drill bit types

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Sct t rt cor bt

Selection criteria

Atlas Copco is an experienced ISO certi-

fied supplier offering a full range of

equipment for all underground and sur-

face exploration drilling applications.

This includes rigs and a full range of

high technology and high quality pro-

ducts, including (ITH) In-The-Hole tools

and core drilling bits which are designedto maximize customer profitability.

All products are designed to mini-

mize downtime and maximize produc-

tivity. Atlas Copco core bits range from

a Series 1 bit for the softest application

to Series 10 bit for the hardest appli-

cation. The numbers correspond to the

different rock groups by hardness, and as

a general rule, the harder the formation,

the higher the series number required.

However, other factors bear on the

choice of bit, most important of whichare the characteristics of the rock

formation, its hardness, grain size, abra-

siveness, competence, and whether the

strata is fractured or changing.

The lift and feed force of the drill-

ing rig, together with its rotation speed

and chuck and rod holding capacity are

other factors. Some rigs have better

controls than others, and this must be

taken into account. Smooth control of

feed force, and accurate control of waterflushing and rotation are key factors,

along with the drillers technique.

A variety of core bit types is avai-

lable based on the diamond cutting ele-

ments used in their construction. The

impregnated diamond core bit is most

popular, followed by surface set dia-

mond bits, tungsten carbide and poly-

crystalline diamond composite bits.

Impregnated diamond bits should

generally be used with a peripheral speed

of 2-5 m/sec, depending on rock condi-tion and machine capacity.

Driller checking outside diameter of an Excore core drilling bit.

Cruc oprtoDrilling with a core bit is intro-duced at an advanced stage of theexploration operation, by whichtime substantial resources havealready been spent. The qualityand continuity of the capturedcore is crucial in the assessmentof a potential mine, making thecore bit a key component of a coredrilling rig. Core bit selection isbased on the size and depth ofhole and the hardness of the rock,taking into account the rig capa-city and condition, the flushingmedium, and the skills of thedriller. To ensure the correct corebit, the drilling contractor needs areliable bit supplier with the righthands-on experience to advise thebest solution for every condition.Atlas Copco manufactures theentire range of core drilling tools,and will recommend and supplythe type and designation most

suited to the application.


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imprtd dmodcor bts

In most geological formations, impreg-

nated bits are more economical to use

than surface set bits as they provide ad-

ditional benefits: greater resistance to

wear in most formations, (particularly

in hard and fractured formations), less

sensitive to abuse, rough handling and

improper use. Synthetic diamonds are

used in the manufacture of Atlas Copco

impregnated bits, with some bits using

natural diamonds as gauge stones. The

consistency of quality, shape, granular

size, and strength make synthetic dia-

monds superior to natural stones.

Impregnated diamond drill bits are

designed to perform as grinders. Dia-

monds are embedded in an infiltrated orsintered matrix, which erodes away at

the same rate as the diamonds become

worn and rounded. Thus new sharp dia-

monds are exposed to continue cutting

through the rock. The combination of

diamonds and matrix determine the bit

performance, and the simultaneous ero-

sion of the matrix and the d iamonds

makes the bit self-sharpening.

The ideal combination of optimal

penetration rate and wear resistance

is matched to achieve the ultimate indrilling economy.

The diamonds are carefully selected

by quality and size for the application.

Through advanced manufacturing tech-

nology an extensive range of drilling

requirements can be satisfied. Conti-

nuous control at each step in the manu-

facturing process ensures that all bits

are of identical high quality. This con-

sistent high quality means more drill

metres per bit. Impregnated diamond

bits are the bit most commonly used in

exploration drilling, and are particularlyrecommended in the hard to extremely

hard formations of rock groups 6-10.

Productivity has constantly improved

due to intensive research and develop-

ment, which has introduced new gene-

rations of synthetic diamonds, metal

alloy and improved production pro-

cesses. As a result, impregnated bits

can be used in almost all applications

except clay, chalk and other unconsoli-

dated formations.

The impregnated bit matrix is avail-able in a Series 1 through to Series 10

according to rock hardness. Extended

channel flushing (ECF), channel

flushing (CF), and face discharge (FD)

waterways can be selected, along with

Torpedo V and JET crown profiles

for competent formations. Atlas Copco

manufactures core bits in 10, 13 and 16

mm crown heights. In terms of drilling

parameters, weight on bit and rate of

penetration have to be taken into ac-

count, as do f luid volume, and rotation

speed. The revolution per rate of pene-

tration is normally in the range of

150-250 rev/in (RPI) or 60-100 rev/cm

(RPC).

