With the upgrade of Industry 4.0, the technology and precision of equipment have been improved. Therefore, the demand for castings produced by precision casting (lost foam sand casting) in the market is gradually increasing. However, during the lost foam sand casting process, the box collapses. It is the most common problem. Box collapse usually occurs in large parts, or semi-closed parts, enclosed in the inner cavity. From the perspective of the entire lost foam casting process, it mostly occurs in the pouring or solidification process. A collapsed box defect can also be called a couch-type defect. Sanzhuji combined the characteristics of the lost foam sand casting equipment, and made the following prevention measures for the collapse of the lost foam sand casting.

1. Brief introduction of lost foam hollow shell casting method
The lost foam hollow shell casting method adopts a new type of super-sintering-resistant paint. The EPS foam in the mold is first burned to form a cavity shell with little residual carbon, and then an advanced and practical high-temperature molten metal is poured. Lost foam casting method.
The biggest feature of this method is the whole process from the manufacturing of the pattern to the casting out of the casting. The operation is simple, reliable, fast, efficient, and low in cost. It can effectively eliminate the casting carbon defects caused by EPS and obtain similar results. Excellent castings with the quality level of investment casting.
Compared with the solid casting process used in the lost foam casting tradition at home and abroad for many years, the lost foam hollow shell casting method only implements a simple and easy operation process in a few minutes before casting—from the gate and the riser. The EPS foam in the mold is burned out at a place of ignition, and all the rest of the operation process is the same as the conventional lost foam casting process. All tooling equipment does not need to be changed or added. As long as there is flammable gas, the lost foam casting can be implemented. Burn first and then pour, and the operation is simple and convenient.
Packing steps: the first step is to bury the shape in dry sand to vibrate and level the box surface; the second step is to bury the runner and riser in the sand box, and the plastic film cover is flat; the third step is to place mud around the pouring port Install the sprue cup after the strip; in the fourth step, place the sand box and connect the vacuum tube.

2. The advantages and disadvantages of the lost foam hollow shell casting process
2.1 Obtain excellent castings to eliminate carbon defects, improve the internal quality of products, and ensure high-quality castings. The so-called carbon defects, because of the objective existence of carbon in the pattern (EPS), causes various defects caused by molten metal pouring and solidification process to be collectively referred to as carbon defects in lost foam casting. Lost foam carbon defects include carbon increase, slag inclusion, wrinkles, uneven composition, poor mechanical properties, coarse grains, hard and brittle surfaces, and deterioration of welding and machining properties caused by the pyrolysis of carbon in the foam. , But also includes pore defects directly caused by carbon.
2.2 Unstable process
2.21 The initial negative pressure of pouring needs to be high (above 0.06MPa). After the EPS foam in the mold is burned, the vacuum of the negative pressure field decreases rapidly, which is easy to cause the casting failure. In order to ensure 0.02 MPa (non-collapse box negative pressure value) after the vacuum is reduced to the lowest value, a higher negative pressure value must be guaranteed at the beginning of pouring. However, if the negative pressure is too high, the surface of the casting is prone to sand sticking and pore defects.
After the EPS foam in the 2.22 type is burned out, during the pouring process, "three leakages" (sand leakage, air leakage, and metal leakage) are prone to occur at the junction of the pouring riser cup and the sprue mouth and the riser, causing the negative pressure value to drop rapidly Defects such as collapsed box and sand inclusion in castings will occur later.

3. Causes of collapsed box defects
3.1 The "flash flow" of molten metal is one of the causes of collapse defects. The so-called "flash flow" of molten metal refers to that during pouring, part of the molten metal that has flowed into the position of the filled evacuated pattern is diverted under external influence. To other parts, the original replacement position is not occupied by molten metal or metal filling. 　　
3.2 The coating has insufficient refractoriness and high-temperature strength, and it is extremely easy to produce the collapse of the lost foam casting. The lost foam pattern has the function of buffering the filling and cooling of the molten metal during the pouring process, and at the same time, it can weaken the erosion of the mold by the molten metal. When the molten metal replaces the lost foam pattern and fills the cavity, the dry sand is mainly supported by the coating. When the strength of the coating is insufficient or the refractoriness is insufficient, the local mold will collapse and collapse, especially the large internal runner The upper part is extremely prone to collapse. 　　
3.3 During the pouring process, the amount of gas generated by the decomposition of the lost foam pattern is too much and urgent, and the mold exhaust speed cannot keep up. In addition, the vacuum pump is insufficient to suck, which may easily cause the mold to collapse and collapse;

