Diamonds Don't Wear ... or Should They? Part 2
Material To Be CutKnowing as much as possible about the concrete can be of enormous benefit. Concrete is a mix of gravel, sand, Portland cement and water. Before you can choose the appropriate blade, you must know the type of aggregate that is to be cut, as well as whether rebar will be present, and the depth of cut. Limestone, slag and coral aggregate are relatively soft and abrasive, providing little problem for the diamond blade to cut. Concrete with river gravel aggregate generally is considered among the most difficult to cut.
The size of the aggregate also can play a factor in the cutting performance of a diamond blade. Concrete aggregates are often in the range of 1 1/2 to 2 inches. Concrete made with 2-inch flint aggregate will be extremely difficult to cut, but concrete with 1 1/2-inch flint aggregate may be cut more easily. This is due to the fact that there is more coarse aggregate per unit volume of concrete than when a larger, maximum size aggregate is used.
In addition to the aggregate, the type of sand used to make the concrete can influence the selection of a diamond blade. Many natural sands are quartzitic and have been rolled by water for many years and are smooth and dull. However, manufactured sand usually contains sharp, abrasive edges that can wear a bond quite quickly.
The type of aggregate has a pronounced effect on blade wear. Hard aggregates shorten blade life and slow the cutting rate, so cutting concrete with a hard aggregate will cost much more than cutting concrete with soft aggregate. Cutting concrete made with hard aggregates also requires more power. If there is enough power, bit speed or blade speed should be reduced.
Blades used to cut hard aggregates should have segments with tough diamonds and a soft metal bond matrix, otherwise the diamond particles will wear even with the bond surface and the blade glazes over and is unable to cut. Likewise, segments for cutting soft aggregates should have hard metal bonds, so that the diamond particles are not lost before their cutting life expires.
Other materials that commonly are cut with diamond blades include asphalt and green concrete. Asphalt or asphaltic concrete, is a mixture of asphalt and aggregates. Green concrete is concrete that is still in the curing stage. Both asphalt and green concrete can be very abrasive and both require special protection for the steel core in spite of the fact that they are soft materials. The abrasive nature of these materials can easily wear away the core just under the attachment point for the segment to the core. Manufacturers can supply blades with undercut protection positioned around the core to help slow the steel core wear.
Reinforcing SteelIt is inevitable that anyone who is involved in cutting concrete will cut into steel reinforcement. The steel can vary from a wire mesh with a small diameter to large reinforcement of over 1 inch in diameter. It costs more to cut concrete with reinforcing steel because blade life will suffer and the cutting production will slow. Blade life can easily be reduced by 50 percent or more depending on the steel cross-sectional area in the concrete.
When a blade encounters steel, it often is accompanied by sparks, which is a sure sign that steel reinforcement has been discovered. The operator should reduce the speed of the blade and decrease water flow. Sometimes using interrupted pressure will aid in speeding up the cutting.
TroublesIn the early days of concrete cutting, many operators learned that if the blade glazed over, they should turn the blade over so that the diamonds would face the concrete in the opposite direction thus exposing new sharp points. If the reason for the polishing or glazing has not been corrected, after one layer of diamonds have been popped out, the blade will once again slow and polish. Unless corrective action is taken, this can cause much waste. The same can happen when the operator hammers the segments to expose new diamonds. Today's diamonds are more likely to embed, not facture, into the bond and increase the smooth bearing surface of the blade.
TroubleshootingSome of the more common problems encountered in the field - and their remedies - are:
Loss of Tension - The loss of tension in a diamond blade can occur for many reasons. The blade core could have become overheated from a lack of sufficient water being applied to the blade or a lack of side clearance that results from uneven segment wear. One should make sure the water supply is adequate and is reaching the core near the collars and sheeting out to the cutting area. A blade with more side clearance, and suited to the cutting application, should be used by the operator.
Blade tension also can be lost when a blade is misaligned on the saw, the blade flanges are not of the proper size, or the blade is not properly mounted on the arbor shoulder, causing the blade to bend when the flanges are tightened. The operator should make certain that the flanges are clean, are of the proper size and are properly mounted and secured.
Segment Loss - Overheating of the blade can cause segment loss. This often is the result of a lack of proper water being applied to the cutting area. Another reason for segment loss may be that the blade specification is too hard for the concrete being cut, causing the blade to become dull. In this instance, an operator should recognize that the material being cut is different than originally believed and a blade with a softer bond might be better suited to the new material. Segment loss also can occur when the blade is subjected to sharp sudden movements while in the cut or upon initial contact with the concrete. The operator should make slow and even contact between the blade and the material to be cut.
Core Cracking - If the operator observes that the core is cracking, the blade specification being used may be too hard for the concrete or other material being cut. The operator should not put excessive pressure on the blade by pushing, jamming, or twisting the blade into the cut. All of these actions can put undue stress on the blade and can cause metal fatigue.
Blade Will Not Cut - A blade that will not cut can be the result of a number of factors. The first is that the blade specification may not be the proper one for the material being cut. The operator should examine the segments on the diamond blade with a loupe to find out why the blade is not cutting. If the operator finds that the surface of the segment is smooth and that the diamonds are not protruding, then the diamonds may be too friable, the bond too hard or the speed of the blade may be too high. On the other hand, if the operator finds that the diamonds are protruding too far from the bond with little bond support, the bond is not resistant enough for the abrasive material being cut, or possibly the diamond/bond combination is not right for the application.
If the operator examines the segment surface and finds that many of the diamonds are missing (popouts), then it is safe to assume that the diamond impact resistance is not sufficient or the combination of the diamond/bond is not right for the cutting application. The operator may find the diamonds in place but with an abnormally high amount of fractures or crushed crystals. The blade may cut quickly initially, but overall life is short because the diamonds are too friable or the blade has been subjected to excessive pounding.
The blade may cut well initially but then slows and eventually stops. The operator may find that the diamonds are in place, but are smooth or have flat tops and still are protruding above the bond surface. In this case, the diamond may be too impact resistant, too large a mesh size, too high a concentration or the diamonds may just not have been pushed to their design operating condition.
Field PerformanceAll of the information presented in this article provides an extensive background on how diamond blades are designed and how they should perform. But once the blade is in the field, it is up to the cutting operator to apply a blade to the job-at-hand in a profitable manner. When operating a diamond blade, an operator should regularly inspect for lost segments, uneven segment wear, developing cracks in the segment or steel core, undercutting overheating, proper diamond exposure, loss of tension or arbor hole/drive pin distortion.
The operator also should regularly check common equipment maintenance points such as:
- blade flanges
- blade shaft bearings
- tension of drive belts
- alignment of the axle and wheel bearings
- water delivery system
These actions will help ensure continued performance in a safe manner. Operators should always follow safe operating procedures at all times.
But what if everything does not go as planned? The operator must be able to evaluate the situation and take action to keep the sawing operation productive. Many variables can affect diamond blade performance and a knowledgeable operator will be able to optimize diamond blade performance.
ConclusionThe proper use of a diamond blade in the construction field requires more than just a good diamond blade and a machine. It requires the skills of a professional cutting operator with the knowledge to effectively utilize the tools in conjunction with the analytical skills learned either on the job or in training.
For optimum performance of a diamond blade in a construction application, this article has shown that, in addition to a trained operator, diamond wear is a good and necessary characteristic. If diamonds do not wear, they are of little value in a construction application. While a gem diamond may last forever when worn on a woman's finger, an industrial diamond for construction applications is only of value when it is, in fact, wearing away.