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MATING PARTS

GRADE & CLASS COMPATABILITY FOR ALL LOCKNUTS

Matching similar materials is the most important design criteria for a trouble free all-metal locknut assembly.  In a mismatched materials assembly, the softer component is forced to conform to the harder component threads causing particle break off.  When enough particulate is removed, loss of torque or galling will occur depending contributing conditions.

IFI 100/107 recommendations:

NUT GRADE BOLT GRADE
A 2, > 90
B 5, > 120
C 8, < 105 & > 150
G 8, < 120 & > 150


IFI, ANSI B18.16.1M recommendations:

NUT CLASS BOLT CLASS
5 5.8 & lower
9 9.8, 8.8 & lower
10 10.9, 9.8 & 8.8

STARTING THREAD REQUIREMENTS FOR ALL LOCKNUTS
A common cause of torque spike occurs when the deflected thread locking element first encounters the male thread is missing or reduced chamfer. After the initial spike, a loss of torque or galling will typically follow depending upon contributing conditions. When designing & specifying male threads for mating to all-metal locknuts the following recommendation is essential.

IFI 100/107 recommendations:
The bolts shall be pointed in accordance with the dimensional requirements for hex cap screws as given in ASME B 18.2.1. The thread surface shall be free of burs or other contamination that might affect the accurate determination of the prevailing-torque developed by the nut.
 
MALE THREAD NICKS, TAPER AND FINISH QUALITY FOR ALL LOCKNUTS
While they may not cause problems on free spinning nuts, male threads with any of the following non-conformances can cause torque to be reduced or amplified depending upon contributing conditions.
• nicks,
• tapers,
• rough finish,
• surface decarb of medium carbon parts,
• incomplete threads.

EFFECTS OF PLATING & COATINGS ON ALL-METAL LOCKNUT THREAD FIT
Most electroplating layers are thin (.0005 to .0003) and have no meaningful effect on thread fit. Organic type plating finishes are thick in comparison (.0003 to .0006). Unless these thicker coatings are accommodated in the assembly, high torque or galling are likely to occur.

EFFECTS OF ELECTROPLATING ON ALL-METAL LOCKNUT PREVAILING TORQUE
Each plating type has a coefficient of friction. When either or especially both the all-metal locknut and the mating part are plated with finishes with low coefficients of friction, torque values will be somewhat higher than when components have higher coefficients of friction. Aztech Locknut products are engineered to perform well within specifications when used with all common electroplating finishes.

EFFECTS OF LUBRICANTS ON ALL-METAL LOCKNUT PREVAILING TORQUE AND CLAMP LOAD
The vast majority of specifications for all-metal locknuts require the use of a dry lubricant. The dry lubricant, typically a wax variant, reduces torque spikes and galling. Dry lubricants are available with various levels of friction coefficients. It is important to know how the lubricant is affecting the clamp load, especially in applications where high clamp loads are required. Aztech can provide testing of the assembly components in a "real life" simulation to assure the desired results are achieved.