Cast iron for gears 2

[petar yovchev]

Hi there,
What kind of cast iron is usually used for gears?.What are the advantages and disadvantages of that compared to the steel gears? Does the teeth surface need further machining or that achieved of the casting process is good enough?
Thanks in advance!

 

[MJCronin]

https://www.geartechnology.com/issues/0113x/large_gear_construction.pdf

MJCronin
Sr. Process Engineer

 

[DAVIDSTECKER]

We have an old gear set that the driven gear was a Meehanite iron which we have replaced with a Class 40 Gray iron or Dura-Bar G2 Gray iron and 4140HT steel for the mating pinion.
We stayed with the Gray iron for the high Graphite content.

 

[BrianE22]

I believe cast iron is cheaper. It damps well. It's easy to machine (but messy). It can be brittle so be careful if there are shocks in your drivetrain.

 

[petar yovchev]

Thank you for the advices
I checked experimentally at home wear resistance of the cast iron and some other materials by friction under certain pressure for certain time at speed 0.35m/s, over greasy and smooth surface (outer ring of ball bearing). I applied 240N (54lbs) of force over 2.2x2.2mm(0.087x0.087inch) area and 2x13mm(0.079x0.15inch) area to obtain respectively 48MPa and 9.2MPa of pressure
I don’t know what is the type of the cast iron that I used. The piece I took was from ball joint puller
Here are the results of the experiment:

So I think the cast iron is durable at low contact pressure but not at high.
In my case the contact pressure is at least 400MPa(58ksi) and I’m afraid that the cast iron is not appropriate
The parameters of the gear are: spur gear, m=3mm (0.12inch), z=80, b=28mm(1.1inch)

I still hope that the piece of cast iron that I used for the experiment is grey iron not ductile even though it was extremely hard to break the piece off so it is not that britle. Maybe the ductile Iron can withstand higher contact pressures without wearing.
What would be the cheapest way for manufacturing that gear?
I want it’s life span to be no less than 5000h

 

[Tmoose]

Some questions about your gear application.
How big, how fast, how many, how much horsepower, what rpm, what service ( shock loads etc) , lubrication provisions.

"Does the teeth surface need further machining or that achieved of the casting process is good enough?"

I'm guessing an as-cast cast iron gear will almost certainly need machining to achieve an adequately accurate involute profile and surface finish.

===========.====

"What are the advantages and disadvantages of (cast iron) compared to the steel gears? "

MJCronin's link provides some information about a gear's pitting resistance ( from contact stress or Hertzian stress ) and bending strength. With proper investigation of your application the minimum requirements for each of those qualities will emerge. The results will determine which materials are suitable, and which are not.

Then there is the matter of size. Small hardworking gears will be made of steel, where the large mating gear //might// be ok if made from a cast iron blank.
===========.==

I am an eccentric and proud "I did it myselfer" but I would be looking hard at "stock" gears available

http://www.sdp-si.com

, Browning, Martin, etc and modifying my design to take advantage of their offerings

 

[BrianE22]

Hobbing is probably the most used process for cutting gear teeth.

 

[petar yovchev]

Here are the parameters of the gear couple:

https://files.engineering.com/getfi...57638&file=Gear_transmition_-__parameters.pdf

The lubrication is in grease. It is for a machine that I invented and I am going to apply for an utility model. I am trying to fing a way to start production and launch it. The problem is that I have no resources to do it myself. If the product is at competative price the enterprice will be defenetely succesive.

"I am an eccentric and proud "I did it myselfer" but I would be looking hard at "stock" gears available

http://www.sdp-si.com"

- as much as I see it is something like E-magazine, I can't see where are there machine parts available to order.

"Hobbing is probably the most used process for cutting gear teeth." I think that one of the benefits of casting big gears is to avoid hobbing

The cast iron may progressively wear at high contact pressures but I forgot the fact that the contact line between the teeth is changing it's position along the envolute profile during the operation so the friction is not concentrated only at one area, so I feel by intuition that the cast iron is suiable for my aplication

And let me sumarize the mamufacturing methods that I know
1 (By casting) Casting > turning (the bore and both sides of the hub), broaching (the keyway)> ready for use
2 (By forging) Cutting round slice > heating up > forging > trimming > turning, broaching, hobbing > heat treatmment
3 ( By turning-the most expencive and low profuctive one) Cutting round slice > turning all the surfaces, hobbing milling (ligtening holes), broaching >heat treatmend (That is how I made that gear for my prototype machine and it was realy time-consuming ang material- wasting )

Now I realize that the first one is significantly cheaper even just due to the save of cutting huge slice.

I will be realy gratefull for some more info and advices about my case!

 

[Tmoose]

"stock" gears available

http://www.sdp-si.com"

- as much as I see it is something like E-magazine, I can't see where are there machine parts available to order.

Try this - SDP-spi's largest gear is around 4 inches/200mm.

http://www.sdp-si.com/PDFS/Spur-Gears-Inch.pdf

============
"And let me sumarize the mamufacturing methods that I know
1 (By casting) Casting > turning (the bore and both sides of the hub), broaching (the keyway)> ready for use ..."

So far you have mentioned making the gear(s) of iron or steel.
I believe you will find For some applications die casting can produce an aluminum, zinc or plastic gear of sufficient accuracy without machining the teeth.
Maybe some of the PM powdered metal technologies can produce a gear with adequate accuracy.

I think there is still some serious gear design left to do before considering any material or method.
MJCronin's link provides some information about a gear's pitting resistance ( from contact stress or Hertzian stress ) and bending strength. With proper investigation of your application the minimum requirements for each of those qualities will emerge. The results will determine which materials are suitable, and which are not.

I don't think you have mentioned operating temperature or service life yet either.

Good hunting Petar.

Dan T

 

[ornerynorsk]

With a cast iron or cast steel gear, you really must plan to do final machining on it. An as-cast surface is not acceptable for accuracy and surface finish. If you could get a gear set to run as-cast, your clearances and backlash would have to be set too far open, it would be very noisy, and you'd almost certainly have excess power loss due to friction. A good gear manufacturing shop will have no trouble in making the gear that you need, they can also advise you of material, best gear geometry, heat treating or surface finishes, etc, if you share at least the essential information regarding your application. You don't have to be a gear expert, there are people who already know the field very well. As a side note, you will find that many "stock gears" are far more expensive to buy than made-to-order, if you have any kind of quantity volume at all.

It is better to have enough ideas for some of them to be wrong, than to be always right by having no ideas at all.

 

[DAVIDSTECKER]

If you're looking for a source of gears try Boston Gear.
In addition to spur gears you may want to look into Helical gears
What they call "Change Gears" are typically for lathes and have a huge number of ratios.
They have a wide variety of material options too.