Manufacturers of silicone medical tubing have used gas convection ovens in the past to cure the extrusion. Problems often occurred during changeover from one size to another, which required moving the existing furnace to gain access to the extruding head. There were also issues with the slow response time of the furnace (over two hours) meaning excessive downtime when warming up or changing oven profiles. This long warm-up/changeover time also created energy waste. In addition, the gas convection oven left manufacturers with quality issues due to limitations in the control of the existing oven.

An infrared chamber heater is the preferred solution for this process. When mounted vertically, the oven does not need to be moved to access the extrusion head. The total chamber-heated length of 42 in (1 m) is nearly one tenth as long as a gas convection oven, which saves 90% of valuable manufacturing space.

The quality of the product also improves with the capability to add a pyrometer inline and instantly adjust the chamber’s intensity to provide consistent heating of the extrusion. Time and energy are also saved because of the chamber heater’s instant on/instant off response, which means the warm-up and changeover times are drastically reduced. For easy cleaning, the chamber opens like a clamshell and has split-quartz liner to prevent out- gassed solids from collecting on the reflector.

Manufacturers of braided hose have preheated the hose with low-density resistance heaters. Some of the issues in this process include limited line speeds of 25 ft/min (7.6 m/min) due to the low heating density of the non-focused resistance heaters. This does not meet the required production throughput.

In addition, the resistance heaters’ high thermal mass cools slowly and continues to provide heat to the product even after the power shuts down or the product stops moving. This slow response may cause a fire when the line stops.

Many manufacturers prefer using focused infrared chamber heaters, which are used prior to the extruder to preheat the raw braided silicone. Additional units are mounted after the extruder to cure the silicone. Manufacturers are able to increase line speeds to 80 ft/min (24.4 m/min). The line is controlled with a speed-detection system to immediately shut off the lamps in the event that the line stops. Best of all, the infrared chamber heater’s even-heating process and precise control improves the surface and reduce scraps.

For more information, contact Research Inc. at sales@pcscontrols.com or go to www.researchinc.com.

Sidebar: IR Curing of Silicone Tubing and Hose

An infrared chamber heater is the ideal solution to problems with curing extruded silicone medical tubing. When IR heaters are mounted vertically, the oven does not need to be moved to access the extrusion head and the footprint is much shorter than that of a gas convection oven, which opens up floor space for the manufacturer.

Manufacturers of braided hose preheat the hose’s inner layer with low-density, slow-responding resistance heaters. The solution is to use focused infrared chamber heaters prior to preheating the raw braided silicone for superior adhesion. Two units are then mounted vertically after the extruder to cure the outer layer and increase the line speed with this heating system. The line is controlled with a speed-detection system and will immediately shut off the infrared lamps if the line stops. Water-cooled chamber heaters prevent overheating and potential fires due to an unexpected stoppage. The surface finish is improved with the infrared chamber heater’s even heating and precise control.

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