Drilling down to the details

Donna Schmidt bites into bits and other drilling consumables for a sharper scope on what technologies are shaping performance and effectiveness

Donna Schmidt
 A Cat MD6250 in the field at a site in Asia

A Cat MD6250 in the field at a site in Asia

When it comes to successful, efficient drilling, the quality of the equipment used is only half of the story. The drilling consumables in use make up the rest of the effort, and at the heart of that are designs and technologies that can help mines work longer, safer and with the best results.

While that sounds straightforward, selecting the best drilling consumable options for a mine's location, geological conditions and other considerations can sometimes prove to be an overwhelming task. Drill bits, for example, are considered to be the starting point of a mine's entire production cycle, so getting this fundamental selection wrong can leave a dent in a mine's bottom line.

GDI reached out to those in the drilling consumables circle to discuss the importance of bit performance, ever-present supply issues for some mines and remedies for that quandary. We also asked about best practices for drillers to make the most of these consumables in terms of higher penetration rates, longer wear life and realising success in one of mining's toughest environments.

Importance of performance

Bit performance can quite literally make or break a drillers' effort, but the quandary for many operators goes back a step further: selecting the right bit. What works for one site in Canada may not work for a US location, and what does not work in Chile may not have success in Australia. As the company notes, a Longyear may move 17in (43cm) per minute in Arizona, US, but just 3in (7.6cm) per minute in Ontario, Canada.

Boart Longyear has drilled down the process of bit selection to five steps, hoping to help mines battle an issue that the company says is often an afterthought.

First, the main objective must be identified, according to Boart Longyear's diamond products engineering team lead Bob Corona: "The overarching objective is always more core in the box, but there are additional elements that need to be considered. For example, a rod trip takes significantly less time at 400ft [122m] than a rod trip at 4,000ft [1,220m].

"While bit life is important, it's less crucial at the top of a hole because that usually means sacrificing penetration rates."


To support higher penetration rates, Boart Longyear's Longyear bit formulas are combined with a new, more open, express geometry

The second step is to determine the ground hardness. Use of the Mohs scale, with an exponential scale from one to 10, will quantify mineral hardness. Minerals with a high Mohs hardness will scratch anything with a lower Mohs hardness and, he adds, all bits offered on the market today will target a specific range of the Mohs scale for best performance.

Third, Boart Longyear recommends selecting a colour bit by referencing the company's diamond bits hardness rating and comparison chart. A purple bit at the soft end of the scale is ideal for a mineral hardness of 1 to 4.5, and bits at the other end of the spectrum are red, which is best for a mineral hardness of 7.5 to 9. Blue, green, yellow and orange bits all fall in between the purple and red bits and the ideal applications of each colour designation have some overlap.

"For example, if you are in a 6.5 rock, select a green bit or a yellow bit," Corona says. "Which one should you try first? It depends.

"If the site is cutting a lot of short holes and bit life isn't a big concern, you would likely have the best luck with yellow - it would penetrate faster than green, but not have as long of life in 6.5 rock. On the flip side, if bit life is a concern because you're drilling deep holes, you may prefer green."

Fourth, Boart Longyear stresses the importance of correct geometry, as each of its drill bits is designed to cut slightly differently. In its line, the company offers standard, tapered, express, stage/GT, deep ID and face discharge.

"Within each colour bar, the express has the ability to cut harder rock than the stage and the stage will cut harder rock than the tapered waterway," he notes, resulting in an ‘open area' percentage.

"Open area is determined by finding the surface area of a disc with the same outside diameter and inside diameter as the drill bit and subtracting the surface area of the drill bit with all the waterways cut in," explains Corona. "What's left is the area of the waterways, flutes and rounds, and the percentage of this number compared to the area of the total disc is the open area. Express has an open area of 30 per cent, Tapered Waterway has an open area of 25 per cent and Stage has an open area of 20 per cent."

