JPS649128B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to an improvement in a method for sealing defects that cause pressure leakage in aluminum die-cast parts by impregnation treatment. In general, the aluminum die-casting method is applied to the production of various machine parts by taking advantage of the high degree of freedom in product shape design, but in the case of machine parts that require pressure resistance, casting defects may occur. There is a problem. Casting defects are generally classified into internal defects and external defects, and it goes without saying that internal defects such as shrinkage cavities, blowholes, and porosity mainly have a negative effect on the pressure resistance of die-cast parts. By the way, the current trend in die casting is toward high-speed, high-pressure die-casting, which has been successful in producing large die-cast parts with high efficiency, but it is not suitable for applications that require pressure resistance and fluid tightness. When used, it was not free from the drawbacks of internal casting defects. Therefore, various efforts have been made to reduce such defects by devising die-casting technology, but even minute internal defects on the micron order or difficult to measure can cause pressure leaks, so die-casting technology This alone has not been enough to eradicate the cause of pressure leaks. An example of a die-cast part that requires the above-mentioned pressure resistance is the housing of a car compressor for automobile air conditioning.Especially in the front housing part, if the ring groove and oil through hole are machined after die-casting, these parts will be damaged. Internal defects in the casting are likely to be exposed in some areas, causing pressure leaks. That is,
In the above-mentioned housing, internal casting defects are difficult to form in areas near the surface or in thin-walled areas;
In other parts, oil or refrigerant gas inside the housing leaks out through the continuous hole-like defects, and the refrigerant gas is lost during use of the car compressor. Here, the size of internal defects in casting that cause leakage or not depends on its diameter and length, and whether or not the defect is enlarged close to the surface. It also depends on the presence or absence of surface defects, etc., so it cannot be determined unconditionally. Therefore, conventionally, the entire die-cast part has been subjected to the impregnation treatment described below. One of the conventional impregnation treatment methods uses water glass such as sodium silicate to impregnate the exposed casting defects on the surface of the die-cast part using either the dip method, the internal pressure method, or the vacuum-pressure method. The water glass was then impregnated into the inside of the water glass, and then the water glass was heat-treated to harden it mainly by vitrification, thereby achieving sealing. Here, properties required of the sealant include excellent sealing performance, oil resistance, water resistance, heat resistance, operability, and cost. For water glass to be used as a sealant, it is essential to heat it at 80°C for about 2 hours and then leave it for about 1 day to harden it, and the longer the curing time, the easier it is to use. It was one of the problems above. An even more serious problem is that during the hardening process or by the user of the die-cast parts, some of the water glass may blow out from the holes in the internal defects in the casting, resulting in it getting into the compressor, for example, and damaging the sliding parts. The problem was that the sealing performance deteriorated in some cases. Mainly because of these problems, organic sealants whose main components are resins such as phenol, polyester, or acrylic have emerged and are now mainstream. However, the biggest drawback of organic sealants is that they are 5 to 10 times more expensive than inorganic sealants, and they also have lower heat resistance than inorganic sealants. There is also the risk of pressure leaks when die-cast parts are used in applications where they are exposed to high temperatures. The present inventor fundamentally improved the situation in which water glass as an inorganic sealant could not be used for die-cast parts that required pressure resistance and fluid tightness due to the problem of blowing out. In addition, we conducted research and development to develop an impregnating sealing method that eliminates the conventional disadvantage of requiring a relatively long time for curing and allows the use of water glass, which is more cost-effective than organic sealants, for pressure-resistant die-cast parts. He discovered that various problems with conventional water glass could be fundamentally solved by hardening water glass by acid treatment, which had not been used at all, and filed a patent application.
