Filter
Top Products
14
14.2 Determining proper tooth pitch
Proper tooth pitch depends on:
a) the size of the section;
b) the hardness of the material;
c) wall thickness.
Solid sections call for
blades with a coarse
tooth pitch, while small
cross-sections require
blades with finer teeth.
This is because when
cutting walls of small
cross-section (1–7mm)
profiles, it is important
that the number of teeth actually making the cut
should not be too few, otherwise the effect
obtained will be one of tearing rather than of chip
removal, leading to a large increase in shearing
stress. On the other hand, when cutting thick
materials or solid sections using an excessively
fine tooth pitch, the chip collects as a spiral inside
the gullet, and since fine tooth pitches have small
gullets, the accumulated chip will exceed the gullet
capacity and press against the walls of the
workpieces, resulting in poor cutting (same
situation with soft materials), greater shearing
stress and hence breakage of the blade.
Table 3
A larger pitch should be chosen when, as a result
of the shape of the piece to be cut, the cross-
section at any given point exceeds the average
cross-section given above.
14.3 Cutting and feeding speed
The cutting speed and the head feeding speed are
limited by the amount of heat generated near to the
points of the teeth. If the head feeding speed is too
high, the cut will not be straight in either the vertical
or the horizontal plane. As we have already said,
the cutting speed depends on the strength
(kg/mm2) and hardness (HRC) of the material and
the dimensions of the thickest section. 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
The blade required for the cold saw is of HM hard
steel type since the machine is to be used for
cutting non-ferrous materials. In addition to the size
and pitch of the teeth, however, 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)