Evaluation of the Pallet Deflection that Occurs Under Forklift Handling Conditions
Huang, Yu Yang
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Industrial forklifts consist of one of the most common handling methods for pallets in warehouses and distribution centers. Pallets deflect while they are being transported by forklifts due to the weight of the unit load. Thus, most of the deflection is observed to occur on the outside edges and corners of the pallet. Several international standards are used in order to define the maximum deflection for pallet bending, including ISO 8611 and ASTM D1185. However, there is still a lack of understanding on the accuracy of these deflection limits and the exact performance of a pallet during a forklift support condition. Understanding pallet bending during forklift support condition and how it affects the stability of a unit load helps create an industry accepted deflection limit that will help to design safer and more cost-effective pallets. For this study, two chapters were proposed in order to assess pallet deflection and unit load stability. The first chapter consisted of measuring and analyzing the vibration levels for three different industrial forklifts affect by factors such as the speed, the payload of the unit load carried, sensor location, forklift type, and road conditions. The results obtained showed that the highest vibration intensity occurred at 3-4 Hz, while the highest overall Grms value observed was 0.145 G2/Hz (between 1-200 Hz). An increase in the forklift speed caused an increase in vibration intensity. In contrast, an increase in the unit load weight carried by the forklift caused a decrease in vibration intensity. Among the three forklifts studied, the gas-powered forklift had the highest vibration intensity, and all forklifts, when driven on asphalt, experienced more vibration. The second chapter of the research project consisted of evaluating pallet deflection under forklift handling conditions. These conditions included fork tines configuration (leveled and 4° angle), unit load condition (bound and unbound), pallet orientation (across width and across length), and type of handling condition (static and dynamic). The results showed that when unit loads were handled in a static condition, they survived the throughout the entire testing. However, when they were tested under a dynamic condition, and specifically, with the unbound unit loads, they did not survive the entire testing. Moreover, unit loads that were tested with the 4° angle forktines configuration tended to survive longer during the dynamic testing. For this particular case, the unit load capacity obtained based on the ISO 8611 standard was too conservative.
General Audience Abstract
Forklifts play an important role in the transportation of materials goods in the supply chain. Pallets experience vibration when they are handled by industrial forklifts. This vibration plus the combined effects mainly due to the unit load weight affects the amount that pallets bend. Thus, depending on the amount of pallet bending, they can produce unit load instability. Currently, there is a lack of understanding of how much pallet bending is acceptable. Therefore, the goal of this research was to understand the behavior of pallet bending when they are handled under forklift conditions. Two experiments were conducted in order to study pallet deflection under forklift handling conditions. The first experiment, which consisted in analyzing forklift vibration, showed that an increase in the forklift speed caused an increase in vibration intensity. In contrast, an increase in the payload of the unit load resulted in a decrease in vibration intensity. Among the three forklifts studied, the gas-powered forklift showed the highest vibration intensity. Forklifts driven on asphalt experienced more vibration in comparison to the ones driven on concrete. The second experiment, which consisted in assessing pallet deflection under a simulated forklift handling condition, showed that unit loads under a dynamic environment (vibration) increased the probability of unit load instability. Furthermore, it was observed that applying stretch wrap to a unit load decreased its instability and at the same time increases its survivability. Also, the results showed that the proposed ISO 8611 deflection limit is too conservative for this particular handling condition.
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