11
Diamond Coring
Factors that influence diamond core performance:
• Amount of coolant
• Dymorig rigidity
• Dymorig condition
• RPM of drill motor
• Feed pressure applied to bit by operator
• Amount of steel
• Size of embedded steel
• Age of concrete
• Aggregate (size, type, hardness, abrasiveness)
• Type of sand–manufactured vs. river (natural)
• Operator technique
• Operator care
• Bit runout
Operator Technique
Core with consistent, firm feed pressure. Do not
subject the bits to sudden impacts. Uneven feed
rate cracks diamonds. Low feed pressure polishes
diamonds, slows penetration and contributes to bit
glazing. High feed pressure can overload the drill
motor or can cause diamonds to pull out prematurely,
particularly when coring embedded steel. Make the
bit work, but do not try to jam the bit through the
material.
If vibration occurs:
1. Stop drilling.
2. Turn motor off.
3. Check for loose bolts, nuts and gib screws. Tighten
if required.
4. Check for bit runout. Replace if required.
If vibration continues to occur, remove the core and
loose material.
If vibration continues to occur after attempting these
measures, return the rig to the nearest MILWAUKEE
service facility.
Water
Water provides two main benefits 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 flushes loose, abrasive particles created
during coring. These particles consist of aggre
-
gate, 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 flushed
from the hole, an unnecessary drag will occur
along the side of the core barrel. This can contrib
-
ute 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 flow. 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
flush the cuttings from the work surface.
Equipment
• Make sure machinery is in good operating condition.
The column, carriage, motor connection and base
should all be firmly 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 vibra-
tion 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 first 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 efficiently, 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. Ex
-
amine the bit immediately. If the diamonds are flush
with the metal, they are underexposed or "glazed."
The following steps will often correct the problem:
1. Reduce water flow 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 flow to flush sand from
kerf.
5. Repeat as needed.
