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Analysis and countermeasures of melt mold casting defects related to the mold shell-3
Characteristics: protruding from the surface of the casting burrs, flying edge, the shape of a straight line or folding line, mostly located in the casting edge, corners and other parts of the casting prone to stress concentration or convex arc surface. The direct cause is that the shell has been cracked, and the metal liquid drilled into the cracks after pouring. Shell cracking is mainly due to the wax mold expansion or melting wax liquid in the dewaxing process can not be timely excluded, the extrusion pressure on the shell caused by.
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Causes |
countermeasures |
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When using high-pressure steam dewaxing, the pressure is insufficient, the boosting speed is slow, or the dewaxing kettle is loaded with too many modules at one time. |
Increase dewaxing steam pressure Maximize steam pressure in the shortest possible time (e.g., within 6-7 seconds). Install a high-pressure steam storage tank between the dewaxing kettle and the boiler, and replace the kettle if necessary. Reduce the number of modules per load |
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When hot water dewaxing is used, the water temperature is low, the heater power is insufficient, or too many modules are loaded in the dewaxing tank at one time. |
Ensure the water temperature is always not less than 90℃ during dewaxing. Increase the power of the heater and replace the dewaxing tank if necessary. Reduce the number of modules per load |
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Poor wax drainage during steam dewaxing |
Improvement of tree formation to facilitate wax removal Addition of auxiliary wax discharge ports If necessary, use a sprue wax with a lower viscosity and a lower melting point than the mold wax for the casting system. If necessary, apply a layer of low melting point, low viscosity sealing wax to the surface of the sprue mold. |
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Shells are too dense |
Reduce the density of the shell and increase the permeability to facilitate the penetration of the molten wax on the surface of the module into the shell and to relieve the pressure on the shell caused by the thermal expansion of the wax mold. |
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Large temperature variations from the beginning of shell making to dewaxing lead to repeated contraction-expansion of the wax mold, which ultimately leads to cracking of the shell. |
Strictly control the ambient temperature from the start of shelling until dewaxing, and keep it as uniform as possible at all times. |
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Insufficient wet strength of the shell |
Adopt suitable binder and refractory material. Strict quality control and management of paint slurry, and the aged and deteriorated paint slurry should be firmly discarded. Drying and hardening according to the process requirements If necessary, use polymer reinforced silica sol or reinforcement treatment. Adequate drying time should be provided from the completion of slurry sealing to wax removal. |