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Thermic-Lance Boring


Thermic-Lance Boring is one method of boring and severing concrete, steel, cast iron and hard to clean materials without noise or vibration in a fraction of the time taken by conventional methods. It is ideal for demolition work, where noise or vibration are unacceptable, or where speed is essential particularly on reinforced concrete. The equipment is extremely simple and easy to operate, and the capital cost in comparison to drills etc. is negligible.

Process

This process was developed in France following the second world war, as a means to assist in the break up of gun emplacements, submarine pens, and other large concrete structures.

The principles of the operation are as follows, Oxygen is fed through a length of steel tube, usually " bore, to a spot on the material which has been previously been heated, and the oxygen combines with the iron to form a slag rich in iron oxides. The slag produced is very fluid which enables cutting and boring to take place. The flow of slag is assisted by the velocity of the gas and vapours expelled within it.

The lance is ignited by applying heat to the end of the tube with oxygen-acetylene equipment. With the addition of a lance packed with mild steel rods the ratio of iron to oxygen is greater thus providing sufficient heat to melt ferrous and non-ferrous materials.

The heat generated from the iron/oxygen reaction is sufficient to melt concrete, the melting point of concrete varies between 1800-2500C. The formation of iron silicate increases the fluidity of the slag produced, therefore the silicate content of the material has an appreciable effect on the speed of operation and the rate of consumption of packed lance and oxygen.

Equipment

Consists of a steel tube packed with steel rods (Aluminium or Magnesium are often added to the packing to increase the heat output) where oxygen is passed through so that when the lance is ignited it becomes a great source of heat, and forms a fluid slag which flows out of the cavity being cut.

  1. Lance holder: contains a gas control valve, steel tube also screws into holder. Cylinder's (oxygen) are connected via a length of rubber hose. Two sizes of lance are available, 3/8" and 3/4" BSP. The steel tubes are approximately 3 meters long.

  2. Oxygen supply: usually connected to three or more 240-300 ft (2500 - 3000 psi), capacity cylinders. The lance can easily be connected to an oxygen supply pipeline where available.

  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 a distance of 10 meters away from the place of work. Suitable fire precautions should also be taken (i.e. 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 overalls or gas equipment can cause severe burns.

Requirements:

  • Welding helmet/Gas cutting goggles for eye protection.
  • Flame retardant safety clothing (i.e. leather aprons, caps etc.).
  • Respiratory equipment (i.e. type 3 disposable respirators).
  • Ear protection.
  • Safety footwear.
  • Hard hats (depending where the work is being carried out.
  • Leak detection solution.
  • Flashback arrestors of the correct type.

Copyright 2001 Weldcare Ltd