Life-time equation

  • bearing load
  • life-time equation
  • load rating
  • loading

The more precisely the operating conditions of a straightening roll are known or can be calculated, the more exactly and reliably its useful life can be determined.

Three different equations are available: for nominal life-time according to ISO, for modified nominal life according to ISO, and for modified nominal life-time based on a new life theory.

The simplest approach is to determine the nominal life-time according to ISO using the relevant equation.

Calculation of the nominal life-time using the equation is sufficient for conventional bearing applications.

In other applications it may be wise to take detailed account of other life-affecting factors as well. This led in 1977 to the introduction of the modified life-time equations.

In a third equation - modified nominal life-time according to the new SKF life theory - a life-time coefficient is added to take account of a fatigue load limit and various other factors affecting the lubricating conditions and the degree of soiling.

The life-time value calculated with the third equation is regarded as the period of use actually covered by a straightening roll in its life-time. As a rule this value deviates slightly from the calculated nominal life-time.

Location of the straightener

  • arrangement of straighteners
  • choosing a location
  • distance to the straightener
  • location of the straightener
  • placement of straighteners

The distance between the straightener and the pay-off or final deflection of the product to be straightened has a major effect on the straightening result. A distance of A £ d p, where d is twice the initial curvature radius or the diameter of the last deflecting roll, guarantees that the initial curvatures will be effectively changed by the straightening process and that the product to be straightened will leave the straightening system with the required final curvature and enter the follow-up machine in a defined condition.

If this distance is exceeded there is a real risk of the product - still under the influence of its initial curvature - turning and twisting before it enters the straightener so that its forming takes place neither constantly nor in the plane of curvature requiring straightening.