Online thickness measurement
The problem
Producing calendered sheet within tolerance is subject to many interacting variables such as top and bottom coating thicknesses, rubber penetration depth, calendar speed, pressure, temperature, compound type and homogeneity, line speed and condition of the calendar rolls.
Measurement and control systems based on scanning x-ray, beta or gamma backscatter sensors and air gauging are problematic for a number of reasons. Read more 
Thickness is calculated from density and is not measured directly.
Control of the calendar nips, roll bending and cross axis are calculated from a three zone analysis and consequently scanning the full width of the sheet is unnecessary and adds cost but no value.
Scanning on a diagonal moving path leads to a slow control response.
Radiation emitting sensors are hazardous and extremely costly and time consuming to maintain.
Air gauging heads must be positioned very close to the rubber sheet and are easily damaged.
For calenders with no existing measurement system, typically sheet thickness is checked manually online by an operator using a caliper or snap gauge on one side of the sheet. However, calliper gauges are inaccurate and subject to significant gauge R&R variability.
For calenders with no existing measurement system, typically sheet thickness is checked manually online by an operator using a caliper or snap gauge on one side of the sheet. However, caliper gauges are inaccurate and subject to significant gauge R&R variability.
The solution
The thickness of solid rubber sheet, coated steel cord or coated fabric ply can be measured immediately after calendaring using Sigmavision’s online thickness measurement solutions. Systems use fixed mounted laser spot sensors that are positioned across the sheet width on a purpose built frame. Any number of sensors may be used though typically three measurements are made along the left edge, centre and right edge of the sheet. Read more
A single row of laser sensors may be used together with a guide roller which acts as a measurement reference. Alternatively a differential measurement may be used where ply vibration does not allow the use of a fixed reference by employing two rows of laser sensors on opposing sides of the sheet.
Each laser sensor projects a spot of laser light onto the surface of the sheet. Light reflected back at a specific triangulation angle onto a photosensitive detector allows the distance to the surface to be calculated. A dedicated software application called STMS (Sheet Thickness Measurement Software) is responsible for acquiring and synchronizing data, processing measurements and reporting results.
Closed loop control may be implemented by employing additional laser and eddy current sensors to measure upper and lower rubber skin thicknesses using the calender bowls as measurement references. Control algorithms provide real time correction of calender nips, roll bending and cross axis.
System features:
Suitable for all grades and colours of natural and synthetic rubber sheet, rubberized fabrics and steel cord.
Turnkey solution including air cooled laser sensor assembly, mechanical frame, free standing controller and display.
Modular construction for multiple measurement points.
Real-time display of measured and target gauges.
Statistical reporting and network compatible.
Simple to set up, operate and maintain.
Measurement accuracy to <0.02mm.
