The document discusses the use of non-contact eddy current displacement sensors from Micro-Epsilon to measure flatness in metal rolling mills. Flatness refers to the evenness of a metal sheet's surface. Conventional contact sensors can damage the sheet surface or require downtime for maintenance. The discussed non-contact system uses sensors to detect tiny vibrations in the sheet induced by fans and calculate tensile stress across the width without contact. This increases quality and availability by eliminating sensor wear and damage to the precision sheet surface.

1. A119_e
Eddy-current displacement sensors
eddyNCDT
Flatness measurement in rolling mills
The requirements on the surface quality of rolled In this case the sheet is pneumatically excited to
sheet are continually increasing. This may be steel vibrate. The amplitude of the vibration is acquired
sheet which is used, for example, for stainless steel with non-contacting displacement sensors from
fronts in kitchens, or also aluminum sheet used in the Micro-Epsilon Messtechnik and from it the tensile
automotive field. The surface must be flawless to stress is computed transversely over the width of the
offer the customer a high quality visual appearance. sheet. The significant advantage of this non-
Consequently, measurement equipment is employ- contacting measurement method is that no damage
ed in rolling mills to acquire the so-called flatness of occurs to the surface. A further, equally important
the rolled sheet. Flatness is taken to mean the advantage is that no wear can occur on the sensors,
surface evenness of the sheet in the unstressed so drastically reducing downtime and the costs for
state. Due to the enormous tensile forces when replacement parts. As a result, this increases plant
rolling the sheet, there is the risk that the tensile availability and the quality of the sheet which con-
distribution varies over the width of the sheet and that forms to current and future quality requirements. This
the sheet will distort in a wave shape at the edges. technique was only made possible by the application
Conventional measurement devices acquire the of non-contacting displacement sensors from
tensile stress using pressure sensors which are MICRO-EPSILON which acquire the smallest
embedded in a measurement roll. However, due to changes in amplitude without any wear and with high
this contacting measurement method, impressions dynamic response. The measurement system itself
of the pressure sensors appear on the sheet surface consists of the displacement sensors and the
and are visible in the end product. Furthermore, only associated electronic evaluation unit in a 19" rack.
one measurement can be taken per revolution of the
measurement roll. Due to a new
type of method developed by
Siemens, the contacting mea-
surement is replaced by a non-
contacting technique which
exerts no force at all on the
sheet and supplies continuous
measurements.
metal rolling mills

2. Application
Measurement system requirements:
- Measuring range 5.6 mm
- Offset: 2 mm
- Resolution 6 µm
- Dynamics to 10 kHz (-3dB)
- Temperature range sensor 0...+150°C
- Temperature compensation +10...+65°C
- Medium air, oil (hydrocarbon)
- Protection class IP67
Decisive advantages:
- non-contact and wear-free measuring principle
- high resolution
- No mutual interaction on the sensors due to
19”-rack for electronics and sensors EU6
synchronization
Principle
measuring oscillator amplitude 100 - 200 µm
distance~5 mm
tensile stress
displacement
sensors
modulator
fan
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