Epc process has been widely used in foreign countries, and in recent years, many domestic enterprises begin to put the equipment into the mold for production, and is widely used trend obviously, through the efforts of colleagues, epc process is bound to bring more benefits to the industrial, at the same time, we also should pay attention to mold method is not everything. There's mastercard & should be selectively into production, to avoid waste.
Lost foam casting process is suitable for application in the following circumstances: (1) of the mass production parts (2) complex parts (use more than two cores, especially the complex inner cavity of the casting, such as cylinder block, cylinder head), complex thing better, of course, but the corresponding technical difficulty is bigger also. (3) can be made in separate parts together, as a whole parts for production.
Epc is not suitable for production of some of the pressure vessel, because we cannot avoid it produces some shrinkage defects, is not suitable for pressure vessel.
1 of epc process in industrial application
The huge superiority of epc has a unique arts and crafts. Due to the advantages of epc, art casting more produced by this method, such as li wei bronze is studied in the lost foam casting production.
Adopts the li wei also studied the process of casting the heat-resisting cast iron boiling furnace hood [2]. RTSi 5.5 heat-resisting cast iron with medium frequency induction furnace melting, casting process for multiple casting line column, each sand box buried layer cast, high production efficiency; The gating system feeding, feeding effect is good. Casting surface quality will improve notably.
Epc is suitable for production of large castings, such as Mr. Wang was studied using resin sand - of epc process production feasibility of large castings.
Dai Binyu using lost foam casting process such as the preparation of Gr/Al composite materials, the wear of the composite material performance test. Results show that the process of the graphite distribution in composite materials evenly, interface combined more closely. And proved that epc method in preparation of composite material technology and equipment is simple, easy to operate. As you can see on epc in the production of composite materials also has a certain production prospects.
Sail, studied the dissolved mold casting of technology in scraper conveyor trough for the application of production obtains a nice effect compared with the original sand mold casting has the following advantages:
(1) the casting surface level off is smooth.
(2) the casting defects such as slag inclusion, sand inclusion of decreased significantly.
(3) casting dimension ring-fenced, small deformation, slot help a lot of machining dimension to not original, make slot help to reduce cost, economic benefit is remarkable.
(4) the labor intensity is reduced, to improve the construction environment, the social benefit is prominent. XiaoChangHao for epc process such as [6] in the harvesters in casting production practice. Through epc casting production practice, solve the common casting relatively complex, product machining allowance, and the problem of large labor intensity, especially the buffer saves 70% of mechanical processing capacity, improve the production efficiency. In epc casting production we also apply it to the grey cast iron, graphite cast iron castings, high manganese steel parts production and good results have been achieved, believe that through further improve and perfect the technology, epc has a broad prospect in the production of mining accessories.
2 lost application defects and corresponding resolving measures
2.1 principle of epc process production steel casting process
To disappear in order to make the bubble shape a trace, prevent casting defects occur, must follow the following principles: (1) create high temperature anaerobic conditions, make the shape in the form of gasification disappeared, instead of disappearing in the form of combustion, the basic principles of this is to prevent the local carburization. (2) balance and feed speed of liquid steel bubble shape of gasification rate, improve the liquid steel temperature, reduce the surface tension, is the basic principle of prevent subcutaneous blowhole. (3) negative pressure field directivity and defective guiding role, all negative pressure loss of the sand box, the box collapse will happen; Partial loss, will occur in sand sand block displacement and cavity. The measures to prevent white defects is "combination hard-wired outside the box".
2.2 control of epc casting technology measures of deformation
2.2.1 foaming agent EPS raw material content of foaming agent should be between 6.0% ~ 6.5%, at least not less than 5.5%. Bead should be bright and clean, uniform particle size.
2.2.2 appearance make
1) pretest bubble, after the steam pressure of 0.04 MPa, and row net pipe steam moisture from the pretest bubble machine. If the heating steam into the pretest probability of steam bubble machine entrained water more, or heating steam condensate can not discharge in time, in the second foam molding EPS particles when water content is high, in the dry (curing) short time or curing temperature is low (< 20 ~ 25 ℃), bead easily into small pieces or clumps. At this time to make the appearance of easy to deformation.
