The viscosity of the adhesive influences the selection of the dispensing device in terms of force application and controllability.
The packaging and the nozzle or mixer influence the type of dispensing device.
The size and position of the adhesive surface and the required process speed influence the choice of the dispensing device and the application nozzle.
The safety class of the adhesive bond determines the required level of training for employes (DIN 2304-1) and management.
The surface treatment of the workpieces (cleaning, primer, pre-treatment) is crucial.
The amount of adhesive dispensed can be influenced by three factors, depending on its viscosity:
- Selection of the device (pressure or speed),
- Temperature,
- Size of the nozzle opening or mixer model
Device selection
The selection of the device also has a direct impact on the discharge quantity.
Manual devices have different gear ratios and are therefore designed for different viscosities. The user must absolutely know this, because nothing causes such a significant drop in performance as quick fatigue due to insufficient force translation.
In pneumatic and battery-operated cartridge guns, the pressure force affects the discharge amount.
A high pressure force consequently results in a high extrusion volume.
For low-viscosity adhesives, the performance characteristics clearly favor pneumatic devices. For high-viscosity and 2K adhesives, on the other hand, the use of battery-operated devices is recommended.
Temperature
The influencing factor of temperature has a direct impact on the viscosity of the adhesive. The warmer the adhesive, the more fluid it becomes. Thus, the discharge amount and, consequently, the discharge speed are higher at high temperatures than at low ones. Moreover, some adhesives cannot be processed with a manual cartridge press without preheating the cartridge.
Viscosity
The (dynamic) viscosity describes the thickness of liquids. It is defined by the frictional resistance that a liquid opposes to deformation caused by a compressive or shear stress. The higher the viscosity, the thicker the fluid – the lower the viscosity, the thinner the fluid. The viscosity of liquids decreases with increasing temperature. The flow behavior, which significantly influences the processing of an uncured adhesive, is an important criterion for adhesive selection and must be considered during curing. For example, there are warm-curing casting resins that are highly viscous at room temperature and only become thin-flowing when heated to a curing temperature of, for instance, +100 °C or +150 °C.
For this purpose, special heating technology devices are used, which can heat adhesives to their processing temperature.
