What should be paid attention to in the design

by:Top Talent     2020-07-15
Generally, malleable iron castings are made of white cast iron blanks through graphitization and annealing, so the wall thickness of the castings should not be too thick, otherwise gray or pitting structures are likely to occur, which reduces the mechanical properties of the castings. According to the data, when melting in a cupola, the maximum wall thickness of malleable cast iron parts should generally not exceed 25 mm; when melting in an electric furnace, the maximum wall thickness should not exceed 35 mm. Generally only suitable for the design of thin-walled small castings, the most suitable wall thickness is 5-16 mm, the wall thickness should be as uniform as possible. In order to increase the regularity, the cross-sectional shape is designed to be T-shaped or I-shaped, to avoid the cross-shaped cross-section, and the locally protruding part should be reinforced with ribs.

Malleable iron castings are cast with molten iron of low-carbon, low-silicon white cast iron composition. The molten iron of this composition shrinks greatly, and it is easy to produce shrinkage holes, shrinkage and cracks in the thick parts of the castings and hot joints, and it is often necessary to set up a riser to compensate. When designing the structure of castings, it is necessary to provide convenience for the riser and to improve its packing effect. In some cases, ribs can be added as supplementary channels to facilitate the elimination of shrinkage holes and shrinkage.

In order to prevent cracks, a structure conducive to free shrinkage should be adopted, or the structural strength where cracks are prone to be strengthened. For some malleable cast irons with larger planes, in order to prevent cracks, grid ribs (grid rib spacing 12-17 mm, rib height 3-5 mm) can be provided on it, of course, this grid The ribs should only be arranged on a plane that does not interfere with the draft. In addition, reinforcing ribs can also be used to prevent cracks at joints of different cross sections.

The malleable cast iron is a large cast iron structure before being annealed without graphitization, which is very brittle and easily broken. In order to prevent the protruding parts on the white blanks that have not been graphitized and annealed from being easily damaged during cleaning and transportation, reinforcement ribs are often used to reinforce the place.

When graphitizing annealing is performed on malleable iron castings, deformation is likely to occur due to graphitization expansion and castings squeezing each other in the annealing tank. This should be noted when designing the casting structure, and reinforcement ribs can also be added to prevent deformation. However, when such reinforcing ribs are not allowed in the product structure, they should be removed after annealing; if there is no hindrance, the removal may not be specified after annealing.

Because malleable cast iron has a certain plasticity, some parts can be corrected on the pressure mechanical forging hammer and improve its dimensional accuracy. In the latter case, in order to obtain a relatively large specific pressure on the squeezed surface, the surface should be as small as possible and should be smaller than the support surface, otherwise the deformation will occur on the support surface that does not need to be compacted . Of course, reducing the size of the extrusion surface can also reduce the tonnage of the press or forging hammer.
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