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December 22, 2021
Blow molding product design
1. Introduction to Design
Blow molding products are widely used in various industries, especially in beverage and pharmaceutical packaging industries. They are also widely used in the toy industry, such as: blown baby bottles, hollow floating parts, Christmas lampshades, toy yachts, children's learning driving accessories And some large toys, such as slide rails, pedestals, etc.
With different product requirements, the focus of product design is also different. For toy products, blow-molded products are more focused on safety and physical testing (considerations of pulling, twisting, throwing, and stress cracking), while for container products, more emphasis is placed on safety and physical testing. Pay attention to the requirements of pressure resistance, corrosion resistance and good barrier properties.
1) R transition at the corners
Generally, the corners and corners of blow molded products must be made R transition, because the expansion ratio at the sharp corners is relatively large, which will easily cause uneven wall thickness. In addition, the sharp corners are also prone to pressure cracking. The R transition of the product can be Make the wall thickness of the product uniform.
2) Increase the structural design of compression, tension and torsion
With different product requirements, some structural designs for compression, tension, and torsion resistance can also be added:
A. If you want to increase the longitudinal pressure resistance of the product, you can design some reinforcing ribs along the direction of the force;
B. If you want to improve the collapse resistance of the product, you can also design the surface into an arc-shaped structure that is conducive to stress and supplemented with reinforcing ribs. The shoulders of bottle products should be inclined, not too straight;
Generally, the bottom of the bottle is made into a concave shape to increase strength and stability. For example, the edible oil bottles we usually see often have some uneven shapes on the surface, which not only increase the strength of the bottle body, but also facilitate the labeling.
2. Blow molding material requirements and introduction
The development and application of blow molding technology is so extensive that it is complementary to the development of blow molding materials. Blow molding materials have gradually developed from the initial LDPE, PET, PP and PVC products, which can blow molding engineering plastics, rubber, and Some composite materials.
1) Special requirements for rubber materials in various blown plastics
A. Extrusion blow molding
Extrusion blow molding is carried out in a viscous flow state, so in order to reduce parison sag and optimize wall thickness distribution, plastics with larger molecular weights are usually used.
B. Injection blow molding
Injection blow molding is carried out under high elasticity. In order to reduce the energy consumption of injection molding parison, some easy-flowing plastics (plastics with smaller molecular weight) are used.
C. Injection stretch blow molding
Amorphous plastics are generally used because they are easier to stretch due to the smaller entanglement between molecules. Although PET also crystallizes, it is still the most important stretch blow molding material, and its crystallization speed is quite slow. In short, most blow molding grade plastics have a medium to high molecular weight distribution.
2) Types of blow molding materials
HDPE, LLDPE, LDPE, PP, EVA are generally used for blow molding industrial products, containers and toy accessories, storage containers for chemicals, etc.
B. Thermoplastic polyester
PETG and PETP are mainly used to blow carbonated beverage packaging bottles, wine bottles, etc., which have gradually replaced PVC and have been widely used. The disadvantage is that their cost is relatively high, and they are mainly used for injection stretch blow molding.
C. Engineering plastics (alloy)
ABS, SAN, PS, PA, POM, PMMA, PPO, etc. have been gradually applied in industries such as automobiles, medicines, home appliances, and chemicals, especially PC and its blended plastics, which can be used to blow high-end containers and automotive supplies (PC/ ABS, etc.).
D. Thermoplastic elastomer
SBS, SEBS, TPU, TPE, etc. are usually blow-molded as rubber materials, while thermosetting plastics, vulcanized rubber, and cross-linked PE cannot be blow-molded.
Commonly used materials for injection blow molding
PE, PET, PVC, PP, PC, and POM are mainly used for containers and structural parts that require high molding accuracy and small volumes;
Commonly used materials for injection stretch blow molding
PETP, PVC, PP, PAN, especially PETP is the most commonly used, and PC, PS, PA can also be used in this process.