As two major hollow blow molding processes, what are the differences between extrusion blow molding (referred to as “extrusion blow”) and injection blow molding (referred to as “injection blow”)? What are their strengths, weaknesses, and applications? What is the machine composition of the two processes? What are the technical difficulties of blow molding production of multi-layer structural products?

What is Extrusion Blow Molding?

“Extrusion blowing” means extrusion blow molding hollow molding. Firstly, the plastic in a viscous flow state is extruded through the extruder, and the tube blank with the same wall thickness or regular distribution according to the shape of the product is obtained through the machine head. Then, the extrusion and blowing mold is clamped, the tube blank is cut, and the high-pressure blowing is carried out. After cooling, the mold is opened to remove the flash edge to obtain the hollow product.

Some characteristics of extrusion blow molding include:

The extrusion blow process has a wide range of applications, which can cover almost all hollow products, especially those with complex, three-dimensional, multi-layer, and large hollow products. However, for small and medium-sized products, especially the production of small and medium-sized containers with high appearance rules, sealing requirements, and appearance quality requirements, there are obvious shortcomings compared with the injection blow process. At the same time, flash will be produced in the process of extrusion and blowing production, which needs to be recovered twice. In addition, because the molding process is open, the density of the product is also worse than that of the injection and blowing product.

What is Injection Blow Molding?

The injection blow process refers to the injection system through the injection action of the raw material from the hot runner into the mold cavity to form a tube blank, and then melt glue, screw back, waiting for the next injection action, and then the mold closing by the blow molding system to complete the blowing. Because this process is a closed molding method, the densification of the product is good, the sealing degree of the bottle is high, and the entire production process does not produce any flash waste, especially suitable for the production of pharmaceutical and cosmetic packaging bottles.

Some characteristics of injection blow molding include:

“Injection blowing” is injection blow molding hollow molding, there are two steps and one step method. Two-step “injection blowing” means that the injection and blow molding are carried out separately by two independent machines. The first step is the injection molding of the tube blank by an ordinary injection molding machine, and the bottle head part (bottle mouth, thread) of the tube blank is completed. The second step is to place the tube blank on the honeycomb heater or automatic circulation heating conveyor belt to heat and adjust the temperature, and then move to the blowing machine and blow the shape with compressed air.

The advantages of the two-step method are: the equipment is simpler and the investment is less; The mouth of the bottle is smooth and well sealed; Fast variety of development, and low mold costs. The disadvantages are: because the injection tube blank and blow molding are carried out step by step, it is easy to be polluted, and the bacteria detection is difficult to guarantee; Product identity is poor, and not suitable for mass production.

One-step “injection blowing” means that injection and blow molding are completed on the same machine, and the equipment generally includes 3 stations (distributed in an equilateral triangle at a 120° Angle). The first station is the injection molding station, the second station is the blow molding station, and the third station is the de-bottling station.

Advantages: The one-step injection and blowing process is ideal for the production of medical bottles. Because the 3 stations run at the same time, the production efficiency is high, the cycle is short, and the automatic counting can be connected with the conveyor belt, which truly realizes the “no contact” with the human hand in the whole process of the production of pharmaceutical plastic bottles, to ensure the hygiene and cleanliness of the products.