KR100437878B1 - High Strength Thin Sand Molding Process - Google Patents

Abstract

The present invention relates to a method for forming a mold suitable for the antigravity vacuum casting method, and after the sand is blown and press-molded using a back pattern having a rubber diaphragm mounted on a cold box molding machine, the mold is cured. It is a blow / squeeze method which is taken out. As a result, it has higher mold strength and melt erosion resistance than the conventional molding method, which reduces casting defects and has excellent degassing properties to obtain a casting product with a good surface state, and material costs such as sand are reduced by 80% compared to conventional molding methods. It is effective. In addition, since the mold cured at room temperature can be manufactured, a high strength sand mold having a thickness of 15-20 mm is produced, which is less favorable to thermal deformation, more economically and environmentally, and has excellent dimensional accuracy than the thermosetting molding method. It is possible to produce high value-added cast stainless steel products with a thickness of 2-3 mm by gravity vacuum casting. The mold manufactured according to the present invention is more than three times more durable than conventional cast iron and tubular exhaust manifolds, and has an emission reduction effect due to a weight reduction of 30 to 50% compared to cast iron, and an exhaust gas temperature of 1000 ° C. or more. It is suitable for manufacturing applicable 2-3mm cast stainless steel exhaust manifolds.

Description

High Strength Thin Sand Molding Process

The present invention relates to a high-strength sand mold molding method having a thickness of 15-20 mm, and more particularly, by using a rubber diaphragm to squeeze the blown molding sand to greatly reduce the amount of material used and to increase mold strength. The present invention relates to a mold forming method suitable for manufacturing high temperature heat-resistant cast products such as cast stainless steel exhaust manifolds of 2-3 mm thickness by increasing the degree of freedom of product design.

In the 1990s, with the strengthening of automobile exhaust regulations in accordance with domestic and international environmental regulations, the catalytic device was placed closer to the engine for quick activation. As a result, the exhaust gas temperature rises and the automotive industry increases the silicon content of the nodular cast iron exhaust manifold from 2.5% to 4.0% to 6.0% and adds 2.0% molybdenum (Mo). An exhaust manifold made of high Si-Mo spherical graphite cast iron with high temperature strength has been developed and applied to an engine having an exhaust gas temperature of about 870 ° C. However, at the exhaust gas temperature of 900 ℃ or higher, it is difficult to apply to the high power engine to be developed in the future due to the durability problem.

In addition, a Ni-resist spherical graphite cast iron exhaust manifold containing nickel (Ni) was developed in early 1980 to improve high temperature characteristics, but it is uneconomical because of high nickel content and low castability.

Tubular exhaust manifolds, meanwhile, were developed in early 1980 to compensate for the high temperature heat resistance of spherical graphite cast iron exhaust manifolds, which were produced primarily by molding and welding 1.5-2 mm stainless steel pipes. As a result, the reduced heat capacity has been shown to reduce the exhaust gas, but it is difficult to plasticize the pipe, which limits the product design. In addition, the welding site may be destroyed by an extreme thermal fatigue cycle of repeating the temperature section of the high temperature, the manufacturing cost also has a disadvantage that compared to the existing product.

The object of the present invention devised in view of the above problems is to be suitable for the production of cast stainless steel exhaust manifold of 2-3 mm thickness, and to provide a method of forming a mold that reduces the amount of material, such as sand and improves the freedom of product design. Is in.

1A to 1F are cross-sectional views sequentially illustrating a molding process according to the present invention.

Figures 2a to 2g is a 2-3mm cast stainless steel exhaust manifold manufacturing process by the mold produced by the present invention.

3 is a process flow diagram of a process according to the present invention.

(Explanation of symbols for the main parts of the drawing)

10; Pattern 20; Back pattern

30; Rubber Diaphragm 40; Loader base

50; Chamber 60; Sand hopper

70; Vacuum Head 80; Induction Furnace

90; Molten metal 100; Shake-out Table

S; Sand, S '; Back-up Sand,

M; Mold

The high-strength sand mold molding method according to the present invention for achieving the above object, in the method of manufacturing a stainless steel manifold of the internal combustion engine by casting, the rubber diaphragm attached to the pattern and the back pattern to the back pattern side Contacting to form a sand blowing space;

Blowing sand in which a known binder and a hardener are mixed into the space between the pattern and the back pattern;

Pressurizing a rubber film toward the pattern side to make the sand blown thin and high in strength;

Injecting a curing accelerator gas into the pressurized mixed sand to cure a mold;

Separating a rubber film from the cured mold;

And ejecting a mold from the pattern using an ejector pin.

