The design of pulp molding products is not only the design of structural equipment. Many properties of the products are determined by raw materials, additives, fillers and production processes. Therefore, the design of pulp molding products is a comprehensive technology of process and structure. We will discuss this from the following aspects.
Basic requirements of paper molding products
The design of pulp molding products is not only the design of structural equipment. Many properties of the products are determined by raw materials, additives, fillers and production processes. Therefore, the design of pulp molding products is a comprehensive technology of process and structure. We will discuss this from the following aspects.
In addition to the general physical strength requirements of paper products, the following properties should be paid attention to in terms of process and structure design according to the different uses of the product to meet specific use requirements.
(1) Absorption: The liquid-repellent properties of molding pulp products, including the absorption properties of liquids such as water, oil, and ink, are especially important for paper tableware.
(2) Product appearance quality: The defects of the product appearance can be observed with the naked eye. These defects include dust, holes, wrinkles, tendons, screen printing, spots, lumps, cracks, curling, depressions, inconsistent color, etc.
(3) Product accuracy: refers to the error between the size, shape and position of the product and the design requirements. According to the current manufacturing method, the precision of molding pulp products can only reach the national standard or below.
Points of structural design
In addition to the strength and toughness of paper products, molding pulp products can also be made into various complex shapes according to functional requirements. When used as a disposable fast food utensil, the shape is relatively simple, and the strength requirement is not high. When used as industrial inner packaging, its shape is very complicated, and it must meet the three major requirements of industrial inner packaging: First, positioning requirements. The packaging product must be able to ensure that the packaged product has a fixed position in the packaging box, and the shape of the packaged product must be synchronized, the contact should be close, and the size should be accurate. The second is buffer requirements. The product as a whole must have a certain degree of toughness and flexibility, and the surface should be a little soft. When it is in contact with the packaged product, it should not damage the surface gloss of the packaged product. It can eliminate the impact of the packaged product from collision and vibration during transportation. The third is bearing. The product is required to have a certain strength and rigidity to support the packaged object and withstand external pressure. In order to meet the above functional requirements of products, in addition to selecting appropriate raw materials, auxiliaries and production processes, structural design is more important.
(1) Functional structure:
The forming process characteristics of pulp molding products determine that the same product can only have one thickness. In order to meet the functional requirements, the shape cavity and vertical ribs can be used when adjusting the strength and cushioning. The shape cavity can increase the overall elasticity and flexibility of the product. Ribs can increase the strength and rigidity of the product. In a relatively large plane, when the load-bearing capacity is high, it can be designed as a corrugated or honeycomb shape.
(2)Process structure:
Because the pulp molding product is a wet paper blank in the early stage of forming, during the production process, water must gradually precipitate, and the shape, position and size of the product will change greatly. The total shrinkage of the product is different at different positions on the same plane and in the same direction. At this time, the product will be warped or twisted. In order to adjust this deformation, only the structural shape is adopted for balance. This structural shape used to adjust shrinkage deformation is called the technological structure of the product.
(3) Principles for determining parameters related to structure:
Draft angle. In the molding process of pulp molding products, the wet paper blank is tightly fastened to the mold, and the pulp fibers will be embedded in the mesh of the wire mold. In order to facilitate the transfer of the wet paper blank, the surface of the product parallel to the demolding direction should have a reasonable draft angle. If the tilt is too small, it will be difficult to demold, which will cause the surface of the product to be drawn or broken, if the tilt is too large, it will reduce the dimensional accuracy of the product and affect the packaging function.
Product thickness. The wall thickness of the product is determined according to the use conditions and the type of slurry, which is an important factor affecting the strength of the product. The increase in product wall thickness is not only to increase the consumption of raw materials, but also determines the production efficiency during adsorption forming. Increasing the wall thickness will also increase the energy consumption of drying and cause quality defects such as dents, shrinkage holes in the product. Therefore, the wall thickness should be reduced as much as possible while meeting the strength of the product. The wall thickness ranges between 0.5-6mm when adopting adsorption forming, and between 3-20mm when adopting press forming.
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