Hyd-Mech S-20DS, Руководство по эксплуатации и обслуживанию, Страница: 116 / 138

9--2 107
Use and maintenance manual S--20DS
adhesive table positioned by the mechanical speed variator indicates the speed in
m/min corresponding to the RPM value indicated on the dial.
Choice of blade
When using band saws to cut metals, an important factor is the choice of pitch,
i.e. the number of teeth per inch (25.4 mm.), which must be suitable for the
workpiece material. The following recommendations may be taken as general
guidelines:
H
thin---walled materials, such as sheet steel, tubes and profiles require a fine
pitch frequency. 3 to 6 teeth should be engaged in the breadth of the material
at any one time;
H
large section cutting requires a coarse pitch to cope with the higher volume of
swarf and optimal tooth penetration;
H
soft materials (aluminium alloys, soft bronze etc.) also require a coarse tooth
pitch.
Saw tooth pitch
The choice of teeth per inch, therefore, depends on various factors:
H
the size of the section;
H
the hardness of the material;
H
workpiece wall breadth.
Very large dimensions require coarse teeth, while small dimensions require finer
teeth. Whatever the case, ensure that there are always at least six teeth engaged
in the cut, with reference to the thinnest vertical walls positioned transversally to
the blade.
Cutting speed and downstroke speed
The cutting speed (m/min) and the downstroke speed (cm 2 /min) are limited by
the heat generated around the points of the teeth. If the downstroke speed is too
high, the cut will not be straight, either vertically or horizontally. The cutting
speed depends, as indicated above, on the tensile strength of the material
(kg/mm 2 ), its hardness (HRB) and the thickness of largest sections. The down-
stroke speed depends on the material thickness. Therefore, large---section, solid
or thick---walled materials (s > 5 mm), can be cut at high speeds, providing there
is sufficient swarf removal from the blade; thin---walled materials, such as slim
piping or profiles, must be cut using low and especially constant downstroke
speeds. A new blade must be worn in, which in effect means lowering the
downstroke speed to about half that of normal (from 60 to 70 cm
2
/min on normal
steels), equal to a removed surface area of about 300 --- 600 cm 2 .