Some Interesting Points in Valve Design.
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T"manufaclure of valves for the petrol engines employed in commercial vehicles is so important that it is becoming almost a specialized trade. Many new processes have been evolved for producing valves which will stand up to long periods • of arduous service without warping, cracking or burning, and a few notes' on how the manufacture of nch valves is carried out by one well-known producer, the Crypt.) Car and Cycle Cc., 14, Mortimer Street, ,London, W.1, may he of interest.
This -firm began to specialize in the manufacture of valves so long ago as 1904, when a specially deSigned forging and finishing plant was laid down, and now the whole works is concentrated on the manufacture of this particular detail of the engine. Valves have been supplied in large numbers to many British makers of commercial vehicles, and at the present time there are orders in hand from vehicle manufacturers who have actually been taking supplies from these works since manufacture was commenced.
Early in 1924 an entirely new forging process, invented by a clever Swiss engineer, was investigated and turned out to be so satisfactory that the firm bought the sole British rights of the patent. To-day, all Crypto valves are made by the new patent process, and it is only possible to believe that forgings can he produced so exact to size and
C48 with such a clean finish by an actual examination of them.
There are two important advantages resulting from the process employed. It enables the production of forgings in which the heads and necks of the valves are tougher, whilst the stems are stiffer and harder than in Valves produced in the ordinary manner. This enables them to stand up to their work without fracture and burning, whilst the harder stems withstand the wear of the guides.
The second advantage is -that the
valves arc extremely close to the finished size, and, apart from the saving
in machining costs which is thus effected, the tough skin, which is reengnized as being the best part of the metal, is not all removed. In finishing valves made by this process, grinding is almost universally adopted, and there is no need to machine under the head. ,The radius at this point can be left with its die finish.
The special nickel steel usually employed contains 3.05 to 3.10 per cent. of nickel, this steel being specially hardened and tempered after machining, but before the final grinding.
Another valve material which is proving very popular is 12.14 per Cent. chromium steel, usually known as stain-. less. It gives uniformly good service and excellent results with the process of forging to which we have already referred:
Quantities of casehardened valves have also been supplied recently to concerns chiming public-service vehicles, whilst for particularly hard service a special alloy valve steel known as Valkroin is employed.
The great importance of utilizing high-class valves for the engines of all types of commercial vehicle -should be obvious. No other power units have to withstand such long and arduous periods of service at a high speed, and failure may wall mean a most serious loss of business, Quito apart from the actual cost of the repairs executed.