Blow Molding & Plastics Discipline

Since 1999

Blow Molding Help and Associates

History of Blow Molding

History

U.S. Patent 237168  was issued on February 1, 1881, to Celluloid Novelty Co. and Celluloid manufacturing Company, New York. This was the first patent for the processing of extruded polymer into a parison for blow molding.

The first applications for blow molding were for cellulose nitrate, and later, in the 1930's, for cellulose acetate. Blow molding remained a relatively small part of the plastics manufacturing scene until the introduction of Low Density Polyethylene (LDPE) in the 1940's. The production of LDPE squeeze bottles by Monsanto caused a rapid expansion of the industry, with containers produced to replace glass bottles for shampoos and liquid soaps.

The mass production of high density polyethylene (HDPE) and polypropylene (PP) in the 1950's led to a further increase in blow molding demand, for applications such as liquid detergents, motor oil, water and milk. The lightweight HDPE one gallon milk container revolutionized the dairy industry, as glass bottles and paperboard were quickly replaced.

The production of polyethylene terephthalate (PET) led to the viability of reheat stretch blow molding. The strain hardening properties of PET allowed the high volume production of bottles able to resist the carbonation pressure in soft drink applications. The high clarity and economics of PET stretch blow molding have made this a popular production method for bottles for water, detergents, and other products.

Extrusion blow molding

In Extrusion Blow Molding (EBM), plastic is melted and extruded into a hollow tube (a parison). This parison is then captured by closing it into a cooled metal mold. Air is then blown into the parison, inflating it into the shape of the hollow bottle, container or part. After the plastic has cooled sufficiently, the mold is opened and the part is ejected.

EBM processes may be either continuous (constant extrusion of the parison) or intermittent. Types of EBM equipment may be categorized as follows:

Continuous Extrusion Equipment

· rotary wheel blow molding systems

· shuttle machinery

Intermittent Extrusion Machinery

· reciprocating screw machinery

· accumulator head machinery

Examples of parts made by the EBM process include dairy containers, shampoo bottles, and hollow industrial parts such as drums.

Basic polymers, such as PP, HDPE, PVC and PET are increasingly being co-extruded with high barrier resins, such as EVOH or Nylon, to provide permeation resistance to water, oxygen, CO2 or other substances. In dairy applications, it is possible to extrude a black light-blocking layer in the center layer of containers, with opaque white resin used in the inner and outer layers.

Compared to injection molding, blow molding is a low pressure process, with typical blow air pressures of 25 to 150 psi. This low pressure process allows the production of economical low-force clamping stations, while parts can still be produced with surface finishes ranging from high gloss to textured. The resulting low stresses in the molded parts also help make the containers resistant to strain and environmental stress cracking.

Accumulator Head Machinery is used for the extrusion blow molding of large industrial hollow parts. Examples of parts produced on this machinery include drums, trash cans, automotive panels, playground equipment, and large containers, such as Jerry Cans, for liquid storage. Most parts produced on accumulator head machinery are single layer; however, specialized machinery is capable of producing parts with up to seven unique layers of plastic - these machines are used primarily to manufacture automotive gasoline tanks with barrier layers.

Description

Accumulator Head Machinery is characterized by the accumulation of melted plastic resin in one or more extrusion heads. As extruders melt the plastic, it accumulates in the heads until the resin is ready to be extruded into parisons. An internal plunger is then activated, using hydraulic pressure, to extrude the parison through an extrusion die, between two open mold halves.

Unlike shuttle machinery or rotary wheel machinery, which are characterized by continuous extrusion, accumulator head machinery utilizes an intermittent extrusion process. This allows large, heavy parisons to be dropped in a few seconds, followed by the rapid closing of the molds. Due to the large, heavy weight of the parisons, it is not practical to slowly extrude the plastic while the prior parison is blown and cooled in the molds. Cycle times of 30 to 120 seconds or more are common in thick-walled parts, and the parisons would cool and sag if extruded slowly over this time period. The intermittent process also allows the machinery to function without shuttling the molds, which is not economical with large, heavy molds and clamping structures.