The present inventor conducted further research and found that using water glass with a molar ratio of SiO ₂ /M ₂ O (where M is at least one kind of alkali metal) higher than that of commonly used water glass, exceeding 4 and below 5.1, resulted in the above-mentioned results. It was found that the various problems were solved more effectively and the sealing performance was significantly improved. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS In order to facilitate understanding of the present invention, the present invention and conventional methods will be described in detail below with reference to the drawings. 1 and 2 schematically show a cross section of an aluminum die-cast part 1 having casting defects. As mentioned above, the casting defects that cause pressure leaks are continuous defects between the inner and outer surfaces of the part, and the types of casting defects are internal defects such as shrinkage cavities and blowholes, and surface defects also contribute to pressure leaks. ing. Figures 1 and 2 show that the casting defects that are most likely to cause pressure leaks are large shrinkage cavities or blowholes in which sealant accumulates, and small blowholes, porosity, or surface cracks that are continuous to these. It shows what is going on. Hereinafter, for convenience of explanation, this will be referred to as a blowhole, and is indicated as "2" in the drawings. In addition, in the drawing,
“3” is impregnated sealant (hereinafter referred to as impregnation liquid)
It is. This impregnating solution 3 is applied using the conventional water glass method.
When heated to 80°C, a blowout 3' occurs as shown in Figure 2. It is believed that the cause of this is the generation of small vapor bubbles 4 in the impregnating liquid. On the other hand, in the case of an organic sealant, the blowout 3' can be prevented by using an anaerobic resin, but the sealing performance is poor and the cost is high. As mentioned above, in the conventional water glass curing method, heat treatment was performed at 80℃ for 2 to 3 hours and then left for 1 day.The curing (solidification) mechanism is based on the vitrification reaction. There is. Note that it is recognized that several months are required for the curing to be completely completed, and it can be said that the blowhole 2 is not sufficiently sealed while the vitrification reaction is progressing. On the other hand, the acid treatment of the present invention is characterized in that a water glass gelation reaction occurs and the reaction rate is high. Furthermore, the feature of the present invention is that the blowout 3' does not occur, and if the water glass is hardened by the gelation reaction, the blowout 3' that occurs in the conventional vitrification reaction can be practically completely eliminated. was completed. The results of the inventor's experiments indicate that the water glass is not completely solidified by the gelation reaction, and that there is no problem in preventing pressure leakage even if it is not completely solidified. Ta. Furthermore, since the gelation reaction has a higher reaction rate than the vitrification reaction, the acid treatment of the present invention causes the hardening of the water glass to proceed rapidly at the outlet of the blowhole 2, and the die-cast parts after the acid treatment It is considered that the blowout 3' is effectively prevented even when the device 1 is left unused or in use. Based on the above experimental results, the inventors of the present invention sought to find conditions for promoting the gelation reaction.
The influence of the SiO ₂ /M ₂ O molar ratio on the gelation reaction was further investigated. If M is sodium,
A small-diameter test tube is completely filled with water glasses with different SiO ₂ /Na ₂ O molar ratios, and then the water glass and acetic acid are brought into contact at the inlet of the test tube for 30 minutes or 2 hours, and water is released from the tip of the gelled water glass. The length was measured. This length is shown in FIG. 3 as the reaction length. In FIG. 3, the horizontal axis represents the SiO ₂ /Na ₂ O molar ratio of water glass, the vertical axis represents the reaction length (mm), and the black and white circles represent the contact times of 2 hours and 30 minutes, respectively. From Figure 3
It can be seen that the reaction length increases as the SiO ₂ /Na ₂ O molar ratio increases, and becomes almost constant above about 4.2. Therefore, in the present invention, the SiO ₂ /M ₂ O molar ratio is set to a value exceeding 4. Here, SiO ₂ /M ₂ O
If the molar ratio is less than 4, the effect of promoting the gelation reaction will be small, while if it exceeds 5.1, the water glass will become unstable as a liquid, making it difficult to impregnate defects in aluminum die-cast parts. Therefore, in the present invention, the SiO ₂ /M ₂ O molar ratio is limited as described above. Generally, in water glass
It is said that if the SiO ₂ /Na ₂ O molar ratio is outside the range of 2 to 4, it will not become water glass. When silica and water glass are sufficiently stirred and mixed for, for example, several hours to several tens of hours, colloidal silica can be dissolved. The present inventor discovered that water glass containing SiO ₂ at a high concentration promotes the gelation reaction, and as described later, it is possible to impregnate and seal defects in aluminum die-cast parts with extremely high reliability. Completed the invention. Also, water glass
When the SiO ₂ /M ₂ O molar ratio exceeds 4, the viscosity of the water glass increases and the permeability to the defects described above decreases, so the amount of water (H ₂ O), which is one component of the water glass, is adjusted. Alternatively, it is desirable to adopt a method such as adjusting the amount of filler added, which will be described later. Adjusting the viscosity by controlling the water content up to 70% provides in most cases a viscosity low enough for defect impregnation sealing of aluminum die-cast parts. In this case, the above reaction length is
Depending on the SiO ₂ /M ₂ O molar ratio, contact time with acid, etc.