Finally, the company recommends testing the selected bit with a focus on three key points: penetration rate, Mohs hardness and bit life. The result will either validate the driller's choice or give it the data needed to adapt.

According to Caterpillar rock tool consultant Fernando Gonzalez, proper characterisation and the ability to adjust to the variables of the application are vital. Mining operations have high expectations, expecting to drill as fast and as long as possible, so the starting point must involve examining all facets.


The Cat Tricone drill bit

That begins with ground conditions, a challenge which he notes can be overcome with the right combination of machine power and bit performance profile.

"These last two must be tuned together to get the most efficient performance from both," Gonzalez says, pointing out that the right bit will give an operator the fastest rate of penetration as well as an acceptable life.

"Penetration will then drive machine loads that will, in turn, drive efficiency. During a drilling cycle, the bit will face changing ground conditions, which will test the limits of its design," he adds. "Understanding these conditions and translating them into an appropriate bit design will give the customer a tool that matches the site and delivers optimum performance."

Robit material specialist and R&D engineer Niko Ojala says that bit selection in the more extreme environments of the world is even further elevated, as the scope of costs and job advancement broaden.

The variance between a good and bad bit performance is extended to the maximum

"The variance between a good and bad bit performance is extended to the maximum, and difference in lifetime and penetration rate follow accordingly," he says. "Therefore, one may get significantly more lifetime and penetration rate out of a good bit in extreme environments, even if the performance difference would be marginal in ‘easy' environments."

While the choice of drill bit alone has a lot to do with costs, the cost factor is also influenced also by fewer disruptions - in other words, less drill bit changes - and costs involved with losing holes due to bit breakages.

"All of these factors influence the overall job advancement, which normally is the basis for making the pay to drillers," Ojala explains.

Bit trends

Much has been talked about regarding the materials and technology that are shaping the future of drill bits. For makers of these consumables, many releases, retooling of technology and other ideas come directly from mine sites and feedback from users.

As with any type of technology, there are trends. Operators are not typically shy about sharing what they want, what changes they need to see to perform their work more effectively and safely, and what ideas others share of methods and products having an impact.

The trend from the perspective of Boart Longyear is a technology that is already part of its product portfolio: diamond coatings, though the company has put its own take on that process.

"By developing a proprietary process of coating diamond bits while in the furnace, Boart Longyear has successfully created a chemical bond between diamond and matrix," Corona says.

"The bond acts stronger than the diamond itself and provides higher diamond projection (up to 80 per cent compared to 40 per cent for mechanical bonding) for improved flushing, higher penetration rates and longer bit life."

Typical diamond coatings, he explains, do not create a chemical bond because of the strong oxide on common titanium coatings and that leads to the same 40 per cent diamond projection as mechanical bonding.

"As a Longyear bit is drilling and the matrix wears down around the bottom, the diamond stays in place longer and acts like a bigger diamond, which results in more metres per bit," he notes.


Going to work with the Longyear GreenBit

Boart Longyear has combined its bit formulas with more open, express geometry to provide support for higher penetration rates. It touts the benefits of improved flushing and the prevention of debris collection with its tapered intermediate waterways. In addition, its Razorcut protrusions on the face of the bit contain diamonds that enable the bit to begin cutting right out of the box, and even on soft ground.

"The arrangement of these protrusions also improves the tracking and balance in the hole when drilling begins," Corona says.

Caterpillar's Gonzalez confirms the OEM has been busy working with its engineers on how to better track critical drilling data that mines can analyse and use even faster. As no two ground conditions are alike, and variables change from hole to hole, there is a great benefit to arming a driller with these details.

"Not so long ago, on-site support engineers and drill operators manually recorded performance parameters and results; they then shared the information with product developers, when and if they had an opportunity. Now, new technologies such as expanded machine computing capabilities enable tracking of critical drilling parameters," he explains.

"Cat Product Link gives engineers access to drilling information so that improvements can be done with more reliable and actionable data."

