AGMA 926-c99 pdf free download.American Gear Manufacturers Association – Recommended Practice for Carburized Aerospace Gearing.
4.1 Materials selection
The following paragraphs describe the suggested materials for carburized aerospace gearing. The grades of steel recommended are based on the indicated specifications of the American Iron and Steel Institute (AISI) and the Society of Automotive Engineers/Aerospace Material Specifications (SAEI AMS). Typical carburizing steels are shown in table 1.
NOTE: It is to be understood that the materials listed are suggestions only and that specific material selection should be made by the engineer on the basis of material hardenabihty, material cleanliness, performance, and economic considerations. Performance critena include, but are not limited to, the following: toughness. notch sensitivity, bending and contact fatigue, bending strength, wear resistance, high temperature and environmental operational characteristics.
4.2 Aerospace quality grades – carburizing alloy steels
For aerospace applications, Aerospace Grade 3 and 2 materials require conformance to ANSI/SAE AMS
2300 quality level, while Aerospace Grade 1 material requires ANSI/SAE AMS 2301. Aerospace Grade 3 and 2 materials may also require additional specific mill processing conditions such as tighter ultrasonic inspection requirements. These requirements are more stringent than those given in ANSI/AGMA 2001 -C95, table 9, note 13 or other industry standards.
4.3 Forgings
When optimum properties and/or reliability are desired, double vacuum melted steel forgings should be used. It is recommended that forgings have a minimum forging cross sectional reduction (ratio) of 3:1. A metallurgical analysis should be performed on one part from the first production run. The analysis should include, but not be limited to, the inspection of grain flow, banding, cleanliness, distribution of inclusions and grain size. Forgings should conform to the requirements of ANSI/SAE AMS 2375B, MIL-F-71 90B or equivalent.
5 Metallurgical properties
5.1 Drawing specifications
The properties usually specified on engineering drawings for carburized aerospace gearing are (1) case depth range, (2) minimum surface hardness (or range). and (3) core hardness range. Surface and core hardness values should be in accordance with table 1. In addition, carburized aerospace gears require limitations on the case and core microstructure as outlined in 5.3 and 5.4.
5.2 Case depth
The case depth for carburized aerospace gearing is specified as the effective case depth normal to the tooth surface at 1/2 whole depth. Effective case depth is defined as the perpendicular distance from the surface of the case on a finished part to a point where the hardness is equivalent to 50 HRC, as measured by a microhardness tester. The tester load used should be 500 grams. Variations in the effective case depth at the gear tooth pitch diameter, root fillet, and center of the root should be specified and mutually agreed upon between the gear manufacturer and purchaser. The minimum effective case depth for gears with respect to diametral pitch should be in accordance with fIgure 1 unless otherwise specified.AGMA 926 pdf download.