Chain Conveyors - HP Requirement Questions...

[CakeMaster]

Hello everyone. I’ve just joined this site, so let me know if I am posting this in the wrong forum…

I’ve recently begun the sizing and selection of electric drive motors and gear reducers for some chain conveyors that will be carrying steel pipe. It will be fairly standard “engineering class” roller chain with oversized rollers. The pipes will be carried on top of the chain in custom v-rests, so there is no rolling or sliding of the pipes themselves.

Most of the chain manufacturers have excellent technical information in their catalogs, but there are two things I can’t seem to find any information on. Here they are:

1) When calculating horsepower requirements of a chain conveyor, does the efficiency of the conveyor chain/sprockets come in to play? I would think that it does, but in every technical reference I’ve seen, the chain efficiency is completely ignored. They do, of course, consider the friction between the chain and the surface the chain is sliding or rolling on, but does this take the place of factoring in the chain’s efficiency? I have been allowing 90% efficiency for every complete chain wrap around a sprocket, but if this is wrong I am greatly over-sizing these drive motors.

2) Also regarding the power requirements – does the chain tensioning device affect the required HP? We normally either rely on the chain’s own catenary tension for large conveyors or use a simple screw adjustment on the tail sprocket of smaller conveyors. I have basically been calculating the chain tension and using 10% of that value in my HP calculation. Is this even necessary?

I can go more in-depth here if needed. Thanks!

 

[tygerdawg]

No specific answers to your questions, but some useful tips.

Gearmotor manufacturers' catalogs and engineering application manuals are wonderful resources for this stuff. My favorite is the English-language version of the German SEW Eurodrive Engineering Applications manuals. Can be gotten free from the German website, but you have to dig for the location of the PDF files. They are in metric and have more rigorous analysis than the others that I have seen.

I'm not sure, but Machinery's Handbook may have some guidelines on sizing / efficiencies for chain conveyors. Certainly chain conveyor manufacturers' catalogs and engineering applications manauals would have this. Try more than one.

For the differnce of a few per cent of efficiency, I'd just go conservative and buy more gearmotor horsepower. Gearmotors are one of the best bargains on the market today, and the cost differential "big" and "bigger" isn't that much. "Bigger" will be a stronger, more robust, more reliable solution solution mechanically.

I would assume that tensioning does affect the overall calculation, but don't know how exactly. Proper tension in a chain is always important (probably for reliability and wear).

TygerDawg
Blue Technik LLC
Advanced Robotics & Automation Engineering

http://www.bluetechnik.com

 

[PeterCharles]

1) "does the efficiency of the conveyor chain/sprockets come in to play?"
YES, does it matter? depends how close you are going to size your motor to the absorbed power.

2) "I have been allowing 90% efficiency"
I would have said 95%. What happens to the inefficiency, surely it ends up as heat. 10% loss on 10 kW is 1 kW, that's a 1 bar electric fire to me, a lot of heat.

3) "I am greatly over-sizing these drive motors"
Surely not just by allowing a 90% efficiency on a chain drive?

4) "does the chain tensioning device affect the required HP"
Comments as point 1

The most significant point is the friction in moving the chain supporting the pipes, this is likely to be where all the power is required. Get the friction wrong here and your motor sizing will be way out.

But remember, you might get grumbles if the motor is one size larger than it need have been when you get it up and running, but that's as nothing to what will be said if it's one size too small and won't run at all!!!

 

[dvd]

Engineering chain friction is a function of the roller diameter and the bushing diameter. You need to know these to calculate friction factor for a particular chain. For a chain that runs unlubricated I have seen this factor be as high as 0.18 and for lubricated chain it may be 0.12.

So 10% seems low to me. Call your chain supplier and tell them your application and lubrication scheme.

 

[eureka]

A very good reference covering all aspects of your questions can be found in:
Belt Conveyors for Bulk Materials. Published by the Conveyor Equipment Manufacturers Association.

 

[CakeMaster]

Thanks for the comments and suggestions, everyone. I’m feeling much better about my HP calculations now…

tygerdawg - I actually came across a PDF of one of those SEW engineering guides about a week ago. It is a GREAT resource to have. Now that I look back, this is the only place I’ve seen that includes the chain efficiency in the conveyor drive sizing. Their example was quite a bit different than mine, though, that’s why I was still unsure about it.

PeterCharles - Actually, I was using 90% efficiency for each complete wrap around a sprocket. Basically, if I have a four-strand conveyor, that would be 4 complete wraps (8 sprockets, each being wrapped approx. 180 degrees). So when I throw the efficiency into my calculations it is actually 0.9^4, or approximately 0.66. That’s why I said “greatly” oversizing – it does make a pretty big difference. I actually just started doing it like this after reading through the above-mentioned SEW guide. You’re right about it being better to oversize, though – sometimes I get myself too worried about oversizing something when it really isn’t a big deal afterall.

dvd - Even though the chain will have oversized rollers, I decided to use a coefficient of friction of 0.2, because this will be a very dry environment and we are not familiar with the company’s maintenance practices (I wouldn’t be surprised if they never lubricate it). The 10% I was referring to has to do with the catenary chain tension – I have been adding 10% of the chain tension into my HP calculations. Not sure if it’s necessary, though…

eureka - I haven’t heard of that one – I will be sure to check into it.