Sawing of marble, granite and other species of rocks for the building industry and other purposes is carried out to large extent in stone gangsaws with diamond segmented blades. Up to 100 saw blades can be fitted in a single set-up.

The demands made on stone sawing call for straight cuts, high cutting speed and maximum utilization of the expensive diamond-segmented saw blades.

STELCO Gangsaw steel meets the demands made by saw blade manufacturers and consumers on the  quality of the blade material.

Some characteristic properties of STELCO gangsaw steel are:-

• High fatigue resistance. this is an important property, since stone saw blades  are frequently exposed  to high and varying loads as well as to vibrations i.e. high fatigue stresses.
• High transition temperature, resulting in less risk of undesirable martensite formation during the brazing of the diamond segments.
• A chemical composition which minimizes the risk of cracks in connection with brazing.
• Good flatness and straightness.
• Square, smooth edges which is a pre-requisite for strong & durable joint between the parent blade & segments.

STELCO maintains a high and uniform quality, delivery after delivery and are supplied in two finishes i.e. Bright & Super blue.

SPECIFICATION

INDIAN STEEL GRADE	CHEMICAL COMPOSITION %
	C	Si	Mn	S	P	Cr%
C-75 / SAE-1075 / C-75S / CK-75	0.70-0.80	0.15-0.35	0.50-0.80	0.035 max.	0.035 max.	—
75Cr1	0.70-0.80	0.25-0.50	0.60-0.80	0.030 Max.	0.030 Max.	0.30-0.40
C75Cr25	0.70-0.78	0.35 Max.	0.60-0.80	0.030 Max.	0.035 Max.	0.15-0.27

Mechanical Properties	:	Hardened and Tempered
Tensile Strength	:	1380 ± 60N/mm²
Surface	:	F.grey,White or Super Blue Smooth surface
Edges	:	Right angled edges
Width tolerance	:	± 0.50 mm
Thickness tolerance	:	± 0.035 mm.
Flatness	:	Max. Deviation 0.10% of strip width
Delivery From	:	Coils/Cut Lengths
Thickness range	:	2.00 – 3.5mm ( Other sizes on request)

STANDARD SIZES

SIZE (MM.)	MASS kg/m	WIDTH TOL±mm	THICKNESS TOL.±mm
180 x 2.00	2.82	0.50	0.030
180 x 2.50	3.53	0.50	0.030
180 x 3.00	4.24	0.50	0.035
180 x 3.50	4.95	0.50	0.035

Other sizes can be supplied on request.

PROCESS FOR MAKING DIAMOND SAW BLADES

TENSIONING THE MIDDLE OF THE BLADE

To give a straight even cut, the saw blade must be capable of withstanding the lateral forces that occur during the sawing process and for this reason the blade is subjected to a pre stressing force in the region of 80-100 kN. The tensioning of the middle zone of the blade gives a better stress distribution for sawing purposes.

Tensioning is done by rolling the full length of the center part of the blade. This is done  before brazing the diamond segments. The hollow caused by tensioning is measured with the aid of a straight edge placed at right angles across the full width of the blade. The space between  blade and straight edge should be 0.2-1.0mm in the middle of the blade. it  must be same on both sides and through out the full length of the blade. Any deviations from the flatness must be rectified by rolling.

BENDING THE BLADE BEFORE BRAZING

When the diamond segments are brazed on the blade, stresses are set up in the brazed edge, with the result that the edge contracts and the blade bends. If the blade is used in this  state the stresses may be sufficient to cause failure.

To  offset  this bending, we recommend rolling the blade before brazing along the edge to which the diamond segments are to be applied. The amount of rolling required for the blade to come straight after  brazing will have to be worked out by process of trial error.

BRAZING THE DIAMOND SEGMENT

Diamond segments are usually brazed using silver brazing alloy and induction heating. If brazing is done at excessively high temperature, untempered martensite will form in steel.  The martensite is hard and brittle and is liable to cause cracking and blade fracture next to diamond segments. A high temperature also negatively effects the rest of the blade by means of decreased fatigue and elastic strength. Therefore it is important to apply the heat as locally as possible and to avoid high temperatures for long period of time. The melting point of the brazing alloy should preferably be below 700°C.

HOLES FOR END PLATES

The holes for end plates can be drilled or blanked. Blanking holes in hardened and tempered stone-cutting steel 2.0-3.5 mm thick make heavy demands on the equipment. The press and the tool must be stable and accurate in view of the great blanking forces involved. Drilling is therefore primarily  recommended . Whatever the method employed, it is important to remove any burrs, because otherwise they will be serious stress raisers.

DRILLING

For drilling we recommended high speed drills with a helix angle of 40°. These drills have a longer services life than drills with a standard angle of 28°. By choosing the right cutting speed one can do a great deal to optimize the service life of the drill. If the cutting speed is too low, the chisel edge will break down, which has the effect of increasing the feed force and pressing the drill into the chuck. If, on the other hand, the cutting speed is too high, the cutting lips of the drill will soon worn down and drill will then slide in the chuck. About 10m/min is a suitable cutting speed

BLANKING

For blanking we recommended hardened and tempered high speed steel of the AISI M2 type. A hardening temperature of 1125°C and tempering twice for 30 minutes at 560°C gives a hardness of 60-62 Rockwell C and the best possible toughness. The punches should have a cylindrical head and their shank diameter should be larger than the diameter of the hole. The clearance between punch & die should be about 5 percent of the strip thickness. A larger clearance -10 percent for example reduces tool wear but increases the risk of slugs coming up with punch.