Injection molding is to inject molten plastic into a closed mold with a lower temperature through a nozzle under high pressure. Both thermoplastics and thermosetting plastics can be injection molded. It can be used to produce various box-type packaging containers, such as various turnover boxes, small boxes, etc., in the production of packaging containers. For box-type packaging containers, the following aspects should be considered in the structural design.
Wall thickness of the container
The design of wall thickness mainly considers three aspects: one is thickness; the other is uniformity; and the third is a smooth transition.
1. Thickness: The wall thickness of the container is mainly determined by its use, plastic type, structure, etc. For thermoplastics, generally should not be less than 0.6mm, usually 2~4mm; for thermosetting plastics, because of its poor fluidity, the thickness is larger, small parts are 1.6~2.5 ram, and large parts are 3.2. ～8mm, the maximum does not exceed 10mm.
2. Uniformity: The uniformity of the wall thickness has a great influence on the quality of the container. If the thickness of a container is too large, it will shrink unevenly and cause defects such as deformation and cracks. Therefore, the equal-thickness structure should be used as much as possible in the structural design.
3. Smooth transition: In some containers, some parts must have different thickness due to structural requirements, such as the turning point of the container, at this time, a gentle transition should be adopted to avoid abrupt cross-section.
Plastics are relatively flexible, and the rigidity of the containers made is poor, and the carrying capacity of the turnover box container is sometimes larger, so various measures to improve the rigidity should be taken in the structure.
1. Add stiffeners: stiffeners can increase the strength and rigidity of the container. The basic requirements for stiffeners are: the number should be large, the wall thickness should be thin, the height should be short, and the slope should be sufficient. toughness;
2. Improve the shape: box-shaped containers are mostly rectangular thin-walled parts, which are easy to deform. Various enhancement measures should be taken to slightly protrude the four side walls of the container to increase the rigidity; it is a belt on the side walls to prevent distortion. Shape reinforcement; edge reinforcement at the edge of the container to prevent mouth deformation; bottom reinforcement at the bottom of the container designed into a corrugated and arch shape.
3. Reasonable support: The bottom area of the box-shaped container is large, but it is not reasonable to use the entire bottom surface as a support. Because the bottom is slightly curved, it will not be flat. Therefore, the surface support should be changed to line support or point support, convex support (ie Line support); raised foot support (ie point support); the height of the projection is generally 0.3~0.5mm.
4. Corner: The corner is the junction of two or three sides. Regardless of the shape of the container, the corner transition must be adopted at the intersection of each side, which can greatly improve the rigidity of the container and improve the filling of the plastic at the same time. Modeling, and can disperse stress and reduce deformation.
In order to facilitate the demolding of the molded part, a suitable demolding angle must be considered when designing the container. If the demolding angle is too small, demolding is difficult and the surface of the container will be damaged; too large will affect the dimensional accuracy.
The draft angle varies with the shape of the plastic part, the type of plastic, the mold structure, the surface roughness, and the molding method. Generally speaking, the commonly used slope of plastic parts along the demolding direction is 1˚～1.5˚, and the minimum is not less than 0.5˚