From the Rolls-Royce experimental archive: a quarter of a million communications from Rolls-Royce, 1906 to 1960's. Documents from the Sir Henry Royce Memorial Foundation (SHRMF).
Explanation of the process of magnetisation and the resulting self-demagnetising force.
| Identifier | ExFiles\Box 35\1\ scan 176 | |
| Date | 12th August 1921 | |
| -6- Contd. PROCESS OF MAGNETISATION AND SUBSEQUENT SELF DEMAGNETISING FORCE. To magnetise a piece of magnetic material, we subject it to a magnetic field of force due to electric currents or other magnetised matter, or both at the same time, (e.g. when an electro-magnet is used). Under this influence, lines of magnetisation are induced in the material, and free magnetism produced. The free magnetism sets up a magnetic field which is superposed upon the original field, and the resulting magnetic field is a combination of the two. The magnetic field due to the free magnetism may assist the original field at some points outside the magnetic material, and may be in opposition to it at others, but at most points inside the magnetic material, the magnetic field due to the free magnetism is in opposition to the inducing field. When the inducing field is removed, some of the magnetisation of the iron disappears, owing mainly to the opposing magnetic force due to the free magnetism. Some, however, remains and with it some free magnetism, but the state of affairs is now, that the magnetic force in the space occupied by the material, is mostly opposed to the direction of the magnetisation. Such magnetic force is called "Self demagnetising force", because it tends to de-magnetise the magnet, and is very largely the cause of loss of magnetism by magnets, when no keeper is used, especially during rough treatment. O.382 (1) 12-8-21 Contd....Y.1012 30 H | ||