JP2001131648A - Impregnating filter for casting and its manufacturing method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a ceramic filter for casting having the constant molten metal impregnating ratio. SOLUTION: This impregnating filter for casting is manufactured by allowing the ceramic filter to contact with molten aluminum alloy and estimating the molten metal impregnating ratio of the ceramic filter from the concentration increasing rate of eluted component into the molten aluminum alloy from the ceramic filter and continuing the contact of the ceramic filter with the molten aluminum alloy until this molten metal impregnating ratio reaches 70%. Elements eluted into the molten aluminum from the ceramic filter are Ca, Si, Zr, Ti, Sr, etc., and the molten metal impregnating ratio can be obtained by measuring the concentration increasing rate of any one or more among these eluted elements. The molten aluminum alloy in contact with the ceramic filter, is desirable to be held at >=750 deg.C.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing an impregnated filter suitable for producing a clean aluminum alloy casting free of foreign matter.

[0002]

2. Description of the Related Art A molten aluminum alloy is fed into a mold cavity from a holding furnace via a gutter, a runner, etc., and is cast into a casting having a predetermined shape. Casting methods include gravity casting, die casting, die casting, semi-continuous casting, and continuous casting. In any case, it is important to increase the cleanliness of the molten aluminum alloy fed into the mold cavity. If the degree of cleanliness is low, the casting will contain many inclusions, and sufficient mechanical strength and formability cannot be obtained. The cleanliness of the aluminum alloy melt can be increased by providing an inclusion filtration chamber in the middle of the melt flow path leading to the mold cavity to remove coarse crystals, foreign substances, and the like floating in the melt. For example, Japanese Unexamined Patent Publication
In JP-A-51656, a filtration unit having a ceramic tube is disposed in a filtration chamber.

A ceramic filter is effective for removing inclusions floating in a molten metal. Among them, a tube-shaped ceramic filter is used for producing a high-quality product. However, even when the molten aluminum alloy is directly injected into the ceramic filter, the molten aluminum alloy does not pass through the inside of the filter smoothly. Therefore, a method of impregnating the inside of the filter with a molten aluminum alloy in advance has been adopted in order to smoothly pass the molten metal. Even in this case, the aluminum alloy melt does not pass through the inside of the filter in a portion where the aluminum alloy melt is not impregnated in the filter. As a result, the filtration area decreases with a decrease in the impregnation rate. As a result, the filtration flow rate locally increases remarkably. .

Therefore, when a new ceramic filter is used, the following pretreatment is performed prior to use in an actual operation. First, the ceramic filter before use is heated and held for several days so that the molten aluminum alloy for casting does not solidify inside the filter, and then the ceramic filter is set inside the filter tank. Next, the aluminum alloy melt is poured into the filter tank, and the aluminum alloy melt is allowed to pass through the inside of the filter while applying pressure or reduced pressure, thereby forcibly impregnating the filter with the aluminum alloy melt. After holding this state for several hours, the ceramic filter is used for actual casting.

[0005]

Even in a pre-treated ceramic filter, there is no means for checking whether or not the aluminum alloy melt is sufficiently impregnated inside the filter.
As a result, the operation may be started using a ceramic filter having a low impregnation rate. A ceramic filter with a low impregnation rate has a low affinity for the molten aluminum alloy, so that the filtration area tends to be small, and the flow rate of the molten aluminum alloy passing through the inside of the filter is fluctuated, thereby causing unstable filtering conditions. In an extreme case, the ceramic filter may become clogged immediately after the start of casting and become unusable. In addition, since the preliminary processing of the filter takes several days as described above, if the filter is suddenly clogged, the next filter cannot be made in time, and the operation is seriously affected. The present invention has been devised to solve such a problem, and based on the finding that the elution rate of a metal component eluted from the aggregate or the binder of the filter is closely related to the impregnation rate, An object of the present invention is to provide a casting filter in which an impregnation rate is easily estimated from a speed and an aluminum alloy is impregnated in advance with an impregnation rate suitable for casting under stable molten metal flow conditions.

[0006]

In order to attain the object, the production method of the present invention comprises bringing a ceramic filter into contact with a molten aluminum alloy and measuring the concentration of a component eluted from the ceramic filter into the molten aluminum alloy. Is characterized in that the contact between the ceramic filter and the molten aluminum alloy is continued until the molten metal impregnation rate reaches 70%. When pressure or pressure reduction is applied to the molten aluminum alloy in contact with the filter, impregnation of the molten aluminum alloy can be promoted. The elements eluted from the ceramic filter into the molten aluminum alloy are Ca, Si, Z
There are r, Ti, Sr, and the like, and the molten metal impregnation rate of the ceramic filter can be obtained by measuring the concentration increasing speed of one or more of these eluting elements. The molten aluminum alloy to be brought into contact with the ceramic filter is preferably maintained at a temperature of 750 ° C. or higher in order to reduce the viscosity and promote the impregnation.

