Gearboxes - Can this speed reducer work as a speed increaser?
Gearboxes - Can this speed reducer work as a speed increaser?
(OP)
I'm looking to purchase a used 4,000 hp gearbox with a single stage helical gears. It was designed to be a speed reducer but I'd like to run it as a speed increaser.
Gear ratio - 14:1
low speed shaft - 1,800 rpm
high speed shaft - 25,200 rpm
the gearbox is single direction. Can i run this as an increaser if i maintain the direction of torque and rotation? i want to be able to drive the 1,800 rpm shaft (at 1800 rpm) and obtain 25,200 rpm as the output.
I did a quick free-body diagram and the thrust loads would remain in the same direction as if used as a reducer. What else do i need to consider? Are mating pairs of helical gears ever machined such that the pinion can't act as the driven gear?
if i inspect this gearbox myself, what should i look for in the gearing?
thanks for any advice,
nick
Gear ratio - 14:1
low speed shaft - 1,800 rpm
high speed shaft - 25,200 rpm
the gearbox is single direction. Can i run this as an increaser if i maintain the direction of torque and rotation? i want to be able to drive the 1,800 rpm shaft (at 1800 rpm) and obtain 25,200 rpm as the output.
I did a quick free-body diagram and the thrust loads would remain in the same direction as if used as a reducer. What else do i need to consider? Are mating pairs of helical gears ever machined such that the pinion can't act as the driven gear?
if i inspect this gearbox myself, what should i look for in the gearing?
thanks for any advice,
nick





RE: Gearboxes - Can this speed reducer work as a speed increaser?
Call the gearbox manufacturer and ask them to bless your misapplication or propose alternatives.
What do you do when this gearbox frags? Do you have a source for more of them?
Mike Halloran
Pembroke Pines, FL, USA
RE: Gearboxes - Can this speed reducer work as a speed increaser?
25,200rpm sounds fast to me. You could have problems with centrifugal force stresses, and maximum bearing speeds. What does the manufacturer think?
--
JHG
RE: Gearboxes - Can this speed reducer work as a speed increaser?
What would i be looking for in the oil sample? The company that manufactured this gearbox was acquired by a company in Germany. The design is 12 years old and the new company is not familiar with the design intent of this gearbox. They prefer not to advise on running the gearbox as an increaser. i asked them for drawings of the gears and bearings so that i could analyze the drive train but I'm not sure if they would be willing to provide that information. Thanks for the input.
JHG,
The gearbox is rated at 25,200 at the high speed shaft and 1,800 at the low speed shaft. we would be operating within the speed and power requirements.
RE: Gearboxes - Can this speed reducer work as a speed increaser?
RE: Gearboxes - Can this speed reducer work as a speed increaser?
One thing that was important in those huge units was that the shape of the gears tended to pump oil from the outer edges to the groove in the center of the gears. When going backwards (or when the screw is driving) the tendency is to try to pull oil from the central groove (where there is minimal oil) towards the edge. I think I remember (from 1977) an issue if you went in reverse longer than a set period (it was days, not weeks as I recall). You might look at the gear lubrication system and see if you can see a lubrication issue running backwards.
David Simpson, PE
MuleShoe Engineering
"Belief" is the acceptance of an hypotheses in the absence of data.
"Prejudice" is having an opinion not supported by the preponderance of the data.
"Knowledge" is only found through the accumulation and analysis of data.
RE: Gearboxes - Can this speed reducer work as a speed increaser?
rp
RE: Gearboxes - Can this speed reducer work as a speed increaser?
"You see, wire telegraph is like a very long cat. You pull his tail in New York and his head is meowing in Los Angeles. Do you understand this? Radio operates the same way: You send signals here, they receive them there. The only difference is there is no cat." A. Einstein
RE: Gearboxes - Can this speed reducer work as a speed increaser?
rmw
RE: Gearboxes - Can this speed reducer work as a speed increaser?
If the original design was intended to be 1800in and 125 out, I wouldn't try it. The bearing selections probably can't handle operating 14x faster, and bearing settings, lubrication design, and lubricant selection will be all different.
As for inspecting the gearing, basic inspection for water damage, pitting, scoring, abrasive, etc on the teeth.
David
RE: Gearboxes - Can this speed reducer work as a speed increaser?
Having dealt with a few gear manufacturers there are two things I would say: (1) it is unlikely that any manufacturer would warrant these gears in this service; and (2) it will probably work because of the safety factors normally built in.
David Simpson, PE
MuleShoe Engineering
"Belief" is the acceptance of an hypotheses in the absence of data.
"Prejudice" is having an opinion not supported by the preponderance of the data.
"Knowledge" is only found through the accumulation and analysis of data.
RE: Gearboxes - Can this speed reducer work as a speed increaser?
My intent was, as zdas04 mentioned, to operating the gearbox in its intended direction and speed... except i will be driving the low speed output shaft. Internally, the thrust loads will be in the same direction. The only difference will be that the tooth contact surfaces will change.
I will look into trying a tooth contact test as rmw suggested and possibly checking oil samples for metal shavings.
RE: Gearboxes - Can this speed reducer work as a speed increaser?
RE: Gearboxes - Can this speed reducer work as a speed increaser?
RE: Gearboxes - Can this speed reducer work as a speed increaser?
Warranty???
R.
RE: Gearboxes - Can this speed reducer work as a speed increaser?
the original gearbox was a speed reducer, output speed = input speed/14, (and a torque increaser, output torque = input torque*14, yes?)
the proposal is to reverse the input and output shafts so that the output speed = input speed*14 and the output torque = input torque/14, no?
i don't see a "torque increase" ?