2017-06-30

Mixing systems for cement-bonded particleboard and light-weight construction materials

Cement-bonded particleboard has been used for more than 30 years in a wide range of applications. The boards are made in large volumes, and production places high demands on the mixing equipment. Light-weight wood chips have to be mixed together with heavy / dense binders. The situation is similar with light-weight construction materials when, for example, expanded clay or foam glass is used as aggregate. The mixers also have to meet other requirements. The grain size should not be reduced during the mixing process. Due to their inherent system characteristics, EIRICH mixers have advantages for both of these aspects.

Mixing quality is becoming increasingly important. Achieving an optimal quality level can, however, be difficult or impossible. The reason is that during the mixing process, de-mixing always takes place (as described in the relevant literature). Investigations on different mixing systems such as single-shaft axial mixers (plow share mixers) and ring trough mixers show that mixing cannot continue for an indefinite time. Depending on the mixing system, the best mixing quality is reached after a certain period of time. If mixing continues after that, the mixing quality is degraded and de-mixing takes place. It is then not possible to produce the optimum mixing quality. The reason for that is the different mobility of the constituents in the material mixture.

The results of these investigations apply to all mixing systems where the mixing tools transport the materials being mixed, but not to EIRICH mixers. On these machines, the material being mixed is transported by a rotating mixing pan. The function of the mixing tool, which is called the rotor, is merely to mix the materials. 100% of the mixture is stirred during one revolution of the pan. As a result, mixing can continue for an indefinite amount of time without de-mixing in production mixers with bottom discharge. The mixing tool continues to run during discharge. In (lab) mixers without bottom discharge, the mixing quality is also generally beyond the capability of other systems.

In particular, conventional mixers have difficulty with heavy / dense mixture materials. This was the reason why EIRICH mixers were used very early on for cement-bonded particleboard. The situation is similar with lightweight concrete. During the mixing process, the materials in the mixture can become wedged in between the mixing tool and the mixing pan, resulting in grain breakage and alteration of the particle size distribution curve. Once again, the advantage of EIRICH mixers becomes evident. Due to the inherent system characteristics, fewer mixing tools are needed and the tools do not come in close contact with the walls. On simple mixing systems, the number of mixing tools increases as the volume increases, but only one moving tool is needed on EIRICH mixers with capacities between 1 liter and 3,000 liters. Larger mixers have two rotors. Even the large 12,000 liter DW40 only has 4 mixing tools. Fewer tools means less of the materials in the mixture get wedged in, and fewer grains are crushed.

EIRICH mixers also have a proven track record with other lightweight materials. Expanded Vermiculite can be gently mixed with silicate binders, for example waterglass. After molding and hardening, this can be used for example as high-temperature insulation material. The inherent system characteristics of the mixer come into play. The speed of the tool can be varied over a wide range, and the materials are well mixed even at low speeds.

When the process is scaled up from lab mixers to production mixers, the number of mixing tools increases. This is a major reason why changes to the process on conventional mixing systems, and even to the formulation, often become necessary when formulations developed on lab mixers are transferred to large production mixers. Upscaling with EIRICH mixers is considerably easier because there are fewer tools. The results of lab development can be introduced faster, and with less effort, into production.

Re-use of polystyrene and polyurethane based insulation materials has increased in recent years. During the recycling process, the materials are ground up for use as lightweight aggregate in concrete and mortar for products such as durable, moisture-resistant ceiling or wall paneling. With EIRICH mixing technology, production is cost-effective and delivers consistent, high-quality results.

EIRICH offers anyone who would like to run feasibility studies the opportunity to perform trials on Test Center equipment which is available at all of the company's sites.

More information:

Contact: Dirk Heuer, e-mail: dirk.heuer@eirich.de