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China street lighting cast part suppliercombined with many years of production practice experience, talk about the causes and preventive measures of shrinkage and shrinkage of castings.
When shrinkage defects appear, you should look for problems from the gating system, because shrinkage defects are greatly related to shrinkage.
(1) The riser design failed to promote sequential solidification. The position and size of the riser must be designed according to the different conditions of the casting cross section. It is necessary to consider which sections are solidified first and which are solidified after there is no riser. The last solidified section must be in the liquid state Mouth or riser.
Cast Aluminum Gates Casting Gates
(2) Insufficient number of Cast aluminum gates casting gates or improper gate design. Insufficient number of sprues is a common cause of shrinkage defects. The filling distance and range of each gate are limited. The size of the filling range depends on the thickness of the section, the temperature of the molten metal and the metal composition. Condensation on thinner sections is fast and cuts the shrinkage channel. Improper gate design, if the cross section of the gate is too small, it will cause premature condensation. At this time, although there is a lot of metal liquid in the riser, it can not be refilled into the casting.
(3) The riser is too small. Too small a riser is also a common mistake. In general, the cross-sectional size of the riser should be larger than the cross-sectional size of the casting that needs to be reduced. Another mistake is to increase the shrinking effect by increasing the height of the small diameter riser. This approach is often unsatisfactory because the diameter of the riser is small and the liquid metal in the riser is easy to condense, even if the height of the riser is increased. To no avail. The ideal shape of the riser should be spherical, because its heat dissipation area is the smallest. In some cases, chilling of thick sections is an effective and practical approach.
(4) Improper ratio of riser neck and casting size. The size of the feeder neck is very important for the shrinkage efficiency. The cross section size of the feeder neck is too small to affect the shrinkage effect. It is necessary to ensure that the metal liquid is unblocked in the feeder neck.
(5) The gate is too large. Shrinkage at the gate entrance or at the gate is usually caused by the gate being too large. Because the entrance of the gate is enclosed in hot sand, if its size is too large, the molten metal at the entrance will remain until it finally solidifies. Since no other metal solution can supplement it at this time, Shrinkage can occur at the gate entrance. The correct design of the riser should first solidify the casting, then solidify the inner gate and the riser neck, and finally solidify the riser. If this sequence of solidification is disrupted, shrinkage defects will occur.
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