There are certain specifications and requirements for lost foam casting. The following aspects should be paid attention to in the molding process: silica sand is generally used in lost foam casting, and its silica content is required to be more than 85%~90%. In terms of air permeability and refractoriness, cast steel and cast iron parts generally use silica sand with a particle size of 0.850~0.300mm. First, put a layer of dry sand with a thickness of about 100mm on the bottom of the sand box, then place the painted EPS mold and the pouring riser in the center of the sand box, fill the sand while shaking, until the dry sand is about 50mm away from the top surface of the sand box Stop adding sand, cover the dry sand with plastic film, then place the sprue cup on the top of the sprue, and remove a layer of loose sand on the film to prevent molten iron from splashing during pouring, burning through the film and causing air leakage and collapse box.
Pouring in the lost foam casting process, the entire process includes seven links, each link has a great impact on the quality of the lost foam casting, of course, the pouring process is also a crucial part of the entire lost foam casting process, Mastering the precautions of the pouring process and strictly controlling every detail in the pouring process is the key to producing high-quality lost foam castings.
The pouring process of lost foam casting is a process in which molten steel is filled and the foam mold evaporates and disappears. The things to keep in mind throughout the process are:
(1) The runner should be filled with molten steel from beginning to end. If it is not satisfied, due to the limited strength of the coating layer, it is easy to cause sand collapse and air intake, resulting in casting defects.
(2) When pouring molten steel, it must be grasped to ensure that it is stable, accurate and fast. Instantly fill the pouring cup, and achieve rapid and continuous flow, ton of molten steel in about one minute. If the molten steel of the castings in the same box is interrupted, air will be sucked in, which may cause the phenomenon of sand collapse or the increase of pores in the castings, resulting in the scrapping of the castings.
(3) Lost foam casting adopts negative pressure closed type, and it must be closed below the pouring cup. When the molten steel enters the molding die, it begins to liquefy and burn, and then vaporizes and disappears. The front end of the molten steel forms a temporary cavity in a short distance, so the designed speed of the molten steel filling and the disappearance of the foam model are roughly the same. In order to prevent the molten steel from high temperature radiation melting other models in the same box, the runner should be a little farther away from the casting model. The position of the vertical runner selects the lowest position of the whole box of castings. When pouring, pay attention to adjust and control the vacuum degree of negative pressure within a certain range. After pouring, keep it in a certain negative pressure state for a period of time. After the negative pressure is stopped, the molten steel is condensed out of the box.
Prevent back spray
Lost foam casting is one of the casting processes. There will be various casting defects in the casting process, which will lead to the defects of castings. Lost foam casting is no exception. Back-spray is a common phenomenon in lost foam casting. When the back-spray is serious, it may endanger the personal safety of the pourer. It must be paid attention to. In order to reduce the spray phenomenon, the following measures can be taken:
First, the density of the foam model should be small. On the premise of ensuring the quality of the foam surface and the strength of the model, the foam should be made as light as possible to reduce the amount of gas generated during pouring.
Second, the foam model must be dried before applying paint. Each batch of foam models should be sampled for the weight change during the drying process, and a baking weight change curve should be drawn. Only when the weight no longer changes, the paint can be applied.
Third, the gating system, especially the sprue and the runner, should not be coated with paint, so that the gas generated during pouring can be quickly and fully pumped away, and no paint is applied, which saves the consumption of paint. Finally, a baffle is placed on the pouring cup, which can block the molten steel that is sprayed back, so that it cannot splash out and endanger the on-site operators.
The use of the above method can effectively prevent the back spray phenomenon in the lost foam casting process, better prevent the defects of the casting, improve the quality of the casting, and also improve the safety of production.
Factors Affecting Accuracy
In lost foam casting, in general, there are many factors that affect the dimensional accuracy of castings, such as the structure, shape and size of the lost foam casting itself, the influence of foam quality, the influence of paint coating, the modeling, The influence of pouring link, etc.
In the entire lost foam casting process, the pouring process is one of the most important links. The four factors of pouring system, pouring speed, pouring temperature, and pouring process are the key processes to improve the quality of castings. Only continuous improvement and perfection can casting Castings with high precision and high quality are produced.
The paint coating also has a great influence on the precision of the lost foam casting. The performance of the coating and the thickness of the coating can affect the size of the pattern, thus affecting the dimensional accuracy of the casting. Therefore, in the lost foam casting, the coating should have good performance, sufficient strength, and at the same time The coating operation process should be reasonable.
Post time: Jul-28-2022