The lost foam casting technology is to use foamed plastic to make a solid mold with the same structure and size as the part, after dipping the refractory adhesive coating, drying it for dry sand molding, vibrating and compacting, and then pouring the molten metal to make the pattern suffer. A casting method for obtaining metal parts conforming to the pattern shape by disappearing thermal vaporization.
Pressure Lost Foam Casting Technology
The pressure lost foam casting technology is a new casting technology that combines the lost foam casting technology and the pressure solidification crystallization technology. A casting method in which a certain pressure of gas is introduced to make the molten metal solidify and crystallize under pressure. The characteristics of this casting technology are that it can significantly reduce casting defects such as shrinkage cavities, shrinkage porosity, and pores in the castings, increase the density of the castings, and improve the mechanical properties of the castings.
Vacuum low pressure lost foam casting technology
Vacuum low pressure lost foam casting technology is a new casting technology developed by combining negative pressure lost foam casting method and low pressure anti-gravity casting method. The characteristics of vacuum low pressure lost foam casting technology are: the technical advantages of low pressure casting and vacuum lost foam casting are combined, and the filling process is completed under controllable air pressure, which greatly improves the casting filling ability of the alloy; compared with die casting, the equipment The investment is small, the cost of castings is low, and the castings can be strengthened by heat treatment. Compared with sand casting, the castings have high precision, small surface roughness, high productivity and good performance; The loss is small, the liquid alloy is fed and solidified under a controllable pressure, the pouring system of the alloy casting is simple and effective, the yield is high, and the structure is dense;
Vibration Lost Foam Casting Technology
The vibration lost foam casting technology is to apply a certain frequency and amplitude of vibration during the lost foam casting process to make the casting solidify under the action of the vibration field. The relative motion between the phase and the solid phase causes the dendrites to be broken, increasing the crystallization core in the liquid phase, refining the final solidification structure of the casting, improving the feeding, and improving the mechanical properties. This technology utilizes the ready-made compact vibration table in lost foam casting, and through the mechanical vibration generated by the vibration motor, the molten metal is nucleated under the dynamic excitation, and the purpose of refining the structure is achieved. method of pollution.
Semi-solid lost foam casting technology
Semi-solid lost foam casting technology is a new casting technology that combines lost foam casting technology and semi-solid technology. Because the process is characterized by controlling the relative proportion of liquid and solid phases, it is also called transformation-controlled semi-solid forming. This technology can increase casting density, reduce segregation, improve dimensional accuracy and casting performance.
Lost Foam Casting Technology
Lost foam casting technology is a new casting method that combines investment casting technology and lost foam casting. The method is to coat several layers of refractory material on the surface of the foamed plastic pattern with the same shape as the part made by the foaming mold. After it is hardened and dried, the foamed plastic pattern in it is burned and gasified to disappear to form a shell, which is roasted. , and then pouring to obtain a new type of precision casting method for castings with higher dimensional accuracy. It has the characteristics of large size and high precision in lost foam casting, and has the advantages of crust accuracy and strength in investment casting. Compared with ordinary investment casting, it is characterized by the low cost of the foamed plastic mold material, the convenient bonding and combination of patterns, and the easy vaporization and disappearance. Complex castings of various alloys in large sizes
Lost Foam Suspension Casting Technology
Lost foam suspension casting technology is a new practical casting technology that combines lost foam casting technology and suspension casting. The technical process is that after the molten metal is poured into the mold, the foam pattern is vaporized, and the suspending agent is mixed in the riser model (or the suspending agent is placed in a specific position of the pattern, or the suspending agent and EPS are used together to make a foam pattern. ) and the physicochemical reaction with the molten metal to improve the overall (or part) microstructure and properties of the casting.
Precautions in the pouring process of lost foam casting
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.
In the lost foam casting process, the whole process includes 7 links, each link has a great influence 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 Precautions for pouring process and strict control of 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. Sanzhuji recommends paying attention throughout the casting process:
1.1 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;
1.2 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;
1.3 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
Back-spraying is a common phenomenon in lost foam casting. Serious back-spraying may endanger the personal safety of the pouring workers. It must be paid attention to. In order to reduce the spraying phenomenon, Sanzhuji suggests that the following measures can be taken:
2.1 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;
2.2 The foam model must be dried before coating. 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 coating can be applied;
2.3 The pouring 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.
Using the above method can effectively prevent the phenomenon of back spray 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.
Sanzhuji summarizes factors that affect 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.
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