Adhering sand phenomenon and adhering sand casting cause analysis
Views: 50 Author: Site Editor Publish Time: 2016-10-18 Origin: Site
In the use of foundry casting or coated sand casting casting process, if the casting operation not skilled, there may appear the phenomenon of adhering sand castings, once appear this kind of circumstance, light person affect the appearance of the casting quality, the most serious casting scrap directly.Foundry, therefore, in the process of production must cause enough attention to adhering sand castings.Casting order network in this paper is to introduce the phenomenon and reason of adhering sand castings.
One, the adhering sand phenomenon
1. The liquid metal machinery adhering sand is the permeability of sand mold and core sand clearance, and the sand sintering and adhesion on the casting surface.It can be a thin layer, also may be a few millimeters thick.Metal sometimes infiltrate the cores of the whole cross section, the inner cavity block, the adhering sand is often impossible to clear, castings have to scrap.
2. The chemistry department of adhering sand liquefaction of metal oxides and metal molding materials formed by the adhesion strong iron silicate scum.It more in the casting gate or thick wall place, especially when the sand mold and sand core is thin and thick castings produced more easily.
3. Chemical mechanical adhering sand adhering sand with simple and easy to identify, adhering sand layer is often do not contain iron.
Second, the adhering sand
1. Enough pressure to make metal liquid permeability sand between higher metal static head pressure.Is formed by casting pouring height and gating system pressure.Such as the pressure more than sand clearance between the resistance of the capillarity formation pressure.The resin MAO = QcosO/r, P in the type of hair for capillary pressure;.For the metal liquid surface tension;E for metal capillary wetting Angle;R for capillary radius.Can form a mechanical adhering sand.Static pressure head of more than 500 mm, foundry sand and coarser, most can produce mechanical adhering sand, unless on coatings.Type also shows that: the greater the, that is, the granularity of sand coarse, body hair is smaller, the more easily produce mechanical adhering sand.
2. The liquid metal flow in the mold dynamic pressure.
3. The mold "explosion" or "choke".The casting pouring combustible gases released when mixed with air and ignited by hot metal liquid formed by the dynamic pressure.
4. Mechanical adhering sand once started, even if the pressure decreases, and metal penetration will continue until the infiltration liquid metal solidification of the frontier.The temperature is lower than the solidus temperature of molten metal, permeability can stop.
5. Chemistry is the most common causes of adhering sand wet and core making use of raw materials, sintering point low refractoriness;Quartz sand is not pure;Pulverized coal or substitute person;Don't use paint or improper use;Pouring temperature is too high;Improper casting to factors such as pulp are in casting.
Above is about the phenomenon of adhering sand casting and adhering sand cause analysis, hope can help to you.
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