In some applications, the parison is extruded over one or more blow pins, which are used to form precise openings in the part, as well as provide an entry point for the blow air. In other applications, the blow air may enter the part through the center of the extrusion heads, or through needles, which puncture the parison.

Due to the size of parts produced, requiring large clamps, the extruders and flow-heads are typically positioned on an upper, "mezzanine" level. The clamp, electrical cabinets, operator station, and hydraulic system are typically positioned on the lower "ground" level.

 

 

 Variations

· In some cases, parts are dropped from the molds, and are removed manually from the machine without an extractor. In some cases, the parts drop onto angled trays, which then slide the parts away from the clamps, for manual removal. This approach may require longer cycle times, to allow the operators to remove the parts. The use of drop slides may also require the clamp of the machine to be elevated, increasing cost and required factory ceiling height.

· In some cases, the parts are moved from the molds into secondary cooling stations. This approach allows the operator to reduce the overall cycle time required to manufacture the part. Most Jerrycans are manufactured using secondary cooling stations.

 

History

· In 1949, Reinhold Hagen of Kautex, Siegburg Germany, develops the first blow molding machine for processing polyethylene.

· In the 1960's, reciprocating screw blow molders were developed, with single or double heads with up to 10 lb (4.5 kg) plastic shot capacity. These were precursors of modern accumulator head machines.

· In 1964, the first prototype plastic fuel tank was produced by Kautex. Uniloy introduced the first "unitized block" construction machine.

· In 1972, Barr Polymer produced the first American accumulator machine. This technology was later sold to Uniloy.

· In 1973, the first commercial polyethylene fuel tanks were produced by Kautex and installed in the production series Volkswagen Passat.

· The first Sterling single 10 lb (4.5 kg) accumulator machine, with a 36 x 30 in (914 by 762 mm) press and MACO IV controller was demonstrated at NPE 1979.

· In the 1980's the advent of modern "engineering plastics" such as Noryl® Modified Polyphenylene Oxide, spurred a generational leap in accumulator head machinery, as early generations of these materials had reduced melt strength. To be able to process these resins, machinery was developed including modern features such as:

o High press closing speeds, > 1200 in. per minute.

o Proportional valve hydraulics used with variable displacement pumps

o Hydraulic pre-fill valves for fast clamp closing and lock-up.

o Entire hydraulic system filtration to 3-10 micrometers, eliminating the need for a separate tank for parison programming.

o In 1994, the first co-extruded (multilayer) fuel tank was utilized in series production. Milacron also produced their first commercial machines that year.

o In 1995, Graham Engineering produced their first commercial accumulator head machine - a dual 10-lb. with 60x40 in. press and MACO 6500 controller. Krupp introduced the first 7-layer accumulator machine.

o In 2002, Graham Engineering introduced the first accumulator machine with PC controls.

o In 2005, Graham Engineering began delivery of 5-head machines, utilizing a shooting pot to accumulate the melt, for high volume production of mid-sized industrial parts.

Reciprocating screw machinery

Reciprocating screw machinery is used for the extrusion blow molding of hollow containers. Examples of parts manufactured from these machines include lightweight HDPE bottles for dairy and water, as well as large 3-5 gallon polycarbonate bottles for water coolers.

Description

Reciprocating Screw blow molding machines are characterized by the use of a reciprocating screw extruder, as is used in injection molding. As the screw melts the resin, the screw moves backward, allowing the melted plastic to accumulate in the end of the barrel. When the screw pushes forward under hydraulic pressure, the plastic is pushed out of the barrel, extruded through a flow-head and die, to form a plastic parison.

Unlike shuttle machinery or rotary wheel machinery, which are characterized by continuous extrusion, reciprocating screw machinery utilizes an intermittent extrusion process. This allows the parisons to be dropped quickly (in some cases less than one second), followed by the rapid closing of the molds.

In most cases, the molds are stationary, and do not shuttle sideways. Rather, the parts are extracted from the molds, and then the parison is dropped between the open mold halves.

