Automated dispensing turns adhesive application into a repeatable machine process — but only if the adhesive’s physical behavior is understood and controlled. One-part epoxy performs exceptionally well in automated dispensing systems, but getting that performance requires aligning three interrelated variables: the material’s viscosity at the point of dispensing, the temperature conditions across the dispenser and line, and the speeds at which the system is expected to run. Getting these right during process setup pays off in consistent bead geometry, minimal rework, and dispensing equipment that runs without constant adjustment.
Viscosity as the Central Process Variable
Viscosity governs everything about how an adhesive flows through a dispensing system and deposits on a substrate. Too high, and the material resists flow through fine tips, requires excessive pressure, and may not wet out properly on the substrate. Too low, and the bead spreads beyond the target area, slumps on vertical surfaces, and may bleed under components before cure.
One-part epoxy formulations span a wide viscosity range — from under 1,000 mPa·s for low-viscosity underfill grades to over 100,000 mPa·s for thixotropic paste formulations designed for gap-filling or dam applications. Selecting a formulation with a viscosity appropriate to the needle gauge, dispense pressure, and target bead geometry is the first step in process setup.
Viscosity is not static. Like most polymers, epoxy viscosity decreases with increasing temperature. A formulation specified at 25,000 mPa·s at room temperature may drop to 8,000 mPa·s at 40°C. This temperature sensitivity is a tool — deliberate warming of the dispensing reservoir allows fine-tuning of flow characteristics without changing the formulation.
Temperature Control at the Dispenser
Temperature-controlled dispensing systems — reservoir heaters, syringe barrel heaters, heated valves — are standard accessories for automated epoxy dispensing, and they’re worth using even when not strictly required. Controlling the material temperature at the dispenser stabilizes viscosity across shifts, reduces the effect of ambient temperature variation between morning startup and afternoon steady-state production, and allows the process to be set once and held reliably.
For one-part epoxy, the upper limit of dispenser heating is constrained by the cure activation temperature. If the material is warmed too aggressively — particularly in a large-volume reservoir — low-level advancement can begin before the material reaches the substrate. In practice, reservoir temperatures below 50°C are well within safe range for most formulations; operating temperature recommendations are provided in the manufacturer’s technical data sheet.
Syringe-level heating is more common than reservoir heating for cartridge-format dispensing. Small syringe heaters apply gentle, even warming to reduce viscosity without risk of bulk advancement. This approach gives the process engineer precise control over material temperature at the dispense point with minimal risk.
If you’re setting up a temperature-controlled dispensing process for a new formulation and want guidance on safe operating temperatures and target viscosity ranges, Email Us — Incure can provide application-specific recommendations.
Tip Selection and Needle Gauge
Needle gauge selection follows directly from viscosity. Standard dispensing guidelines recommend matching inner diameter to viscosity: lower-viscosity materials can be dispensed through finer gauges (23 to 27 gauge) at lower pressures; higher-viscosity pastes require larger gauges (14 to 18 gauge) to flow without excessive pressure that risks tip clogging or syringe distortion.
Tip length also matters. Longer needles increase flow resistance for a given gauge, requiring higher dispense pressure to maintain the same flow rate. For fine-pitch applications where the tip must reach into a cavity or between closely spaced components, flexible, thin-wall needles reduce added flow resistance compared to rigid stainless-steel cannulas.
Tapered tips and bent tips are available for applications where the dispense angle to the substrate is constrained. For robotic dispensing where the tool path is fixed relative to the substrate, tip geometry directly affects access and deposit consistency.
Line Speed and Deposit Consistency
In robotic dispensing, bead geometry is determined by the interaction of dispense rate (volume per time), robot speed (distance per time), and tip height above the substrate. Changing any one of these while holding the others constant changes the bead. Setting up a stable bead geometry means establishing a fixed relationship between all three.
A common process parameter approach is to fix dispense pressure and tip temperature, then vary robot speed to achieve the target bead width at a specified tip height. This approach keeps the material behavior constant and adjusts the deposition geometry through motion control — which is typically the most precisely controllable variable in the system.
At very high line speeds, the material’s surface tension and relaxation behavior become relevant. A material that forms clean start and stop points at moderate speed may tail or string at high speed. Testing the dispense program at or above the target production speed — not just at a comfortable development pace — reveals any flow behavior issues before production qualification.
Startup, Shutdown, and Idle Management
One of the process advantages of one-part epoxy in automated dispensing is the absence of pot life pressure during idle periods. If the line stops for a maintenance interval, a jam downstream, or a scheduled break, the material in the syringe and valve does not advance toward gelation. When the line restarts, the first dispense event will behave the same as the last one before the stop.
For very long idle periods — overnight or multi-day shutdowns — the standard practice is to remove the syringe from the dispenser and return it to refrigerated storage. The dispenser and valve remain primed with a small amount of material; a brief purge cycle at restart clears any material that warmed and relaxed during the idle period.
Documenting idle management procedures in the process specification ensures that line operators follow consistent practices and that dispense quality after a restart is not left to individual judgment.
Process Qualification and Ongoing Monitoring
Automated dispensing processes should be qualified across the full range of operating conditions: minimum and maximum ambient temperature, beginning and end of syringe life, and at both ends of the acceptable line speed range. Bead width, height, and start/stop geometry should be measured and documented against the specification limits.
In production, ongoing monitoring of dispense weight — measured by periodic weigh-check of a dispense event — is a reliable, non-destructive method for detecting drift in dispense volume. A dispense weight outside specification is an early indicator of viscosity change, tip wear, or pressure system drift, all of which can be addressed before they produce a reject.
Contact Our Team to discuss process setup and formulation selection for your automated dispensing application.
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