The Omega Strain effect
and the
Oval Reduction Factor (ORF)

In a nutshell, the Omega Strain is a balancing effect, and ORF (Oval Reduction Factor) is the numerical factor assigned to control this effect.

The value of ORF may be assigned in the range 0.6 to 1 (1 is the default value).

What happens

Take a pass sequence, say round-oval-round (RD-OV-RD). If we set ORF to 1, we obtain the standard design schedule, displaying R1% (percentage area reduction between entry round and OV) and R2% (percentage area reduction between OV and final round).

Now maybe you find that the ratio R1%/R2% is too high (and consequently too high the absorbed power in the oval pass). To fix this problem you can assign ORF<1, which will lower the above considered ratio.

Before looking at an example, let us stress the concept that ORF<1 is mainly recommended when working with ‘circular’ rounds, i.e. rounds having almost identical diameters in all the directions of their cross-sectional profile. In the stretching mill, the ideal ratio between nominal round diameter and actual round width should be 0.998. A sort of utopia, you see.

The Omega Strain feature is available in the most recent Linebow programs, those using in the stretching mill RD-OV-RD sequences only. Namely, 2ROUND, 3ROUND, RDBILLET.

The Omega Strain feature is not available in the other Linebow programs, those using in the stretching mill all types of ‘definite’ passes – Squares, False Rounds and Rounds. But these programs, including our thoroughbred (DESFILE), have another powerful feature, the secret door. Through the secret door you can force any square to false round and any definite pass to round. To learn more, click www.passdesign.com/public.htm and look for “The secret doors of Linebow”.

An example with a refurbished program – TWORF

To enrich the roll pass designer’s toolbox, we just produced TWORF, which is basically a version of TWOPASS having the Omega Strain feature.

TWORF considers three basic sequences: SQ-OV-SQ, SQ-OV-RD, RD-OV-RD. Like TWOPASS, TWORF sends its output to the screen, but it is very easy to print it to a file. This is what we did with the example below, considering how to obtain RD 30 from RD 40.

Now we can anticipate the results (full output screens are shown below) and leave their exploitation to the fantasy of roll pass designers.

The 1^st screen comes from ORF =1, showing R1% = 31.61 and R2% = 17.36.

The 2^nd screen comes from ORF=.8, showing R1% = 27.96 and R2% = 21.55.

The output screens

Note that you won’t find here the variables R1% and R2%: you will just read R%, but the suffixes 1 and 2 are implicit from their position in the sequence (first deformation, stand #4 to stand #5; second deformation, stand #5 to stand #6).