* A detailed description of the kiln's construction is given in Rural Technology Guide No. 13 available from the Tropical Products Institute. (34)
1. Description
2. Manufacture
The kiln consists of two interlocking cylindrical sections (1, 2) and a conical cover (3). The cover has four equally spaced steam release ports (4) which may be closed off with plugs (5) as required. The kiln is supported on eight air inlet/outlet channels (6) arranged radially round the base. During charring, four smoke stacks (7) are fitted on to alternate air channels.
Fig. 17. The T.P.I. Steel Kiln
You will need the following tools and equipment.
1) Sheet metal bending rolls able to take sheet at least 900 mm wide and 3 mm thick.2) Angle bending rolls for bending the reinforcing angles (a skilled blacksmith should be able to make these if rolls are not available).
3) Oxy-acetylene welding/cutting equipment.
4) Engineer's large vice.
5) Hand tools, e.g. hacksaw, files, hand drill and bits.
6) Clamps for holding pieces during welding.
Also desirable but not essential:
7) Guillotine or bench shear.
8) Folding machine for sheet metal up to 3 mm thick.
9) Electric arc welding equipment. (This would speed up construction).
The materials required (with their metric measurements) are listed below. Good results may not be obtained if changes are made in dimensions or proportions of the kiln. If you wish to make major modifications to the design please approach TPI before starting work.
Construction and assembly instructions follow. Fig. 18 is a dimensional constructional drawing. Read instructions carefully before starting to construct kiln.
2.1. List of Materials
|
|
Part |
Material |
Quantity sufficient to cut: |
|
Base section
|
Top and bottom rings |
50 mm x 50 mm x 3 mm mild steel m.s. angle |
6 pieces, each 2 430 mm long |
|
Body (Construction Method 1) |
3 mm m.s. sheet (Note 1) |
3 pieces, each 2 430 mm x 900 mm |
|
|
Body (Construction Method 2) |
3 mm m.s. sheet |
3 pieces each 2 480 mm x 900 mm n |
|
|
Upper section
|
Top ring |
50 mm x 50 mm x 3 mm m.s. angle |
3 pieces, each 2 398 mm long |
|
Bottom ring |
50 mm x 50 mm x 3 mm m.s. strip |
3 pieces, each 2 398 mm long |
|
|
Body |
2 mm m.s. sheet |
3 pieces, each 2 448 mm x 900 mm |
|
|
Top cover
|
Cover sectors |
2 mm m.s. sheet |
2 pieces, cut to dimensions shown in Fig. 22 |
|
Steam ports |
50 mm x 3 mm m.s. strip |
4 pieces, each 630 mm long |
|
|
Lifting handles |
10 mm diameter m.s. rod (concrete reinforcing tar) |
4 pieces, each 500 mm long |
|
|
Steam port covers (4 per kiln)
|
Bodies |
Either 50 mm x 3 mm m.s. strip OR 140 mm diameter steel pipe. (Use pipe if available) |
4 pieces, each 440 mm long OR 4 rings, each 50 mm wide |
|
Top discs |
3 mm m.s. sheet |
4 discs, each 190 mm diameter |
|
|
Handles |
5 mm diameter steel rod (concrete reinforcing bar) |
4 pieces, each 180 mm long |
|
|
Base channels (8 per kiln)
|
Channel sections |
3 mm m.s. sheet |
8 pieces, each 500 mm x 500 mm |
|
Spigots (Note 2) |
Either 3 mm m.s. sheet OR 120 mm diameter steel pipe |
8 pieces, each 375 mm x 150 mm OR 8 pieces, each 150 mm long |
|
|
Smoke stacks (4 per kiln) |
|
Thin-walled steel pipe OR 2 mm m.s. sheet |
4 pieces, each 2 300 mm long (Note 2) OR see instructions to calculate quantities required. |
Use Corten "A" or similar weathering steel for the sheet metal parts.
Corten "A" or similar weathering steel for the sheet metal parts is recommended to give a longer kiln life. Weathering steels contain up to 3% copper, chromium, vanadium and phosphorus. They form a durable oxide layer needing no further protection. If weathering steel is not available or if the kiln is to be stored for some time before use, paint the outside of the kiln with red oxide primer or other suitable rust inhibiting paint. Once the kiln is in use, the paint will be progressively burnt off but will give some protection against external corrosion.
The steel pipe used for the smoke stacks should be of the thin walled type (2-3 mm wall thickness). The sizes shown on the drawing (Fig. 18) may be altered. Any diameter of pipe from 100 mm - 150 mm can be used. The pipes must fit properly on to the spigots in the base channel.
Fig. 18. Constructional drawing of TPI kiln
2.2. How to make the base section
Fig. 19. Kiln base section
Top and bottom rings:
1. Cut six 2 430 mm lengths of 50 mm x 50 mm x 3 mm m.s angle.2. Take three of these lengths to make the bottom ring. Bend each length, using the bending rolls or by blacksmithing, to a radius of 1 160 mm. The vertical flange must be on the INSIDE.
