Mining and soil seasoning:

No particular mining technique is required for VSBK, as long the mining area is free of stones and, in particular, free of lime stones/lime noodle (lime blowing). However, not every soil that is suitable for brick-making suits VSBK. In general, soil with a low vitrification temperature (low lime content) is easier for VSBK operation. To achieve high brick quality, mined soil should be seasoned for at least 30 days.

Mixing, pugging, moulding and drying

Seasoned soil is mixed with fine coal dust in a specific ratio (mechanic or hand dosing and mixing are possible) and pugged through special pugmil. Bricks are moulded manually or mechanically with an extruder or other brick moulding machines. The moulded bricks are then dried following specific drying methods, until the humidity is below 3% by weight of dry green bricks.

Loading and fire control

Dried bricks are transported on the loading platform via a ramp, a lift or ideally horizontally via a slope side bridge. The bricks stored as buffer on the firing platform are loaded into the top of the shaft every two hours, following a specific loading pattern. After the new bricks are loaded, the shafts are covered by lids to assure good combustion and to protect the firing crew from exhaust gases. While the major part of the fuel has already been mixed as coal powder into the bricks, the fire position and the exact temperature is controlled by varying the quantity of coal lumps loaded between the bricks.

Unloading

The bricks are supported by removable steel bars that are usually removed in every two hours for unloading fired bricks. During the unloading, the screw jack releases the support bars by pressing the unloading trolley against the lowest brick layer, lifting the entire load by a few millimetres. After the support bars are removed, all the loaded brick (including the fire) are slowly lowered by the screw jack or hydraulic cylinders by four brick layers before the steel bars are put back in position. The bricks above the steel bars rest in a stable position and the separated four lowest brick layers are lowered further to the bottom of the unloading tunnel, where they are pushed on the rail trolley to the cooling chambers.

The unloading procedure takes about 15 minutes per shaft and can be done by two fire-masters (one fire-master with a hydraulic unloading mechanism). Loading and unloading is repeated every two hours, around the clock and seven days a week. Several firing crews share the work in 2-3 shifts per day. The number of fire masters per shift depends on the level of mechanisation and the workflow management. A four shaft VSBK of the Kabul design requires at least seven fire-masters per shift. Lifting equipment and hydraulic unloading equipment reduce the number of firing crew needed, particularly during the night shift.