FEP Tubing Expansion by Patented Apparatus & Process
The EBD process for making heat-shrink tubing involves injecting hot air into an external constraint to act as an air bearing and keep the tubing from sticking. FEP (fluorinated ethylene propylene) and other materials that require constraining during expansion can now be done without using silicone oil. Some of the important parameters are:
- Balancing the externally injected hot air pressure with the internal expansion gas.
- Controlling injected air temperature so that it maintains the expansion process at varying flow rates.
- Adjusting the pressure and temperature in multiple injection areas to maintain the process flow.
- Connecting the pressure, temperature, flow rate, draw ratio and line speed controls to keep the processes moving automatically at production speeds.
This process was made to work years ago on a basic expanding free-expanding machine using manual controls. Constantly adjusting several independent temperature controllers, flow controllers, pressure regulators and line speed allowed it to work up to 1 FPM. Production rate using silicone oil is expected to be 5-8 FPM, so automated controls were needed to make this new process practical. Development continued on the controls and process so that current speeds and quality are comparable to the standard silicone-lubricated process. Patents awarded in 2016 cover the inventive process and apparatus.
We are now expanding FEP tubing at production rates from reel to reel. Potential customers have been providing spools of tubing for experimental expansion for a few years. We do not want to sell a few machines to a few companies as that would dilute the value of the IP. We would prefer to sell the patents and a machine or two along with full fabrication and process documentation to the right buyer.
Current expansion of FEP has reached the goal of 1.6 to one ratio from expanded to recovered diameter with length change of less than 5%. Reel-to-reel runs of 500 feet are now possible with a setup loss of about 50 feet. Setup starts at a lower temperature and speed with production settings reached after a few minutes. Continuing development is focused on making this a production process that can handle a variety of sizes with minimal time for setup changes.
Expansion Process Control
Process development for constrained expansion can be targeted to the physical properties of the RAW tube via a multitude of control types. These controls are accessed via the “touch enabled” graphic user interface via a single screen. Values can be changed on the fly by entering a value or by toggling values up or down by a set amount. Allowing on the fly changes would allow the transition from startup to established expansion during a run. Once the values are established, a recipe can be created for the specific product that reflects all the control values for ease of future product runs.
Quick Change Tooling
Changing from one expansion size to another can be done quickly and easily on the tube expander. Once the system is off and cooled, simply unscrew and remove the core and replace it with the desired expansion diameter core. Enter the desired recipe and start the machine. The tooling changes takes less than 30 minutes. The current design supports expansion diameters from .06 “ to 3/8”.
Product Transport Control
During the expansion process the product may increase or decrease in length as it travels thru the chamber. To combat any line slack and to maintain a constant tension in the product an EBD Caterpuller drive is placed on either side of the process chamber. As well as supporting the main product line speed, each caterpuller speed can be easily adjusted on the GUI screen. Speed changes can be made to compensate for product expansion length changes, maintain a constant tension and to mitigate any line slack. This adjustment would be part of the specific product recipe for expansion.
Product in situ Measurement
A laser micrometer is located on either side of the expansion chamber. Thus a micrometer measures the outside diameter of the product tubing before (RAW) and after expansion with superior accuracy. Both dimensions are shown on the GUI screen allowing the operator to fine tune the final size of the expansion as well as compare and validate the RAW tubing dimensions. With this information recipes could be generated to adjust for any variation of the input tube size to achieve an even more consistent output dimension.
The tube expander expands tubing in a reel to reel configuration, starting with a reel of RAW tubing and ending with a reel of expanded tubing. Both Take-up and Payoff ends will support reel sizes up to a 24” flange diameter and a 8“ hub width. Using a traverse on the take-up end the product is neatly spooled between the hub flanges. This spooling pitch is configured on the GUI to support the needed expanded diameter. Tension for the spooling is controlled by a closed loop dancer control with configurable tension.
Sample Expansion Results:
Preliminary results have shown a Standard deviation for expansion of .0001 with shrink results reflecting a 1.6/1 expansion ratio. The chart represents taking measurement samples every .08 inches using the laser micrometer on the exit side of the process chamber. As we are not a tube manufacture we are always looking for material to evaluate. Send us your samples for a free evaluation.