Wednesday, 13 January 2016

Baffles in Side-Fired Kilns

The object of using baffles in side fired kilns is to keep the direct radiant heat from the edges of the piece(s) being fired.  If the edges receive direct radiant heat, they increase in temperature more rapidly than the interior of the piece.  This means the edges become sticky and seal before upper layer of the interior begins to conform to the lower layer.  This seals air into the piece.

The materials and placing of the baffles is important.

Baffles can be made from almost anything that can withstand the heat of the firing.  There is an argument that light-weight materials such as fibre board, vermiculite board, or fibre paper should be used to reduce electricity costs.  Heavier pieces such as brick and kiln shelf pieces require more energy to heat them up.  They then of course, store heat that needs to be released on cooling, so slowing the cool down and increasing the risk of devitrification.

The placing of the baffles is important too.  Baffles protect the glass edges from radiant heat until the general heat of the kiln can come into effect over the whole of the piece.  This means that if the baffles are placed against the elements at shelf level, the element above can still give radiant heat to the edges.  Therefore, baffles placed near the glass are better.  They protect the edges from radiant heat at whatever level the side elements are placed.  This is more important for pieces that are further from the edge of the shelf, than those nearer the edge, as the centrally placed glass can “see” the radiant heat from the upper elements.