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Why the Segment of Diamond Blades Can Break Off

Hanjiang Wang — Mon, 13 Jun 2011 02:52:15 +0000

A common problem diamond blade users may encounter is that one (or more) segment break off the diamond blade. This problem is often known as segment loss, which not only means the damage of the diamond blade, but may cause serious security issues because of the segment flying out.

A laser welded diamond blade with a segment lost

The reasons of segment loss (break) of diamond blades are diverse. If diamond saw blades has no problem in quality and the segments are connected to the blade’s steel core firmly, the following causes may lead to segment loss:

1. Wet diamond blades are used with inadequate water or even dry

During the cutting process, if there is no adequate water flowing on both sides of the diamond blade and in the cut, excessive heat may be generated and there may be some abrasive slurry remaining in the cut.

If the wet diamond blade is laser welded, the abrasive slurry can wear away the blade’s steel core just beneath the segment. This problem is often called undercutting. Serious undercutting can cause the segment to break from the steel core.

If the wet diamond blade is silver brazed, the excessive heat can cause the silver solder which connects the segments to the steel core to be melted, and then the segments may break off.

So adequate water is critical to the wet cutting job, for it can avoid overheating of the diamond blade and can wash out the abrasive slurry. Overheating can also make the diamonds on the segments become blunt. If a wet diamond blade is used without any water (dry), it may take just a few seconds for the blade to be damaged.

2. Dry diamond blades are not used properly

Laser welded diamond blades can be designed to cut some materials without water. However, if dry laser welded diamond blades are used dry arbitrarily, the segment may still break off the diamond blade.

As dry cutting utilizes the air as its coolant, dry diamond blades should be used in the intermittent and shallow sawing mode to allow the air to flow around the blades to dissipate the heat. You can read our how to use diamond blades in dry cutting article for more information. If a dry diamond blade is used in continuous or deep cutting, the blade may be overheated and may lose its segments.

Not all materials can be cut dry. Some very hard materials, e.g., concrete with strong reinforcement, should still be cut with water. Wet cutting can improve cutting efficiency, control dust, and extend the diamond blade’s life.

3. Problems related with the saw machine

If the saw machine’s blade shaft or shaft bearings are worn, the diamond blade may jump up and down in the cutting process. This can lead to segment loss. Replacing the shaft or shaft bearings can resolve the problem.

Some other reasons can also make the diamond blade flutter and then cause segment loss. These reasons include: the diamond blade is mounted on the shaft incorrectly; the nuts or bolts which hold the flange and blade shaft together are not wrenched tight; there is dirt, sand or other materials between the blade steel core and the flange.

4. The material being cut slips and jams the diamond blade

This situation is typically seen in masonry or tile sawing applications and may cause segment loss. To avoid this, the operator should make sure that the material is seated securely on the saw machine, and that he holds the material firmly through his entire cutting process.

Basic Properties of Diamond

Hanjiang Wang — Tue, 12 Apr 2011 05:59:20 +0000

Diamond can be either natural or synthetic, and has the following basic properties:

