and the temp. of the cooling water.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to iron-containing zinc alloy shot for blasting.

Blasting is a well-known method for cleaning metal surfaces. The blast-last method is a method of removing scale, etc. that adheres to the surface of the object to be treated by projecting particles onto the surface of the object. Projected particles include steel shot, stainless steel cut wire, aluminum cut wire, alumina particles, and other machine tools. Various things are used. Generally, when shot blasting a product, it is desirable to change the blasting shot material depending on the material to be blasted, and usually the same type of metal shot as the material to be blasted is used. However, when blasting aluminum die-casting or small die-casting, aluminum cut wire (aluminum cannot be made into a shot, so the wire is cut)
There is a high risk of explosion of powdered aluminum, so steel shot and stainless steel cut wire are used. However, when steel shot is used, rust occurs due to adhesion of powdered iron powder, and when stainless steel cut wire is used, there are problems such as deep cutting at the edges and damage to the material. Therefore, in place of these, zinc shots have recently become important.

Due to its moderate softness and other physical properties, zinc shot exhibits a good blasting effect (abrasive effect) without damaging the material, and does not impair the beauty or corrosion resistance of the product. The unit price is also relatively low.

Generally, zinc shot for blasting is manufactured by making high-purity zinc, called the purest zinc, into shot. As a preferred method for the shot forming method, a method in which the molten metal is naturally allowed to fall into water from a molten metal reservoir set on a water tank through a nozzle with a fine pore size has been proposed, and good results have been obtained.

Spheroidized shot without sharp edges can be produced, mainly in the grain size range of 1000-1400 microns.

In particular, when aluminum die-cast products were cast using such zinc shot, blackening of the die-cast surface was observed. The finished state of shot blasted products is determined by the material of the product to be treated, the material and form of the shot, and the blasting conditions (shot discharge speed, number of discharged particles, etc.), and the cause of blackening is a mixture of various factors. I think that the. As a result of many studies, it was found that one of the effective measures to prevent blackening is to slightly increase the hardness of zinc shot compared to conventional methods.

Adding alloying elements can be considered as a method to improve the hardness of zinc shot, but the added elements can improve hardness and are harmful to the properties of zinc shot, such as grain boundaries, ductility, and toughness. It must not have any influence. Further, when producing shot by the above-mentioned underwater gravity drop method, the viscosity of the molten metal has a large effect on the shape and other properties of the produced shot, so the alloying element must not increase the viscosity of the molten metal. It has been discovered that iron is effective as an additive element that satisfies these requirements. By adding iron in an amount of Q, 01 to tO%, a zinc alloy shot for blasting having an appropriate Vickers hardness of 40 to 60 can be produced. Preferably, the iron-containing zinc alloy shot is produced by an underwater gravity drop method.

Thus, the present invention provides a zinc alloy blasting shot consisting of zinc alloy grains containing from 0.001 to 0.001% iron by weight. Furthermore, the present invention maintains a molten zinc alloy containing 0.01 to tO heavy iron in a reservoir equipped with a nozzle on the bottom wall, and naturally drips it into water through the nozzle. A method is also provided for producing zinc alloy blasting shot comprising zinc alloy grains containing up to 50% iron.

The present invention will be explained in detail below.

The zinc alloy shot for blasting according to the present invention contains 0.0% iron.
It is added in an amount of 01 to 10% by weight. An iron content of less than 0.01% provides the desired hardness improvement effect, while an iron content of more than 10% results in too high a hardness.

Impurities that are unavoidably contained in the zinc used during manufacturing are mixed into zinc alloy shot, but it is preferable to maintain the level of impurities at the level of the purest lead, or at worst the level of distilled zinc or runoff zinc. Should. Cadmium is easily entrained in zinc, but cadmium should be reduced to a minimum for environmental hygiene reasons at shot blasting sites.

