Exam 3 Flashcards
List four decision criteria when choosing between extrusion blow molding and injection blow molding process
- Part size
- Wall thickness
- Tooling cost
- Cycle time
Why PET carbonated beverage containers are made by stretch blow molding rather than extrusion blow molding
The container results in biaxial orientation and increased properties, the biggest advantage is improved in mechanical properties, so less material can be used making the part cheaper.
define blow ratio
Mold diameter/ parison diameter
Draw a schematic and describe the programmable parison? explain its advantages over non-programmable one
In parison programing, the mandrel or bushing is movable. wall thickness can be controlled better
Advantages: reduction in plastic used, even wall thickness, equal weight distribution, fast production
Can thermoforming be used to manufacture thermoplastic composite parts with glass woven matts? describe a process that may lend itself to this application
yes, it has been proven possible to thermoform woven glass mat fiber by using a 2 part mold to help the part gain the correct shape and making sure the radius of curvature does not exceed 5 degrees. draft angels should not exceed 3 degrees. the laminates are also assisted y heating for 120 seconds at
In thermoforming polystyrene has a larger processing window that polypropylene. Why?
because it has a lower degree of crystallization. More amorphous materials have larger Tg ranges which helps the material to stretch and deform in thermoforming rather than moving directly from solid to liquid
You are thermofroming a part using a square blank. all the parts made on Monday have different final dimensions compared to all the other parts you have been making. the engineers have checked all the possible paramters and they claim that they are all the same as before. What are some possible reasons for this
It is possible that the blanks were turned 90 degrees, having a different orientation of the blanks will affect the outcome of the part
Two advantages and Two disadvantages of rotational blow molding
Advantage: Wall thickness, good for hollow parts
Disadvantage: waring, long cycle times
why rotational molding is not an ideal candidate for production of reinforced parts
Fiber reinforcement adheres poorly to cavity
Why almost 85% of roto-molded parts are made of PE
It is available in powder form, It has a low cost and is lightweight, easily moldable and has good impact strength.
Dry flow is used as a measure to quantify the grade of powders used in rotation molding. Define “dry flow”
Dry flow is the amount in area that long pellets are able to move through a given area
When do you recommend the utilization of transfer compression molding in place of conventional compression molding
Transfer compression molding is better for larger parts that would require a lot of pressure to extrude the material. It is also recomended for reinforced materail that should be more isotropic ( less influenced by flow of material)
