Abstract: A method for breaking a hard compact material such as rock or concrete. The method includes drilling a hole into the material, gripping a portion of the wall of the hole by applying a radially outwardly directed force thereto, and applying an axially outwardly directed force to the gripped region in order to cause cracks to arise in the wall of the hole. One of the forces is generated by means of sequentially repeated axially directed impacts. The apparatus for carrying out the method comprises a gripping means and a wedge means slidable relative to the gripping means. The gripping means and the wedge means have cooperating wedge surfaces. A rear extension member having a shoulder is attached to the wedge means. A hammer piston reciprocable in the apparatus housing delivers sequentially repeated axially directed impacts upon the shoulder.

Abstract: A process for the production of a carbon article is provided by which a synthetic organic fibre which is capable of conversion to high strength, high modulus carbon fibre and which has been partially so converted is impregnated with a synthetic organic resin and the resin/fibre impregnate subject to a carbonization treatment in an inert atmosphere at a temperature of at least 1000.degree. C. Preferably the fibre is polyacrylonitrile which has been heated at a temperature of 200.degree. to 250.degree. C in an oxidizing atmosphere. The resin may be a phenol/formaldehyde resin, a polyvinylidene chloride resin or a polyfurfuryl alcohol resin. The process is particularly suited to the production of carbon articles in the form of fibre or rod by drawing the fibre first through the resin to impregnate it and then through a die to form the resin/fibre impregnate.