Chapter 2 Final (blow molding focused) Flashcards
What is blow molding?
Blow molding is a manufacturing process used to create hollow plastic parts by inflating a heated plastic tube (parison) inside a mold until it takes the shape of the mold cavity.
What are the three main types of blow molding?
The three main types of blow molding are injection blow molding, extrusion blow molding, and stretched blow molding.
What is the purpose of the parison in blow molding?
The parison is a hollow tube of molten plastic that is inflated inside the mold to form the desired shape of the final product.
What is injection blow molding?
Injection blow molding is a process where a preform (a hollow tube of plastic) is first created by injection molding and then transferred to a blow mold where it is inflated to form the final product.
What are the advantages and disadvantages of injection blow molding?
- the ability to produce parts with accurate material thickness in specified areas, no scrap to reprocess, and high precision in part dimensions.
- But requires two different molds: one for the preform and another for the actual blowing operation, which increases equipment costs.
What is extrusion blow molding?
Extrusion blow molding is a process where molten plastic is extruded into a hollow tube (parison), which is then clamped into a mold and inflated to take the shape of the mold cavity.
What are the advantages and disadvantages of extrusion blow molding?
- ability to use most thermoplastics and thermosets, efficient material blending, and lower cost compared to injection molding.
- But higher machine costs, the need for purging and trimming which produces waste, and sometimes requiring a second operation for finishing.
What is stretched blow molding?
Stretched blow molding is a process where a preform is first stretched longitudinally and then inflated radially to produce high-quality containers with improved mechanical properties.
What is the purpose of stretching the preform in stretched blow molding?
Stretching the preform aligns the polymer molecules, which improves the strength, clarity, and barrier properties of the final product.
What types of products are typically made using stretched blow molding?
Stretched blow molding is commonly used to produce high-quality containers such as PET bottles for beverages.
What types of plastics are commonly used in blow molding?
polyethylene (PE), polypropylene (PP), polyvinyl chloride (PVC), and polyethylene terephthalate (PET).
Why is PET commonly used in stretched blow molding?
PET is commonly used in stretched blow molding because it has excellent clarity, strength, and barrier properties, making it ideal for beverage bottles.
What are some common defects in blow molding?
uneven wall thickness, flash (excess material), warping, and surface imperfections like orange peel.
How can uneven wall thickness be prevented in blow molding?
Uneven wall thickness can be prevented by ensuring proper parison control, uniform heating, and consistent air pressure during the blowing process.
What causes warping in blow-molded parts, and how can it be prevented?
Warping is caused by uneven cooling or stress in the material. It can be prevented by ensuring uniform cooling and proper mold design.
What is the orange peel effect in blow molding, and how can it be avoided?
The orange peel effect is a surface imperfection that resembles the texture of an orange peel. It can be avoided by ensuring proper material flow, uniform heating, and smooth mold surfaces.
