Paragon Xpress Kilns For Annealing, Art Clay, Beads, Ceramics, Dichroics, Enamelling, Fusing, Glass, Heat Treating, Lost Wax Burnout, Silver Clays, PMC, Porcelain, Pottery, And Raku.

Fireplace, forge, and furnace bricks are very hard, tough, and solid. Often, they're not cemented together so, if you have a conventional fireplace at home, remove a brick and you'll notice a few hair line cracks and missing corners, chips, and flakes. Some might have cracked in half, but they still function. To retain heat, the bricks are dense and heavy.

A kiln made using these would be very heavy and need a much larger and stronger metal frame and case. They're hard to cut, so making joints and element grooves, and using element pins, is almost impossible. The kiln would be more expensive to make and transport and, once in your studio, would be hard to move: try lifting your night-storage heater. And a 500mm square kiln lid made from 24 bricks would probably collapse.

Kiln bricks look like fine sponge. They're light, fragile, and are made to insulate, not store heat. They heat and cool quickly so that the programmer can control the temperature. They can be cut, drilled, and made with joints and element grooves.

Unlike a fireplace, forge, or furnace, kilns are usually used for ramp-hold firings with multiple segments, so are continually cycling through heating and cooling. As the temperature changes, the bricks expand and contract and soon develop fine cracks. If the interior of a kiln expands by about 3mm per 500mm, then contracts, then expands, something has to give.

Even assembly stresses or small changes in temperature can cause fine cracks during manufacture, factory testing, shipping, or first use. These are normal and won't affect the functionality. And the kiln won't fall apart because the bricks are held together within a metal frame. Replacing a whole set of bricks is pointless: the new set will probably develop a tiny crack immediately. To quote Paragon: hairline cracks can appear at any time, even in a new kiln.

The bricks are made by firing a clay-based composition in a kiln. They usually contain silica and alumina as the primary raw material mixed with other materials. The maximum service temperature increases with increasing alumina content.

Kanthal A1 And APM Element Wire.

Most kilns use Kanthal A1 element wire. However, for continual high-temperature high-precision professional use, some use Kanthal APM. Kanthal APM has slow ageing and a low change in resistance over time. It has excellent surface oxide properties, which gives good protection in corrosive atmospheres as well as in atmospheres with high carbon potential, and no scaling.

Kanthal A1 is a ferritic iron-chromium-aluminium alloy for use at temperatures up to about 1400°C. The alloy has a high resistivity and very good oxidation resistance. Kanthal APM is an advanced powder metallurgical, dispersion strengthened, ferritic iron-chromium-aluminium alloy for use at temperatures up to about 1250°C. The alloy forms an excellent, non-scaling surface oxide, which gives good protection in most furnace environments.

Kiln elements are usually coils. Coiling reduces the apparent length of the element. For example: a coil containing 3000mm of wire can make an element as short as 200mm. That's quite a space saving and this allows the effects of the wire to be concentrated in a smaller area and building kilns that don't fill a room.
Generally, the thinner or longer the wire is, the higher the resistance. Similarly, the shorter and thicker the wire is, the lower the resistance. The resistance causes heat to be generated and the wire will glow red hot.

During the first firings, an aluminum oxide layer is built-up on the surface, which helps protect it in subsequent firings. This is why users of new kilns are told to do an initial empty-kiln firing to season the elements. However, the elements are quite soft at ceramic-firing temperature and, if not well supported, can sag and distort during firing. Which is why Paragon's elements are held in place in dropped recessed grooves.

If an element eventually fails and breaks, it's difficult to repair without specialised equipment.

Paragon Kilns, Furnaces, and Ovens For Annealing, Beads, Ceramics, Enamels, Glass, Jewellery, Knife Making, Lost Wax, Silver Clays, Heat Treating, Lampwork, Porcelain, And Vitrigraph.