This article uses simple language to deeply break down the working principles, core technologies, and selection criteria of these three systems, and includes frequently asked questions and solutions. It helps purchasing, engineering, and maintenance personnel understand hot melt adhesive machines at once, enabling them to select the right equipment, use it effectively, and reduce malfunctions.

I. The Relationship Between the Three Major Systems

The complete workflow of a hot melt adhesive machine can be summarized in four steps: solid adhesive melting → stable adhesive delivery → precise adhesive spraying → rapid curing.

Temperature control system: Determines whether the adhesive is in its optimal melting state, preventing carbonization, nozzle clogging, and maintaining stable viscosity.

Adhesive delivery system: Determines whether the adhesive pressure is stable, the flow rate is uniform, and the adhesive supply is continuous and uninterrupted.

Adhesive spraying system: Determines the shape of the adhesive, the accuracy of the adhesive quantity, the application position, and whether stringing or tailing occurs.

These three systems form a closed loop: unstable temperature control → abnormal viscosity → fluctuations in adhesive delivery pressure → uneven adhesive spraying → adhesive failure. Conversely, the adhesive spraying requirements define the adhesive delivery parameters and temperature control range. Only when these three systems work together stably can the equipment operate efficiently and sustainably for a long time.

II. Temperature Control System

Core Function

The optimal working temperature for hot melt adhesives is typically between 160℃ and 220℃. Temperature deviations exceeding ±5℃ will result in significant problems:
* Low temperature: Poor adhesive flow, slow dispensing, easy clogging of the spray gun, insufficient bond strength.
* High temperature: Adhesive carbonization, discoloration, brittleness, odor generation, increased waste, and contamination of the piping.

Professional equipment aims for precise temperature control within ±1℃ throughout the entire process, with independent temperature control in three sections: the glue tank, the glue hose, and the spray gun head, ensuring consistent adhesive condition from start to finish.

Working Principle: PID Closed-Loop Intelligent Control
The temperature control system is not a simple heat-stop cycle, but a real-time closed-loop system of detection-comparison-adjustment:

1. Thermocouples and temperature sensors collect the temperature of each zone in real time.

2. The controller compares the measured values with the set values.

3. The PID algorithm quickly outputs a power adjustment signal, avoiding overshoot and lag.

4. Solid-state relays (SSRs) execute the switching, precisely adjusting the heating output.

Key Technologies and Configuration

Multi-zone independent heating: Separate temperature control for the glue cylinder, glue hose, and nozzle, adaptable to different hose lengths and glue types.

High-precision sensor: Fast response, minimal drift, and stable performance even after long-term use.

Anti-dry burning and overheat protection: Automatic power-off in case of abnormal temperature, ensuring safety.

Teflon-coated, non-stick inner liner: Reduces glue residue, minimizes carbonization, and facilitates cleaning.

Temperature Control System Q&A

Q1: The equipment displays a normal temperature, but the adhesive still doesn't dissolve and the nozzle gets clogged. Why?
A: This could be due to sensor misalignment, aging heating element, or excessive carbon buildup in the inner tank. Carbon buildup can cause insulation, resulting in the displayed temperature being correct but the actual adhesive temperature being insufficient. We recommend regularly cleaning the inner tank, calibrating the sensor, and replacing aging heating elements.

Q2: The same equipment becomes unstable when using a different adhesive. How do I adjust the temperature?
A: First, check the recommended temperature range provided by the adhesive manufacturer. The standard should be smooth dispensing, without stringing, and without carbonization. Typically, EVA adhesive is 160–180℃, and polyamide and polyurethane are 180–220℃. Test at a low temperature first, then gradually increase the temperature to avoid direct high temperatures.

Q3: Does the temperature control need adjustment in winter and summer?
A: Yes. In low ambient temperatures, heat dissipation is fast, so the temperature of the tubing and nozzle can be increased by 5–10℃. In high ambient temperatures, the temperature should be decreased to avoid overheating and carbonization.

III. Glue Delivery System: The "Power Heart" for Stable Glue Dispensing

1. Core Function: To stably, quantitatively, and continuously deliver the molten adhesive from the glue cylinder to the spray gun. The smaller the pressure fluctuation, the more uniform the adhesive spraying. Key performance indicators: pressure stability, flow accuracy, compatible viscosity, and durability.

2. Comparison of Three Types of Pumps: Gear Pump, Screw Pump, Piston Pump

(1) Gear Pump

Principle: Gears mesh and rotate, squeezing the adhesive forward.

Advantages: Fast response, stable flow rate, moderate cost, simple maintenance, suitable for medium to low viscosity (1000–20000 CPS).

Applications: High-speed mass production lines for packaging, box sealing, and hygiene products.

(2) Screw Pump

Principle: Screw rotation propels the adhesive, providing stable pressure and low shear.

Advantages: High pressure, low vibration, low noise, suitable for high viscosity adhesives containing a small amount of filler.

Applications: Furniture edge banding, mattress lamination, automotive interior trim, PUR reactive hot melt adhesives.

(3) Piston Pump

Principle: Piston reciprocates, providing intermittent high-pressure adhesive supply.

Advantages: Extremely high pressure, suitable for ultra-thick adhesives; Disadvantages: Fluctuating flow rate, high maintenance costs.

