ACO moisture measurement systems – the innovation at Wienerberger,

At the location Wiener-
berger Deest (Nether­lands), moisture measurement in clay has always been an important subject. With an accurate and reliable measurement, production failures due to too high or too low moisture content can be reduced. If the clay has a too high moisture content, the dimensions of the roofing tiles will not be consistent; also the tile will stick on the gypsum mould. If the moisture content is too low, the tile can crack in the dryer and the gypsum plaster will be worn out. For this reason Wienerberger searched on the market for an appropriate solution, which was found in the cooperation between Wienerberger and ACO Automation Components, Wutöschingen, Southern Germany.

The first solution proposed by ACO was an automatic moisture measuring system in the plant for special shaped tiles. In this plant, special roofing tiles are made, which on account of their shape require a higher moisture content (22 to 24%). The clay is moisturized in a circular screen feeder. A part of the clay comes from the (indoor) storage; another part is return clay coming from the special shaped tile department. Here lies the problem: The return clay has a higher moisture content compared to the stored clay. A precise moisture measurement prevents the clay from becoming too moisturized due to the return clay by reducing the amount of water added.


The moisture measurement system TFM1

This special clay moisture measuring device type TFM1 is used in the clay processing industry in brick manufacture and measures the moisture of critical materials such as clay, loam, lime, limestone, special ceramics and sand.

Due to the difficult structure of these materials, the moisture measurement is dependent on constant pressure conditions on the material. A compressing unit developed by ACO prevents the measured result from being influenced by different densities. The electro-mechanical device TFM1 compresses the material always with the same (adjustable) pressure, so that the readings of the moisture sensor are reproducible. The output signal of the sensor is a signal from 0-10V DC or 0/4-20 mA and is averaged (filtered). It can be directly hooked up to any PLC controllers or command circuitries.

The TFM1 helps to achieve constant moisture in the production process, which in turn extends the service life of the press and improves the quality of the products.


Moisture measurement at Wienerberger

The clay coming from the circular screen feeder falls onto a swivel plate, where a metal plate guides the clay into the TFM1. Controlled by a timer, a cylinder pushes the clay over the sensor (»2). As this happens with a constant pressure, Wienerberger obtains reproducible and accurate moisture measurement results. This solution has been operating meanwhile for over four years.

The second solution was a new idea offered by Wim van Gelder of the Engineering & Product Development: to place the digital moisture sensor behind a ceramic window directly into the press head (»3).

› Location: under the press head

› Product: clay

› Density: almost constant 1700 kg/m3

› Measuring range: 18 to 25% H2Owt, goal between 21 and 22% H2Owt

› Temperature: ambient

The tiles made in this part of the factory are the core business of Wienerberger, Deest. Therefore the moisture measurement is an essential part of the automation of this part of the plant. A new PLC will be added to the automation process of Wienerberger to implement this parameter into the control system. This solution with ACO digital moisture sensor system works excellently and will be presented to other plants of the Wienerberger Group.

A special press head is adjusted for the implementation of the moisture sensor. Wim van Gelder designed the special ceramic window to the requirements of the moisture sensor. Since the moisture sensor “looks” through the ceramic window, an accurate moisture measurement is the end result.


Digital moisture sensor DMMS

The ACO digital moisture sensors are developed for the toughest applications and for industrial use. They are developed in according with practical experience for permanent use and function according the principle of HFC-FFM (High Frequency Capacitive + Field Frequency Modulation). Without any problem the sensors can also be retrofitted in the pro­cess. By using the norm signal output or the Profibus DP interface (RS232), the sensor can be connected to any SPS or controller without additional software. Only for the configuration of the sensor is PC-software required.

The advantages of these moisture systems for Wienerberger are easier controlling of the plant and quality control of the tiles by the press operators.

Mirande A. Wolvekamp BSc, ACO Automation ­Components, Moisture Measuring Systems and Industrial Components and Wim A. J. van Gelder, ­Engineering & Product Development Wiener­berger B.V.

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