JPS6133734A - Surface treatment of metallic mold for casting - Google Patents

Abstract

PURPOSE:To improve the quality of a product, the life of a metallic mold for casting and the productivity by forming a surface treated layer having more than specified hardness and thickness on at least part of the metallic mold and forming a ceramic layer thereon to a specific thickness thereby preventing the injury by the thermal impact arising from pouring. CONSTITUTION:The surface layer having >=700 hardness Hv and >=10mum thickness is formed by a diffusion penetration treatment of a carburizing method, nitriding method, tufftriding method, etc. to at least part, such as hole-casting pin part of a base material for the metallic mold for casting and in succession thereto, the new ceramic layer consisting of titanium carbide, titanium nitride, etc. is formed to 5-20mum thickness by a physical adsorption method such as vacuum deposition method, ion plating method or sputtering method onto said layer. The upper layer has poor wettability with the molten metal and has the coefft. of thermal expansion approximate to the coefft. of the thermal expansion of the surface treated layer formed on the base material and therefore said layer prevents the injury and exfoliation by the thermal impact during pouring at a high temp. The product quality is thus improved, the metallic mold life is extended and the productivity of casting is improved.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a method for surface treatment of casting molds, and particularly to molds used in die casting methods and high pressure casting methods, and parts of these molds. The present invention relates to a surface treatment method suitable for cast pins.

[Conventional technology]

A conventional technique will be explained using a die casting method as an example.

In the aluminum die casting method, products are formed by injecting molten aluminum alloy at a temperature of 600" to 700°C into the product cavity of a mold at a high speed of 30 to 80 m/s. Galling occurs early on in areas that are directly hit by high-speed molten metal.This galling is particularly noticeable on small diameter casting pins that cannot be water-cooled, located near the gate of the mold. It is necessary to replace the parts, which is a problem in production.

For example, when an automobile transmission case with a casting weight of 8 kg was produced by die-casting using molten aluminum alloy (JIS ADC12 alloy) using a die-casting machine of 165 (liters), the molten metal was directly exposed to the molten metal from the gate. The located φ25 x 30 m (7) cast-out piers (manufactured by JIS 5KD61) were severely galled, and the cast-out pins had to be replaced approximately once every 8 hours (approximately 300 shots).

Therefore, as a countermeasure to this problem, the currently known tuftride method,
When tests were conducted by applying surface treatment methods such as ion brating, TD, and CVD to cast pins, the lifespan was extended by 2 to 3 times compared to when no surface treatment was applied, but the most The long-life model developed galling after about 1,000 shots, and it was necessary to take down the mold and replace the cast pin.

[Problem that the invention seeks to solve]

Incidentally, periodic maintenance of the mold is performed every 2,500 shots, for example, and a cast pin that does not require replacement until the periodic maintenance of the mold is desired.

However, as mentioned above, the conventional cast pin has a diameter of 300 mm.
The mold had to be taken down and the cast pin replaced after ~1,000 shots, which caused the problem of poor productivity.

In order to take countermeasures against this problem, we investigated a cast-out pin that had been subjected to TD treatment and found that approximately 10 μm of the NbC layer had peeled off, and it was confirmed that molten aluminum alloy had adhered to this area. .

Therefore, it is thought that the life of the mold can be extended by taking measures to prevent this surface treatment layer from peeling off.

[Means for solving problems]

According to the present invention, the above problems are solved by the following method for surface treatment of a casting mold.

That is, the method for surface treatment of a casting mold of the present invention is a surface treatment method for forming a layer with excellent heat resistance and wear resistance on the surface of the casting mold, the method comprising: a base material of the casting mold; A first surface treatment layer having a Hv of 700 or more is applied to at least a portion of the
After the above formation, a second surface treatment layer made of new ceramics is then formed on the first surface treatment layer to a thickness of 5 to 20 μm by physical adsorption.

The mold to which the present invention is applied may be any mold as long as it is for casting, but in particular, molds for die casting, high pressure casting, etc.
Suitable for molds into which high-temperature molten metal is injected at high speed. Also,
Among molds, it is most effective when applied to cast pins.

In the present invention, the diffusion infiltration treatment method for forming the first surface treatment layer includes the known carburizing method, nitriding method, tuftride method, sulfurization method (sulsulf method), 'rD treatment method, and metal infiltration method. Zinc penetration method (Sheradizing), aluminum diffusion coating method, chromium diffusion coating method, silicon penetration method (Shelardizing), boron penetration method (Boronizing)
etc. can be used.

This first surface treatment layer must have a thickness of 10 μm or more, and must have a hardness of Hv700 or more in terms of Viccanis hardness. Therefore, no matter which of the above-mentioned diffusion/infiltration treatment methods is selected, the treatment must be carried out under conditions such that Hv is 700 or higher.

Also, a second surface treatment layer is formed on the first surface treatment layer. This second surface treatment layer is formed by physical adsorption (PVD). Here, as the physical adsorption method, the well-known vacuum evaporation method, ion blating 1. Sputtering, etching, etc. can be used. This second surface treatment layer is made of titanium carbide (TiC), titanium nitride (Ti
It is made of new ceramics such as N). Further, the coating thickness of the second surface treatment layer needs to be 5 to 20 μm. This is because if it is thinner than 5 μm, sufficient effects cannot be achieved, and if it is thicker than 20 μm, it may cause peeling.