Applications: High-viscosity structural adhesives, heavy-duty material bonding.

3. Key Configurations of the Glue Dispensing System

Pressure Feedback and Compensation: Automatic pressure stabilization prevents inconsistent glue dispensing due to production line speed variations.

Multi-stage Filtration: Prevents impurities from entering the pump body and nozzle valve, extending their lifespan.

Recirculation Valve: Regulates pressure, protects the system, and provides safer pressure relief during shutdown.

High-Temperature Resistant Seal: Suitable for long-term operation above 200℃, preventing glue leakage and aging.

4. Glue Delivery System Q&A

Q4: Pressure fluctuates, glue line thickness varies. How to troubleshoot?
A: Prioritize checking three points: ① Pump body wear and increased clearance; ② Filter blockage; ③ Air or glue leaks in the pipeline. Clean or replace the filter element, check the seals, and repair the pump body if necessary.

Q5: Gear pumps always struggle with high-viscosity glues. What to do?
A: ① Upgrade to a high-pressure gear pump; ② Improve temperature control to make the glue thinner; ③ Increase the pump size, leaving a 15-20% flow margin; ④ Shorten the pipeline and reduce bends to lower resistance.

Q6: Why doesn't the machine dispense glue after a period of shutdown?
A: Glue has solidified and blocked the pipeline and nozzle due to cooling. Preheat the entire machine, maintain the temperature of the pipeline and nozzle, and then gradually increase the pressure; for long-term shutdowns, it is recommended to drain residual glue or periodically maintain the temperature.

IV. Adhesive Spraying System: Precision Coating

1. Core Function: The adhesive is delivered stably and applied to the product according to the required shape, position, weight, and speed, determining the final bonding effect. Core requirements: no stringing, no tailing, regular adhesive shape, high repeatability, and fast response.

2. Adhesive Application Methods and Scenarios

Dot Adhesive: Electronic fixing, mask ear loops, single-point fixing in packaging.

Line Adhesive: Carton sealing, cardboard box side sealing, furniture edge sealing.

Spiral Adhesive: Non-woven fabric lamination, hygiene products, breathable bonding.

Fiber/Spray Adhesive: Large-area thin coating, labels, lamination.

Scraper/Roller Coating: Large-area lamination of boards, leather, mattresses.

3. Core Component: Glue Dispensing Valve

The high-frequency glue dispensing valve is crucial for accuracy:

Response Frequency: Standard 100–300Hz, high-speed lines require even higher frequencies.

Repeatability: Within ±0.5%, ensuring consistent glue application for every drop and every segment.

Sealing Material: High-temperature resistant fluororubber, long lifespan, leak-proof.

Gun Head Structure: Anti-stringing design, clean and residue-free glue application.

4. Glue Spraying System Q&A

Q7: Stringing and trailing always occur, affecting appearance and efficiency. How to solve this?
A: ① Appropriately increase the nozzle temperature to reduce glue viscosity; ② Reduce linear speed or increase valve response speed; ③ Adjust the glue shut-off delay; ④ Replace with an anti-stringing nozzle; ⑤ Check if the air pressure is stable.

Q8: Glue volume fluctuates greatly, and parameter adjustments are unstable. What's the problem?
A: This is mostly caused by unstable glue delivery pressure and worn nozzle valve. First, stabilize the pressure, then check the valve needle and valve seat seals; replace severely worn parts.

Q9: Do I need to replace the entire spray gun if I need to change the glue type for different products?
A: No. Most equipment can be flexibly adapted to multi-variety production by changing nozzles, adjusting air pressure, and modifying the program to switch between points, lines, spirals, and sprays.

V. Collaboration of Three Major Systems: How to Make Equipment More Stable and Durable

1. Selection Logic

First, determine the adhesive: viscosity, type, and operating temperature → determine the temperature control range.

Next, determine the process: speed, adhesive form, and application width → determine the spraying method.

Finally, determine the pump type: flow rate and pressure requirements → match gear, screw, or piston pumps.

2. Daily Maintenance Points

Temperature Control: Regularly calibrate the temperature, clean the heating surface, and check the sensor.

Adhesive Delivery: Regularly replace the filter, check the seal, and lubricate moving parts.

Adhesive Spraying: Clean the nozzle, check the valve needle, drain residual adhesive, and prevent clogging.

3. Quick Troubleshooting Approach

Abnormal temperature → check the temperature control system.

Abnormal pressure, no adhesive output → check the adhesive delivery system.

Stringing, uneven application, adhesive leakage → check the spraying system.

By checking in the order of "temperature control → adhesive delivery → spraying," 90% of problems can be quickly located.

VI. Summary

The core competitiveness of a hot melt adhesive machine lies in its three major systems: temperature control, adhesive delivery, and adhesive spraying. Stable temperature control ensures good adhesive quality; stable adhesive delivery ensures accurate quantity; stable adhesive spraying ensures strong adhesion.

Whether purchasing new equipment or maintaining existing equipment, mastering these three systems can help you avoid 80% of the pitfalls, making your production line more efficient, reducing waste, and ensuring more stable quality.

If you encounter specific problems during selection, commissioning, or troubleshooting, please feel free to consult us free of charge. We can provide a customized solution and quotation based on your adhesive, process, and production capacity.