Objective  In order to solve the problems that the seed guard belt is easy to deviate and slip in application of the combined type-hole metering device of rice precision hole seeder, which leads to serious wear of the seed guard belt and high rate of seed damage.

Method  The synchronization principle of seed protection mechanism was analyzed, and the shaft sleeve structure(A) and the hardness of seed guard belt(B) were optimized. A two-factor experiment with different bushing structures (A₁ as nylon bushing structure, A₂ as needle bearing & copper bushing structure) and hardness of seed guard belt (B ₁, B₂, B₃, B₄ and B₅ represented the hardness of 40, 45, 50, 55 and 60 HA, respectively) was designed using rice variety ‘Peizataifeng’ and ‘Xiushui134’ seeds as test materials.

Result  The experimental groups of A and B had the highly significant effect on the damage rate of rice seeds (P < 0.01), and there was a significant interaction between A and B ( P < 0.05). A ₂B₂ and A₂B₃ had the least effect on seed damage rate. There was a highly significant difference between A₁ and A₂, and seed damage rate of A₂ was significantly lower than that of A₁, indicating that A₂ was better than A₁. There was no significant difference between B₂ and B₃, but B₂ and B₃ had significant difference with other groups. The experimental group A had a significant effect on hill diameter, B had no significant effect on hill diameter, and the groups of A₂B₂, A₂B₃ and A₂B₄ had the less effect on hill diameter. There was a significant difference between A₁ and A₂, and A₂ was significantly better than A₁.The results of test showed that the wear of seed guard belt of A₂B₃, A₂B₄ and A₂B₅ were less after working for 100 hour. The grouo A₂B₃ was the optimal with the wearing volume of 72.6×10⁻³ mm³ and seed injury rate of 0.04%, and the hole forming ability and sowing effect were both the best.

Conclusion  The optimized design of needle bearing & copper bushing shaft sleeve structure is reasonable. It can significantly reduce the friction coefficient between sleeve and shaft, is more resistant to high temperature and wear resistance, effectively improves the synchronization of seed guard belt, and significantly improves the reliability and sowing quality of seed platter.