Characteristics and remedy of slag inclusion in flux of sand casting

Defect characteristics and detection methods

The dregs are dark brown and irregular in shape near the inner gate and the dead corner of the casting or in the body of the casting. It is found after appearance inspection or X-ray fluoroscopy and machining. The X-ray film is white dots or snowflakes. After machining, it turns brown gray after being placed in the air for 1H. After clearing it, it shows smooth holes on the inner surface.

Causes of formation
  1. The flux or modifier used does not meet the requirements of the alloy
  2. Misuse of other alloy fluxes
  3. The alloy liquid is not allowed to stand before pouring or the standing time is not enough, and the flux is not floating and is suspended in the alloy liquid
  4. Incomplete slagging after modification
  5. The crucible, ladle, tools and washing are not complete
  6. Poor slag retaining function of pouring system
  7. The slag retaining plate at the bottom of the teapot type or the lift type crucible is not welded firmly and has leakage, which results in poor slag retaining effect

Ladle out the first package of alloy liquid in the crucible, and then spray the crucible with flux

Prevention methods and remedial measures
  1. Select appropriate flux according to alloy brand, and mix evenly before configuration. After preparation, it shall be placed in the dryer or constant temperature box. It must be preheated at 150-200 ℃ for 1-2h before use. The flux for washing ladle, crucible and tool should be renewed frequently
  2. Properly design and make the pouring system, which is conducive to slag discharge and collection. Filter screen (device) can be installed on the pouring system
  3. The flux for washing ladle, crucible and furnace shall be heated to over 750 ℃, and the ladle, crucible and tools shall be washed to bright yellow. After washing, the detergent on ladle, crucible and tools shall be completely removed, and then the alloy liquid can be scooped out
  4. When ladling alloy liquid in the crucible (furnace) with ladle, the flux and dirt adhered on the internal and external surfaces shall be cleaned to prevent slag (impurities) such as flux from being brought in
  5. After modification, a layer of sodium fluoride can be sprinkled on the surface of alloy liquid as thickener to make the slag crusted and easy to remove
  6. Remove the slag before pouring
  7. After refining, the alloy liquid should be placed on the bright mirror surface
  8. Scrape off the slag on the crucible and slag baffle plate after refining the alloy liquid
  9. When ladling alloy liquid continuously in the same crucible, do not sprinkle flux on the liquid surface of the crucible, but sprinkle sulfur or mixed protective agent of 50% sulfur and boric acid with an interval of 5 ㏕ or more. Do not sprinkle flux in the ladle
  10. During continuous pouring, keep the inclined position of the crucible unchanged, and do not return the crucible to its original vertical position. The same is true for pouring two molds in the same ladle
  11. The raw materials shall be sandblasted and shall not contain more flux and slag
  12. Before use, test whether there is leakage at the welding position of slag guard plate of ladle or portable crucible with water. If there is, weld it well
  13. Sufficient weight of alloy liquid shall be considered during batching, so as to maintain a certain head height after pouring
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