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).
The merits of different varnishes for field coils and design options for armature shafts.
| Identifier | ExFiles\Box 181\M7\ img011 | |
| Date | 12th August 1912 guessed | |
| -2- Messrs Royce Ld., (contd) field magnets, I think it is absolutely necessary that sufficie- nt capacity of vacuum drying apparatus should be installed, and I think that varnish with a linseed oil base quite unsuitable for impregnating field coils, and that without delay we ought to find out the best system of impregnating these coils with a hot bitumen compound, and if a plant is required for this process it should be procured at once, and in the meantime for these coils I think it would be wise to use a varnish with a spirit as a solvent which can easily be driven off by means of heat whereas varnish with a linseed oil base requires oxidisation which seems impossible to obtain in a deep field magnet. Referring to the armature varnish it seems here that the present system of using a varnish with a linseed oil base is quite reasonable. The better insulating results obtained from this varnish and the possibility of oxidising the varnish would make one conclude that this system is the best one that is known. Referring to the armature shaft & core it seems as though we had to choose between 2 systems, the first one would be an enormously large shaft castellated so as to form about 16 keys (which need only be shallow) about half space & half keys, the armature plates being centred at the top of the keys, and the end plates being centred by their bores i.e. at the bot- tom of the keys, the reason for this arrangement being obvious. The only objection that can be raised to this arrangement is that it is impossible to change a shaft without stripping the armature otherwise this is undoubtedly the least expensive plan that can be adopted with security, and I am strongly in favour | ||