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From Extruding to Boxing

Originally Published MPMN May 2002

EQUIPMENT NEWS: Extrusion and Tube Processing

From Extruding to Boxing

New devices offer improved efficiency and operator comfort

Katherine Sweeny

Tube fabrication and processing are essential parts of the medical manufacturing industry. Recent developments in these technologies enable manufacturers to extrude tubing more efficiently, automatically cut and store tubing, and blast chemical residue from finished products. These products and others are described in this section.

Laser tube processor is efficient and user-friendly

A laser system cuts tubing with a diameter ranging from 0.25 to 1.125 in. The Pro Stent-2 system, available from Stent-Cil Inc., incorporates the Lasag 246FC laser source, which is designed for fine cutting operations. It was developed with the goal of producing a reliable, highly accurate, and user-friendly turnkey system for the cutting of small-diameter tubing. The system enables a single operator to monitor and operate up to three systems. An efficient assist-gas usage design minimizes laser energy during the cutting process. This low energy level, combined with cooling water, translates to less heat being applied to the part and, in turn, a smaller heat-affected zone than is possible with a conventional laser cutter.

Additionally, the captured process allows tighter tolerances to be kept when processing small-diameter tubing. Parts coming off the machine typically do not have dross or slag left over from the cutting process, which means less time in the electropolishing postprocess.

Written with a graphical interface, the system's motion control software provides visual feedback of laser parameters and program parameters, video feedback of the cutting surface, system-status messages, parts counts, and timers, all on a single LCD screen. The software runs industry-standard NC code to drive the motion system and interact with the auxiliary controls for assist gas, water flow, and laser control.

Applications include the manufacture of stents, catheters, suturing devices, auditory-canal implants, and specialized hypodermic needles. The most common types of tubing that can be cut are stainless steel and nitinol, however the system can be used to cut many other types of metallic tubing. "Users need only supply stock to cut, attach the water source, and tell the system what part to cut and how many," says vice president of marketing Shane Kirk. "The system then automatically indexes and manipulates the stock throughout the manufacturing cutting process."

Tubing shrinker is suitable for cleanroom use

The Glo-Ring from Eraser Company, Inc., uses infrared heating to shrink tubing.

A single-element bench unit with solid-state heat controls can shrink long lengths of heat-shrink tubing and other materials on cable assemblies and wire harnesses. The Glo-Ring from Eraser Company, Inc., radiates focused infrared heat at temperatures of up to 1500°F, and features a temperature controller for variable heat intensity. It can be fitted with ½, 1-, 2-, or 3-in.-diam gold-plated plug-in quartz elements, with special element configurations also available. Heating elements open and close by activating the electrical foot switch. Quartz elements are protected by guards for safety and to prevent accidental damage. According to company spokesperson Nancy Shenker, the Glo-Ring was "initially developed for use in the manufacturing world as a substitute for heat guns; the medical industry picked up on it because it does not require the use of hot air, making it suitable for cleanroom use." The unit measures 4½ x 5 x 9 in. A triple-element bench version and a handheld unit are also available. Applications include medical tubing for catheters and IVs.

Tubing cutter box loads short-length tubing

Vulcan Machinery's cutter also box loads elastomeric tubing.

A tubing cutter is designed for high-speed box loading of FPVC medical tubing up to 120 in. long. Offered by Vulcan Machinery Corp., the tubing cutter can be configured to fill three in-line boxes at 80 cycles per minute, and production throughput rates up to 240 pieces per minute are achieved. A three-axis servo-driven in-feed, rotary indexing, mechanical discharge, and automatic box-oscillating system replace standard pneumatic discharge units. Typically, pneumatic discharge, system cycle rates are limited to less than 60 pieces per minute, requiring large volumes of compressed air and higher maintenance. "FPVC tends to retain a set as it continues to cool after accumulation," says company spokesperson Bryan Friend. "By decreasing the overlapping that occurs with common discharge systems, higher quality standards are achieved."

The servo-driven mechanical discharge and accumulation system significantly minimizes these problems and increases production efficiency. Also, the automatic box exchange and oscillation system reduces labor, improves product distribution, and delivers increased end-product quality. Process parameters are entered using a software-driven, four-line LCD with soft-touch keypad entry. As the operator scrolls through various password-protected set-up menus, current variables are displayed and new values may be entered.

The machine cuts tubing to a desired length, discharges it pneumatically from a conveyor at the end of the line into an adjacent plastic-lined box, and transports it to a final assembly area for attachment of fittings, coiling, and tying. The tubing lengths are automatically and evenly distributed. The efficiency derived from the mechanical collection and uniform delivery to bulk containers eliminates the need for intermittent bursts of air, resulting in an economical and potentially cleaner performance.

Vacuum sizing system quickly and efficiently creates tubing

The 2.0 PVS from RDN Manufacturing Company, Inc., cools and sizes small-diameter tubing.

