JPS61130430A - Cleaning method of molten al or al alloy refined by gaseous chlorine - Google Patents

Abstract

PURPOSE:To remove efficiently impurities from molten Al or Al alloy refined by gaseous chlorine and to clean the molten metal by filtering the molten metal by pulverous sodium chloride or potassium chloride as a filter aid. CONSTITUTION:The pulverous sodium chloride and/or potassium chloride is added at about 0.005-0.1wt% as the filter aid to the molten Al or Al alloy refined by gaseous chlorine and an inert gas is blown thereto to stir the molten metal and to disperse uniformly said sodium chloride and/or potassium chloride. The grain size of the sodium chloride, etc. is properly selected according to the pore size of a filter consisting of a porous refractory material, etc. The molten metal is preferably filtered after the filter is precoated by circulating the molten metal dispersed with the above-mentioned filter aid circulated in the initial stage of filtration. The fine impurities in the molten metal are thus effectively removed and the decrease in cleanliness is hardly obviated even if the slight chlorides mentioned above enter the molten metal subjected to the filtration.

Description

[Detailed Description of the Invention] [Industrial Application] The present invention efficiently removes and cleans impurities in molten Al or Al alloy (hereinafter referred to as A alloy) refined with chlorine gas. It is about the method.

[Conventional technology]

Molten Al alloy contains a considerable amount of impurities that come from raw materials and molten raw materials such as Al alloy scrap, and impurities that are mixed in or newly generated during the smelting process, and these impurities cause various product defects. Cause. Therefore, when casting Al alloys, impurities are removed by refining the molten Al alloy with chlorine gas or flux, and fine impurities are cleaned by removing F with a filter made of porous refractory material before the casting process. I am sending it to

[Problem that the invention seeks to solve]

The present inventors have also been industrially conducting melting, refining, filtration, casting, and secondary processing of Al alloys for some time, and based on their experience, they used the same P material and set the same filtration conditions. I learned that even in some cases, there may be a noticeable difference in the cleanliness after filtration depending on the refining method of the molten Al alloy. That is, even when the same filtration conditions are set, high cleanliness can be obtained with flux-refined Al alloy molten metal.
The cleanliness of Al alloy molten metal that has been subjected to chlorine gas refining is quite low, and in most cases product defects due to impurities appear in the former (those that have been subjected to chlorine gas refining).

Under these circumstances, the present invention aims to provide a technology that can effectively remove impurities and improve the cleanliness of molten Al alloys that have been subjected to chlorine gas refining.

[Means for solving problems]

The gist of the present invention is to use finely powdered sodium chloride and/or potassium chloride as a filter aid when removing impurities from a molten Al alloy refined with chlorine gas.

[Effect]

As a result of investigating the reason why the filtration behavior differs significantly depending on the refining method as described above, the following facts were confirmed. That is, as a furnace material for filtering molten Al alloy after refining, for example,
Porous refractory materials with a pore diameter of about 200 to 300 μm are used, such as those described in No. B8-26886, U.S. Patent No. 8539667, and Japanese Patent Publication No. 56-85625, etc., but Al alloys that have undergone flux refining are used. When pouring the molten metal, some of the flux components remain in the molten metal and act like a filter aid, accelerating filter clogging. The impurity removal effect is considerably improved. However, since molten Al alloy refined with chlorine gas does not contain substances that act as filter aids as mentioned above, some of the fine impurities that are smaller than the original filter mesh pass through the filter, resulting in improved cleanliness. It has become clear that this is hindering the improvement of

From this point of view, it was thought that in order to increase the filtration efficiency of molten Al alloy refined with chlorine gas, it would be effective to use a filter aid in the filtration process using a filter. Based on these predictions, we investigated the impurity removal effects when using various filter aids. As a result, although silica and/or alumina-based, nitride-based, etc., which have traditionally been widely used as filter aids, functioned well as filter aids, some of them passed through the filter and formed aluminum. In some cases, it got mixed into the molten alloy, reducing the cleanliness. For this reason, we conducted experiments to find a substance that has excellent effects as a filter aid and does not have a negative effect on molten aluminum alloys.As a result, fine powders of sodium chloride and potassium chloride were found to be excellent as filter aids for molten aluminum alloys. It was confirmed that it can perform the functions described above. i.e. sodium chloride and/or
When fine powder made of potassium chloride is used as a filter aid, it is possible to remove as much as possible the fine impurities that cannot be removed by chlorine gas refining and cannot be removed by subsequent general filtration. Moreover, these chlorides are hardly mixed into the molten metal and reduce the cleanliness, and it is possible to obtain a cleanliness that is comparable to that of the Al alloy molten metal obtained by filtration treatment after flux refining. can.

