Causes of hot loosening of mold bolts, locking schemes, and regular inspection specifications | Failure protection of high-temperature mold fasteners
Under high temperature repeated thermal cycles, bolts loosen and elongate, causing 42% of the inserts to shift, aluminum to run on the parting surface, and cooling inserts to leak water.
Ordinary grade 8.8 carbon steel bolts under long-term working conditions above 250 ℃ will experience yield strength attenuation, plastic elongation, and loss of preload force.
The bolt did not use anti loosening gaskets or high-temperature thread glue, and under the alternating cold and hot conditions, the thread gap slipped and gradually loosened.
Insufficient pre tightening torque, the pre tightening force returns to zero after heating and expansion; Excessive torque, bolt pre tension overload, direct fracture.
The distance between the bolt hole and the heated area of the mold cavity is too close, and the bolt temperature is higher than that of the surrounding template, which amplifies the expansion difference and tends to loosen.
The locking sequence of multiple bolts is disorderly, the force on the inserts is uneven, and local bolts fail first due to overload, resulting in chain loosening.
Low pressure die-casting molds (LPDC), reverse pressure casting molds (CPC), differential pressure casting molds for wheel hubs, low-pressure casting molds for wheel hubs, gravity casting molds, motorcycle wheel hub casting molds, structural component casting molds, aluminum alloy wheel hub molds, aluminum casting forming molds, low-pressure casting tooling molds, inserts, cooling inserts, and mold frame pressure plates are high-risk locations for bolt failure. Zhejiang Xinfeng Machinery's export molds uniformly use high-temperature resistant 12.9 grade alloy bolts, matched with disc springs to compensate for thermal expansion and contraction, without relying on ordinary spring washers. Locking follows the principle of diagonally increasing pressure in 2-3 steps to reach the target torque. Every 4000 cycles of shutdown and re tightening inspection; The three high-temperature workshops have been shortened to 2500 mold cycles. Once the bolt is stretched or the thread is damaged, it should be replaced directly and not reused. Many customers use ordinary bolts for long-term production, which is stable in the early stage. However, after thousands of molds, the inserts suddenly shift, causing significant scrap.
FAQ
1. Question: What is the recommended grade for high-temperature mold bolts?
Answer: Priority is given to 12.9 grade high-temperature resistant alloy bolts.
2. Question: Is it a better anti loosening solution than ordinary elastic pads?
Answer: Disc spring compensation, adapted to changes in preload force caused by thermal expansion and contraction.
3. Question: What are the key points for bolt locking operation?
Answer: Diagonal step-by-step locking, apply 2-3 times to the rated torque.
4. Question: What is the regular bolt re tightening inspection cycle?
Answer: Two shifts have approximately 4000 cycles, and three shifts have 2500 cycles of high temperature.
5. Question: Short plate of 8.8 grade carbon steel bolt?
Answer: Strength attenuation above 250 ℃ makes it easy to elongate and loosen.
6. Question: Can elongated deformed bolts be reused?
Answer: Reuse is prohibited, replace the bolts directly with new ones.
