What is casting hot cracking? How to eliminate it? What measures are used?
(3) the use of phosphoric acid curing agent, because sulfonic acid curing agent easy to cause the surface of the casting of sulfur, causing cracks in the surface of the casting, become a crack source(4) using thermal expansion coefficient of smaller molding materials, such as chromite, sand, etc. instead of quartz sand(5) to reduce the thickness of the sand core, such as using hollow sand core, for example, a kind of valve casting, only by reducing the thickness of the core sand layer and changing the connection method of core bone, it eliminates the hot cracking defects of the casting(6) use cold iron reasonably or find other cooling measures in a crack prone place(7) using the coating which can effectively reduce the sulfur leaching4. casting structureThe size and shape of the casting, is decided by the designer, production can not be changed. However, in the corner of the garden size, the thickness of the transition process, in consultation with the relevant departments to make appropriate amendments in accordance with the design, casting production requirements.The above factors have an effect on hot cracking of cast steel. But for a specific casting, only some of the factors may be the main ones
2. resin sand casting process(1) to meet the requirement of filling of castings, the pouring temperature of molten steel shall be reduced as much as possible. The carbon steel of 0.19%C is poured at 1550 DEG C and poured at 1600 DEG C, and its thermal cracking resistance is almost twice as high(2) for thin wall castings, a higher casting speed should be adopted. For a cast steel, the weight is 125Kg, the wall thickness is 15mm, the casting time is 14 seconds, no hot cracking occurs, and the crack is observed until 40 seconds(3) it is an effective measure to prevent the hot cracking of cast steel parts by setting up anti cracking bars at the crack of casting(4) loosening the box in time will also help reduce hot cracking because it can reduce the shrinkage stress of the casting3. molding materials(1) reduce the amount of resin added, or modify the resin, so that the resin has a thermoplastic, so that furan resin in high temperature without coking or less coke, so as to ensure that it has a good high temperature tolerance(2) adding additives in furan resin sand, the resin sand with thermoplastic or blocked; the most serious in the contraction, wood powder, foam beads; or in the mold plastic parts into the corresponding block of concessions, improve its high temperature deformability.
Measures to prevent hot cracking defects in castingIn order to make resin sand casting, especially furan resin sand casting to avoid or reduce thermal cracking, the following measures can be taken:1. alloy aspects(1) the sulfur content control of castings, should be below 0.03%, and avoid type casting. (sulfide sulfide appears in steel castings in three forms, namely I, II and III, the sulfide type along the grain boundary, a discontinuous shape, easy to cause the casting hot cracking.) through the adjustment of distribution pattern of manganese and sulfur to alter sulfur.(2) for carbon steel, S+P should be less than or equal to 0.07%, because the additive effect of sulfur and phosphorus, the hot cracking tendency of increase.(3) A1 -, should be less than or equal to 0.1% residues A1 residual aluminum; A1 residual high, is conducive to the formation of A12S3, and may even form the steel A1N, the fracture showed "rock", greatly reduce the steel anti cracking ability.(4) the steel grain refinement can. Such as adding rare earth and calcium in molten steel, both deoxidation and desulfurization, and grain refinement. The determination of NiCrMoV steel showed that under the same conditions, the liquid steel rare earth calcium + treatment, compared with untreated molten steel, its cracking resistance more than 2 times.
