Silicon carbide abrasive is mainly used for grinding which of the following materials?

A cutting process in which material is cut by a high-velocity jet of high-temperature ionised gas is known as:

Which of the following combinations of statements about hot extrusion processes is completely correct? 1. In forward hot extrusion, metal flows in the same direction as ram movement and friction exists between billet and container wall. 2. In backward hot extrusion, metal flows opposite to ram movement and billet-container friction is essentially eliminated. 3. In backward hot extrusion, extrusion pressure increases with billet length due to increased friction at container wall. 4. In hot extrusion of steels, molten glass is used as a lubricant and thermal insulator.