JPS609082B2 - Spheroidized zinc grain manufacturing method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing metal particles, and particularly to a method for producing fine spherical metal particles simply and efficiently.

As a method for manufacturing spherical metal particles, a physical spheroidization method has been proposed in which the shape is modified by dropping metal particles into a cooling medium or by transporting metal particles obtained by gaseous mist through a spiral tube. .

However, when producing metal particles by dropping into a cooling medium, small particle sizes cannot be obtained;
The particles with a mesh size or larger account for nearly 90%, and this method is not suitable as a method for producing fine metal particles with a mesh size of 100 mesh or smaller.

In addition, although the method of passing the entrusted metal lacquer and the spiral tube exposed to gas has some effect in eliminating sharp protrusions, it is still insufficient to be called spherical. This not only complicates the structure of the equipment but also complicates operational management.

Therefore, the conventionally proposed methods cannot be said to be satisfactory in obtaining fine spherical metal particles. Incidentally, in recent years, there has been a strong demand for producing fine spherical particles of metal such as zinc, cadmium, lead, copper, etc. for the purpose of improving the quality of powder compacts. For example, alkaline batteries have recently become increasingly smaller and thinner, and as a measure to extend battery life, it is desired that the zinc used in electrode moldings be fine particles and spherical. It is difficult to produce such fine, spherical metal particles using the methods described above, and it is necessary to establish a new method. The present invention has established a method for easily manufacturing fine spherical metal particles in order to eliminate the drawbacks of the above-mentioned prior art and to meet the demands in this field.

As a result of a detailed study on the gas atomization method in which a metal solution is dispersed into droplets using a layer mist gas, the inventors have discovered that the method of atomizing a metal solution into droplets using a layer mist gas results in the discovery of a method for dispersing a metal solution into droplets using a layer mist gas. It was found that the temperature of the gas has an important influence on spheroidization. Accordingly, the temperature of the mist gas is considered to be room temperature, and it has been generally believed that raising the temperature slows down the solidification of the droplets and is rather harmful. The droplets produced by the atomization fall through the metal particle collection hopper, solidify during that time, and are collected at the bottom of the hopper. It has a decisive influence on the success or failure of development. One theory is that when a metal solution is exposed to room-temperature atomized gas and subjected to the atomizing action, the atomized droplets are rapidly cooled, resulting in local solidification and subsequent spheroidization due to the accompanying viscosity change. It seems to have a negative effect. Therefore,
It is rather preferable to raise the temperature of the mist gas. however,
Raising the temperature of cough fog gas too high may have the opposite effect, as it delays the solidification of the droplets. In addition, it has also been found that spheroidization progresses suitably by suppressing the opportunity for metal and oxygen to bond to a predetermined limit or less during the entire period from the generation of metal droplets to their solidification. For this purpose, it is necessary to maintain not only the oxygen concentration in the mist gas but also the oxygen concentration in the atmosphere within the metal particle collection hopper below a predetermined limit.
The upper limit of oxygen concentration depends on the metal being treated, but is generally set at 8%. By using such oxygen concentration control in conjunction with the use of the above-mentioned heated atomized gas, it becomes possible to produce metal particles that are more spherical. Thus, the present invention provides a method for producing metal grains, which comprises dispersing a finished metal body into droplets using atomized gas, and dropping the metal particles into droplets in a metal grain collection hopper to collect them in a bottle. It is characterized by the use of

Furthermore, the present invention is characterized in that the fog gas is used when the temperature is raised, and the oxygen concentration in the fog gas and the oxygen concentration in the atmosphere inside the metal particle recovery hopper are set to 8% or less. below,
The present invention will be described in detail.

The target metals in the present invention include all metals in general from which metal particles can be produced by a spraying method, but in particular metals with high affinity for oxygen, such as zinc, cadmium, lead, or alloys thereof, are targeted. Ru.

The metal solution is maintained at a predetermined temperature in a storage container installed on the metal particle collection hopper and released through a nozzle provided at the bottom of the storage container, and immediately after release, it is dispersed into fine droplets by a mist gas.

The dispersed pongee droplets solidify as they fall within the hopper, and are collected as metal particles at the bottom of the hopper. The temperature of the metal solution should be as close to the melting point as possible, but it must be within a temperature range that allows atomization.

For example, in the case of manufacturing zinc particles for batteries, the purest zinc (9
9.99% Zn) was used, and the solution temperature was 450-60
It is assumed to be 0qo. Since the temperature of the solution is correlated with the solidification time of the atomized pongee droplets, if the pongee droplets are not sufficiently solidified when they collide with the hopper wall, they are likely to flatten or become distorted due to the impact. In order to obtain sufficient solidification, it is desirable to select the solution temperature in consideration of other factors of the equipment. If the hopper has a large volume and the time required for the dispersed pongee droplets to collide with the hopper wall is relatively long,
The solution temperature can be increased. However, since the use of a large hopper is undesirable because the equipment becomes bulky, it is preferable to keep the port body temperature low. Preferably, the side walls of the hopper exhibit a curved surface.

This is because, as mentioned above, if the atomized metal is not sufficiently cooled before it hits the side wall, it is likely to deform, so the curved surface is used to soften the impact as much as possible. The higher the atomizing gas pressure is, the better in order to obtain fine particles, but if it is set too high, the dispersed droplets may hit the side walls and the like and be deformed, or the droplets may become flattened due to pressure impact, which is not preferable.

