Archive for the ‘welding’ Tag

This week I have been mostly making …. fireboxes.   1 comment

Heavy firebricks are laid on the concrete floor to protect it

Heavy firebricks are laid on the concrete floor to protect it

The wood-fired kiln I am building has a lower and an upper half. The lower half is where the wood is burnt to generate the heat needed to fire the clay pottery. It is built from heavy fire-bricks which, although they need to be heat tolerant do not need to be particularly good insulators. They are cheaper and more robust than the High Thermal Insulation  (HTI) bricks which will be used for the upper half. The kiln has two fireboxes Рeach one the equivalent of a hearth in a domestic fire.  They are located at the front and back of the kiln with one of them being stoked from the left hand side of the kiln and one from the right.

The first course of bricks protects the concrete base from extremes of heat.

 

 

A hole is drilled into the concrete where each set of 4 bricks meet.

A hole is drilled into the concrete where each set of 4 bricks meet.

While laying the floor bricks holes are drilled in the foundation slab to allow steam to escape easily.

 

 

 

 

 

 

 

Firebox course 1. This is the trickiest course to lay as the bricks are not all exactly the same length and the side walls have gaps in them.

Firebox course 1. This is the trickiest course to lay as the bricks are not all exactly the same length and the side walls have gaps in them.

The first course of bricks must be carefully planned to make sure the corners are square. Lots of measuring and set square usage. It incorporates supports for the ash grates which hold the embers from the burning wood until they are thoroughly burnt.

 

 

 

 

 

 

The fire bars on the left support the long billets of wood used to fire the kiln. As they burn they break up into embers which fall onto the ash grates below.

The fire bars on the left support the long billets of wood used to fire the kiln. As they burn they break up into embers which fall onto the ash grates below.

The ash grates and the fire bars (brick course 4) are made from mild steel angle iron and weldmesh. I measured and cut the pieces of metal and a friend in the village welded them together.

 

 

 

 

 

 

Fire boxes second course. The outer bricks are laid flat whereas the inner bricks are laid on their sides.

Fire boxes second course. The outer bricks are laid flat whereas the inner bricks are laid on their sides.

The second and third courses are pretty straight forward except that a number of bricks must be cut. For the heavy bricks I used an angle grinder and for the HTI’s I used an old panel saw which was no longer sharp enough for wood.

 

 

 

 

 

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Fire boxes third course. Ash grates in position.

No mortar is used. The slight unevenness of size in the bricks is accommodated by adding a thin layer of fire-clay slip mixed with sand between courses.

 

 

 

 

 

The fourth course supports the fire bars

The fourth course supports the fire bars

The fourth course supports the fire bars. The inner wall, just below the fire bars is partly made from HTI brick as it is easier to cut and is not subject to much wear and tear in this location.

 

 

 

 

 

 

Fire box course 5. The fire bars are not in position as the weight of the sixth course bricks is needed to prevent the central support bricks being pushed downwards by the unevenweight of a single set of fire bars on one side.

Fire box course 5. The fire bars are not in position as the weight of the sixth course bricks is needed to prevent the central support bricks being pushed downwards by the uneven weight of a single set of fire bars on one side.

Fifth course.

 

 

 

 

 

 

 

 

Fire box course 6

Fire box course 6 with fire bars in position.

Sixth course.

 

 

 

 

 

 

 

Fire box course seven. This serves as the foundation for the ware chamber.

Fire box course seven. This serves as the foundation for the ware chamber.

Seventh and final firebox course. Great care is taken to make sure the brickwork is level from front to back and side to side.

 

 

 

 

 

 

The fire box roof. Kiln shelves laid on ceramic fibre paper. The gaps at each end are where the heat from the fires will rise into the ware chamber.

The fire box roof. Kiln shelves laid on ceramic fibre paper. The gaps at each end are where the heat from the fires will rise into the ware chamber.

The fire-box roof, which is also the ware chamber floor is made from 25mm thick kiln shelves laid on a couple of layers of ceramic fibre paper (which is more like felt than paper) This provides a good seal between the upper and lower parts of the kiln and evens out the minor unevenness in the final course of firebox bricks.

 

The next stage is to build the ware chamber – the place where the pots to be fired are placed – out of HTI bricks.