Sensitive, water-cooled copper coils in induction furnaces are protected by a concrete wall (coil grout) beneath refractory (thermal insulation). Removal of the worn refractory material with a hammer drill is expensive and may cause damage. A tear-resistant, mica-based layer enables separation of residual (sintered) refractory from the concrete wall when pushed out and in such protects the coil, elongates service life of the refractory in the crucible and reduces maintenance costs.
Coreless induction coil furnaces are typically lined with a 10cm thick Silica-Quartz-based that, depending on the nature of the smelt, degenerates after some 200 applications (2-6 weeks with medium frequency furnaces). Removal of the old, used, mass and slag as well as the following relining of a crucible furnace with heat insulation demands caution and experience. Getting the coil grout surfaces sufficiently smooth, so that no defects in the coil wall arise, is labor- and time consuming.
Newform, a supplier of mica lining worldwide for 17 years and operating on 5 continents, provides an asbestos-free and biodegradable mica-based layer to serve as a slip-plane of used refractory during demolition. The slip-plane material consists of fiberglass-reinforced mica paper (ca. 0,3mm to 0,5mm thick) laminated with a heat-resistant binder and can be combined with 2mm Calcium-Silicate-paper when required in larger furnaces, where the wall is rather uneven.
Slip-plane Newform Combi G is a flexible, cold formed laminate comprised of phlogopite and calcium silicate fiber with a special silicon binder. The approximately 2,3 to 2,5mm thick fiber for the isolation of induction furnaces tolerates temperatures up to 1,050°C, compensates surface unevenness of the concrete wall and thus reduces cavities.
This generally 1 meter wide and odorless "wallpaper" is delivered on a 25 m long roll that is cut to the required size and mounted vertically on the coil side of the crucible furnace (Fig. 1). It is fixed at the top with glue (water- and halogen free) or tape. The mica side faces the interior of the furnace (Fig. 2). The mica coating ensures less friction and better glide between the refractory material and the coil grout.
Newform Foil PGM is about 0.3mm to 0.5mm thick, glass-fiber reinforced and preferably used for smooth interior walls of the furnace to be found usually in smaller furnaces (<2ton).
Both Mica-based slip-planes further compensate refractory movements caused by the permanently active smelt.
Highly effective while remaining safe for health and environment.
The asbestos-free insulation fibers and insulation foils for induction furnaces are based on muscovite or phlogopite mica (Fig. 3). Mica is a layered silicate with a high electrical resistance. It is heat resistant and in addition resistant to almost all media, such as alkalis, gases, oils and acids.
According to Hazardous Substances 91/155/EEC Regulation, mica has no health risks, both in storage and during installation and removal. Thus, no special measures have to be taken with respect to the removal of the insulation fibers and insulation films in induction furnaces. The material decomposes in nature into its individual components and can be safely disposed as construction debris in municipal waste landfills.
Mica slip plane for ferrous and non-ferrous foundries
Effective application for coreless induction coil furnaces:
Mica-based linings are flexible and easy to handle, and have replaced asbestos in most countries of the world paying attention to non-hazardous products to maintain the health of foundry personnel.
Glass fiber reinforced, non-toxic, delivered on roll 1m wide and 25m long, they serve as:
• Slip-Plane mica with high tensile strength
• Safety-Layer protecting the coil against refractory material movements
• Separating-Layer gas diffusion barrier
• Isolation-Layer electrical and thermal protection
Newform Combi G (Mica/High-temperature CaSi-paper)
Newform Foil PGM (Phlogopite/Muscovite mica, fiberglass-reinforced)