Injection Blow Molding

What is Injection Blow Molding?

Injection blow molding is a procedure that combines several different techniques. First, a preform is injection molded and then blown into the desired shape, necessitating the use of two molds: one for the preform and one for the final blown form. For large-scale production of hollow things, injection blow molding is used. Bottles, jars, and other containers are the most common applications. Unlike extrusion blow molding, injection blow molding provides better aesthetic and dimensional quality bottles.

Injection Blow Molding Process

Since it is essentially two forming processes combined into one, injection blow molding involves more steps than other forms of blow molding. First, a parison made of plastic is formed when a thermoplastic preform is heated to molten form and injected around a hollow mandrel called a blow stem. Once semi-cured but still soft and formable, the newly formed parison, which is still around the stem, is placed into the blow molding chamber. The steel blow stem then extends, forcing the plastic to elongate to the desired size of the product, which will also increase its overall strength.

Then, compressed air is injected through the hollow blow stem and into the parison. The almost-molten plastic inflates like a balloon and is blown against the walls of the mold cavity, taking its shape. After it cools and hardens, the newly formed plastic container is ejected from the mold. It exhibits a seamless design and does not need to be trimmed. Injection blow molding machines use multiple mandrels and may form up to 12 containers simultaneously.

Injection Blow Molding Machines

When selecting an injection blow molding machine, there are three primary considerations. The first is the plastifier's capacity to plasticize enough plastic material to achieve maximum cavitation. Because the IBM machine's cycles are quite fast, the plastifier's recovery time can be a limiting issue regarding how many cavities can be made or how quickly a cycle can be used in production.

The second factor is the clamp tonnage capacity of the injection station. Clamp tonnage is computed by multiplying the predicted area of the preform as it is cut on the horizontal plane by the number of cavities and the injection pressure required to fill the parison injection mold with thermoplastic material.

Injection pressures for LDPE, HDPE, and PP are typically 3000–5000 psi, but injection pressures for PVC, polycarbonate, and PET can be as high as 8000–10,000 psi. With an injection clamp ranging from 5 to 180 tons and a hydraulically actuated clamp, injection blow molding machines are offered. The dry cycle, or the time it takes for the mold to open, index the table, and close, is the third significant consideration when choosing an IBM machine. This cycle wastes time for the consumer and should be kept to a bare minimum. Machines with a 1.5-second open, index, and closure time are available, whereas others require 2.7 seconds.

Advantages of Injection Blow Molding

• There should be no scrap with the right tool and a well-managed shop. In the mold, all of the bottles are completely finished. Scrap is generated during the startup process and due to color mixing problems. Re-run junk does not affect the process.
• During cavity filling, the injection blow receives some orientation from the injection stage. Also, because the temperature of plastic drops by roughly 150 degrees, styrene orients into a strong container. There is no influence on P.E.
• When employing transparent materials, containers are always clear because some orientation happens during blow-up in the hoop direction, and polypropylene is clearer.
• With retractable bottom plugs in the blow mold, there is a lot of creative freedom for bottom forms.
• Accuracy is great for plug inserts for squeeze bottles or cap seals for flexible materials (nose or deodorant spray).