Design and experiment of the clamping horizontal belt type stretch film feeding and forming device for packaging machines

Abstract: The loss ratio of fresh fruit and vegetable has been as high as 25%-30% of the yield during circulation and sales in China. Wrapping mechanized engineering can be an effective way to reduce the fruit and vegetable loss after harvest. However, the current stretch film packaging in the manual or semi-automatic modes cannot meet the high demand for the mechanized packaging industry at present. In this study, a new type of clamping belt-type device was designed for the stretch film feeding and forming in the packaging machine for the fresh fruit and vegetable. The device was mainly composed of a clamping horizontal belt, a vertical and horizontal conveyor belt, as well as the longitudinal sealing mechanism. Among them, the clamping horizontal belt served as the key component to realizing the feeding of stretch film and covering the upper part of the packaging material. A mechanical and physical model of the films on the upper part of the load tray was established, according to the core components of the clamping horizontal belt. Specifically, the unilateral pressure was determined less than or equal to 5.82 N, and the inclination angle of the clamping horizontal belt was in the range of 12°≤α≤18°. The parameters were then calculated to fully meet the requirements, when the clamping distance of the horizontal belt was 250 mm. Since the clamping pressure of the upper and lower belts was depended on the adjustment distances of the ball screws, the test data was selected to fit the relationship equation between the clamping pressure and the adjustment distances. The height was calculated as 10 mm between the feeding and feeding point of the clamping horizontal belt and the bottom surface of the support, particularly meeting the demand for the feeding of the stretch film. The working parameters were set as the test factors, including the feeding speed for the clamping horizontal belt, the depression depth of the fluent strip parts, and the inclination angle of the clamping horizontal belt. The left offset and right offset were used as the test indicators of the performance of the device. The PVC stretch film with a width of 350 mm and the PP tray containing fresh carrots were selected as the test materials. The test results show that the three determinants were ranked in the descending order of the conveying speed, depression depth, and inclination angle in the test indicators. The test data was fitted to obtain the quadratic multiple regression equation of test factors and indicators. The optimal working parameters were achieved on the software Design-Expert 8.05b, where the conveying speed was 292 mm/s, the depression depth of the fluent strip parts was 10 mm, and the inclination angle of the clamping horizontal belt was 16.3°. The left offset and right offset were 10.5 and 11.4 mm, respectively, indicating the basic consistence with the prediction of the model. The working efficiency of the feeding and forming device was 23 bags/min. The packaging performance was achieved that the stretch film on the upper part of the tray was smooth, transparent, and without tearing, and the stretch film at the bottom of the tray was sealed longitudinally and neatly, which met the national requirements of packaging machines for the fresh fruits and vegetables. This article can provide a promising theoretical reference for the subsequent mechanized packaging of fresh fruits and vegetables.