How do I achieve a constant bulk density during pre-foaming?

This is a question that probably everyone has asked themselves at some point. But how are perfect results actually achieved and what is necessary to obtain a reproducible bulk density? The answer lies in the interaction of three main players:

Actor 1 - the weighing system

The weighing system must be as accurate as possible. The Erlenbach preexpander EMBead achieves this by using an exact weighing-cell which guarantees a tolerance of +/- 0.1g. But not only the accuracy of the weighing-cell is important, but also the regular control and calibration of the unit is of high importance. Upon delivery of the EMBead you will receive the necessary equipment to perfectly calibrate and exactly adjust the weighing-cell of the unit. This is the only way to ensure that the weighing process is always 100% accurate. Another important point is the exact dosing of the material through the dosing flaps. For this, Erlenbach uses the latest flap control system to ensure optimal and accurate fine dosing. 

Actor 2 - the steaming

The individual design of the steam piping for each preexpander size guarantees an optimal supply of steam. Special pipe sockets, which act as steam distribution - in connection with slotted sieves, which guarantee an open area of more than 60% - cause a homogeneous flow of steam over the entire floor area.  The exact regulation of the steam pressure with digital PID-regulators in the inlet & venting area guarantees a maximum control deviation of +/- 0.02 bar. With this uniform saturated steam flow in the foaming vessel, the EMBead ensures a homogeneous bead size distribution in the pre-foamed material and lays the foundation for a perfect bulk density. 

Actor 3 - the postweighing

Samples from the fluidized bed are automatically weighed in the Erlenbach bulk density control system (ESN10). In this unit, too, another exact weighing stone is used, which should be checked and calibrated regularly. The bulk density determined by the ESN10 is transmitted to the control system of the preexpander. This way the bulk density is recorded and can be used for later control, evaluation or quality aspects. On the other hand, the weighed bulk density is used to control the initial weight. If there is a deviation in the bulk density, the system automatically corrects the value of the initial weight. Thus, the use of the ESN10 bulk density control system guarantees an efficient use of raw materials and contributes to a maximum economic use of the pre-expansion system. See more in our animation. 


The well thought-out concept of the system offers a high degree of accuracy and safety and thus guarantees exact results. The goal is: a high material quality after a gentle pre-foaming process, with the maximum transparency of available data. The EMBead preexpander combines all this in an optimally tuned system.