Adhesives, lubricants and other assembly fluids are used to build a wide variety of medical devices. On automated production lines, these materials are often applied with pneumatic dispense valves
Although dispense valves may be a small part of the overall assembly line, choosing the valve that is most appropriate for a specific application can significantly increase yields, reduce rejects and lower assembly costs. Valve integration can be streamlined and production lines kept running at maximum efficiency by carefully matching the valve to both the application and the fluid being applied, and using a dedicated valve controller to simplify setup and operation.
Matching valve to the application
Although it is possible to achieve similar results with different valves, some designs will perform better than others in specific applications.
A diaphragm valve, for example, is a good choice for UV-cure adhesives because this design will minimise turbulence that could produce bubbles in the fluid. There are no seals to wear out and leak, and the fast, clean cutoff will eliminate drips that could cause functional or cosmetic damage to parts. For reactive fluids like cyanoacrylate or ‘super glue’, the same diaphragm design with wetted parts made of inert Ultra High Molecular Weight (UHMW) polymer will keep fluid from curing inside the valve.
When making very small deposits or dispensing watery fluids like solvents, a needle valve is typically recommended. Because the needle seats in the tip adapter, there is virtually no dead fluid volume remaining between shots. A well-designed needle valve with self-adjusting packings to compensate for wear can provide tens of millions of trouble-free cycles before maintenance is required.
For thicker fluids and filling applications, a piston valve with an adjustable flow control will provide good results. The piston design produces a faster flow rate than diaphragm and needle valves, and a snuffback action as the valve closes will prevent fluid from dripping or oozing between cycles. These are just three general-purpose designs. Other configurations include precision spray valves for critical coating applications, aseptic valves for dispensing sterile fluids, and piezoelectric valves capable of speeds as fast as 150 cycles per second.
Valve controllers maximise accuracy and efficiency
Once the valve has been selected, the most effective way to integrate it into the assembly line is with a dedicated valve controller.
Pneumatic dispense valves use a combination of fluid pressure, valve open time, and tip size to determine the amount of fluid applied. Higher pressures, longer open times and larger tip will produce larger deposits; lower pressures, shorter times and smaller tips will result in smaller deposits. Once initial setup has been completed, valve open time can be adjusted in increments as small as 0.001 second to fine-tune the size of the fluid deposit.
Manufacturing personnel sometimes ask why a dedicated valve controller is recommended, when they could actuate the valve by indexing or other mechanical means, or link it to an existing programmable logic controller (PLC). The simplest explanation is that a dedicated controller is the easiest, most accurate way to adjust valve open time, and it puts this capability right at the dispensing station. By supplementing-rather than replacing-a PLC, a valve controller can provide several important benefits.
Easier, more precise control of deposit size – A valve controller provides an easy way to determine the optimal deposit size, and is simple to use. If valve open time needs to be adjusted after the initial deposit size has been established, the operator or supervisor can simply scroll up or down in 0.1, 0.01, or 0.001 second increments. Once the settings have been determined, they can be documented and used each time that device is produced.
Higher output with less downtime – Automatic assembly machines often use PLCs to sequence functions, but in many cases these do not allow ‘on-the-fly’ adjustment of the fluid deposit. Since the valve that actually dispenses the fluid might not be viewable by the person making the adjustment, they would need to shuttle between the PLC and the dispensing station to check the results. A dedicated valve controller makes it simple to change settings and observe the effect immediately, eliminating the need to pause the assembly line.
Greater convenience and efficiency – A controller with an end-of-cycle feedback circuit and I/O connector for interfacing with a PLC is useful in processes where it is desirable to detect the end of a dispensing cycle. This circuit can be used to signal back to the PLC, trigger another device in sequence, or initiate other operations linked to the completion of the dispense cycle.
Finally, valve controllers also provide a fast, easy way to purge the dispensing system of any air introduced when filling the fluid reservoir. Purging is most efficient at the valve, where the operator can quickly confirm that all air bubbles have been removed.
Controlled application of adhesives and other assembly fluids can help medical device manufacturers increase yields, reduce rejects, and minimise downtime. Carefully matching the dispense valve to the process and using a dedicated valve controller to streamline valve setup and operation are cost-effective, easily implemented ways to meet these objectives.
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