Quality Control in Tire Production

Automotive tires provide the only physical link between the vehicle and the road surface. In terms of safety and performance, impeccable, top quality tires are essential. Consequently, quality control is a pressing concern in tire manufacture. As a way of calculating the thickness of the rubber layers directly in the calender procedure, Micro-Epsilon presents an innovative solution.

Around 70% of globally generated natural rubber is used for tire manufacture. Within this sample, the tire industry produces more than 1 billion tires annually. In the preparation arena, the textile or steel cord is rubber-coated on both sides using 4-roll calenders.

These constituents equip the tire with sustainability and driving stability. The cord is covered by compressing it with rubber on the top and the bottom surfaces in the roller gap. Regulating the spatial dimensions of the rollers also adjusts the density of the consequent material and the crowning or wedge form.

Inline Thickness Measurement

In order to safeguard the optimal quality of the manufactured rubber webs, and to guarantee the safety features of the eventual tire product, total control of the material thickness is required. Striving to achieve complete efficiency, or alternatively optimized input of raw materials, the process is subject to completely automatic regulation.

One of the major functions of the calender process is the manipulation of thickness, which is the determining factor in the operation of the product. Quantifying the thickness represents a significant challenge in the process, as the black rubber web surface, extreme temperatures and vapors in rubber production considerably enhance the pressures on the sensors.

Micro-Epsilon has therefore developed an ingenious system for measuring thickness calculations directly in the calender system. The thicknessCONTROL TCP 8303.ET embodies a hybrid of two alternative sensor technologies integrated within a singular sensor head.

Thickness profile measurement in calender and roller-head systems directly at the calender roll.

Thickness profile measurement in calender and roller-head systems directly at the calender roll.

Within the integrated model, an inductive eddyNCDT sensor based on eddy currents assesses the distance from the surface of the calender roll to a high level of accuracy. While an optical laser triangulation sensor computes the distance from the surface of the rubber web, the difference between the two measurement values permits the determination of the thickness of the rubber web.

Eddy Current Meets Laser Triangulation

The eddy current sensor is utilized to calculate the distance from the sensor to the roll, as it measures through the rubber. This is possible because only metallic substances can be picked up by the eddy current sensor. Therefore, rubber does not distort the measurement signal.

The eddyNCDT displacement sensors implemented by Micro-Epsilon are actively temperature-compensated and so are resistant to temperature instability. Moreover, the operating sensor head in this sensor combination is adjusted with such precision that it generates an accurate distance signal in the range used, notwithstanding a considerable offset distance.

The distance from the surface of the rubber web is ascertained using a laser triangulation sensor. Optical calculation practices typically offer very accurate results, but often struggle when being confronted with matte and dark surfaces. The optoNCDT 2300, which is in operation in the thicknessCONTROL TCP 8303.ET apparatus, is furnished with the so-called A-RTSC (Advanced Real-Time-Surface-Compensation) component. This real-time surface compensation feature innovatively regulates the light intensity of the sensor while measurements occur, and simultaneously maintains optimal measurement results, even on tricky surfaces such as black rubber.

The applied optoNCDT sensor is exceptionally fast and affords a variable measuring rate up to 49 kHz. Consequently, the sensor can be individually adjusted to the process speed.

Complete System Including Adjustment Mechanics

Micro-Epsilon optimally merged the two sensors in the thicknessCONTROL TCP 8303.ET system. The optoNCDT sensor quantifies through a center hole of the eddyNCDT sensor, which guarantees locally accurate, coterminous measurements. Both sensors are contained within a water-cooled preservative casing, which also fortifies the sensors against high ambient temperatures.

Provisioned with the water cooling system, the sensor head can operate in ambient temperatures reaching 200 °C, and is therefore perfectly suited to the ambient conditions in tire manufacture. The auxiliary compressed-air purge apparatus prohibits vapors and steam from accumulating on the sensor lens.

The sensor head is incorporated into a mechanical network, which assures sustained distance between the sensor head and the surface of the calender roll. It also regulates the angle of attack depending on the process-relevant adjustment of the roll. In order to accurately identify the thickness, this sensor combination must be oriented in such a manner that it aims at the center of the roll.

Comprehensive Software Package

The measuring system determines the thickness of the whole width of the rubber web. Consequently, the system is fitted with a linear axis that authorizes transverse movements. Obtainable measuring width options encompass 1,400 mm, 1,800 mm and 2,200 mm. The thicknessCONTROL TCP 8303.ET is available in two models with measuring ranges of 10 mm and 20 mm. The resolution of the thickness measurement is 0.3 μm or 0.5 μm and the accuracy ±5 μm or ±10 μm, respectively.

Based on the combination of two different sensor technologies in one sensor head, Micro-Epsilon has developed the thicknessCONTROL TCP 8303.ET, an innovative system for thickness measurements directly in the calender system.

Based on the combination of two different sensor technologies in one sensor head, Micro-Epsilon has developed the thicknessCONTROL TCP 8303.ET, an innovative system for thickness measurements directly in the calender system.

In order to ensure comprehensive monitoring of a 4-roll calender, two thicknessCONTROL TCP 8303.ET systems are employed, which respectively supervise the product thickness from the upper (rolls 1 and 2) and the lower roller gaps (rolls 3 and 4).

The thicknessCONTROL TCP 8303.ET is completed with a downstream measurement of the total thickness. The comprehensive software package supplies the thickness control process of the calender with the thickness data from various measuring systems.

On top of the measuring systems for 4-roll calenders, Micro-Epsilon also offers a broad range of other measuring and inspection systems for quality control in the tire industry.

This information has been sourced, reviewed and adapted from materials provided by Micro-epsilon.

For more information on this source, please visit Micro-epsilon.

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