Baking furnaces

Furnaces

Baking furnaces are usually oil or gas-fired kilns, single-chamber furnaces or tunnel kilns. Small-dimensioned parts are also baked in electrically heated muffle, pit or push-rod furnaces. In ring furnaces and single chamber furnaces, it is possible to place the stock into steel containers (saggers), embed them in the packing material, and arrange these saggers in the chamber instead of placing pieces directly into the brick boxes of the furnace chamber. This handling is preferred in the case of shapes of different dimensions, as it allows a more advantageous usage of space. Also the loading and unloading procedures can be automated.

Ring furnace

A ring furnace is a kiln with 20 or more chambers interconnected forming a ring and having the advantage of the most efficient utilisation of the heating energy as the chamber just being fired preheats the other unheated chambers with gaseous pyrolysis products from the binder. At the same time, the fresh air for the burners is passed over the already fired chambers, thus cooling them down and warming itself by heat exchange. One cycle for one chamber with a final temperature of 1000 C and an average heating rate of two degrees per hour takes three weeks. The burner device is then transferred to the adjacent chamber, so that a kiln of this type can be operated continuously for several years. The major disadvantage of a ring furnace is limited temperature control. Due to the coupling of the chambers, temperature changes have a marked influence on the entire furnace.

Loading – Ring Furnace

• Furnace Cell Bottoms are covered with a sheet of aluminium coated paper to prevent pitch and packing media from sticking

• Furnace cell bottoms are covered with a specified amount of packing meida

• Stock is loaded vertically in one or two layers, in single or multiple rows

• Spacings are specified for: stock-to-end, stock-to-side, and stock-to-stock distances.

• A minimum of 250mm of top is required

• A layer of refractory bricks are placed on top of media to reduce oxidation and blowing into flue ports .

Single-chamber furnace

Pit furnaces may be rate-controlled with variable temperature programs, but they are not that economic in utilizing the heat energy. Therefore, they are mostly used for smaller lot-sizes requiring variable heating programs. A car-bottom baking furnace is a special type of a single-chamber furnace. Here, a flat-bed car with containers is removed from the furnace after baking and a newly prepared car is immediately brought in. Possible automation also offers a considerable advantage. Electrically heated furnaces for small-dimensioned parts are operated in the same way. Push-rod and conveying-belt furnaces, which are used for the manufacture of parts pressed to size, or to near net shape, are operated in an inert atmosphere. Therefore, the embedding of the parts in the packing media may be omitted.