Whats the best way to make these bottles? Heres a guide to the major types of blow molding equipment and processes.

Whether you are new to blow molding or have been in the industry for 30 years, it can still be confusing to know what type of machinery or process is best for your next application. Having designed and built machinery for every type of blow molding process, I have identified six primary machinery processes for packaging applications.

These are:

1) Shuttles (Continuous extrusion)

2) Wheels (Continuous extrusion)

3) Injection Blow

4) Injection Stretch Blow (one-step)

5) Reheat Stretch Blow (two-step)

6) Reciprocating Screw (Intermittent extrusion)

Some people may refer to these differently and some may argue several of these should be grouped together. But for sake of discussion, this article will address these six types – first defining the technologies, and then giving a quick look at the pros and cons of each. Remember, too, that processing technology changes quickly, and you should always check with your machinery supplier to learn about their latest capabilities and improvements.

Shuttle Machinery

This is the most popular type of machinery for blow molding high-density polyethylene (HDPE) and polypropylene (PP) containers around the world. Literally thousands are sold every year.

A shuttle machine consists of either single or dual clamps that shuttle (or slide) from under the die head to a blow pin assembly for blowing. The machines come in all sizes and configurations from single cavity to as many as 20 to 30 cavities, and bottle sizes from a few ounces up to a 10-liter jerry can. Included in the shuttle group is the long-stroke type machine. Popular manufacturers include Bekum, SIG, Automa and Magic to name only a few of hundreds.

PROS

Relatively inexpensive for small- to medium-volume production requirements.

Can deliver containers with a calibrated neck.

Typically trims the container prior to exiting machine.

Most flexible in container size and number of cavities.

Can handle coextrusion.

Can handle all shapes including handleware.

CONS

Cannot process polyethylene terephthalate (PET).

Hydraulics and controls can be complex.

May require multiple machines for very high production volumes.

Difficult to consistently process multiple parisons, the hollow tube of molten plastic that is inflated to take the shape of the mold, to form the container.

Wheel (Rotary) Machinery

The rotary blow molders are the machine of choice for very high volumes of containers, for markets such as liquid detergent, motor oil and juice in North American markets. Wheels are typically chosen over shuttles because of processing ease (and cost) due to single-parison technology and lower cost per container for high volume applications. This is especially true for coextrusion and multilayer applications.

Wheel machines can be designed to handle a wide range of container sizes, but are typically committed to a narrow range of container variation after built. Because the containers are blown with a needle (instead of a blow pin), it is not unusual to blow containers in a neck-to-neck configuration to increase the production output.

Wheels come in various configurations, including indexing, continuous motion, vertical (like a ferris wheel), and horizontal (like a merry-go-round). Some even now have the capability to produce calibrated neck containers. Most, however rely on downstream trimming equipment to trim and finish the container. Major manufacturers include Wilmington Machinery and Graham.

PROS

Lowest cost method for high volume production requirements.

Simple design and controls for maintenance.

Single parison well suited for multilayer application for repeatability and cost.

Easy to utilize in-mold labeling.

Can achieve very high production volume from a single machine.

CONS

Typically cannot be converted to a different number of cavities, once built.

High investment requires a commitment to high-volume production situations.

Requires secondary trimming and finishing equipment.

Injection Blow Machinery

These machines inject-mold a preform onto core rods and then index the core rods to a blow station to blow the container. Machines typically have three to four stations to allow for checking condition and part removal. They are utilized extensively for very small containers such as pharmaceutical and hotel shampoo type containers. Major manufacturers are Jomar, Procrea and Milacron.

PROS

Scrapless process, meaning there is no flash to trim and no regrind.

Typically suited for containers 0.5 liter and smaller.

Capable of running a wide range of materials.

High quality injection-molded neck finish.

CONS

Very high tooling cost per container – typically 40 to 50 percent of the machine cost.

Difficult to run co-injection or multilayer containers.

Minimum cycle time typically 12 to 15 seconds.

Cannot do handleware.

Injection Stretch Blow (one-Step)

This process is almost entirely dedicated to PET and more recently, polypropylene applications. The process is very similar to Injection Blow described above, except for two areas.

First, the preforms are not transported on core rods but instead are held by the neck finish. Second, during the blowing process, rods stretch the preform prior to blowing to orient the material. For materials such as PET, this biaxial orientation substantially increases the physical properties-to-weight ratios. Major manufacturers include Aoki and Nissei.

PROS

Scrapless process, meaning no flash to trim and no regrind.

Allows for biaxial orientation for strength and clarity.

High-quality injection-molded neck finish.

Typically suited for 0.5-liter up to 20-liter containers.

Suitable for PET containers, including for noncarbonated beverages.

Capable of lower volume production applications.

Does not require separate preform mold and machine.

CONS

Higher tooling cost.

Minimum cycle is typically 12 to 15 seconds.

Cannot produce carbonated beverage containers. (Theres not enough biaxial orientation, due to high preform temperatures at blowing.)

Not well-suited for polyolefins.

Cannot blow handleware.

Difficult to run co-injection or multilayer.

Reheat Stretch Blow (Two-Step)

This process is also almost 100 percent for PET applications. The process utilizes preforms made on a stand-alone injection-molding machine, stored and then reheated and stretch-blown similar to the one-step process above.

Here however, the pre-forms are blown at a lower temperature, allowing the maximum amount of biaxial orientation and therefore the maximum strength-to-weight ratios. The reheat process can be used for ultra-high output type applications, such as carbonated soda bottles, while other machines can be smaller for medium- to high-volume production requirements. Major machinery manufacturers include Sidel.

PROS

Can be very high-speed production (40,000 containers per hour).

Produces a very high strength-to-weight ratio container.

Can purchase or make preforms.

Primarily PET material.

Machines for low- and medium-volume application are becoming available.

CONS

Cannot mold handle-ware.

Not typically suitable for polyolefins.

User must have a separate preform mold and injection-molding machine, or purchase pre-forms.

For low-volume production, if special design pre-form is required, cost can be high.

Reciprocating Screw (Intermittent extrusion)

This is the most popular and cost-effective method to produce lightweight dairy and juice containers. In this process the extruder feed screw reciprocates similar to an injection molding machine. The molds are stationary under the die head, where they simply open and close, but do not shuttle. As the screw moves forward, the parison is pushed out into the molds for blowing.

For lightweight containers, cycle times can be very fast – sometimes under 5 seconds. Major machinery manufacturers include Rocheleau and Uniloy.

PROS

Capable of very fast cycle times.

Simple machine motions, since clamps do not move.

Capable of 16 cavities for small bottles, or eight 1-gallon containers. Smaller models are available.

Relative low cost per cavity.

Can easily run homo-polymers and very low melt temperature materials.

CONS

Limited primarily to monolayer applications.

Primary materials are HDPE and limited amount of PP.