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15
The feeding speed depends on the cross-section
of the material. Solid or thick-walled materials
(thickness>5mm) can therefore be cut at high
speed providing there is sufficient swarf removal by
the blade, while thin-walled materials such as
tubes or thin profiles must be cut with a low feeding
speed.
A new blade requires a break-
in period, during which time about half the
normal feeding speed should be used.
14.4 Coolant
The cooling fluid ensures that the blade teeth and
material in the area of the cut do not overheat. The
fluid must be an excellent lubricant so as to prevent
abrasion of the teeth and welding of the chips to
the teeth (seizing).
14.5 Blade structure
For non-ferrous metals, it is common to use
circular saws with a brazed hard metal HM cutting
edge, consisting of a disc made of alloy tool steel
(71Cr1) on which the shape of the teeth and the
seats for the cutting edges are made of Widia K10.
These saws have shown excellent wear resistance
but low resistance to impact, which is in any case a
minor problem with non-ferrous materials.
Table 4
14.6 Types of blades
In addition to the size and pitch of the teeth, the
blades also have different geometric characteristics
in accordance with their particular use:
tooth cutting angle – may be negative or positive
tooth sharpening – may be BW with an alternate
raked tooth or C with a roughing tooth raked on
both sides and a non-raked finishing tooth
tooth pitch – the distance between the crest of
one tooth and the crest of the next tooth (tooth
pitch = T)
14.7 Teeth shape
“
C” TYPE SHARPENING (HZ)
Coarse toothing with roughing tooth raked on both
sides and non-raked finishing tooth. The roughing
tooth is about 0.3 mm higher.
Coarse toothing with roughing tooth and finishing
tooth. Used in saws with pitch greater than or equal
to 5 mm for cutting ferrous and non-ferrous
materials with solid or solid-profiled
sections.
Figure 14-1
“
BW” TYPE SHARPENING DIN 1838--UNI 4014
Coarse toothing with teeth alternately raked to the
right and left.
Toothing generally used on cut-off machines for
cutting ferrous and alloy materials with tubular and
profiled sections.
Figure 14-2
POSITIVE AND NEGATIVE CUTTING ANGLES
The cutting angle may vary from positive to
negative depending on the cutting speed, the
profile and the type of material to be cut.
A positive angle determines better penetration of
the tool and hence lower shear stress and greater
ease of sliding for the swarf over the cutting edge.
On the other hand, the cutting edge has lower
mechanical resistance, so that as the breaking load
of the material to be cut increases, the cutting
angle decreases from positive until it becomes
negative, thus offering a cutting edge with a larger
resistant section.
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