3. Pre- heating : Oxygen/Acetylene is normally used to heat the end of the lance.
OPERATION
To start the operation, the end of the lance is heated to ignition temperature by means of an Oxy/ Acetylene torch. Oxygen is then fed through the lance promoting fusion at the lance point, and the reaction becomes self-supporting. The heat generated fuses the lance and concrete, the flow of slag being assisted by the velocity of the oxygen.The boring operation is not difficult, the lance being fed into the hole as boring progresses. Holes 3 meters in length can be bored horizontally, although it would be better to incline the object, if possible, to allow the slag to flow freely out. Boring vertically down can be carried out successfully, but after the first 12” the oxygen pressure has to be increased to expel the molten slag. The slag produced will be expelled from the front until you have pierced through the complete thickness. Slag can therefore be thrown several feet towards the operator.When starting, if a free edge is not available to commence boring then the technique is to pierce a hole through completely in the middle. When boring, the lance is kept aimed slightly downward and the slag kept in motion by a forwards and backwards motion. Sand placed beneath the slag will protect the floor.
SAFETY
Thermic boring should be carried out in the open air, although good ventilation could allow work inside. When working outside, the removal of flammable materials for distance of 10 meters away from the place of works is mandatory. Suitable fire precautions should be taken (Le.extinguishers). Wind direction should also be taken into account when boring. Oxygen has no smell or taste and is difficult to detect, yet in the presence of oil or grease, it can cause rapid oxidation which produces so much heat that ignition can occur Therefore oil or grease on overall or gas equipment can cause severe bums.