4. Measures to solve the collapse of the lost foam empty shell casting
Sanzhuji analyzed the shortcomings of the above two processes, combined with the key points of the lost foam casting process, tried to improve the pattern packing operation process and perfect the vacuum negative pressure system. After production and application, the entire casting process achieved good results, and the lost foam shell was empty. The shortcomings of the casting process are solved.
Packing steps: the first step is to bury the pattern in dry sand to tap; the second step, the sprue and riser are protruding from the flask surface; the third step, the plastic film cover is flat, and the sprue and riser are convex Out to break the plastic film. In the fourth step, put an appropriate amount of adhesive sand on the plastic film around the sprue and riser pattern to smooth it, and install the sprue cup. The fifth step is to place the sand box and connect the vacuum tube.
Through the improvement of the pattern packing operation process, after the EPS foam in the mold is burned out, the "three leakage" phenomenon that is prone to occur at the junction of the sprue cup and the sprue opening and the riser during the pouring process can be controlled.
The initial negative pressure value of pouring can also be appropriately selected in the normal range (0.025～0.06MPa), thereby solving the pouring defects caused by high negative pressure. The traditional pattern boxing operation is relatively simple. After the plastic film is covered and vacuumed, the inside and outside of the sand box can reach the air pressure balance. However, when the lost foam shell casting method is used, that is, the EPS foam in the cavity is burned, the sprue cup and the sprue mouth The plastic film at the riser joint is burned, causing the pressure balance between the inside and outside of the entire flask to be out of balance, the vacuum degree drops rapidly, the vacuum degree (negative pressure value) in the cavity during the pouring process is seriously distorted, and the sprue cup is connected with the sprue and riser Air leakage is unavoidable at all places, which can lead to sand leakage and liquid metal leakage in severe cases.
The packing operation process of the pattern is improved, that is, the sprue and riser patterns protrude and break through the plastic film. Put an appropriate amount of bonding sand on the plastic film around the sprue and riser pattern to smooth out the inside and outside of the cavity, and vacuumize The air pressure balance can be achieved inside and outside the back cavity. When the lost foam hollow shell casting process is used, that is, after the EPS foam in the cavity is burnt out, the difference in air pressure inside and outside the cavity changes little, and the reading of the negative pressure gauge can more truly reflect the vacuum degree of the casting process. In addition, the bonding sand around the sprue and riser pattern is hardened, so that the contact surface between the plastic film and the pattern remains relatively sealed, which can also prevent the "three leaks" phenomenon and achieve the excellent effect of the lost foam hollow shell casting process to produce castings.

5. Summary
Improve the pattern packing process, after being applied to the lost foam hollow shell casting process, it overcomes the original process shortcomings, eliminates box collapse, guarantees the quality of castings, reduces the rejection rate, improves the process level, and is beneficial to the lost foam hollow shell casting process Promotion and application.Qingdao Sanzhuji Equipment Manufacturing Co., Ltd. specializes in the production of sand reclamation equipment, Sand casting equipment, Sand mixer, no-bake resin sand mixer, Jolt squeeze molding machine, Multi- Piston Moulding Machine,foundry molding machine, flaskless moulding machine, shot blasting machine, dust collector, according to the amount of old sand recovered Carry out plan customization, and provide sand reclamation equipment installation, commissioning, and training. Welcome guests to visit the factory.

Qingdao Sanzhuji Equipment Manufacturing Co., Ltd. specializes in the production of sand reclamation equipment,foundry machines,Sand casting equipment,GS high efficiency rotary mixer,no-bake resin sand mixer,Jolt squeeze molding machine/Jolt-squeezing moulding machines,Multi- Piston Moulding Machine/Hydraulic multi-piston moulding machine,foundry molding machine,flaskless moulding machine,shot blasting machine,dust collector,according to the amount of old sand recovered Carry out plan customization, and provide sand reclamation equipment installation, commissioning, and training. Welcome guests to visit the factory.