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Water
Water provides two main benefi ts during coring:
1.
Water acts as a coolant, eliminating the heat caused by the friction of
the coring action. This preserves the integrity of the diamonds, the bond
matrix, the segment solder, and core tube. Without a coolant, the heat
buildup during coring can cause all of these components to fail.
2.
Water fl ushes loose, abrasive particles created during coring. These
particles consist of aggregate, sand, diamond particles and various
metals from embedded steel and the core bit matrix. The hole must
be free of debris to allow the core bit to work. If loose particles are not
properly fl ushed from the hole, an unnecessary drag will occur along
the side of the core barrel. This can contribute to bit glazing through
lack of power as well as motor damage through amperage increases
due to bit resistance. In addition, loose particles tend to wear the bit
tube, which can eventually result in the loss of segments.
Monitor water fl ow. Water volume should be adjusted until water return is
a muddy, solid color. Clear water or clear streaks indicate too much water
volume. Excess water is a leading cause of bit glazing and failure. Other
factors contribute to glazing, but water adjustment is one of the most easily
controlled by the operator. Excessive water prevents adequate segment/
material contact. When the bit segments do not properly contact the work
surface, the desired "controlled erosion" effect which maintains bit sharp-
ness does not occur and the bit begins to glaze. This happens especially
with smaller diameter bits. Adequate water volume varies according to the
bit diameter. Use only enough water during coring to fl ush the cuttings from
the work surface.
Equipment
•
Make sure machinery is in good operating condition. The column, car-
riage, motor connection and base should all be fi rmly connected and
should not vibrate during coring.
•
Motors should be of proper size (amperage and RPM) for the diameter
of the core bit used. Consult motor guide in catalog.
•
Always make sure the Dymorig is rigidly mounted with an anchor or
vacuum; any movement or vibration will shorten the life of the core bit.
Standing on the rig's base as a form of anchoring is dangerous and
does not provide the necessary rigidity.
Diamond Core Bits
•
For the fi rst 2 or 3 holes, use light feed pressure, so the new diamond
gradually breaks in.
•
Lower the bit very slowly onto the work surface. Use light feed pressure
until the bit crown has penetrated or "seated" into the material.
•
If the core bit encounters embedded steel, slow down the feed pressure
and let the bit core at its own pace. Don't force the bit. Typically the
water around the bit will clear when embedded steel is encountered.
Do not allow any vibration whatsoever or severe diamond breakage or
pullout will occur.
•
Keep bits sharp.
Bit Glazing & Diamond Core Motor Shear Pins
Bit binding is caused by one of two things: a dull (glazed) bit or a poorly
stabilized rig.
Causes of bit glazing:
•
Wrong RPM for bit diameter
•
High feed pressure
•
Low feed pressure
•
High steel content in work surface
•
Large, hard aggregate
•
Too much water
•
Low motor power
A sharp bit typically has good diamond exposure and will cut/grind almost
anything in its path, including embedded steel.
Sharpening Procedure for Core Bits
To work effi ciently, diamond core bits must maintain good diamond exposure.
Many factors work together to provide the "controlled erosion" cycle of the
tool's segment to occur. When this "controlled erosion" cycle is altered,
the bit can become dull or "glazed." Glazing becomes noticeable when the
coring feed rate slows dramatically or the bit does not cut. Examine the bit
immediately. If the diamonds are fl ush with the metal, they are underex-
posed or "glazed."
The following steps will often correct the problem:
1.
Reduce water fl ow until it becomes very muddy. Continue using as little
water as possible until penetration increases.
2.
If the bit does not open up, remove from hole. Pour into the kerf a thick
(1/4") layer of silica sand (the coarser the better).
3.
Resume drilling for approximately 3 to 5 minutes with very little water
and at a lower RPM if possible.
4.
Gradually increase water fl ow to fl ush sand from kerf.
5.
Repeat as needed.
The Effects of Steel in Coring
•
To self-sharpen, diamond-impregnated core bits require interaction
with an abrasive material. This abrasive material wears away the metal
composition in the segment's matrix. As this is done, sharp diamonds are
exposed and the grinding action created by the diamonds continues.
•
Embedded metal (rebar) is not an abrasive material. It does not provide
the degree of abrasiveness required for matrix wear to occur and expose
sharp diamonds embedded in the segment's matrix.
•
A high degree of exposure to embedded metal by the bit's segments
creates glazing. Glazing prevents the bit from cutting and coring.
page 11
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