What are the causes of ejection rod breakage?
Release time:
2020-09-27 12:02
Source:
Fatigue failure.Ejection barThe working process of the ejection bar is a process of alternating stress, so any factor that causes stress concentration may lead to fatigue failure. For example: 1) Steps with large changes in shaft diameter. 2) Transition parts without fillets, undercuts, etc. 3) Surface scratches or machining threads accidentally damaging the surface of the shaft. 4) The surface roughness of the thread is too large. 5) The thread is compressed for a long time, and the surface is damaged due to insufficient surface strength (at the mold adjusting nut). 6) Improper heat treatment of the thread surface can cause stress concentration. 7) Material defects.
Overload fracture caused by the type of ejection bar depends on the deformation of the four bars to obtain clamping force. If the lengths of the four bars are different, the deformation will be different. For example, if one of the four is shorter, the shorter bar may bear a load far greater than the 1/4 clamping force it should bear, which will cause fracture. Temperature strain can cause fracture. If the lengths of the four bars are different, for example, one bar is long and three bars are short, the thermal stress caused by a sudden high temperature or a drop in the longer bar will be constrained by the other three bars and be static, causing the bar to fracture. If the mold becomes uneven due to compound strain, the comprehensive error of the connecting rod length (hinge), bearing seat height, and ejection bar length is too large. After straightening the connecting rod, the force on both sides will be uneven. Then: 1) Cause the rear template to swing, the tie rod to bend, and under the action of bending stress and tensile stress, the tie rod is easy to break. 2) If the product spews water, inexperienced operators will usually further increase the clamping force, which will cause the tie rod to break and the mold to deform due to overload. The damage caused by instantaneous impact stress is because the toggle type can only release the clamping force before opening the mold. Therefore: 1) The instantaneous impact when opening the mold will cause machine vibration and damage to the tie rod and other parts. 2) Because the entire clamping part (including the mold) is under stress for a long time, it will cause premature fatigue failure of the parts.
Solution 1. In the design, avoid abrupt changes in shaft diameter. At steps or undercuts, try using larger fillet transitions, select materials with better comprehensive performance, and special treatment must be carried out to solve the problem of thread surface hardness (wear), and also try to reduce surface stress concentration, improve surface finish, and minimize stress damage. 2. Ensure machining accuracy, especially the length of the connecting rod, the height of the bearing seat, the accuracy of the crosshead, and the positioning accuracy of the bearing seat on the template. 3. After assembling or disassembling the mold adjusting nut, pay special attention to the length of the four tie rods, and the distance between the mold adjusting nut and the rear template must be adjusted. 4. Analyze the reasons for product blushing, do not unilaterally increase the clamping force, if the mold is found to be uneven, it should be ground flat, if the length of the connecting rod is uneven, it should be corrected, including copper pads, paper, etc., or the corrected mold adjusting nut.
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