穴盘苗自动移栽钵体力学特性试验

Experiment on mechanical property of seedling pot for automatic transplanter

穴盘苗钵体的力学特性,是穴盘苗自动移栽机取苗机构设计的重要依据。以黄瓜为育苗对象,选用镇江培蕾育苗有机土,使用128孔正方形锥体穴盘,在Venlo型玻璃温室培育穴盘苗。试验时,穴盘苗苗龄28d,长出两片子叶和第一片心叶,钵体含水率范围为54.21%～60.47%。对穴盘苗钵体进行了平板压缩、加卸载循环和蠕变试验,试验仪器为TA-XT2i型质地分析仪,测前、测试、测后速度均为1mm/s。钵体压缩试验测试10mm压缩量下的抗压特性,试验重复20次,钵体加卸载循环试验测试2、4、6、8mm压缩量下的加卸载特性,每个压缩量重复10次,钵体蠕变试验试验测试2、4、6、8N不同加载力下的蠕变特性,保持时间为120s,每个测试力重复10次。试验表明穴盘苗钵体的抗压力与变形呈非线性变化,抗压力随着变形的增大先缓慢增大再显著增大。在平板压缩过程中,钵体无明显的屈服破坏点。穴盘苗钵体的压缩破坏是从钵体盘根较少的区域开始,逐渐扩大破碎度。在弹塑性方面,随着压缩量的增大,滞后损失、抗压峰值力均增大,弹性度减小,并且穴盘苗钵体压缩变形越大,其塑变能力越强,具有一定的可塑性,可以从两侧或四周夹紧钵体而不破坏其整体性。利用Burgers模型能有效表征穴盘苗钵体的压缩蠕变特性,获得了对应的黏弹性参数。通过钵体不同压力下的蠕变试验,得到随着加载力的增大,瞬时弹性系数、延迟时间均减小,在1s内,加载力为2、4、6、8N时,钵体平均蠕变量分别为0.0244、0.0308、0.0446、0.0549mm,表明其蠕变量比较小,这对快速夹取穴盘钵体的夹紧松弛特性影响不大,即钵体一旦夹紧不会松弛掉落。

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.