Successful concepts for ready-mixed special dry plaster

Eirich mixing technology has been successfully employed for many decades for the preparation of ready-mixed special dry plaster. This can be understood as all types of plaster from masonry mortar, screed and special mortar such as adhesive mortar, filler gypsum and repair mortar.

Besides the simple mixing of sand with gypsum or cement and lime, many applications call for mixing colour pigments and light materials, such as polystyrene and drying additives of all kinds to provide an absolutely homogenous product. The mixing process is of decisive significance as far as this is concerned. Perfect distribution of the smallest quantities of additives (which are often added in quantities in the ppm range as well as the optimal opening up of fibres can only be ensured by using an adequately good mixer.

The actual difference between Eirich intensive mixers (Fig. 1) and all the other mixing systems used throughout the world is to be seen in the unique mixing principle. A rotating mixing container takes over the transportation of the mixing material to a variable mixing tool which ensures adapted intensive mixing at the transfer point. Separation of the mixed material and the actual mixing operation makes it possible to vary the speed of the mixing tool and, as a consequence the input of energy into the mix over a very wide range. Unlike ring trough, planet or pipe mixers which operate at a peripheral tool speed of 2 to 5 m/s, the Eirich mixers can work at speeds of between 2 and 40 m/s.

Some 20-30 charges per hour are possible (with or without ­colour pigment and light materials) when preparing trade mortar in discontinuous operation. Mixers  with an advantageous filling ­capacity of 750 l, 1500 l and 3000 l are frequently used. Larger mixers with capacities up to 7000 l are available for higher outputs.

The main features of the EIRICH intensive mixer apart from the rotating mixing container include the fast running mixing tool (frequency-controlled vortex system) and a static combined tool as bottom wall stripper. In addition, the mixer can be equipped with an automatic, pneumatic inner cleaning system. This is particularly important when fast changeover to another recipe is required, for example, when mixing colour pigments under the mix and changing from grey to white cement.

There are many advantages for the user:

­– Excellent homogeneous mixing

­– Perfect mixing of small quantities of additive

– High quality mixing at medium tool speeds

­– Careful mixing of light additives under the mix at low tool speeds

­– Optimal opening up of fibres

­– Colour pigments are completely fractionised and mixed without the development of stripes

­– Unaltered high mixing quality even in the case of partial ­charges (up to 30  % of the nominal filling capacity)

­– Significantly less wear when compared with pipe mixers: no fast running knives and whirling shafts, with seal outside the product

– ­High availability

– ­Simple servicing and maintenance

­– Long tool service life

­– Good accessibility

All these factors have a direct influence on the economic efficiency of production.

The small number of tools required as well as their constructive design and the use of special materials ensure low expenditure for service and maintenance. Primary wear parts can be easily replaced thanks to the size of the different parts and easy fastening methods. It has been possible to improve the service life of wear parts to a considerable extent by developing special mixing tools on the basis of modern materials.

Eirich delivers turnkey dry ­mortar plants including the steel construction work and the silo, dosing, weighing and conveying technology and sand drying and sifting facilities (Fig. 2). Bagging, palleting and foil plants are planned and incorporated into the project.

The complete plants are generally controlled by means of a ­Siemens PLC of the S7 family or a suitable control system from Allen Bradley including the Eirich EDS batch control function module as well as a PC-based visualization and operating system, batch logging and formula management.

The PC based and EIRICH-MIC-NT multi-station control system has been developed especially for use in complex dry mortar plants (for example, in the case of several mixer lines). This system incorporates:

­– The Oracle high performance data base system for up to 10 000 different recipes

­– Operation of the plant sequences for up to 8 mixer lines

­– Registration of operation, production and quality data

­– Order, stock and warehouse administration

­– Extensive possibilities for balancing out mixes through freely definable filter functions

­– Data exchange with an ERP system supplied by the customer