Solving the common defects of sand slag in vanishing mold

In vanishing mold products, common defects mainly include sand inclusion slag inclusion. In order to solve the defects of sand inclusion slag inclusion, it is necessary to systematically comprehensively analyze the causes of the defects, so as to better develop corresponding measures.

1. Defect analysis

In the production of vanishing die, the preparation of coating is the most important process in the production of vanishing die, it is the core process of the manufacturer. The most restricting factor of product quality is coating.In order to study the source of the defects of sand slag inclusion, it is necessary to make a comprehensive analysis of the defects in the casting.

1.1 Analysis of Sand Inclusion Defects Analyze the sand inclusion defects find out the following reasons that may lead to sand inclusion:(1) there is loose sand on the surface of the sprue cup, which is tight during tamping, it is rushed into the cavity during pouring;(2) the shape of the sprue cup is appropriate, resulting in excessive scouring force on the straight sprue during casting, washing off the coating layer of the straight sprue, punching the molding sand in the sand box into the mold cavity, resulting in sand infilling;(3) The coating layer of the sprue itself is thin the ability of resisting molten steel scour is poor, so it is necessary to brush the coating on the sprue again to ensure the thickness of the coating layer;(4) in the bonding, after the casting the sprue are bonded with hot melt adhesive, the adhesive tape has a very low high temperature resistance strength. Once the molten steel is poured here, it will be burned immediately, the molding sand in the sand box will be rushed into the mold cavity the gap, resulting in sand clip;(5) direct sprays castings after painting, the suspension mode on the paint car is appropriate, resulting in too many places to repair when packing, if the repair is incomplete the repair layer is thin, it will directly produce sand inclusion.

1.2 Analysis of slag inclusion defects Based on the collective wisdom of technical personnel, the reasons for slag inclusion are summarized as follows:(1) the slag is completely removed before casting in the ladle;(2) in the pouring process, the ladle continues to produce slag, slag scraping personnel did timely scraping slag, steel slag with molten steel into the cavity, slag inclusion;(3) the paint in the raw materials of individual refractory added too much, inappropriate, molten steel reaction, produce a certain compound.

2. Solutions

After analyzing the defects of sand slag inclusion, the technicians in the workshop solved them two aspects of coating  white mold bonding process.

2.1 Adjustment of formula of EPC coating

First of all, we must understand the composition of paint, in order to better solve the problem of paint.Evanishing mold coatings support protect the foam model, prevent liquid metal seeping into sand, absorb decomposition products allow decomposed gases to pass through the coating, maintain the integrity of the cavity formed after the foam model evaporates, keep liquid metal heat escaping quickly.Therefore, the vanishing mold coating should have sufficient refractoriness, certain mechanical strength, appropriate heat preservation thermal conductivity, appropriate air permeability the ability to absorb liquid decomposition products, smooth surface, sufficient coating performance, no chemical reaction with the foam model other properties.Evanishing mold coating is mainly composed of refractory aggregate, suspending agent, binder, dispersing medium additives to improve some properties of coating.

2.2 Adjust the white die bonding process

On the basis of adjusting the formula, the production workshop strengthens the brush coating process adjusts the bonding process.

(1) first paint to brush evenly, too thick brush less than the parts;(2) after the white mold coating is dried, the coating falls off cracks are repaired by brushing, then the box can be set up after drying;(3) in the group of box bonding, the white mold should be taken gently, the coating layer shall be knocked off.The place reserved for bonding sprue, the coating layer should be completely scraped off;(4) improve the bonding process, no longer use paper tape, with alcohol paint instead;(5) the thickness of the casting coating layer is controlled at about 1mm, the coating is brushed twice.Direct runner brush three times, the thickness is about 1.5mm;(6) Before casting, each package must be cleaned with slag polymerization agent.