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Thread: POWTECH 2004: m-tec mathis technik

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    POWTECH 2004: m-tec mathis technik gmbh

    Stand 9-315

    New Gravimetric Small Component Metering System with High Metering Accuracy

    by Axel Friese (Sales Director)

    Automated bulk material metering technology is playing an increasing part in many sectors of the building material, chemical and foodstuffs industry. Manual metering and weighing of very small quantities is being replaced by automatic systems, and particular attention should be paid to all types of dry bulk materials with good or poor flowing properties. These bulk materials must be metered and weighed continuously with high accuracy and then transferred to the following process without leaving any residue.

    In principle, metering means taking an accurately defined quantity of raw materials from the stock of material and feeding it to the following processes. One piece of equipment which fulfils this function in the batch operation and can also be used under constricted installation conditions is the POWERDOS small components metering systems (Fig.1) supplied by m-tec mathis technik gmbh Neuenburg, Germany.

    The advantage of this system lies in the relatively wider metering range very small quantities can be metered very accurately and larger quantities very rapidly. This means that 5g can be metered from a raw material container for one batch and then 5kg for the next batch. In both cases the metering time lies between 20sec and 40sec depending on the required accuracy. The metering accuracy is 1g for both relatively small and relatively larger metered quantities.

    The enormous dosing range, which cannot be achieved with comparable accuracy and metering time by a metering screw, is made possible by a patent metering valve and a matching adjustable metering control system. Each raw material container is provided with a metering valve at its outlet. The actuating motors and the hopper weigher are mounted on a chassis. The chassis, which is driven by electric motor and controlled by incremental displacement measuring system, drives under the individual silos where the metered addition of the predetermined quantity takes place. This enables materials to be metered from 10 or more raw material containers with only one metering unit and one weigher. The system can be equipped with fixed silos, Big-Bags or bag emptying stations for storing the raw materials, so theoretically there can be an unlimited number of metering stations.

    The hopper weigher is also a new development. The cylindrical scale container is placed on a single-point-measuring cell in hybrid design. The use of just one measuring cell makes the structural design substantially simpler and the tare weight significantly lower, so one 50kg measuring cell is sufficient for a container volume of 40litres.

    The complete absence of parallel circuits is also an advantage. This means that the weighing result is not affected by electric cables, pneumatic lines or compensators in the way that happens with the usual hopper weigher designs. Only the product being metered is weighed, which also has a beneficial effect on the weighing accuracy. The measuring cell is protected by a mechanical overload protection system.

    The geometric shape of the weighing container and the smooth surface in conjunction with a high frequency roller vibrators guarantees virtually residue-free emptying of the weigher. A suction systems ensures dust-free metering during the metering process, and is designed and controlled so that it has no effect on the weighing accuracy.

    In practice there are two different options for installing the metering system. Installation situation 1 (EBS 1) applies when there is sufficient space available near the mixer. The system is then installed so that the travelling weigher drives automatically to the docking position at the mixer. At the docking position the weighing container is emptied into the mixer. When the emptying is complete the travelling weigher is taken back under the metering stations and another metering process can take place.

    EBS 2 is chosen if access to the mixer from the inlet spouts is difficult or impossible. For this installation situation the POWERDOS will not installed near the mixer platform. Depending on the space conditions in the plant the metering system can be placed on the platform below the mixer or also on the ground.

    To avoid contaminations and ensure that accurately weighing quantities are obtained the weighing material is not emptied into a transport container. The weighing container also becomes transport container after it has been transferred to a lifting turnstile at the transfer point. The lifting turnstile is designed to take two weighing transport containers and, by rotating through 180, enables the empty container to be exchanged for a second container which has already been filled. So this guarantees that the metering and weighing process can take place at the same time as the transport, including the emptying into the mixer, which substantially shortens the process time. The transport takes place on a rail system; an there are no restrictions with respect to the rail routing. The weighing container is emptied when it reaches the transfer position above the mixer.

    The small components metering system used in conjunction with weighing and metering electronics provided a cost effective and operationally reliable system for automating manual metering while fulfilling the quality requirements.

    Tests are possible at our Research & Development Centre. The first Powerdos started at the end of March 2003.

    For more information on m-tec mathis technik gmbh, please visit:
    http://edir.bulk-online.com/profile/...is-technik.htm
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