Reciprocating extrusion blow molding machinery is used to manufacture monolayer parts, as intermittent processes are now well suited for co-extrusion. These machines can be broken down into at least two major families:

 

Variations

· Side Shift Clamps can be utilized to allow the production of bottles with offset necks.

· Neck-to-Neck molding can be used to make two bottles per parison simultaneously. This requires needle air blow, and eliminates the possibility of pre-finished necks. Although possible for small, single-serve spin trimmed bottles, this practice has not yet achieved commercial acceptability due to the added complexity of capturing two containers with a free-falling lightweight parison.

· Shot Pot Extrusion allows the use of a continuous extrusion system, and optional screen changer. In this approach, the resin is extruded into a shot pot accumulation chamber, then forced through the flow-heads by activating a hydraulic ram cylinder. This can lead to an improvement in cycle time through faster parison drop speeds, and in some cases, lower melt temperatures.

· Parison Programming is utilized in some industrial applications, but is not normally required due to the fast drop speeds and relative uniform wall thickness in properly designed lightweight HDPE containers.

 

Water Bottle Machinery

This equipment was originally engineered to be simple, versatile, and capable of producing basic bottles and containers. However, without integral bottle trimming capability, most applications were centered on the production of various “niche” industrial, recreational, automotive, and novelty type products.

This family of machines utilizes a reciprocating screw extruder with a direct feed “flow through” die head design for forming the parison. Cantilevered clamp systems are non-shuttling for simplicity and provide open access for convenient part extraction.

 

In the mid to late 1970’s the 5-gallon polycarbonate water bottle market began to develop and Improved Blow Molding, working with GE Plastics, designed and supplied a number of special "B30" model blow molding machines to meet the need. That “niche” market enjoyed significant domestic growth in the ‘80’s and significant growth worldwide in the ‘90’s.

Both Single and Dual Head configurations are common in the industry. Hydraulic extruders are commonly used. The use of hydraulic compaction blow pin assemblies to allow the production of necks with unblemished sealing surfaces has improved the performance of the containers by greatly reducing the number of "leakers."

 

History

· Lightweight Bottle Machinery

o The Rocheleau Tool & Die Co., Inc. is established in 1938 by Leopold A. Rocheleau. They later develop a niche in reciprocating screw machinery for small containers.

o In the 1950's, the Uniloy Division of Hoover Ball & Bearing becomes the first American supplier of blow molding machinery. They go on to develop machinery and patents for the production of "hollow-handle" plastic bottles for the dairy packaging market.

o In 1985, Uniloy was purchased by Johnson Controls, and continues market dominance in light weight dairy bottle machinery.

o APS Plastics Systems is formed by former Uniloy employees in 1997.

o Uniloy became part of Milacron Inc. in 1998.

o In 1998, Liberty Blow Molding also emerges, competing with Milacron in large bottle reciprocating screw blow molding.

o Liberty is purchased by Uniloy in 1992, after achieving 40% market share in four years, and shipping some 100 machines.

o Graham Engineering purchases the technology of APS Plastics Systems in 2003. GMG capitalizes on refinements such as shot pot technology as a viable alternative to reciprocating screw extruders.

· Bottle Machinery

o This equipment product line is relatively old, originating in 1960 and produced by IMPCO, a NH based injection molding machine manufacturer. IMPCO (a.k.a. Improved) subsequently became part of Ingersoll-Rand Co. in 1964.

 

o In the mid to late 1970's the 5-gallon polycarbonate water market develops.

o IMPCO was subsequently purchased by Goodman Equipment Corporation of Chicago in 1979.

o The Improved Blow Molding B15-R35, B30-R180, and B37-R250 product line was purchased from Goodman Equipment Corp. by Graham Engineering in 2000. At that time, around 800 Improved machines has been sold.

o GMG redesigned the product line, introducing the C30 machine in 2001. This machine was noteworthy in that it was designed for optimum production of PC water bottles, at up to 150 bottles per hour, and utilized PC controls.