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 cool- ant, the heat buildup during coring can cause all of these compo- nents to fail.
2.Water flushes 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 flushed 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 seg- ments.
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 ad- equate segment/material contact. When the bit segments do not properly contact the work surface, the desired "controlled erosion" effect which maintains bit sharpness 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 cor- ing 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 diam- eter 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 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 dia- mond 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 al- most anything in its path, including embedded steel.
Sharpening Procedure for Core Bits
To work efficiently, diamond core bits must maintain good diamond expo- sure. 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 notice- able when the coring feed rate slows dramatically or the bit does not cut. Examine 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 wa- ter and at a lower RPM if possible.
4.Gradually increase water flow to flush sand from kerf.
5.Repeat as needed.
The Effects of Steel in Coring
•To
•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 ma- trix.
•A high degree of exposure to embedded metal by the bit's segments creates glazing. Glazing prevents the bit from cutting and coring.
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