Diamond crystals can be synthetically grown in a wide variety of qualities, shapes and sizes. Synthetic diamond has replaced natural diamond in virtually all construction applications because of this ability to tailor-make the diamond for the specific application. Diamond is grown with smooth crystal faces in a cubo-octahedral shape and the color is typically from light yellow to medium yellow-green. Diamond is also grown to a specific toughness, which generally increases as the crystal size decreases. The size of the diamond crystals, commonly referred to as mesh size, determines the number of diamond cutting points exposed on the surface of a saw blade. In general, larger mesh size diamond is used for cutting softer materials while smaller mesh size diamond is used for cutting harder materials. However, there are many interrelated factors to consider and these general guidelines may not always apply.
Synthetic diamond can be grown in a variety of mesh sizes to fit the desired application. Mesh sizes are generally in the range of 20 to 50 U.S. Mesh (840 to 297 microns) in construction applications. The size of the diamond crystals as well as the concentration determines the amount of diamond that will be exposed above the cutting surface of the segments on the blade. The exposure, or height, of diamond protrusion influences the depth of cut of each crystal, and subsequently, the potential material removal rate. Larger diamond crystals and greater diamond protrusion will result in a potentially faster material removal rate when there is enough horsepower available. As a general rule, when cutting softer materials, larger diamond crystals are used, and when cutting harder materials, smaller crystals are used.
The diamond mesh size in a cutting tool also directly relates to the number of crystals per carat and the free cutting capability of the diamond tool. The smaller the mesh size, the larger the diamond crystals, while larger mesh size means smaller diamond. A 30/40 Mesh blocky diamond has about 660 crystals per carat, while a 40/50 Mesh diamond will have 1,700 crystals per carat.
Specifying the proper mesh size is the job of the diamond tool manufacturer. Producing the right number of cutting points can maximize the life of the tool and minimize the machine power requirements. As an example, a diamond tool manufacturer may choose to use a finer mesh size to increase the number of cutting crystals on a low concentration tool, which improves tool life and power requirements.
Impact strength can be measured, and is commonly referred to as Toughness Index (TI). In addition, crystals are also subjected to very high temperatures during manufacturing and sometimes during the cutting process. Thermal Toughness Index (TTI) is the measure of the ability of a diamond crystal to withstand thermal cycling. Subjecting the diamond crystals to high temperature, allowing them to return to room temperature, and then measuring the change in toughness makes this measurement useful to a diamond tool manufacturer.
The manufacturer must select the right diamond based on previous experience or input from the operator in the field. This decision is based, in part, on the tool's design, bond properties, material to be cut and machine power. These factors must be balanced by the selection of diamond grade and concentration that will provide the operator with optimum performance at a suitable cost.
In general, a greater impact strength is required for more demanding, harder-to-cut materials. However, always using higher impact strength diamond that is more expensive will not always benefit the operator. It may not improve, and may even degrade tool performance.
Contrary to a popular advertising campaign, a diamond is not forever. The exposed diamond cutting points eventually wear away, and if not for some provision to replace these cutting points, the blade or bit would soon be useless. This process is actually desired as it provides a new layer of diamond crystals to continue the cutting action.
The ideal life of a diamond starts as a whole crystal that becomes exposed through the segment bond matrix. As the blade begins to cut, a small wear-flat develops and a bond tail develops behind the diamond. Eventually, small microfractures develop, but the diamond is still cutting well. Then the diamond begins to macrofracture, and eventually crushes. This is the last stage of a diamond before it experiences a pop-out, where the diamond quite literally pops out of the bond. The blade continues to work as its cutting action is taken over by the next layer of diamonds that are interspersed throughout the segment.
The metal bond matrix, which can be made of iron, cobalt, nickel, bronze or other metals in various combinations, is designed to wear away after many revolutions of the blade. Its wear rate is designed so that it will wear at a rate that will provide maximum retention of the diamond crystals and protrusion from the matrix so that they can cut. The diamond and bond work together and it is up to the manufacturer to provide the best combination based upon the specific cutting requirements. Critical factors for both sides to address are the bond system, material to be cut and machine parameters. The combination of diamond and bond accomplishes a number of critical functions:
E Separation and support for the diamond
E Control of the segment wear rate
E Introduction of new diamond cutting points
E Optimum diamond retention
E Distribution of the impact load of the diamond as it grinds
Cutting Edge and Operator Certification students receive a magnifying loop so that they can observe the different phases of the life of the diamond crystals. If the diamonds are becoming polished, the operator needs to change the operating conditions or switch to a more suitable blade for the application.
