Injection molding is the injection of molten plastic under high pressure through a nozzle into a closed mould with a lower temperature. Thermoplastics and thermosetting plastics can be injection molded. It can be used to make various packaging containers on the packaging containers. Such as various turnover boxes, small boxes, etc. For box-type packaging containers, the following aspects should be considered in the design of the structure.
1.Wall thickness of the container
The thickness of the design mainly considers three aspects: First, thickness; Second, uniformity; Third, smooth transition.
1 Thickness: The thickness of the container is mainly determined by its use, plastic type, structure, etc. For thermoplastics, generally not less than 0. 6mm, often choose 2~4mm; for thermosetting plastics, because of its poor fluidity, the thickness is greater , Small pieces of 1. 6~2. 5ram, large pieces of 3. 2~ 8mm, maximum not more than 10mm.
2 Uniformity: The uniformity of the wall thickness has a great influence on the quality of the container. If the difference in the thickness of a container is too large, the shrinkage will not be uniform, resulting in defects such as deformation and cracks. Therefore, the equal thickness structure should be adopted in the structural design. .
3 Smooth transition: In some containers, some parts need to have different thickness due to structural requirements, such as the container turning point, then a gentle transition should be used to avoid cross-sectional sudden changes.
2.Improve stiffness
Plastics are relatively flexible, and the rigidity of the manufactured containers is poor. However, turnover containers are sometimes loaded with large amounts. Therefore, various measures should be taken to increase the rigidity of the containers.
1 Additional stiffeners: Reinforcements can increase the strength and stiffness of the container. The basic requirements for stiffeners are: The number of stiffeners should be large, the wall thickness should be thin, the height should be short, there should be enough slope, and the bottom of the stiffener should have a circular arc transition. The direction of reinforcing ribs should be aligned with the material flow direction in order to increase the toughness of the plastics;
2 To improve the shape: The box-shaped containers are mostly rectangular thin-walled parts that are easily deformed. Various reinforcing measures should be taken. The four sides of the container are slightly convex outwards to increase the rigidity; the strip-shaped reinforcement is made on the side walls to prevent twisting. Edge reinforcement at the edge of the container to prevent deformation of the mouth; in the bottom of the container is designed to be corrugated, and the shape of the arch is reinforced at the bottom.
3 Reasonable support: The bottom area of the box-shaped container is relatively large, but it is unreasonable to use the entire bottom surface as a support. Since the bottom part is slightly arched, it should be uneven. Therefore, the surface support should be changed to line support or point support, and the flange support (ie, line support). ); raised foot support (ie, point support); raised height is generally 0. 3~0. 5mm.
4 Corner: The corner is the junction of two or three faces. No matter how the container's shape is, all corners must use rounded corner transitions. This can greatly improve the rigidity of the container, and at the same time improve the mold filling property of the plastic. , And can disperse stress and reduce deformation.
3. Stripping slope
In order to facilitate the demoulding of the molded part, it is necessary to consider the proper draft angle when designing the container. If the draft is too small, it is difficult to remove the mold and damage the surface of the container; if it is too large, the dimensional accuracy will be affected.
The draft angle varies depending on the shape of the plastic part, the type of plastic, the mold structure, the surface roughness, and the forming method. In general, the common inclination of the plastic part along the stripping direction is 1o~1.5o, the minimum Not less than 0.5o.