Gray and ductile iron castings defects and improvement measures
1. Poor demolding
Iron castings defect characteristics:
During the molding operation, there is sand sticking on the template, and there are cracks, sand falling, floating sand and other phenomena in the mold cavity.
Causes:
A. Rusting of the template
B. Uneven spraying of the parting agent
C. Poor exhaust, unreal sand shooting
D. Too small draft angle or too little sand intake
E. The finish of the model or flow path is not enough, and there is a reverse draft
F. The molding sand is too dry
G. The template is not preheated sufficiently
Improvement measures:
A. Repair the fillet, polish carefully, and improve the finish
B. Increase the number of vents to avoid poor draft caused by unreal sand shooting
C. Increase the draft angle
D. It is recommended to insert copper sleeves in holes with small diameters and large depths
2. Iron castings parts sand holes, sand squeezing
Defect characteristics:
Hole or obvious lack of meat on the surface or inside of the casting containing sand particles
Causes:
A. Low water content of the molding sand
B. Improper design, long punching time, long baking and “water migration” cause low local strength of the molding sand, forming sand holes
C. Improper flow path design, molten iron flushing during pouring causes sand holes
D. Poor flow path or mold draft, cracking, sand falling
E. There is “sand falling” in the cavity, such as the molding chamber is worn, the gate cup sinks, the press (solid) device presses on the gate or there is sand falling above the molding chamber
F. The sand core has burrs or floating sand, and it is not blown clean when the core is lowered
G. The template is deformed, causing sand squeezing and sand falling
Improvement measures:
A. Polish the model and grind the flow path to reduce the sand slag caused by poor demolding
B. Use a comprehensive pouring system when designing the scheme to improve the slag blocking effect of the pouring system
C. Recalculate the scheme and it is recommended to minimize the inlet of the riser to facilitate the floating of sand slag
D. Increase bottom injection or side inlet
E. If the mold accessories are worn, replace them in time
F. If the pouring time is too long or the mold cannot be punched at the same time, recalculate the scheme
G. If there is sand squeezing, when confirming that there is no problem with the panel, fillet the corners or make anti-pressure strips at the parting line at the sand squeezing position
H. Thin the inlet or the edge pressure to improve the slag blocking ability
I. Make a slag collection bag on the scheme
J. Change the position of the inlet to avoid the part that is easy to be blasted Position (do not make inlet on the sand core blowing port)
3. Iron castings parts cold shut (insufficient pouring)
Defect characteristics:
The appearance of the casting is incomplete, there are crack-like gaps or interruptions, and the metal edges at the cracks or interruptions are smooth
Causes:
A. The design of the scheme is unreasonable, the pouring time is too long or the mold cannot be punched at the same time
B. The liquid flow heads of multiple inlets have solidification blockage or flow head oxidation, causing the two flow heads to be unable to merge together
C. The pouring temperature is too low and the molten iron has poor fluidity
D. Intermittent pouring during pouring operations, no full cup pouring
Improvement measures:
A. Recalculate the scheme and speed up the pouring speed
B. Add exhaust ducts, speed up the punching speed, and reduce the punching resistance C. Reasonably set the water inlet position to avoid cold shut due to oxidation and cooling of molten iron at a distance from the gate
D. Increase water inlet at the cold shut position to increase the temperature there
4. Shrinkage
Defect characteristics:
Shrinkage：A large number of dispersed shapes are distributed on the cross section of the casting Irregular tiny holes or crack-like holes
Shrinkage holes: holes with large volume, rough wall surface and extremely irregular shape in castings
Causes of formation:
A. Low CE value of molten metal
B. Low riser temperature, early solidification, poor shrinkage compensation
C. Unreasonable riser position or size, volume shrinkage during molten iron solidification and no compensation, resulting in volume loss, which is concentrated in one place to form shrinkage holes, and locally dispersed to form shrinkage
D. Unreasonable riser neck shape or cross-sectional area, shrinkage compensation channel blocked, so that the riser fails to play a shrinkage compensation role
Improvement measures: A. Change the riser position or shape, change the solidification sequence so that the shrinkage parts that could not be compensated can be compensated, and eliminate shrinkage holes or shrinkage B. Place cold iron in an appropriate position C. Change the water entry position to obtain a reasonable temperature field and solidification sequence D. Increase the riser volume E. Increase (or reduce) the riser neck F. Increase the water entry of the riser and increase the riser temperature.
