Lost mold casting

In 1958, h.f.salroyer patented a technique for making metal castings using a developable foam model.The original model used was made of polystyrene (EPS) plates with sand molding containing binder.Germany's Grunzweig and Harrtmann bought the patent and developed and applied it.The technology of producing castings with dry sand without binder was later patented by t.r. Smith in 1964.The use of a non-binder dry sand Process prior to 1980 must be approved by the Full Mold Process (Inc), after which the patent is invalidated.

The most common and practical method is to put the model coated with refractory material into a sand box, and fill the model with dry sand all around, pouring liquid metal instead of foam plastic model. This casting process is called: lost mold casting (EPC), gasification mold casting and solid mold casting.The lost mold casting committee of the American foundry association adopted "lost mold casting" as the name for the process.Precision casting

Lost foam casting is an innovative casting process for the production of non-ferrous metal power system components, including cylinder body, cylinder head, crankshaft, gearbox, intake pipe, exhaust pipe and brake hub.The process flow of epc is as follows:

1) pre-hair foam

Model production is the first step in the epc process. Complex castings, such as cylinder heads, require several foam models to be made separately and then glued together into a whole model.Every block model needs a set of mould for production, in addition in the gluing operation may also need a set of clamping fixture, used to keep the accurate positioning of the blocking, molding process of the model was divided into two steps, the first step is to pretest probability polystyrene beads to the appropriate density, generally by rapid heating steam, this phase is called pretest bubble.

2) model forming

Through pretest bubble bead for stabilizing treatment first, and then sent to the hopper of molding machine, through the hole of feeding material, mold cavity after full of pretest bead, began to pass into the steam, to soften bead, expansion, packed with all the gaps and glue as a body, this completes the manufacturing process of foam model, this phase is called autoclave molding.

After molding, the mold is cooled by a large flow of water in the water-cooling chamber 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. Therefore, careful operation must be taken during demoulding and storage to prevent deformation and damage.

3) model cluster combination

Before use, the model must be stored for an appropriate period of time to make it mature and stable. The storage cycle of the typical model is up to 30 days, while the model formed by the mold with unique design only needs to be stored for 2 hours. After the model is matured and stable, the segmented model can be glued together. 

Block model gluing is performed on automatic gluing machine using hot melt adhesive.The joint of the gluing surface should be sealed firmly to reduce the possibility of casting defects

4) model cluster dip coating

For each box can produce more castings pouring, glue joint will sometimes many model clusters, immerse model clusters in the refractory coating, and then in about 30 to 60 c (86-140 - f) air circulation oven dry in 2 ~ 3 hours, after drying, the model cluster into the sand box, fill in the dry sand vibration compaction, must make all models cluster internal hole cavity and peripheral dry sand are tight and support.

5) pouring

After the model cluster is filled solid through dry sand vibration in the sand box, the mold can be poured. After the molten metal is poured into the mold (casting temperature is about 760C/1400F for aluminum and 1425C/2600F for cast iron), the model gasification is replaced by metal to form the casting.Figure 1 is the sand box and casting schematic diagram of the vanishing mold process.

In epc process, casting speed is more important than traditional cavity casting.If the pouring process is interrupted, the sand mold may collapse into waste products.Therefore, in order to reduce the difference between each casting, the best use of automatic pouring machine.

6) shakeout cleaning

After casting, the casting is solidified and cooled in the sand box before sand fall.Castings castings are fairly simple and the tilting box castings fall out of loose dry sand.The casting is then automatically separated, cleaned, inspected, and transported into the casting box.

Dry sand can be reused after cooling, rarely using other additional processes, metal scrap can be used in production remelting.

1.2 advantages of epc process

The lost mold casting process has advantages in technology, economy and environmental protection.

1.2.1 technical aspects

1) the degree of freedom of model design increases

The new process makes it possible to design the form and add additional functions to the model from the first stage.For example, a diesel preheater has a special feature that can be manufactured using a lost foam casting process rather than traditional casting methods.

2) sand cores used in casting production are exempted

3) many castings can be made without riser shrinkage

4) complex shape and structure can be obtained by improving casting precision, and high-precision castings can be produced 100 times, and the deviation of casting wall thickness can be controlled within -0.15~+0.15mm

5) no flash is generated on the model joint surface

6) it has the advantage of reducing casting weight by about 1/3

7) reduce the processing allowance

Machining allowance can be reduced, even for some parts can not be processed.This greatly reduces the investment in machining and machine tools (for example, by half for different cases).

8) compared with the traditional cavity casting, the investment in the mold decreases.

9) completely eliminate the traditional falling sand and core process

1.2.2 economic aspects

1) can produce complex castings as a whole

With the new process design, the block model can be glued together to form the whole model and cast into complex integral parts, which can benefit from 1 to 10 times as much as the original multiple casting assembly parts (such as diesel preheater).

2) reduce workshop personnel

The establishment of a lost mold casting plant employs fewer workers than a conventional foundry plant, and this factor should be considered.

3) flexible casting process

The flexibility of the casting process is important because the new process has the potential to simultaneously produce a large number of similar or different castings in a sandbox, and the casting system is therefore very flexible.In short, we can say that each advantage is compatible with economic benefits and improves working conditions.

1.2.3 environmental protection

Polystyrene and PMMA produce carbon monoxide, carbon dioxide, water and other hydrocarbon gases when burned at levels below European standards.Dry sand can use natural silica sand, 100% repeated use, no binder.The coating used in the model is made up of additives such as binder added in water, without pollution.