S e c t i o n 1 - P a g e 1 1 May 2013 Matching Bolt and Shell Thr eads - While North American mines typically use UNC thr ead specs, other countries can use dif fer ent thr ead types. Car e must be taken not to mismatch shells and bolts fr om various manufactur ers. A minimum UNC class 1A thr ead spec should be met on all thr eads as per ASTM F432 guidelines. DSI - Mining exceeds ASTM specs and r olls thr eads to a class 2A specifcation. Support Nuts - While they ar e sometimes used on TBE bolts, the practice of installing a nut below the anchor shell should be avoided on for ged head bolts. If the support nut comes in contact with the shell, friction between these two surfaces will pr event the bolt fr om elongating pr operly and will give false tor que r eadings as the bolt is tensioned. Headed bolts should be fr ee to elongate into the hole thr ough the expansion shell. TBE Bolt Nuts - Do not run the nut on a TBE bolt to the end of the thr eads and onto the shank. Str ength can be r educed by as much as 50 Each r evolution of the nut onto the shank r educes the thr ead engagement length. Notching of TBE bolt thr eads - Notching thr eads on TBE bolts is a poor installation practice and must be avoided. This practice locks the nut onto the bolt which then makes the TBE bolt act as a for ged head bolt. Deep gouging can r educe the bolts str ength. Pr oper Grade Plates - Thin or weak plates will deform at low bolt tension. High tor ques will pr oduce lower tension values. The bolt could also rip thr ough the plate during installation or by bolt loading. Plate should meet ASTM F432 specs. The minimum spec is a grade 2 plate which has less than 0.25 deection when the load on the plate is incr eased fr om 6,000 to 20,000 lbs. Har dened Steel W ashers - Har dened steel washers should be used between the for ged head or nut and the plate washer . The washer r educes friction and enhances the tor que-tension r elationship. Minimum grade should be T ype 2 (ASTM F432 spec) and hole size in plate washer should be no mor e than 3 / 8 " diameter lar ger than bolt size. A spherical seat washer can also be used to r educe friction. W ooden W ashers - Although seldom used nowadays, wooden washers help pr event the plate fr om cutting into mine scr een (mesh) when pr esent. The wood may cause tension bleed of f however . Car e must be used to watch for r otting ofthe wood. Perpendicular Installation - Bolts should be installed as near perpendicular to the r ock surface as possible. Bolts not perpendicular to the plate and r ock surface will be mar ginally weaker and will not be pr etensioned pr operly . The following example using a 5 / 8 " for ged head r ock bolt installed with 180 ft-lbs tor que illustrates the scope of the pr oblem. Installation Quality Guidelines continued Angle fr om Perpendicular Installed T ension Reduction Ultimate Br eaking Load Reduction 0 13,030 lbs - 26,780 lbs - 10 10,280 lbs 21.125,690 lbs 4.120 5,230 lbs 59.825,060 lbs 6.4" 30 3,280 lbs 74.823,050 lbs 13.9 Results from lab testing conducted at Stelco. www .dsiundergr ound.com