ASTM D5648 Torque-Tension Relationship of Adhesives on Threaded Fasteners

Scope:

The standard ASTM D5648 describes the test method to determine the torque-tension relationship of adhesives that are applied onto threaded fasteners, for locking and sealing. When a threaded fastener such as a nut and bolt or screw is tightened onto a load, clamping forces on the load increases. The reaction from the clamped load increases the tension acting on the fastener, making it stretch. The torque needed to tighten the threaded fastener onto the load also changes due to increasing tension, as the clamped load is squeezed tight. To ensure the correct tightening of joints held together by threaded fasteners, it is important to understand the relationship between applied torque and the resultant fastener tension. It is then possible to either control the torque needed to develop the desired level of fastener tension or control tension to stay within a torque range. The torque-tension relationship is very sensitive to friction.

The ASTM D5648 test is important in applications where thread locking and sealing adhesives are applied on threads of fasteners, to prevent their loosening in service. The ASTM D5648 test involves load testing bolt, nut, and washer assemblies, after adhesive application on the threaded surfaces. The torque-tension measurements during nut tightening establish their relationship for various sample and adhesive combinations.

Procedure:

The ASTM D5648 procedure is conducted using a test bolt, test washer, and test nut loosely fitted into a test fixture. The hardened test washer is placed over the exposed end of the bolt contacting the fixture. Initially, the nut is hand tightened till it contacts the hardened washer. Accurate tension and torque measuring devices are needed to measure bolt tension and applied torque. The nut is then slowly tightened, at a speed not exceeding 30 r/min, to reach a pre-set tension. Upon tightening and increasing the clamp load, the measured tension and applied torque are measured till the desired tension is reached. It is important to stay below the yield strength of the bolt material.

Specimen size:

The ASTM D5648 prescribes the following test specimen sizes, though the supplier and user can agree on other sizes and materials:

Bolts: Phosphate and oil treated, at least 1½ inch long with a hexagonal head, 3/8 inch size, 16 threads per inch Unified National Coarse thread series (3/8 by 16 UNC) and grade 5 as per SAE J429.

Steel Nuts: Type II, Style 4, nominally 21/64 inch thick as per Fed. Spec FF-N-836

Hardened Washers: conforming to Table 1 of SAE J174.

Result:

The result is expressed as the K value, which is the nut factor in the basic elastic torque-tension equation and is dimensionless.

Conclusion:

The standard ASTM D5648 describes the test method to determine the torque-tension relationship of adhesives that are applied onto threaded fasteners, for locking and sealing.