The European Approach to Quality Control
in Rail Grinding
(continued)
A number of target profiles
are used in preventive and corrective grinding applications.
European railways, which carry more mixed traffic and less
heavy haul than in North America, rely on a complex system
to describe and measure the tolerances. In Germany, for example,
reference points at the highest point at the top of rail, 14
mm below that point on the gauge face and at 5 degrees tangent
to the field side of the rail are used to define and measure
tolerances (See Figure 1). The maximum radial deviation from
the target profile is measured at the gauge side, offset at
25 to 30 mm from the centerline of rail.
Acceptance values vary depending on line speeds on the Germany
railways. On lines with speeds of 160 km/h or less the acceptance
value for grinding is +/- 0.5 mm. For very high speed lines with
operations at 280 km/h, the maximum deviation at the gauge corner
zone is +/- 0.2 mm. While acceptance values are rigorous, there
are allowances for some percentage of the finished rail to be
outside of the spec. On track with speeds of 160 km/h or less,
for example, 15% of the peak-to-peak lengths with an acceptance
value of +/- 0.5 mm may fall outside the tolerances. But on very
high speed lines with speeds of 280 km/h, nothing may be outside
these (+/- 0.5 mm) tolerances and only 10% of the lengths measured
may be outside +/- 0.2 mm. "These area very demanding tolerances," Schoech
said.
Grinding contractors meet these tolerances by using modern grinders
that incorporate trolleys with longitudinal measurement systems
to record short-, medium- and long-wave classes for both right-
and left-hand rails. A laser-based transverse profile measuring
system lets the operator know if he is within specifications.
Operators can plot the profile at any location to determine whether
the as-ground profile is within the limits.
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