Transcript PowerPoint Template

MTE 427 MACHINE DESIGN
Design of Spur Gears
Pichet Pinit
14 Sep, 2008
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Lewis Bending Equation
Page  2
Lewis Bending Equation: Dynamic Effect
Dynamic Factor
As a general rule, spur gears should have a face width F
from 3 to 5 times the circular pitch p.
Page  3
Lewis Bending Equation: Dynamic Effect
Page  4
Do Ex 14-2 as Homework according the changes.
Stress Concentration Factor
In these equations l and t are
from the layout in Fig. 14–1, is
the pressure angle,
is
the fillet radius, b is the
dedendum, and d is the pitch
diameter.
Page  5
Surface Compressive Stress
Page  6
Surface Compressive Stress
Page  7
AGMA Stress Equation
Two fundamental stress equations are used in the AGMA methodology,
one for bending stress and another for pitting resistance (contact stress).
Page  8
AGMA Stress Equation: Bending Stress
Two fundamental stress equations are used in the AGMA methodology,
one for bending stress and another for pitting resistance (contact stress).
Page  9
AGMA Stress Equation: Pitting Resistance
Two fundamental stress equations are used in the AGMA methodology,
one for bending stress and another for pitting resistance (contact stress).
Page  10
AGMA Strength Equation: Bending Stress
Two fundamental strength equations are used in the AGMA
methodology, one for bending stress and another for pitting resistance
(contact stress).
Page  11
AGMA Strength Equation: Pitting Resistance
Two fundamental strength equations are used in the AGMA
methodology, one for bending stress and another for pitting resistance
(contact stress).
Page  12
AGMA Strength Equation: Allowable Bending Strength
Page  13
AGMA Strength Equation: Allowable Bending Strength
Page  14
AGMA Strength Equation: Allowable Bending Strength
Page  15
AGMA Strength Equation: Allowable Bending Strength
Page  16
AGMA Strength Equation: Allowable Bending Strength
Page  17
AGMA Strength Equation: Allowable Contact Strength
Page  18
AGMA Strength Equation: Allowable Contact Strength
Page  19
AGMA Strength Equation: Allowable Contact Strength
Page  20
AGMA Factors
Important factors of AGMA used for gear analysis are as following,
• Geometry Factor
• Elastic Coefficient
• Dynamic Factor
• Overload Factor
• Surface Condition Factor
• Size Factor
• Load-distribution Factor
• Hardness-ration Factor
• Stress Cycle Factors
• Reliability Factor
• Temperature Factor
• Rim-thickness Factor
• Safety Factors
Page  21
AGMA Factors: Geometry Factors
Bending-strength Geometry Factor, J (YJ)
Page  22
AGMA Factors: Geometry Factors
Bending-strength Geometry Factor, I (ZI)
Page  23
AGMA Factors: Elastic Coefficient
Elastic coefficient CP (ZE)
Page  24
AGMA Factors: Dynamic Factor
Dynamic factor, KV
Page  25
AGMA Factors: Overload Factor
Overload factor, KO
Page  26
AGMA Factors: Surface Condition Factor
Surface condition factor, Cf (ZR)
The surface condition factor Cf (ZR) is used only in the pitting
resistance equation. It depends on
• Surface finish as affected by, but not limited to, cutting, shaving,
lapping, grinding, shot peening
• Residual stress
• Plastic effects (work hardening) Standard surface conditions for
gear teeth have not yet been established.
When a detrimental surface finish effect is known to exist, AGMA
specifies a value of Cf (ZR) greater than unity.
Page  27
AGMA Factors: Size Factor
Size factor, KS
If KS is less than 1, use KS = 1.
Page  28
AGMA Factors: Load-distribution Factor
Load-distribution factor, Km
Page  29
AGMA Factors: Load-distribution Factor
Load-distribution factor, Km
Page  30
AGMA Factors: Load-distribution Factor
Load-distribution factor, Km
Page  31
AGMA Factors: Hardness-ratio Factor
Hardness-ratio factor, CH
The hardness-ratio factor CH is used only for
the gear. Its purpose is to adjust the surface
strengths for this effect.
Page  32
AGMA Factors: Hardness-ratio Factor
Hardness-ratio factor, CH
When surface-hardened pinions with hardnesses of 48 Rockwell C
scale (Rockwell C48) or harder are run with through-hardened gears
(180–400 Brinell), a work hardening occurs. The CH factor is a
function of pinion surface finish fP and the mating gear hardness.
Page  33
AGMA Factors: Hardness-ratio Factor
Hardness-ratio factor, CH
When surface-hardened pinions with hardnesses of 48 Rockwell C
scale (Rockwell C48) or harder are run with through-hardened gears
(180–400 Brinell), a work hardening occurs. The CH factor is a
function of pinion surface finish fP and the mating gear hardness.
Page  34
AGMA Factors: Stress Cycle Factors
Stress Cycle Factor, YN and ZN
Page  35
AGMA Factors: Stress Cycle Factors
Stress Cycle Factor, YN and ZN
Page  36
AGMA Factors: Reliability Factor
Reliability Factor, KR (YZ)
The reliability factor accounts for the effect of the statistical
distributions of material fatigue failures.
Page  37
AGMA Factors: Temperature Factor
Temperature Factor, KT (Y)
For oil or gear-blank temperatures up to 250°F (120°C), use
KT = Y = 1.0. For higher temperatures, the factor should be
greater than unity. Heat exchangers may be used to
ensure that operating temperatures are considerably below
this value, as is desirable for the lubricant.
Page  38
AGMA Factors: Rim-thickness Factor
Temperature Factor, KB
When the rim thickness is not sufficient to provide full support
for the tooth root, the location of bending fatigue failure may
be through the gear rim rather than at the tooth fillet. In such
cases, the use of a stress-modifying factor KB or (tR) is
recommended. This factor, the rim-thickness factor KB,
adjusts the estimated bending stress for the thin-rimmed gear.
Page  39
AGMA Factors: Safety Factor
Safety Factor, SF and SH
To render SH linear with the transmitted load, it could have been
defined as
Page  40