RU1771875C - Mould for preparation of bimetallic steel-cast iron castings - Google Patents

Abstract

Usage: in foundry in the manufacture of castings with a viscous steel core and a surface layer of cast iron, which has increased hardness and wear resistance. The inventive carbon-containing material is compactly placed at a distance from the working surface of the mold equal to (0.06 ... 0.5) from the width of the working cavity forming the carbonized wall of the casting. 1 silt.

Description

The invention relates to foundry and can find practical application in the manufacture of castings with a viscous steel core and a surface layer of cast iron with increased hardness and wear resistance.

A casting mold of graphite or with a coating containing graphite is known, which is heated before pouring to 700 .., 1800 ° C and incubated with cast steel for 5 ... 60 min.

Known foundry mold has the following disadvantages. The manufacturing process of molds from graphite is very energy intensive and very time consuming. Graphite coatings having a small thickness do not saturate the surface layers of the carbon casting sufficiently to form a layer of cast iron of the required thickness. Increasing the thickness of the coating reduces the dimensional accuracy of the cast. In addition, when heated and held at a temperature of 700 .., 1300 ° C in an oxidizing atmosphere, graphite is intense LO

but is oxidized, resulting in lower levels. The reactivity of the coating and the dimensional accuracy of the castings, to their defeat by gas shells. Therefore, heating and aging of the molds should be carried out in a protective atmosphere or in vacuum, which requires the use of sophisticated equipment and scarce molding materials, as well as high energy costs

The purpose of the invention is to improve the quality of castings, reduce energy and labor costs.

The invention is illustrated in the drawing.

In the manufacture of the lower half-mold, a cavity is provided for backfilling the carbon-containing material and for setting up the jumper rod. The mold and the core are made of sand-clay, liquid-glass or other gas-permeable mixture. Carbon-containing material can be coal dust of any brand with a volatile release.

Xj

"-AND

with

vj SL

substances not less than 20% or coal tar pitch.

The thickness of the layer of carbon-containing material should be within (0.2 ... 0.5) of the thickness of the carbonized wall of the casting.

When the steel is poured into the mold, it warms up, and at a certain moment the carbon-containing material is thermally decomposed, the gas mixture being released, which consists mainly of methane, heavy hydrocarbons, a small amount of nitrogen, hydrogen, carbon monoxide and carbon dioxide.

The gas mixture migrates through the pores in the molding sand to the surface of the casting. In the gap formed due to shrinkage of the casting, hydrocarbon gases wash the surface and undergo pyrolysis at temperatures above 900 ° C according to the reaction

Snng

 P . C +

m

H2

Pyrolytic carbon deposited on the surface of the casting diffuses into the steel and carbonizes it to cast iron. In this case, a smooth decrease in the carbon concentration from the surface to the center reduces the likelihood of delamination and increases the service properties of the casting.

The main condition for high-quality carbonization is the beginning of thermal degradation of coal immediately after crystallization of the surface layers of the casting is completed, which is ensured by the thickness of the jumper rod, i.e. the distance from the placed carbon-containing material to the working surface of a horizontal casting mold equal to (0.06 ... 0.5) of the width of the working cavity, which forms the carbonized wall of the casting.

If the thickness of the jumper rod is less than 0.06 of the width of the working cavity that forms the carbonized wall of the casting, heating of the filling to the temperature of the onset of thermal degradation will occur before the formation of a crust of crystallized metal on the surface of the casting, which leads to the formation of gas shells.

At a depth of carbon-containing material at a distance of more than 0.5 of the width of the working cavity forming the carbonized wall of the casting, heating will occur too late, resulting in insufficient carburization.

The foundry form consists of the upper 1 and lower 2 half-forms. A carbon-containing material is loaded into the cavity of the lower half-mold

material 3, which is covered by a web or web 4.

The application of the invention is as follows.

A casting mold is used to produce a 50 kg bowl casting with a wall thickness of 40 mm from 40L steel, with a casting temperature of 1540 ° C, the inner surface of which must have increased wear resistance.

Half-molds are made of liquid-glass plastic self-hardening mixture, shaking the seal. During assembly, the cavity of the half-mold is covered with coal dust of grade Ж (GOST 25543-83) in an amount of 0.5 kg. The cavity is closed from above by a jumper rod made of a liquid glass quick-hardening mixture according to the CO2 process.

EXAMPLE 1 A 2.4 mm thick jumper rod was used. The resulting casting has a layer of cast iron with a thickness of 3.0 ... 3.5 mm with an average carbon content in it on the carbonized surface

2.5 ... 3.2%.

No gas flakes were found in the surface layer of the casting. .

Example 2. Used a jumper rod with a thickness of 20 mm The resulting casting has a cast iron layer 1.1 .., 1.5 thick on the carbonized surface with an average carbon content of 2.4 ... 2.9% in it.

Using the proposed foundry

molds for the manufacture of bimetallic steel-cast iron castings provides the following advantages compared to existing methods:

the start of gasification of the carbon-containing material after crystallization of the surface layers of the casting, which is ensured by a certain depth, prevents the formation of gas shells and improves the quality of the casting;

the use of the heat of the molded steel for gasification. The carbon-containing material eliminates the heating and aging of the mold after pouring

at high temperatures;

The presence of a protective reducing atmosphere in the mold during the cooling period of the casting eliminates the oxidation and decarburization of the casting surface and prevents the formation of surface cracks.

Claims (1)

SUMMARY OF THE INVENTION A foundry mold for the manufacture of bimetallic steel-cast iron castings containing and placed in half-molds carbon-containing material, characterized in that, in order to improve the quality of castings, reduce energy and labor costs, the carbon-containing material is compactly placed on a race from the horizontal horizontal working surface equal to 0.06-0.5 wide cavity, designed material, for example coal dust, 5 carbonized casting wall. placed in a compact form at a distance from the working surface of the horizontal casting mold, equal to 0.06-0.5 of the width of the working cavity, forming