(2) the pretest bead curing time should be 10 ~ 12 h, pretest bead curing time control is lax, shape size deformation is very difficult to control.
(3) for the wall thickness of 3.5 ~ 4 mm tube, the density of pretest bead should be controlled at about 26 g/cm3.
(4) check before moulding mold exhaust was clear and filling pressure is more than 0.05 MPa, otherwise will affect the degree of full filling material to form a local bead reticulate, reduce the appearance of strength, make the shape during ripening and deformation in the subsequent working procedure.
5. When using high steam pressure molding can reduce the curing shrinkage.
6 degree of control cooling after pressed the shape forming, modulus before to make the appearance fully cooled to below 80 ℃, the secondary foam termination, to get good appearance, dimensional stability to prevent shape deformation modulus.
7) after the modulus of shape should be under 50 ~ 60 ℃ dry 3 ~ 8 h to ensure cure.
2.2.3 bonding and group process
(1) binder quality directly affects the quality of the mould. Before bonding, like flat vertical parting surface polishing. When bonding force light and evenly.
(2) of the structure is compact, low rigidity thin wall castings, set of mould can be added a technology support, in order to improve the rigidity of the model.
(3) on the coating, choose a suitable place for inside and outside at the same time immersed in paint.
(4) appropriate coating thickness. Coating can enhance the surface strength of appearance, can prevent the shape deformation in the process of handling, modelling. (5) drying when placed reasonable, prevent stress resulting from the uneven deformation.
2.2.4 fill sand molding process
Between (1) of SPR and casting, not too close to the distance between clusters, generally is 90 ~ 120 mm, this is to prevent the basic conditions of local heat unevenly.
(2) the sand temperature control under 50 ℃, prevent appearance local deformation during the filling sand molding operations; (3) reasonable type buried location, the model of large plane in a vertical or tilting pouring position.
(4) when the sand filling shape inside and outside layer filling height should be uniform.
(5) choose reasonable vibration technology parameters to make dry sand shape parts, to prevent local firm, dry sand vibration too much will cause deformation.
2.2.5 casting process
(1) pouring maintained steady, rapid and continuous filling iron liquid, prevent iron liquid during the filling process flows when big small, streamer, flow phenomenon.
(2) the negative pressure lost foam casting is the most important fundamental factors. Negative pressure in the process of pouring should acuity 0.02 MPa; The original vacuum degree can be a little higher (> 0.035 ~ 0.05 MPa).
(3) to release the vacuum pump is going to make the casting in the free shrinkage state, in order to reduce casting stress. Pump stop too early, the casting surface is not completely solidified, crust layer strength is low, easy to cause deformation of the casting, the dimension precision of casting; Stop pump too late, because the vacuum type intensity is higher than ordinary sand mold casting, casting shrinkage prone to cracking. This requires the casting structure, the pouring temperature, casting size and thickness. In principle, in about 5 min (with the size and decide) wall thickness, wall thickness > 20 mm, the weight is more than 100 kg, 5 min after pouring stop pump; Below 100 kg of casting, casting can be stopped after the release of vacuum pump. For more than 100 kg of thick wall (> 30 mm) casting can be appropriately prolonged negative pressure, to speed up the cooling speed; And thin-walled tube, casting can release the vacuum pump is going to end.
If is for large deformation problem of casting, attention also should be the following aspects:
(1) volume density should be consistent (molding + group), density control between 18 ~ 22 kg/m3.
(2) after the paint brush, the school flat leveling machine dry before application.
(3) increase when necessary tooling (current processing after formal production tooling).
(4) using reasonable technology and the sand box buried box negative pressure structure.
(5) control box of time.
2.3 sand washing
Sand washing are common defects in lost foam casting, the following parts are sand washing measures to prevent them [10] :
(1) prevent direct runner and sprue cup joint sand washing measures are:
1) make the sealed plastic film away from heat source;
(2) use high temperature binder refractory clay sculptures sprue cup with the SPR joints;
(3) direct runner and sprue cup made of an organic whole.
