How to measure the fluidity data of alloy prototype model
How to measure the fluidity of the alloy prototype model
The size of the alloy fluidity value. It is usually measured by the length of spiral fluid specimens. Pour the metal liquid into the spiral sample mold, the longer the spiral sample is poured, the better the fluidity.
alloy shrinkage and its effect on casting mass basins
during solidification and cooling of castings, the phenomenon of reduced volume and size is called contraction. The metal is cooled from the pouring temperature to the room temperature through three shrinkage stages: Liquid shrinkage, solidification shrinkage and solid shrinkage. In the stage of liquid shrinkage and solidification shrinkage, the casting is prone to shrinkage and shrinkage defects. The shrinkage of these two stages is represented by the shrinkage of the body. The solid-state shrinkage phase only causes changes in the external dimensions of the casting, making the casting easy to produce defects such as internal stress, deformation and cracks. The amount of shrinkage is indicated by the line shrinkage.
factors affecting the shrinkage of the alloy
(1) Cast alloys with different chemical composition have different shrinkage. In common alloys, the shrinkage of cast steel is large, and the gray cast iron is small. Silicon promotes the reduction of shrinkage, and sulfur increases the shrinkage.
(2) The higher the pouring temperature, the greater the overheating of the alloy, and the liquid shrinkage. The pouring speed is slow or the continuous pouring of high-temperature alloy liquid in the clear riser, so that the liquid and solidification shrinkage of the casting are compensated in time, the total volume shrinkage of the casting is reduced, and the shrinkage volume is also reduced.
(3) Casting conditions and casting structure casting materials have a great influence on the cooling rate of castings. The wet type has a greater cooling capacity than the dry type, narrowing the solidification area and reducing shrinkage. The cooling capacity of the metal type is greater, so the shrinkage is more significantly reduced.
The side value method for the fluidity of the alloy prototype model
The alloy is not free to shrink in the mold, but is blocked to shrink. On the one hand, the reason for the obstruction is due to the mechanical resistance of the mold and core to the shrinkage of the alloy; On the other hand, the cooling rate of each part of the casting structure is different, which restricts each other and creates resistance to shrinkage. Therefore, the actual line shrinkage of the casting is smaller than the free line shrinkage of the alloy.
shrinkage and shrinkage
when the liquid metal is solidified in the mold, if the shrinkage is not replenished, holes will be formed in the place where the casting is solidified, this hole is called shrinkage. According to the size and distribution of holes, shrinkage holes are divided into two categories: concentrated shrinkage and dispersed shrinkage. Generally, the concentrated shrinkage cavity is called the shrinkage hole, and the dispersed shrinkage hole is called the shrinkage hole.
(1) The formation of shrinkage cavity often occurs in the upper part of the casting or in the thick part. The shrinkage cavity is a hole with large volume, irregular shape, inverted conical shape, and rough inner surface. Alloy with pure metal, co-crystal composition or narrow crystal spacing is prone to shrinkage.
The formation process of shrinkage cavity is shown in Figure 2-As shown in 4, after the metal liquid is full of mold [Figure 2-4 ()] , Due to the heat absorption of the mold, the metal close to the surface of the cavity is quickly reduced to the solidification temperature, forming a layer of shell [Figure 2-4 (B)] , The temperature continues to decline, the solidification layer is thickened, the remaining liquid volume is reduced, and the liquid level is reduced without replenishment. There is a gap in the casting [Figure 2-4 (C)]; The temperature drops again, the Shell continues to thicken, and the liquid level drops continuously. When the interior is completely solidified, the shrinkage cavity is formed on the surface of the casting [Figure 2-4 (D)]. The casting that has produced shrinkage has cooled from the solidification temperature to room temperature, and the outer profile size of the casting has been slightly reduced due to solid shrinkage [Figure 2-4 (E)〕.
(2) The alloy with a wider crystal spacing is easy to form shrinkage during solidification. The formation process of shrinkage is shown in Figure 2-As shown in 5, the picture is a cylindrical casting. The casting begins to solidify from the outer layer first, but the solidification front is uneven [Figure 2-5 ()]; The heat dissipation conditions in the circular direction are similar, and the solidification front reaches the center almost at the same time, forming a simultaneous solidification zone and dividing it into many small liquid zones [Figure 2-5 (B) ], When these small liquid areas with a large number of quantities are solidified and contracted, they are not replenished to form a contraction of pine kernel Figure 2-5 (C)] E
shrinkage is divided into two categories: macro shrinkage and micro shrinkage. The former is mostly distributed below the shrinkage hole or at the central axis of the casting section, which can be observed with the naked eye or magnifying glass (Figure 2-6). The latter is distributed in branches or crystals, and is small in size and can only be observed under a microscope. The existence of micro-shrinkage basically does not affect the mechanical properties of the alloy, so it is not treated as a defect in general castings. When the casting has high air tightness or special physical and chemical performance requirements, it is necessary to prevent micro-shrinkage, but it cannot be ensured by selecting an alloy that does not produce shrinkage.
(3) The method of preventing shrinkage cavity is caused by the lack of metal liquid supplement during solidification and contraction. Therefore, as long as the casting solidification is reasonably controlled and the sequential solidification principle is adopted, the shrinkage cavity on the casting can be prevented.
The process measures of the sequential solidification principle are: add a riser in the upper part or thick part of the casting, so that the solidification of the liquid alloy starts to solidify from the point away from the riser, then it is solidified near the riser, followed by the order of solidification of the riser (Figure 2-7) After the solidification part is achieved, the effect of the first solidification part is reduced, so that the shrinkage cavity is transferred to the riser. The riser is the excess part, and the casting without shrinkage defects is obtained after removal. When there are many large parts of the casting, the sequential solidification can be achieved by adding process measures that combine cold iron with the riser (Figure 2-8). Cold iron is made of cast iron or steel, and its function is to speed up the cooling rate of large parts. Sequential solidification is mainly used for alloys with large solidification shrinkage and small crystal spacing. For example, cast steel, brass and other castings.
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