Process Variables vs. Bubble Geometry

Variable to increase Film thickness Bubble diameter Frost-line height 

This table highlights how making one adjustment in the process affects all three of the bubble characteristics. A skilled operator must understand these interrelationships to accurately adjust the process so that all the geometry requirements are within specification. Even though many blown film lines today are automated to adjust for changes in process conditions, the above relationships still exist and it is the responsibility of the system (manual or automatic) to take the proper corrective action. 

Simulator Exercise Try increasing each of the four variables in the table individually. During each increase, observe the affect on each quantity in the measurements panel. It may be beneficial to record and plot, using spreadsheet software such as Excel, the values with each change to see which measurements are affected most by each adjustment. 

In the following paragraphs, a description is given of each of the relationships identified in Table 4.1. The assumptions here are 

only one process variable increases at a time while the others remain constant, and 

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