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ay
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une
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to regrind the jaws twenty times. When considering production
volumes, this represents approximately 20-25 thousand tons of
profile production.
Using a similar analysis as the previous section dealing with the
cold rotary saw, Attl have calculated tool costs (main blade, slitting
blade, cutting jaws) for a production of 26,000 tons of tubes/profiles
per year as follows:
• Main blades
€1,500
• Pre-cut blades €1,100
• Cutting jaws €1,200
Total
€3,800
The cost of €3,800 is about ten times less than that of cutting
tubes and profiles using a rotary saw.
One of the most important parameters concerning the cutting of
profiles/tubes is the quality of the cut surface. In this respect, Attl’s
experience and that of its customers is quite conclusive.
Cutting of square and rectangle profiles
For these types of profiles, all the aforementioned SJ shear modules
are used. The cut is in one axis. Profiles from 10 x 10mm to 80 x
80mm and wall thickness 1-4mm can be sheared. The quality of cut
surface is very good and comparable to that of the cold rotary saw
method.
The times of the cut are 0.6-1 second, enabling the use of the
full mill speed. Thus this type of technology is very effective and
economically advantageous.
Comparison and economic evaluation of flying
shear cutoff versus rotary saw
A) Production costs
B) Energy requirement
C) Waste, ecology
D) Increased production as a result of using shear cutoff technology
A) Production costs
This can include purchase costs of the tools and their maintenance,
replacement and sharpening, which are necessary for an annual
mill production of around 26,000t.
As mentioned above, production costs attributable to the use of
flying cold rotary saw cutoff are in the region of €38k to €45k per
year.
Also above are the costs attributable to the use of flying shear
cutoff, namely €3,800 per year. This section is concluded in table 1:
Blade
and jaws
Rotary
saw blade
Difference
per year
Purchase,
maintenance
per year (€)
€3,800
€38,000
€34,200
The above information points to savings directly attributable to the
tooling costs in the region of €34,000 in favour of the shear cutoff
method.
B) Energy requirement (savings)
The energy necessary to cut profiles by flying saw, including the
motion of the cart, is around 140kW/hour. In comparison, energy
spent by the flying shears, including the motion of the cart, is
approximately 104kW/hour.
Savings from using the shear method as opposed to sawing is 140-
104 = 36kW/h. 36 x €0.14 = €5.04. Based on €5.04 x 4,200 hours,
the result would be €21,000 per year.
Energy savings of €21,000 per year is quite significant.
C) Waste, ecology
Increasing importance is currently being given to minimising
or removing the negative effects on the environment by waste
products. In the case of a saw, the waste effects are considerable
and can be expressed in terms of costs for the removal of the solid
metal saw waste and dust. Both methods produce approximately
19.6t of waste material per year.
Considering the type and shape of the sawing waste, it can be said
that about one third of the total amount (ie 6,532kg), consists of
larger metal particles and saw dust. The rest of the waste is in the
form of dust particles in the air, which have to be sucked away and
removed through filters; these costs are hard to evaluate.
Tool expense saving per year
€34,000
›
Figure 2
:
Detail of a flying shear cutoff unit SJ 38x2.4, with blades driven by
SEW servomotor