The Latest Process and Appliance Developments
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External Broaching, the Centreless Principle in Internal Grinding, the Use of Cemented Carbide, Forging in Solid Dies, and Nickel-clad Steel are Among Important Recent Advances in Motor Engineering
1V4ETALLURGICAL discoveries range LV1 in their effect and application from the finished motor to the repair shop and the production plant. In this article are summarized a few recent developments with more than a little bearing on motor manufacture and maintenance.
A process of special value and new development is external broaching. Particularly is this of interest to the commercial-motor industry, for the reason that it has been chiefly applied to the machining of large engine cylinder blocks, small shackle pins, etc. These parts possess flat and uneven surfaces, and external broaching takes the place of different types of milling.
The new machining process has been made possible only by the production and design of new machinery, both hydraulic antrmechanical, for vertical,
rotary or horizontal work. Furthermore, the broaches themselves are specially designed for the work, and are often sectionally constructed to allow of inexpensive replacement.
External Broaching.
For the benefit of the uninitiated, a broach is a tapered tool which is pulled through a cylindrical hole in a part to finish or enlarge it. The application of broaching to external cylindrical surfaces is new, and means that the tool is itself hollow, and the interior is pulled over the exterior of the cylindrical part to finish it as required.
Another process of importance is the application of the centreless principle to internal grinding in a newly invented machine tool. By the aid of this machine, it becomes possible to grind tapered, straight, interrupted, continuous, or blind holes in parts with external surfaces of a finished cylindrical character, ranging from quite small holes up to those 3 ins, in diameter and 3 ins, in length.
An excellent finish is given, and the process is adaptable to and economical for both quantity output and small lots. In one works, over 200 different parts, in which are included both shafts and nuts, have been ground in this manner, and considerable economy in working time is claimed as a result.
The use of cemented carbide (tungsten carbide, principally) has been greatly developed. Among uses of interest to the commercial-motor industry are valve stems and seats, nozzles, gauges and lathe centres. A new type of cemented carbide has been produced for use on cast-iron, non-ferrous metals and other materials of a non-metallic
character. This substance is said to give better performance.
Every development in testing machines and methods is directly bene
ficial to the motor industry. It is worthy of note that a new appliance has been invented for testing, among other things, the toughness of hardened steels, particularly steels employed in the manufacture of dies and other tools.
Known as a torsion impact tester, this machine serves the useful purpose of indicating the most suitable type of heat-treatment to which steels high in carbon should be subjected. So far. its application has been confined to the case-hardening steels, the cast-irons, etc., but there is no reason why it should not ultimately be used for all those steels and the like, the testing of which by the notched-bar method is not satisfactory, owing to slight variations in the form of the notch.
Forging of metals is an operation of great importance, and an improvement of recent date lies in the employment
of solid, instead of split, dies. The use of these dies is necessarily restricted to simple forms, possessing no grooved part. The dies, before contact with the work during forging, have to be freed from cooling water by means of compressed air, as otherwise the formation of a small steam pocket might occur, with consequent detrimental effects on the forging finally produced.
Nickel-clad Steel.
An interesting new development is nickel-clad steel, American in origin. To make this material, large blocks of the steel are rolled down to plates 2+ ins, thick, which are pared to dimensions and cleaned by sandblasting. The thickness of the nickel is approximately one-ninth that of the steel.
Two nickel-clad plates are rolled together, arranged thus: steel plate, nickel plate, a parting mixture, nickel plate and steel plate. The two plates of steel project beyond the nickel plates, and the entire collection of sheets is closed by welding across the edges of the steel plates. The first rolling unites the nickel and the steel. On conclusion of the rolling process, the edges of the sheet are pared, and the two united plates parted.
America has developed a process of giving a mirror finish to the surfaces of cylinder bores. It is claimed that this process enables the surfaces to resist the hammering action of piston rings, and is beneficial in increasing the resistance to corrosion. As evidence, a test is detailed of an oil engine, in which honed cylinders were fully run-in after 45 hours of continuous running, as against 200 hours for cylinders with a finish produced by the aid of reamers. A considerable diminution in cylinder wear was also reported, and oil consumption was lower. The finish is produced by internal honing.
New Liquid Carburizer.
Many commercial-motor manufacturers and repairers will be in.terested in the new liquid carburieer, first discovered on the Continent. This carburizer consists of two substances. The first is melted in a receptacle which it fills within :3-4 ins, from the top. Small quantities of the second substance, which is a carbon compound, are then added to the surface of the liquid.
The parts to be carburized are usually hung on rods or set in a basket of metal and sunk in the liquid for a period which depends on the depth of case desired. A test carried out gave 250 tons of steel treated in 1,237 hours, using 1 lb. of material A for every 75 lb. of steel, and 1 lb. of material B (carbon) for every 300 lb. of steel, at 900 degrees C.
Cast-steel pots are usually employed, and the life of this part is reported as double that when cyanide is used, A depth of case of 0.018 in. was secured in a case-hardening period of two hours at 870 degrees C.
The protection of metal parts by coatings has greatly developed and a new type of coating is rhemium. This is quite a satisfactory coating material, and gives a surface free from pits and pock-marks. whilst the coating itself offers high resistance to certain strong acids, whether hot or cold.
Cadmium-zinc coatings have also proved most successful, and another recent coating process is the electrodeposition of a thin film of tellurium on lead. The coating is then heat-treated to enable the tellurium to combine with the lead, and this gives a surface much more resistant to acid attack than is the lead surface free from tellurium.
Finally, one may mention a new impact wrench, for tightening or loosening nuts. This tool will spin down a 1-in, or larger nut at 700 r.p.nn, and then set it with sharp torsional blows applied at the rate of 1,400 per minute.