A vacuum sizing system is designed for cooling and sizing small-diameter tubes. The design allows close-tolerance sizing of nonsilicone medical materials, such as flexible PVC and urethanes, which are difficult to vacuum size. The Model 2.0 PVS from RDN Manufacturing Company, Inc., vacuum sizes these materials at higher rates than extrusion process techniques, according to the company. A vacuum is created through the use of a blower. "Instead of free-sizing tubing or using a direct-acting liquid-ring vacuum pump for conventional sizing, we use a regenerative-blower vacuum system to equalize vacuum pressure between our top sizing tank and our lower reservoir tank," says vice president of sales Tom Malec. "We also use a solenoid to constantly monitor and correct vacuum fluctuation and measure vacuum in inches of water rather than mercury."

The reservoir tank separates the air and water, and the vacuum level is equalized with the upper tank for stability. The front end of the tank features a quench chamber to precool the tubing and seal the vacuum compartment, and a vacuum sizing sleeve is mounted on the entrance within a water well to provide a film of water on the tube as it enters the tank. The system has a soft-touch keypad with digital readouts for easy viewing of vacuum and temperature levels.

Tubing expander suitable for elastomeric tubing

The 875AC from Lakeview Equipment Inc. is capable of expanding elastomeric tubing.

A tube expander operates pneumatically for dependability and efficiency. The 875AC from Lakeview Equipment Inc. is suitable for vinyl, polyurethane, and other elastomeric tubing with durometer ratings ranging from 35 to 90. The unit is supplied with a nonmarring base and a foot pedal with a regulator and gauge. Cam-operated jaws provide controlled expansion. Jaw sets may be used in combination with any cam for flexibility while maintaining fixed tube expansion.

Blaster eliminates material residue from tooling

Available from Comco Inc., the MicroBlaster removes material residue from tooling.

A blaster can be used to clean tooling employed in the tubing extrusion process and in postprocessing of the extruded product. Prior to the physical extrusion of the tubing, microabrasive blasting is used to remove material residue from extrusion tooling. Its use prevents the residue that can result from chemical cleaning processes. The focused abrasive stream of the MicroBlaster, provided by Comco Inc., enables removal of molding residues without compromising or damaging the delicate and complex geometries of this type of tooling.

In postextrusion applications, the MicroBlaster is used to prepare surfaces of the product to impart a texture or roughen the surface. This surface alteration promotes bond adhesion and integrity for components that are added to the tubing or catheter. In a majority of these applications, a soft, water-soluble abrasive media is used, eliminating the hazards and complexities associated with using harsh chemicals to accomplish the task.

Microabrasive blasting is suitable for deburring and texturing of hypodermic needles and cannulae, surface preparation for bond adhesion, and deburring and cleaning of stents.

Automated tester finds defects in catheters and insulated wire

A catheter fault detector (CFD) finds exposed metal braid in plastic-jacketed catheters and identifies flaws in insulated wire. Offered by ASG, the CFD is a fully automatic tester that operates at rates up to 20 in. per second. It can be used as a stand-alone tester or integrated into automated processing and testing systems. Catheter feeders and sorters can be supplied to automate the testing process. The machine generates an electromagnetic field, which it couples into the test specimen. It then detects voltage fluctuations in this field around the insulation defect.

According to company spokesperson Paul Ogden, the machine was developed because "the common approach using conventional microscopic inspection is expensive and not completely effective in detecting small defects such as voids, pits, and frayed wires."

Servo cutter precisely measures tubing

A servo cutter designed for manufacturing tapered tubing combines precise cycle control with process functionality. Supplied by Davis-Standard, the cutter's user-friendly operator interface features a graphic representation of an entire bump-tube cycle. Processors can take advantage of 25 set points per screen for exacting ramp-up and -down control, and cut points can be selected at any stage throughout the cycle. Extruder and melt-pump output can also be controlled. The cutter can be operated in either on-demand or flywheel mode, and has a maximum cut capacity of 1 in. OD. A low-pressure air regulator provides a steady source of stable air for rapid cycling within the entire range of the bump profile.

Extruder mixes plastic with additives

Traditionally, tubing made from plastics with colorants, radiopaque materials, and other additives requires compounding before it is extruded. This can raise costs as well as damage PVC and other heat-degradable plastics. A single-screw extruding system avoids these problems by compounding plastic in a single pass. The Mixtruder from Harrell Inc. can introduce additives to plastic by performing a rough tumble-mix at room temperature. It then places the mixture into a hopper and can also add materials to the plastic via a multicomponent weigh feeder that introduces the appropriate proportions of each component to the hopper. The system's mixing screw enables elogational mixing and reentrant flow. The Mixtruder is also capable of extruding powder feed stock.

Copyright ©2002 Medical Product Manufacturing News

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