SAND CASTING EQUIPMENT.

The gating system of steel castings does not need to fully consider the functions of slag collection and inoculation like iron castings. Therefore, the craftsmen are often not very particular about the design details of the gating system for steel castings, especially the selection of the water entry position is often more arbitrary. . As a result, a series of product quality problems have been caused, and even in the face of these quality problems, technicians often habitually find out the reasons from the aspects of molten steel quality, process feeding and operation, delaying the resolution of quality problems. xinyuanzhuGroup has gone through a lot of detours in the design of the gating system, and has accumulated a lot of experience in solving such problems.


Several examples of improving water entry position of pouring system
The solution of serious water marks on the surface of anchor lip products
The anchor lip product is a typical thin-walled product, the wall thickness is generally 20~30mm, the maximum outline size is 3500~4500mm, and the material is GS-45. 10 years ago, our process was very successful in controlling the size and product wall thickness, but the gate from The inner circular riser is cut under, and after the product is poured, it is found that the surface water pattern is particularly serious, and there are many grooves and sand holes.
Later, the gate was changed to enter the water from the lowest point of the product, and a small riser was placed opposite the water entry position. The surface quality of the casting was improved and an unexpected effect was achieved. The problem of water marks was fundamentally solved, and sand holes rarely appeared. Weld repair is required. According to the same process idea, we have produced various types of anchor lip products later, and the product quality has been very stable.


Solution to the problem of insufficient pouring of impeller products
The impeller is a product on a high-head hydro-generator. The blade is in the shape of a bucket. The wall thickness of the blade is very thin and uneven. The thinnest part is only 3~5mm. The quality control of the blade position is very important. The material is ZG20Mn.
The initial pouring process was to enter the water from the bottom of the inner hub. It was found that many blades of the casting had poor water flow, leaving holes and gaps of different sizes. Later, it was changed to enter the water from the inner hub and the outer flange at the same time, and the pouring temperature was increased. Because the blade position is too thin and has a curved surface transition in several directions, the quality problems of the blade position are basically difficult to be welded and repaired, and several consecutive products have been reported, and the loss is relatively large.
Improved pouring process: an annular pouring channel (equivalent to a cross gate) is set at the lower part of the mold, and a slot gate is set from the lower part of each blade to connect with the annular channel. The impeller products casted by this process have full blades and less cracks in the sand holes, and the overall quality of the product is greatly improved. Users have great confidence in the quality of our impeller products.


The solution to the subcutaneous crack of the lifting lug seat of the slag tank
Gross weight 21T, material ZG230/450. Since there are many ribs on the surface of the product, the pouring direction selected at that time is the big mouth upward. The pouring mainly adopts the return water from the side bottom. Considering the high product, a layer of gate is set at the end face of the slag tank. When the molten steel rises to close to this height, the upper gate is opened for relay pouring. Initially, the water inlet position of the upper gate is selected at the subsidy under the large riser. No abnormality was found after the casting was poured, and the lifting lug seat MT and UT were qualified. However, after the lifting lug seat was processed, the oblique probe UT was used to check, and many superficial linear defects were found, with lengths ranging from 5 to 50 mm. have this problem. Later, we got a little inspiration from the balance of temperature distribution. The water entry position of the upper gate avoids the heat concentration area under the large riser, and the subcutaneous crack at the lifting lug seat is easily solved. Shaozhu produced about 150 pieces of this product later, and the quality is all the same. very stable.


Application practice of stepped gate
Shao casting with stepped gates was widely used before the mid-1990s, and products with a certain height such as hollow shafts and oil cylinders were used. In the production practice, we found that the stepped gate has a bad influence on the internal quality of the product. There are often many problems exposed during UT inspection or deep processing of the product, and the phenomenon of sand inclusion and slag inclusion is more common. On-site observation of the pouring process found that the upper gate always entered the water early, causing the cold steel hanging on the molding wall and the dirt floating on the surface of the molten steel to be involved in the molten steel. When the molten steel rose to the position close to the upper gate, the upper gate was often The molten steel flowing through is discontinuous and sealed, which cannot balance the temperature. Therefore, we gradually reduce the use of stepped gates, because the product structure needs to be relay poured as much as possible when layered gates are used, and even if stepped gates are used, the upper and lower distances should be shortened.


There are many examples of improving the quality of cast steel products by improving the introduction position of the gating system, such as guide wheels, gears, hinge seats, brake turntables, fuselage, racks, etc., which will not be listed here. Thin-walled turntables The optimization of the pouring process for rack products is also described in detail in the author''s previous article.


summary
The selection of the introduction position of the gating system has a great influence on the internal and external quality of steel castings. Xinyuanzhu Group has many cases of improving the quality of steel castings by changing the introduction position in production practice, and has accumulated a set of experience in the selection of the introduction position. To sum up There are the following points:
Fill as soon as possible
Try to enter the water from the lowest part of the mold, so that the molten steel can rise smoothly, and the floating sand and slag inclusions can fully float;
Water is poured from the thin part of the casting to avoid insufficient pouring in the thin position and reduce the stress caused by the difference in wall thickness of the casting;
Less or no stepped gate
The measures such as variable diameter inner gate, slot gate, and tangential water entry of the inner gate are effective in improving the pouring quality.
To avoid the frontmost part of molten steel advancing in the molding sand (often the dirtiest molten steel) from accumulating in critical areas of the product.