A Technical Guide to Dispensing
It doesn’t matter if you’re dispensing glue, oil, grease, epoxy, silicone, sealant, cyanoacrylate, solder paste, UV-cure, or any other assembly fluid. Sometimes it’s the little things that may be overlooked that could make all the difference. Simply adding an air filter/regulator or learning how to properly adjust your syringe dispenser’s pressure might be all you need for the perfect workflow.
These tips from Techsil and Nordson EFD cover the best practices for using both air-powered precision fluid dispensers and manual syringes to give you the most precise and consistent deposits in the shortest amount of time.
How to Prevent Air Bubbles in Syringe Barrel Dispensing
Entrapped air in your syringe could result in oozing, drooling or a little ball of material forming at the end of your dispense tip. There is a range of advice and application tips which can help prevent air from impacting your deposit consistency.
When working with low-to-medium viscosity fluids it is advised to hold the barrel at an angle, this prevents them air bubbles from forming. Ensure a piston is used to help keep the air out whilst dispensing. If you do find that there are air bubbles in your syringe, hold the syringe with the tip end facing upward and gently tap the syringe. Any air bubbles should them rise to the top; remove the tip cap and push the piston slowly upward to remove any large bubbles which have formed at the top.
For medium-to-high viscosity fluids it is advised to use a centrifuge. When thicker fluids contain entrapped air, bubbles will compress after each dispense cycle. Using a centrifuge to remove the air prior to dispensing is the best fix.
Storage Advice: Store syringes in an upright position (with the tip cap facing down), this allows air pockets to rise to the top.
How to Optimise Benchtop Syringe Dispenser Performance
Find the Right Deposit Size
Dispensing accurate, repeatable fluid deposits is a benchtop fluid dispenser’s single most important job. Setting up an air-powered fluid dispenser to do exactly that requires three simple steps:
- Choosing the right dispensing tip Take the diameter of the dot you need to make and cut it in half. Use that as the baseline from which to experiment to find the right internal diameter (ID). If you are making a line, cut the width of the line in half.
- Setting the air pressure The air pressure setting establishes how much fluid will flow through the tip. Start at 0 psi and slowly work your way up. As you increase the psi, watch to see what comes out of the dispensing tip. Stop increasing once you’ve established a consistent fluid flow.
- Setting the time The timer setting establishes how quickly each deposit will be made and the size of the deposit. Start at 0.2500 seconds and increase or decrease the time until you have reached the right deposit size. For faster production, increase the pressure and decrease the time. This will reduce overall dispense time, delivering higher throughput.
Plant Air Quality
The two most common factors that can affect the accuracy and consistency of fluid deposits when using an air-powered (or pneumatic) fluid dispenser are:
- Plant air fluctuations Most companies use one air compressor to supply an entire plant. This can make it difficult to maintain the consistent air pressure required by dispensing equipment, especially when that air is used by multiple work stations at different times throughout the day.
- Contaminants such as oil, dust and water Though most air compressors have filters, most filters aren’t fine enough to catch tiny particles of oil, dust, and water that can clog fluid dispensing equipment, causing it to fail.
Both plant air fluctuations and contaminants in your air supply can cause inconsistent fluid deposits. Installing a 5-micron filter/regulator between your plant air supply and your benchtop syringe dispenser helps prevent fluctuations and contaminants from slowing production.
When something goes wrong with Benchtop Syringe Dispensing
There may be times when you press the foot pedal of your syringe dispenser and nothing happens. In most cases, there is no problem with the dispenser itself, rather some simple issue that may need to be adjusted. Asking yourself these four questions may be all you need to get started again:
- Is the dispenser plugged in?
- Is the air hose connected?
- Is the power turned on?
- Is the foot pedal connected?
If each question is answered yes and you still have a problem, there are additional tests you can do to resolve your issue. First, remove the adapter head and step on the foot pedal to see if air is flowing through the dispenser. If not, make sure nothing in that factory is impeding air flow to the dispenser.
Next, check the safety clip to make sure it is open. If it’s closed, no fluid will be dispensed. Third, check for fluid clogging in the dispensing tip. Replace your dispensing tip with a new tip to see if a clog is preventing fluid from being dispensed.
Lastly, check the vacuum suck-back feature to be sure it is properly set. Also consider using an adapter assembly with a filter trap in line of the adapter hose to prevent fluid from entering the dispenser. If you have tried all of these techniques and still have problems, contact your Techsil representative.
How to Select the Right Piston for Dispensing Success
Pistons may be a small part of your process but they are an important component for acheiving accurate results. Pistons are used to apply an even, consistent force against the fluid inside your syringe barrel ensuring uniformed dispensing, control and wastage reduction. Nordson EFD offers six different types of specilially designed pistons to delvier precise, repeatable deposits whatever your application.
Below are some factors to consider when selecting the right pistons:
Perfect Interface Fit
Each EFD piston features a specific interference fit specifically designed for the fluid being dispensed. Our white Optimum® piston works best with about 90% of dispensable fluids. It features the perfect fit between the outer diameter of the piston and the internal diameter of the syringe barrel. This allows smooth piston travel. Its precision-wiping edges scrape the inside walls of the syringe clean of fluid, minimizing waste.
Prevent Piston Bounce
Piston bounce occurs when the piston separates from the fluid inside your syringe barrel. It’s caused by entrapped air under the piston. EFD offers three unique piston styles that minimize piston bounce — the orange Flatwall piston, the beige SmoothFlow™ piston, and the Clear Flex piston. Each is designed for use in a specific application.
Special Set up for Watery Fluids
Watery fluids and thin cyanoacrylates require a specialized piston to deliver accurate results and prevent premature bonding. EFD’s blue LV Barrier piston features a small hole, allowing air to pass through to pressurize the fluid and make the deposit. The hole also allows vacuum suction to prevent dripping between dispense cycles.