There are no particular restrictions on how sodium chloride or potassium chloride is used as a filter aid, but the most common methods are: (1) blowing the above-mentioned fine powder into a molten Al alloy using an inert gas; This is a method in which it is poured onto a molten alloy, stirred by bubbling with an inert gas, and dispersed into the melt.

When implementing these methods, in the initial stage of the filtration process, the filter may not be sufficiently clogged with chloride, and the cleanliness may not be sufficiently improved. In such a case, W! at the initial stage of filtration! It is a good idea to cause the filter to become clogged by circulating hot water for a while (perform a so-called pre-coat treatment), and then perform full-scale filtration. In addition, fine powder of chloride may be attached to the filter at an appropriate stage from the final stage of manufacturing a filter made of porous refractory material to the filtration treatment under conditions similar to the pre-coating treatment described above. if there is,
- It is also possible to omit the timely introduction or mixing of fine chloride powder. In addition, when the above-mentioned fine powder is mixed into the Al alloy molten metal, the preferred amount of the fine powder added is 0.005 to 0.1* based on the weight of the molten metal, and if it is less than this, the function as a filter aid is insufficient. Not demonstrated, while 0.196
If it exceeds this, the filter tends to become excessively clogged and the filtration speed tends to slow down.

As the filter used in the present invention, various porous refractory materials such as those shown above can be used, but the particle size structure of the fine powder is determined to achieve the best filtration efficiency depending on the pore size of the porous refractory material. It is preferable to select it appropriately so that the following can be obtained.

In the present invention, only sodium chloride and potassium chloride among alkali metal chlorides are selected as filter aids for the following reasons. In other words, lithium chloride has a lower melting point than sodium chloride, etc., and it melts at the normal Al alloy melting temperature, so it cannot function as a filter aid, and it also cannot function as a filter aid. This is because it is extremely expensive and lacks practicality.

〔Example〕

Example 1 JIS 5056 series Al alloy molten metal (
commercially available industrial potassium chloride (average particle size: 100 μm, 501j) was blown into the solution (looOKf) along with nitrogen gas,
It was filtered using a tubular filter (grade HB) manufactured by Tokyo Kyokuryokurozai Co., Ltd. Using this molten metal, a billet with a diameter of 200 mm was manufactured by a semi-continuous casting method, extruded into a solid rod shape at R = 25 (n = 10 mm), and linear defects on the surface of the solid rod (n = 10 mm) were formed using a semi-continuous casting method. The occurrence status (due to impurities) was investigated. For comparison, the occurrence of linear defects on the surface of the solid rod was investigated in the same manner as above, except that the injection of potassium chloride was omitted.

As a result, no linear defects were observed in the former case (potassium chloride added), but in the latter case (no potassium chloride added), one out of 10 solid rods had a linear defect. Ta. It should be noted that no significant difference could be observed regarding the lifespan of the filters.

Example 2 Defiltration treatment, semi-continuous casting and solid bar extrusion were carried out in the same manner as in Example 1 except that commercially available industrial sodium chloride (average particle size 80 μm) was used in place of potassium chloride. When the occurrence of linear defects was observed, no linear defects were observed in any of the 10 solid rods.

When a similar experiment was conducted using half of each of potassium chloride and sodium chloride, no linear defects were observed.

〔Effect of the invention〕

Since the present invention is configured as described above, it is possible to obtain the same cleanliness even from molten Al alloy that has undergone chlorine gas refining as that of molten aluminum that has undergone flux refining, and eliminates linear defects caused by fine impurities. This can be prevented as much as possible.

Claims (1)

[Claims] A method for cleaning molten Al or Al alloy, which comprises filtering the molten Al or Al alloy using finely powdered sodium chloride and/or potassium chloride as a filter aid when removing impurities from the molten Al or Al alloy refined with chlorine gas. .