What elements are contained in malleable steel pipe fittings?

On the inner surface of the thin wall, a flake graphite layer with a thickness of about 0.2-0.6 mm is sometimes formed when the rare earth content is the lowest. It has no essential effect on the strength of the casting. "When the Shougang foundry produced 4.5 tons of malleable iron ingot molds, it was found that there was an ink layer with a thickness of <1.5 mm on its outer surface. The existence of the ink layer was not good for castings subjected to fatigue loads. The ink layer The production is mainly the result of the interaction between molten iron and the surface of the mold and core. Since the Su and mold materials themselves contain a certain amount of sulfur, during their drying process, part of the sulfide produced by fuel combustion will also be adsorbed on the surface of the mold and core. , these sulfur will consume magnesium, cerium, calcium and other elements on the surface of molten iron to greatly reduce the content, or it is related to "the oxidation of the casting surface, which greatly reduces the rare earth content (1/3-1/2 times)", it is considered that in addition to sulfur , Nitrogen other than oxygen will also produce a sheet ink layer. The generation of a sheet ink layer is the result of the combined action of the three elements of sulfur, oxygen, and nitrogen.

In order to prevent the occurrence of ink flakes in malleable steel casting, the sulfur content in molding, core materials, coatings and fuels should be as low as possible. At the same time, adding more titanium and cerium to molten iron can effectively overcome this type of defect.

The direct cause of mold sticking caused by malleable steel casting is that the strength of molding sand is too low, that is, the adhesion force between sand grains is less than the adhesion force of sand grains on the pattern. The specific reasons are as follows:

1. Pouring Riser System
The design of the gating riser system generally has little effect on the occurrence of sticky succulent defects.

2. Molding sand
(1) The molding sand is overheated. Hot sand tends to become brittle and break easily under shear.
(2) The performance of the molding sand is unqualified. Usually the formulation of the molding sand is unqualified, such as too much water, uneven sand mixing or too many auxiliary materials.

3. Core making
Sand cores that have become sticky in the core box cannot be placed into the mold. If there is a chemical reaction between the sand core binder and the release agent, it will also lead to sticky mold. Wet sand core refers to the sand core that is molded from the pattern during molding, and is brought out of the sand mold after the mold is ejected. Generally in the upper type, it is called hanging sand; in the lower type, it is called tap sand core. Some thin-walled steel castings also use core boxes to make wet sand cores, and then put them into sand molds without drying. This is a veritable wet sand core. Narrow and high hanging sand or tap sand cores are prone to sticky molds and succulents. Especially for machine molding, molding machines, and fast production pace, it is difficult to find the bad situation that the wet sand core is stuck by the shape. On the contrary, it is more likely to produce sticky mold and fleshy defects than manual molding and molding. This defect occurs on wet-cast castings.