Bearings, Lubricants and Couplings

Chapter 16

Bearings

Used to reduce friction between two surfaces

Different designs to accommodate rotational or linear motion

Different designs for different load directions

Bearing Loads

Radial Load Load acting perpendicular to the axis

of the shaft

Thrust Load Load parallel to the axis of the shaft

Combination Load Both radial and thrust loads applied

to the bearing

2 categories of bearings

Plain bearings Rolling element bearings

Plain Bearings

Operation is based on sliding action between 2 parts

Bearing will have a press fit into the housing and a clearance fit to the shaft

No moving parts Also called sleeve bearings, journal

bearings and bushings

Plain bearing materials

Bronze-needs to be lubricated Phosphor bronze-oil impregnated Various plastics

These materials allow low friction movement

Rolling Element Bearings Have moving parts to reduce friction Several types

Ball Bearings Most common High speed applications

Roller Bearings Cylindrical roller element Higher load capacity, lower speeds Several styles

Bearing Symbols

Bearings are purchased parts Different symbols used depending on

drawing type Schematic symbols used for machine

layout drawings

3D models of products using bearings can use a simplified 3D model of any bearings in the product

Machine Layout Drawing

Lubrication

Roller bearings require lubrication Too much can result in high temps

and bearing failure Too little and friction will cause heat

and failureLubricants Oil-slippery hydrocarbon liquids Grease-semisolid, a fluid lubricant

with a thickening agent

Assets of Oil Easy to control

volume Travels well Carry away heat Carry away

products of wear

Assets of Grease Stays put Less

maintenance Seals out

moisture

Couplings

Devices used to join two shafts together

3 categories

1. Solid Couplings

Used only when driving and driven shafts are mounted to a solid base (can’t move around)

2. Flexible Couplings

Compensate for unintentional misalignment

Prevent shock from being transferred between the shafts

3. Universal Couplings

Used when shafts are at an angle to each other (angle can change)

Also called universal joints

Flexible Shafts

Transmits power at angles and around corners

Helically wound wire designed to transmit rotary motion

TEST REVIEW Mechanism Linkage Cam Cam follower Bearings Plain bearing Roller bearings Ball bearings Couplings Flexible couplings Universal couplings

Gear types and orientation of their shafts: Spur Bevel Worm Rack and pinion

Gear train problem Plastic gear advantages (3) Bearing loads list and explain Assets of oil Assets of grease