Metal founding – Process – Shaping liquid metal against a forming surface
Patent
1997-02-04
1998-07-28
Lin, Kuang Y.
Metal founding
Process
Shaping liquid metal against a forming surface
164112, 164 97, B22D 1914, B22D 2700
Patent
active
057851093
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to a method for casting wear resistant parts, and particularly to a preferred method for casting wear resistant parts requiring a high degree of hardness.
BACKGROUND ART
Conventionally, as a method for casting parts which aims at increasing the longevity of the parts by increasing the hardness of the portions required to have wear resistance, there is the following art.
After casting a part in a specified form by using low-carbon steel, cementation is applied to increase the amount of carbon on the surface of the part, and the hardness on the surface is increased by quenching, etc. If necessary, tempering is conducted to make a wear resistant part having both wear resistance and toughness. It is known that a wear resistant part can be made by casting by using medium carbon steel and then, after casting, by conducting high-frequency induction hardening, which can be performed in a short time.
With the cementing method, the surface can be highly hardened with a hardness Hv as high as 850; however, when a greater hardened depth is required, for example, when a depth of some 2 mm or more is needed, the treatment takes an extremely long time, so that there is a disadvantage of the parts being expensive. In addition, in a high-frequency induction hardening method, it is necessary to produce a quenching coil for each cast part in every kind of form, and it is difficult to obtain a constant hardness and hardened depth except in the case of cast parts of a simple form.
As another conventional art, an insert-casting method includes the steps of setting superhard chips on a surface in a casting mold and of pouring molten steel, the above-described chips are bonded and an extremely hard wear resistant part is obtained (refer to, for example, Japanese Patent Application Laid-open No. 2-187250). Wear resistance is obtained by setting a fine thread of high-alloy steel in the form of a net at a fixed seat provided in the casting mold, coating this fine thread with superhard alloy particles if necessary, and by pouring molten steel (refer to, for example, Japanese Patent Application Publication No. 3-28974).
However, with this superhard chip insert-casting method, when an insert-casting portion with relatively low hardness is worn so that the superhard chips are in a state of being exposed, etc., the superhard chips with low toughness are damaged and broken by impactive load, etc.; therefore there is a disadvantage of a short life of a part, even though superhard chips with extremely high hardness are provided. In the method using a fine thread of high-alloy steel, breakage and damage are rarely caused, but the method of holding superhard alloy particles in a specified portion is difficult, and there is a disadvantage of a large number of man-hours required.
Further, in Japanese Patent Application No. Laid-open-714288 the applicant for the present invention proposed that wear resistant parts with high hardness can be obtained by coating the surface of a casting mold with graphite powder, etc., then pouring molten steel into the coated mold to form a high carbonate hardened layer on the surface of the part, and by applying heat treatment if necessary.
However, such a coating method, whereby the hardened depth is about 3 mm, has a disadvantage of being unable to form a thicker hardened layer.
BRIEF SUMMARY OF THE INVENTION
The present invention is made in order to eliminate the above-described disadvantages of the conventional art, and its object is to provide a method for casting wear resistant parts which is capable of forming a hardened portion at a desired position with ease, and which is preferred for producing cast parts having both wear resistance and toughness.
The method for casting wear resistant parts relating to the present invention is a method for casting wear resistant parts including a superhard portion, and is characterized by including the steps of filling the cavity of a holding member, which can be melted by molten steel, with a hardened portion forming
REFERENCES:
patent: 887648 (1908-05-01), Kemery
patent: 1374509 (1921-04-01), Lomax
Komatsu Ltd.
Lin Kuang Y.
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