Power Rating of Poly-V Belts

[Sub MandrelParticipant @submandrel]

Engineering’s best kept secret?

[Sub MandrelParticipant @submandrel]

How can you work out the power a poly-v belt can transmit?

It seems that it rises with rpm (rather than being related to belt speed or pulley diameter, so presumably these have little effect).

There's a graph here: http://www.naismith.com.au/pdf/poly_v_v_pulley.pdf bu, unhelpfully, it doesn't say what number of ribs it is referring to!

If it's for a per rib, then the 4-rib pulley I will be using for my lathe will be fine, if its for 8 (normal maximum width) then it will be marginal and I could get slip at low speeds.

This is more an academic question than a serious one as experience with my mill suggests that 4 ribs should be plenty for a 400W motor.

A useful note in the document link to above: for pj section correct tension is when the belt is stretched by 0.5%, measured between tow marks on the belt.

Neil

[Keith LongParticipant @keithlong89920]

Neil

Try looking at the Gates catalogue. I think that has more info than Naismith and includes a "watt / per rib" table. Might taske a bit of working through.

Keith

[John Stevenson 1Participant @johnstevenson1]

Years ago I had to do a lot of design work using Poly V belts and managed to get hold of a design book.

Far in front of what is published by Naismith.

It's a good guide but the arc contact ratio has to be taken into account as does the service factor which also is affected by small diameter pullies.

As a guide and guessing some sizes at 3,000 revs with equal pullies having a 180 degree contact arc and the pully diameter at 50mm then one rib will carry 0.41 Kw.

[Michael GilliganParticipant @michaelgilligan61133]

Neil,

This, from Conti, might help

MichaelG.

[John Stevenson 1Participant @johnstevenson1]

True and rather funnny story.

Could be long so go get a coffee.

Many years ago I was associated in the re-design of the Poole wood lathe known as the 28/40

The original design was done in wales and the manufacture was done in Taiwan.

Taiwan at this time is about where India is now, loads of crap was being produced and no follow on with the factories.

The biggest problem with this lathe was a big speed range it needed which was achieved by three sets of expanding pullies on 3 shafts but low speed meant plenty of belt slip and loss of torque.

Ray Poole asked me to look at doing a better design using an Inverter drive.

Silverdrive had tried and failed as they just relied on the inverter for the speed range which meant that low torque was even worse than the varispeed machine.

I used an uprated inverter and 4 speed on poly vee belts which cured all the problems and made a nice smooth machine with bags of torque for bowl turning.

Biggest problem I had was because the original shafts were on machined fixed centres the pulleys had to match so the belt length remained constant.

So out came the design book and there was every formulae in there except how to work out D2 given D1, the belt length and centre distance, plenty for blet length and centre distance but these for me were written in stone.

So a call to the people who published the design book but I could not get across what i wanted, or more to the point they were not interested.

Basically the big formula that took into account arc contact , Pi, theta, ear of bat and tongue of newt needed transposing so I was working out what D2 was ??????

However algebra was not my best subject at school.

[b] SCHOOL ??????? [/b]

So sent School a fax addressed to the Maths department explaining as I was born in 1948, the year that nice Mr Bevan said we were going to be looked after from the cradle to the grave would they mind doing this transposition for me as I wasn't paying attention that day ?

Two days later got a fax back with the transposed formulae.

Now that's what I call service.

[Michael GilliganParticipant @michaelgilligan61133]

Good story, John

… I doubt the present generation will give service like that !!

MichaelG.

______________

Neil,

For a quick sanity check; consider the typical 12volt Car Alternator

Rated at something like 80A [i.e. more than one Horsepower], they are commonly driven by four-rib Poly-V belts.

MichaelG.

[Keith LongParticipant @keithlong89920]

Quote

"Neil,

For a quick sanity check; consider the typical 12volt Car Alternator

Rated at something like 80A [i.e. more than one Horsepower], they are commonly driven by four-rib Poly-V belts.

MichaelG."

 

Not to mention the air-con compressor and the power steering pump – all off the same belt.

Keith

Edited By Keith Long on 24/08/2013 15:53:12

[Sub MandrelParticipant @submandrel]

Ah but cars use K-belts, the next size up from J-belts.

John says "As a guide and guessing some sizes at 3,000 revs with equal pullies having a 180 degree contact arc and the pully diameter at 50mm then one rib will carry 0.41 Kw"

As my pulleys are 1 1/2" diameter, equal sized, I have a 4-rib belt and a 400watt motor, I think I will have a reasonable margin.

Thanks all,

Neil

<actually cutting metal today!!!>

[John Stevenson 1Participant @johnstevenson1]

For the example quoted a K section will handle 0.64Kw so roughly half as much again.

[oldveloParticipant @oldvelo]

Hi Neil

I run a metal cutting bandsaw with 6 ribbed J section poly vee belts with the drive wheel pulley of

150 mm dia drive @ 26 RPM with no sign of slippage.

Eric

[Author]

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