Most fluids which are sprayed are not pure water; although the majority of the readily available data on Spraying Systems Co. products are provided for water. While water does provide a useful baseline, fluid properties such as viscosity, surface tension, and density (specific gravity) can have a significant effect on the resulting spray plume characteristics generated by a nozzle. Spraying Systems Co. utilizes commercially available instruments to characterize these fluid rheology properties. These instruments may be used for a material assessment alone or as part of a spray test, by determining or setting the material properties prior to spray characterization.
Rheology assessments can be conducted using the following equipment:
- Brookfield DV2TLV Viscometer (Viscosity)
- Kruss K20 Tensiometer (Surface tension, Density)
- Pycnometer Bottle (Specific gravity)
- Refractometer (Index of Refraction)
Understanding the fluid properties like viscosity, surface tension, and density can be very helpful in selecting nozzles to properly distribute and atomize any material. Knowing these properties allows for engineers to more accurately select a nozzle for a given fluid and application. Furthermore, understanding detailed rheological trends, such as viscosity versus temperature or shear rate can often explain difference from spraying at different location with different process controls.
An automotive supplier contacted Spraying Systems Co. requesting proof of concept testing to spray coat a substrate with a new formulation. Viscosity, surface tension, and density were analyzed first which provided the information to narrow in on the style of nozzle to attempt to spray this slurry. This resulted in the quick determination of the appropriate nozzle to spray this fluid providing additional test time to test for the optimal nozzle operating conditions, height and spacing to evenly coat a wide moving substrate with multiple overlapping nozzles.
Food Heating for Coating
A food manufacturing company required a nozzle to spray coat a substrate. The material was heated and successfully sprayed in the Spraying Systems Co. lab. After returning to the production facility, the customer experienced issues recreating the spray solution. It was determined the spray material temperature was not carefully controlled at the production facility. A second round of testing was conducted, and the spray quality was examined while reducing the material temperature and examining the resulting material viscosity change. An acceptable range of temperature was determined, based on the viscosity trend, to allow for an acceptable spray. This new information allowed the production facility to be monitored and controlled to adequate precision using the known temperature requirements.
Figure 1: Viscosity versus temperature relationship for aqueous methylcellulose suspension of 1,000 cP at ambient temperature.
Figure 2: Viscosity versus shear rate relationship for a food adhesive.