The lubricants are used in bearings to reduce friction between the rubbing surfaces and to carry away the heat generated by friction. In the previous article, we discussed the different types of Bearings. Sliding Contact Bearings are one of the types of bearings depending upon the nature of contact. Wedge Film Journal Bearings are Hydrodynamic Lubricated Bearings that come under Sliding Contact Bearings. Let us discuss the different Oil used in Bearings and their Components.
A containing is a moving machine component that supports a book. While delivering the load, it allows a relative movement between the members ‘ call surfaces. Due to the relative movement of the phone surfaces, a certain amount of power is lost in overcoming viscous resistance.
A little thought will reveal that the comparative movement between the contact surfaces causes a certain amount of power to be lost in overcoming resistive resistance. If the massaging surfaces come into direct contact, there will be quick wearing. A level of fluid may be provided to minimize frictional opposition and wear and, occasionally, take away the heat generated. The fluid used to distinguish the blog and holding is usually a nutrient oil refined from hydrocarbon, but veggie oils, silicone oils, greases, etc., may be used.
Oils used in Bearings
The oils are employed in bearings to lessen tension between the massaging areas and to transfer the heat generated by friction. It even protects the holding against corrosion. The following three categories are used to categorize all oils:
- Liquid
- Semi-liquid
- Solid
Mineral hydrocarbons and chemical oils are the typical liquid oils used in joints. Because of their affordability and balance, mineral oils are most frequently used. Where they might be retained, wet oil are typically used.
Grease is a semi-liquid sealant with a higher stiffness than hydrocarbons. When slow speed and high stress are present, the oils are used, and it is undesirable to have oil flow from the bearing.
Where oil movies may be maintained due to pressures or temperatures, good lubricants can be useful in reducing friction. They ought to become softer than the lubricating material. The most prevalent good lubricant is graphite, either alone or in combination with oil or wax.
Components of Oil
1. Viscosity
It is used to determine a liquid’s level of flexibility. It is a natural characteristic that allows an oil to kind, keep, and resist shearing a buffer movie under heat and pressure. A sealant must have a higher viscosity to avoid thinning and squeezing out of the film the higher the heat and pressure.
A flat disk moving parallel to a fixed plate while moving under a pressure P and being separated by a thin video of a liquid lubricant of thickness h, as depicted in the following illustration, can be understood as the basic definition of viscosity.
The lubricant’s particles adhere firmly to the moving and stationary sheets. A linear slip or shear between the particles covers the entire height ( h ) of the film thickness, accompanied by the motion. If A is the plate’s area in contact with the fluid, then the product shear tension is applied.
τ = P / A
The shear stress ‘ magnitude is directly related to the velocity gradient ( dV/dy ), according to Newton’s law of viscous flow. It is assumed that
- The space between the two areas is completely filled by the fluid.
- The lubricant’s motion on each area is the same as that on each surface.
- The lubricant’s movement is non-existent and does not match the plate’s speed.
where Z is a constant of proportionality and is known as the absolute viscosity ( or simply viscosity ) of the lubricant.
The velocity gradient is pretty close to frequent as shown in the above figure when the fluid lubricant’s thickness is small, which is the case with bearings. This means that the velocity gradient is very roughly constant.
Let us replace in the above calculation
When τ is in N/m2, h is in yards and V is in m/s, next the product of total stiffness is given by
But, the common exercise is to express the overall viscosity in mass units, like that
So the system of overall stiffness in S. I. products is pound / m-s.
The Saybolt general viscometer measures the stiffness of the lubricant. It determines how long it takes for a tube of a certain diameter and length to move under a specified head of oil with a specified volume of oil at a particular temperature. The Saybolt general stiffness is calculated in seconds as the time. The following formula may be used to convert Saybolt’s universal viscosity in seconds to absolute viscosity ( in kg/m-s ):
Z = Specific gravity of oil ( 0.00022S – ( 0.18 / S ) kg / m-s
Where
Z = Absolute viscosity at temperature t in kg / m-s
S = Saybolt universal viscosity in seconds
The following table shows how much the total viscosity changes for frequently used lubricating oils depending on heat.
| S. No. | Type of oil | Total stiffness at a temperature of °C in kg/m-s. | |||||||||||
| 30 | 35 | 40 | 45 | 50 | 55 | 60 | 65 | 70 | 75 | 80 | 90 | ||
| 1 | SAE 10 | 0.05 | 0.036 | 0.027 | 0.0245 | 0.021 | 0.017 | 0.014 | 0.012 | 0.011 | 0.009 | 0.008 | 0.005 |
| 2 | SAE 20 | 0.069 | 0.055 | 0.042 | 0.034 | 0.027 | 0.023 | 0.02 | 0.017 | 0.014 | 0.011 | 0.01 | 0.0075 |
| 3 | SAE 30 | 0.13 | 0.1 | 0.078 | 0.057 | 0.048 | 0.04 | 0.034 | 0.027 | 0.022 | 0.019 | 0.016 | 0.01 |
| 4 | SAE 40 | 0.21 | 0.17 | 0.12 | 0.096 | 0.78 | 0.06 | 0.046 | 0.04 | 0.034 | 0.027| | 0.022 | 0.013 |
| 5 | Specification 50 | 0.3 | 0.25 | 0.2 | 0.17 | 0.12 | 0.09 | 0.076 | 0.06 | 0.05 | 0.038 | 0.034 | 0.02 |
| 6 | SAE 60 | 0.45 | 0.32 | 0.27 | 0.2 | 0.16 | 0.12 | 0.09 | 0.072 | 0.057 | 0.046 | 0.04 | 0.025 |
| 7 | SAE 70 | 1 | 0.69 | 0.45 | 0.31 | 0.21 | 0.165 | 0.12 | 0.087 | 0.067 | 0.052 | 0.043 | 0.033 |
2. Oiliness
It is a cooperative property of the bearing surfaces in contact with the lubricant. It is used to evaluate the coating qualities under boundary conditions where consumed video acts as the only barrier between base metal and steel. There is no absolute estimate of sebum.
3. Density
This characteristic is useful for changing the kinetic viscosity from total viscosity, but it has no bearing on the lubricating value. Statistically
Total viscosity = ρ× Kinetic viscosity ( in m2/s )
where ρ = Density of the coating oil.
The mass of most of the hydrocarbons at 15.5°C differs from 860 to 950 pounds / m3 ( the average price may be taken as 900 kg / m3 ). The density at any other temperature ( t ) may be obtained from the following relation, i. e.
ρt = ρ15.5 – 0.000657t
where ρ15.5 = Density of fuel at 15.5° C
4. Viscosity catalog
The word stiffness index is used to describe the degree of viscosity variation in relation to temperature.
5. Flash place
When a flame is brought within 6 mm at the oil’s area, it is the lowest heat at which enough vapor is released to help a transient flash without really igniting it.
6. Fire place
When an oil ignites, what temperature does it produce enough vapor to lose it without stopping?
7. Point of failure or melting place
When an fuel cools, the temperatures at which it stops moving will be zero.
