How to select of Coefficient Friction as per requirement

Introducing Of Friction

        Friction is the force that resists motion when two surfaces come into contact. When there is relative motion or an effort at motion between two surfaces, it acts in the opposite direction of the applied force. The abnormalities in the surfaces that come into touch with each other induce friction, and the force necessary to overcome these irregularities is what causes friction.

         Friction is classified into two types: static friction and kinetic (or sliding) friction. Static friction is the force that must be overcome to move an item that is at rest, whereas kinetic friction is the force that acts on an object that is already moving.

         Friction is a significant factor in many engineering and physics applications. While it might be an impediment in certain instances, it can also be beneficial in others, such as when employed to generate heat or create traction between two surfaces.

 Type Of  Friction Coefficient?

There are several forms of friction, such as:

• Static friction: This is the friction that occurs between two stationary objects in contact with each other.
• Kinetic friction: This is the friction that occurs between two objects in motion relative to each other.
• Rolling friction: This is the friction that occurs when an object rolls over a surface.
• Fluid friction: This is the friction that occurs when an object moves through a fluid, such as air or water.
• Internal friction: This is the friction that occurs within a substance, such as the friction between molecules in a solid or liquid.
• Coulomb friction: This is a type of friction that occurs between two solid surfaces in contact, and is proportional to the normal force acting on the surfaces.
• Viscous friction: This is a type of fluid friction that occurs when the fluid resists the motion of an object moving through it, and is proportional to the velocity of the object.
  

What Is Friction Coefficient?

        The friction coefficient has been utilized in research and engineering for a long time. Friction is not a basic force in and of itself. This dimensionless quantity, conceptually defined as the ratio of two forces acting perpendicular and parallel to an interface between two bodies in relative motion or impending relative motion, turns out to be useful for depicting the relative ease with which materials slide over one another under specific conditions. Although both static and kinetic friction coefficients may be measured easily in the laboratory, the time- and condition-dependent properties of friction coefficients associated with both clean and lubricated surfaces have proven incredibly difficult to predict a priori from fundamental principles.

What Is Friction Coefficient Formula?

.         The friction coefficient is a dimensionless constant that describes the relationship between the force required to move an item across a surface and the normal force pushing the object against the surface. It is represented by the symbol " μ " (mu) and has the following definition:

μ = F/N

        The coefficient of friction, μ denotes the amount of friction that exists between two surfaces. A low coefficient of friction means that the force required for sliding is less than that necessary when the coefficient of friction is large. The coefficient of friction is calculated as follows:

Frictional force   =μ×normalforce,

F = μ N

where F is the moving force and N is the normal force pushing the item against the surface.

 

Whose Is Decided By The Friction Value

        The friction coefficient varies based on the materials and conditions of the object's interaction with the surface. The friction coefficient between two materials having rough surfaces, for example, will be greater than the friction coefficient between two materials with smooth surfaces. The coefficient of friction is a critical metric in several disciplines, including physics, engineering, and material science.

        The friction coefficient is a dimensionless variable that defines the connection between the force required to move an item along a surface and the object's normal force on the surface. It is represented by the symbol " μ " (mu) and is defined as the ratio of friction force between two surfaces to normal force pushing the two surfaces together.

        The coefficient of friction can be used to calculate the force necessary to move an object over a surface or the maximum angle at which an object on an inclined plane will remain stationary. It is a crucial idea in physics, engineering, and many other disciplines.

        The friction coefficient measures the resistance to sliding or motion between two in contact surfaces. It is commonly represented by the symbol μ (mu) and is defined as the ratio of the force needed to overcome friction to the normal force pressing the two surfaces together.

        A multitude of variables can affect the friction coefficient, including the nature of the materials in contact, the roughness of their surfaces, and the presence of any lubricants or impurities. It is a dimensionless number with values ranging from 0 (for absolutely smooth, frictionless surfaces) to 1 (for severely rough surfaces) (for extremely rough, high-friction surfaces).

The friction coefficient measures how much force is necessary to move one surface over another when two surfaces are in contact. It is commonly represented by the symbol " μ " (mu) and is defined as the ratio of the force required to move an item over a surface to the normal force pressing the object down onto the surface.

Following are some common friction coefficients for different bearings and materials:

•           Dry steel on steel: 0.4-0.6

•           Steel on steel (lubricated): 0.05 - 0.10

•           Dry brass on steel: 0.3-0.4

•           Dry bronze on steel: 0.15-0.2

•           Dry graphite on steel: 0.1-0.2

•           Oil-lubricated steel on steel: 0.02-0.06

•           PTFE (Teflon) on steel: 0.04-0.06

•           Nylon on steel: 0.1-0.15

•           Ceramic on steel: 0.2-0.3

•           Steel on bronze: 0.15 to 0.25

•           Steel on graphite: 0.1 to 0.15

•           Steel on Teflon: 0.04 to 0.1

•           Steel on oil-lubricated bronze: 0.05 to 0.15

•           Steel on oil-lubricated Teflon: 0.02 to 0.04

•           Bronze bearing: 0.12 - 0.14

•           Teflon bearing: 0.04 - 0.05

•           Graphite: 0.10 - 0.20

•           Rubber: 0.5 - 1.0

•           Ice on ice: 0.01 - 0.10

•           Wood on wood: 0.25 - 0.50

•           Bronze bushing on steel shaft: 0.15 - 0.20

•           Ceramic on ceramic (dry): 0.15 - 0.20

•           Ceramic on ceramic (lubricated): 0.005 - 0.010

•           Rubber on concrete (dry): 0.7 - 0.8

•           Rubber on concrete (wet): 0.3 - 0.4

•           Bronze on bronze: 0.08 to 0.14

•           Graphite on steel: 0.1 to 0.15

•           Glass on glass: 0.4 to 0.6

 

Note that these values are only approximate and may vary depending on the specific materials and conditions involved. Additionally, the friction coefficient can be affected by factors such as temperature, velocity, and pressure.

Table No.-1

Coefficient Of Friction
Deep Deep Groove Ball  Bearings	0.00151
Self-Aligning Ball  Bearings	0.00101
Angular Contact Ball Bearings	0.0024
Cylindrical Roller Bearings	0.00112
Needle Roller Bearings	0.0025
Spherical Roller Bearings	0.0018
Taper Roller  Bearings	0.0018
Thrust Ball  Bearings	0.0013
Cylindrical Roller  Thrust Bearings	0.0050
Linear Motion Rail Guide	0.002-0.003
Linear Bush (Ball Type)	0.001-0.003
Ball Screw (Rolled Type	0.003-0.004
Dovetail Sliding	0.2
Gibb Way	0.5
Steel to Steel (Greased)	0.15
Copper to Steel	0.3
Al to Steel	0.45
Steel to Steel	0.58

Table No.-1

Mechanism Efficiencies
Acme Screw with Brass Nut	0.35-0.65
Acme Screw with Plastic Nut	0.50 -0.85
Ball Screw	0.85 - 0.95
Chain and Sprocket	0.95 - 0.98
Pre-Loaded Ball Screw	0.75 - 0.85
Spur or Bevel Gears	0.90
Timing Belts	0.96-0.98
Worm Gears	0.45-0.85
Helical Gear (Reduction)	0.92

 

Please keep in mind that these are approximate values that can change depending on factors such as surface roughness, temperature, and other environmental conditions. Furthermore, the coefficients of friction can vary greatly depending on the specific types and grades of materials used.

This value reference is SKF, THK,MISUMI