Coal Age

JAN 2016

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observation. In harder drilling the clogging was rarely observed because the hard mate- rial requires a slower drilling rate. After modifications, clogging was essentially eliminated. This is attributed to the feed rates being set properly and being con- trolled by the feed package. Dust Exposure/Cutting Size: The dust exposure is believed to have improved at all mines where the testing was performed. The size of the cuttings was observed to be much larger after the machine parame- ters were set and the rotation speed decreased. This was evident by examining the material in the pre-cleaners. The larger cuttings were anticipated since the rotation was now slower for a similar feed rate, thus allowing the bit to bite a larger piece of material per revolution resulting in less fine, respirable dust. The occurrences of steel clogging that led to blowouts were reduced by controlling the feed rate in soft- er materials. This kept the operators from being exposed to blowout dust. An impor- tant observation was made concerning the amount of fine dust being generated. Before the larger motors were installed, when a resin cartridge was inserted in the hole, a large amount of fine dust would fall out of the hole. Once the motors were changed and the drill tuned up, the amount of dust observed coming out of the hole when the cartridge was inserted was signifi- cantly less. It is strongly believed that these changes will decrease exposure for the operators. It will be necessary to carry out time weighted operator exposure studies in order to quantify this improvement. Further dust testing is being planned and may be the subject of a future paper. N o i s e : N o i s e r a t e s o f t h e d r i l l s w e r e improved significantly. At one mine, the instantaneous noise level was observed to have decreased by 6 dB while drilling hard strata. It is believed that this is the result of a greater portion of the energy going into cutting the material. Further noise surveys are needed to quantify the improvements to the operator exposure on a time weighted basis. M a i n t e n a n c e C o s t s : A n i m p o r t a n t result of setting the drill parameters is t h a t w e a r a n d t e a r o n t h e m a c h i n e i s reduced. The drill will run at lower pres- s u r e s t h r o u g h o u t m o s t o f t h e d r i l l i n g cycle. In one instance, a mine was having ongoing issues with feed cylinder fail- ures. When the machine was reviewed, the pressures were very high. This mine h a d a t o r q u e i s s u e w h i l e i n s t a l l i n g torque-tension bolts, so they were reluc- tant to reduce the pressure settings. By c h a n g i n g t h e i r 1 . 5 - i n . m o t o r s t o 2 - i n . motors, the torque issue was resolved. Not only did the machine drill better, but t h e r a t e o f f e e d c y l i n d e r f a i l u r e s d e c r e a s e d s i g n i f i c a n t l y . T h i s d e m o n - s t r a t e s a m a j o r b e n e f i t o f t h e p r o j e c t : maintenance costs are reduced because the drill does not have to work as hard to drill the holes. Lower temperatures on hydraulic components were noted dur- ing the testing. While watching the drill o p e r a t e , i t i s e a s y t o s e e t h e r e d u c e d stress on mechanical components after these improvements are made. Several of the mines that participated in the study later reported notable decreases in main- tenance costs on their roof bolters. Note: The authors of this article are all on staff with J.H. Fletcher in Huntington, West Virginia. Cotton serves as mechani- cal engineer, Burgess is the vice president of engineering and Martin is the compa- ny's southern district sales manager. January 2016 www.coalage.com 27 r o o f b o l t i n g c o n t i n u e d

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