Experiment on mechanical property of seedling pot for automatic transplanter

Abstract: Mechanical properties of bowls for cucumber plug seedlings are vital to design the picking seedling machinery of plug seedlings automatic transplanter. With cucumber as the object of plug seedling, plug seedlings were cultivated in the Venlo green house using the regular cubic tapered trays and organic soil of Zhenjiang's Peilei. When mechanical properties of bowls for cucumber plug seedlings were tested, age of plug seedling was 28 days, two cotyledons and the first central leaf were on the seedlings, and the moisture of bowls was from 54.21% to 60.47%. Tests of compression, loading-unloading and creep for cucumber plug seedlings were conducted. Test instrument was TA-XT2i analyzer, and all of test speeds were 1 mm/s. Compressive properties of bowls were tested under compression of 10 mm, which were repeated 20 times. In the loading-unloading tests, loading-unloading properties of bowls were tested under 2, 4 and 8 mm compression, respectively, which were repeated 10 times for every compression. Creep tests with 120s holding time were carried out under 2N, 4N, 6N and 8N loads to analyze creep properties of bowls, respectively, which were repeated 10 times for every load. Testing results showed that relations between capacity of resistance for compression and deformation were non-linear. The resistance capacity for compression with deformation increased slowly at first and increased significantly at last. In compression process, there was no obvious yield failure point for plug seedlings. Compression failure for plug seedlings was mainly occurred from less packing area, and then degree of fragmentation was gradually expanded. In the elastic-plastic features, with the increase of compression, the plastic strain energy Ep and peak force Fmax increased, and the degree of elasticity rc decreased. The greater compressive deformation of bowls, the stronger plastic capacity of bowls possessed. Capacity of plastic deformation for plug seedlings is strong with a certain degree of plasticity, causing clamping bowl from both sides or around the body. Compressing creep characteristics of bowl for plug seedlings could effectively be expressed by Burgers model and corresponding viscoelastic parameters are obtained. With the increase of loading force, instantaneous modulus of elasticity E1 and transmit delay Trel decreased. When the loading forces were 2N, 4N, 6N and 8N, the creep amount of bowls were 0.0244, 0.0308, 0.0446 and 0.0549 mm, respectively. Research show creep degree of different compression forces for plug seedlings is relatively smaller, which has no significant impact on fast clamping the bowl, and in other words the bowl is clamped it will not fall off because of relaxation.