In addition, it was confirmed in the following experiment that it is desirable to form the second surface treatment layer by a physical adsorption method. That is, φ2
Prepare multiple cast-out pins made of JIS 5KD61 of 5 x 30 mm, and use the base material without surface treatment, those with tufftride treatment, those with TD treatment, and titanium nitride by sputtering (a type of physical adsorption method). Four types of coated materials were prepared, and in order to evaluate their molten metal resistance and wettability, molten aluminum alloy (JI) was prepared at 700°C.
A molten metal resistance test was conducted for 5000 cycles under the conditions of immersion in SADC12) for 1 minute and forced air cooling for 1 minute.

The results are shown in FIG. From FIG. 2, it can be seen that the physical adsorption method is superior to other treatment methods.

[Effect]

According to the surface treatment method for a casting mold of the present invention, since the first surface treatment layer is formed by the diffusion infiltration treatment method, this first surface treatment layer has excellent heat resistance and wear resistance. It has excellent adhesion strength to the base material. Further, on this first surface treatment layer, a second surface treatment is applied which has a coefficient of thermal expansion closer to that of the first surface treatment layer than the base material, has high hardness (Hv2000 or more), and has poor wettability with the molten metal. Since the layers are formed, the second surface treatment layer and the first surface treatment layer do not easily peel off even if high-temperature molten metal hits them directly at high speed.

〔Effect of the invention〕

As described above, the method for surface treatment of a casting mold according to the present invention provides the following effects.

(a) Since the second surface treatment layer is provided on the first surface treatment layer, it will not easily peel off even after long-term use. Therefore, galling and the like do not occur, and the life of mold replacement or casting pin replacement is significantly extended, and productivity is improved.

(b) Since the durability of the mold has been improved, the injection speed of molten metal can be increased, and therefore the quality of the product can be improved.

(c) Since the life of the mold is extended, costs can be reduced.

〔Example〕

Next, embodiments of the present invention will be described with reference to the drawings.

First, it is made of JIS 5KD61 and is φ25 x 30 *
Prepare multiple cast-out pins marked *. This cast-out pin is KC
The sample was immersed in a salt bath containing N, KCNO as the main component and having a constant composition by adding K 2 Co to perform soft nitriding treatment (tuftride method). At this time, the treatment temperature was 570°C. As a result, a carburized-nitrided layer was formed as a first surface treatment layer on the surface of the cast pin.

Next, the cast pin provided with the first surface treatment layer was placed in a sputtering bath, and a titanium nitride layer was formed as a second surface treatment layer by sputtering. As a result, a second surface treatment layer was formed on the first surface treatment layer.

The above operation was performed by changing the immersion time in the salt bath during the tuftride method treatment in 11 ways, and the thickness of the first surface treatment layer was 11.
I got different cast pins on the street.

At this time, there were 6 types of first surface treatment layers with a thickness smaller than 10 μm and 10I! Five types of products with a diameter of m or more were obtained. When forming a second surface treatment layer on this cast-out pin, the treatment time etc. are changed and the thickness of the second surface treatment layer is 5.
3 types of smaller than μm, 5 types of 5 to 20 μm
Two types of samples larger than 20 μm were formed.

The resulting 11 types of cast-out pins were mounted in die-casting molds, and a durability test was conducted to investigate the occurrence of galling. The results are shown in FIG. Here, the ○ mark indicates that no galling occurred even after using 5000 shots, and the ∆ mark indicates 1500~1500 shots.
For those with galling after 2000 shots, × mark is 100
Indicates that galling occurred at 0 shot or less.

As is clear from FIG. 1, the thickness of the first surface treatment layer is 0 μm or more, and the thickness of the second surface treatment layer is 5 to 2 μm.
It can be seen that the durability of cast-out pins in the range of 0 μm is more than five times that of the conventional one. Therefore, the casting pin subjected to the surface treatment method of the casting mold according to the present embodiment does not need to be replaced until normal mold maintenance or even during mold maintenance as the case may be; Productivity is significantly improved compared to

Similar tests were also conducted on i8) a combination of the tuftride method and sputtering of titanium nitride, a combination of carburization and sputtering of titanium carbide, and a combination of the C1 sulfur method and mixed sputtering of titanium carbide and titanium nitride. , results similar to those of this example were obtained. As a result, the thickness of the first surface treatment layer and the second surface treatment layer was 10 μm or more, even if the treatment methods were different. It was confirmed that the second surface treatment layer preferably has a thickness of 5 to 20 μm.

Although specific embodiments of the present invention have been described above, the present invention is not limited to these embodiments, and includes various embodiments within the scope of the claims. .

[Brief explanation of drawings]

FIG. 1 is a graph showing test results according to examples of the present invention, and FIG. 2 is a graph showing results of molten metal resistance tests for various surface treatments.

Claims (1)

[Claims] (1) A surface treatment method for forming a layer with excellent heat resistance and abrasion resistance on the surface of a casting mold, wherein at least a part of the base material of the casting mold is subjected to a diffusion infiltration treatment to have an Hv of 700 or more. The first surface treatment layer is 10 μm thick.
A method for surface treatment of a casting mold, which comprises forming a second surface treatment layer made of new ceramics with a thickness of 5 to 20 μm on the first surface treatment layer by a physical adsorption method. .