Zone regulation of casing inflation gas

In a system for the production of flexible film tubing which system includes means for continuously introducing an inflation gas into the interior of the tubing and means for continuously unidirectionally advancing the tubing from a first zone to a second zone, apparatus to maintain a preselected inflation gas pressure differential between the first zone and the second zone comprising, in combination:

• A pair of nip rolls consisting of a first roll and second roll disposed in tube flattening nipping contact on the continuously advancing tubing,
• said first roll having a smooth transversely flat resilient circumferential surface,
• said second roll having a circumferential surface provided with alternate lands and grooves extending transversely across the width of its circumferential surface, means to continuously selectably vary the contact pressure exerted on the advancing tubing by said pair of nip rolls, and
• rotational drive means operably connected to one of said rolls,
• whereby a continuous succession of selectably variable volume inflation gas accumulation chambers is formed, one chamber at a time,
• in the advancing tubing in the grooves of the second roll coacting in nipping relationship with the first roll, and the successive inflation gas quantities in said accumulation chambers are passed from one of said zones to the other.

A method for maintaining a preselected inflation gas pressure differential in a flexible tubing continuously advancing from a first zone at a first pressure into a second zone at a second pressure, comprising the steps of:

• inflating said tubing with a supply of inflation gas to one of said zones;
• forming a continual series of accumulation chambers sequentially, one at a time, in the advancing tubing by flattening the tubing at two spacedly adjacent lines of pressurized nip contact extending transversely across the tubing to accumulate successive quantities of inflation gas in said chambers;
• regulating the volume in each of said accumulation chambers by adjustment of the nip contact pressure;
• advancing said continual series of accumulation chambers formed in the advancing tubing into the second zone;
• and
• simultaneously sequentially releasing the pressurized nip contact across the tubing,
• whereby inflation gas in one of said zones passes to the other of said zones through said continually formed accumulation chambers.