1. 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

2. Presentation Overview
Blow Molding
Blow molding process, background, & methods
Laboratory objectives
Experimental operating conditions
Experimental results
Rotational Molding
Rotational molding background
Conclusion

3. 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

4. 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

5. Different Methods of Blow Molding
Pinch-neck & in-place process
Neck-ring, trapped-air & continuous-parison process
Pinch-parison rotary process (shown)

6. Two Basic Processes for Blow Molding
Injection blow molding
Extrusion blow molding
The difference between the two is in the production of the parison

7. 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

8. 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

9. 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

10. 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)

11. Blow Molding Laboratory Objectives
Extrusion blow mold five satisfactory bottles with Flex blow molding machine
Become familiar with controls and process of blow molding

12. 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

13. 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

14. Results of Experiment
Several bottles were produced with varying quality
Enough relevant samples were collected for analysis

15. 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

16. 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

17. 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

18. Processing: Rotational Molding
*Rotational Magazine

19. 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

20. Rotational Molding Laboratory Objectives
Produce one satisfactory part using LDPE and pigment
Practice and become familiar with controls and process of rotational molding

21. 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

22. 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.

23. 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

24. 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)