1. Introduction to lost form casting
EVC technology is a method of bonding foamed plastic models similar in size shape with the casting into model clusters, brushing refractory coating drying, burying them in the dry quartz sand for vibration modeling, pouring liquid metal under certain conditions, gasifying the model taking up the position of the model, solidifying cooling to form the required casting.
2. Features of lost form casting
(1) Compared with the traditional process, lost form casting technology has the obvious characteristics of “high efficiency simple production”.
(2) Good quality high accuracy are the major characteristics of lost form casting technology.
(3) Easy to master the technology convenient production management.
(4) Reduce the labor intensity improve the working environment.
Lost form casting process flow
Evanishing mold casting is to dip the appearance made of foam plastic with refractory coating, put it into the sand box, fill the sand without binder moisture, fill the foam plastic mold vibrate, then the sand is fastened into the casting mold.
(1) The production of foam plastic mold refractory coating.
(2) Vibration fastening of the sand after the foam mold is embedded in the sand box.
(3) Maintain the vacuum degree of the sand box in the pouring process.
The main performance index of lost form casting coating is wet strength, dry strength, absorbability, suspension, air permeability, coating popularity.
Risers Pouring in lost form casting
1. Simple introduction of riser
In the process of cast iron, two operations of cooling solidification are needed, which result in the formation of liquid solidification shrinkage in the casting process.
(1) Through the “direct filling”, the effective elimination of shrinkage cavity is realized.
(2) Through the “riser”, to achieve casting feeding.
2. The casting
(1) Pouring characteristics: according to different castings to choose different gating system, top injection, side injection, bottom injection.
(2) Pouring process parameters.
Pouring temperature: Because the gasification of foam plastic mold needs to absorb enough heat the metal liquid front, the pyrolysis of foam plastic mold will make the temperature of metal liquid drop about 60℃, so the pouring temperature of metal liquid in lost form casting is 50℃ ~ 100℃ higher than that of conventional casting.Casting speed: the faster the casting speed, the more stable the metal liquid flow, the easier the casting deformation;The slower the casting speed is, the greater the temperature drop of the metal liquid front will result in cold isolation, the collapse of the box will make the casting scrap.
Defects prevention of lost form casting
1. The adhering sand
Causes: in the case of coating cracking, because the compactness of molding sand is enough, molding sand particles are too large vacuum degree is too high to produce the first kind of sticky sand;In the coating is too thin local brush to the case, because the metal liquid temperature is higher, the vacuum degree is larger when the second kind of sticky sand.
Prevention control measures: improve coating thickness fire resistance;The tight strength should be too large in order to avoid damaging the coating;Choose the right negative pressure;Choose fine raw sand;Pouring temperature should be too high;Choose the right pressure head.
In fact, there are many kinds of air orifice classification, different stomatal types, the required prevention treatment measures are greatly different, which also requires targeted prevention treatment according to the causes of different stomata.
3. Shrinkage cavity porosity
Volume shrinkage occurs when metals change liquid state to solid state, including liquid state shrinkage, solidification shrinkage solid state shrinkage.
Prevention control measures: increase the volume of feeding riser use reasonable riser shape;Cooperate with the use of cold iron;Increase the temperature of the metal liquid in the riser;When casting ductile iron, the negative pressure is increased immediately after casting to improve the mold stiffness.