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. In production of packaging containers, it can mainly produce various box-type packaging containers, such as various turnover boxes, small boxes, etc. For box-type packaging containers, following aspects should be considered in structural design.
1. Wall thickness of container
Design of wall thickness mainly considers three aspects: first, thickness; second, uniformity; third, smooth transition.
① Thickness: Wall thickness of container is mainly determined by its use, plastic type, structure, etc. For thermoplastics, it is generally not less than 0.6mm, and 2~4mm is often selected; for thermosetting plastics, because of its poor fluidity, thickness should be larger, small part is 1.6~2.5ram, and large part is 3.2 ~8mm, maximum does not exceed 10mm.
② Uniformity: Uniformity of wall thickness has a great influence on quality of container. If thickness difference of a container is too large, shrinkage will be uneven, resulting in defects such as deformation and cracks. Therefore, an equal-thickness structure should be used as much as possible in structural design.
③ Smooth transition: In some containers, when thickness of some parts must be different due to structural requirements, such as turning point of container, a smooth transition should be used to avoid sudden changes in section.
2. Improve stiffness
Plastics are relatively flexible, and rigidity of containers made of them is poor, and turnover box containers sometimes have a large bearing capacity, so various measures to improve rigidity should be taken in structure.
①Adding reinforcing ribs: Reinforcing ribs can enhance strength and rigidity of container. Basic requirements for reinforcing ribs are as follows: number of ribs should be large, wall thickness should be thin, height should be short, slope should be sufficient, bottom of ribs should be in a circular arc transition, direction of reinforcing ribs should be consistent with direction of material flow to improve toughness of plastic;
② Improve shape: Most of box-shaped containers are rectangular thin-walled parts, which are easy to deform. Various reinforcement measures should be taken to slightly bulge four side walls of container to improve rigidity; it is belt-like reinforcement at side wall to prevent distortion; edge reinforcement at the edge of container to prevent deformation of nozzle; bottom reinforcement at the bottom of container designed to be corrugated and arched.
③ Reasonable support: Bottom area of box-shaped container is large, but it is unreasonable to use the entire bottom surface as a support. Because bottom is slightly arched, it will not be placed flat, so surface support should be changed to line support or point support, convex edge support (ie line support); raised foot support (ie point support); height of bump is generally 0 .3~0.5mm.
④ Corner: Corner is intersection of two or three sides. Regardless of shape of container, rounded transitions must be used at intersection of each surface, which can greatly improve rigidity of container and improve plastic filling model. It can disperse stress and reduce deformation.
3. Demoulding slope
In order to facilitate demoulding of molded part, a suitable demoulding slope must be considered when designing container. If demoulding slope is too small, demolding is difficult and damages surface of container; if it is too large, dimensional accuracy will be affected.
Demolding slope varies with shape of plastic part, type of plastic, mold structure, surface roughness, molding method, etc. Generally speaking, commonly used slope of plastic parts along demolding direction is 1º~1.5º, and minimum is not less than 0.5º.
Damage status and nursing measures of mold products in injection molding workshop
Injection mold should test various properties of mold under normal operation of injection molding machine and mold, measure size of final molded plastic part. Through this information, existing state of mold can be determined, damage to cavity, core, cooling system and parting surface can be found. According to information provided by plastic parts, damage state of mold and maintenance measures can be judged.
Springs and other elastic parts are most easily damaged during use, usually break and deform. Method to take is to replace. During replacement process, you must pay attention to specifications and models of springs. Specifications and models of springs are confirmed by three items of color, outer diameter and length, and can only be replaced if three items are same.
During use of mold products, punch is prone to breakage, bending and gnawing, and punch sleeve is generally gnawed. Damaged punches and sleeves are generally replaced with parts of same specification. Parameters of punch mainly include working part size, installation part size, length size, etc.
Parts also need to be fixed from time to time. It is necessary to check whether fastening parts are loose or damaged. Method is to find parts of same specification for replacement.
During maintenance, check relationship between parts and whether there is any damage, repair damaged parts, check whether there is air leakage with pneumatic jacking material, and take measures for specific situation. If trachea is damaged, replace it.
It is necessary to focus on tracking and testing of several important parts of mold: function of ejection and guide parts is to ensure opening, closing movement of mold and ejection of plastic parts. If any part of them is stuck due to damage, it will lead to production stoppage, so it should be maintained frequently. Lubrication of mold thimble and guide post (the most suitable lubricant should be selected), regularly check whether thimble and guide post are deformed and surface damaged. Once found, they should be replaced in time;
After completing a production cycle, professional anti-rust oil should be applied to working surface, motion and guide parts of mold, and special attention should be paid to protection of elastic strength of bearing parts with gears, rack molds and spring molds to ensure that they are always in top working condition;
At the same time, attention should be paid to the cleaning of runner, because the longer time is, the more scale, rust, silt and algae will be deposited in cooling channel, which will make the section of cooling channel smaller and cooling channel narrower, which greatly reduces heat exchange between cooling liquid and mold. rate and increase production cost of enterprise. For hot runner mold products, maintenance of heating and control systems is beneficial to prevent production failures.
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