Lost foam casting The most common and practical method […]
Lost foam casting
The most common and practical method is to put the model coated with refractory material into the sand box, fill the model with dry sand tightly, and pour liquid metal to replace the foam model. This casting process is called: lost foam casting ( EPC), gasification mold casting and solid mold casting, etc. The Lost Foam Casting Committee of the American Foundry Association adopted "lost foam casting" as the name of the process.
Lost foam casting is an innovative casting process that can be used to produce non-ferrous and ferrous metal power system parts, including: cylinder blocks, cylinder heads, crankshafts, gearboxes, intake pipes, exhaust pipes and brake hubs. The process flow of lost foam casting is as follows:
Model production is the first step of the lost foam casting process. For complex castings such as cylinder heads, several foam models need to be made separately, and then glued into an overall model. Each block model requires a set of molds for production. In addition, a set of molds may be required in the gluing operation to maintain the accurate positioning of each block. The model's molding process is divided into two steps. The first step is to The polystyrene beads are pre-expanded to an appropriate density, which is generally carried out by rapid heating with steam. This stage is called pre-expansion.
2) Model forming
The pre-expanded beads must be stabilized first, and then sent to the hopper of the molding machine, and fed through the feeding hole. After the mold cavity is filled with the pre-expanded beads, steam is introduced to soften the beads. Expansion, filling all the gaps and bonding into one body, thus completing the foam model manufacturing process, this stage is called autoclave molding.
After molding, the model is cooled by a large flow of water in the water-cooled cavity of the mold, and then the mold is opened to take out the model. At this time, the temperature of the model is increased and the strength is low, so care must be taken during demolding and storage to prevent deformation and damage.
3) Model cluster combination
Before the model is used, it must be stored for an appropriate period of time to make it mature and stable. The typical model storage period is up to 30 days. For a model formed by a uniquely designed mold, it only needs to be stored for 2 hours. After the model is matured and stabilized, it can be divided into two parts. The block models are glued together.
The block model gluing is performed on an automatic gluing machine using hot melt glue. The joints of the glued surface should be tightly sealed to reduce the possibility of casting defects
4) Model cluster dip coating
In order to produce more castings per box, sometimes many models are glued into clusters, and the model clusters are immersed in refractory coating, and then dried in an air circulation oven at about 30-60C (86-140F) for 2 to 3 After hours, dry, put the model clusters into the sand box, fill with dry sand and vibrate tightly. All the internal cavities and peripheral dry sand of the model clusters must be compacted and supported.
After the model cluster is firmly filled with dry sand in the sand box, the mold can be poured. After the molten metal is poured into the mold (the casting temperature is about 760C/1400F for cast aluminum, and about 1425C/2600F for cast iron), the model is vaporized. The metal is replaced to form a casting. Figure 1 is a schematic diagram of the sand box and pouring of the lost foam process.
In the lost foam casting process, the pouring speed is more critical than the traditional hollow casting. If the pouring process is interrupted, the sand mold may collapse and cause waste. Therefore, in order to reduce the difference between each pouring, it is best to use an automatic pouring machine.
6) Falling sand cleaning
After pouring, the casting solidifies and cools in the sand box, and then falls out. The casting sand falling is quite simple, and the castings fall out of the loose dry sand when the sandbox is overturned. Subsequently, the castings are automatically separated, cleaned, inspected, and transported away in the casting box.
Dry sand can be reused after cooling, and other additional processes are rarely used. Metal scrap can be remelted and used in production.