Castings deformation is an common problem in casting production, so how to prevent it? Let’s learn together.
Causes of Casting Deformation
(1)The casting structure design is unreasonable. The difference between the thickness of the casting wall is too large, which makes the cooling rate of the casting uneven,and affects the normal shrinkage and deformation of the casting;
(2)The shape and dimensions of the casting caused by the casting stress do not conform to drawings;
(3)The sand box structure design is unreasonable. The distance between the box stop and the convex part of the casting is too close, and the amount of sand is small, which hinders the normal shrinkage of the casting;
(4)Improper setting of pouring (riser) opening. The gate or riser is too close to the box stop or the convex part of the casting, and the amount of sand is small, which prevents the normal shrinkage of the casting;
(5)The core bone eats less sand or the core sand has poor retreat performance, which hinders the normal shrinkage of the casting after pouring;
(6) Premature boxing will cause the castings to cool rapidly and unevenly, which will affect the normal shrinkage of the castings and sometimes cause the castings to burst;
(7)The wooden mold material is not dried or the wooden mold structure is improperly made, and the setting position is incorrect. The size of the wooden mold is shrunk and the actual objects do not match the drawings;
(8)Slam the wooden mold when modeling, make the wooden mold bend and warp, and the cavity will be out of shape;
(9)The modeling sand is not balanced and uneven, and the wooden mold is skewed incorrectly;
(10)The sculptor disassembled the mold from the wooden mold, but did not put the mold in place when sculpting, and lacked a mold in the casting;
(11)After the wooden mold is finished, and the core box is made or not, the sculptor will not fit the clay core according to the wooden mold and cast a solid iron casting.
(12)When the casting enters the pit, the casting part is not placed properly, the middle is suspended or the triangle is effective, and the suspended part is not tightly pillowed, so that the casting is deformed during aging.
Knowing that there are so many more reasons to cause the casting deformation, following let us study the prevention method.Prevention Method of Castings Deformation
(1)Improve casting structure
In the preparation of the casting process or in the production practice, it is found that the casting structure design is unreasonable and the wall thickness difference is too large, it is recommended that the relevant department propose a modification of the casting structure plan. Regarding the casting angle, adjust the position and number of gate risers to achieve sequential solidification, uniform cooling and simultaneous shrinkage.
(2)The casting itself is deformed due to casting stress
When making wooden molds or shapes, relative technical measures should be taken to make corresponding reflexes. As shown in Figure 4-36 to Figure 4-38. Keep the casting straight after shrinking.
(3)When designing a sand box or selecting an old sand box, there should be a certain amount of sand between the box stop and the raised part of the casting.
Generally, the amount of sand eaten is not less than 60mm, and the medium and large pieces are not less than 120~180mm. If necessary, after pouring, when the casting has not yet shrunk, shovel or dig out the sand between the box stop and the protruding part of the casting to allow the casting to shrink freely and normally.
(4)Set the pouring (riser) position reasonably
There must be a certain distance between the pouring (riser) mouth and the box stop to keep a certain amount of sand. If necessary, after pouring, when the casting has not yet shrunk, knock out the molding sand at the pouring (riser) opening, and knock off the pouring (riser) opening when necessary to allow the casting to shrink freely and normally.
(5)When making core bones, you must leave a certain amount of sand to eat
See Table 3-1. At the same time, the core sand must have a certain degree of concession. Add 2% to 3% sawdust to the core sand and sift it with a fine screen. Add 3% to 5% of the coke from the oven, crush it, and sieve with 8 to 10 mesh. After the two are added to the core sand and mixed and milled, the air permeability, concession and temperature resistance of the core sand are improved.
(6)Boxing of castings after pouring should not be too early
After pouring, castings should not be boxed too early, especially for machine tool bed gearboxes and large and medium-sized castings. At the same time, water chilling is not allowed to avoid aggravated cooling of the castings and allow the castings to cool and shrink freely and obtain high-quality castings. However, there are some types of castings with simple structure, such as heavy dead iron, etc. In this case, watering and chilling in advance is allowed.
（7）To make a wooden mold, the wood must be dry and the structure must be reasonable. After the wooden mold is made, the core and movable parts must be marked. At the same time, the self-inspection and the special inspection are combined to avoid errors such as shrinkage of the wooden mold size and processing allowance. After modeling, the wooden mold should be laid flat and filled to avoid warping and deformation of the wooden mold.
（8）Wet pit modeling: Fill the top of the pit with paving sand, similar in shape to the wooden mold, and then put in the wooden mold, plug the molding sand and compact it with wooden strips (as shown in Figure 4-41, purpose: knock wood Mould and scraper) Place it on the wooden mold, use a hammer or wooden hammer to strike the strips in order to make the wooden mold sink and firm the surface to avoid warping of the wooden mold, and then put a pressure iron on the wooden mold to pick up sand Balance and pound the sand in order to avoid the movement of the wooden mold.
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