3. Check that the ends fit together well - if not, trim the ends with a hacksaw.
4. Tack weld into a ring.
5. Check that the ring rests flat on the ground - if not, break and re-weld or twist until it is satisfactory.
6. Complete the welds.
7. Take the remaining three lengths to make the top ring. Form them into a ring with the vertical flange on the OUTSIDE.
8. Make the top ring in the same way as the bottom ring.
2.2.1. Body (Method 1)
1. Cut three pieces of 3 mm thick m.s. sheet each 2 430 mm x 900 mm.2. Remove any sharp edges.
3. Bend the pieces to a radius of 1 160 mm, using the bending rolls.
4. Tack weld the edges of the pieces together to make a cylinder.
5. Check that the rings fit well on the cylinder and tack weld them in place at three points round the cylinder. Note that the bottom ring fits OUTSIDE the cylinder and the top ring fits INSIDE the cylinder.
6. Check that the cylinder stands upright on the ground.
7. When satisfactory, weld the seams. The side seams should be continuos welds. Any gaps will allow air to get into the kiln.
8. Weld the rings. In this case, several welds spaced round the cylinder will be adequate, as any gaps will be sealed with earth or sand when the kiln is in use.
2.2.2. Body (Method 2)
For ease of welding this alternative method can be used.
1. Cut three pieces of 3 mm thick m.s. sheet each 2 480 x 900 m.2. Remove any sharp edges.
3. Bend the pieces to a radius of 1 160 mm, using the bending rolls.
4. Tack weld the edges of the pieces together to make a cylinder. The extra length of each piece gives an overlap of 50 mm at each joint.
5. Fit the bottom ring OUTSIDE the cylinder; the top ring INSIDE.
6. Check that cylinder stands upright on the ground.
7. Weld the side joints, inside and out. The outside welds should be continuous to prevent air getting into the kiln. The inside weld may be intermittent. It is easier to weld an overlap than to weld two plates which butt together and this method also gives an allowance for errors.
8. Weld the rings finally into position as before.
2.3. How to make the upper section
Fig. 20. Kiln upper section
Top and bottom rings:
1. Cut six 2 398 mm lengths of 50 mm x 3 mm m.s. strip.2. Take three of these lengths to make the bottom ring. Bend each length to a radius of 1 145 mm.
3. Tack weld the lengths together to form a ring.
4. Lay the ring flat on the ground to check that it is true.
5. Complete the welds.
6. Take the remaining three lengths to make the top ring.
7. Bend to a radius of 1 145 mm with the vertical flange OUTSIDE.
8. Weld into a ring as described above.
2.3.1. Body
1. Cut three pieces of 2 mm m.s. sheet, each 2 448 mm long x 800 mm wide.2. Bend to a radius of 1 145 mm.
3. Make up into a cylinder as described for the base section (Body: Method 2). Note that the flat ring is welded INSIDE at BOTTOM: the angled ring is welded INSIDE at TOP.
4. Make sure at the tack welding stage that the cylinder fits on to the base section correctly.
2.4. How to make the top cover
Fig. 21. Dimensions of top cover sector (4 required to make cover)
1. Mark out 4 sector shaped pieces of 2 mm m.s. sheet to the dimensions shown in Fig. 21. Two pieces can be cut from one sheet as shown in Fig. 22.2. Cut out sectors, remove any sharp edges.
3. Mark out and cut out a 150 mm diameter hole in each sector for the steam release port.
Fig. 22. Cutting two sectors from standard sized sheet metal
2.5. How to make the smoke stacks
Base channels (8 required)
1. Cut eight pieces of 3 mm m.s. sheet, each measuring 500 mm x 500 mm.2. Bend and fold up as in the drawing (Fig. 18) into channels. If no folding machine is available the bending can be done in a bench vice. Mark the bend lines on the metal and make each bend in several stages. Do not try to form each bend to 90 in one attempt.
3. To make the spigots cut eight 150 mm lengths of 120 mm diameter steel pipe OR cut eight pieces of 3 mm mild steel, each measuring 375 mm x 150 mm and roll up into tubes of about 120 mm diameter. Make sure they are all as nearly as possible of the same diameter.
4. On each channel mark the centre of a hole 100 mm from one end.
5. Carefully cut out the holes until they are the same size as the inside diameter of the spigots.
6. Weld the spigots into position over the holes. Make sure they are upright.
Smoke stacks (4 required)
These stacks must fit over the spigots in the base channels. They must not be a tight fit. Otherwise, when the kiln is in use and hot, they may be impossible to remove. However, they should not be too loose either.
1. Simply cut four 2 300 mm lengths, if suitably sized steel pipe is available.2. If no pipe is available, make the stacks from sheet metal. They can be made in one piece if a large set of bending rolls (2 300 mm wide) is available. Otherwise, make the stacks in several sections and join together.
3. Divide the length of the stack (approximately 2 300 mm) into the smallest number of equal lengths which can be formed to the bending rolls available. Add about 50 mm to each length to give some overlap for assembling the stack sections.
Check that this dimension will still fit between the rolls, i.e. for 900 mm wide rolls, three lengths of 770 mm will give a stack height of 2 310 mm. Adding on assembly allowance of 50 mm gives: 770 + 50 = 820 mm section length.
4. Cut the required number of pieces from 2 mm m.s. sheet.
5. Form into tubes. These tubes should be of slightly different diameters so that the top section is smallest and fits tightly into the section below, which, in turn, will fit tightly into the next section down, and so on. The bottom section should fit well, but not tightly, on to the spigots in the base channels. Make sure that all the stacks will fit all the channels so that the stacks can be easily changed round when the kiln is in use.
6. Assemble the tube sections, pushing each section about 50 mm into the section below.
Make sure that the assembled stack is reasonably straight and will stand upright on the channel sections.
7. Weld the stacks together but do NOT weld the stacks onto the channels.
