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Production and prevention of sand defects in EPC equipment

Qingdao Shengmei Machinery Co.,Ltd | Updated: Apr 27, 2017

In the process of re-production of EPC equipment, there will be sand defects, how to prevent this situation in advance?

Reasons for the defects of sand clamp
The sand clamping is another main form of casting inclusions defect, mainly in the molding sand with the molten metal pouring into the cavity and is stuck inside the casting. Sand clip and slag the appearance of the difference is: After machining the sand is the white granular, the size of the sand grains, more found in the casting position of the upper surface of the subcutaneous. The main ingredients of the sand clip are SiO2, such as the coating is broken when pouring, the coating together with the type of sand into the casting of molten iron and the formation of sand clip. Because the sand is the molten iron flowing through the type of broken wall into the sand caused by the pouring edge, so the other parts of the castings can often see the sand clip. In contrast, molten iron slag generally enters the mold at the initial stage of pouring, its distribution is relatively concentrated, and the distribution of sand clip is relatively scattered. Compared with the traditional sand mould casting, the EPC adopts dry sand molding, the sand clamping defect is generally dispersed and the granular, rarely block. The main reasons for the defects of sand clamp are that the adhesive seam is not tight, the casting system has sharp angle, the coating is too thin, the local leakage coating and the low strength of the coatings are caused. In addition, the pouring cup and the top of the direct runner contact the site, such as tight seal, dry sand is easy to enter the straight runner with molten iron into the cavity formation of sand. It is necessary to note that the formation of sand clip is not only the molding use of sand, paint, slag, poured cup knot into the formation of the cavity of the defects, commonly known as sand clip.

Measures to prevent sand clamping defects
(1) Guarantee coating continuous, homogeneous, complete: according to our country lost foam casting raw materials, craft and negative pressure pouring in the actual situation, small casting coating thickness general control in 1~2mm advisable. Pouring system due to hot metal scouring time long, momentum, the gate coating is generally thicker than the casting coating, the actual operation can be thickened. Control the entire coating does not crack, not breakage, do not leak white.
(2) To improve the appearance of bonding quality: the appearance and the gate of the bonding seam should be tight, there is no openings and gaps, to prevent the penetration of the seams of paint. The appearance and the gate junction should be smooth transition, avoid the runner and the appearance of the adhesive site there is sharp angle, resulting in pouring sand.
(3) To improve the coating strength: the appropriate coating strength is conducive to resistance to hot metal scouring, paint ratio, refractory binders and organic binders to match reasonable, so that the coating has a good comprehensive strength, enhance the ability to withstand high temperature scouring. Bentonite, Silica sol, water glass and other inorganic binders are conducive to maintaining the high temperature strength of coatings.
(4) Use of special pouring cups and sealing mud: Dry sand molding need to use plastic film sealed sand box, the foam straight runner top cover under plastic film. The above need to place or erect the pouring cup, such as for erection of pouring cup of the iron mouth to have a certain straight segment to make the Tieliu cylindrical whereabouts, the erection should be with the foam straight runner Center to the positive; for placing poured cups under the combination of refractory mud and plastic film with tight, in both cases to master the outlet of the cup is less than the direct runner, to prevent the high temperature metal liquid flow will dry sand rushed into the castings.

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