6/20/2023 0 Comments Ace paint viscosity meter![]() ![]() Reverse roll coating can give shear rates over 100,000 s -1, and the paint in direct roll coating probably sees shear rates of at least a few thousand s -1.ĭifferent viscometers measure viscosity at different shear rate ranges. Brushing involves similar shear rates.Īirless spray has a higher range of 10,000 to perhaps a million s -1. air spray gives shear rates of 1,000 to 40,000 s -1. Paint application is a high shear stress, high shear rate process. One reason for this is that rotational viscometers often display shear rate values as speed changes or it is easy to calculate shear rate from the viscometer speed. Although the key parameter affecting viscosity is the shear stress, people in the paint industry historically have looked at viscosity as a function of shear rate. This is called shear thinning, and the rate of deformation of the paint as it is sheared is called the shear rate (units are reciprocal seconds, s -1). Shearing of paint breaks up its structure and the viscosity drops to a lower level (often much lower) than the paint had at rest. Direct roll coating is thought of as a low shear process (the application roller often just kisses the substrate), but the doctor blade and pre-application rollers may apply high shearing stresses. This also is true of reverse roll coating. With spraying and brushing, a high shearing stress is applied to the paint. ![]() Shearing can be envisaged in terms of placing a small amount of liquid in the palm of your hand and smearing it by passing your other hand over the first one. All aspects of paint flow, including stirring, pumping, transferring, sagging, and application involve shearing actions. However, that viscosity is not measured under just any set of conditions or done with just any viscometer. s) provides acceptable spraying, brushing, or roll coating.There is a rule of thumb in the paint industry that a viscosity of approximately 100 cps (1 P, 0.1 Pa I thought that I would extend my answer to other application methods and share the information. I recently was asked about the optimum viscosity for spraying paint. ![]()
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