		Description
Mechanical Properties	Hardness	Diamond is almost the hardest material on the earth. On the Mohs scale of mineral hardness, its hardness is 10 — the hardest. Its microhardness is about 100000 MPa. Its Rockwell hardness is about 1.56 times of CBN’s, 3.7 times of tungsten carbide’s, 4.4 times of corundum’s and 8.5 times of quartz’. Diamond’s hardness is different on its different orientations (crystal planes). Because of its very high hardness, diamond can be used to make various diamond tools such as diamond saw blades, diamond core drill bits, diamond cup wheels and diamond polishing pads, to cut, grind or polish hard or abrasive materials, e.g., stone, concrete, asphalt, ceramics, bricks and carbide alloy.
	Brittleness	Though diamond is very hard, it is relatively brittle. It splits along its crystal cleavage planes when receiving a certain impact. The brittleness of diamond is also related to its crystal completeness. Crystal defects can generate internal stress and even lead to natural split. While complete crystal has a fairly high toughness and its split pressure can reach 30 – 100 MPa. So “impact toughness” is one of the main indexes to measure the quality of industrial diamonds.
	Density	The density of diamond is normally 3.47 – 3.56 g/cm³. Pure and complete-crystal diamond’s density is 3.52 g/cm³.
	Cleavage	The cleavage of diamond happens most likely along the <111> plane (a triangle that consists of the three diagonals of the three adjacent planes of a cubic diamond lattice).
	Fracture	The fracture surface of diamond can have a complex structure, and is often conchoidal or irregular-shaped.
Optical Properties	Color	Pure diamond has no color, but it is fairly rare. The color of diamond is often yellow, green, brown, rose, blue, grey and black. This is related with the impurities it contains and its crystal defects.
	Luster	Diamond often has the so-called “diamond gloss”, which means quite strong reflected light, shining but not metallic. A few diamonds have oil sheen, glass gloss or even no luster, which is usually caused by long-term chemical corrosion, radiation effects, invasive alien substances or other materials coated on their surface.
	Transparency	Pure diamond is transparent, and impure diamond can be translucent or even opaque.
	Refractive index	Pure diamond’s refractive index is 2.40 – 2.48, which is the highest in transparent minerals. The higher refractive index, the higher reflectivity. Diamonds that are specially designed and processed can reflect almost all the light that comes to their sides and interior.
	Dispersion	Diamond’s dispersion coefficient is 0.063, which is also the biggest in transparent minerals. The bigger dispersion coefficient, the better spectroscopy result. When a white light comes into a well-cut diamond, the light can be split into different colors of light because of the diamond’s dispersion effect, and the diamond looks dazzling.
	Luminescence	Diamond can shine distinct green, sky-blue or blue fluorescence under cathode ray, medium-brightness or weak sky-blue fluorescence under X-ray, distinct or medium-brightness sky-blue, purple or yellow-green fluorescence under ultraviolet, and light green-blue phosphorescence in darkroom after exposure under sunlight.
Thermal Properties	Thermal conductivity	Diamond is a good heat conductor. Different types of diamonds have different thermal conductivity. Some diamonds have super thermal conductivity.
	Thermal expansion	Diamond’s thermal expansion coefficient is very small at low temperature, but increases rapidly with the rising of temperature.
	Heat resistance	Diamond’s ignition point is 720 – 800 °C in oxygen and 850 – 1000 °C in air. The flame is blue when diamond is burning.
Electromagnetic Properties	Magnetism	Pure diamond is not magnetic. But as containing impurities of catalyst alloy, e.g., Ni, Co, Fe, Mn, Cr, synthetic diamond is magnetic. The more catalyst impurities, the more magnetic the synthetic diamond is. Low magnetism indicates the diamond’s good crystal and its good quality.
	Electrical conductivity	Normally, diamond is a poor electrical conductor. Its electrical conductivity increases when temperature rises. Some diamonds are good semiconductor.
	Photoconductivity	When diamond is irradiated by ultraviolet of 2.1 x 10^-4 – 3.0 x 10^-4 mm wavelength, there are photocurrents generated in the diamond.
	Triboelectricity	When diamond rubs on the surface of glass, hard rubber or plexiglass, positive charge can be produced on the diamond.
Surface Properties	Lipophilicity & Hydrophobicity	Diamond cannot be wet by water, but can be easily wet and stuck by oil. This property can be utilized to extract diamonds using oil when making synthetic diamonds.
Chemical Properties	Chemical stability	Diamond has very good chemical stability. It does not react with acid and alkali under room temperature. Its surface can only be oxidized a little by just a few oxidants under high temperature (below 1000 °C). So acid and alkali can be used to refine synthetic diamonds.

Types of Saw Blades

Hanjiang Wang — Tue, 19 Oct 2010 08:39:46 +0000

Perhaps the often sighted saw blade is a long steel plate with many saw teeth on one side to saw wood. Actually, besides this traditional woodworking saw blades, there are wide categories of saw blades for various uses. Just say the saw blades’ shape, the base of a saw blade can be a long steel plate, a circular blade, a closed steel band, a thin wire, or of other shapes. The blade’s teeth are often designed to have many styles to fit the needs of cutting different types of objects. Saw blades can also have no teeth but have just a continuous cutting edge.

From the perspective of the material used to make the saw blade, there are common steel saw blades, High Speed Steel (HSS) saw blades, carbide tipped saw blades, solid carbide saw blades, diamond saw blades, etc. Here we say some of them in more detail.

1. High Speed Steel (HSS) Saw Blades

The whole saw blade is made of High Speed Steel (HSS). HSS saw blades are mainly used to cut steel, copper, aluminum and other metal materials. They can also cut non-metallic materials. The grade of HSS greatly influences the performance of the saw blade. HSS saw blades of higher grade HSS have a higher hardness in high temperatures, and often have a longer lifespan. If stainless steel or other high-strength steels is to be cut, HSS saw blades made of cobalt HSS (e.g. M35, M42) should be used, for cobalt can increase the HSS material’s capability to keep its high hardness under the high temperature generated in cutting these high-strength steels.

