1958, H.F.Shroyer invented the technology of manufacturing metal castings with expandable foam plastic model and obtained a patent. Firstly, the model is made of polystyrene (EPS) board, and molding sand with binder is used. German companies Grunzweig and Harrtmann bought this patent and developed and applied it. The technology of producing castings with binder-free dry sand was later patented by T.R.Smith in 1964. The use of binder-free dry sand process before 1980 must be approved by Full Mold Process, Inc., after which the patent will become invalid.
The most common and practical method is to put the model coated with refractory into the sand box, fill the model with dry sand, and pour liquid metal instead of foam plastic model. This casting process is called EPC, EPC and EPC. EPC Committee of American Foundry Association adopted "EPC" as the process name.
Lost foam casting is an innovative casting process, which can be used to produce non-ferrous and ferrous metal power system parts, including cylinder block, cylinder head, crankshaft, gearbox, intake pipe, exhaust pipe, brake hub and other castings. The technological process of EPC is as follows:
1) pre-foaming
Model production is the first process of EPC. Complex castings, such as cylinder head, need several foam models to be made separately and then glued into a whole model. Each building block model needs a set of molds to produce, and in addition, a set of clamping tools may be needed to maintain the accurate positioning of each building block during the gluing operation. The forming process of the model is divided into two steps. The first step is to pre-send polystyrene beads to the proper density, which is usually carried out by rapid steam heating. This stage is called pre-foaming.
2) Model formation
Pre-foamed beads should be stabilized first, and then sent to the hopper of the molding machine through the feed inlet for feeding. After filling the mold cavity with pre-foamed beads, steam is introduced to soften and expand the beads, filling all gaps and sticking them together. This stage is called autoclaving.
After molding, the model is cooled by the large flow of water in the water cooling cavity of the mold, and then the mold is opened to take out the model. At this time, the temperature of the model increases and the strength is low. Be careful when demoulding and storing to prevent deformation and damage.
3) model clustering combination
Before the model is used, it must be stored for a proper period of time to make it mature and stable. The storage period of a typical model is as long as 30 days, while the model formed by a uniquely designed mold only needs to be stored for 2 hours. After the model is solidified and stabilized, the block model can be glued and bonded.
Glue the block model with hot melt adhesive on the automatic gluing machine. Bonding surface joints should be sealed firmly to reduce the possibility of casting defects.
4) Dip coating model group.
In order to pour more castings in each box, sometimes many models are glued into clusters, immersed in refractory coatings, and then dried in an air circulation oven at about 30 ~ 60 ℃( 86- 140 F) for 2 ~ 3 hours. After drying, put the model dough into the sand box, fill it with dry sand, and vibrate and compact it, so that all the dry sand in the inner cavity and periphery of the model dough must be compacted and supported.
5) pouring
After the mold cluster is firmly filled in the sand box by dry sand vibration, the mold can be poured. After molten metal is injected into the mold (the pouring temperature of aluminum casting is about 760C/ 1400F, and that of cast iron is about 1425C/2600F), the mold is vaporized and replaced by metal to form the casting. Figure 1 is a schematic diagram of sand box and pouring in EPC.
In the process of EPC, pouring speed is more critical than traditional EPC. If the pouring process is interrupted, the sand mold may collapse, resulting in waste products. Therefore, in order to reduce the difference of each pouring, it is best to use an automatic pouring machine.
6) Sand falling cleaning
After pouring, the casting is solidified and cooled in the sand box, and then the sand is dropped. Casting sand shedding is very simple, and the castings in the inclined sand box fall out of loose dry sand. Then the castings are automatically separated, cleaned, inspected and put into the casting box for transportation.
Dry sand can be reused after cooling, and other additional processes are rarely used, and metal waste can be remelted in production.
Advantages of 1.2 EPC process
EPC has many advantages in technology, economy and environmental protection.
Technical aspects 1.2. 1
1) The freedom of model design is increased.
It is possible for the new process to carry out modeling design, and some additional functions can be added to the model from the first stage. For example, the diesel preheater has a special functional component, which can be manufactured by EPC process instead of the traditional casting method.
2) The sand cores used in casting production have been eliminated.
3) Many castings can be fed without riser.
4) improve the casting accuracy
Castings with complex shapes and structures can be repeatedly produced at 100, and the wall thickness deviation of castings can be controlled between-0.15 ~+0.15 mm.
5) The joint surface of the model does not produce flash.
6) It has the advantage that the casting weight is reduced by about 1/3.
7) Reduce machining allowance
The machining allowance can be reduced, and even some parts can not be machined. This greatly reduces the investment in machining and machine tools (for example, the investment can be reduced by half according to different situations).
8) Compared with the traditional cavity casting, the mould investment is reduced.
9) The traditional procedures of sand dropping and coring are completely cancelled.
1.2.2 Economic aspects
1) can produce complex castings as a whole.
Using the new process design, the block model can be glued to form an integral model and cast into a complex integral part, which can benefit 1 to 10 times more than the original assembly parts of multiple castings (such as diesel preheater).
2) Reduce workshop personnel
The number of employees employed in establishing EPC foundry is less than that in traditional foundry, so this factor should be considered.
3) Flexible casting process
The flexibility of casting process is very important, because the new process may produce a large number of similar or different castings in the sand box at the same time, and the gating system is therefore very flexible. In a word, we can say that every advantage is in line with economic interests, and it also improves working conditions.
1.2.3 environmental protection
When polystyrene and PMMA are burned, carbon monoxide, carbon dioxide, water and other hydrocarbon gases will be produced, and their contents are lower than the allowable standards in Europe. Natural silica sand can be used for dry sand, and 100% can be recycled repeatedly, without binder. The paint used in the model is composed of additives such as adhesive added to water, which will not cause pollution.