Blow Molding and Rotational Molding Presentation MatE 186 03/13/02 Group 2 Members: Brandon Cheney...
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Transcript of Blow Molding and Rotational Molding Presentation MatE 186 03/13/02 Group 2 Members: Brandon Cheney...
Blow Molding and Rotational Molding Presentation
MatE 186
03/13/02Group 2 Members:
Brandon Cheney
Adam Falk
Rick Kruger
Jaquelina Lee
Diane O’Donnell
Santosh Iyer
Joumana Zeid
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
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
Blow Molding Background
• Blow molding technique has been used in making glass for centuries, but only recently (late 1950’s) 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
Different Methods of Blow Molding • Pinch-neck & in-place process• Neck-ring, trapped-air & continuous-parison
process• Pinch-parison rotary process (shown)
Two Basic Processes for Blow Molding
• Injection blow molding
• Extrusion blow molding
• The difference between the two is in the production of the parison
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
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
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
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)
Blow Molding Laboratory Objectives
• Extrusion blow mold five satisfactory bottles with Flex blow molding machine
• Become familiar with controls and process of blow molding
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
Blow Molding Operating Conditions
• The extruder die was heated to 280°F and the barrel was heated to 290°F
• 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
Results of Experiment
• Several bottles were produced with varying quality
• Enough relevant samples were collected for analysis
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
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
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
Processing: Rotational Molding
*Rotational Magazine
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
Rotational Molding Laboratory Objectives
• Produce one satisfactory part using LDPE and pigment
• Practice and become familiar with controls and process of rotational molding
Rotational Molding Operating Conditions
• Rotational molder was pre heated to 350°F 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
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.
Lab Activity Conclusion- Rotational Molding
• Even though product was satisfactory, it wasn’t 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
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)
Thank You!!!