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Causes and prevention of slag inclusion defects

Qingdao Shengmei Machinery Co.,Ltd | Updated: Sep 04, 2017

1. The generation and prevention of metal slag defects:

1.1 When molten iron is melted, more or less slag is produced, especially when the burden is seriously rusted or iron filings molten iron is used to produce a large amount of molten the process of pouring, the slag easily goes into the mold with the molten iron, leaving it in the interior of the casting and forming black slag after solidification.

Because the density of slag inclusion is smaller than that of molten iron, it usually floats above the casting. The corner of the casting has a hindering effect on the slag. When the slag goes up, it is easy to be stranded, so the slag inclusion is also common in this part.EPC is pouring under vacuum has strong adhesion wall effect of molten iron, molten iron is preferentially along the wall filling, so under normal circumstances, EPC surface rarely seen in slag eyes, slag in subcutaneous casting.The main components of slag are metal oxide, carbide and so on. Molten iron slag is the main source of slag inclusion in epc. According to the causes of slag inclusion and the parts that are easy to produce, and combining the characteristics of metal mold filling in lost foam casting, the main measures for preventing the molten iron slag from casting are worked out as follows:

(1)Strengthen the work of skimming and slag disposal:Before release,the Slag Conglomeration Agent is sprinkled on the surface of hot metal and the slag is removed,let pour into the ladle molten iron slag in as little as possible.The slag conglomeration agent is sprinkled on the surface of molten iron in ladle and keep for 2~3min,let the slag floating polymerization, and then fully grilled scum or dregs before pouring. 

(2)Adopt teapot ladle pouring:When pouring remove the dregs in ladle spout,The bag is blown clean, ladle mouth blown clean sweep,then there will be no scum in the pouring out of,thereby minimizing the possibility of pouring slag into the castings,this is the best slag remove method,particular attention should be paid to the quality of the ladle lining, which can not cause the lining material to fall into the casting.

(3)Set the bottom pouring sprue and slag riser:The bottom pouring sprue can make the molten iron move from bottom to top smoothly,to fully ordered foam gasification and floating scum, casting slag is arranged on the top of the riser, easy to collect and remove scum.for the important castings, it is necessary to use the bottom pouring sprue and the slag riser.

(4)Adopt filter screen:The filter screen has very good filtration function to the tiny slag, especially in the early stage of pouring, the effect is obvious,But often in the later stage of the casting, the filter net is burned and pushing off the slag is failed, so the filter screen has enough fire resistance and erosion resistance.if we can control the clean molten iron, it is not necessary to use the filter; if the flow of slag more, even if the filter will fail.

1.2 Appearance defects and prevent casting residue when pouring EPC, foam and high temperature molten iron strong physical and chemical reactions, which in severe foam pyrolysis and gasification, gas produced by vacuum pump suction.Practice has proved that the pyrolysis of any foam can not be completely gasified, and eventually produce a trace of solid residues, commonly known as residues, the main component of carbon.When the molten iron is filled, the solid residue can not be discharged in time, and it will remain in the casting, forming a lost model and some black lump slag.The shape of the residue is almost the same as that of the slag. Sometimes, the two slag inclusions come together at the same time. It is difficult to distinguish because of the similar color.The number of solid residues in EPC is related to the density of foam pattern, the amount of adhesive used, the permeability of paint and molding sand, and the pouring temperature.According to the causes of the appearance of slag inclusion and the easily formed parts, measures for preventing the residue defects in castings are formulated as follows:

(1)Control the density of foam patterns:The lower the shape density, the faster the pyrolysis and gasification reaction, the less the solid residue, the more favorable to the casting molding, and reduce the chance of slag inclusion.In general, EPS pattern density control in 18 ~ 23 g/cm3, if the appearance itself is not easy deformation, the appearance of good shape, as far as possible in the lower density control.

(2)Reduce the amount of adhesive:Bonding pattern and gate should use adhesive, the amount of gas and residue of all kinds of glue is much larger than foam itself.Bonding pattern and pouring head, we should do as little as possible glue, for reducing slag, improve quality.But sufficient bond strength shall be guaranteed.

(3)Appropriately increase pouring temperature:The increase of hot metal temperature is beneficial to the full gasification and decomposition of the shape, and to reduce the amount of residue. But the improvement of the pouring temperature should be based on the prevention of sand sticking in the casting.

(4)Use hollow sprue:Hollow sprue smooth filling for molten iron, and reduce gas and residue, the difficulty of hollow sprue, the foam sheet cutting runner, but also as far as possible to choose low density board, density in 14 ~ 18g/cm in the actual production often ignore the sprue like density.

(5)The bottom pouring system is adopted:The bottom pouring type molten iron is filled from bottom to top, and the shape is decomposed and decomposed from bottom to top, which is favorable for discharging and rising of pyrolysis products.Top pouring, molten iron disorder, easy formation of foam slag entrainment.

(6)Setting run-off riser:A small slag riser is arranged at the top of the casting to float the residue and to assemble in the riser.For important castings, the principle of setting down slag riser is that they are many and small, scattered and homogeneous.In practical production, the slag riser shall be installed with the site of slag inclusion in the casting.

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