Method for eliminating shrinkage and air holes of pump valve casting

In the production of pump valve castings, defects such as shrinkage and pores are often encountered. The amount of repair welding and grinding is quite large, and the surface is not very beautiful. At the same time, some holes are found in the boreholes, and there are leaks in the test Phenomenon and scrapped. Here are some solutions.

1. Strictly control the pouring temperature and pouring speed according to the process requirements. After the riser is filled, the riser will be refilled.

2. In addition to heightening and increasing the slope, the riser also adopts a heat insulation riser, which not only saves the molten steel and improves the effect of the riser, but also prevents the rapid cooling of water glass sand, which affects the shrinkage effect and prevents the Shrinkage occurs at the junction of the riser root and the valve casting.

3. Improve the design of the valve casting process. The original process pouring system uses a refractory tee. The molten steel meets and merges at the bottom, causing sand blasting, and the exhaust gas is not smooth, resulting in air holes. Due to the fast cooling speed of water glass sand, Therefore, slag, sand, and gas cannot float into the riser, causing many surface defects.

4. Because the height of the box is not high, the height of the riser does not meet the requirements. It is relied on the riser to pour water, hinder the exhaust, and cause the phenomenon of slag, sand, and gas backflow. Mouth box, increase the height and capacity of the riser, reduce the amount of molten steel pouring also correspondingly reduce the defects caused by the phenomenon of sand, slag and gas reflux.

1. Switch to local water glass and curing agent, which not only can obtain materials in situ, reduce costs, but also improve the performance of molding sand, improve the quality of molds, and reduce the root causes of various defects.

5. Changes to the pouring system. ① The pouring method that connects the three-way refractory pipes at the two ends of the flange is changed to use four inner runners from one end of the small flange to enter the molten steel to exhaust the cavity, slag, and floating sand to the riser. Unblocked. ② Increase the cross-section area of ​​the sprue, and change the original qb50mm refractory pipe to qb70mm refractory pipe to increase the flow rate and increase the pouring speed. ③ Cancel the two big dark risers that were connected to the refractory tube at the two ends, and use two bright risers on the small flange to facilitate exhaust and shrinkage. It also improves the uneven distribution of the heat nodes and is not suitable for sequential cooling Claim. ④ In places where iron-clad sand is often caused, water glass chrome ore is drained to eliminate the defects of iron-clad sand.

6. Change the type of riser covering agent. Although the original covering agent can add heat and heat to the riser, it will quickly crust, which not only affects the shrinkage effect, but also seriously affects exhaust and slag discharge. It is now used Homemade coverings are both cheap and effective.