type
There are three kinds of pallets: wooden, steel and plastic, among which wooden pallets are the most common. Wood pallet materials require high bending strength and impact resistance. It is usually made of hardwood, but there are also plywood and medium density fiberboard. According to the service life of pallets, they can be roughly divided into disposable pallets and reusable pallets. The former requires design and materials for one-time handling, so the cost is low. There are two common types: pallets with or without feet (Figure 1) and pallets with feet (Figure 2). There is no "foot" tray, and there is no pad under the countertop. The structure is simple and the price is the cheapest. Forks of forklift trucks can enter from two directions, which is suitable for carrying light objects. There is a "foot" tray and a fixed pad under the desktop, which is firm in structure and expensive. Forks of forklift trucks can enter from four directions and are suitable for carrying heavy objects. The structure and materials of reusable pallets should meet the requirements of reuse. There are two common types: cushion structure and truss structure.
Figure 1
The structural type of the cushion block in Figure 2 (Figure 3) is single-sided load, which cannot be turned up and down. All the fulcrums on the table are supported by fixed pads, which can be designed so that the forks of the forklift can enter from two directions or four directions. Widely used in the handling of packaging, wooden cases, cartons, barreled goods, etc. It is the most common pallet in industry. The truss structure (Figure 4) has a large table and can support a large load. The lower part of the desktop is supported by a truss, and the upper and lower sides of the support can be turned over for use. Forks of forklifts enter from two directions, but they are only suitable for motor forklifts and are widely used to carry large and heavy packages, boxes and barrels.
Figure 3
In addition to the above two basic structural types, Figure 4 also has a pallet with "wings" and wooden strips (commonly known as "wings") protruding from the desktop, which are used as hooks when loading and unloading goods (Figure 5). In order to further improve the efficiency of loading and unloading, there are also wooden pallet boxes, which are used to put bulk goods such as fruits, vegetables and metal parts into the boxes. The bottom plate of the box is the table top of the tray, and the trays are connected into a whole, which is called box tray (Figure 6).
Fig. 5 The supporting weight of the pallet varies with different objects. The United States usually divides the load into three grades: 2500 pounds, 250 1 ~ 4000 pounds, and more than 4000 pounds. Pallets are mainly connected by round nails or U-shaped nails, and the production has been mechanized and linked, which requires the products to undergo simple treatment of moistureproof and anticorrosion.
Production investigation
In industrialized countries, due to large product output and large commodity circulation, in order to improve the efficiency of loading and unloading, wooden pallet also consumes a lot. According to reports, in 1985, there were 2,500 professional manufacturing enterprises in the United States, with 44,000 employees, producing 450 million wooden pallets annually, and the trend is increasing year by year. The most commonly used pallet size is 48″×40″. At present, a wooden molded tray has been developed, which is made of wood shavings and adhesive in a mold at one time. Not only the production efficiency is high, but also there is no metal connector, which is not harmful to the handling of goods. Clean and convenient, and the price is competitive. It has been well received by users and defense industry departments, and is being widely promoted and applied. In addition, Britain, France, the Federal Republic of Germany, Japan and other countries also use a large number of wooden pallets, which are produced by many professional factories, and there are also professional norms or standards in product design, production, inspection and use. ISO 445- 1984 wooden pallet standard has been formulated by the international organization for standards.
Figure 6 Wooden pallets in China are rarely produced in professional factories, and most of them are attached to wooden box factories. The production capacity is small and there is no uniform standard. They are mainly used for packaging and transportation of foreign trade exports. 1989 Guangdong Zhanjiang Wood Molded Products Factory imported Werzalite molded patents and equipment from the Federal Republic of Germany, and established a wood shavings molded pallet workshop with an annual output of 400,000 pieces, which sold well all over the country. With the development of China's commodity economy and the increase of product circulation, the transportation level will improve and the demand for wooden pallets will increase accordingly. Therefore, this product has its development prospect.
Internal heating vertical distillation tank
See wood dry distillation.