SAE AS 7240A:2015 pdf free download – Washers, Spring Lock, Carbon Steel, Procurement Specification for
1. SCOPE
1.1 Type
This procurement specification covers plain helical lock washers fabricated from heat treated carbon steel.
1.2 Application
Primarily for use with threaded fasteners; not recommended for use at temperatures higher than 450 °F (230 °C).
2. REFERENCES
2.1 Applicable Documents
The following publications form a part of this document to the extent specified herein. The latest issue of SAE publications shall apply. The applicable issue of other publications shall be the issue in effect on the date of the purchase order. In the event of conflict between the text of this document and references cited herein, the text of this document takes precedence. Nothing in this document, however, supersedes applicable laws and regulations unless a specific exemption has been obtained.
3.1.1 Chemical Composition
Shall conform to the following percentages by weight, determined by wet chemical methods in accordance with ASTME 350, by spectrographic methods in accordance with Federal Test Method Standard No. 151, Method 112, or by other analytical methods approved by purchaser:
3.1.1.1 Check Analysis
Composition variations shall meet the applicable requirements of AMS 2259.
3.1.2 Condition
Hardened, tempered, and plated.
3.2 Fabrication
3.2.1 Helix
Washers shall be coiled so that the free height is approximately twice the thickness of the washer section. Gap and relationship of the severed ends shall be such as to prevent the washers tangling.
3.2.2 Finish
Washers shall be plated in accordance with AMS 2400.
3.3 Properties
Parts shall conform to the following requirements:
3.3.1 Hardness
Shall be 45 – 53 HRC, determined in accordance with ASTM E 18, after removing the plating and any decarburization
3.3.2 Temper
After the first compression to flat, the free height of a washer shall be not less than 0.66 times the original free height.Subsequent compressions to flat shall not further reduce this free height by more than 0.005 in (0.13 mm) but the free height after ten compressions to flat shall be not less than 0.66 times the original free height.
3.3.3 Toughness
A portion of washer shall be firmly gripped in vise jaws having sharp edges. Ends of washer shall be free and an axis passing through the slot shall be parallel to top of vise. An equal portion of washer shall be gripped in wrench jaws. Edges of wrench jaws shall be sharp and in a plane parallel to top of vise. Free portion of washer, between the grip of vise and wrench, shall be approximately 25% of washer diameter. Movement of wrench in the direction that increases the free height of the washer shall twist the lock washer through 90° without evidence of fracture. When a washer fractures because of twist, the structure at the point of fracture shall show a fine grain; the washers shall deliver, at the instant of fracture, a tough, springy, reactive shear.