It has been proved by a lot of practice that the process design of gating system is the key problem that restricts the casting quality and performance of cylinder block iron castings under sand mold conditions, which has attracted extensive attention of manufacturers. Cylinder block castings have many machining surfaces, complex shape and structure, and belong to complex structural parts, and the minimum wall thickness is usually only 3-5mm. According to this characteristic, the design of gating system requires that the molten metal injected into the mold cavity should be uniform and fast, avoiding inclusion of gas, sand and other debris.
At present, horizontal pouring process is the main pouring method for cylinder block iron castings. According to the different location of the liquid metal introduced, the gate types are summarized as follows: bottom pouring is a traditional pouring form, which is easy to produce uneven temperature gradient and is not conducive to riser feeding. The top pouring type is beneficial to overcome some common casting defects, but the filling stability of liquid metal is poor, so it is rarely used by manufacturers. Middle injection type, its comprehensive process is the best, the upper and lower position of the main bearing is the water inlet position, which is used by most manufacturers. Step type, wide application range. Its comprehensive processability is the best. Step type horizontal pouring is a common technology. This method has strong adaptability and obvious advantages, and is suitable for machine modeling, core assembling and. However, the casting process is often accompanied by box expansion, core lifting and other defects, such as sand drop, sand inclusion and porosity.
With the popularization and application of the rapid prototyping technology of Dieless casting, the core assembly and vertical casting technology of cylinder block provides a new method and equipment for the production of single piece and small batch cylinder block, which is the development trend in the field of cylinder block iron castings manufacturing in the future. The bottom pouring with vertical pouring can reduce the adverse effect of the step horizontal pouring process, and realize the function effect that the scum and air hole are concentrated on the top of the casting, and the overflow is easy to shrink and exhaust. If these measures still can not eliminate the casting defects on the top of the casting, the top size of the casting can be extended, and the defective parts can be removed by machining, so as to obtain the cylinder block iron castings with low defect rate.
It is very important to design feeding riser technology of cylinder body iron castings, which directly affects the qualification rate and performance of castings. There are many kinds of feeding riser technology, which can be summarized as follows: Flash riser, blank holder riser, open top riser, necking riser, etc. In order to obtain a good riser and feeding effect, the design of riser system should pay attention to the following schemes and principles: good exhaust effect; moderate hot metal overflow; riser cleaning is convenient and conducive to improving casting surface quality. In addition, the selection of riser position on the casting is also very important, which is of great significance for obtaining qualified castings. According to the traditional feeding theory, the riser should avoid the processing surface and be placed in the thick, thick and hot spot as far as possible, and the thermal interference effect of the riser should be low.