[0007]

For example, when removing inclusions floating in an aluminum alloy melt using a tubular ceramic filter, as shown in FIG. 1, a filtration unit 2 having a plurality of tubular ceramic filters 1 is connected to an inclusion filtration tank. 3 and the molten aluminum alloy M
₀ is sent to the inclusion filtration tank 3. When the molten aluminum alloy M ₀ in the inclusion filtration tank 3 receives the molten metal pressure and passes through the tubular ceramic filter 1, inclusions derived from refractories floating in the molten metal and coarse inclusions crystallized from the molten metal are formed. Is filtered and separated by the tubular ceramic filter 1. The molten aluminum alloy M ₁ of the inclusions is removed cleaned,
It is sent to the mold via the tapping pipe 5. The molten aluminum alloy M ₁ which is cleaned, Ca derived from aggregate and binder of the ceramic filter, Si, Zr, Ti, contains Sr or the like. These metal components are aggregate and binder is subjected to a reduction reaction of the ceramic filter when injected molten aluminum alloy M ₀ to the new filter, eluted in molten aluminum alloy M ₁ results.

The present inventors have measured the concentration of the eluting element contained in the molten aluminum alloy M _{1 that} has passed through the ceramic filter, and found that there is a close correlation between the change over time in the concentration and the impregnation rate of the ceramic filter. I found something. This correlation means that the impregnation rate of the ceramic filter is estimated from the change with time of the concentration of the eluted element. Emission analysis, chemical analysis, and the like can be used to measure the concentration of the eluted elements, but luminescence analysis that can provide an analysis result in a short time is preferable. Specifically, using a ceramic filter having various impregnation rate, the time course of elution element concentration was measured for the molten aluminum alloy M ₁ having passed through the ceramic filter, grasped in advance the relationship between the concentration increase speed and impregnation ratio of Keep it. In actual use, the rate of increase in the concentration of the dissolved element in the filter tank is measured, and the measured value is applied to the relationship between the previously obtained increase rate of the concentration and the impregnation rate, and the molten metal impregnation of the filter corresponding to the measured value is performed. Estimate the rate. In the filter whose estimated value of the molten metal impregnation rate exceeds 70%, the adaptability to the aluminum alloy molten metal is sufficiently improved. Therefore, the ceramic filter is used until the rate of increasing the concentration of the dissolved element corresponding to the molten metal impregnation rate of 70% is obtained. And contact with the molten aluminum alloy. When pressurizing or depressurizing the aluminum alloy melt, the impregnation of the ceramic alloy with the aluminum alloy melt is promoted, and the time until the impregnation rate reaches 70% is reduced.

It is preferable to measure the rate of increase of the concentration of the eluted element over a period of three hours from the start of the injection of the molten aluminum alloy M ₀ into the filtration chamber. In a state where three hours or more have passed, the elution rate of the metal component eluted from the filter into the aluminum alloy melt is reduced, and the effect of the increase rate on the impregnation rate is reduced. However, small amounts elution between not reaching the injection beginning 30 minutes, because the density difference of the aluminum alloy melt M ₀ fed into the ceramic filter is small, difficult to measure the rate of increase of concentration. For this reason, it is preferable to use, as the measured value of the concentration of the eluted element, a value from the start of the injection to the lapse of 3 hours. When pressurizing or depressurizing the aluminum alloy melt, it is preferable to estimate the impregnation rate from the rate of increase in the concentration of the eluted element from when the aluminum alloy melt was pressurized or depressurized last. In this way, the molten metal impregnation rate of the ceramic filter can be easily determined, so that the aluminum alloy melt can be supplied to the mold under stable conditions without clogging even when the aluminum alloy melt is filtered during actual casting. Will be possible.

[0010]

EXAMPLE Si: 0.017% by weight, Fe: 0.013
Wt%, Cu: 0.036 wt%, Ti: 0.0015
Wt%, Mg: 2.72 wt%, Zn: 0.0020 wt%, Na: 0.0002 wt%, Ca: 0.0001
A weight of 760 ° C. aluminum alloy melt at a temperature of 760 ° C. was fed into the inclusion filtration chamber, and the aluminum alloy melt was pressurized to impregnate the ceramic filter. As a ceramic filter, electrolytic alumina is used as an aggregate, and Al ₂ O ₃ -B
₂ O ₃ —MgO—SiO ₂ —CaO—TiO as binder, average pore diameter 440 μm, tube bulk specific gravity 2.18 g
/ Cm ³ filter, capacity 800mm × 104
22 pieces were set in a filtration tank of 0 mm x 750 mm.

