Injection Blow Molding Basics

Injection blow molding is a manufacturing process that combines the accuracy of injection molding with the minimal waste and rapid processing of blow molding. Injection blow molding can be used with plastics and is generally used to make hollow shapes such as bottles. The manufacturing process is more expensive than other blow molding techniques, so larger containers are generally fabricated using extrusion blow molding. The final products of injection blow molding have no seams, and can be glass clear.

Injection Blow Molding Process

The injection blow molding process has three phases: Injection of the material into the preform mold; blowing of the preform, or parison, into the product mold; and ejection of the product from the machine. A commonly used machine configuration is a three-stage blow molding machine, which rotates through 120 inches for each phase of the process. In the injection phase, molten plastic or glass is injected into the preform mold over a core pin, which forms the interior of the parison and finishes the interior of the neck. At this point, the neck of the container is fully formed. The parison is removed from the mold and inserted into the blow mold. The parison is inflated inside the blow mold by pressurized air. After a cooling period, the product is ejected from the machine, tested for leaks, and moved to another station for labeling or finishing.

Designing for the Injection Blow Molding Process

Designing products to be fabricated using injection blow molding includes selecting a thermoplastic resin for the product application, designing the mold geometry to take into account material shrinkage during cooling, calculating the right amount of material to be injected and choosing the right pressure to inflate the parison in the mold. Tolerances in the core rod and preform mold design are critical so that the core rod sits exactly in the center of the mold and the resulting parison has constant wall thickness prior to blowing.

Products Fabricated Using the Injection Blow Molding Process

Injection blow molding is used to create hollow products such as bottles, and is generally only used for small containers such as medicine bottles or single-serve beverage containers. The injection phase of the process can create a neck with very fine tolerances, with designs such as screw threads or threads for childproof caps. Unlike standard injection molding, undercuts can be incorporated into an injection blow molded design for some products, such as mascara bottles.

How to Texture Injection Molds

Injection molds receive a finish to eliminate the machining marks from the mold. High-speed machines typically do this polishing. In some cases, a textured finish is desired. A chemical etch procedure creates the texture based on a pattern. This process usually is manual.

Mold Texturing

1

Create a design of the desired texture as a photocopy or digital file.

2

Transfer the design to a negative. This can be easily done with a scanner. Most scanners have the capability to scan to a negative output file. Or, if the file is already digital, many photo editing software packages have the option to convert a file to a negative.

3

Transfer the negative to a flexible elastomeric material with the desired texture. This is not a do-it-yourself activity for the average person. In general, commercial equipment, often a laser engraver, is required to complete this step. A commercial provider of this type of service should be considered.

4

Placing the textured elastomeric material on the mold surface and add the chemicals to etch the mold. The exact chemical used depends on the specific metal of the mold. It is generally one of the stronger acids.

5

Completely wash the mold of all chemical residues.

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what's blow molding

Plastic blow molding technique is developing rapidly for plastic process . The thermoplastic resin obtained by extrusion or injection molding of plastic tubular parison hot ( heated or softened state ) , placed inside the mold cavity , then closed mold immediately, pour into air, blowing the plastic parison inflation and close to the inner wall of the mold cavity, cooled mold , that get all kinds of hollow plastic products.

 Technical Overview     Blow molding process during World War II began for the production of low-density polyethylene vial. In the late 1950s , with the development of high-density polyethylene birth and blow molding machines , blow molding technology has been widely used. Hollow container volume up to thousands of liters, and some have adopted computer-controlled production . For blow plastics are polyethylene, polyvinyl chloride, polypropylene, polyester, etc. , resulting into the empty containers are widely used in industrial packaging containers.

According to the production method of the parison , blow molding and extrusion blow molding can be divided into the injection blow molding, a newly developed multi-layer blow molding and stretch blow molding.

 

 Prospects    In recent years , with the development of a variety of functional beverages and wine packaging market , a variety of multi-layer co-injection - blow molding technology become a hot market .

Flexible step production technology

Injection stretch blow molding hollow articles having uniform thickness, good dimensional stability, light weight , high strength , etc., and therefore a very wide range of applications . As the injection stretch blow container craft production mostly PET, PP, PE, PVC and other materials as raw materials, and the use of these raw materials to produce bottles with light, portable, non-toxic , transparent, unbreakable , good barrier properties , etc., making it more and more as an alternative medicinal bottles were used in carbonated drinks, juice drinks , water , edible oil , alcohol , cosmetic products, pharmaceuticals and other industries packaging.

Injection stretch blow a two-stepprocessing method and one-step process . One step from raw material to complete the entire container molding process on a single device. Two-step process from the raw materials needed to complete the two devices to products molding process . Two-step method is mainly suitable for mass production , and flexibility, both equipped with a multiple injection blow molding machine can also be equipped with more than one injection blow molding machine . Of course, this should be based on production to match the main injection machine and blowing may be.