Industrial Mixers for the Treatment of Powders intended for 3D Printing

The layered structure is achieved through the generation of computer-controlled 3D CAD components, in which a generally fine powders is melted using an energy source, usually a laser. Subsequently, powder is added again, the laser begins to melt again in the specified places and binds the bottom layer. The materials used can be metals, plastics, ceramics, synthetic resins, carbon and graphite materials.

Cell biology laboratory research is also being carried out on the production of tissues or organs from an additive manufacturing process, in which completely different attachment systems are used.

Use of Powders in 3D printing

3D printing is an interesting aspect of Industry 4.0. As a key technology in digitization, and combined with other additive processes, it will revolutionize production methods. The process can be used under three conditions: a complex geometric structure, a small number of parts and a high degree of customization.

This is the case, for example, when it is necessary to repair machines, whose complex spare parts are no longer available. The previously designed three-dimensional element is transformed into a physical element by direct data conversion.

Unlike conventional chip removal manufacturing processes, no assembly, castings, and product-specific tools are required. Depending on the savings made on the volume of the components, more particularly on the elimination of material removal, it is possible to reduce the process of using resources by material removal

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The process generates the mechanical and technological properties during the manufacturing process. In addition, it is possible to create complex structures that cannot be achieved with a conventional manufacturing process. Thus, 3D printing becomes more economical as the complexity of the component geometry increases and the number of parts produced decreases.

3D printing is used in many branches of industry. Beyond the classic components of mechanical construction, automotive engineering, model making and architecture, the manufacture of medical and dental prostheses is possible. Ideally, the method is also suitable for the rapid implementation of intermediate results obtained in structural bionics; especially when trying to transfer strength structures from plant fibers into modern load-bearing structures.

Treatment of powders in the Manufacturing Process

First, a powder bed with sufficient charge density is sprinkled. Thanks to a precisely controlled energy supply, the sets of particles merge into the target structures. The excess powder is removed and ideally prepared for use for further laminate construction. The particles must be sufficiently stable; particle sizes, mass densities and densities must be largely preserved.

On the other hand, the work steps must follow one another quickly in order to guarantee economic efficiency. These processes are mainly carried out with pneumatic vacuum conveyors, which requires relatively high transport speeds and can promote the generation of abrasion. The polymer powders used must be perfectly conditioned.

Similar processing problems are also encountered with 3D laser micro-sintering from metal powder. The application of the powder in the powder bed is done by means of a squeegee. This process is often time consuming. The fluidity of the powders used has a great influence on the homogeneity of the bed.

The powders should flow as freely as possible. It is therefore necessary to favor shapes of spherical particles and a narrow particle size distribution. Agglomerates must be removed; otherwise, flat or linear defects will form in the construction part. The adhesion to the squeegee and the treatment platform is disturbing but it is difficult to avoid them.

Most of the metal powders used have a particle size of less than 10 µm and behave cohesively.

In practice, the powders are sometimes conditioned by a coating of nanoscopic additives. These operations are carried out in precision mixers or with the fluidized bed process. This makes it possible to avoid undesirable accumulations or agglomerations and to improve the fluidity of the powders. – The powders are made in an automated way.

Role of the mixer in the process

Mixers, vacuum dryers and synthesis reactors perform important functions in powder metallurgy and polymer fabrication. Ribbon blender mixer is the best option for you.

Nanoscopic coating of each particle can be done if the coating agent is in the form of a weak solution or suspension and is microfine mixed into the powder. It does not require anything other than a uniformly moistened powder; every particle should be completely wetted. If the liquid phase is then dried, uniform coating of each particle occurs. The drying process should ideally take place by stirring under vacuum, in a particularly fast and delicate manner.

To solve such a step in the process, it is recommended to use a vertical mixer-dryer, in the center of which turns a propeller-shaped mixing tool. This creates a flow of the mixtures by carrying the products upward at the periphery and letting them flow downward in the center with gravity. The flow process takes place – without any dead space – at a low rotational frequency and with minimal shear stress for the particles.

All the particles are in permanent relative motion with respect to each other and circulate throughout the mixing chamber. Evaporation of the liquid phase is favored by the heating of the powders. It is not only the surfaces of the mixing chamber that have a double wall.

The shaft of the mixing mechanism, the arms of the mixing tool and the propeller are also designed as a jacket and thermal fluid (thermal oil, water or steam) circulates through them in a closed circuit.

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