During a period of 1 to 2 hours from the start of the injection of the molten aluminum alloy, the concentration of the components contained in the aluminum alloy transmitted through the ceramic filter was measured by emission spectrometry, and the rate of increase in the concentration of the eluted element was determined. After the measurement, the ceramic filter was taken out of the inclusion filtration chamber, and the molten metal impregnation rate of the ceramic filter was determined. The molten metal impregnation rate was calculated by dividing the weight difference of the ceramic filter before and after contact with the aluminum alloy molten metal by the specific gravity of the molten metal, and dividing this value by the cavity volume of the ceramic filter (volume of filter material × porosity). . In addition, the impregnation rate of the molten aluminum alloy was variously changed by adjusting the pressing conditions of the molten aluminum alloy. Table 1 shows the measurement results of the molten metal impregnation ratio together with the concentration increasing speed. In addition, calibration curves representing the relationship between the concentration increasing rate and the molten metal impregnation rate for each eluting element are shown in FIGS. As is clear from Table 1 and FIGS. 2 to 6, the molten metal impregnation ratio had a linear relationship with the increasing rate of the concentration of the eluting element derived from the ceramic filter. Therefore, FIG.
By using the calibration curve shown in FIG. 6, the molten metal impregnation rate of the ceramic filter can be determined from the rate of increase of the concentration of the dissolved element, which is relatively easily measured.

[0012]

Next, the increasing rate of the Ca concentration is 4 ppm /
Use a timeless ceramic filter for actual casting,
The molten aluminum alloy having the composition described above and having a temperature of 760 ° C. was passed through a ceramic filter at a flow rate of 100 kg / min and semi-continuously cast. Although the amount of filtration exceeded 200 tons by repeating casting using the same filter, the clogging did not occur in the ceramic filter, and the flow rate of the aluminum alloy melt did not significantly fluctuate. Therefore, the molten aluminum alloy could be poured into the mold under stable conditions, and a casting with high cleanliness could be manufactured.

[0014]

As described above, the impregnating filter for casting according to the present invention has an impregnating amount sufficient for the aluminum alloy melt injected at the time of casting without causing clogging. An aluminum alloy has been impregnated beforehand. The molten metal impregnation rate of the ceramic filter can be easily estimated from the increasing rate of the concentration of the eluting element contained in the molten aluminum alloy that has passed through the ceramic filter. When using a ceramic filter whose molten metal impregnation rate is adjusted in this way, the molten aluminum alloy can be fed into the mold under stable conditions during casting, and a highly clean casting can be manufactured with high productivity.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view of an inclusion filtration chamber incorporating a filtration unit having a plurality of tubular ceramic filters.

FIG. 2 is a graph showing the relationship between the rate of increase in Si concentration and the impregnation rate of molten metal in a ceramic filter.

FIG. 3 is a graph showing the relationship between the increasing rate of the Ti concentration and the impregnation rate of the molten metal in the ceramic filter.

FIG. 4 is a graph showing a relationship between a Ca concentration increasing rate and a molten metal impregnation rate of a ceramic filter.

FIG. 5 is a graph showing a relationship between a Zr concentration increasing rate and a molten metal impregnation rate of a ceramic filter.

FIG. 6 is a graph showing the relationship between the increase rate of the Sr concentration and the impregnation rate of the molten metal in the ceramic filter.

[Explanation of symbols]

1: tubular ceramic filter 2: filtration unit 3: filter chamber 4: hot water outlet 5: hot water pipe M _0: before filtration of the molten aluminum alloy M _1: molten aluminum alloy after filtration

 ──────────────────────────────────────────────────の Continuing from the front page (72) Inventor Yuichi Hasegawa 161 Kambara, Kambara-cho, Anbara-gun, Shizuoka Nippon Light Metal Co., Ltd. F-term (reference) in Kambara Factory 4D019 AA03 BA02 BA05 BB07 CA03 CB06 4E014 NA08 4K001 AA02 BA23 EA06

Claims (5)

[Claims] 1. A ceramic filter is brought into contact with a molten aluminum alloy, and the impregnation rate of the molten metal in the ceramic filter is estimated from the rate of increase in the concentration of components eluted from the ceramic filter into the molten aluminum alloy.
A method for producing an impregnated filter for casting, wherein the contact between the ceramic filter and the molten aluminum alloy is continued until the temperature of the filter reaches the temperature of the filter. 2. The method for producing an impregnated filter for casting according to claim 1, wherein a pressurizing or depressurizing treatment is performed to promote impregnation of the ceramic filter with the molten aluminum alloy. 3. Ca, eluted in a molten aluminum alloy,
2. The method for producing an impregnated filter for casting according to claim 1, wherein the concentration increasing speed of one or more of Si, Zr, Ti, and Sr is measured. 4. The method according to claim 1, wherein the temperature of the molten aluminum alloy to be brought into contact with the ceramic filter is maintained at 750 ° C. or higher.
A method for producing the impregnated filter for casting according to the above. 5. An impregnated filter for casting, wherein the impregnation rate of the molten metal estimated from the increasing rate of the concentration of the elution element derived from the ceramic filter contained in the molten aluminum alloy in contact with the ceramic filter is 70% or more.