I am designing building a gravity power conveyor to move dirty dish trays about 45ft inside of a restuarant.   Does anyone have a rule of thumb or a formula for the incline of the roller system?

A lot is going to depend on the bearings for the rollers, size of the rollers, weight of the dishes necessary to start the plate/tray moving at a given angle. You want to stay near the minimum slope to keep the speed at the far end down. You could attempt to figure all that out.
or
Take an educated guess at the angle and make the leg supports adjustable.

Comprehension is not understanding. Understanding is not wisdom. And it is wisdom that gives us the ability to apply what we know, to our real world situations

It would be nice to have someone who has done it before to make an educated guess.   I limmited to 15" of fall across 45'.   If this will not work then I need to go a different route.

"One test is worth 10,000 opinions."

Find a local roller conveyor company that has some used/scrap/new sections of roller conveyor laying around their warehouse.  Call 'em up, make your pitch.  Grab a few "dirty dish trays" before you leave. Stop by Lowes/HomeDepot on the way over and pickup a carpenter's inclinometer.  It's all downhill from there.  (erk!  snicker!    )  

TygerDawg
Blue Technik LLC
Virtuoso Robotics Engineering
www.bluetechnik.com

Thats great advice tygerdawg! I hope you are not a Georgia dawg

Actually, it's "Geaux Tigahs" with a little "Go Pack" thrown in.

TygerDawg
Blue Technik LLC
Virtuoso Robotics Engineering
www.bluetechnik.com

My two cents:  I would throw in a very big "BUT" here... just because you might be able to get it to work well in a relatively sterile environment like a warehouse with a few sample "clean" trays does not mean it will still work after a few months in a kitchen with all kinds of stuff oozing down into the bearings over a long time.  This is known technology.  I would try to learn what I could by looking at as many similar installations as possible.  

Point 2 - I've been in the machine design field long enough to know that ANY equipment intended for use around food has to meet some pretty strict codes, usually has to withstand high temperature washdowns, certain materials are verboten, etc.

Point 3 - My gut tells me to avoid any kind of rolling element bearings in this application because of the need for lubrication and their tendency to gum up.  I would go for plain bearings, a.k.a. bushings, probably plastic.  Gravity isn't a very strong driver in this case.  And I think the internal friction building up over a period of time could be significant.

I agree with jboggs.  

Gravity is a horrid power choice, given the environment, and the level of sophistication available and the personnel turnover therein.

It needs to have a motor and a switch with an on position and especially an OFF position.

 

Mike Halloran
Pembroke Pines, FL, USA

Thanks for the advice.   We have a motor driven conveyor system now that is a maintenance nightmare...hence the gravity thought.   I agree that it would probably be just as much of a problem with gravity unless you could put it at such an angle that the trays would slide without rollers.   In this case you would start breaking dishes.

A system like that represents a learning opportunity.
Review the maintenance records, and follow them back to root causes.
Fix those, recurse, and you eventually get a better product, or at least more effective maintenance procedures.
 

Mike Halloran
Pembroke Pines, FL, USA

Agree with Mike. Have you identified the root causes?  Not the symptoms - the causes.

I suspect that the root causes of the maintenance problems on the driven conveyor would have the same effect, create similar symptoms, on a gravity conveyor.

Hey, I'm not saying give up on the gravity conveyor.  I'm saying understand all the facts before you make a financial commitment.

Also, do you really need cylindrical rollers?  I've seen "skate wheel" conveyors work really well in gravity feed situations.  The reason is that skate wheels have nearly no inertia compared to rollers.

gatech50, if they're Homer Laughlin (American made) dishes, go with the steep angle. You'll be supporting the economy and we can always use the business.

Seriously, the dishes could add significant weight and if you get them moving they will 'crash' at the end. I would take the advice of improving the belt you have.

Are the dishes contained in bus-bins? I can imagine about 35 or 40 feet of incline with a level end section to decelerate the bins. We have a conveyor system which has a slope of 4.50 inches per 10 feet, with an overall transport length of around 120 feet. It does very well as a gravity conveyor IE keeping the velocity manageable.

I agree that you would want to avoid a motorized system in a foodservice kitchen, no need to introduce another maintenance routine. It's unlikely that your local health code would require it to be "washdown", but it would likely need to be of corrosion free materials, whether plastic or metal. It would not have to be rated for incidental food contact on the "dirty side" of the kitchen.

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.