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Core Cracking

Core Cracking – Safety and Performances
As outlined by the Saw Manufacturers Institute (SMI), Occupational Safety and Hazards Association (OSHA), and American National Standards Institute (ANSI) all cores should be inspected at regular intervals and must be retired immediately if core cracking is observed. Safety is the number one concern of these governing bodies and should be for your operation too. That said, it is also important for you to get the best performance and greatest value from your diamond tools. The following is valuable information regarding the manufacture of diamond cores and cutters best practices that will help you minimize the chance of core cracking , maintain safety and achieve the performance levels required for the job.
MANUFACTURING:

1. Material & Fabrication Process:
The combination of raw material and the fabrication processes are the key elements in the manufacturing of a steel core. The steel used in the manufacture of cores is perfectly suited for the application by having high strength, toughness, abrasion resistance to meet the demands of today’s cutting applications and higher powered saws. The composition of steel also accepts laser welded or brazed segments with minimal changes to the mechanical properties. Laser cutting of the core is the most desirable manufacturing process because punching, milling and grinding can cause micro cracks and stress concentrations which increase the likelihood of core cracking.

2. Heat Treatment:
Heat treatment is the process in which the steel core’s microstructure is rearranged to manipulate the mechanical properties like strength, hardness and fatigue resistance. Post tempering relieves stress and helps to flatten the core after quenching. It is optimal to achieve a surface hardness of Rockwell 38Rc for high abrasion resistance. In addition, a lower core hardness is desirable since it increases fatigue resistance and overall core life. Hardness is also critical for Flatness and tension since, cores with inconsistent hardness (spotty hardness) are difficult to smith and will not hold tension. This will cause premature failure of the diamond tool.

3. Surface Grinding:
Rotary surface grinding removes surface imperfections such as raw material crown, scale & scratches this helps to normalize and level the surface reducing the possibility of core cracking from stress concentrations.

4. Leveling, Smithing & tensioning:
Proper leveling, smithing and tensioning insure longer life, better performance and greater value for you. Cores that are leveled and smithed flat will take and hold tension much longer than cores without. Tensioning, leveling and smithing will give you a core that runs true longer. Cores that run true will not wobble, heat up or fatigue nearly as fast. This can significantly increase the core life and performance.

5. Machining the Outside Diameter:
Machining the outside diameter is critical for the core balance and concentricity. Cores must be concentric to ensure proper segment mounting and balance. This will also minimize the likelihood of hammering while cutting especiaially if the segments are also OD ground.

The following are cutter’s best practices will help you minimize core cracking, increase performance and give you the most value from your diamond tools.
CUTTER’S BEST PRACTICES:
1. Correct tool for the job:
In order to specify the correct diamond tool for the job you need know the hardness of the material to be cut, the tool speed, the equipment power, the cooling method and the mounting type. The correct diamond tool for the application will increase diamond tool performance and reduce core cracking.

2. Operational Speed:
The operator must make sure that they run the diamond tool at the correct RPM to get the best performance from the diamond tool and insure the safety of the operators and others in the work area. Over speeding and over feeding a diamond tool will cause premature tool failure by increasing the amount of heat in the core and exceeding the mechanical properties of the steel. Below is the recommended rpm for 9500 surface feet per minute blade speed.

3. Equipment / Machine Care:
Keeping your equipment in good working condition is critical to the safety of your operators and the performance of your diamond tools. Without proper maintenance and care of your equipment the life and performance of your diamond tools is greatly reduced.

4. Blade Shaft Bearings, Collars & Mounting Hardware:
Vibration is one of the main causes of core cracks and blade fatigue. Maintaining your blade shaft bearings, collars and mounting hardware are essential to reducing vibration and increase diamond blade performance by minimizing hammering.

5. Coolant to the Diamond Blade:
Heat is another one of the main causes of core cracking and loss of tension. Without tension your diamond blade will not run true; contact the sidewall, generate excessive heat, and fail prematurely. Therefore, a wet blade must have ample water to cool it properly; And for a dry cutting tool, it is essential to operate within the blade manufacturer’s recommended tool speed and not to apply too much side load. These practices will help the blades operate within the design temperature and help to insure diamond blade performance and life.

The above information will help you keep your employees safer and the performance of your diamond tools at a profitable level. If you have any questions please call you diamond tool manufacturer for help.