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.

What Is the Blow Molding Process?

Blow molding is used to produce plastic bottles.

Blow molding is a method for making a variety of hollow plastic products. Molten plastic is extruded, in a tube shape, from a die, then a mold closes around it. The plastic is then inflated.

History

Blow molding first appeared late in the 1800s, but modern polyethylene bottle production did not commence until the early 1940s.

Types

The blow molding process can take four forms: reheat and blow molding, injection blow molding, stretch blow molding and extrusion blow molding. The machinery can vary significantly, though the major difference tends to be the point of plastic inflation.

Uses

The various processes are used to create a range of products, including bleach and milk bottles. Stretch blow molding is used in the production of PET (Polyethylene terephthalate) bottles, which are widely employed for carbonated beverages.

Plastics

The plastics used in the various blow molding processes can include HDPE (high density polyethylene), LDPE (low density polyethylene), PP (polypropylene), and PVC (polyvinyl chloride).

Disadvantages of Blow Molding

Blow molding is the process in which hollow, plastic containers are made. Air is blown into molds to form items such as thermoplastic bottles, tubing and milk jugs. While blow molding allows companies to manufacture high volumes of plastic containers, which are significantly cheaper than glass, there are a few disadvantages to the process. Some disadvantages include environmental hazards and a significant dependence on petroleum.

Environmental Disadvantages

Plastic products made by the process of blow molding aren't biodegradable, which presents an obvious environmental hazard, especially when empty containers find their way to landfills. When disposed of in landfills, plastic products are buried and remain in the earth forever. Their oil-based material then becomes part of the soil and runs the risk of threatening plant life, animals and groundwater.

Dependence on Petroleum

Aside from the gasoline industry, plastic manufacturers depend on millions of gallons of petroleum in their quest to produce blow-molded products. Because oil is the most important agent in thermoplastics and blow molding is becoming more streamlined and automated, the process plays an ongoing threat on a diminishing world oil supply.

Process and Material Limitations

Although blow molding has been automated and can produce mass quantities of products, the process is largely limited to hollow forms. These forms are delicate and contain various thicknesses which must be precise, which often results in wasted material in the process of arriving at containers with proper dimensions and specifications. In some cases, thermoplastic is stretched to save on material, which can lead to substandard containers.

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Dangers of Injection Molding

Many plastic products are pressed by an injection molding machine.

Many common plastic items are created using an injection molding machine, and manufacturers point to the machine's efficiency and speed in pressing out plastic products. Much of the injection molding process is automated, and in many cases, the machine operator's role is merely to monitor it. While operation requires minimal training, there are several potential dangers to running an injection molding machine.

Heat

Depending on the type of material used, the melting point for plastic ranges from 250 to 650 degrees Fahrenheit. An injection molding machine will heat up enough to not just melt the plastic, but allow it to flow smoothly into the mold. Burns are a hazard, whether from the machine's heated surfaces, melted plastic or from the freshly molded product. In addition to eye and face protection, heat-resistant gloves may be needed while operating the machine.

Caught In the Press

On an injection molding machine, the platens join together to form the actual mold, and the plastic is molded under pressure before it is ejected. This constant movement creates a hazard, as fingers can be crushed or amputated in the press. Long hair and jewelry can also get hung up in the machinery, severely injuring the operator. Reaching into a molding machine to free up a stuck part is particularly dangerous.

Peripheral Machinery

While not part of the injection molding process, waste plastic is often thrown into a grinder that can shred the scraps--or anything else that gets into the grinder--in seconds.

Fumes

Plastics and polymers are made from different chemical compounds that, when melted, may give off hazardous fumes. An injection molding machine should only be operated in a well-ventilated area.

Flying Objects

While most products made via an injection molding machine are ejected in a controlled manner, there is still the possibility of flying objects. Eye and face protection should be worn when operating the machine.

Slipping and Falling

Good housekeeping is essential when running an injection molding machine. Scraps of plastic can quickly collect on the surrounding floor area quickly, and it is easy to lose your footing and fall. New plastic is often shipped in pellet form, which can be hazardous if spilled.

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Steps of Injection Molding

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Many popular plastic items are produced by injection molding.

Injection molding has continued to grow since the late 19th century. Capable of producing small items such as combs, it is also used to create parts for airplanes and medical supplies. It is hard to imagine the world without the products it produces. The process was patented by John Wesley Hyatt and his brother Isaiah in 1872. Today, injection molding is used to produce about 30 percent of all plastic products. The process is relatively simple, but expensive. Thus it is usually only used to mass produce items.

Instructions

1

Clamp the mold shut. This will hold the mold in place while the mold is filled with melted plastic. It will also keep the mold still while the plastic cools.

2

Inject the melted plastic into the mold. The plastic starts out as polymer resin pellets which are poured into a large open-bottomed hopper. A motor turns the auger, feeding the pellets into the cylinder where they are melted and turned into molten plastic, then pushed into the mold. The auger injects the melted plastic into the mold at a pressure between 10,000-30,000 pounds per square inch. The auger then holds the plastic, forcing more plastic in to fill the mold completely. This guarantees that the final product will not contain any gaps. A gate closes keeping the plastic inside the mold while it cools. Molds are usually either water ic belting. 35+ years' experience.

3

Drill small holes into the mold, if it is cooled by water or another liquid. The cooling period accounts for about 85 percent of the molding process. The temperature of the water is usually between 33 and 60 degrees Fahrenheit. Water below freezing can be used. However, glycol, or a similar additive, needs to be used to keep the water from freezing. The major disadvantage to using water to cool the mold is the buildup of condensation.

4

Loosen the clamp and open the mold. Remove the plastic part that was just created. Then clean the part, removing any excess plastic.

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.