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Casting misrun and cold insulation defects

by:BoQiao Machinery     2020-12-28
Misrun and cold shut is fairly common defects in casting, in many cases, these two kinds of defects in fully scrap castings in the first or second. Misrun is not full of mold cavity and the formation of liquid metal incomplete castings, the characteristics of this kind of defect is casting wall has a smooth round the edge of the perforation, or one or more of the terminal is not full of casting metal liquid; Cold-lap refers to the two strands of metal together, because of their failure to fully fusion and obvious discontinuity defects of castings, such as the appearance of the defect, often appears as a smooth round edge crack or wrinkles. The characteristics of these two kinds of defects: it is easier to find in the casting inspection; Second, in addition to the cleaning process, the causes almost exists in each process of the casting. Combined with many years' production practice of the author and refer to the below information, talk about the reason of misrun and cold shut castings and its prevention measures. 1. Casting and appearance design, 1) Caused by uneven casting section thickness of the metal flow, in some casting design, thin cross section is located in the part of the liquid metal is difficult to achieve, it is difficult to properly set the gating system. Where possible, to deal with this kind of design modifications, when cannot change the design, will be expected to adopt complicated gating system, to avoid this kind of defect. ( 2) Casting section are relatively thin, this design failed to account for the rule of metal flow and solidification. If designers can't upset the cross section, the only remedy is to improve the pouring temperature of the metal, or modify the chemical composition of the metal, in order to improve its liquidity. There is also a good make up for the solution is to use does not produce rapid cooling mold ( Core) , but that would make the cost of production increase, so where possible should change the design. 2. ( 1) Appearance or the core box of wear and tear caused by casting thin section, sand wear is quite a strong material, will cause the shape wear, causing the casting section thinning, lead to produce misrun and cold shut defects. Effective prevention measures is to establish a regular inspection system, the defective appearance check out. ( 2) Image intensity difference! In modelling or core, under the pressure of the shape deformation due to insufficient strength, appearance and core boxes such as mold and core deformation. Both liquid metal will cause the failed to according to the expected flow, and can form casting thin section. Correction of the reinforcement method to be like. ( 3) Shape or core box positioning, its causes are positioning pin and pin has been wear and tear, locating pin too little quantity is too small or dowel dimensions are prone to wear and tear. On the upper and lower die plate according to the center line of the installation is divided into two and a half of the look, also can appear dislocation defect. If the sample not try pouring casting, it is hard to confirm partial shipments on the upper and lower die plate is aimed at the two halves of the shape. Primary measures to prevent to produce this kind of defect is to strengthen the inspection. 3. Sand box and its preparation ( 1) Box wrong box casting is too thin, up and down of the cause of the defects including: wear dowel pin, positioning pin bending, pin set of wear and tear, or in cases of ear contains foreign impurities. Due to the wrong box is one of the main causes of casting defects, so must regularly carry out repairs and maintenance for these parts. ( 2) Shape improperly installed, this kind of situation is generally installed workers caused by the careless operation. Shape and mold on the centerline on the floor must be very clear, so that was easy to check. ( 3) BoPing casting pouring slope is not enough, for some castings with thin, to make the sand box when pouring can maintain a declivity, forms a closed gas, otherwise it will cause metal flow. After sand box tilt, the height of the box to keep enough, the gate location than casting vertex. ( 4) Sand box enough stiffness or reinforcement is undeserved, also can make deformation of sand mold and produce misrun and cold, so must use has enough strength of sand box, use for a considerable time before using sand box should be reinforced. ( 5) On the box is too shallow, may cause the hang type, thus narrow the casting section, the thinning, that produce the defects of misrun. When pouring thicker castings, there are insufficient for metal pressure on the box is too shallow and lead to shrinkage and intrusion porosity; And when pouring thin castings, the consequences are off the sand or the defects of misrun. 4. Poured riser system ( 1) The sprue, runner and sprue improper way of section size, in order to avoid the phenomenon of metal flow pulsation, design of gating system should be in accordance with the following requirements, which must make the sprue and runner possesses enough size, to ensure the smooth sending metal to all internal sprue.
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