If you've worked with two-component dispensing machines, you've likely encountered this: same batch, some products cure perfectly, while others remain soft and tacky — even with uncured gel cores when cut open. The first instinct usually points one of two directions: either pump wear causing A/B ratio drift, or workshop temperature fluctuations altering adhesive viscosity. Many operators tear down the pump first, only to find it wasn't the problem at all. This guide breaks down how to distinguish these two root causes, the correct troubleshooting sequence, and the verification methods that settle it.
Identify the Symptoms
Pump Wear — Causing Persistent Ratio Deviation
Core essence: Volumetric efficiency drops in either the A or B pump. Each cycle dispenses less than the theoretical volume, producing a persistent, unidirectional ratio deviation.
Typical signs:
• Defects are not random or sporadic — an entire batch comes out soft.
• Switching to a fresh drum of adhesive does not improve the issue.
• Static weighing test: 10 consecutive A/B samples show average ratio deviation from the setpoint, with poor repeatability.
• Severe wear: abnormal noise from the pump at idle; adhesive seepage at seal positions.
Common wear scenarios: High-filler epoxy adhesives (with thermally conductive fillers such as alumina) — the filler particles act like sandpaper, continuously abrading the plunger and sealing rings; stator wear in progressive cavity (screw) pumps.
Temperature & Viscosity — Causing Flow Drift
Core essence: Two-component adhesive viscosity is temperature-sensitive. Lower temperature means higher viscosity. At the same pressure/rotation speed, dispensing flow rate drops. A and B components often have different viscosity-temperature coefficients — when temperature changes, both flow rates decay at different rates, indirectly shifting the ratio.
Typical signs:
• Morning startup with a cold workshop: mass curing defects. As the workshop warms up, defects reduce or disappear.
• Same machine: frequent issues in winter, rare in summer.
• Static weighing: A/B ratio passes under constant temperature; when barrel/lines cool, the ratio starts drifting.
• New and old adhesive perform the same; the drum feels noticeably cool to the touch.
⚠ Key Misconception: Many operators assume temperature only affects flowability, not ratio. Temperature only fails to affect ratio when the A and B viscosity-temperature curves are completely identical. The vast majority of epoxy and PU two-component adhesives have vastly different A/B temperature-viscosity characteristics.
Verification Methods
01 Constant-Temperature Static Weighing Test
Soak the A and B adhesive barrels to the target process temperature, holding long enough for uniform temperature throughout. Collect 10 groups of A/B dispensed material, weigh each separately, and calculate the actual ratio.
• Stable ratio across 10 samples: Pump wear is ruled out.
• Ratio fluctuates with adhesive temperature: The issue is locked in as a temperature-viscosity problem.
02 Insulation Comparison Test
Run two parallel groups: one without barrel/line heating, one with active temperature control to stabilize adhesive temperature. Compare curing results and weighed ratios between the two groups. If heating significantly improves defect rates, the root cause leans toward adhesive viscosity rather than mechanical wear.
03 Pump Wear Verification
Under constant temperature, if multiple weighings show persistent ratio deviation with high scatter in repeat tests, disassemble the pump and inspect plunger/stator surface scratches, seal swelling or damage. Visible wear marks confirm a mechanical root cause.
Solutions
If Root Cause Is Pump Wear
• For high-filler systems, prioritize wear-resistant pump components — tungsten carbide plungers, wear-resistant stators.
• Establish a regular pump inspection routine: daily weighing to verify ratio. Don't wait for defects before scheduling maintenance.
• Check filters regularly to prevent large filler particles from entering the pump and accelerating abrasive wear.
• Verify whether the adhesive causes seal swelling. Swollen seals also reduce volumetric efficiency and mimic wear symptoms.
If Root Cause Is Temperature-Induced Viscosity Drift
• Apply independent temperature control to A/B dual barrels, supply lines, and pump body. Don't only heat the barrel — on long lines, the cold line section is the main variable.
• Temperature control target: not "higher is better." Follow the recommended range in the adhesive datasheet. Excessive temperature shortens pot life.
• Add preheat standby logic to machine programs: automatic dispensing only starts once adhesive temperature reaches the setpoint.
• Evaluate adhesive selection: switch to materials with better-matched A/B viscosity-temperature coefficients, reducing temperature sensitivity.
Combined Factors (Both Causes at Once)
• Minor pump wear barely passes under normal conditions; when temperature drops and viscosity rises, pump load increases, leakage grows, and ratio goes out of spec.
• Mismatched A/B supply pressure: after viscosity changes, pressure compensation is insufficient, amplifying flow deviation.
• Mixing nozzle blockage or backpressure changes also interfere with dispensing, mimicking ratio instability. Rule these out during troubleshooting.
Troubleshooting Sequence
Step 1: Observe temperature correlation
Check whether defects correlate with ambient temperature fluctuations → initial classification.
Step 2: Constant-temperature A/B weighing
Perform A/B weighing under stabilized temperature to verify ratio stability.
Step 3: If constant-temp ratio fails
Inspect pump, seals, and filters for mechanical wear or damage.
Step 4: If constant-temp passes but drifts when cooled
Root cause is adhesive temperature vs. viscosity matching — address thermal control.
Step 5: Rule out secondary factors
Finally, check mixing nozzle backpressure and dual-line supply pressure differences.
What's Your On-Site Experience?
When curing defects show up on the shop floor, do you start with weighing verification, or do you tear down the pump first? In high-filler thermal epoxy applications, which pitfall hits more often — pump wear or temperature drift?
• Do you weigh first, or open the pump first when defects appear?
• In high-filler thermal epoxy: which is the more common culprit — wear or temperature?
