Design of Machine Elements Exam 1

Annealing

Heated above critical temp, held, then slowly cooled

Refines grain structure, softer, increases durability

Quenching

Controlled cooling rate prevents full annealing

Less perlite, more martensite and/or bainite

Increased strength, hardness, brittleness

Tempering

Reheat after quenching to temp below the critical temp

Relieves internal stresses

Increases ductility slight reduction in strength and hardness

Case hardening

Process to increase hardness on outer surface while retaining ductility and toughness in core

Addition of carbon to outer surface by exposure to high carbon solid, liquid, or gas at elevated temp

Can also be achieved by heat treating only the outer surface

Spur gear

Straight teeth

Helical gears

Teeth cut at an angle

Bevel gears

Cone shaped gears with teeth cut on the surface of a truncated cone

Worm gears

Screw-like worm messes with a worm wheel

Clearance circle

Dedendum circle

Fillet radius

Clearance

Tooth thickness

Dedendum

Is the radial distance from the bottom land to the pitch circle

Addendum

Is the radial distance between the top land and the pitch circle

Pitch circle

Is a theoretical circle upon which all calculations are usually based

Bottom land

Flank of gear

Face of gear

Addendum circle

Face width of gear

Top land of gear

Pinion

Is the smaller of two mated gears

Circular pitch

Is the distance, measured on the pitch circle, from a point on one tooth to a corresponding point on an adjacent tooth

Is equal to the sum of the tooth thickness and the width of space between each tooth

Common pressure angle

20 to 25 degrees

Conjugate action

When surfaces roll/slide against each other and produce constant angular velocity ratio

Most common is involute profile

Involute profile

Most common conjugate profile

Can be generated by unwrapping a string from a cylinder, keeping the string taunt and tangent to the cylinder

Interference

Occurs when contact occurs below the bass circle

Pitch-line velocity

Is the linear velocity of a point on the gear at the radius of the pitch circle