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Reduction gearboxes made of machine steel gear have a maximum limit to prevent changing their physical properties (softening). They change their properties as a result of the temperature increase which is subject of many variables: friction between gear teeth, ambient temperature, quality of bearings are among the main dependencies. The most typical engineering solutions are such as making gear of different stronger materials which withstands higher temperatures, oil bath or liquid cooling.

I want to know what are possible ways to increase the durability of the same gear in a given gearbox. I can heat the gear pieces to a high temperature using torch that makes it "tempered" or "annealed" making it stronger. Which one of those known processes intended specifically for this purpose and how do I find the procedure (heating, followed by cooling or not...) and temperatures needed to alter the structure of the steel?

Also are there other ways to increase the rotational speed limit beside gear tempering and gearbox cooling? Assume for this topic that bearings do not limit the speed.

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  • $\begingroup$ Why do you think the bearings will or won't be the limit? have you checked the rotational speed of bearings? $\endgroup$
    – Solar Mike
    Dec 16, 2018 at 21:35
  • $\begingroup$ I don't think about bearings in this post because it is another topic. This topic is targeting the ways to eliminate the known limitation of the gear. $\endgroup$
    – VladBlanshey
    Dec 16, 2018 at 21:40
  • $\begingroup$ How can you be sure it won't become a limiting factor? Perhaps shaft flexing and centrifugal forces may be relevant... $\endgroup$
    – Solar Mike
    Dec 16, 2018 at 21:41
  • $\begingroup$ I don't even need to research the manufacturer's used bearings - it is easier to replace bearings with high rotational speed bearings which are easy to find on line with well defined specs. Not so with gear pieces... $\endgroup$
    – VladBlanshey
    Dec 16, 2018 at 21:44
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    $\begingroup$ Bearings are not to be heat treated by the end user, only gear part. $\endgroup$
    – VladBlanshey
    Dec 18, 2018 at 3:42

3 Answers 3

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The easiest way to accomplish this is to install a lubricating pump that circulates the oil in the gearbox through an external cooling radiator. You may also need to force-feed the pressurized oil into the bearings through passageways machined into the bearing mounts.

Oil cooling and pressurized oil feed is what allows a sport bike engine to run at 16,000 RPM while developing more than 150HP, and why the gearbox on the weedcutting deck (which did not have pressurized lubrication or an oil cooler) on my tractor was limited to 3200 RPM and 15 HP.

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  • $\begingroup$ Thank you very much . This is the perfect answer I was looking for. Is there "accepted answer" button here? I don't see it. Even my "up" flag is rejected because of less than 15 reputations... fine, I let you know this is the best answer to this question. $\endgroup$
    – VladBlanshey
    May 21, 2019 at 18:32
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If you wish to increase the speed of your gearbox, you must alter the gear ratios. Properly cooling the mechanical components may increase its efficiency, but that will not increase its speed above what it is designed for, only bring its actual speed closer to its designed speed.

To increase durability, you can run it lubricated with oil. That will reduce friction/temperatures reducing wear and improving efficiency, thus leading to longer service life

In order to harden the gears via heat treatment, you must know what material they are made out of. Not all steel can be hardened by heat treatment. Now given a steel that can be hardened by heat treatment, you must know the proper pre-heat(if necessary) and hardening temperatures, proper soak/hold times, and proper method of quenching(water,oil,air,etc). Maximum hardness is retained in minimal quenching time. After hardening, the part needs to be tempered to reduce brittleness and re-introduce toughness. Without knowing the gear material, its not possible to do this properly*

*Id bet there are some old-time toolmakers/blacksmiths that can properly heat treat without much information or process controls, that's due to skill, practice, knowledge, and experience.

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  • $\begingroup$ Gear ratio of the gearbox does not increase the limit of the input-output max frequency but only does just that - provides output frequency in relation to the input. The limit of the gearbox speed (input-output) only depends on the quality of the gear materials, bearings and lubrication, and on the resultant temperatures at max input frequency. Lubrication is already done in all closed "self-lubricating" gearboxes. The only changes I think I could do are changing the bearing to the higher speed and to heat process the gear to increase their resilience to the heat - hence my question posted. $\endgroup$
    – VladBlanshey
    Dec 24, 2018 at 3:36
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Gearbox temperatures have no affect on steel gears. However , bearings ( bushing type) are strongly affected by temperature , a primary function of lube oil is to cool bearings. For a typical babbitt , the difference between 200 and 300 F is substantial.

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