Apparatus for expanding polymeric tubing

Plastic article or earthenware shaping or treating: apparatus – Control means responsive to or actuated by means sensing or... – Control means responsive to product weight or dimension

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Details

4253871, 425388, 425392, 425DIG1, B29C 5528

Patent

active

061393061

DESCRIPTION:

BRIEF SUMMARY
This invention relates to an apparatus and method of expanding polymeric tubing, particularly for expanding heat recoverable polymeric tubing.


BACKGROUND OF THE INVENTION

U.S. Pat. No. 3,370,112 to Wray and U.S. Pat. No. 3,086,242 to Cook et al disclose processes and apparatus for expanding tubing by employing a pressure differential between the inside and outside of the tubing. Both of these patents are incorporated by reference herein for all purposes. Cook et al and Wray describe processes for producing heat recoverable tubing by cross-linking and expanding a tube of polymeric material. In both cases, the tubing is expanded by employing a pressure differential between the inside and outside of the tubing. The first step in the process is to cross-link the tubing. After the tubing is cross-linked, it is heated to a temperature equal to or above its crystalline melting temperature or range so as to melt the crystals in the material. While the tubing is at the elevated temperature, a pressure differential is imparted across the tubing wall to expand the tubing. While subjected to this differential pressure, the tubing is passed through a cooling zone to cool the tubing to a temperature below the crystalline melting temperature or range. The pressure differential is imparted by continuously supplying air to the interior of the tubing, while applying ambient or sub-ambient pressure outside the tubing. Upon re-heating, the tubing will recover to the configuration it had when cross-linked.
An alternative method of imparting a pressure differential is to trap a bubble of air within the polymeric tubing while again applying ambient or sub-ambient pressure outside the tubing. Over time, the pressure in the tubing bubble will drop as a result of permeation of gas into the tubing wall and also by way of air escaping through the ends of the bubble of air. As the pressure drops, the outer diameter of the tubing becomes smaller, resulting in production of tubing that may not meet the required specifications.
An attempt to increase the amount of tubing processed which meet desired specifications by using a bubble of air is described in U.S. Pat. No. 3,687,585 to Takagi et al. Takagi et al discloses confined movement between the ends of a bubble of air. However, the increase in the amount of tubing processed is limited by the space available in which the ends of the bubble of air can be linearly separated from each other. Once the space has been consumed, additional air must be supplied to the inside of the tubing by ceasing production and restarting the process.


SUMMARY OF THE INVENTION

I have invented an apparatus and method for continuously expanding tubing by substantially increasing the ability to compensate for loss of gas pressure, even with limited space.
A first aspect of the invention comprises an apparatus for expanding polymeric tubing comprising: passed, the polymeric tubing having a wall; through which expanded tubing can be passed; of the tubing so that, in use, a bubble of pressurized gas is trapped within the tubing between the first and second sets of nip rolls, and such that the pressure differential across the tubing wall causes the tubing to expand; it emerges from the cooling chamber; rolls and which comprises a plurality of lower pulley wheels and a plurality of upper pulley wheels, the lower and upper pulley wheels being such that the expanded tubing follows a sinuous path which passes successively between lower and upper pulley wheels; wheels based upon the sensing of the outer diameter of the expanded tubing, the length of said sinuous path being adjustable between a minimum length and a maximum length, the difference between the minimum and maximum lengths being at least 25 feet.
A second aspect of the present invention comprises a method of expanding polymeric tubing comprising: and a second set of nip rolls; second nip rolls, thereby causing the heated expandable tubing to expand; expanded configuration; downstream from the cooling chamber and between the first and second nip rolls, an

REFERENCES:
patent: 2936491 (1960-05-01), Hamlin
patent: 3086242 (1963-04-01), Cook et al.
patent: 3370112 (1968-02-01), Wray
patent: 3687585 (1972-08-01), Takagi et al.
patent: 3960997 (1976-06-01), Sorensen
patent: 4978223 (1990-12-01), Kutchenriter et al.
patent: 5810236 (1998-09-01), Yoshida et al.
Search Report for International Application No. PCT/US97/09377.

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