2. Carbide Tipped Saw Blades

Each of this saw blade’s steel teeth is tipped (via welding) with a small piece of sharp tungsten carbide block. This type of blade is also called TCT (Tungsten Carbide Tipped) saw blade. Carbide tipped saw blades are widely used to cut wood, plywood, laminated board, plastic, grass, aluminum and some other metals. The performance of the blade is greatly influenced by the quality of the small carbide blocks tipped and the number of its teeth, and is also influenced by the quality of the blade’s steel body.

3. Solid Carbide Saw Blades

The whole saw blade is made of tungsten carbide. Comparing with HSS saw blades, solid carbide saw blades have higher hardness under high temperatures, and are more durable, so they have replaced HSS saw blades in many fields. However, the toughness of tungsten carbide is lower than HSS’, so solid carbide blades’ cutting edge can be chipped when the cutting parameters are not proper or the machine is not very precise.

4. Diamond Saw Blades

This type of saw blade has small-sized industrial diamonds (synthetic or natural) fixed on its base to utilize the diamonds to cut (actually grind) hard and brittle, or abrasive materials. As diamond is almost the hardest material on the earth, diamond saw blades can easily cut stone, concrete, asphalt, bricks, glass, ceramics, semiconductor materials, gem stone, etc. The methods by which diamonds are fixed onto the base of the blade include metal bonding, electroplating, vacuum brazing, etc. There are many types of diamond saw blades that are used in various fields.

Wholly Sintered, Silver Brazed and Laser Welded Diamond Saw Blades

Hanjiang Wang — Sat, 12 Jun 2010 10:12:03 +0000

Perhaps the most commonly sighted diamond circular saw blades are the sintered metal-bonded ones, on which diamonds are mixed and sintered with metal bond materials to form the blades’ cutting edges — diamond segments. Normally, these blades are made via 3 methods: wholly sintering, silver brazing and laser welding. The diamond blades made via these 3 methods are different and have their respective features and applications.

1. Wholly Sintered Diamond Saw Blades

Wholly sintered diamond blades are made by putting the steel cores along with diamonds and metal bond materials into molds, and then sintering them in sintering machines. Blades of this type are often referred to just as sintered diamond blades. Normally, their diameter is no bigger than 400 mm. One of the reasons maybe is for the limitation of the size of the sintering machines.

Generally, the main steps in making sintered diamond blades are: First, put the steel cores, diamonds and metal bond materials into high-strength steel molds. Second, put the molds into a press machine to press them to form the blanks without heating. Third, take out the blanks from the steel molds and examine the blanks. Fourth, put the blanks into graphite or stainless-steel molds. Fifth, put the molds into a sintering machine and sinter them to produce the diamond blades.

In the above fifth step, there are many types of sintering machines which can be chosen. Some sintering machines can exert pressure on the blanks during the sintering process. This can make the diamond segments of the blade be well alloyed, and the segments’ density is high. The produced blades are normally called hot-pressed diamond blades. These blades have a longer service life. However, some sintering machines cannot exert pressure on the blanks when sintering. The produced blades are normally called cold-pressed diamond blades. These blades’ diamond segments’ density is low and porosity is high. This can improve the cooling condition when the blades are being used, but will also lead to a shorter service life.

Sintered diamond blades can be used to cut granite, marble, concrete, asphalt, ceramics and many other building materials. Some of them can only be used in wet cutting (e.g. continuous rim diamond blades), while some of them can be used in both wet and dry cutting (e.g. segmented diamond blades, turbo diamond blades and turbo wave diamond blades).

In making sintered diamond blades, the steel cores are also put into molds and sintered. So the diamond blades can be produced in bulk, and the production output is high. But also for this reason, the steel cores cannot be quenched, so their hardness and toughness are not high, and so the steel cores may deform in high-load and high-intensity cutting processes. Therefore, in some cases sinter diamond blades’ cutting efficiency cannot be very high.

2. Silver Brazed and Laser Welded Diamond Saw Blades

When silver brazed or laser welded diamond blades are made, the diamond segments on the blades need to be firstly produced. Normally, the method for making these diamond segments is hot pressing, and is similar to the method used to make the sintered diamond blades, while there is no the steel core’s participating. When the diamond segments are available, they are silver brazed or laser welded onto the steel cores to form silver brazed diamond blades or laser welded diamond blades.

Silver brazed diamond blades’ diamond segments do not necessarily need a transition layer. They are brazed to the steel cores via silver-based brazing films which normally contain 40% – 50% silver. The connection between the diamond segment and the steel core depends on the melted and penetrated silver solder, so the connection strength is not very high (normally, its bending strength is 350 – 600 MPa). Silver brazed diamond blades can only be used in wet cutting, because if they are used in dry cutting, the high temperature generated in the dry cutting can cause the silver solder to be melted, and the diamond segments may fall off the blade and fly out and may hurt the operator.

