Blow Molding and Rotational Molding Presentation MatE 186 03/13/02 Group 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 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 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 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)