It will change, but you will get enough value. In the present invention, aluminum die-cast parts are subjected to impregnation and sealing treatment, so it is undesirable if the aluminum is eroded by the acid reacted with water glass. Therefore, by taking advantage of the property of aluminum that is easily passivated and basically using an oxidizing acid, the purpose of impregnating and sealing can be achieved without practically damaging the aluminum die-cast parts. The inventor tested the corrosion loss of aluminum using hydrochloric acid, nitric acid, citric acid, formic acid, and acetic acid at a concentration of 2N, and oxalic acid at a concentration of 1N, and confirmed that there was almost no corrosion loss except for hydrochloric acid. did. In particular, organic acids showed good results. Furthermore, when the gelation of water glass was tested using the above-mentioned acids other than hydrochloric acid, sufficient gelation occurred when the amount of acid added was 0.5 to 1.0 ml per gram of the impregnating solution. Basically, any acid that does not corrode aluminum can be used in the present invention.
Examples are phosphoric acid, chloric acid, iodic acid, selenic acid, arsenic acid, boric acid, acetalic acid, benzenesulfonic acid. One or more of the above acids may be used in combination. In determining the amount of acid to be added, water glass is a polymer, and it is not realistic to define an accurate acid molar concentration. Furthermore, since the impregnating liquid contains water and the like in addition to water glass, it is not practical to determine the weight ratio of the acid added to the impregnating liquid. For the above reasons, the amount of acid added to a given impregnation liquid should be determined experimentally. Next, water glass basically has an alkali silicate salt as its main component, and the alkaline component is at least one of sodium, lithium, and potassium, particularly sodium as the alkaline component, and sodium as the acidic component. There is no restriction at all as long as it is a known water glass in which SiO ₂ is used. Furthermore, the water glass may contain Fe ₂ O ₃ or other metal oxide fillers in a broad sense. Moreover, as water glass for impregnating and sealing treatment, there are commercially available water glasses containing shrinkage preventive agents and the like in addition to the above-mentioned fillers, and there is no problem even if the water glass contains this. Furthermore, the aluminum to be treated in the present invention is JIS standard, which is normally used for die casting.
-H-2212 series alloys are included, and it goes without saying that it is not limited to pure aluminum. Embodiments of the present invention will be described below. As already mentioned, the drawback of the conventional heat curing method for water glass is that the curing time is long, but this point can be fundamentally solved by the action of acid. The acid treatment time according to the present invention depends on the acid temperature, acid concentration, and type of acid, but is about 10 to 30 minutes when an industrially commonly used acid is used at room temperature. Moreover, there is no need to leave it alone. Examples of the acid treatment method include a method of immersing the aluminum die-cast part in an acid aqueous solution, an alcohol solution, or another solution, and a method of spraying an acid solution. Note that the impregnation of water glass and the acid treatment can be performed in the same container or in separate containers. Further, when immersing an aluminum die-cast part in an acid solution, the acid solution can be pressurized and heated to accelerate the curing reaction. In addition, if acid and water glass are mixed in advance, the water glass will harden instantly and will not be impregnated into the blowhole. Therefore, acid treatment should be performed after water glass is impregnated into the blowhole using a known method. is necessary. Note that when heating acid, the water in the water glass (bound water) will melt when the temperature reaches 100°C.
Temperatures close to 100°C must be avoided at all costs, as the gas is released all at once. Therefore, the temperature of the acid should be as low as possible below 100°C, e.g. 80°C.
℃ or less is desirable. As a pretreatment for the process of the invention, if necessary, the aluminum die-cast parts may be cleaned, degreased, deburred, masked, etc. to remove any sources of interference with water glass impregnation and acid treatment.
