TPT May 2007

New trends for tube and profile separation concepts by shear and cold rotary saw By Ing Jan Attl, Attl a spol sro, Prague, Czech Republic

Background Attl a spol sro was established in 1921 by two brothers, Karel and Alois Attl. The factory successfully designed and produced small forming machines for both the domestic market, the European export market, South America and Palestine. The company was nationalized in 1951 and returned again into the ownership of the Attl brothers, this time Jan and Karel, after the Velvet Revolution in Czechoslovakia in 1989. Since 1992 the company has been designing and manufacturing production mills for open profiles and has grown to specialise in mills for longitudinally welded tubes and profiles. Attl a spol sro can supply a tube mill from a single source, which is a special capability in Europe. The company has developed its own knowledge-base for the decisive components of a mill. These are:

versus shearing. Issues include quality of the shear plane, dividing time, financial concerns regarding production times, energy savings and last but not least, ecology.

Evaluation of cutting profiles with cold rotary saw

Cutting by cold rotary saw is currently the most commonly used method to divide profiles and tubes, since it leaves a high quality cutoff face, while affording sensible production speeds. Commonly used peripheral (cutting) speed is in the region of 120-300m/min. The usable speed depends on the type of blade and material of the product being cut. Lower cutting speeds are desirable in order to obtain a longer blade life, while higher speeds are often employed to utilise the maximum production speed of the mill, when the minimum cutting time is needed. In this analysis, the extreme cases of the process will not be addressed as often presented by other manufacturers. This article is primarily interested in the standard applications of flying cutoff from various manufacturers, which cover 60-80 per cent of commonly employed production mills in various parts of the world.

• Vertical strip accumulator • Calibration of profiles and tubes • Forming and calibrating sections of the mill • HF welding generator

• Flying shears cutoff in combination with flying cold rotary saw • Bundling machine for profiles and tubes at the exit of the mill

Attl a spol sro invests considerable effort in the development and design of these above individual components, as their standard decides the productivity, life and overall parameters of a mill. In the mills produced by Attl, it is possible to cater for practically all types of longitudinal welding of profiles and tubes, such as:

Graph 1

• HF generator – own design • TIG; Plasma • Laser – Trumpf; Rofin

In the following article, the details will be presented for one of the most important components of the mill – the flying cutoff machine for profiles and tubes.

Graph 1 shows cutting times expressed as possible production speeds for a mill equipped with flying cold rotary saw. The values in graph 1 have been compared with values achievable in the actual production by several factories in the Czech Republic, Slovak Republic and Germany. It is evident that using a cold rotary saw limits production capacity of a mill with increasing diameter and wall thickness of a tube. Information has been used from a leading Czech tube producer about the life of the rotary saws and production costs attributable to the component of a flying saw cutoff module. After taking an average of the data it is possible to say that for a production line with the capacity of 26,000t/year (tube and profiles from ST 37 material), 120 replacement rotary saws are likely to be required. Each blade costs in the region of €150 and can be re-sharpened twenty times. The total cost of the cutting blades including the sharpening can be estimated between €38k and €45k per year.

Introduction Since 1996, Attl a spol sro has, in addition to the process of dividing by flying saw, facilitated 14 different applications of dividing tubes and profiles by shear. It is the findings, suggestions and conclusions based on this experience that will be detailed here. It is the aim of this article to be clear and conclusive. Next to a HF welding generator, the efficiency of the flying cutoff machine has a decisive influence on the capacity of the whole production mill. However, here we will not evaluate the ability to divide tubes or profiles in regards to the production speed and tolerances of the cut length. These aspects have been sufficiently mastered and will not be addressed here. This article will focus on the issues involved in comparing the individual types of dividing the tubes and profiles, by rotary saw

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M ay /J une 2007