|Improved Cookstoves a Training Manual (Peace Corps, 1984)|
|Metal stove construction|
Use of a template or pattern when cutting stove parts helps ensure dimensional accuracy and speeds production. The template can be drawn on paper at first. A more permanent copy can be cut out of sheet metal. To prevent its loss through use as a stove itself, weld metal bars to it lengthwise. For a spherical or cylindrical pot, template design is straightforward. Prepare such a template following the steps below:
1. The length of the template is given by
L = C + G + S+ T
C is determined by the measurement of the pot around its widest circumference. G is determined by the desired pot-to-wall gap, G = 2 (gap). For a gap of 4 mm, G = 2.5 cm; for 6 mm, G = 3.8 cm; for 8 mm, G = 5.0 cm. A gap of four to six mm is recommended. Increase it only if excessive smoke comes out the door or the heating rate is too slow. S is determined by the amount of overlap in the seam. It is preferable to weld the stove together end to end to prevent the creation of a small vertical channel by which the heat can by-pass the pot. If the seam is crosswelded or folded, typical values for S will be 1 cm. T is determined by the thickness of the metal Used. One typically uses 1 mm (T=0.3 cm) or 1.5 mm (T=0.47 cm) thick metal. Thus, for a 90 cm circumference pot, a 4 mm gap, an end to end welded seam, and 1 mm thick metal we find:
L = 90+ 2.5+0.3 = 92.8 cm
2. For spherical pots, template height H is determined by the sum of the airhold height (A), the grate-to-pot height (P) and the amount necessary to extend a few centimeters above the pot's maximum circumference when in place on the stove (h).
H = A+ P + h
Typical values for A are 3 cm and for P. 0.4 of the pot diameter. For cylindrical pots the height h is typically 5 cm to 10 cm. The best height h is determined more precisely by comparing the increased efficiency and reduced fuel use caused by the additional height versus the increased cost of the extra metal. Additional height can also be provided at the top and bottom of the template, typically 1 cm each, to allow the edge to be folded over to protect against sharp edges and increase the stove's rigidity and strength.
3. Stoves usually have four airholes, about 3 cm by 3 cm each (A=3 cm). Space them symmetrically, but far enough away from the door and the seams to avoid weakening the stove. Cut the airholes on two sides only so that when bent upward and inward they can act as supports for the grate. For larger pots or soft ground soil where the stove will sink in the ground, larger airholes may be necessary. Alternatively, for soft soil conditions a ring-shaped platform can be cut and attached to the stove bottom if necessary and cost effective.
4. Space pot supports evenly around the stove, but offset them from the damper/fuel opening and air vents if appropriate so that the stove is not weakened. The height Z for the pot supports above the top of the airholes (where the grate will rest) is given by the sum of the fuel thickness (4 cm) P. the distance from the bottom of the pot to the top of the fuel (W) (3-5 cm for boiling position and 8-10 cm for simmer position), the distance that the air hole flaps fold upward A (3 cm). (Note: There are two pot positions, simmer and boil.) Therefore:
Z = F+ W+ A
5. The door size is somewhat arbitrary and is determined by the locally available wood size. Typical sizes for a 90 cm circumference pot are 12 cm wide by 9 cm high. Place the bottom of the door at the grate position-the top of the airholes. Make the top of the door several centimeters below the bottom of the pot so that the hot gasses are guided up around the pot rather than out the door. If necessary, decrease the door height to ensure that it is below the bottom of the pot.
6. The grate is a circle of sheet metal cut to fit snugly into the finished cylinder. Punch the center diameter with a 30 percent hole density of 1 cm holes.
To produce stoves in quantity:
1. Trace the template on a sheet of metal as many times as desired
or as space permits.
2. Cut each form out in outline. Cut the door, pot support holes and strips for the airholes.
3. Roll the metal into a cylinder. The cylinder should be as straight and smooth as possible.
4. Cut out other components such as pot supports and stabilizers and put them into place.
5. Cut the grate and punch the holes in it.
6. Weld the stove together. Weld pot supports into place. Alternatively, fold all seams together.
7. Place the grate in the stove, fold the tabs from the airholes inward and upward.
8. Paint it with heat resistant paint where available.