HOME  > Low Cost Automation Tutorial  > #072 Sliding Guides - 2: Friction and Wear
Low Cost Automation Tutorial

#072 Sliding Guides - 2: Friction and Wear

Category : Linear Motion Components
April15, 2011

Friction forces are generated when solid objects in contact make relative motion. These friction forces must be managed properly with lubrication and etc, or may result in troubles shown below.

1.Friction of solid objects resulting in seizures.
2.Wear begins and accelerates.
3.Increased power losses.

It is important to manage the friction and wear.

(1) About Friction

There are to types of friction.
 a)Sliding Friction
 b)Rolling Friction

The sliding friction is the type seen with Gib Slides (previous Vol.), skies and sleds. The [Fig.] shown below is an ancient Egyptian mural. It depicts a scene of transporting a large stone statue. A man can be seen at the center pouring friction reducing lubrication.


Show below are friction coefficients of various material combinations.

Material CombinationsFriction Coefficient μ
Mild Steel vs. Mild Steel0.4
Hard Steel vs. molybdenum disulfide0.15
Skies vs. Snow0.05

The rolling friction can be represented by Linear Motion Guides (previous Vol.), miniature ball guides, and etc. where friction occurs with balls and rollers. If the sliding friction is to be defied as the "Sled Era", the rolling friction can be dabbed as the "Rolling Cart Era".

Rolling friction coefficient examples are shown below. (Sliding friction coefficient and rolling friction coefficient cannot be compared equally.)

Material CombinationsRolling Friction Coefficient f(cm)
Hardened Steel vs. Roller/Balls0.0005〜0.001
Mild Steel vs. Mild Steel0.02〜0.05
Pneumatic Tire vs. Road0.05〜0.15

(2) About Wear

When solid objects are in contact without any lubrication between them, minute surface features are in directly coupled states. Friction occurs when this coupled features are decoupled by sliding motion, and this is the friction resistance (force). When the decoupling occurs, minute sections of material is ripped away where contacting. This is the wear. When the friction increases, the wear simply increases also.

Proper lubrication is needed to prevent wearing. Selecting appropriate lubrication is important, especially for mechanisms with high motion speeds and clean room applications.