Oil viscosity: understand the subject
In general, it is possible to say that viscosity is the amount of resistance of a fluid to shear or flow. In other words, it is an inverse measure of fluidity. Or it could even be a measure of effort that tries to split the fluid, bypassing the friction between layers and molecules.
Thus, it characterizes the resistance of a fluid to flow. When comparing water, which is thin, with vegetable oil, which is thick, it is intended to say that the former has a low viscosity, while the other has a high viscosity, respectively. In this way, what happens is that the higher the temperature, the more the viscosity increases, compensating for the thinning of the base oil.
A high viscosity liquid therefore generates more heat in the system than a low viscosity liquid. In many industrial applications, the oil viscosity should be 150 SSU at 38 C°. The speed with which a given fluid passes through a pipe is directly related to its flow, which can be measured by calculating centimeters per second. The change in fluid direction has the potential to generate heat. Thus, the diameter of a pipe can generate as much heat as several meters of pipe. This occurs because of the friction caused by the collision of the molecules that face the obstacle of the curve.
Measurement of oil viscosity
Most industrial hydraulic systems require a fluid with a viscosity index of 90 or more. Thus, its index indicates how a fluid changes in viscosity when the temperature changes. When its index is already high, the temperature does not interfere.
Oil oxidation, which, in addition to the low lubricating capacity, generates an increase in fluid viscosity, occurs because of a reaction between the oil and the oxygen in the air. And it can increase because of the high temperature of the oil, metallic catalysts and the increase in the supply of oxygen itself.
Thus, alternatives need to be applied to avoid this situation. Common and oriented are: corrosion inhibitors, which protect the metal; extreme pressure or anti-wear additives for high pressure or high temperature points; and defoamers, which propose air bubbles to release large bubbles of fluids.
Storage of hydraulic fluids
Fluidity and viscosity therefore need to be at adequate levels for the good performance of the hydraulic system. In this way, its fluid is stored in a reservoir. These can be L-shaped, suspended reservoirs and conventional reservoirs. These are most commonly used among industrial hydraulic reservoirs.
Due to the heating generated by the hydraulic system, it is necessary to use coolers or heat exchangers next to the reservoirs to avoid overheating. They can be air, water, or circuit.
Final considerations on the importance of caring for the viscosity of fluids in hydraulic systems
Considering that the hydraulic fluid must have the lowest possible viscosity level, it is possible to ensure that the maximum reduction of pressure loss in the pipeline and penetration of the component gaps to lubricate them occurs. However, it is necessary to ensure that this viscosity is not too low, as this would lead to leaks between high and low pressure zones. The pump type and system operating temperature will therefore determine the choice of viscosity level.
Thus, the consequence of using less viscous oils is the wear of the system parts, which is also less. This reduces the number of equipment repairs, exchanges and maintenance.
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