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side of the machine had a considerably higher maximum thrust force on the bit. Also, the bypass cartridges were out of adjustment, so the feed package valves were not properly controlling the feed rate. The rotation speeds averaged 645 rpm, and the rotation reliefs were set at 1,900 psi and 2,000 psi. The feed rate when using the starter tool in the softer material averaged 1.7 in. per second (in/s). When using the finishing tool in the harder material, very low feed rates were measured at an average of less than 0.8 in/s. The average bit life was 8 ft per bit. T h e d r i l l s t e e l w a s c l o g g i n g o n n e a r l y e v e r y h o l e , m o s t l i k e l y d u e t o t h e f a s t rotation speeds and high feed rates in the soft material. The clogging of the steel was slowing t h e d r i l l i n g p r o c e s s a n d w a s c r e a t i n g blowouts, which is a burst of dust out of t h e h o l e . T h e d r i l l w a s s t a l l i n g i n t h e h a r d e r m a t e r i a l a b o v e 4 f t . S t a l l i n g o c c u r r e d a s t h e o p e r a t o r r e d u c e d t h e rotation speed to help drill the harder material at the top of the hole. The 2-in. gear-rotation motors were installed, and the drill parameters were set. The new rotation speeds were approximately 485 rpm on both sides. The new maximum thrust pressure was set to 1,600 psi on both sides so that each side had approxi- mately the same thrust force available. T h e m a x i m u m r o t a t i o n p r e s s u r e w a s turned up just slightly to 2,000 psi on both sides. In the softer material of the first 3-4 ft, the feed rates were set at 1.75 in/s, which was very close to what they were prior to the modifications. However, the feed rates obtained in the harder material improved to an average o f 1 . 6 i n / s , w h i c h r e p r e s e n t e d a 1 0 0 % increase in feed rate. This also demon- strated that the pressure compensated flow control was holding a relatively con- sistent feed rate, and the high relief was not cracking open. The bit life improved 20% to more than 10 ft per bit. With the increased torque of the larger motors, the operators could slow the rotation in the harder material without stalling the motors. Clogging of the drill steel was virtually eliminated. Noise was observed to decrease by 6 dB as shown on instan- t a n e o u s r e a d i n g s . T h i s m i n e c h o s e t o implement the changes across the board and is still reporting similar results. Mine B was operating DDR mast feed machines. They had medium hard, and consistent material to drill. The initial survey showed that the maximum thrust pressure setting was at 1,500 psi for both booms. Th e y we r e a ch ie ving a ppr oxi- mately 580 rpm with the 1.5-in. rotation motors. The rotation high-volume relief was set at 1,900 psi on both sides. The feed package valve was out of adjustment for controlling the feed rate. T h i s s e t u p w a s d r i l l i n g w i t h K e n n a m e t a l S V T 1 1 9 d r i l l b i t s a n d installing 42-in. resin bolts. The feed rate on average was 2 in/s. The bit life was low, requiring 4 bits to bolt a single row. The overall time to install a bolt was 68 seconds. A f t e r t h e 2 - i n . g e a r - r o t a t i o n m o t o r s w e r e i n s t a l l e d , t h e r o t a t i o n s p e e d s d e c r e a s e d t o a p p r o x i m a t e l y 4 7 5 r p m . T h e m a x i m u m p r e s s u r e f o r f e e d w a s reduced slightly to 1,450 psi. The maxi- mum rotation pressure was unchanged. T h e f e e d r a t e w i t h t h e n e w s e t u p w a s slightly decreased to 1.75 in/s. The most significant performance improvement observed was in bit life. They were now able to bolt three rows with just two bits. The overall time to drill and install a bolt was approximately the same. Noise and dust levels decreased. However, the mine will need to perform further testing to quantify the results. This coal company chose to roll out the same changes to all of its mines. They later reported tooling sav- ings of $3,000 per section, per month. Mine C was operating RRII arm feed m a c h i n e s . T h e i r c o n d i t i o n s w e r e s o f t shale for the first 5 ft of material followed by thin bands of medium hard sandstone f o r t h e r e m a i n i n g d r i l l i n g . T h e y w e r e installing 4-ft resin bolts and 12-ft cable b o l t s . T h e s e t u p u s e d T L - 2 d r i l l s t e e l s and Kennametal SV119 bits. The maxi- mum thrust pressure was recorded to be 1,350 psi on both sides of the machine. One interesting observation is that the feed package appeared to be tuned close to optimal settings. The rotation high- volume reliefs were set at 1,900 psi. The rotation motors averaged 670 rpm, with the right side being slightly slower than the left. This drill had an initial feed rate of 2.4 in/s in the relatively soft material that they were drilling. The mine was get- ting good bit life of 52 ft per bit. Plugging was occurring in the soft material. In the harder material at the top, the drill would stall when the operators slowed the rota- tion speed to approximately 330 rpm for the difficult drilling. A f t e r t h e r o t a t i o n m o t o r s w e r e changed, the rotation speed was reduced to approximately 500 rpm on both sides. The maximum feed pressure increased slightly to 1,500 psi since this was not enough to bend the steel and the hard c o n d i t i o n s n e e d e d m o r e t h r u s t . T h e average feed rate was unchanged at 2.4 in/s, and the bit life was also unchanged at 52 ft per bit. The clogging of the drill steel previously noted was essentially eliminated. With the increased torque, the operators were now able to slow the rotation speed in the harder bands without stalling the motors. This drill was not able to realize the same improvements to bit life as most machines in the study. This was attributed to the fact that the feed package was prop- erly tuned already. The dust and noise lev- els appeared to have been reduced significantly, which was attributed pri- marily to the lower speed of the rotation motors. To date, this mine has elected to not incorporate these changes to its fleet. The test machine was put back to its origi- nal condition. Mine D mine was operating RRII arm feed machines in extremely hard drilling c o n d i t i o n s . T h e y w e r e i n s t a l l i n g 6 - f t t o r q u e t e n s i o n b o l t s a n d 1 0 - f t c a b l e b o l t s . T h e d r i l l i n g s e t u p i n c l u d e d McSweeney's HOTL 7/8-in. round drill steels, 36-in. starters, drivers, 24-in. mid- dle sections, and finishers. The bits being used were Kennametal RKCV 400 1RR. The maximum thrust pressure was recorded at 2,000 psi on both sides of the machine, but the feed package was com- r o o f b o l t i n g c o n t i n u e d 24 www.coalage.com January 2016 Figure 2 — Feed package valve in various loading conditions.