Grinding; General Rules; Grinding Hints; Grinding Instructions - Atlas Copco SECOROC Grind Matic HG Instructions D'utilisation

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Grinding

DANGER
Before starting to grind a drill
bit, make sure that there are no
traces of explosive in the flushing
holes of the drill bit. To clean out the
flushing holes, only use a wooden
rod, copper wire or flushing water.
Do not use other implements.
CAUTION
The exhaust air from pneumatic
components contains oil, which can
be injurious to your health if in-
haled. Always adjust the lubricator
so that the correct dosage is ob-
tained.
Make sure that the grinding
station or work place is well ventilat-
ed.
Always wear goggles, protective
clothing, gloves and ear protectors
during grinding.
Wear an approved dust mask, or
arrange a satisfactory dust extrac-
tion system. This is especially
important when dry grinding
indoors.
Before fitting or removing a
grinding cup, the incoming com-
pressed-air hose must be disconnect-
ed.
Beware of the risk of fire or
explosion that might be initiated by
sparks from the grinding work.

General rules

Use grinding cups of the right size for the
buttons in question (see page 52).
The drill bit must be well secured for
grinding, so that it does not move.
Be aware that the grinding cup is hot
after grinding.

Grinding hints

The rate of bit wear depends on the rock
formation, and is highest in rocks with a
high quartz content. A suitable grinding
interval should be determined according
to the rate of bit wear. It is more eco-
nomical to regrind too early rather than
to suffer poor penetration rates and risk
damaging the drill bit through overdrill-
ing. A few hints about the care of drill
bits:
When to regrind
Button bits should be reground when the
penetration rate drops, or if any of the
cemented-carbide buttons are damaged
(fractured buttons should be ground flat).
It is both practical and economical to
redress the buttons when the wear flat
reaches about 1/3 of the diameter of the
button.
Look out for "snake skin"
If microscopic fatigue cracks – so-called
"snake skin" – begin to appear on the
cemented car-bide buttons, the cracks
must be ground away. In any event, bits
should be re-ground after 300 metres of
drilling at the most. This should be done
even if there are no visible signs of wear
and the pene-tration rate continues to be
good. If snake-skin is not removed, the
cracks will deepen and ultimately result
in button fracture.
Do not grind away too much
cemented carbide
Do not grind too much on the top of the
buttons. Let a few millimetres of the
wear flat remain on top of the button.
Always grind broken buttons flat
A drill bit can remain in service as long
as the gauge buttons maintain the
diameter of the bit.
6
Fractured buttons must always be ground
flat to prevent chips of cemented carbide
from damaging the other buttons.
Avoid grinding the perimeter
Gauge-button anti-taper has to be re-
moved by grinding, although excessive
reduction of the bit diameter should be
avoided. Leave about 2 mm of the wear
flat.
If necessary, remove some of the bit-
body steel below the gauge buttons, so
that a clearance (taper) of 0.5 mm is
maintained.
If the flushing holes start to deform,
open them up with the aid of a rotary
burr or steel file.

Grinding instructions

To obtain the correct button shape, the
grinding machine should be handled as
follows:
When grinding spherical cemented-
carbide buttons, move the grinding
machine with GC cup evenly over and
around the centre of the button.
When grinding ballistic cemented-
carbide buttons, hold the grinding
machine with GC-T cup upright over the
button.
Do not press too hard. The weight of the
machine itself is usually sufficient feed
force.
The diamond-impregnated grinding cup
can also be used to remove small
amounts of steel from around the button.
However, excessive grinding of steel will
soon clog up the grinding cup. If this
happens, the cup can be "opened up"
again by rubbing it against a whetstone
(available as an accessory), or by
rotating it against a discarded silicon-
carbide grinding wheel. The right cup to
use for removing steel from around the
button is a GC-B boron-nitride cup.
Grind down the steel by about 1.5–2 mm
by holding the machine directly over the
button.
The Grind Matic HG is delivered
equipped for air cooling of the grinding
cup. A kit for converting the machine for
water cooling is included in the package.