Hereinafter, the above-described embodiment of the present invention will be described using an example of the manufacturing process of the exhaust manifold.

1A to 1F are schematic cross-sectional views sequentially illustrating a molding process of the mold, and FIGS. 2A to 2G are a manufacturing process diagram of a 2-3 mm cast stainless steel exhaust manifold by a mold manufactured according to the present invention. 3 is a flow chart of a process according to the present invention.

As shown in the drawing, the molding process according to the present invention is performed by introducing a blow / squeeze function using a back pattern having a rubber film attached to a cold box. A 20mm thick High Strength Thin Sand Mold is produced.

First, as shown in FIG. 1A, the rubber film 30 attached to the back pattern 20 is sucked while bringing together the pattern 10 and the back pattern 20 to closely adhere to the back pattern 20. At this time, sufficient space is formed between the pattern 10 and the back pattern 20 on which the rubber film 30 is mounted to allow the sand S to be blown. Reference numeral 15 is a strip pin which is an eject pin.

Then, as shown in FIG. 1B, the sand S mixed with a known caking agent and a curing agent is blown into a space formed between the pattern 10 and the back pattern 20. At this time, the amount of sand to be blown should be enough to form a sufficient thickness of the mold after the pressing step, the next step. Moreover, it is preferable that the ratio of the said well-known binder and hardening | curing agent is 55:45.

After blowing the sand, as shown in FIG. 1C, the rubber film 30 is pressed toward the pattern 10 (Squeezing). At this time, about 50% of the volume is reduced while the blown sand is pressurized.

After the pressurization process, as shown in FIG. 1D, the curing accelerator amine gas is blown into the pressurized sand. At this time, the blowing accelerator gas is blown and the air is blown so that the blow accelerator gas is uniformly penetrated between the sand particles. When the curing accelerator gas is blown in this manner, a thin sand shell mold is formed in about 40 seconds or so.

After the mold is sufficiently cured, the vacuum pressure is again applied to the back pattern 20 to separate the rubber film 30 from the molded mold M [Fig. 1E], and the mold M is taken out by the extractor [ 1F].

After the upper and lower molds are manufactured by the molding process as described above, the assembled molds are transferred to the casting process.

The casting process applied to the present invention is a new casting method which improves the problems of the existing gravity casting, and then vacuums the assembled mold using the vacuum and mold loading device 70 to move into the interior of the furnace 50. The antigravity vacuum casting is used to quickly suck and fill the molten metal 90 into the mold M by pressure. Reference numeral 40 denotes a loader base and 60 a sand hopper.

As described above, the molding method of the mold according to the present invention can easily produce a high-strength mold having a thin and complicated shape by using a blow / squeeze method of curing and taking out the mold after press molding the sand blown using a rubber film. have. As a result, the degree of freedom of product design can be increased, and manufacturing costs can be reduced, and material costs can be reduced by 80% compared to conventional molding methods. In addition, since the mold cured at room temperature can be produced, it is environmentally friendly compared to the thermosetting molding method, there is no deformation by heat, and the molten corrosion resistance is high.

In addition, the anti-gravity vacuum casting method enables the production of thin castings of various materials and shapes, and since the injection is directly in the molten metal, the injection temperature can be lowered, so the material properties are excellent, and the inclusions such as slag and oxide penetrate the castings. This is significantly lower. In addition, the advanced automation process that deviates from the simple casting operation of the operator also has the effect of improving productivity and cost reduction.

As described above, by using the mold molding method and the antigravity vacuum casting method according to the present invention, the durability improvement is more than three times that of the conventional High Si-Mo spheroidal graphite cast iron and tubular exhaust manifold, and the exhaust of spherical graphite cast iron such as High Si-Mo The heat capacity is reduced by 30% -50% weight reduction compared to the manifold, so that the exhaust gas reduction effect can be obtained by shortening the catalytic reaction time, and the 2-3mm stainless steel can be applied to the engine of exhaust gas temperature of 1000 ℃ or higher. Exhaust manifolds can be manufactured.

Claims (3)

In the method of manufacturing a stainless steel manifold of an internal combustion engine by casting, a diaphragm 30 mounted between the pattern 10 and the back pattern 20 is brought into close contact with the back pattern 20 to intake sand. Forming a; Blowing sand (S) mixed with a known caking agent and a curing agent into a space between the pattern (10) and the back pattern (20); Pressing the diaphragm 30 toward the pattern 10 to thin the blown sand S; Blowing a curing accelerator gas into the pressurized sand to cure a mold; Separating the diaphragm 30 from the manufactured mold M; And ejecting the mold from the pattern (10) using an ejector pin (15). delete delete