Blow molding

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Revision as of 09:48, 12 February 2007

Definition

Blow molding is used to manufacture hollow plastic parts, and can be performed via extrusion, injection or stretch processes.

Process

Extrusion blow molding (EBM)

1) Plastic is extruded into a hollow tube (called a parison).

2) Melted plastic accumulates at end of barrel around which tube is extruded, closing the form.

3) The parison is captured in a metal mold.

4) Air is blown into the cavity, stretching the parison into the desired shape.

5) The part is removed from the mold after sufficient cooling.

EMB can be continuous or intermittent. If it is continuous, blow molds may either rotate or shuttle with respect to a fixed extrusion head. In intermittent processes, the molds are stationary and the parisons are dropped into them.

Injection blow molding (IBM)

1) Molten plastic is injected into a hollow mold around a core rod.

2) The outer mold is removes.

3) The remaining core rod and initial form are clamped into a cooled blow mold.

4) The rod is removed and pressurized air creates the final shape.

This is the least common type of blow molding, for use with small bottles or one time only applications.

Stretch blow molding (SBM)

The stretch blow molding process.

1) Forming of parison.

2) Parison placed into neck of bottle (final mold).

3) Core rod stretches parison into bottle, with an initial air pressure of 70 to 350 psi.

4) When stretch rod reaches the bottom of mold, pressure is increased to 580 psi creating the final form.

This type is most preferable because it offers optimal structural and cosmetic advantages, especially in the case of withstanding forces of carbonated beverages. Also, there is no resulting flash, but only a line where the mold halves meet.

Blow molding

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 '''Extrusion blow molding (EBM)'''
-Plastic is first extruded into a hollow tube (called a parison), which closes at one end when the melted plastic accumulates at the end of the barrel around which the tube is extruded.  Then, this parison is captured in a metal mold where air is blown into the cavity, stretching the parison into the desired shape.  Finally, the part is removed from the mold after sufficient cooling.
+) Plastic is extruded into a hollow tube (called a parison).
+) Melted plastic accumulates at end of barrel around which tube is extruded, closing the form.
+) The parison is captured in a metal mold.
+) Air is blown into the cavity, stretching the parison into the desired shape.
+) The part is removed from the mold after sufficient cooling.
 EMB can be continuous or intermittent.  If it is continuous, blow molds may either rotate or shuttle with respect to a fixed extrusion head.  In intermittent processes, the molds are stationary and the parisons are dropped into them.
 '''Injection blow molding (IBM)'''
-Least common, IBM begins by first injecting molten plastic or glass into a hollow mold containing a core rod. The outer mold is the removed, leaving the initial shape around the rod.  Both are then clamped into a cooled blow mold, the rod is removed, and pressurized air creates the final shape.  The part is removed from the mold.
+) Molten plastic is injected into a hollow mold around a core rod.
-'''Stretch blow molding (SBM)'''
+) The outer mold is removes.
-Here, an initial form is also created.  This shape is first placed within the neck of the final mold.  The form is then stretched with a core rod with an initial air pressure of 70 to 350 psi, until the stretch rod reaches the bottom of the mold and pressure is increased to 580 psi.
+) The remaining core rod and initial form are clamped into a cooled blow mold.
-This type is most preferable because it offers optimal structural and cosmetic advantages, especially in the case of withstanding forces of carbonated beverages.  Also, there is no resulting flash, but only a line where the mold halves meet.
+) The rod is removed and pressurized air creates the final shape.
-[[Image:24-441_07_Team06_Inside_the_mold.jpg|thumb|The stretch blow molding process.]]
+This is the least common type of blow molding, for use with small bottles or one time only applications.
+'''Stretch blow molding (SBM)''' [[Image:24-441_07_Team06_Inside_the_mold.jpg|thumb|The stretch blow molding process.]]
+) Forming of parison.
+) Parison placed into neck of bottle (final mold).
+) Core rod stretches parison into bottle, with an initial air pressure of 70 to 350 psi.
+) When stretch rod reaches the bottom of mold,  pressure is increased to 580 psi creating the final form.
+This type is most preferable because it offers optimal structural and cosmetic advantages, especially in the case of withstanding forces of carbonated beverages.  Also, there is no resulting flash, but only a line where the mold halves meet.
 ==Application==