A simple method for determining the viscosity of paint for application with a gun
High-quality car painting is the result of a combination of science and art. The master of his craft will certainly take into account many parameters so that the result exceeds expectations. The selection of the optimal value of paint viscosity when carrying out car repair work is the key to success. To do this, use the instructions and experience of the one who carries out the coloring.
What is paint viscosity?
One of the main properties of any paint is its viscosity. This indicator characterizes how much the liquid resists mixing or movement. It is customary to measure a physical property:
- in stokes;
- in square meters per second;
- in DIN.
The latter option is typical for foreign manufacturers that take German or European standards as a basis. In this case, seconds are recorded that will be required to spray a certain amount of varnish from a hole of a specific diameter.
This indicator depends on the ambient temperature, as well as the composition of the paint. Initially, manufacturers already determine the average option for any coloring matter. But the master needs to adapt the indicator for the spray gun in order to get a high quality coating.
What does this setting affect?
Determining the physical indicator of paint for the master is important for several reasons:
- any surface needs to be leveled, the higher the viscosity, the worse the voids are filled;
- a thick layer of coating can form smudges;
- a thin layer dries better, which provides grip and durability in the future;
- a large number of models of spray guns cannot work with very viscous paints.
So that the coating does not fly off during the operation of the car, and the corrosion protection is reliable, the composition must lie flat. Therefore, efforts are required to select the desired parameter of the coloring liquid.
If the atmospheric pressure drop is not enough for the spray gun to work, then instead of spraying it will have to be washed from the solidified dye. The working pressure of the industrial spray gun pump is up to 200 atmospheres. More budget and simple models have a lower level, but air is supplied to both the nozzle and the paint tank.
If you go too far with thinning the composition, you will have to apply several layers from the spray gun, which will lead to additional time.
What is the norm?
A special tool, a viscometer, helps to determine the physical indicator. The cost of such devices ranges from several hundred rubles for a rather primitive version to hundreds of thousands, if we are talking about laboratory accuracy. Particularly experienced craftsmen are able to calculate it with a ruler.
The procedure for using the device is quite simple:
- plug the outlet (you can use your finger);
- pour paint into the funnel;
- prepare the start of the stopwatch;
- simultaneously start a leak from the funnel and a stopwatch;
- fix the time.
In order for the readings to be correct, you must first make sure that the ambient temperature is 18–22 degrees, otherwise there will be a high error.
If the initial viscosity satisfies, then they start working with paint from the spray gun. It is useful to compare the installed version with the one indicated on the package.
In the absence of data, you can focus on the average viscosity of the paint (time in seconds):
- 15–20 - parameter for automotive enamels;
- 20-30 - the norm for glaze;
- 15-25 is a good level for oil paints or enamels.
Technology for creating the required viscosity
To reduce the indicator, so as not to disturb the mechanism of the spray gun, use a solvent. You can derive a formula to determine the required volume of thinner. Most often, they act by the selection method: gradually add a solvent and take readings again.
Solvents are usually classified as follows:
- fast, which can be used even at temperatures up to 20 degrees, ensuring no smudges;
- slow, the evaporation of which takes a long time, and the operating temperature should be above 25 degrees, but the composition of the spray gun will spread better on the surface;
- normal, evaporation rate and operating temperature are between the above data.
If the car is being painted metallic or pearlescent, it is preferable to use slow thinners.
Two-component dyes are considered more difficult to work with: acrylic based on an organic solvent, polyurethane, epoxy. Such compounds are diluted after they are mixed with a hardener. If you neglect this rule, it will be impossible to work with paint.
When preparing these paints, the mechanism is as follows:
- according to the instructions, paint and hardener are mixed in the right proportion;
- check the current viscosity;
- dilute to normal if necessary.
In order for the proportion to be correct, a measuring ruler or a special transparent container is used, where the volumes are determined. The correct approach when taking into account viscosity will also affect the economical consumption of paint, which is beneficial for both the customer and the contractor.