Chapter 2 Final (blow molding focused)

Question 1

What is blow molding?

Answer 1

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.

Question 2

What are the three main types of blow molding?

Answer 2

The three main types of blow molding are injection blow molding, extrusion blow molding, and stretched blow molding.

Question 3

What is the purpose of the parison in blow molding?

Answer 3

The parison is a hollow tube of molten plastic that is inflated inside the mold to form the desired shape of the final product.

Question 4

What is injection blow molding?

Answer 4

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.

Question 5

What are the advantages and disadvantages of injection blow molding?

Answer 5

• 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.

Question 6

What is extrusion blow molding?

Answer 6

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.

Question 7

What are the advantages and disadvantages of extrusion blow molding?

Answer 7

• 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.

Question 8

What is stretched blow molding?

Answer 8

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.

Question 9

What is the purpose of stretching the preform in stretched blow molding?

Answer 9

Stretching the preform aligns the polymer molecules, which improves the strength, clarity, and barrier properties of the final product.

Question 10

What types of products are typically made using stretched blow molding?

Answer 10

Stretched blow molding is commonly used to produce high-quality containers such as PET bottles for beverages.

Question 11

What is the role of air pressure in blow molding?

Answer 11

Air pressure is used to inflate the parison inside the mold, forcing it to take the shape of the mold cavity.

Question 12

What happens during the cooling cycle in blow molding?

Answer 12

During the cooling cycle, the inflated plastic part solidifies and takes its final shape. The mold is then opened, and the part is ejected.

Question 13

What is the purpose of the mold in blow molding?

Answer 13

The mold defines the shape of the final product. The parison is inflated inside the mold to form the desired shape.

Question 14

What types of plastics are commonly used in blow molding?

Answer 14

polyethylene (PE), polypropylene (PP), polyvinyl chloride (PVC), and polyethylene terephthalate (PET).

Question 15

Why is PET commonly used in stretched blow molding?

Answer 15

PET is commonly used in stretched blow molding because it has excellent clarity, strength, and barrier properties, making it ideal for beverage bottles.

Question 16

What are some common defects in blow molding?

Answer 16

uneven wall thickness, flash (excess material), warping, and surface imperfections like orange peel.

Question 17

How can uneven wall thickness be prevented in blow molding?

Answer 17

Uneven wall thickness can be prevented by ensuring proper parison control, uniform heating, and consistent air pressure during the blowing process.

Question 18

What causes flash in blow molding, and how can it be minimized?

Answer 18

Flash is caused by excess material escaping from the mold seams. It can be minimized by ensuring proper mold clamping force and precise parison control.

Question 19

What causes warping in blow-molded parts, and how can it be prevented?

Answer 19

Warping is caused by uneven cooling or stress in the material. It can be prevented by ensuring uniform cooling and proper mold design.

Question 20

What is the orange peel effect in blow molding, and how can it be avoided?

Answer 20

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.

Question 21

What causes bubbles in blow-molded parts, and how can they be minimized?

Answer 21

Bubbles are caused by trapped air or moisture in the material. They can be minimized by properly drying the plastic before processing and ensuring adequate venting in the mold.