Accuracy is Critical

Each stainless-steel needle, or cannula, must be bonded to a polypropylene hub with a specific amount of UV-cure adhesive. The ability to regulate, document and repeat the amount of adhesive allowed to flow into the hub’s recess is critical, according to Production Manager Jim Hoover.

Under-application could result in the cannula separating from the hub during injection or retraction. Over-application must also be avoided since excess adhesive could build up on the hub. This would prevent the needle from retracting and defeat the purpose of the new product.

Air-powered bench-top dispensers from EFD Inc., East Providence, R.I., had proven accurate and reliable in building the syringes used in the government-mandated clinical trials, so Retractable Technologies asked EFD to help design a semiautomated system to meet its expanding production needs.

Unlike the bench-top operation, in which the operator applied adhesive to one syringe at a time, the syringe manufacturer now needed a system capable of making 10 deposits at once. While output needed to be increased, accuracy and process control had to be maintained.

After discussing the new objectives, EFD recommended its Model 740V, an adjustable needle valve designed to make microdeposits of low- to medium-viscosity fluids. Deposit size, the company explained, would be determined by a combination of fluid pressure, flow-control setting, tip size and valve open time.

A New Way to Improve Process Control

To take full advantage of the 740V’s precision-dispensing capabilities, EFD recommended pairing each valve with a dedicated, microprocessor-based VALVEMATE™ 7000 controller. This would ensure the required process control by allowing each valve’s dispense-time setting to be adjusted in increments as small as 0.001 seconds – without stopping the production line.

Realizing the benefits the “one valve/one controller” approach could bring to its dispensing operation, Retractable Technologies designed a semiautomated tabletop-assembly machine and had it fabricated by a local machine builder.

In the new setup, 10 valves are fixed in a rack with 10 controllers mounted above them. A manifold at the rear of the machine distributes plant air to each valve/controller system, while adhesive is supplied from pressurized tank reservoirs.

The individual controllers made valve setup and adjusting the deposit size fast and easy. Once optimal settings were determined for the first system, it was a simple matter to program the remaining nine to produce the same results.

Retractable Technologies’ new dispensing method has proven to be fast, efficient and, most important, accurate and repeatable. After placing a loaded work holder in position, the operator simply lowers a bar to cycle the valves and make 10 identical deposits.

Repeatability and More

Hoover says the company’s decision to go with dedicated controllers has been a tremendous help in maintaining process control. “They make it easy for us to set specific operating parameters for air pressure, fluid pressure and dispense time, but still allow the operator to make minor adjustments within a narrow range of approved settings.”

An advantage of this approach is that if something goes amiss, the operator knows to look elsewhere to isolate the cause of the problem because the system operates within documented parameters. “It literally forces you to take the proper corrective action,” Hoover says.

“We needed something that was accurate, repeatable and easily validated, and we found it. We’re very pleased with the accuracy of these systems, particularly with their repeatability,” he concludes.

For more information on precision dispensing capabilities, contact EFD at 977 Waterman Ave., East Providence, RI 02914-1378; phone 800-556-3484; fax 401-431-0237.

For more information on the VanishPoint™ disposable syringe, contact Retractable Technlogies, Inc., 511 Lobo Lane, P.O. Box 9, Little Elm, Texas 75068-0009; phone 972-294-1010; fax 972-294-4400.