Laser welded diamond blades, however, have many advantages. Laser welding is a kind of fusion welding. It causes the junction of the diamond segment and the steel core to be melted and then form a metallurgical connection. The depth-width ratio of the weld is high, which can reach 5:1 or even 10:1. So the connection strength is high and the bending strength can reach 1800 MPa. Therefore laser welded diamond blades can be used to cut some relatively softer materials (e.g., many kinds of stone) without the water cooling (dry cutting). But please note, when cutting very hard or abrasive materials, for example, concrete containing reinforcing rebar, the laser welded diamond blade should still be used with adequate water. Otherwise, the diamond segment itself may break or the steel core below the segment may wear off and break, and then cause serious security issues. Laser welded diamond concrete saw blades are usually made for wet cutting applications.

The diamond segments used on laser welded diamond blades have a transition layer. This layer has no diamonds and is normally 1.5 – 2 mm thick. Its function is to connect the working layer (containing diamonds) of the segment to the steel core.

Like sintered diamond blades, silver brazed and laser welded diamond blades can also be used to cut many building materials, such as granite, marble, concrete, asphalt and ceramics. Because these blades’ diamond segments are welded onto the steel cores, these blades have to be produced piece by piece, so their production output is lower than sintered diamond blades’. However, because the steel cores do not participate in the sintering, the steel cores can be quenched and processed with other heat treatments, so their hardness and toughness can be high, therefore the diamond blades can be used in high-load and high-intensity cutting processes without deformation and high cutting efficiency can be gained.

Also because silver brazed and laser welded diamond blades’ steel cores can be treated separately, the blades’ diameter can be large, which can reach several meters. Also, the steel cores can have many designs to meet various requirements. For example, the steel core can be designed as a sandwich type which has two layers of steel cores outside and one layer of damping material in the middle. This design can reduce the noise generated in the cutting significantly, and this blade is a kind of silent diamond blade.

Features of Bronze Bond Applied in Diamond Tools

Hanjiang Wang — Tue, 09 Feb 2010 03:56:21 +0000

There are many kinds of metal bonds applied in diamond tools, for example, the cemented carbide bond whose skeleton is tungsten carbide, and Fe-based bond whose composition is mainly Fe and Ni. But the most widely used metal bond is bronze.

The bond strength of the bronze bond is high, and this can help to make better use of diamonds. Its wear resistance is good, it can withstand a larger load, and its thermal conductivity is also good. Bronze-bonded diamond tools are mainly used to process non-metallic brittle materials, such as ceramics, glass, stone, concrete as well as gemstone and semi-conductor materials. They are suitable for coarse grinding, half-fine grinding and profile grinding, and are suitable for cutting and edge grinding.

Bronze bonds also have some shortcomings. Its self-sharpening capability is not good. Bronze-bonded diamond tools’ grinding efficiency is lower than the resin-bonded ones’. If they are not properly used, block and heat may be caused, and their dressing is difficult.

Bronze Bonds Used in Diamond Tools' Manufacture

Hanjiang Wang — Tue, 02 Feb 2010 04:11:05 +0000

The bond material used in metal-bonded diamond tools can be Cu-based alloy, Co-Ni alloy, Fe-based alloy and carbide-based alloy. Bronze bond material is a kind of Cu-based alloy, and is widely used in metal-bonded diamond tools’ manufacture.

The bronze bond has high strength and hardness. Its shrinkage is small and it is easy to generate dispersed shrinking holes. In addition, the thermal conductivity of Cu is only lower than the expensive Ag and is higher than other metals. This helps to decrease the temperature generated in the diamond tools’ working process and avoid burns on the workpiece.

The often adopted metal materials in the bronze bond are the powders of Cu, Sn, Zn and Ag. Sometimes some non-metal materials, such as graphite, are also added. As the objects to be processed and their processing requirements vary, the composition of the bronze bond may also be different. According to the number of metal elements in it, bronze bonds can be categorized into binary-alloy series, ternary-alloy series and multi-alloy series.

1) Binary-Alloy Series: In this series, the Cu-Sn alloy is the most common used. Some graphite is also added into the bonds of this kind.

2) Ternary-Alloy Series: This series is composed by adding a third metal element into the binary-alloy series bonds. The third metal element can be Ag, Ni, Zn, Fe, Pb, etc.

3) Multi-Alloy Series: This series bonds base on the Cu element, and have 3 or more other metal elements, such as Sn, Zn, Pb, Ag, Ni, Co, Fe, Cd, Mo, etc.

