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Blow molded panels assembly
C-90A Room Air Purifier Friedrich Corporation, TX
Work performed  with Industrial Design Associates, Inc.

 Materials & Manufacturing Processes:
 Blow Mold
Stretch Blow Mold
Injection Blow Mold
Stretch Blow molding (preform)

       Blow molding is a manufacturing process by which hollow, thin wall plastic parts are formed. In general, there are three main types of blow molding; Extrusion Blow Molding, Injection Blow Molding, and Stretch Blow Molding or preform.  Blow molding is standard practice in materials including LDPE (Low Density Polyethylene) and PET (polyethylene terephthalate) is used for squeeze bottle and jug containers historically replacing glass in shampoos and liquid soap packaging.  HDPE (High density polyethylene) and polypropylene (PP) applications include liquid detergents, motor oil, water and milk.  The production of (PET) led to the viability of reheat stretch blow molding allowing high volume production of bottles which able to resist the drop impact, carbonation pressures and cooling in cold and hot fill, liquid container packaging, filling and sealing applications. The high clarity and economics of PET stretch blow molding is the process used for manufacturing bottles for water, detergents, and other liquid house-hold products. PET blends and layered film technology has lead to other applications including beer bottles. (see Rocky Light)

       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 tool  clamping, resulting lower polymer tension stresses in the molded parts improving the containers resistant to mechanical force strain and environmental stress cracking.   Surface finishes can range from high gloss to heavily textured.

       In Extrusion Blow Molding (EBM), a thermoplastic is melted and extruded into a hollow tube or parison.  This parison or tube or bag of softened plastic is captured by closing the core-cavity, temperature controlled, aluminum or steel tool.  Pressurized air is then blown into the parison, closed mold - inflating into the interior core-cavity surface wall geometry, mold shape of the hollow bottle, container or part.  After the plastic has cooled sufficiently, the mold is opened and the part is ejected.  Types of EBM equipment may be categorized including: continuous extrusion (constant extrusion of the parison) and intermittent extrusion machinery.  Examples include dairy containers, shampoo bottles, hoses, pipes, and hollow industrial parts such as drums.

    

 

(Courtesy of Ball Corp)
       An example is the Ball Corporation working with Coors new PET (polyethylene terephthalate) bottle which incorporates Ball Corp.'s Amazon HM(TM) multilayer barrier technology which is a nylon composite material that provides both an active oxygen barrier and a passive carbon dioxide barrier. The bottle design is complimented with the trademark Rocky Mountains with an embossed grip texture, silhouetted around the shoulder.  PET  is a form of polyester used to make strong, lightweight, shatter-resistant, clear or color tinted bottles.



     Basic polymers, thermoplastic materials including LDPE (Low Density Polyethylene) and  HDPE (High density polyethylene) and polypropylene (PP) are common.  PET (polyethylene terephthalate) and PC (polycarbonate) are increasingly being coextruded with high barrier resins, such as EVOH or Nylon, to provide permeation resistance to water, oxygen, CO2 or other substances.  These extrusion process , engineered plastics materials and technology advances including multi-layered or coextrusion of different types of thermoplastics combined with EBM are being developed to achieve the desired structural, optical chemical UV and color fade resistance, among others, for both interior and exterior specified environmental performance.

 

Injection blow molding

       The process of Injection Blow Molding (IBM) is used for higher precision applications the production of hollow glass and plastic objects in large quantities. In the IBM process, the polymer is injection molded onto a core pin; then the core pin is rotated to a blow molding station to be inflated and cooled. This is the least-used of the three blow molding processes, and is typically used to make small medical and single serve bottles. The process is divided into three steps: injection, blowing and ejection.

    The injection blow molding machine is based on an extruder barrel and screw assembly which melts the polymer. The molten polymer is fed into a manifold where it is injected through nozzles into a hollow, heated preform mold. The preform mold forms the external shape and is clamped around a mandrel (the core rod) which forms the internal shape of the preform. The preform consists of a fully formed bottle/jar neck with a thick tube of polymer attached, which will form the body.

       Preform is a process where the parison is first stretched mechanically with a stretch rod. As the rod travels down low-pressure air (70 to 350 psi) is introduced blowing a 'bubble'. Once the stretch rod is fully extended, high-pressure air of up to 40 bar (580 psi) blows the expanded bubble into the shape of the blow mold.   The preform mold opens and the core rod is rotated and clamped into the hollow, chilled blow mold. The core rod opens and allows compressed air into the preform, which inflates it to the finished article shape.

After a cooling period the blow mold opens and the core rod is rotated to the ejection position. The finished article is stripped off the core rod and leak-tested prior to packing. The preform and blow mold can have many cavities, typically three to sixteen depending on the article size and the required output. There are three sets of core rods, which allow concurrent preform injection, blow molding and ejection.

Another application of injection blow molding is in the production of soft elastic gelatin capsules for pharmaceutical applications. Two strips of gelatin are pressed together in a rotary die which cuts out the desired shape of capsule while the fill liquid is injected. Afterwards, they are cooled and dried to yield a firm, strong capsule.

       The main applications are bottles, jars and other containers. The Injection blow molding process produces bottles of superior visual and dimensional quality compared to extrusion blow molding. The process is ideal for both narrow and wide-mouthed containers and produces them fully finished with no flash. A sign of injection blow molding is the seam where the two halves of the mold meet

Manufacturing Engineering & Processes (ManufE)
 

Injection Mold (IJ)
RIM  Reaction Injection Mold
Lost Core Injection Mold
Gas Assist Injection Mold

Thermoform  (Vacuum form)
Compression Mold
Twin Sheet Thermoform

Blow Mold  (Top of Page)
Stretch Blow Mold
Injection Blow Mold
Stretch blow molding (preform)

Roto Mold
Spin Cast Mold

Extrusion
Coextrusion

Metal Forming
Cast & Die Cast

 

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