The segments that are attached to the blade must be wider than the core, otherwise the blade core will wear quickly and render the diamond blade useless. The overlap of the segment over the blade core is called side clearance, and it allows the blade to turn in the cut without dragging on
The manufacturer tensions blades (sometimes called smithing) at the factory so they will run straight at the design cutting speeds. Proper tensioning allows the blade to remain flexible enough to bend slightly under the cutting pressure and snap back into position. The manufacturer will also check for concentricity and straightness or run-out. During the manufacturing break-in, or grinding and dressing process, individual diamond crystals are exposed on the outside edge and sides of the diamond segments or rim. These exposed surface diamonds make the blade ready to cut right out of
The traditional method that has long been used to attach segments to the steel core is brazing. A silver solder, placed between the segment and the core, is heated above the melting point to bond the segment to the core. The type of solder used melts at high temperatures (above 400?F). This melting temperature is below the temperature a blade encounters during dry sawing, and is the reason that braze welded blades should not be operated dry.
The diamond segment and the steel core are fused together by a laser beam. The laser beam melts a portion of the steel core and the segment backing metal, forming a weld. This weld is stronger than either the steel core or the segment, and does not melt at the higher temperatures encountered when cutting dry.
The operating speeds for cutting hard material such as stone have been found to be best around 10,000 sfpm (surface feet per minute) or the surface speed of the diamond cutting segments on the periphery of the blade. This operating limit has been established as an optimum speed for cutting masonry and concrete. The diamond blade operating speeds (Figure 4) have been developed to provide operators with recommended operating speeds and maximum safe speeds in terms of rpm. The table provides a recommended operating speed and a maximum safe speed for a range of blade diameters. Attaching a tachometer to the machine?s blade shaft can check machine speeds. Class participants in CSDA?s Cutting Edge and Operator Certification training classes receive specific information on blade speeds and a blade speed calculator so that they can adjust machine rpm in the field when operating blades of different diameters.
It is important for the operator to use the correct operating conditions to maximize blade performance. For optimum blade life and cutting speed, the actual operating speed will most likely have to be adjusted for the type of material encountered. In general, higher operating speeds make the blade act harder and tend to lengthen blade life, but slow the cutting. Decreasing blade speed will make the blade act softer, but blade life will also decrease.
When in doubt about the correct operating speed for a particular material, it is better to choose a lower speed rather than a higher speed. Once the blade is cutting well, the speed can be increased to optimize life of the diamond blade. When cutting softer materials at a faster peripheral speed, a faster forward traverse rate and more water should be used.
If the design speed is not achieved, the blade will tend to wander as cutting begins. When a blade is said to be out of tension, the amount of dish is not correct. Such a blade would wobble from side to side while out of the cut, and it wanders when placed in the cut. An out-of-tension blade cannot be made to cut a straight line.
an effect upon tool performance. Operating a machine with less power than is required can result in blades that will polish or glaze over, resulting in slow cutting speeds.
In order for a saw blade manufacturer to provide the proper cutting tool, it is necessary to know the maximum horsepower of the machine. Generally, but not always, blades with soft bond segments will break down faster if used with high-horsepower equipment. On the other hand, blades with hard bond segments cut better when used on high-horsepower equipment.
Diamond cutting tools require that pressure be applied for maximum performance. Sufficient pressure must be applied to maintain sharp cutting crystals. If too little pressure is applied, the diamond crystals are likely to become dull and polish. Conversely, too much pressure can also damage the diamond cutting tool.
Blades used to cut hard stone 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 softer stone should have hard metal bonds, so that the diamond particles are not lost before their cutting life is used up. Aggregate hardness can be measured using the Mohs Hardness Scratch Test. This test kit is included in CSDA training courses and students are taught how to use this tool to help select the right diamond blade.
Loss of tension
The loss of tension in a diamond blade can be caused 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 may also 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 and of the proper size and are properly mounted and secured.
Overheating of the blade can cause segment loss. This is often 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 stone 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 can also occur when the blade is subjected to sharp sudden movements while in the cut or upon initial contact with the stone. The operator should make slow and even contact between the blade and the material to be cut.
If the operator observes that the core is cracking (Figure 5), the blade specification being used may be too hard for the stone 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 (pop-outs), 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 fast 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 are still 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.
The operator should also regularly check common equipment maintenance points such as:
E Blade flanges
E Blade shaft bearings
E Tension of the drive belts
E Alignment of the axle and wheel bearings
E Water delivery system
These actions will help ensure continued optimum 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 utilize his or her skills to optimize diamond blade performance.
For optimum performance of a diamond blade, this article has shown that, in addition to a trained operator, diamond "wear" is a good and necessary characteristic. 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 wearing away.