Structural design considerations for injection molded containers

Injection molding is to inject molten plastic under high pressure through the nozzle into the closed mold with low temperature and molding. Both thermoplastic and thermosetting plastics can be injection molded, and they can be mainly used to make various box-type packaging containers, such as various crates, small boxes and so on. For box-type packaging containers, the following aspects should be considered when designing the structure.
 

1. Wall thickness of the container

The design of the wall thickness mainly considers three aspects: one is the thickness; two is uniformity; three is a smooth transition.

1). Thickness: the wall thickness of the container is mainly determined by its use, plastic type, structure, etc. For thermoplastic plastics, generally should not be less than 0. 6mm, often selected 2 ~ 4mm; for thermosetting plastics, because of its poor mobility, the thickness should be larger, small pieces of 1. 6 ~ 2. 5ram, large pieces of 3. 2 ~ 8mm, the maximum does not exceed 10mm.

2). Uniformity: the uniformity of wall thickness has a great impact on the quality of the container, a container if the thickness difference is too large, will make the shrinkage is not uniform, resulting in deformation, cracks and other defects. Therefore, in the design of the structure should try to use an equal-thickness structure.

3). gentle transition: in some containers, some parts must be of different thicknesses due to structural needs, such as container turning, then a gentle transition should be used to avoid abrupt changes in cross-section.
 

2. Increase the stiffness

Plastic is more flexible, made of poor rigidity of the container, and sometimes the carrying capacity of the crate type containers and larger, so in the structure should take a variety of measures to improve the rigidity.

1). Additional reinforcement: reinforcement can enhance the strength and stiffness of the container. The basic requirements of the reinforcement is: the number of appropriate, wall thickness should be thin, height should be short, there is enough slope, the bottom of the reinforcement should be a circular transition, should make the direction of reinforcement and material flow direction in order to improve the toughness of plastic;.

2). improve the shape: box described as mostly rectangular thin-walled pieces, easy to deformation, should take a variety of enhancement measures, the container four side walls slightly convex outward to improve the stiffness; is in the side walls to prevent distortion and band enhancement; in the edge of the container to prevent the mouth deformation and edge enhancement; in the bottom of the container designed to corrugated, arch shape and bottom enhancement.

3). Reasonable support: box describes the bottom area of the vessel is large, but the entire bottom surface as support is not reasonable, because the bottom is slightly arched is not put flat, so the surface support should be changed into line support or point support, convex edge support (i.e. line support); raised foot support (i.e. point support); the height of the projection is generally 0. 3 ~ 0. 5mm.

4). Corner: corner is the intersection of two or three surfaces, regardless of the shape of the container, the intersection of the surfaces must be rounded transition, which can greatly improve the rigidity of the container, while improving the plastic modeling, and can disperse the stress and reduce deformation.
 

3. Demoulding slope

In order to facilitate the release of molded parts, a suitable release slope must be considered when designing the container. If the release slope is too small, it will be difficult to release the mold and damage the surface of the container; if it is too large, it will affect the dimensional accuracy.

The release slope varies depending on the shape of the molded part, the type of plastic, the mold structure, the surface roughness, and the molding method. Generally speaking, the common slope of the plastic part along the demoulding direction is 1º~1.5º, and the minimum is not less than 0.5º.