Hyd-Mech P 225, Use And Maintenance Manual

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P 225 28
CHAPTER 8
-- Choice of blades
When using the P 225 pendulum saw it is important to select the
correct type of blade for the material to be cut. This chapter ex-
plains the limitations and specific applications of the different ty-
pes of blades.
8.1 -- Choice of blade
The different types of blades that can be used on the P 225 must
satisfy the following general requirements:
-
FINE TOOTH PITCH -- for thin walled materials such as
steel plate, tubes and profiles;
-
COARSE TOOTH PITCH -- for large cross--sections;
--
for soft materials
(aluminium alloys and soft
alloys in general);
8.1.1 -- Tooth pitch
The choice of the most suitable tooth pitch depends on a number
of factors:
a) the size of the section;
b) the hardness of the material;
c) the wall thickness.
Solid sections require discs with a coarse tooth pitch, whereas
small cross--sections need blades with finer teeth. This is
because when walls of small cross--section (1
7 mm) profiles
are cut, it is important that the number of teeth actually making the
cut is not too small, otherwise the effect obtained will be one of
tearing rather than of swarf removal, leading to a large increase
in shearing stress.
On the other hand, when cutting
thick materials or solid sections
using a blade with an excessively
fine tooth pitch, the swarf collects
as a spiral inside the gullet, and
since fine tooth pitches have small
gullets, the accumulated swarf will
exceed the gullet capacity and
press against the walls of the wor-
kpieces, resulting in poor cutting
(same situation with soft mate-
rials), greater shearing stress and
hence breakage of the blade.
S in mm Pitch T
10 4
30 6
50 8
70 10
90 12
130 16
Choice of tooth pitch T as a function of cross--section to be cut
S S
sp
for steel solid pieces and profiles
S and sp
in mm
Pitch T
10 sp=0.5 3
30 sp=1.5 4--5
50 sp=2.5 5--6
70 sp=3.5 6--7
90 sp=4.5 7--8
130 sp=6.5 8
KEY:
s = diameter or width of the solid piece to be cut in mm
sp = thickness of the wall to be cut in mm
T = tooth pitch in mm
A larger pitch should be chosen when the cross--section at any
given point exceeds the average cross--section given above as
a result of the shape of the piece to be cut.
Type of swarf:
A
-- Very fine or pulverised swarf indicates an excessively low
feeding speed and/or cutting pressure.
B
-- Thick and/or blue swarf indicates that the blade is
overloaded.
C
-- Long, spiral swarf indicates that cutting conditions are ideal.
8.1.2 -- Cutting and feeding speed
The cutting speed in m/min and the feeding speed in cm
2
/min are
limited by the amount of heat generated near the points of the
teeth. If the feeding speed is too high, the cut will not be straight
in either the vertical or the horizontal plane. As we have already
seen, the cutting speed depends on the resistance (kg/mm
2
) and
hardness (HRC) of the material and the dimensions of the
thickest sections. The feeding speed depends on the
cross--section
of the material. This means that large
cross--section solid or thick--walled materials (s > 5 mm) can have
a high feeding speed provided there is sufficient swarf removal
by the blade; thin--walled materials, such as thin pipes or profiles,
must be cut with a low and above all constant feeding speed. A
new blade requires a wearing--in period, during which time a
feeding speed of about half normal speed should be used.
8.1.3 -- Lubricating/cooling fluid
The lubricating/cooling fluid must ensure that the blade teeth and
material in the cutting area do not overheat. Furthermore the fluid
must be supplied with a sufficient quantity and pressure to
remove the swarf from the cutting area. It must be an excellent
lubricant to prevent abrasion of the teeth and welding of the swarf
to the teeth (seizing).