Production of the gravel

For the production of the foam glass ballast, the following raw materials are generally used:

  • Glass flour from recycled glass
  • Blowing or foaming agent
  • Water
  • Glass mat
  • Kaolin

The glass flour is produced by means of suitable grinding processes from recycled waste glass. Due to application and environmental compatibility guidelines regarding the foam glass ballast as a final product, not all recycling or waste glass can be used contrary to rumors on the market of foam glass. In the case that no recycled glass is present, the base glass for producing the foam glass can of course be melted from the classic glass raw materials. For the realization of such a furnace and optimization of the glass composition, we are happy to assist you.

The blowing agent consists of a mixture of a carbon carrier and other, environmentally friendly additives.

The glass fleece serves as a carrier material to transport the mixed with the blowing agent and water glass flour via a chain link belt through the foaming oven. The kaolin (in a water suspension) serves as a release agent, so that the glass fleece does not stick to the conveyor belt (chain link belt) during the foaming process.

Manufacturing process

The various raw materials (glass flour, blowing agent and water) are dosed out of your storage containers and mixed and applied as a slightly moist powder on the glass fleece (endless belt). The task height can be adjusted to the millimeter with a scraper. The glass fleece, soaked in the kaolin / water suspension, serves as a carrier material for transporting the glass powder through the oven. The foaming oven consists of a continuous furnace divided into several zones. Each zone has its own temperature control and function during the foaming process. Basically, the foaming process can be divided into 5 steps, with the first four taking place within the oven.

  • Heating and Drying
  • Sintering
  • Foam
  • Pre-cooling ("freezing" of the foam structure)
  • Cooling down

As a result of the cooling process, the endless foam body disintegrates into smaller pieces (10-60 mm) after the furnace exits and can be loaded immediately after cooling and transported to the customer or to the construction site.


The powder grains stick together during the sintering process and forms a cake with many small homogeneously distributed cavities in which the blowing agent is located. These cavities are different in size due to an existing grain size distribution in the glass flour. If the temperature is increased, the expanding gas formed by chemical reactions increases the pressure in the bubbles. Increasing the temperature lowers the viscosity of the glass. The cake is foamed when the pressure in the bladder exceeds the resistances through the glass (viscosity).

Furnace technology

The foaming furnace consists of a tunnel kiln, which is composed of different modules. Inside a chain link belt runs through the furnace on which the mixture of glass powder and blowing agent etc. or the foam carpet is transported. The heating of the furnace is generally carried out with natural gas burners used in the modules. Depending on requirements, however, LPG or electric heating can also be installed. Thus, each module can be individually heated to set different temperature profiles in the oven can.