Definition - The resistance offered to the movement of one body past another body with which it is in contact. The amount of friction depends on the nature of the contact surfaces and on the magnitude of the force pressing the two bodies together, but not on the surface area of the contact surface.
Friction and Coatings - Dry film lubricants offer very unique performance properties when friction is a concern. In most cases, solid film lubricants provide a lower coefficient of friction than traditional wet lubricants. Much of this improved performance comes from the resin's lubricating properties. Depending on the resin system, the lubricant can substantially decrease both the static and dynamic friction. Due to their performance properties, many of these dry film lubricants are used for performance problems associated with rolling and sliding friction.
The following is a graphical example of Friction :
Types of Friction
There are two kinds of friction: static friction and kinetic friction:
Static friction is the force between two stationary objects. Static friction
is always greater than kinetic friction. In fact, at the momentary point
when objects start to move in relation to one another, the friction, called
starting friction, is at its highest.
You may recall when you try to move a heavy object, the most force is
required to start it moving. Once an object is in motion, it tends to
stay in motion.
There are several types of kinetic friction, including sliding friction
and rolling friction. Sliding friction, flat objects moving against each
other, is greater than rolling friction, a rolling object moving against
a surface. (This principle is applied in ball bearings.)
The Coefficient of Friction
The coefficient of friction is the value of the force necessary to move
one body over another horizontal body at a constant speed, divided by
the weight of the body. For example: if a force of 30 newtons is necessary
to move a body weighing 200 newtons over another horizontal body at a
constant speed, then the coefficient of friction is 30 / 200 or 0.15.
Many different materials yield different coefficients of friction. E/M
engineered coatings are designed to reduce the coefficient of friction
significantly. Two benefits are less force required to move the body and
less wear.
Torque / Tension and Friction
When component design involves the assembly of nuts and bolts, it is important
to determine the required minimum clamping force and the yield point of
the fastener. The torque strategy is achieved by minimizing the clamp
load and not the yield point of the fastener. When a bolt meets resistance,
such as clamping a flange, it continues to rotate until there's a balance
between the torque and the sum of bolt tension and friction. To express
this relationship mathematically:
| T = K x D
x F |
| T |
K |
D |
F |
| Torque (twisting force) |
Constant that compensates for thread friction
(friction constant) |
Nominal diameter of bolt |
Induced force (clamp load) |
K-factor varies significantly since it is the net effect of as many as
70-80 variables. The fastener finish is the most important. In an extreme
case changing the fasteners finish alone can increase clamp load up to
100%. Other factors that affect K-factors are fastener material, insertion
speed, hardness, and thread tolerance.
Application Examples
The following are examples of components with friction problems and
the engineered coating services that solve these problems.
| Component
/ Part |
Problems Solved
|
Industry
|
| Adjusting Screws for Chairs |
Friction |
Fasteners |
| Box Magazines - 30 Round |
Friction, Wear, Corrosion |
Military |
| Double Ended Shafts |
Friction |
Automotive |
| Electronic Switching Components |
Anti-seizing |
Chemical Processing |
| Engine Fasteners |
Anti-seizing |
Aerospace |
| Fasteners For Aerospace |
Anti-seizing |
Fasteners |
| Fasteners for Modem |
Friction |
Fasteners |
| Flange Bearings |
Friction |
Automotive |
| High Pressure Tubing Connectors |
Friction, Cost effectiveness |
Industrial |
| Lead Screw for Step Timer |
Friction, Wear |
Industrial |
| Seat Belt Bolt |
Friction |
Automotive |
| Seat Belt Bolt |
Friction ( Torque ) |
Automotive |
| Pins |
Friction, Wear |
Industrial |
Questions
Please see identify problems for a quick response to any type of friction
and/or other questions that you have on how Everlube Products' coatings can
help solve your design challenges.
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