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!!!