Understanding Diamond Blades
Diamond blades are often used for cutting green concrete, concrete, reinforced concrete, brick, block, pavers, concrete slate, natural stone, asphalt, roof tiles, ductile iron pipe, steel rebars, ridge concrete pipe, etc. A diamond blade ia s circular steel core with a diamond bearing edge. The edge can have one of the three configurations: continuous rim, segmented or serrated. Diamond segments or rims are made up of a mixture of diamonds and metal powders. Diamonds used in blades are almost exclusively manufactured diamonds in various grit sizes and quality grades. In the manufacturing process, the metal powder and diamond mixture would be hot pressed at high temperatures to form a solid metal alloy in which the diamond grit is retained. The segment or rim is slightly wider than the blade core. This side clearance allows the cutting edge to penetrate through the material without steel drag. The diamond segments then silver or laser welded to the steel core. Alternate methods of manufacturing diamond blades include eletroplating diamond crystals directly to a steel core. The steel core can be vary in design. Some of them have slots (also called gullets) between each segment to provide cooling and slurry removal, while others have a single continuous rim for smoother chip-free cutting. The type of core that has to be used depends of the type of materials that will be cut.
A diamond blade does not actually cut, instead, it grinds. The diamond crystals in each segment will expose when grinding through the materials. The new layer of the diamond crystals will continue expose during grinding until the segment wear out. The bond is term used for the softness or hardness of the metal powder being used to form the segments and hold the diamond crystals ib place. The bond controls the rate at which the diamond segments wear down and allow new layer od the diamond crystals to become exposed at the surface to continue grinding with a sharp edge. The most important step is matching a blade with the right bond to your specific cutting materials. In addition, the diamond grit size, hardness and concentration of the diamonds in each segment should also match the nature of the material to be cut. For example, the diamond segments contain small grit size of diamond crystals is used for cut harder materials. Because smaller diamonds are more easily able to cut into hard materials.
Diamond blades, cup wheels or core bits work best when cutting wet. The water will prevent the blade from overheating, greatly reduce the amount of harmful dust created by cutting, and will help remove the slurry faster during cutting. Diamond cannot withstand the forces involved at the elevated temperatures of dry cutting on ceramic, glass tiles and abrasive materials, and will be subject to rapid diamond segments wear and possible failure. Blade is greatly extended by wet cutting. However, many blades are designed to operate either wet or dry. When water cannot be used, measures should be taken so the operator does not inhale dust created by cutting, which poses a very serious health risk. When doing dry cutting, the blade should be allowed to cool off periodically. Cooling can be increasing by allowing the blade to spin freely out of the cut. This allows cool air to pass between the segments.
Diamond Blade Production Procedure:
1. Matrix Powder Preparation - During this process, the manufacturer first mixing of well-selected metal powders so as to achieve the predetermined chemical composition, particle shape and size distribution. Binding agents and lubricants are often added to the powder at this stage so as to reduce dust and prevent segregation when the powder is subsequently handle or processed, but also to minimize wear of steel dies and to reduce oxides during subsequent cold and hot pressing operations respectively. Second, when the powder is to be cold pressed by means of the volumetric equipment a further granulation step is necessary to obtain good flow and required packing characteristics of the powder. Irrespective of the processing stage, organic binders are used to cement the powder particles together and to impart adequate mechanical strength to the granules. The binder must have suitable thermal properties, which permit its complete removal from the segments during the hot pressing cycle. Otherwise, the segments have higher residual porosity, which may degrade their quality and create problems with brazing or laser welding to the steel core.
2. Matrix Diamond Mixture Preparation - The diamonds may either be used in as-received condition or coated with a suitable powder prior to mixing with the matrix powder. Undoubtedly, the mixing process has a great effect on the quality of the final product. Non-uniform distribution of both matrix powder particles and diamond crystals will cause premature wear of the segment. Therefore, when each diamond crystal is separately coated with the matrix powder, the formation of diamond clusters in the segment is practically eliminated and consequently better diamond distribution is guaranteed. Another advantage of using diamond-containing granules is longer life of the cold press steel dies due to efficient separation of hard abrasive particles from the compacting tool elements.
