Air Controllers and Air Control - White Paper
2Pages

From the Desk of Mike Ferrandino; owner Medical Extrusion 101 extrusio@msn.com medicalextrusion101.com Air Controllers and Air Control Air controllers are an integral part of a medical extrusion line. They are used in free extrusion of medical tubing for two reasons: sizing and structure. • Sizing o Air is one of the main inputs for free extrusion. o Air pressure is used to increase or decrease the diameter of the inner lumen (s) of a tubing. ■ Increasing the air pressure being supplied to a lumen will increase the diameter of that lumen. It will also make the wall of the structure surrounding the affected lumen a tad thinner (provided extruder output and linespeed stay the same.) ■ Decreasing the air pressure being supplied to a lumen will reduce the diameter of that lumen and subsequently increase the wall, around the lumen, marginally. o Control of air supplied to the process has a 1:1 relationship with process control. ■ Stable air pressure input helps create and maintain a stable process ■ Unstable air input is detrimental to the well-being of what could otherwise be a stable process. • Structure o Air pressure helps maintain the overall structure of the extruded form until the molten material has had a chance to cool and re-solidify. Notes for air controller use in general free extrusion: • Strictly observe the operational and set-up guidelines in the owner’s manuals. o Never crank up the supply air to a process beyond recommended guidelines to ‘get a little more out of the controller’, damage could result. ■ There are numerous ways to increase the effect of the air on the process without exposing the run, or the equipment, to excessive pressure • Dimensional surging can result from poorly executed changes to the air being supplied to the process. Once surging starts, it compounds itself (see the Medical Extrusion 101 paper on Accumulated Dimensional Instability.) • If having ‘air problems’ try removing all of the air from the process and gradually add it back into the process. This will often eliminate dimensional surging related to air supply Air Control during taper tube (bump) extrusion: • Taper Tube or bump extrusion is a free extrusion discipline where air and speed changes are coordinated to produce tubing with different sized cross-sections over the length of the part • A mode of operation where cyclical changes are being made to the air being supplied to the process. These cyclical changes are typically high and low settings for air pressure. Speed changes with the puller are usually coordinated with the changes in the air pressure. Air changes during bump extrusion need to be correctly timed, accurate, ‘smooth’, and consistently executed from cycle to cycle over the entire run. MicroAir www.onlinecontr

From the Desk of Mike Ferrandino; owner Medical Extrusion 101 extrusio@msn.com medicalextrusion101.com o For optimum operation in a bump mode, the step-down valve must be properly ‘tuned’ to insure smooth, clean, crisp changes in air supply to the process. Tuning of the air controller for use in bump extrusion is a critical element for successful operation. Changes in air pressure and puller speed must both be smooth to insure proper sizing and formation of the transitions from one set of dimensions to the next, cycle after cycle. o If changes are not accurate the target dimensions cannot...