Technical Paper
www.ireng.org
Achieving high value in kiln insulation and furnace refractories
Steve Chernack, Manager – Engineering Accounts, Morgan Advanced Materials (contributing: Chris Johnson, Applications Engineering and Drafting Services Manager; Roger Patrick, Product Manager - Fired Refractory Shapes; Randy Bishop, Product Manager - Electrical Carbon; Dr. Michael Rozumek, R&D Director)
In any manufacturing process involving a kiln or furnace, the need for consistency is key to ensuring ‘right first time’ components – whether this applies to processing temperatures, atmospheric content, or the overall firing process.
While the quality of the kiln and furnace infrastructure itself is of course crucial to achieving this, what is no less important is the correct selection and use of refractory products involved in the process, whether these be high temperature insulation systems, kiln cars and furniture, or fired refractory shapes.
The importance of correct material selection
In all of these areas, poor product selection or incorrect matching of the material to the application has the potential to result in inefficient or ineffective processing, wasted energy and process time, and possibly even reputational damage if a crucial order deadline is missed due to an unresolved processing issue. Above all, unnecessary downtime while failed materials, such as insulation systems, are replaced, cannot be countenanced. Put simply, best practice in material selection, system design and installation will go a long way towards achieving optimum production efficiency and system uptime based on the amount of cycles that can be undertaken before these systems need replacing
It is inevitable that products will at some stage need to be replaced and, perhaps for that reason, the focus among many individuals with responsibility for specifying or purchasing kiln insulation and furnace refractories has traditionally been on achieving the lowest unit cost. However, as with so many things, the best price does not necessarily mean best value and the focus should always be on finding the best solution rather than the cheapest product which will almost inevitably require more frequent replacement. With the cost differential between, for example, a lower-grade insulation system and a premium product paling into insignificance compared with the cost of downtime while these systems are replaced, it is in an area where even a modest time investment or investigation of total life cycle costs can pay major dividends.
Achieving the best insulation system
Insulation systems are integral to ensuring processing temperatures are not just high enough but consistent throughout the kiln or furnace and help to ensure uniformity of parts. Minimising the loss of heat through the sides and top of the kiln or furnace is not just key for processing, though – it also
contributes towards operator safety as external surfaces are not so hot, while energy costs are reduced too as more heat is retained inside. While natural gas costs are relatively low currently, it cannot be assumed that this will always be the case, and many companies are in any case taking commendable steps towards reducing their carbon footprint on a voluntary basis, irrespective of any legislative compulsion to do so.
Insulation systems need not just to offer minimal heat transfer. There may also be a requirement for thermal shock resistance, in applications where rapid heating or cooling are employed. Resistance to corrosion is also often a key attribute depending on the application as are physical strength and flexibility.
Depending on the process, a choice can be made between high temperature insulation wools such as refractory ceramic fibers (Kaowool® or Cerafiber®), alkaline earth silicate fibers (Superwool®, and polycrystalline fibres or combinations of high temperature fibers with insulating firebricks or special duty castables (Kao-Tab®, Kao-Tuff®)). Whatever solution is considered, specifiers and purchasers should take steps to satisfy themselves about the quality and consistency of the materials used, and the integrity of the manufacturing process of these products. Inconsistency in either of these areas will likely result in substandard performance, with more frequent replacement also necessary. Rather than simply buying on price, therefore, investigations should first be made to ascertain how suppliers’ processes are benchmarked between different facilities, as well as establishing the existence of quality plans and what use is being made of comparative testing methods. If the manufacture of the lining material can be proven to be consistent, then its performance in key areas such as heat transfer can be accurately predicted and relied upon – vital where accurate temperature control is needed.
For processors seeking to reduce downtime even further, the use of a lining material suitable for a higher temperature than the actual process will employ is more and more frequently being considered. The latest polycrystalline fibres, for example, are manufactured by a chemical process rather than the melt and attenuation process more commonly used for other lining materials. However, the chemical and thermal stability of polycrystalline systems mean they can, for example, offer extended service life – up to 10 years is not uncommon – compared with refractory ceramic fibres, while also delivering better performance in areas such as heat transfer.
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ENGINEER THE REFRACTORIES
May 2016 Issue
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