Solving the common defects of sand and slag in vanishing mold

In vanishing mold products, common defects mainly include sand inclusion and slag inclusion. In order to solve the defects of sand inclusion and slag inclusion, it is necessary to systematically and 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, and 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 and 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 and 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 not tight during tamping, and it is rushed into the cavity during pouring;(2) the shape of the sprue cup is not appropriate, resulting in excessive scouring force on the straight sprue during casting, washing off the coating layer of the straight sprue, and 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 and 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 and 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, and the molding sand in the sand box will be rushed into the mold cavity from the gap, resulting in sand clip;(5) direct sprays and castings after painting, the suspension mode on the paint car is not appropriate, resulting in too many places to repair when packing, if the repair is incomplete or 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 not completely removed before casting in the ladle;(2) in the pouring process, the ladle continues to produce slag, slag scraping personnel did not 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, or inappropriate, and molten steel reaction, produce a certain compound.

2. Solutions

After analyzing the defects of sand and slag inclusion, the technicians in the workshop solved them from two aspects of coating and 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 and protect the foam model, prevent liquid metal from seeping into sand, absorb decomposition products and allow decomposed gases to pass through the coating, maintain the integrity of the cavity formed after the foam model evaporates, and keep liquid metal heat from escaping quickly.Therefore, the vanishing mold coating should have sufficient refractoriness, certain mechanical strength, appropriate heat preservation and thermal conductivity, appropriate air permeability and the ability to absorb liquid decomposition products, smooth surface, sufficient coating performance, no chemical reaction with the foam model and other properties.Evanishing mold coating is mainly composed of refractory aggregate, suspending agent, binder, dispersing medium and additives to improve some properties of coating.

2.2 Adjust the white die bonding process

On the basis of not adjusting the formula, the production workshop strengthens the brush coating process and adjusts the bonding process.

(1) first paint to brush evenly, not too thick or brush less than the parts;(2) after the white mold coating is dried, the coating falls off and cracks are repaired by brushing, and 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 not 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, and 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.


Post time: Mar-05-2021