ICGCM Papers:
New Ground Control Product Developments
 
 
Development and Application of the TT Anti-Friction Washer for Use with Tensioned Roof Bolt Systems
33rd International Conference on Ground Control in Mining
Development and Application of the TT Anti-Friction Washer for Use with Tensioned Roof Bolt Systems
by
Thomas A CookTravis M SubJohn C Stankus, Jennmar Corporation, Inc, Pittsburgh, United States
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[Conference] 33rd International Conference on Ground Control in Mining
[Price] Free  [Comments] 0
[Topical Area] New Ground Control Product Developments
[Author] Thomas A CookTravis M SubJohn C Stankus, Jennmar Corporation, Inc, Pittsburgh, United States
[Abstract] 
Key Conclusions:
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The “TT” washer was developed by Jennmar Corporation and Keystone Mining Services, LLC in early 2012. The “TT” anti-friction washer is comprised of two specially coated hardened steel washers. The “TT” washer has been extensively tested and applied in the Sewickley, Pittsburgh, and Indiana #5 coal seams. The test results indicate an average increase in installed load and tension/torque ratio of 20%. More importantly the consistency of installed load is improved with a significant reduction in the standard deviation of values. This paper will detail the development and testing of the “TT” anti-friction washer with case studies of actual mine wide applications.
Key Findings:
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Due to various reasons, the consistency of the installed tension is not always maintained. The reasons that affect this inconsistency of installed load include the plastic washer becoming dislodged and shredding or tearing before the bolt torqueing cycle is complete. This condition prevents the plastic washer from completely acting as an anti-friction medium for the complete bolt torqueing cycle
Objective of the Paper:
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The most popular and widely used anti-friction washer configuration consists of a plastic washer that is used in conjunction with a standard hardened steel washer. This washer configuration has performed well in the field in terms of increasing the bolt installed tension (or load) and related tension/torque ratio. The tension/torque ratio being the amount of tension achieved per one ft/lb of applied torque. The “TT” washer through extensive field testing out performs the plastic washer.
Problem Statement:
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The effectiveness of tensioned roof bolt systems has been well researched and documented over the years. Higher and consistent installed tension has been shown to improve the beaming effect and associated roof stability especially in laminated roof strata. To accomplish higher and more consistent bolt installed tensions, various types of anti-friction washers have been developed and applied to many types of tensioned roof bolt systems. In addition to increasing bolt installed tension, these washers also provide a lubricating effect that minimizes sparking during the bolt torquing cycle.