3. Hot Pressing or Cold Pressing - The hot pressing process consists of the simultaneous application of heat and pressure so as to obtain a product nearly free from internal porosity. Compared to the conventional cold press/sinter PM stage, hot pressing requires holding the powder for shorter time (usually 2-3 minutes) at substantially lower temperature, but under a compressive stress, to reach higher density level. Due to the limited resistane of commercially available syntheic diamonds to elevated temperature, as well as to the growing demand for excellent mechanical properties of the matrix, the intrinsically rapid, hot pressing technique has gained widespread use in the production of diamond impregnated tool components. On the other hand, cold pressing is an optional operation in the producting of conventional segments with uniform structure. Although additional equipment is required, cold pre-pressed segments reduce graphite mould wear during the subsequent hot pressing operation, and increase the densification process productivity since the purpose designed graphite mould takes more segments per hot pressing cycle than conventional one filled with loose powder. The cold pressing operation becomes mandatory, however, when multi-layer segments are produced. Typical cold pressing operations are performed in steel dies at low to medium pressures.
4. Deburring - Following hot pressing the segments require cleaning and removing edge residuals. This is carried out during deburring operation, which is usually performed by means of tumbling the segments with coarse alumina or silicon carbide grit.
5. Brazing or Laser Welding - When all the segment manufacturing stages have been successfully completed, there is a need to attach the segments to a steel support to produce a diamond saw blade. In general, either brazing or laser welding may be used at this stage. Brazing is well established, particularly for the manufacture of blades for wet cutting of natural stone, which can be re-tipped; whereas laser welding is mainly used in the mass production of small diameter, dry cutting circular blades. In the latter case, the heat generated during sawing softens conventional braze joints and hence there is a risk that a whole segment breaks off the steel center during a high speed, dry cutting operation on hard materials. Since the bending strength of laser welded seam achieves 1800 MPa, compared with 350 to 600 MPa for brazed joint, laser welding practically eliminates the possibility of segment detachment.
6. Truing and Dressing - The objective of the Truing operation is to render the segments concentric with the bore of the circular sawblade and to clean their sides and reduce lateral run-out. The subsequent dressing operation is performed so as to remove the martix from around the diamond particles, to produce sufficient protrusion and allow efficient sawing from the outset.
7. Tensioning - The segments themselves, even when perfectly tailored to the application requirements, do not guaranteed the proper action of the diamond saw balde. The steel centre accumulates stresses during fabrication. Since they are never perfectly symetrical, the saw blade is incapable of spinning without wobble. Therefore the steel centre must initially be subjected to an operation of neutralising the unequal stresses to cause it to lie flat. Skiful leveling, as it is generally termed, is then followed by the actual tensioning which consists in the addition of extra stress to stretch the centre section, which counteracts the centrifugal force tending to elongate the rim section of the rotating blade.
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Cutting Depth & Operating Speed Guidelines
- Diamond blade operating speeds base on 9500 SFPM (Surface Feet Per Minute).
- Diamond blade cutting depths listed above are approximate. Actual cutting depth will vary with the exact blade diameter, flange and saw types.
- The optimum blade RPM will depend on the machine and material and may vary from these values. The optimum RPM range for Concrete and Masonry products is +/- 10% of the recommended RPM listed in this chart. The optimum RPM range for hard, dense materials such as Stone and Tile is 10~25% less than the recommended RPM listed in this chart.
- New blades need to be broken in. New blades have a thin film that covers the segments. As it the film wears off the diamond compound begins to show through.
Diamond Core Bit Drilling Tips
Always secure the drill rig either with a mechancial anchor, vacuum system or by use of the jack screw. NEVER stand on the base and drill without anchoring.
Level the drill rig by use of the base leveling screws and a small level attached to the column permanently or by a magnetic strip on the level. This procedure will ensure a perpendicular hole.
Never let the bit spin in the hole without applied pressure. This will cuase the diamonds to round off and the bit segments will heat and glaze over.
Turn on water before starting the drill motor. Otherwise, the water jacket seals heat up and become brittle, losing water.
When your bit encounters steel (rebar), relax pressure about 1/3 and allow the bit to cut at its own rate. DO NOT PUSH THE CORE BIT.
When finished drilling, turn the water down very low and back the core bit out of the hole with the motor running.
When drilling high PSI concrete or concrete with very hard aggregate (such as river rock, flint rock, etc), the bit will sometimes glaze over. To open or redress the bit, do one of the following:
1). Decrease water by 50% for a few minutes and as the bit starts to increase speed, gradually increase the water until the flow is back to the original state.
2). Pour masonry sand into the slurry then follow the above directions.
3). Add a sandblast media such as "Black Beauty" to the slurry and following the above instructions.
4). Drill the bit into a cement block, soft vitrified grinding wheel or cinder block. Repeat the procedure until the bit is open again.