US2288999A - Gear production - Google Patents

Description

' teeth is indicative of Patented July 7, 1942 UNITED STATES PATENT OFFICE GEAR PRODUCTION Victor Fabian, Hamburg, Germany No Drawing. Application August 28, 1939, Serial No. 292,241. In Germany April 25, 1935 1 Claim.

The present invention relates to the production of gears of an excellent hardness.

It has been proposed in the past to produce gears by case-hardening, low carbon, unalloyed or alloyed, steels containing a substantial amount of chromium, nickel or molybdenum. The carbon content of such steels usually varies between ,10 and .20%. This proposal was carried into effect by cementing" or carburizing the work pieces and subsequently hardening the same.

Preferably an annealing or hardening step was interposed. This procedure is objectionable not only because case-hardening is cumbersome in practice but also because of the time-consuming nature thereof.

A further method sugg'estedby the art involved the bringing of the teeth flanks of the gears only up to a certain depth to-the hardening temperature and then quenching; The adoption of this method has been negatived because it is exceedingly troublesome to effect when dealing with mass production. Moreover in all instances where a gear with a particularly high hardness was desired it was necessary to resort to the use a of alloyed steels. Because of the cost of the alloying metals, their utilization in the amounts required caused a material increase in the expense oi the process.

I have now found that it is possible to avoid the objections inherent in the prior art procedures and produce highly hardened gears without resort to the use of large amounts of the aboveexpensive alloyingmetals by-selecting for the gears a steel containing from .5 to .l%, preferablyOIl to 0.8%, of carbon and hardening the gears while correlating the temperature of treatment with certain factors pertaining to the steel and gear selected" for use.

Generally stated myprocess involves heating the gears to a hardening temperature above that usual for the steel selected for the gears, the

steel having for gears with an increasing tooth modulus, a decreasing critical cooling speed, and quenching the gears in a bath, the temperature of which lies only a little above, say about 20 C.,

r The factors with which I correlate the hardening temperature are the martensitic transformation point of the steel in question. As previously noted the steels should contain from .5 to 1% carbon. They may contain other elements such as manganese, silicon, chromium, nickelor copper, but in such cases they will be weakly alloyed, the amounts of such elements not exceeding the limits subsequently given. The temperature to which the gears are heated is from 10 to 40 C. in excess of the usual hardening temperature. Thus it is known that for a steel containing from .7 to .8% carbon, the hardening temperature when the steel is to be water-quenched, should be about 780 C.. If such a steel be used to form gears to be hardened by my method the most advantageous hardening temperature would be about 800 C. The particular temperature within the stated range will vary depending not only on the steel composition but also as previously noted on the tooth modulus and the over all size of the work piece. However, it is comparatively simple when these factors havebeen iixed to select the temperature producing optimum results.

The correlation of the tooth modulus of the.

steel with the "critical cooling speed thereof and the size of the work pieces is of importance for the reason that with'increasing tooth thickness it is preferable to use a steel which is hardened through to a greater extent, that is a steel with a smaller critical cooling speed. The adoption of this measure is founded on the larger amount of heat which must be removed from the work piece.

The small critical cooling speed of the steel used may be achieved according to the general practice of adding the usual small amounts of silicon and manganese, i. e. from about .1 to

Iwishto' about .7 with steels containing from .5 to 1% 01' carbon, or by the addition of small amounts of such metals as chromium, nickel and copper,

that is amounts up to 0.5%.

I observed from my experiments that with steel of a certain manganese content, 1. e., .1%,

a through-hardening of the gears resulted at a content as said modulus varies. Thus to obtafii satisfactory hardening as said modulus varies from 1 to '7, the manganese content must progressively shift from .1 to .'7% i. e., with a modulus of 2, the manganese will amount to 2%, with a modulus of 5, the manganese will amount to .5%, and so on.

The tooth modulus also governs to a large ex tent the duration of the quenching operation, although here too the over all size of the work piece must be considered. It is therefore preferable to establish the period of quenching for each tooth modulus of each work piece.

The following example will serve to illustrate my invention although it is to be understood that my invention is not restricted thereto.

Example A gear, formed of an unalloyed carbon steel, containing .7 to .8% carbon and .1% manganese, and having a tooth modulus of 1 was heated above its transformation point to 800 C. and quenched in a salt bath comprising barium chloride maintained at a temperature of about 200 ing, for gears with a tooth modulus M ranging from 1 to 7, such tooth modulus of the gears with the critical cooling speed of the steels of the gears, so that for gears with a tooth modulus increasing within'said range, the steels thereof have a decreased critical cooling speed, heating the'gears to a temperature above the critical hardening temperature of said steels and quenching the gears in a bath, the temperature of which is maintained slightly above the point of martensitic formation of said steels, the rate of quenching being higher the higher the critical cooling speed and vice versa,

C M equals 0 being the circumference of the gear and N the number of teeth.

VICTOR FABIAN.