Machinery's Handbook, 31st Edition
MANUFACTURING WITH PLASTICS 585 maintained on the threaded closures where the mold halves meet; elsewhere they are looser, comparable to those of sheet thermoforming. As in thermoforming, when a par- ticular product, such as a half-gallon or 2-liter bottle, warrants a very high production rate, highly automated, multi-station machines are economical.
Air
Top Air Cushion Escape
Plug
Bottom Air Cushion Escape
0 Seconds
Air Cushion
Heater Plastic in Clamping Frame
3
1
2
3
Air
Vacuum
0 Seconds
Top Air Cushion Escape
Cavity Mold
3
1
2
0 Seconds
Bottom Air Cushion Escape
1
Air
Vacuum
3
1
2
Air
4
Air
Vacuum
Plug Returning
Plug Returning
Air Escape
0 Seconds
0 Seconds
3
1
3
1
2
2
2
5
Air
Vacuum
Air
Vacuum
Fig. 14. Five Stages in the Cycle of Air-Cushion Vacuum Forming with Controlled Air Pressures at Stages 3 and 4. Removal and Trimming Follow Stage 5.
Crosshead Die
Cutting Knife
Parison
Rising Mold Halves
Lower Mold, Extrusion Continues
Air
Part Ejected
Fig. 15. Six Stages of Extrusion/Blow Molding
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