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AGMA Allowable Contact Stress for Steel Gears Table

Gear Engineering and Design

AGMA Allowable Contact Stress, s_ac, for Steel Gears Table

The allowable stress numbers for gear materials vary with items such as material composition, cleanliness, residual stress, microstructure, quality, heat treatment, and processing practices. For materials other than steel, a range is shown, and the lower values should be used for general design purposes.

Allowable stress numbers shown in the table below are determined or estimated from laboratory tests and accumulated field experiences. They are based on unity overload factor, 10 million stress cycles, unidirectional loading and 99 percent reliability.

The grade cleanliness requirements apply only to those portions of the gear material where the teeth will be located, to a distance below the finished tip diameter of at least two times the tooth depth. On external gears this portion of the gear blank normally will be less than 25 percent of the radius.

Material	Heat treatment	Min. Surface Hardness1	sac Allowable contact stress number2 lb/in2
			Grade 1	Grade 2	Grade 3
Steel3	Through hardened4	see figure 1	see figure 1	see figure 1	----
	Flame5 or induction hardened5	50 HRC	170,000	190,000	----
		54 HRC	175 000	195 000	----
	Carburized and hardened5	see table 9	180 000	225 000	275 000
	Nitrided5 ( through hardened steels)	83.5 HR15N	150 000	163 000	175 000
		84.5 HR15N	155 000	168 000	180 000
2.5% Chrome (no aluminum)	Nitrided5	87.5 HR15N	155 000	172 000	189 000
Nitralloy 135M	Nitrided5	90.0 HR15N	170 000	183 000	195 000
Nitralloy N	Nitrided5	90.0 HR15N	172 000	188 000	205 000
2.5% Chrome (no aluminum)	Nitrided5	90.0 HR15N	176 000	196 000	216,000

Notes:

¹ Hardness to be equivalent to that at the start of active profile in the center of the face width.
² See tables 7 through 10 of the standard AGMA/ANSI -D04 for major metallurgical factors for each stress grade of steel gears.
³ The steel selected must be compatible with the heat treatment process selected and hardness required.
⁴ These materials must be annealed or normalized as a minimum.
⁵ The allowable stress numbers indicated may be used with the case depths.

Click on image to enlarge

Figure 1 Allowable contact stress number for through hardened steel gears, s_ac

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Source:

• ANSI/AGMA American National Standards Institutue. American Gear Manufacturers Association Specification AGMA 201-D04