We have constructed a Hoffman kiln in Uganda this year, and now share the construction experience here. The brick production line capacity is 25,000,000pcs/year.
I. Foundation: construction must start from the deepest part and from bottom to top part. The earliest construction part is main flue. Foundation should constructed on the original ground (soil), it need remove the soil to original ground if had partially soft soil locally, once soft soil still available 2M under ground, it could use stone for pad to -0.69 than uniform processing, soil dry density not less than 1.5g/cm, kiln inner foundation should earth cutting 0.4m of soil surface layer then use 3:7 spodosol for tamp to -0.15, and then use fine dry soil powder fill the gap after roll paving dry bricks.
II. Kiln body masonry
1.Wall: All wall should keep mortar joint filled, slurry brickwork mortar joint usually is not less than 3mm, sand slurry brickwork mortar joint is usually not more than 7mm.
2. Sloping core: according to specified gradient in the drawing construction, and use #75 mortar masonry.
3. Interior buttress: sloping core and interior buttress should be specified bricking brickwork, and according to masonry requirement add masonry, buttress height up to flue base plane, is 2050mm
III. Arch masonry
1. Kiln inner arch should use high class brick (grade over #150) for masonry; it is best using shale bricks or gangue bricks. It must use shale bricks or refractory bricks for masonry if it was used to firing shale brick or gangue bricks future, because clay brick refractoriness can not meet shale brick firing temperature.
2. Before construct the arch, it needs battening nail cotton rope on the center arch, each layer construction must correction by cotton rope, make each layer bricks must parallel circle rays.
3. Arch closing bricks masonry based on 3/4, then using wooden hamper knock them down slowly.
4. Afther finished arch construction, Intensify its gap by inserting tiles, tile inserting should use wooden hamper knock it down.
5. After finished arch construction, it need fill soil for buttress and arch two sides, soil filling height up to 2M then disassemble the arch mould.
6. Kiln door arch support installation should after the kiln main arch mould support installation, kiln door arch should be closed to kiln main arch mould, construct the kiln door arch then main arch, main arch bricks should press onto the door arch bricks.
7. Filling soil should use a little dry fine soil but not too dry, the moisture should be controlled between 10~2%, compact the filling soil per 20 Kg.
IV. Expansion gap
Expansion gap is lock mouth type, in not allowed any sundries into gap, open side fill asbestos cord.
V. Duty room onto the kiln: Duty room door direction should toward to kiln length so that is convenient to watch the kiln upside condition. Duty room length: outdoor 2.2M, indoor can be
VI. Kiln brushing: after construction acceptance, use slurry fine brushing the inner kiln room, the slurry thickness is not more than 3mm, slurry made from sieving clay with saline. Saline ration is: water :salt =10:3, it also can use refractory coating spraying, each kiln room consumption is 90kg.