1. Where can I use graphite insulation?
Graphite insulation comprises graphite fibres and resins. Consequently it has similar limitations to graphite in terms of its oxidation resistance.

  • Oxygen O2 399°C
  • Water H2O 732°C
  • Carbon Dioxide CO2 1010°C

Graphite insulation finds uses in vacuum furnaces, sinterHIP furnaces, HIP, Hot presses, controlled atmosphere and non-oxidising furnaces. There are many sub-divisions within each of the above.

2. How does graphite insulation compare to a metal screen system?
Graphite insulation is substantially more efficient than a metal screen system. For example if we consider a hot zone temperature of 1000°C a graphite system will have losses of between 3.5 kW/m² of outer wall surface area; a metal system would be approximately 20% higher, at say 4.2-4.5 kW/m²
3. Is my current insulation pack efficient?
Below is a typical graph of losses per square metre versus hot zone temperature for a graphite insulation system. Note the figures are substantially the same whether one considers rigid felt or vacuum formed insulation.

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Calculate the external hot zone surface area. Read off the losses per metre square of hot zone. Multiply these two figures to give the losses at the soak temperature. If your actual losses from the furnace (excluding pumpsets etc) is significantly greater than this then your hot zone is costing you money!!

4. How do I know when to change my insulation package?
The graph discussed in the previous section can be used to compare historical data from furnace records. System deterioration can be recorded facilitating planned maintenance schedules thereby minimising unplanned downtime.
5. Can I use carbon fibre composite (CFC or C-C) in any furnace?
No. CFC is composed of elemental graphite in different phases or morphologies. Hence it suffers similar limitations in terms of oxidation resistance. Typical guidelines for untreated CFC are given in the answer to Q1. That said various treatments exist to protect CFC and improve its oxidation resistance.
6. Why should I use CFC to line the hot face of my insulation?
In furnaces subject to high gas flows and pressures during quenching, CFC significantly improves package lifetimes. The benefit in reducing downtime easily exceeds the extra capital cost of the material. Additionally the CFC protects the insulation from mechanical damage, another all-too-common cause of short lifetime for insulation packages.
7. What benefits are derived from using CFC in carrier systems?
Nowadays most furnaces operate at or near the limits of conventional alloy systems.

  • The strength of CFC remains constant up to 1800°C.
  • CFC is non distorting.
  • High strength to weight ratios; lightweight fixtures.
  • Greater furnace capacity can be achieved with judicious design.
  • Long lifetimes
8. Where else can I use CFC?
CFC has many and varied uses. It has exceptional chemical resistance leading to use in the petrochemical industry.Low thermal conductivity, high oxidation resistant grades are available for use in hot glass handling.

High friction coefficient grades for use as brake discs in aircraft, heavy goods vehicles and increasingly in the automotive industry.

It can be purified to very low ppm which is ideal for structural components in semiconductor manufacture.