Get the most from your diamond blades

Reduce concrete cutting costs with proper blade selection and use

Cutting concrete is hard work. It literally puts two extremely abrasive materials — diamond and concrete — against each other with speed and power.

If the selection and use process goes correctly, the diamond blade wins and you have accurate, fast cuts at the lowest possible cost. But if any part of the process is missed, misjudged or changes, the diamond blade can lose some or all of its advantage and you can end up with a dull, worn or damaged blade, a poor cut, or no cut at all.

The Concrete Sawing and Drilling Association (CSDA) has developed several training materials on concrete cutting. It shares tips on how to cut concrete in this article and also offers training videos, handbooks and operator certification classes. Contact CSDA at 727-577-5004 or go to www.csda.org for more information.

Diamond blade make-up
Almost all diamonds used in concrete cutting blades are man-made. They allow the blade manufacturer to best match the diamond grade to the specific cutting application.

Generally, the diamond toughness increases as crystal size decreases. Larger mesh sizes are used to cut softer materials such as green concrete and asphalt; smaller mesh-sized diamonds are used on blades to cut harder concrete and stone.

The amount of diamond used in the blade can affect cutting ability. The diamond concentration is measured by CON, where 100 CON equals 72 carats per cubic inch. Blades used in construction applications are between 15 and 50 CON. A 32 CON blade has 23 carats of diamonds per inch, or about four carats per segment.

Diamond shape also affects cutting ability, varying from tough, blocky crystals to more friable crystals with less-defined geometry.

Diamond crystals with blocky shapes and sharp edges are generally better suited for tougher applications such as concrete and stone cutting. This structure doesn’t fracture as readily, providing the maximum number of cutting points with minimum contact. They usually require less horsepower for cutting and offer longer blade life.

Lower-grade diamonds have irregularly shaped and angular crystals. They cost less and are used in less severe cutting applications.

Diamond blade manufacturers also look at impact strength (known as Toughness Index or TI) and the Thermal Toughness Index (TTI), which is the diamond’s ability to withstand thermal cycling. These properties affect the blade’s cutting ability.

The bond plays an important role in the blade’s cutting ability. It is the “glue” that holds the diamonds in the segment and is made up of a variety of metals that are mixed with the diamonds, pressed together to form the segment, then heated (but not melted) to the point where the diamonds and metals bond. The segment is then brazed or laser-welded to the metal blade core.

Blade selection in the field
Confused yet? Don’t be. While these factors are important to blade manufacturers in the design process, users only need to match the blade size and running speed with the saw, then select the blade that best matches the job. Your diamond blade distributor or supplier can also offer valuable selection advice. But before you call, collect the information to answer the questions in Table 1.

If you are cutting green concrete or asphalt, consider using a blade with undercut protection, which helps slow core wear and improves blade life.

Saw manufacturers explicitly identify blade type and rpm that can be used with their units and blade manufacturers plainly label blades with operating parameters.

Efficient cutting needs horsepower. An underpowered saw will run the blade too slowly and in turn glaze the diamonds, reducing cutting ability.

Making the cut
Check the operator manual for specific inspection points before operating the saw. Generally, the inspection checklist covers checking blade flanges, blade shaft bearings, drive belt tension, axle and wheel bearing alignment and water delivery operation.

Always wear the personal protection equipment and follow the directions and warnings listed in the saw’s operator manual.

When starting the cut, it’s best to start with a slower speed, then fine-tune blade speed to maximize productivity.

Faster speeds usually make the blade act harder, which can improve cutting in softer materials. In harder materials, slow the blade speed slightly which makes the blade act softer and in turn, cut more aggressively.

In softer, yet abrasive materials that cut easily, move the saw forward a bit faster and use more water to cool the saw and remove swarf. Never increase rpm past the blade’s maximum recommended rpm.

Set the saw so it cuts 8' to 10' per minute. Coolant should flood the cut, using 1.3 to 2.6 gal. per minute. Check cutting depth often to assure a consistent cut.

When the blade encounters rebar or other metal reinforcing materials, sparks will fly. Reduce blade speed and water flow and allow the blade to cut through the steel. Interrupted pressure on the saw may help the saw cut through the metal. Once it cuts through, resume normal cutting speed and water flow.

Diamond blades are designed to wear in the cutting process, exposing a fresh abrasive edge as the concrete wears away the diamonds and the bonding material. Any cutting problems must be addressed by changing blade speed or selecting a different blade for the job.

Troubleshooting
The CSDA offers some ideas when a diamond blade can’t make the cut:

The blade doesn’t run true at rated rpm. Blade manufacturers “tension” blades to run true at the rated rpm so the blade has a very slight dish shape that flattens at operating speed. If it loses this tension, it won’t run true, causing vibration and poor cutting.

It can lose tension from overheating and uneven wear from poor alignment. The only solution is prevention with good operating practices.

When installing the blade, make sure it is properly aligned and that blade flanges are the correct size. The blade must mount flush with the arbor shoulder, preventing the blade from bending when flanges are tightened.

During operation, make sure the water reaches the blade core near the collar, then sheets out to the cutting edges. If side wear is a problem, select a blade with more side clearance.

Segments break off the blade: Segments can break off if the blade overheats or if the blade’s specification is too hard for the material being cut. Sharp, sudden saw movements while the saw is entering or in the cut can also knock off segments.

Prevention is the cure. Make sure plenty of water reaches the core to cool the blade and use slow, even pressure while cutting.

Cracked core: Any crack in the core is a sign the blade may be too hard for the material or the operator is stressing the blade by pushing, jamming or twisting the blade in the cut.

Blade won’t cut: This is one of the most common complaints with a host of possible causes. To find out, use a loupe (a small magnifying glass) and examine the segments for:

• Smooth segment surface: Indicates the bond is not breaking up or the diamonds are too friable and wear faster than the bond. Decrease cutting speed or use a blade with a softer bond.

• Diamonds stand high on the segment: Indicates the bond is wearing too fast and unable to support the diamonds. Increase cutting speed or use a blade with a harder bond.

• Popped-out or missing diamonds: Indicates the bond may not be right for the application. Adjust speed or change to a different blade specification.

• Diamonds are in place, but many are crushed or highly fractured: The diamonds may be too friable for the application or the blade has been subjected to excessive pounding.

• Diamonds with rounded or flat tops protruding above the bond surface: Indicates the diamonds may be too impact-resistant, have a mesh size larger than what is needed, or the diamond concentration is too high for the application. Change cutting speed or blade specification.

If you still can’t determine why the diamond blade won’t cut efficiently, contact your diamond blade or concrete saw distributor or supplier for advice.

Published in the May/June 2002 issue of Contractor Tools and Supplies magazine.

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