Vertical mixers prepare high performance ceramics

In our daily life we encounter the most diverse synthetic materials. Technical utensils of every day use in particular increasingly contain high performance ceramic materials. Alongside plastics, the greatest development potential is predicted for ceramic materials, because in terms of durability, heat resistance and hardness, ceramics are considered to be unique. As a high-temperature resistant material in energy production, industrial ceramics serve equally well as protection against corrosion, acid and wear in process equipment construction or as semiconductors in electrical components.

In the production of high-quality ceramics, the raw materials are placed in the state of a large specific surface area with particle sizes of approx. 0.1 to 0.08 µm and a suitable grain size distribution. The highest possible purity is crucial. Subsequently, the individual components – mostly oxides, nitrides, carbides or borides of aluminium and silicon – are intensively deagglomerated. Such small particles are particularly inclined toward the formation of agglomerates, which would hinder a homogeneous formation of the structural constitution of the sintered material.

So that no function-impairing defects develop, attention is to be paid to maximum cleanliness. The highest demands are placed on the individual process steps; from the chemical breakdown, grinding, dispersion, sifting, doping, homogenisation and dispersion in the wet phase to drying, compounding, gravitational separation, calcination, regrinding, dissolution, crystallisation, vacuum drying and further to shaping and filling.

The perfection in the process engineering ultimately leads to an increase in the strength, temperature resistance, acid resistance, ductility, conductivity, transparency, depth of colour etc.

The process of manufacturing industrial ceramic materials is thus divided into individual sections. Most processes take place in continuously working process apparatuses, whose parameter settings are made on the basis of upstream material analyses. As such, continuously occurring individual steps are to be carried out in sections and the intermediate products are to be collected as batches in containers, silos, mixers or big bags. Representative analyses provide that homogeneous populations are found. The batch sizes to be homogenised in powder metallurgy vary between 50 litres and 20,000 litres. amixon® mixers are being used increasingly in order to obtain ideal mixing qualities. The characteristic flow pattern of the vertical mixers provides for short dwell times.

Short process times minimise abrasion

The mixing of solids and the deagglomeration take place in amixon® mixers as a quality-determining step. Three amixon® designs have different main areas of use. Since even cleanroom conditions sometimes have to be met, growing importance is attached to hygienically compliant apparatus designs.

The mixing devices are formed as helical springs, which are connected to the shaft by horizontally arranged arms. The dry, damp or suspended mixtures are screwed upwards in the outer area by the rotation of the helical spring and flow downwards along the shaft in the central area.

This flow pattern is further overlaid by strong transverse mixing in the twin-shaft mixer, which is equipped with two mixing devices rotating in the same direction. In this way, component compositions of up to 1:1 000,000 can be mixed in approximately 0.5 to five minutes according to a technically ideal homogeneity. In practice, the mixing quality obtained cannot be improved any further.

The ideal mixing quality is obtained independently of the constitution of the mixing products (differing characteristics such as particle size distribution, particle shape, moisture, adhesion and bulk density). The filling level can thereby vary from ten to one hundred per cent of the useful volume without the attainable mixing quality being impaired.

The use of twin-shaft mixers covers almost all demanding solid mixing tasks with very short dwell and cycle times or bulk density changes. This type of mixer is also suitable for so-called mechanical alloying by the addition of coating ingredients and subsequent isostatic pressing.

The vertical single-shaft mixer type VM, on the other hand, is primarily used where high mixing qualities are demanded, but the mixing times may last five to eight minutes or longer. Due to the three-dimensional shifting flow, it is possible in one and the same machine

  • to mix extremely gently – at a low mixing device speed or
  • to mixed very intensively and deagglomeratingly – at a higher mixing device speed and with the additional use of a cutting rotor.

The process engineering characteristics of these vertical mixers give rise to a broad range of applications. With goods that are at risk of oxidation, for instance, the peripheral speed of the mixing device can be adjusted to less than 1 m/s so that expensive measures for rendering inert may be dispensed with. A further advantage results from the calm mode of operation: due to the relatively low mixing device speed, hardly any vibration is generated, so that the mixing machines can be mounted on weighing cells, allowing the mixture to be weighed with an accuracy of 500 g. 

Batch tracing and product purity are the keys to success!

Occasionally the material producer demands a precision mixer which, in addition to ideal mixing qualities, should also exhibit one hundred percent residue emptying. Cone mixers equipped with typical, patented amixon® details are used here. In powder metal factories, for example, amixon® mixers are in operation that can mix 4000 kg of preparations and subsequently discharge them, leaving behind residues of only a few grams.

A further single-shaft mixer derivative offers interesting handling features for pilot processing with small quantities. It feeds and empties itself automatically by taking up the contents of standard drums without contamination and filling the mixture back into the drums after mixing. Here, the entire processing, i.e. the loading, the mixing preparation, the filling and the quality assurance takes place in standard drums. Pharmacy compliant cleanroom production can thus be comfortably implemented.

At this point it should be noted that results gained in a small amixon® mixer are transferable to large amixon® mixers. As such, results from a pilot plant can be reliably implemented in large mixing machines with the aid of works’ own conversion factors. Inspection and cleaning can be carried out in an ergonomically exemplary way. The apparatus is operated virtually emission-free.

Apparatus standards that are common in the pharmaceutical and foodstuffs industries are also increasingly making inroads into powder metallurgy and nanotechnology. One example of this is the inspection doors, which are manufactured according to the ‘clever-cut®’ design. These are inspection openings that are free of dead spaces and seal extremely close to the product. Microbiological controllability is certified for them.

Mixers from amixon® guarantee the user a wide range of benefits.

  • Low-contamination mixing, little abrasion and wear due to low speed!
  • Ideal mixing qualities even with the most difficult tasks! => as such, it is a worthwhile investment with a view to future tasks.
  • Largely residue-free and segregation-free emptying! => need-compliant material supply; for fast discharge through a large discharge device; for slow dosing discharge through a small discharge device.
  • Bearing and drive of the mixing device only at top the mixing chamber! => practically maintenance-free shaft bushing and sealing.
  • Large, hygienic inspection door! => contamination-free production, comfortable inspection and cleaning with minimum handling effort.

The amixon® team will be pleased to demonstrate the user benefits to you during a visit to our works’ own technical centre. Put us to the test with your original goods – we can assure you in advance that you will gain a great deal of information.

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