As a result, operations are reporting an easier time tuning their bits to achieve optimum performance, and customers are also receiving bits faster. An added advantage of Cat Product Link is in product design, which can now be performed and implemented more rapidly.

Smart databases will predict future customer needs and will further accelerate new product development and delivery to the site

"The future of drilling relies not only on smart computing but on connecting machine, bit and ground. Smart databases will predict future customer needs and will further accelerate new product development and delivery to the site," Gonzalez says.

For Robit, according to Ojala, consistency in product quality is what is shaping the future of drill bits, along with the fact that the overall drill bit technology is simply using better materials than ever before.

This consistency, he says, is not just in the end product, but also in the raw material used, the manufacturing processes to produce the end result and especially in the heat treatment process.

This is an area where automated manufacturing can play a crucial role.

"Consumers want to experience the same quality they got at the time of testing drilling consumables and have no variance in performance," Ojala says. "Even if the manufacturers believed they were making an improvement of some sort, those should be considered carefully together with frequent users before deliveries."


Bit performance is an elevated feature in extreme environments for two reasons; costs and job advancement

Another development, from Robit's point of view, is the collection of drilling data and its use to optimise drill set-up with consumables. For example, Ojala explains, sensors installed on a drill can collect actual penetration rate along with actual drill rig set-up values.

"Making small adjustments in set-up will make it easy to compare them to earlier parameters, and fairly soon a driller can use the optimal set-up for each particular environment and type of drilling consumables," according to Ojala.

Best practice

Armed with the perfect drill bits for a specific operation's needs, there remains just one further, but imperative, consideration. What are the best practices the driller can put into place to make sure that bits serve the mine as long and as efficiently as possible?

Boart Longyear senior product manager Chris Lambert says getting the most from diamond bits comes down to six elements: rotational speed, weight/force on the bit, torque, penetration rate, water flow and sharpening.

"The best way to save money on consumables like bits is to check your drilling methods," he notes. "[Doing so] could decrease your operating costs and add more cash to your bottom line."

One of those factors, weight (force) on the bit is the main method of controlling both penetration rate and bit life. In short, if high bit loads are needed to cut rock, a higher series bit should be used to keep increased hole deviation from occurring, along with excessive core barrel, rod wear and down-hole failures.

"Increasing the bit series normally results in lower bit weights required for the same penetration rates. If the weight on bit is too low, both the penetration rate and torque drops, resulting in low life and productivity," Lambert points out.

The resulting condition is called polishing. He describes the phenomenon of diamonds wearing faster than the matrix until the face is flat, leaving no diamonds protruding from the face.

"Polishing is caused by the friction and heat accumulating in the diamond as it rubs rather than cutting the rock. If the weight on bit is too high, characterised by very little or no increase in penetration rate for additional weight, the result is constant sharpening and rapid wear," he notes.

Caterpillar says the opportunity of drilling data capture and tracking can also be a challenge for operations. In addition, some operations find that another obstacle is having a clear understanding of drilling costs and how they tie to the actual ground conditions being encountered.

"Technology is a great tool for monitoring and tracking performance, but don't discount manual logging and feedback," says Gonzalez. "Many times, the driller sees and feels minute changes that may indicate slight differences in the rock formation that will greatly change bit penetration and overall performance."

He adds that a systematic approach to data collection and formatting permits solid feedback - just don't underestimate the key facet of open communications between a mine's operations, planning and management teams.

"Never forget the driller has boots on the ground. The driller's feedback and reports often help clarify data conundrums and help identify the root source of problems," he says.

Supply issues

How are supply issues best tackled, particularly for remote mines? For Robit, it is all about logistics and having a primary, secondary and even a tertiary plan.

"Logistics are obviously the more important the further away mines are located from ‘everyday' delivery services, like courier companies," Ojala notes.

"Since a shortage of drilling consumables is not an option for these sites, one wants to work with the most reliable suppliers and have a ready laid out contingency plan for unforeseen situations. [A] triple-layered plan is better than no contingency plan, even if there was some cost involved."