It is not necessary to use water as in other types of earth drilling. Many of those drills work with compressed air which caries the rock bits and the dust . The air coming from the hole goes through one or more cyclones and is cleaned by the centrifugal forces. The very fine dust can be retained by a filter.

The way rock is fragmented is different from metals cutting so the durability problems are different. Rock is split by local pressure from the bit which generates cracks and metals are cut by shear forces which generate high friction and a lot of heat.

It depends what kind of tool you use their behaviour depends on their design. And every kind of stone needs an optimal but specific tool.

Thank you ... that helps a lot.

I recall being taught many decades ago that backhoe mounted pavement breaking tools had a rate limit and I think it was in strokes per minute. The problem when that was exceeded sufficiently was that the soft iron core heated up with a higher coefficient of thermal expansion than the case hardened steel surrounding it. The result was a catastrophic failure with bits and pieces of hardened steel flying away at high speed.

Was this true, or was it a motivational speech from a teacher?

Hello jcrock

Pavement breaking tools don't actually have a "soft iron core", but a tough steel core.

They normally do not have "case hardening", but often do have molybdenum and other materials which can withstand impacts as a welded or clad "overcoat", similar to bulldozer blade facing materials.

So your teacher was not entirely correct, in those far off days.

However there have been cases where impact tools have shed a toughened or hardened covering.

In the early days of tungsten carbide tooth saws and cutting tools, the bond to the parent sawblade/toolbit, or the support base between the tungsten carbide insert/s and the parent blade/toolbit was sometimes insufficient, under load and/or localised heating, with resultant failure, along with personal and property damage.

In some cases, the damage was lethal.

Refer: http://en.wikipedia.org/wiki/Tungsten_carbide

Kind Regards....

Answers

1. Yes, most of the time. But the rock is not "hammered" but gently persuaded it should't be where it is.

2. Yes.

3. Part A: Core? On most rock drillbits water is pumped down through the middle of a hollow bit and mud and scrapings are flushed away on the outside of the bit.

Part B:Yes. I have seen drill bits melt into slag when the water flow is broken.

Jcrock, Ran an Ingersoll-Rand Vertical track drill in a limestone mine for about 5 years. Noisy S.O.B. That particular drill used compressed air to flush out the pulverized limestone. It was then vacuumed up and the dust dumped behind the unit.

I would drill 22 foot deep 2 1/2" diameter holes, pack them with ANFO and an accelerator, usually Det-Gel.

The shot covered a grid about 50 feet square. I think it worked out to be about a square mile after five years.

Regards, Blue

Guest,

From your description, you must have been in a cloud of dust for ~ 5 years. How did you protect your lungs? Have you suffered silicosis or other dusty lung disease symptoms? Have your co-workers suffered any of these symptoms? Thanks for taking time to respond.

Jcrock, Call me "Blue". That drill had a collar that dropped down around the bit with a pretty powerful (80 HP hydraulic driven) vacuum fan that took most of the dust away.

You have to understand the mine I worked in was pretty much a "pirate" operation. By that I mean: less than fifty employees; so they were exempt from labor board and union rules, most of the men working there were still reporting to their Parole Officer; so they couldn't quit without going back to jail, and they used equipment that should have been buried at a crossroads with a stake through it's heart.

One man was killed shortly after the mine opened: lack off training, he didn't speak English so his instruction was substandard.

I "dodged the bullet" SIX times in those five years. I will elaborate further in another post if you're interested.

See Ya Blue

Blue,

Sounds, indeed, like your working conditions were sub-standard. Your drill was more protective than the one I am evaluating if It had a collar/hood at the top of the hole and a vacuum pump to move the drill dust out of your work zone.

FYI, the drill I am evaluating was used in a surface quarry without the additional problems of an underground mine, which I surmise is where you worked.

Additional insights would be appreciated.

HAVE FUN ... BE SAFE

Jcrock, Yeah, substandard is a good word for it. I called it hell. The owner and the general manager only used any safety equipment for two reasons: 1) MSHA, Mine Safety and Health Administration, said they had to (2 Dead men don't move rock.

I spent most of the day at least four hundred feet underground.

The men working there had to nearly close the mine to get a Port-a-let placed in the mine. And then it was taken out to be cleaned only when the Superintendent couldn't stand the stench.

Some of the equipment was so decrepit and dangerous to use that when the MSHA inspectors showed up the operators were told to take the equipment and hide it. There was a scaler unit, an old track hoe, that regularly caught fire because of a hydraulic leak.

While operating a CAT 773 50-ton haul truck, the CAT 988 long boom loader loading me ran over a jackleg, (an unexploded loaded hole) that had been there for at least a week undiscovered by the Superintendent. The resulting explosion lifted the front of that loader four feet off the ground and blew me out of the drivers seat onto the floor of the passenger side to the cab. The Super's first comment after seeing the crater in the floor and the damage done to the loader said and I quote, "Why the hell aren't you mucking out that heading and what the hell did you a**holes do to my loader!"

No concern if we were hurt, only making rock to pay his bonus.

That was only one of the many ways we were shown that our lives were not of any importance.

I have to stop now, because if I continue, I may be tempted to solve ALL of that man's problems for him.

Blue

My career has been in occupational safety and health.

I have not been responsible for mining, so appreciate your candor very much.

I have a colleague who is now working for MSHA in Colorado ... he is very frustrated with the inefficiencies of that governmental agency.

HAVE FUN ... Live SAFELY

Jim Rock

Jcrock, I am no longer in the "hole". I understand your colleague's frustration, as I watched Inspectors come and go with nearly nothing done to increase safety. You see it was cheaper for the owner to pay the fines than to actually fix the problems.

The S.O.P. was for the inspector to give a weeks notice for a "surprise" inspection, (!!) then show up at the office and review the paperwork for an hour, giving time for the equipment in violation to be hidden, then actually come into the mine. We were told to only answer questions that were asked directly of us, and not ask questions if we wanted to keep our jobs.

The only violations that got the management excited were known as "S&S" violations. These conceivably could cause the inspectors to shut down the mine.

Some things that they missed: 55-gallon drums of used oil and antifreeze buried on the property, old equipment, old tires and batteries shoved off into section under an old collapse, (these actually caught fire once and shut down the mine for a day) and no it was NOT reported!

I have been nearly killed SIX times by falling rocks, jackleg explosions, flying drill steel and once nearly falling 15 feet off of a belt line that we were told to shovel because the motor stalled out. The belt line had no safety "belt off" points. Another worker grabbed my mining belt. Thanks J.R.

Anyway, I hope that I have been of some help.

Regards, Blue