Surface set diamond bits

Surface set diamond bits can be used to

drill in soft to medium hard sedimen-tary formations, but in hard rock im-

pregnated diamond bits are normally

more cost effective. Surface set bits are

designed to utilize specific diamond

size and quality according to the appli-

cation, they are available in step and

semi-round crown profiles, with a choice

of CF waterways for consolidated rock

or FD waterways for use with triple tube

core barrels to avoid core washing out

in soft formations. Step profile is nor-

mally used for standard and thick kerfwire line bits and is suitable in almost

all kinds of formations, where they offer

good penetration rate and stability.

Semiround profile is used for conven-

tional and thin kerf wire line bits.

Atlas Copco surface set bits are

manufactured to the highest standards

in the industry, for the ultimate in drilling

performance. They employ a hard type

of matrix for all formations, and use

selected and processed diamonds with

a highly polished surface. These stones

have a high impact resistance, and havebeen developed from many years of

practical field experience. If the for-

mation is soft a larger stone is utilized

which results in fewer sones per carat.

Harder formations require smaller sto-

nes. The setting patterns are important

to the long service life, high penetration

rate, and adaptability to changing for-

mations that characterize this type of

bit.

Atlas Copco uses best quality pro-

cessed N, S and P diamonds suitable forhard to soft formations. Most common

Jet

Extended Channel Flushing

Torpedo "V"

Face Discharge

Diamond Surface Set (SS)

Poly Crystalline Diamond Composite (PDC)

Tungsten Carbide Insert (TCI)


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quality is S, which is a natural, selected-,

processed diamond, suitable for almost

all applications. The size of diamonds,

or stones per carat, is important because

the harder the rock, the smaller the

stones.

Tungsten carbide (TC) bits

TC core bits are used for drilling in

non-consolidated formations and in

overburden, and for cleaning dr ill

holes. They are used for soil investi-

gations and geotechnical drilling, and

can also be used for mineral exploration

for coring in softer rock formations.

Atlas Copco manufactures two diffe-

rent types of bits with octagonal tungsten

carbide inserts. Another type of tung-

sten carbide bit with more cutting edgesthan standard TC bits is Corborit,

recommended in medium to medium-

hard sedimentary formations.

All TC bits can be used in clean-out

operations, such as for the removal of

steel fragments from a drill hole.

Po-crst dmodcompost bts (PDC)

PDC bits are an alternative to TC bits

and surface set diamond bits, when

drilling in non-consolidated and me-

dium hard rock formations such as

salt, potash, limestone, and clay stone

with no crystalline or chert or similar

intrusions.

Atlas Copco offers two types of PDC

bits known as Diapax and Tripax. Diapax

bits have brazed round PDC inserts,

while Tripax bits have brazed cubicor triangular PDC inserts embedded

in the matrix and are recommended for

harder sedimentary formations.

Reaming shells

A reaming shell should always be used

in a coring system. It is a core barrel

component, which joins the bit to thecore barrel outer tube. The outside sur-

face of the reaming shell is set with dia-

monds to a specified diameter, normally

larger than the bit diameter. This pro-

vides a constant hole diameter inde-

pendent of bit wear, and accommodates

changing the bit without getting stuck

in the hole. They also serve as a stabi-

lizer, reducing vibration and prolonging

the life of the bit.

Reaming shells are designed with a

tapered leading edge to ream the hole.Well designed waterways, reinforced

with PDC pins, facilitate effective flu-

shing and contribute to long service

life and good drilling economy for both

reaming shells and drill bits.

For some core barrel systems there

are optional reaming shells, longer than

the standard, designed with two or three

diamond set gauge rings. The longer

reaming shells have to be used together

with an optional extension sleeve for

the inner tube. Double and triple ring

reaming shells are used to improve holedeviation problems.

Impregnated reaming shells full hole

profile are also available, when added

stability is required.

Casing and rod shoes are manufac-

tured to handle a broad range of con-

ditions, from unconsolidated over-

burden to broken, abrasive formations.Impregnated standard and heavy duty

casing shoes as well as surface set

casing shoes are available, rod shoes

are available only in an impregnated

design.

Summary

To maximize drilling efficiency, choose

the right drill bit and utilize sound drill-

ing practices. There is no substitute for

testing the system at site, because all

sites are different, all formations are

different, and all clients requirements

are different.

grr Bc

Atlas Copco representative discussing diamond tool selection with driller.


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drill bit types

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