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On roller straightening machines set up behind the cutting units it is necessary to install input and output vertical rollers (two for input and two for output) with separate regulation and provisions for movement along the console (or working part of the shaft). They should be arranged at the closest possible distance to the horizontal rollers.
The optimum spacing of the rollers can be determined according to the formula.
where t is the spacing of the rollers in ram, is the maximum rolling diameter of the rolls of the finishing stand in ram, and is the maximum thickness of the wall of the profile being straightened.
The spacing of the rollers can be increased by 10-20% if it is necessary to increase the safety factor of the rolls or the bearings.
Analysis of the operation of machines for straightening sections at our combine and at other plants has shown that for successful operation such machines should have not less than nine rollers (four above, five below).
Although the roller straightening machines installed behind the 300 mills of our combine have nine rollers, the first lower roller (feed roller) does not participate in the straightening. Therefore, the lack of one triangle is constantly felt when straightening a number of profiles. The shafts of the machine should be of a single type and of equal strength, since the machine can be used for operation in both directions.
All roller straightening machines should have the possibility of regulation of the straightening speed. If the machine is intended for operation in the technological stream (rolling-straightening-cutting or rolling-cutting straightening), then its capacity should be somewhat higher than the capacity of the mill. Experience has shown that for roller straightening machines installed in front of the cutting units the speed of straightening should be 6-8 m/sec with the possibility of automatically reducing the speed at the moment of intake or discharge of strips from the machine. For machines installed behind the cutting units, the straightening speed should be 1.5-4.5 m/sec. In this case it is not necessary to change speeds during intake or discharge of strips, but the maximum speed of the feeding and discharge roller conveyers should be 10-15% greater than the maximum speed of straightening, while the minimum speed of the roller conveyers should be 10~ less than the speed of straightening.
Machines for straightening sections with an upper pressure unit do not have systems for equilibration of the upper rolls and the chocks. This reduces the periods of service of the threaded and connecting parts of the mechanism and makes the console roller straightening machine unsuitable for multiple-thread straightening prematurely. The creation of an equilibration system on such roller straightening machines wil1 improve their technological effectiveness and increase the inter repair period. The roller straightening machines with a lower pressure unit do not have such drawbacks, and therefore the higher expenditures for their installation are very quickly recouped. They are most effectively installed behind mills where the profiles are cut into measured lengths on saws.
For automation of the adjusting process, the roller straightening machines should be equipped with a system of reckoning the position of each shaft (indicators of pressures). The distance between the centers of the lower and upper rows of rollers should be selected in the following manner:
1) The minimum distance with a given spacing of the rollers is established constructively, proceeding from possibilities for arranging the bearings and chocks;
2) the maximum distance should be equal to a double spacing of the rollers minus 10 mm (from the condition of efficient utilization of the maximum dimensions of the straightening rollers).
The mechanism for axial regulation of the shaft on modern machines should have roller bearings for axial support. Investigations conducted by the author have shown that axial stresses occurring when straightening even the heaviest profiles are inappreciable. This made it possible to replace the special bronze rings in the mechanisms for axial regulation of the roller straightening machines of the 500 mill by roller support bearings.This replacement was made in the complex with the introduction of precise calibration of the rollers which sharply improved the quality of rolling and reduced standstills of the straightening machines: The straightening of any profile in two planes is done in a single pass. For best operation of the mechanism for axial regulation, it should be sealed in order that finely dispersed dross should not fall into it. The necessary and sufficient magnitude of the axial displacement of shafts for machines with roller spacings up to 550 mm amounts to +15 mm and 220 mm for roller spacings greater than 500 mm.