Hot melt glue machine with hand gun

Seven factors that affect the opening time of hot melt adhesives

July 28 , 2021

1. Ambient temperature

The ambient temperature has an important influence on the open time of the hot melt adhesive. As soon as the adhesive leaves the nozzle, the temperature drops. So in cold production areas, the adhesive will cool faster, thereby shortening the open time. In warm production areas, the adhesive temperature drops more slowly, so the open time can be extended.

2. Substrate temperature

Like the ambient temperature, the temperature of the substrate is also important. If the adhesive is applied to the cold substrate, the open time will be shortened and the assembly time will also be shortened. Therefore, it is recommended that you store the substrate to be bonded in the production area one day in advance. In this way, the foam can reach ambient temperature overnight.

3. Ventilation

The effect of ventilation is often underestimated. The flowing air extracts a large amount of heat energy from the adhesive. An open door or air flow from an air conditioner can have a huge impact on the opening time, even if they only last for a short period of time. Therefore, you should ensure that your production line does not run between two sliding doors or ventilators, nor is it exposed to airflow in other ways.

4. The distance between the nozzle and the substrate

As mentioned earlier, once the adhesive leaves the nozzle, the temperature of the adhesive drops. The greater the distance between the substrate and the nozzle, the greater the heat loss and the shorter the opening time. In fact, a distance of three centimeters is sufficient. The small distance also has another benefit: it means that the machine can be controlled more precisely.

5. Nozzle size

In automatic gluing, the diameter of the nozzle determines the amount of adhesive that reaches the substrate. The nozzle must provide a consistent volume of adhesive for the foam. If the nozzle used is too small, the adhesive will be applied to the substrate with great force. As a result, the nozzle velocity is too high relative to the conveyor belt, resulting in an uncontrolled zigzag pattern. Generally speaking, in automatic gluing, the 1.5 mm nozzle is most suitable for bonding soft foam.

6. Pressing machine

Using a press, press the adhesive into the foam structure. High-quality presses and the correct use of presses are necessary to achieve maximum bond strength. Therefore, the foam should be pressed for at least 30 seconds. This seems to be a long time, but in practice we often find that it is easy to reach this time because it must be assembled. . Usually, the mattress is pressed longer! Pressing for a long time can produce stronger adhesion and faster working speed.

7. Assembly

One of the main advantages of hot melt adhesives is that they quickly develop initial viscosity during the cooling process. This makes quick assembly and processing possible. Similarly, the assembly speed of the substrate can be increased, which increases the open time so that the adhesive does not cool down quickly. These two substrates ensure that the adhesive stays fluid longer, so the process slows down and then the adhesive reaches its final strength. In order to produce the best bonding effect, make sure that the entire bonding process is not too fast or too slow.

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