TPT May 2007

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 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: A) Production costs

› Figure 2 : Detail of a flying shear cutoff unit SJ 38x2.4, with blades driven by SEW servomotor

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.

Blade and jaws

Rotary saw blade

Difference per year

Purchase, maintenance per year (€)

€3,800

€38,000

€34,200

Tool expense saving per year

€34,000

156

M ay /J une 2007