In order to obtain as uniform and fine atomization effect as possible, it is necessary to select an appropriate pressure, taking into consideration the dimensions of the discharge nozzle at the bottom of the reservoir, etc. For example, in the case of zinc, it generally ranges from 1 to 5k9/m2, with 2k9/m2 being preferred. According to the invention, the atomizing gas is used at elevated temperature rather than at normal temperature.

As previously mentioned, the solution flowing down from the bottom nozzle of the reservoir is first exposed to the atomizing action as a pressurized atomizing gas. At this time, if a mist gas at room temperature is used, the resulting droplets will cool down too quickly, possibly resulting in partial solidification, which will prevent the natural spheroidization process. Therefore, it is necessary to raise the temperature of the mist gas so that the metal solution is not initially subjected to too rapid a cooling effect. The heating temperature can vary depending on the temperature of the solution metal, and can range from room temperature to near the temperature of the solution metal. However, if the temperature of the mist gas is raised too much, the solidification of the droplets will be delayed, and there is a risk that the metal particles will collide with the hopper wall and be deformed while the droplets are not fully solidified. It is preferable to select an appropriate mist gas heating temperature by comprehensively considering the solution temperature, hopper design dimensions, mist gas pressure, etc. For example, in the case of zinc, 100 to 350 qo is appropriate. Furthermore, it is preferable to suppress the oxygen concentration of the false mist gas to 8% or less.

This is to minimize the chance of contact between the metal solution and oxygen during atomization to minimize the formation of oxides. As the mist gas, nitrogen gas, CO2 gas, argon, or other inert gas is used. In addition,
It is preferable that the oxygen concentration of the atmosphere in the metal particle collection hopper, where the molten bottle remains in an unsolidified state after atomization, is controlled to be 8% or less.

For this purpose, it is necessary to design the equipment so that the inside of the hopper is well sealed from the surrounding atmosphere. Appropriate sealing means must be provided at the connection between the metal solution reservoir and the hopper and at the metal particle collection port. The above upper limit of 8% was determined by measuring bulk specific gravity of various metals and understanding the degree of spheroidization through microscopic observation.

For example, in the case of zinc, which has a strong affinity for oxygen, the following results were obtained. The bulk density increases as the metal grains become more uniform and spherical, and provides a very clear indication of the properties of the metal grains. It was judged to be excellent.

Next, examples and comparative examples using zinc lacquer bath will be described. Example 1 Zinc grains were produced using air having a floor fog pressure of 2k9/earth pressure as a mist gas for a zinc port hot water maintained at 550%.

Three air temperatures were used: room temperature, 150°C, and 30,000°C. The bulk density of the produced grains was measured. air temperature
Umbrella specific gravity room temperature
2.8150pm
3.2530030
3.25 Most of the particles obtained were in the range of 100 to 200 mesh.

Example 2 A test was conducted using nitrogen gas instead of the air in Example 1 and maintaining the atmosphere in the recovery hopper at an oxygen concentration of 1.5%.

The bulk density of the produced grains was improved as follows. nitrogen temperature
Bulk specific gravity 150q0
4.1030pi0
4.12 Similarly, most of the particles were in the 100-200 mesh range.

As shown in the examples, by increasing the temperature of the dawn mist gas and preferably controlling the oxygen concentration to a low concentration.
．． Zinc particles having a bulk specific gravity of 20 or more are produced, which means that the produced zinc particles are rectified and spheroidized.

Furthermore, in contrast to the method of dropping into a cooling medium, fine particles in the 100 to 200 mesh range, which are particularly required for alkaline batteries, are produced in high yield. Since the bulk specific gravity of the zinc particles thus produced according to the present invention is about 1.3 pitch higher than that of conventional products, it makes a significant contribution to increasing the capacity of 4-inch batteries such as alkaline batteries. In addition, in the past, alkaline batteries could not be made with a constant particle size, and the majority of batteries were long and thin, so zinc wire was also cut into pieces of a certain shape. Another great advantage of the present invention is that spherical objects of a certain size can be manufactured continuously by a simple spraying method without relying on such troublesome methods. As explained above, the present invention, contrary to the conventional concept, improves the temperature of atomized gas by raising the temperature of the atomized gas, and also by strictly controlling the upper limit of oxygen concentration throughout the entire process from atomization to solidification. We succeeded in producing fine spherical metal particles simply and efficiently using the fog method.

Claims (1)

[Scope of Claims] 1. A method for producing zinc grains, which comprises dispersing a zinc solution into fine droplets using atomized gas, allowing them to fall through a zinc grain collection hopper and collecting them, wherein the zinc solution is heated to 100 to 350°C. A method for producing spheroidized zinc particles, characterized in that spheroidized zinc particles are produced by using atomized gas. 2. In a method for producing zinc grains, which consists of dispersing zinc solution into fine droplets with atomized gas, and allowing the droplets to fall and be collected in a zinc grain collection hopper, the atomized gas heated to a temperature of 100 to 350°C is used. Also, a method for producing spheroidized zinc particles, characterized in that spheroidized zinc particles are produced by controlling the oxygen concentration in the spray gas and the oxygen concentration in the atmosphere in the zinc particle recovery hopper to 8% or less.