As the core component of slurry pumps, impellers require high quality, and whether the initial unbalance exceeds the standard is a key indicator to determine the quality of impellers. Generally speaking, each type of impeller has corresponding imbalance requirements based on its size and quality. Once the initial unbalance exceeds the standard, it is necessary to carry out grinding, which is not only time-consuming and laborious, but also due to the high hardness, high wear resistance, and poor toughness of high chromium cast iron A05, the impeller may crack or even be scrapped during the grinding process.

Reason: Uneven coating application
The mass of a small impeller in a slurry pump is only a few thousand grams, and the smaller the impeller mass, the higher the requirement for unbalance. At this time, if the coating is not evenly applied, even if the coating thickness differs by 1mm, it may affect the size of various parts of the impeller and bring relatively large unbalance.
Solution: Improve the painting method
The combination of spraying and manual brushing can effectively reduce the weight of castings. To save costs, homemade coating mixing equipment using compressed air as power can not only improve production efficiency but also effectively ensure coating thickness. Adopting the wet polishing method, fine silk materials are used for wet polishing, and silk cloth is dipped in diluted coating for brushing. The original brushing surface is corrected, and the diluted coating is filtered to remove impurities and ensure the smoothness of the brushing surface. Uneven areas (pits, protrusions) are repaired and leveled to ensure uniform brushing thickness without leaving any marks.
Reason: Casting defect
Production practice has proven that most impeller castings with large initial unbalance have casting defects, such as shrinkage and porosity under the riser neck. Therefore, reducing the occurrence of casting defects is important for reducing the initial unbalance of the impeller.
Solution: Improve process tooling
(1) The pouring system is changed to iron liquid entering the riser from the upper annular sprue, and then entering the mold cavity through the riser, making the cold riser become a hot riser, ensuring that the temperature of the riser is higher than that of the casting, making the riser have a supplementary shrinkage effect, and improving the supplementary shrinkage efficiency.
(2) Replace the lower part of the riser with a sand core to ensure that the resin of the surrounding sand is not excessive, improve the compactness of the sand, and apply diluted coating to the lower part of the riser.
(3) Before pouring, the resin sand mold should be baked with a hot air blower at a temperature of 200 ℃ for 1 hour to prevent moisture absorption and reduce the gas generation of the resin sand.
(4) The temperature of the molten iron should be controlled at around 1450 ℃. Before pouring, it should be left to stand in the bag for 2-3 minutes. The pouring temperature should be controlled at the lower limit of the process as much as possible to reduce the gas generation of the resin sand.
Reason: Inaccurate positioning
The sand mold positioning pin used during box closing has relatively poor positioning accuracy. Once the sand mold positioning pin is damaged during the box closing process, it is likely to affect the positioning accuracy, causing deviations in the casting size and increasing the initial imbalance.
Solution: Improve positioning accuracy
Replace traditional sand mold positioning pins with metal positioning pins to increase positioning accuracy and further ensure the size of the box. Apply the metal positioning pin system to the impeller casting of the slurry pump, improve and perfect it according to the size of the casting and sand box, and arrange for a dedicated person in the sand mixing process to be responsible for the recovery of the metal positioning pin. Sort and place it according to specifications for use in the next production.