Aluminum alloy casting mold ejector pin sticking, causes and long-term improvement plan
Pin sticking is a common fault in continuous mass production of molds, which can cause casting top deviation, deformation, and pulling, forcing the production line to stop and disassemble.
The unilateral gap between the top pin and the guide sleeve is less than 0.015mm. After heating up, the probability of jamming increases by more than 60% due to thermal expansion and compression.
If the gap exceeds 0.06mm, aluminum liquid is prone to enter the fitting gap, forming aluminum slag bite, which can also cause the top pin to get stuck.
The recommended clearance range for conventional top pin matching is 0.02-0.04mm, taking into account both guidance accuracy and thermal expansion margin.
Splashing of aluminum liquid and accumulation of release agent residue at the root of the ejector pin are the most common causes of intermittent jamming, accounting for 64% of faults.
There are more ejector pins in the circular mold of the wheel hub, making it easier for dust residue to accumulate, and the inspection pressure is higher compared to the mold of the chassis shaped parts.
There are many sand and dust factories in the Middle East, with high levels of impurities in the air. The speed of slag accumulation in the top needle matching area is 2.5 times that of inland factories.
When designing molds, Xinfeng Machinery will add slag discharge slots on the ejector pin plate to reduce the accumulation of residue at the ejector pin fitting position.
Many factories deal with sticking by directly grinding the outer circle of the top pin, and the gap continues to increase after grinding, resulting in repeated aluminum running problems in the later stage.
After the wear of the nitride layer on the surface of the ejector pin, the friction coefficient increases and the frequency of jamming increases, requiring the replacement of a new ejector pin spare part.
The guide sleeve of the ejector pin plate is worn, the guide is offset, and the ejector pin is subjected to lateral force. Even if the clearance is qualified, it will continue to be stuck and pulled.
The fatigue fracture of the ejector spring prevents the ejector pin from fully resetting, resulting in direct compression and bending of the ejector pin during mold closing, which is a destructive fault.
The selection of springs should match the ejection stroke, and high-temperature resistant springs should be selected for high temperature conditions. Ordinary springs decay rapidly in an environment of 200 ℃.
Google casting mold ejector pin sticking belongs to the long tail keywords of operations and maintenance, suitable for maintenance engineers to search and consult.
This type of malfunction belongs to the high-frequency problem of existing molds, and the content can be taken on by old customers for operation and maintenance consultation to enhance trust.
The internal pressure of CPC molds is high, and aluminum slag on the parting surface is more likely to enter the needle gap, resulting in a higher frequency of stuck maintenance than LPDC molds.
During each mold maintenance, clean the residue at the root of the ejector pin and apply high-temperature lubricating grease, which must be suitable for the aluminum casting conditions.
Improper selection of lubricating grease can lead to the formation of hard carbon deposits after high-temperature carbonization, which in turn exacerbates the sticking of the ejector pin.
During mass production, the sticking of the ejector pin is mostly not a sudden occurrence. Early warning signs such as abnormal ejector noise and slow return may occur.
Establish a checklist to record abnormal noises and return delays, maintain in advance, and avoid sudden downtime causing greater losses.
## FAQ
Q: What is the recommended interval for the clearance of the top pin?
A: Conventional 0.02-0.04mm, with reserved thermal expansion allowance.
Q: What happens if the gap is too small?
A: The risk of jamming increases by more than 60% due to thermal expansion and compression.
Q: What is the main cause of needle sticking?
A: Aluminum slag and mold release agent residue accumulate, accounting for 64% of the faults.
Q: What are the hidden dangers of polishing the top pin to solve the problem of jamming?
A: The gap becomes larger, and subsequently the aluminum liquid enters the gap and repeatedly gets stuck.
Q: How to choose a spring for high temperature working conditions?
A: Choose high temperature resistant springs to slow down elastic attenuation.
Q: Is the maintenance frequency of CPC mold ejector pins higher?
A: Yes, aluminum slag is more likely to enter the fitting gap.
Q: What are the signals in the early stage of needle sticking?
A: Abnormal noise and slow return are warning signals.
Q: Can lubricating grease be used freely for top pin lubrication?
A: No, it needs to be adapted to high-temperature casting conditions to avoid carbonization and carbon deposition.