Zinc alloy shot is produced by adding a specified amount of iron to the purest zinc and making it into shot using a general-purpose method. Further, since distilled zinc and runoff zinc already contain a specified amount of iron, the molten metal may be prepared as is or by adding iron up to a specified amount. Furthermore, since distilled zinc and runoff zinc still contain a considerable amount of impurities, it is also advantageous to pass them through a rectification column once to remove impurities. For example, by passing distilled zinc once through a rectification column,
A molten zinc alloy containing approximately 0.03% iron, substantially free of cadmium, and having a low content of expensive indium can be obtained.

Shot formation can be achieved using a number of granulation methods known in the art, such as spraying, impingement, which involves dispersing the molten metal over a disk, but the preferred method is the underwater natural method. . As mentioned above, in this method, droplets of molten metal are allowed to fall gently and naturally into water from a molten metal reservoir provided on a water tank through a nozzle. By carefully controlling the nozzle-water surface distance, water temperature, etc., it is possible to produce shots with appropriate particle shape and particle size distribution.

FIG. 1 shows an example of equipment for carrying out the above-mentioned molten metal gravity fall method. This equipment consists of a water tank 1 and a molten metal reservoir 10. The water tank 1 includes a molten metal dripping section 2 and a generated shot extraction section 6.
It consists of The molten metal dripping section 2 has an inclined bottom wall 4, and the produced shot extraction section 6 is made of, for example, a stainless steel wire gauze, for receiving the produced shot produced in the molten metal dripping section 2 and discharged along the inclined bottom wall 4. A basket-like collection container 5 is stored at the bottom end. A molten metal reservoir 10 is installed directly above the molten metal dripping section 2 by a suitable support structure 11. The molten metal reservoir container 10 is divided into a pouring chamber 12 and a reservoir chamber 13, and a nozzle 15 is provided on the bottom wall of the reservoir chamber.
is equipped with. A thermocouple 16 for measuring the temperature of the molten metal and a float 17 for measuring the depth a of the molten metal are provided in the reservoir chamber 13. The distance between the lower end of the nozzle 15 and the water surface is displayed as b. Water is supplied to the water tank 1 through a water injection pipe 6, while water is discharged through an overflow section 7. Furthermore, a circulating water pipe 8 incorporating a suitable pump is provided. A thermometer 9 for measuring water temperature and a heater 20 for controlling water temperature are provided in the water tank dripping section 2, and an injection heater 21 is provided in the shot extracting section 3. These heaters 20 and 21 are connected to a thermistor.

The molten zinc stored at a predetermined depth and temperature in the molten metal storage container 10 is discharged through a nozzle 15 onto the water surface directly below it, and is cooled and solidified by the water at a predetermined temperature in the water tank 1 to form a shot. and accumulates in a collection container.

Preferably, the nozzle A'15 is made of ceramic, such as alumina, silicon nitride, silicon carbide, or the like. It has been found that the produced shot is greatly influenced not only by the nozzle diameter but also by the nozzle material, and that it is better to use ceramic rather than metal for the zinc shot grains that are the object of the present invention. This seems to be related to the problem of wettability between the 1llu molten lead and the nozzle surface, and the better the breakage of the molten zinc drop from the nozzle when the molten zinc drop is released from the nozzle, the more spherical the shot will be. It is easy to change and stabilize.

An example of nozzle 15 is shown in Figures 2 and 3, here of a five-hole type. The number of nozzles used in the reservoir container and the number and arrangement pattern of nozzle holes in each nozzle can be determined as appropriate in relation to the production speed and the like. The nozzle 15 is fitted into a hole formed in the bottom wall of the reservoir 10 so that its lower end slightly protrudes from the hole. The nozzle hole formed in the nozzle 15 has a profile as shown in FIG. and defines the nozzle hole diameter referred to in this specification.

