Half-Web (or Partial) Cutting Cycle

The HG shields that have not yet advanced will be triggered as the shearer leaves the HG Cleanup area and goes back into the partially pushed area on its way to the TG. This can be seen in the picture below. (Notice that the HG shields have not yet begun to push.)

Half-Web Cycle – Step 3 – Cutting Head to Tail

As the shearer continues to move toward the TG, the conveyor will then start pushing to the stroke set by SRB parameter “H->T Push Stroke”, usually 98% or higher.

SRB Parameter “H->T Push Stroke”

The picture below shows the shearer in mid face with a conveyor push following it towards the tailgate.

Half-Web Cycle – Step 4 – Still Cutting Head to Tail

The full push will follow the shearer all the way to the TG until the entire conveyor is pushed. The picture below shows the longwall state when the shearer reaches the tailgate.

Half-Web Cycle – Step 5 – Shearer in Tailgate

The coal face has two snakes but the shields are straight and the conveyor is completely pushed on the entire face. The longwall is in the same state as the Initial Position picture shown previously. The system is ready for the shearer to go back to the headgate and repeat the entire cycle.

Shearer Cleanup Problems

If the shearer does not clean-up sufficiently to allow the shields to push to a full 100% stroke, the parameter “H->T Push Stroke” can be set to a lower value, such as 90%. © Caterpillar 88

In the above description, the phrase “completely push” or “full push” refers to this value. The tailgate pushes to this value as the shearer is cutting to the head, and the rest of the face will push to this value on the head to tail pass.

Full Web Cutting (Unidirectional)

Full web cutting starts with the longwall in the state shown in the following picture:

Full-Web Cycle – Initial Position

On the tail to head pass, shields will be advanced. The conveyor will only be pushed in the tailgate area, for a distance determined by SRB parameter “Snake Push”. In this area, both top and bottom coal must be cut to allow the shields to advance and the pan to be pushed.

SRB Parameter "Snake Push”

The picture below shows the shearer leaving the TG and the shields starting to pull.

Full-Web Cycle – Step 1 – Cutting Tail to Head

When the shearer has traveled far enough and enough shields have advanced, the conveyor will be pushed completely in the tailgate. This allows the shearer to snake back in to a “full-web” cut when it re-enters the tailgate on the next pass. SRB parameter “T->H Push Stroke” is set to 0 to prevent the rest of the shields from pushing.

SRB Parameters “T->H Push Stroke”

After the shearer leaves the tailgate area and cuts both top and bottom coal for the distance set by “Snake Push”, there are two cutting options: both top and bottom coal can be cut or the trailing drum can be raised from the floor to leave a bench of coal. The top coal must be cut so the shields can advance. One advantage to leaving a bench is that the shearer can be operated from the headgate side, keeping operators away from the dust. With either option, the shield movements are the same.