First of all, if by “manual process” you mean a squeeze bottle or squeeze tube, you can forget about getting any type of process control. The control of the deposit is predicated on the “squeeze” of the operator. All operators will squeeze differently and even the same operator will squeeze differently as the day progresses. This type of method might be acceptable for a noncritical application, but medical device companies need process control, repeatability and predictability, none of which you will get by using a squeeze tube or squeeze bottle.

Using a time-pressure dispensing system is a great way to take control of a watery cyanoacrylate application. The most common dispensing system for a watery cyanoacrylate is a time-pressure system using a syringe as the fluid reservoir. To achieve the best process control, you want to choose a dispensing system that has a digital readout of all the important parameters: pressure, time and vacuum control. These digital settings can be documented and added to the work instructions for the specific project that you are working on.

The next choice will be the size of the reservoir you want to use for the application. A good rule of thumb is the smaller the deposit size that you are making, the smaller the reservoir you should use. Typically, a 3-cc reservoir can dispense hundreds to thousands of small dots of cyanoacrylate, depending on the dot size. If you are making larger dots or beads of cyanoacrylate, you will want to use a larger reservoir. The recommended fill level for watery fluids in the reservoir is two-thirds full.

Once the reservoir is filled, a piston should be inserted directly above the fluid, leaving approximately a 1/8-in. gap between the bottom of the piston and the fluid. Special pistons with a small hole are best for watery cyanoacrylates. In these cases, the piston serves two primary purposes: the hole allows air to flow through, pushing the cyanoacrylate out of the reservoir, and the piston acts as a barrier to prevent the cyanoacrylate from getting drawn back into the dispensing system.

The inner diameter (ID) of the dispensing tip should be based on the dot size that you are trying to make. Again, a good rule of thumb is to choose an ID that is approximately one-half the dot size. For watery cyanoacrylates, Teflon-lined or polypropylene tips are the most chemically compatible and will resist clogging.

Finally, the general parameters for dispensing a watery cyanoacrylate are low pressure (usually less than 3 to 5 psi), a pulse time that achieves the appropriate dot size (this is usually a trial-and-error process; it will probably end up at approximately 100 milliseconds), and an appropriate vacuum setting that will prevent the cyanoacrylate from dripping out of the dispensing tip.