Stable production of zinc alloy shot for blasting is possible by selecting an appropriate combination within the following condition range: Zinc molten metal temperature 550~b! Depth 30~60cIIL Nozzle hole diameter 0.3~ α7+wt Nozzle bottom end to water surface distance 101111 or less Water temperature 30
-50°C The temperature of the molten metal in the reservoir is controlled at a temperature of 550-610°C. If the molten metal temperature is lower than 550° C., the produced shot will not become spherical but will tend to become linear, and production will not be stabilized. On the other hand, when the temperature exceeds 610°C, evaporation of the molten zinc increases, and the resulting shot becomes spheroidized and its particle size distribution becomes unstable.

The molten metal depth provides a static pressure head as a driving force for the molten metal dripping through the nozzle, and if it is less than 60α, the production rate will decrease and the yield will also be affected. A molten metal depth exceeding 60 cm deteriorates the spheroidization of the produced shot and the stability of the particle size distribution.

The nozzle hole diameter should be 0.3 to Q to obtain a shot mainly of 1.4 to 0.7 wφ, 71111. Preferably it is around 0.5 fiφ. If the nozzle hole is smaller than this range, clogging will easily occur, and if it is wider than this range, the generated shot will be larger.

The distance between the lower end of the nozzle hole and the water surface is preferably as small as possible, 10 fl or less. The molten metal dripping from the nozzle hole receives an increased impact on the water surface as this distance increases, making it more likely to become flattened. However, if this distance is made too small, the tip of the nozzle will be submerged in the water due to the shaking of the water surface, hindering the continuity of operations.

The nozzle is also more likely to crack. A spacing of about 3 to 5 centimeters is preferred.

The water temperature is 30 to 50°C, preferably around 45°C.

If the temperature is lower than 30°C, the cooling effect will be too strong, making it difficult for the produced shots to become spherical, while if it exceeds 50°C, the number of shots with large particle sizes will increase, and the yield of t4 to 0.711+1φ shots will decrease.

The zinc alloy shot used in the present invention is 500~
It is a spherical shot mainly having a particle size of 2000μ, especially 10oO to 1400μ.

The Vickers hardness ranges from 40 to 60, making it suitable for blasting various die-cast products, especially aluminum die-cast products.

EXAMPLE Zinc alloy shot was manufactured using equipment as shown. Adding iron wire for zinc to the purest zinc to make 0.05%Fe
-Zn and 0.10XFe-Zn alloy melts were prepared.

The test conditions were as follows: Molten metal temperature: 600°C Molten metal depth: 50cm Nozzle = made of g-silicon Nozzle diameter: o, 6m Water surface to nozzle distance: 3 Oboro Water temperature: 40 to 47°C Production shot The particle size distribution was: +168
0μ 4.3% -1680~+1400 21.6% -1400~+1000 62.9% -1000~+710 110% -710μ 0.3% Vickers hardness of produced shot (Test load N1N10O using the purest zinc It is shown below along with the shot.

rl, 0515 Fe-'l, n 45.3[110X
It can be seen that the addition of Fe-Zn4B,9 iron increases the hardness of the shot. When we used this shot to plaster an aluminum die-cast product, a beautiful appearance was obtained.

As described above, the present invention has succeeded in developing a zinc alloy shot having improved hardness and other properties that is particularly suitable for spot blasting of die-cast products, and provides an extremely excellent finished appearance. .

[Brief explanation of drawings]

FIG. 1 is a partially sectional front view of an example of shot manufacturing equipment, FIG. 8A2 is a top view of the nozzle, and FIG. 3 is a sectional view of the nozzle taken along line X-X# in FIG. 2. 1; Water tank 2: Molten metal dripping section 3 Nijotsu extraction section 5: Collection container 10: Molten metal reservoir container 15: Nozzle L: Water surface Fig. 2 Fig. 3

Claims (1)

[Scope of Claims] 1) A zinc alloy shot for blasting consisting of zinc alloy grains containing 101 to 10% by weight of iron. 2) When a molten zinc alloy containing 0.01 to 1.0% iron is held in a reservoir equipped with a nozzle on the bottom wall and allowed to drip naturally into water through the nozzle, 0.0
A method for producing zinc alloy shot for blasting consisting of zinc alloy grains containing 1 to 10% by weight of iron.