(2) the measures to prevent sand washing at the bottom of the SPR is:
1) pad brick; (2) around the refractory mortar. (3) the measures to prevent straight, runner sand washing are: (1) increasing horizontal, SPR coating; (2) brush and fine sand, sodium silicate refractory, to increase the impact resistance ability.
(4) to prevent the sprue and runner by it of sand washing measures are: (1) with refractory mortar seal; (2) brush thick quick drying coating, wet when buried box, 3 ~ 5 min in advance with vacuum drying.
2.4 control of blowhole defect factor
Control air hole needs to control suitable pouring temperature and the reasonable pouring position, mainly from the reasonable casting speed and the degree of negative pressure under the aspects:
(1) straight made hollow sprue can prevent spillage and prevent the first water backwash. With small golden belong to liquid first point sprue cup full of SPR again flow quickly closed SPR, vacuum degree, until the liquid metal pouring basin sank no longer.
(2) epc process appropriate gating system form is enclosed, to prevent air hole has a better effect. When pouring liquid metal has been full of sprue cup, spillover, splash damage. Sealing film, to ensure balanced pressure field, make the compactness of sand is greater than the shear sand for casting, no box, collapse collapse.
(3) are not allowed to stop in the process of casting and streamer pouring process are not allowed to block, the streamer, once the SPR bare in the air, under the action of negative pressure air into the cavity formation porosity defect, make the casting scrap.
(4) to determine the reasonable vacuum degree is the assurance of exhaust gas, slag, and prevent the adhering sand factor.
(5) production capacity suitable sprue cup is an essential tool for liquid metal, pouring the eddy current, do not produce the metal liquid has the function of slag and impurities in the metal liquid floating set to the sprue cup, liquid surface filling to prevent impurities generated porosity. Lost the influential factors of the iron carbon defects and the prevention measures.
2.5 to prevent carbon defects (wrinkled skin) strategies and practices
2.5.1 choose higher pouring temperature In does not produce sand inclusion and under the premise of adhering sand, increasing pouring temperature, as far as possible make die.it gasification discharge, more die-lost casting pouring temperature on the clay sand process commonly add 40 ~ 80 ℃, box generally higher than 1420 ℃.
2.5.2 higher coating and sand permeability coating permeability is usually selected above 20 cm / 8 mm, thickness is in commonly 0.8 mm effect is better. High permeability is conducive to decomposition of gas discharge, but high permeability is higher demands on the strength of the coating. Choose the appropriate sand particle size, the repeated use of the sand dust processing, generally half a year to replace a new sand. To regular cleaning glue paste on the blockage in the sand box mesh pyrolysis products, otherwise it will lead to the formation of carbon defects. Improve casting method of the permeability of concrete:
(1) to improve permeability of sand, choose coarse sand (> 20 mesh), control the amount of binder, control the moisture content is less than 6%;
(2) more than Mr. Blow hole or a vent riser;
(3) within the mold set up several air passage;
(4) choose reasonable coating. 2.5.3 choose appropriate gating system of epc casting pouring way can choose bottom note, step gating, top note. But must ensure that the metal flow smoothly and quickly filled with mould, and in determining the pouring position must fully consider the shape of the casting. As the height is not small castings using the top note, for large or large castings, as far as possible with disperse runner or more layered casting stage, avoid the runner is too concentrated, so conducive to the smooth metal, quickly filled with mold, has a better function to improve casting quality. When choosing epc riser, should consider adopting dark riser as much as possible.
2.5.4 set slag riser
2.5.5 proper shape or change parts machining allowance Thicker spare parts of the finish for the castings to remove, so can reduce carbon defects formation. For mild carbon defects of local really is not easy to eliminate the dead Angle, can be appropriately increase the machining allowance, the defective parts removed after processing.
2.5.6 in foam plastic surface spraying accelerate gasification material In spray a layer of foam plastic mold surface gasification quickly nitrocellulose or other than plastic coating, can not only improve the appearance of the surface quality, and helpful to the foam of the gasification and prevent the formation of the pyrolysis products.
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