How to Solve Glue Stringing from Hot Melt Glue Gun Nozzles?

Glue stringing—those annoying thin threads that form when glue stretches from the nozzle to the workpiece—is a common issue during hot melt adhesive application. Fortunately, it can be fixed with targeted adjustments. Here’s how:

1. Optimize Equipment Parameters

Adjust Temperature Settings

• Problem: Too low a temperature makes glue thick and slow-flowing, increasing stringing. Too high a temperature breaks down the adhesive, causing messy drips and strings.

• Fix: Follow the adhesive manufacturer’s recommended temperature (e.g., 150–170℃ for Loctite 3542). Use an infrared thermometer to check the nozzle’s actual temperature (not just the machine’s display) and tweak in 5–10℃ increments until flow is smooth.

Stabilize Air Pressure

• Problem: Unstable air pressure or leaky hoses/solenoid valves cause uneven glue extrusion, leading to strings.

• Fix: Check for air leaks and replace old hoses or loose valves. Set pressure to 0.4–0.6MPa (adjust per your machine’s specs) using a pressure regulator.

2. Choose the Right Adhesive

Switch to Low-Viscosity, Fast-Curing Glues

• Problem: Thick, slow-curing adhesives (like some EVA-based types) have strong cohesion, making strings hard to break.

• Fix: Use adhesives with a melt index above 500g/10min (e.g., Fuller 9646) to reduce stickiness. Fast-curing options (e.g., ITW 94167) cut curing time by 30%, minimizing stringing.

Add Modifiers (If Needed)

• Problem: Overly strong cohesion in glue causes persistent stringing.

• Fix: Mix in 5–10% plasticizer (e.g., paraffin oil) to lower viscosity, or 0.5–1% nano-silica to improve thickness control—just test first to ensure bond strength stays strong.

3. Adjust Operating Processes

Shorten Nozzle-to-Workpiece Distance

• Problem: If the nozzle is more than 5cm from the workpiece, gravity stretches the glue into strings as it falls.

• Fix: Keep the distance between 1–3cm. Use programmable settings (like Z-axis tracking) to maintain this gap consistently.

Optimize Speed and Glue Output

• Problem: Slow dispensing or too much glue causes buildup and stringing; too fast leads to uneven cuts.

• Fix: Increase dispensing speed (e.g., from 10mm/s to 20mm/s) and reduce dwell time. Calculate glue needs precisely (e.g., a 1mm-diameter dot needs ~0.005ml) to avoid overflow.

Use the Right Nozzle

• Problem: A nozzle with a too-small diameter (<0.3mm) clogs easily, increasing pressure and stringing.

• Fix: Match the nozzle size to the glue dot (e.g., 1mm nozzle for 2mm dots). Teflon-coated nozzles reduce residue, cutting down on strings.

4. Maintain Equipment Regularly

• Clean Nozzles and Lines: Wipe nozzles with alcohol daily and ultrasonically clean glue lines monthly to remove carbon buildup.

• Replace Worn Parts: Swap out aging pins and seals every 3 months—worn parts cause leaky valves, which worsen stringing.

[Image Suggestion 1: A side-by-side comparison. Left: Nozzle too far from workpiece, showing long glue strings. Right: Nozzle close (1–3cm), with clean, string-free application.]

[Image Suggestion 2: A checklist graphic: “Temperature Calibration → Air Pressure Check → Nozzle Cleaning → Adhesive Selection” with simple icons for each step.]

By combining proper equipment settings, smart adhesive choices, and careful operation, you can eliminate glue stringing—resulting in cleaner, more efficient bonding. If issues persist, check for old glue in the tank (clean out any left for over 8 hours) or faulty solenoid valves.