Refractories and other products for the complete solution every time

Promat HPI are the leading global supplier of high performance insulation solutions. As well as being the market leader in microporous and calcium silicate technology, we offer "catalogue products" including fibre matrix products and a range of refractory bricks and other products aimed at the furnace, kiln, and oven applications. Whatever your insulation problem, we have the solution.
Technology

Refractory (fire bricks, castables, bonding agents, accessories)

Heat insulating materials such as fire bricks and castables are normally specified for the refractory linings of industrial thermal processes such as furnaces. With high porosity and low thermal conductivity, they serve to reduce process heat requirements by controlling heat losses.

The term "heat insulating bricks" normally refers to those heat insulating materials which are specified for use up to 1000 oC and which are often mistakenly referred to as "rear insulation materials". They are made from several naturally occurring raw materials.

Kieselguhr, also known as diatomaceous earth, is a soft, siliceous sedimentary rock that is easily crumbled to a fine powder with a typical particle size between 10 µm and 200 µm.

Vermiculite is a hydrous, silicate mineral that is classified as a phyllosilicate and that expands greatly when heated. Vermiculite expands rapidly when the mineral is heated quickly above 700 oC. Because of the pressure exerted by the water in the intermediate layer as it evaporates, the structure becomes exfoliated and can occupy 20 to 30 times its original volume. It can be used for the manufacture of bricks, boards, and shaped parts.

Perlite is an amorphous volcanic glass that has a relatively high water content, typically formed by the hydration of obsidian. It occurs naturally and, similar to vermiculite has the unusual property of greatly expanding when heated sufficiently.

Lightweight refractory bricks are shaped refractory products with a total porosity ˃ 45% and an application temperature ˃ 800 oC.

The bricks are shaped by casting, centrifuging, or pressing. Sulphite liquor, gypsum, or concrete can be added to strengthen the mixture and speed curing.  The bricks are fired at a temperature corresponding roughly to the final classification temperature of the product.

Bricks with complicated shapes are hand formed using vibration or moulding.

Castables have similar composition to the refractory bricks and together with the bonding agents and other accessories they complete the range of resale products available.
Properties and application advice
The requirements for lightweight refractory bricks are diverse and in some cases even contradictory

On the one hand
  • high thermal insulating capability and low bulk density,
on the other hand
  • sufficient mechanical strength but also good workability.
Additionally
  • high thermal resistance under a multitude of atmosphere conditions
  • as well as resistance to temperature shocks and changes
is required.

The operation of the industrial furnace is a decisive criteriion for the behaviour of lightweight refractory bricks in service. Fur furnaces operated on a continous basis the mass of the constructed refractory lining plays a less important role in energy efficiency. The degree of thermal insulation is significant for efficient operation, so that bricks with low λ-values are preferred.

The basic rule is:
The lower the bulk density, the lower the thermal conductivity. There is demand for a bulk density adapted to the service temperature. This demand is basedon the existence of a minimum thermal conductivity and the shift to higher bulk density a higher temperatures

Special knowledge is required with regard to maximum service limit temperatures. The classification temperature as producer information is usually determined in the lab on standard half size bricks. Shrinkage should not exceed 2% after being subjected to heat on all sides for 24 hours

In practice the start of shrinkage and softening, due to the long-term effect of high temperatures, static pressure, vibrations, reduced atmosphere ore fluxed vapours, is approximately 100 to 200 K below the classification temperature determined in the lab.

If there is chemical attack by gas or dust-loaded constituents as part of the furnace atmosphere, the following has to be considered:
  • Reducing furnace atmospheres require bricks with low iron content (carbon bursting).
  • Furthermore it has been determined that higher shrinkage occurs in reducing atmospheres.
  • Alkaline vapours and condensates result in modification of the structure and melt phases (alkali bursting).
  • CaO-bonded bricks are sensitive to overheating due to short sintering ranges.
  • Sulphur contents in the brick can attack heating elements in electric furnaces.
The thermal conductivity values indicated in brochures are valid for normal atmospheres. The values change e.g. under inert gas. In H2 atmospheres the actual thermal conductivity can be up to 7 times higher. Furthermore the heat flow changes as a result of increased furnace pressure. In a vacuum the heat transfer decreases via the gas phase.

Measurements of thermomechanical behaviour such as resistance to permanent compression and refractoriness under load are much more informative than the classification temperature or shrinkage.
Product portfolio

Refractory bricks

  • PROMATON®
  • Bonding agents: ALSIBLOCK®, K84
  • Castables: PROMACRETE®, PROMACAST®, PROMAFLOW® 

Vermiculite products

  • PROMACLAD®
  • MICATECH®