As the cost of shrink tubing used in the production of catheters has increased, and supply chain issues caused delivery delays, FEP shrink tubing, for example, has become a very expensive throw-away item for medical device manufacturers. Engineering Resources Group (ERG), a product and process development company that specializes in automated processes for fabrication, assembly, inspection, and testing operations, works closely with clients to determine the best ways to meet their tubing manufacturing needs. ERG provides solutions designed to improve client processes and reduce costs. Some medical device manufacturers have turned to ERG for machinery to enable them to make the tubing in house. It can be a painstaking process working with a delicate feedstock. ERG engineers, however, have developed a fully automated, self-contained process that is simple to operate. One key to this development is a unique puller assembly that deftly handles the fragile tubing as it enters and exits, facilitating the system’s automation.
How the System Works
ERG has developed a way to create shrink tubing from regular tubing through a process that includes pressurization, lubrication, heating, expansion, cooling, washing, and drying. The first step of the process employs a Versa Caterpillar puller with pneumatic belt closure, pulling the tubing from a spool in a controlled way and presenting it to the system. Powered by servo motors with planetary reduction gearboxes, the model C-22 pullers are well suited for the task because they provide uniform pressure and consistent feed rates. ERG uses a, FDA-approved 40-durometer Neoprene belt; however, a variety of belt material options are available to choose from. Although this model puller can handle speeds of up to 450 ft per minute, the ERG process generally runs at between 10 and 20 ft/min. Maintaining that speed is critical so that the tubing isn’t stretched or deformed.
After passing through the first Versa puller, the tubing is lubricated to ease its journey through the other system stages. It is heated and then pressurized with nitrogen, which allows the pressurized tubing to expand. Then the tubing passes through a water bath for a controlled cooling process where it freezes in the stress of expansion. Next it enters a drying chamber before it is pulled by another Versa C-22 Caterpillar Puller on the back end, which presents the finished tubing to a special automated cutter that produces the desired lengths while maintaining the pressure in expansion process.
The C-22 pullers apply just enough pneumatic pressure to convey the tubing through the system without deformation. The input and output puller speeds are controlled by the machine controller with the output puller being primary and the input puller speed offset as needed to prevent the tubing from stretching.
The caterpillar design applies uniform pressure over the entire traction length. Pressure is adjustable, allowing a different grip on tubing with thicker or thinner sidewalls, for example. This adjustable, uniform pressure moves the tubing through the process without any elongation or other deformation. Compact C-22 pullers fit nicely within the machine’s overall enclosure, as well.
Pneumatic Actuation Is Key
In addition to the uniform pressure and compact size, a key aspect of the puller design is its pneumatic actuation. ERG chose the Versa Caterpillar pullers because they open and close pneumatically, allowing the process to be automated for control and safety.
“Whenever there’s an alarm or an error in the system, the expander’s controller sends a signal to open the pneumatic cylinders without stopping the belts,” says Chris Ross, ERG president. “Then, once the situation is attended to, we send another signal to close the pneumatic cylinders and get back into production.”
Ross highlights the Versa pullers’ functionality and longevity. The C-22 has a 2-in.-wide belt with a 9-in. traction length and a maximum opening of 2 in., which easily accommodates the tubing that ERG uses. Should ERG opt for a larger tubing size, the company’s C-44 features a 4-in.-wide belt and a 4-in. opening, while the model 418 provides 18 in. of traction length; both are available with pneumatic opening.
Ross began testing the Versa pullers around 2016 and has been using them ever since. Several other pullers ERG initially considered use hand cranks to change the distance between the feed belts. Though functional, these cranks would not allow the automation that is ERG’s hallmark.
Ross says that Versa Machinery is the ideal companion to ERG’s process automation. “We’ve used them on every machine of this type that we build here,” he says . “We use them exclusively. We looked at others, but even if the form and fit were right, without the pneumatic belt opening we couldn’t use them.”
In addition to being ideal for automation, the Versa pullers are designed to be durable. All Versa pullers include heavy-duty steel tables with a 3/8-in.-thick steel plate and ¼ × 2-in. angle iron. Custom stainless-steel guarding was added for this ERG medical application. That guarding, along with a durable powder coat paint, ensures the pullers can work for years in some of the toughest environments imaginable. “We’ve replaced some belts as needed, but we’ve never had to repair or service a puller,” says Ross.
With this combination of durable, automated machines from Versa, and ERG’s automation experience and innovation, medical device manufacturers have access to a system option designed to ensure that their shrink tubing will be made efficiently and cost-effectively.
This article was written by Logan Montgomery, Versa Machinery, Elkhart, IN. For more information, visit here .