The Advantages and Disadvantages of Hot Press in Diamond Tools' Making

Hanjiang Wang — Tue, 26 Jan 2010 07:55:54 +0000

In diamond tools’ manufacture, the hot press method has below advantages:

1) The pressure in hot press method is low, so the requirement to the press machine is also low, and graphite or cast-iron molds can be used instead of the ones made of high-strength alloy steel.

2) The bonding strength is high, so this method can be applied to produce complex-shape products and the reject rate can be lowered.

3) The products can be sintered with molds, so their expansion and contraction can be controlled and their sizes can be kept well. After stripping, there will be no elastic aftereffect on the pressed blanks.

4) The heating time is short and the production period is also short. This is convenient for small batch production.

5) The low pressure of this method reduces the possibility of diamonds’ crush.

6) The blank materials are sealed in molds, and will not contact with air. The heating time is short. Protective gas may not be used. These simplify the sintering process.

7) The sintering process can be better controlled.

The hot press method also has some disadvantages:

1) There are many production links in this method, and its production efficiency is not high.

2) This method needs many graphite molds, and needs many times of mold loading and stripping.

3) The graphite molds are apt to be damaged, for example, be burned to be defective or be cracked by expansion.

The Advantages and Disadvantages of Cold Press in Diamond Tools' Making

Hanjiang Wang — Tue, 19 Jan 2010 09:31:20 +0000

Cold-pressed diamond tools are much cheaper than hot-pressed diamond tools. They are still widely used in many applications. The cold press production method has some advantages:

1) The forming of the tools does not need heating equipment, and the operation is easy.

2) The mold need not to be heat-resistant, and has a longer service life.

3) The forming production efficiency is high. The tools can be sintered in bulk.

4) The density of the formed blanks is lower than the one got via the hot press method, and their porosity is higher. This can help the cooling when these tools are used in grinding or cutting.

5) The formed waste products can be recycled timely.

The cold press method also has some disadvantages:

1) After sintering, the size of the pressed blanks changes considerably, especially for those complex-shape tools.

2) The bonding strength between the pressed blank and the tool’s body is low, and issues may arise from these bonding positions.

3) The pressure in the cold press is high. This may lead to the crush of the diamonds, and then influence the performance of the tools. There is a raw blanks’ movement procedure in the cold press method, and the raw blanks may be bumped and broken.

4) The requirement to the forming performance of the raw materials is high. The molds need to be made of high-strength alloy steel.

5) The requirement to the workers’ blank-pressing skills is rather high.

3 Making Modes of Metal-Bonded Diamond Grinding Wheels

Hanjiang Wang — Mon, 11 Jan 2010 04:28:36 +0000

Metal bonds are widely used in diamond grinding wheels‘ manufacture. Among these metal bonds, Cu-Sn alloy is the mainly adopted bond. There are 3 modes in the metal-bonded diamond grinding wheels’ making.

1) Cold-Press Mode: This mode is to first press the working layer (containing diamonds) and the transition layer (not containing diamonds) of the diamond segments to their forms directly on the grinding wheel’s body, and let the segments connect with the wheel’s body via teeth, slots or other manners. Then, put the grinding wheels into sintering furnaces to sinter without press.

2) Semi-Hot-Press Mode: This mode is an improved version of the cold-press mode. When the diamond grinding wheels are being sintered in the furnace, appropriate molds will be applied and some pressure will be added, but the pressure is much lower than the one in the hot-press mode.

3) Hot-Press Mode: This mode is to directly sinter the diamond segments in molds under a certain pressure in the dedicated sintering press machine, and then fix or connect the diamond segments onto the grinding wheel’s body via high-frequency welding, laser welding or mechanical mosaic method.

Advantages of Diamond Grinding

Hanjiang Wang — Tue, 29 Dec 2009 10:24:34 +0000

As diamonds have many excellent mechanical properties, for example, high hardness, big strength, good wear resistance and low friction coefficient, they have obvious advantages when being used in grinding contrasting with the common abrasives.

1) Diamond grinding is efficient, and the grinding force of it is small. The grinding temperature generated during it is lower. This can avoid burns and cracks on the surface of the workpiece.

2) Diamond grinding’s quality is good, and its precision is high.

3) The diamond grinding tools’ consumption is low, and the tools have a longer service life. This can reduce the processing costs.

4) The processing conditions of equipment, tools and workpieces can be improved, and the energy consumption can be reduced. Also, the working conditions of the operators can be improved.

5) Diamond tools not only can process materials which common tools can not process, but also create conditions for developing new materials and new equipment.