Additionally, the aluminum die-cast part can be first passivated and then impregnated with water glass, followed by acid treatment with the most desirable acid for hardening the water glass. Further, as a post-treatment, water washing and drying are performed to prevent acid from remaining on the surface of the aluminum die-cast part. If there is a steam generating facility, water washing can be performed using a steam jet, and the time required for subsequent drying can be significantly shortened. After the above-mentioned post-treatment, products such as car compressors are inspected for pressure leakage, and if any defective products are found, the impregnation and sealing treatment of the present invention is applied again. Hereinafter, an example of preventing pressure leakage and blow-out of aluminum die-cast parts will be described. A large number of aluminum test pieces with holes as shown in FIG. 4 were prepared. In the figure, D=4
The dimensions were set as mm, H=5 mm, and d=0.6 mm. The test piece was placed in a high-pressure steel impregnation container 10 shown in FIG. After charging, increase the pressure inside the container to 4 cm for 10 minutes.
The pressure was reduced to below Hg, and then an impregnating liquid (water glass) at 30° C. and a specific gravity of 1.29 was injected into the container 10 from the tank 11, and the pressure was increased to 6 kg/cm ² for 15 minutes. The following table shows the number of water glasses blown out when the test pieces were dried at 60°C and 80°C after solidifying the water glass with 5N CH ₃ COOH solution for 30 minutes.

[Table] Therefore, it was found that those with a SiO ₂ /Na ₂ O molar ratio of 4.2 had excellent sealing performance. Therefore, this impregnation liquid was used to seal defects in aluminum die-cast parts of the front housing of an engine. The moisture content of the water glass was 70%, and the drying temperature was 60°C. The above die-cast part that has been subjected to the above treatment (no blowing out at all immediately after treatment)
A durability test was conducted under the conditions shown in Table 2. As a result, it was confirmed that the method of the present invention has durability and reliability that can be applied to actual equipment. In addition, instead of the above impregnating liquid with a SiO ₂ /Na ₂ O molar ratio of 5.0, an impregnating liquid with a SiO ₂ /M ₂ O molar ratio of _5.0 was used.
wt%, _K2O 0.5wt%, _Na2O 4.22wt%,
When a similar experiment was conducted using the composition of the remaining water (however, the drying temperature was only 60°C), the number of blowouts out of 20 was zero.

[Table] In the table, the mark ○ means there is no balloon, and the mark X means there is a balloon.
In the conventional heat treatment drying method using a water glass-based impregnating liquid, 80% of the aluminum die-cast parts were marked with an "X" under condition 1. On the other hand, when the SiO ₂ /Na ₂ O molar ratio was 3.4, under condition 1, 16% was similarly marked with an x mark. Next, under condition 2, when the SiO ₂ /Na ₂ O molar ratio was 3.4, 50% was marked with an x. The inventor also tried a method in which gel-like silica was precipitated by contacting water glass with CO ₂ gas, but
The desired impregnation and sealing treatment could not be achieved. Therefore, it was found that even in the case of precipitation of gel-like silica, completely different results can be obtained depending on whether CO ₂ or acid is used. In other words, the excellent overall properties of the present invention cannot be explained only by the precipitation of gel-like silica;
It can be said that the influence of high SiO ₂ /M ₂ O on the molar ratio reaction rate or the influence of other acids is decisive. Regardless of the theoretical explanation, the present invention has great industrial significance because the pressure resistance reliability of die-cast parts is greatly improved.

[Brief explanation of the drawing]

Figures 1 and 2 are conceptual cross-sectional views of aluminum die-cast parts to explain the impregnation sealing treatment, and Figure 3 shows the influence of the SiO ₂ /Na ₂ O molar ratio of water glass on the reaction length. FIG. 4 is a cross-sectional view of the test piece, and FIG. 5 is a cross-sectional view of the impregnation treatment container. 1...Aluminum die-cast part, 2...Blow hole, 3...Impregnation liquid, 3'...Blowout, 4
...Steam bubbles.

Claims (1)

[Claims] 1 After impregnating the defective parts of an aluminum die-cast part with water glass having a molar ratio of SiO ₂ /M ₂ O (where M is at least one alkali metal) of more than 4 and less than 5.1, the water glass is mixed with an acid solution. A method for impregnating and sealing a pressure leakage defect in an aluminum die-casting part, the method comprising contacting.