The shaft sleeve is one of the main parts of the gear pump. It is installed on the two ends of the high-speed gear to support the bearing. It must have sufficient strength and good wear resistance. In order to ensure the performance requirements of the parts, our factory uses non-standard aluminum-tin alloy, and the role of Cu is to strengthen the matrix. Sn can form a softer, low melting point Al-Sn eutectic and increase wear resistance.
The original heat treatment process is 515℃ solid solution 6h water cooling, 180℃ aging 8h air cooling. There are two problems with this process:
It can be seen from the metallographic observation and mechanical property test data that the 250℃×7h treatment process is ideal. The Al-Sn eutectic is distributed along the grain boundary in a broken network. On the one hand, the distribution of the Al-Sn eutectic is relatively uniform to ensure good wear resistance. On the other hand, the Al-Sn eutectic does not have a divided matrix, which makes the alloy better The plasticity and toughness. The higher hardness can be obtained by the 250℃×7h treatment process because the alloy contains less Cu and the metal mold has a fast cooling rate. During the casting cooling process, Cu has been ensured to melt into the solid solution and play a quenching effect. The increase in hardness through natural aging also proves this.
The tensile strength of 250℃×7h air cooling process is 47% higher than that of 515℃×6h water cooling+180℃×8h air cooling process. The 250℃×7h air cooling process temperature is slightly higher than the melting point of the Al-Sn eutectic, in order to obtain the broken network distribution of the Al-Sn eutectic through a shorter holding time without overburning the eutectic.
On the basis of the process test, a small batch (400 pieces) of trial production was carried out. After the hardness and metallographic inspection and the product delivery test on the test bench, all the products were qualified.
The process was officially put into production in 1996, and hundreds of thousands of shaft sleeves have been produced, all of which are qualified. The work efficiency is increased by 1.3 times, and it can save about 70,000 yuan a year and save more than 80,000 kW.h of electricity.
