Production of foam glass gravel

The production of foam glass gravel requires the following raw materials:

  • Glass powder from glass cullet
  • Foaming agent (dry or wet)
  • Water (for wet process only)
  • Glass fleece
  • Kaolin

The glass powder is usually produced from glass cullet (preferably container glass) by milling. For reasons of production and product quality guidelines as well as environmental sustainability related to the final foam glass gravel product, not every glass cullet (contrary to different opinions in the foam glass market) can be used. In case recycling glass is not available, the glass from which the foam glass is made can be produced from classical glass raw materials. For the realization of such a melting furnace and optimization of the glass composition, we are happy to assist you.

The foaming agent consists of a mixture of a carbon containing carrier and other environmentally safe additives.

The glass fleece serves as carrier material to transport the mixture of glass powder and foaming agent by use of a metal conveyor belt through the tunnel furnace. The Kaolin (in a water suspension) serves as separation material to prevent sticking of the glass fleece to the metal conveyor belt.

Production process

The different raw materials (glass powder, foaming agent and water) are taken from their storage vessels, weighed, mixed and dosed on to the endless glass fleece mat. The glass fleece, soaked in the kaolin suspension, serves as carrier material to transport the mixture of glass powder and foaming agent through the furnace.

The foaming kiln (tunnel kiln) consists of several zones (modules). Each module has its own purpose in the foaming process and its own temperature. Generally, the foaming process can be subdivided in to five steps. The first four take place in the furnace.

  • Heating and drying
  • Sintering
  • Foaming
  • Pre-cooling ("freezing" of foam structure)
  • Cooling

During the cooling step (step 5) after exiting the furnace the endless foam ribbon breaks down in smaller pieces (0-60mm). After complete cooling, the foam glass gravel can directly be loaded onto suitable trucks and supplied to the customer.

Foaming Process

During sintering of the mixture of glass powder and foaming agent, the glass grains bond together and form a sort of cake, which contains millions of small homogeneously distributed bubbles which contain the foaming agent. Because of the grain size distribution of the glass powder, the small bubbles in the foam cake have different sizes. Increasing the temperature inside the kiln causes chemical reactions forming gas inside the bubbles. By this, the pressure inside the bubbles increases. The increasing temperature also reduces the glass viscosity. The foaming starts when the gas pressure inside the bubble exceeds the external forces acting on the bubble (glass viscosity).

Furnace Technology

The foaming kiln is a continuous tunnel furnace consisting of different modules. A metal conveyor belt (chain link belt) transports the material to be foamed (mixture of glass powder and foaming agent on a glass fleece) through the furnace. Gas burners in each module are usually used to heat the furnace. Alternatively electrical heating can be supplied upon request. In this way each module can be heated to different temperatures to be able to apply different temperature profiles inside the furnace.