Blow Molding and Rotational Molding Presentation

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Blow Molding and Rotational Molding Presentation

• MatE 186
• 03/13/02
• Group 2 Members
• Brandon Cheney
• Adam Falk
• Rick Kruger
• Jaquelina Lee
• Diane ODonnell
• Santosh Iyer
• Joumana Zeid

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Presentation Overview

• Blow Molding
• Blow molding process, background, methods
• Laboratory objectives
• Experimental operating conditions
• Experimental results
• Rotational Molding
• Rotational molding background
• Laboratory objectives
• Experimental operating conditions
• Experimental results
• Conclusion

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Blow Molding Process

• A tube of extruded plastic, called parison, is
  clamped between two female halves of a mold. Air
  pressure then forces the parison to form against
  the walls of the mold. Sometimes referred to as
  Molding Technique
• Actually an extrusion process, since the material
  is shaped by being forced through an extruder

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Blow Molding Background

• Blow molding technique has been used in making
  glass for centuries, but only recently (late
  1950s) has it been tailored for the plastics
  industry
• The first blow-molded part was a rattle, formed
  by heating two sheets of celluloid and clamping
  them together in a mold. Forced air expanded the
  celluloid to form the rattle

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Different Methods of Blow Molding

• Pinch-neck in-place process
• Neck-ring, trapped-air continuous-parison
  process
• Pinch-parison rotary process (shown)

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Two Basic Processes for Blow Molding

• Injection blow molding
• Extrusion blow molding
• The difference between the two is in the
  production of the parison

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Injection Blow Molding

• More accurate in producing the desired container
  wall thickness in particular areas
• Also called transfer blow because the preform is
  transferred to the blowing mold

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Advantages and Disadvantages of Injection Blow
Molding

• Advantage
• Can easily reproduce any shape with varying
  thickness
• No scrap or excess bottom weld to recycle
• Low cost of materials and equipment
• Disadvantage
• Two molds are needed one to make the preform,
  and the other for the air blowing process

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Extrusion Blow Molding

• Parison is extruded continuously, except when an
  accumulator or ram is used
• The parison is closed up in the mold halves,
  closing off the bottom half of the parison
• Air is forced in from the top, expanding the
  parison against the mold walls

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Advantages and Disadvantages of Extrusion Blow
Molding

• Advantage
• Can produce strain-free articles at high
  production rate
• Low cost of materials and equipment
• Disadvantage
• Recycling of scrap is necessary
• Difficult to control thickness of the wall
  (called programming)

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Blow Molding Laboratory Objectives

• Extrusion blow mold five satisfactory bottles
  with Flex blow molding machine
• Become familiar with controls and process of blow
  molding

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Blow Molding Experimental Equipment

• Flex blow-molding machine (PM micrometer)
• Extruder A die which forms a molten parison of
  thermoplastic material
• Hopper Raw materials in the form of pellets are
  fed through the hopper
• Blow Mold Gives the parison its final shape

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Blow Molding Operating Conditions

• The extruder die was heated to 280F and the
  barrel was heated to 290F
• Polyethylene and pigment were added to the hopper
• Air pressure was set at 10psi
• Cold water bucket was placed under the mold to
  collect waste

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Results of Experiment

• Several bottles were produced with varying
  quality
• Enough relevant samples were collected for
  analysis

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Defects in Experimental Product

• Bubbles present in the parison could be
  attributed to
• Presence of moisture in the raw material
• Contamination of raw material
• Higher extruder die temperature
• Excess parison stretching or thinning which could
  be attributed to
• High stock temperature
• Uneven thickness of parison which could be
  attributed to
• Higher melt temperature
• Uneven heating of the extruder die

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Lab Activity Conclusion- Blow Molding

• The experiment was a success
• Obtained a good number of satisfactory bottles
• For best results
• Always watch the temperature dials
• Pack polymer pallets to avoid air bubbles
• Aim for uniform thickness when molding

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Background Rotational Molding

• This process has been in existence since the
  early 1930s
• The introduction of micro-sized polyethylene in
  the late 1950s has provided the industry with an
  ideal material for the rotational molding process
• Since that time, the industry has continued to
  grow at a steady rate

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Processing Rotational Molding
Rotational Magazine
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Advantages Rotational Molding

• Well suited to producing relatively large,
  hollow, seamless parts which are partially or
  totally enclosed
• Ideal for small or large parts of unusual shape
  that cannot be produced as one piece by other
  processes
• Relative to their size, rotationally molded parts
  can have thinner walls than similar parts made by
  other processes
• Rotational molding tends to produce an increasing
  wall thickness on outside corners of parts

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Rotational Molding Laboratory Objectives

• Produce one satisfactory part using LDPE and
  pigment
• Practice and become familiar with controls and
  process of rotational molding

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Rotational Molding Operating Conditions

• Rotational molder was pre heated to 350F for 45
  min
• Mold was coated with mold release agent
• 80 Powder LDPE and pigment was added to the
  bottom of the mold
• Mold was rotated and heated for 45 min
• Mold was cooled for 5 min in water bath

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Rotational Molding Results

• Two satisfactory products were produced gray
  football and green baseball
• Exterior shape of the football and baseball were
  acceptable. However, the wall thickness for the
  football and baseball were not even.
• A smaller size football, which only had one side,
  formed inside the external football. The same
  thing happened to the baseball.
• Excess polymer powder was found inside both of
  the products.

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Lab Activity Conclusion- Rotational Molding

• Even though product was satisfactory, it wasnt
  perfect
• Interior product was due to the mold falling out
  of its holder
• For better results
• Check for technical problems before starting the
  molding process.
• Avoid Stopping process once started
• Leave in the molder for sufficient time
• Avoid putting too much polymer powder in molder

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Conclusion

• Blow molding and rotational molding are common
  polymer processing techniques
• Both processes can be completed using equipment
  in the SJSU lab
• Experiments demonstrated versatility of the
  different molding processes (different colors,
  shapes, sizes, and materials available to suit
  specific applications)

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Thank You!!!