Warming up technology

Heat transfer by convection – Advantages and benefits for our customers

  • "Convection", this type heat transfer occurs at treatment temperatures up to 800°C and has a wide range of applications, above all for thermal treatment of semi-finished products of non-ferrous metals.

  • Furnaces with "forced circulation" are employed for nearly all types of heating and treatment.

  • Classical circulation furnaces with "return flow or cross-flow of the thermal stock" can be markedly upgraded in their flow performance. Higher flow volumes as well as a high and very constant flow pressure due to high-performance fans and an optimisation of flow uniformity by means of novel distribution systems yield grossly improved treatment results.

  • Increasing demands on the quality of heat treatment, throughput of ever-higher quantities requested by the automotive industry and permanent pressure on acquisition and operating costs have led to the development of highly efficient flow and admission systems. Notably to heating by means of targeted impinging stream. This admission system is called "jet heating" and has a heating-up speed that is 3 – to 4 times higher than a classical circulation furnace. A further distinguishing feature of "jet heating" is an extremely uniform heating of the entire furnace content.

    These heating systems have already frequently proven with leading companies, e.g. in the non-ferrous (NF) semi-finished products and plate glass sectors. "Jet heating" could even be established in new applications, e.g. during plate glass tempering where "jet heating" provides the following advantages in comparison to conventional heating processes:

    • The heating-up time is reduced by ca. 30 %.

      A further (possible) reduction should not be aspired in favour of temperature homogenising.

    • Heating is performed symmetrically from above and below.

      Bowl formation can be largely avoided due to the "cold" conveyor rollers. Thus, surface sliding scratches are reduced and transport safety is enhanced; i.e. panes do not warp.

      In addition, the "cold" rollers prevent caustic lines (alternating inflections in glass panes).

    • Temperature distribution across the glass surface is ideal.

      The heat transfer rate does not fluctuate, even in the edge and corner areas of large-sized panes. This means that the useful width is almost identical with the net furnace width.

    • The process temperature is lower by ca. 50 to 100 °C.

      Even though the heating-up time is shorter by ca. 30 %, the process temperature is between 50 and 100 °C lower than with radiation furnaces. Thus heat losses and thermal loads on all components in the furnace are reduced.

    • Glass with printed surfaces can be processed without any problems.


      Convective heat transfer allows for heating of coated and/or printed panes without any problems. There are no temperature differences between printed and not printed areas.

    • The set-up time "good glass to good glass" is shorter.

      Due to the lower roller temperatures there is no negative starting-up effect (as is customary in radiation furnaces).

    • Temperature distribution in the glass is more homogeneous.

      The homogeneous temperature distribution in the glass improves the tempering result and/or reduces the tempering time.

    • The heat transfer behaviour is more dynamic.

      The control behaviour of a convection furnaces is more dynamic and allows for operation in narrower temperature intervals.

    "Cold operation"

    In case that the glass outlet temperature has to be slightly raised such may be effected by increasing the nozzle outlet speed and/or the distance between the nozzles and pane, while the furnace temperature can remain constant.