Calculating load (N) exerted by a 1000 litre drum

[prephil]

Hi,

I'm looking to select some caster wheels for a trolley. It's going to carry a drum that can hold 1000 litres of fluid. I need to know what force in Newtons this will exert in order to select suitable caster wheels? Is there an engineering formula for this or some sort of tool that can be downloaded to calculate the force exerted?

God bless,

Phil.

 

[zeusfaber]

Are you actually planning to buy and fit these casters, or is this something you've been asked to work out to see whether you know how to do it?

A.

 

[prephil]

I need to purchase and fit them, probably from Misumi.

 

[zeusfaber]

I'll take that as an assurance that this isn't a student post (those aren't allowed here).

You won't find a formula for converting Litres to Newtons (not done often enough to be worth printing) - so you'll need to do this in two stages (serials 2 and 4 below).

I'd use "kilograms" as my intermediate step.

1. Confirm the size of the drum (1000l seems a bit big to be moving on a trolley with caster wheels) - or are you just going to move empty drums? If that's the case, make sure you have some way of keeping it that way, then skip step 2.

2. Convert litres to kilograms (need to know the density of the fluid you're carrying to do this)

3. Don't forget the weight of the empty drum and trolley frame

4. Convert kg to newtons (there's just under ten of them to the kg in this corner of the galaxy)

5. Don't forget to allow for the number of wheels you're fitting - or for the fact that the load might not be equally shared between them.

6. Don't forget to check whether the floor will bear this sort of load once it's concentrated on the small contact patch the wheels will give you.

7. Don't get between the trolley and wherever it thinks it wants to go. A tonne of liquid skating around on casters might be a bit wilful. Don't forget to post a video.

A.

 

[rb1957]

some comments ...

2) make sure you're using the MASS density of the liquid, and not the WEIGHT density (how much a liter weighs) ... a 1000 lt of water weighs 1000 kg (i think) which would be 4540N.

4) becareful with your units ... the mass of the liquid and the MASS of the frame (tho' most likely you'll have the weight of the frame, probably in kgs (that'd be kilogramforce ... 1kg = 10N)

5) multiply the resultant weight by a factor, 2?, 4?
then divide by the # of supports

7) how do you plan to brake this beast ?

 

[zekeman]

A 1000 lt of water has a mass of 1000 kg and weighs 9.8*1000=980 Newtons
Why does this simple problem lead to so much confusion.
Everybody knows that 1000cc of water weighs 1 kg or about 2.2 lbs and 1kg is 9.8 N. So you can call 1Kg mass (or weight as a practical matter). What does it matter?
It's the physicists that cause all of this.This problem is located on this planet, not Mars.

 

[MechanicalChef]

The fluid in question is mercury. :evil:

 

[prephil]

Hi,

No I'm not a student but thanks for the humour (laughed at 'post the video'. Not actually going to be transporting the 1000l schutz container around. It's stationary and used to fill 15 gallon drums instead which will be portable. So then, won't be much fun making a video of those.

Will follow the advice given. Thanks very much all.

God bless.

Phil.

 

[prephil]

After all that arguing I'm a bit confused. Is the following procedure correct?

Given:
Size of drum = 15 Gallons / approx 57 litres (working in metric as I'm Irish)

Density of monomer = 1kg/litre

Weight of drum approx. 3kg

Weight of frame approx. 10Kg

57 * 9.8 = 558.6
3 * 9.8 = 29.4
10 * 9.8 = 98
Total = 686

Multiply by factor of 4 = 2744

$ wheels therefore load of 686N/Kg

 

[handleman]

Now I'm confused, as your original post said the moving drum would be 1000 liters. If what you're moving is only 57 liters it's much easier. If monomer density is 1kg/liter then you're moving a total weight of approx. 70 kgf (57+10+3). Using 10 Newtons = 1kg (plenty close for this case) you're talking about a total weight in newtons of 700N. This is actually pretty light weight for a cart. If you want a good safety factor, just make sure the casters are rated for the full weight of the cart. That will automatically give you a safety factor of at least 3. I say 3 because it's possible for the full weight of the cart to be distributed to three wheels in the case of either a warped/damaged frame or uneven floor.

That being said, unless you need to have a static-dissipative rubber wheel or a shock absorbing wheel almost all of the casters in Misumi are rated around 700N and above.

If you were actually moving the 1000 liter tank the weight would be something close to 20x the 700N weight (assuming a similar allowance for tank and frame weight) or about 14,000N. In that case you won't be able to get a safety factor of 3, but CKZJ100 is rated to 9,000N. If you again assume a worst-case 3 wheels carrying the load, you have 27,000N capacity, which is a safety factor of 27,000/14,000 or about 2.

 

[rb1957]

"wheels therefore load of 686N/Kg"

what is a N/kg ? you've calc'd a load of 686N per wheel (with a safety factor of 4). handleman is pointing you towards some wheels that lift this; that the wheel allowable is very close to your load can be defended by your relatively high safety factor.

but wouldn't 15 gallons be 15*4.54 = 68 lt ? which would throw your calc's out a bit, but i think you could still use these 700N wheels.

 

[zeusfaber]

Having got all that Metric Vs Imperial debate out the way, please let's not start arguing the merits of US Vs Imperial Gallons (though it's important, prephil, that you're sure which type you're being asked to work with)

Imperial Gallons - 4.54 l

US Gallons - 3.79 l

Handleman's advice looks pretty sound.

A.

 

[rb1957]

never thought to check US gallons ... that'd fit the 57 lt

 

[Denial]

Handleman's (and Zeusfaber's) point about the possibility of the weight of the cart being shared by only three wheels should be taken a bit further. The sharing in this case will NOT be equal. Most probably the wheel diagonally opposite the lifted-off wheel will be taking almost zero weight, with the total weight shared pretty much equally between the two wheels on the other diagonal.

 

[amorrison]

zekeman

m x a = f
1000kg x 9.8m/s***2 = 9800 Newtons

 

[mayt4u]

Hey, after all of this what happened to the vidio???

 

[prephil]

Haha, That was a good joke alright.

 

[Cockroach]

V = 1000 L = 1.0 m^3
rho = 1000 kg/m^3 [water]
W = (1000 kg/m^3)(1.0 m^3)(9.81 m/s^2) = 9810 N

Take this weight and divide by total number of wheels intended to be used on the trolley. I would multiply that by 1.5 just as an additional safety factor against dynamic loading or shock loading. This is the rating of the caster wheels intended for usage with a water medium.

If the fluid is mercury (Hg), then rho = 13546 kg/m^3 so that W = 132886 N. You follow the same logic as the water computation. Done.

Awesome observation Zekeman, yes, this planet and not Mars. But if the application was on Mars, then use castors rated for 3810 N using water, 51610 N using Hg.

Kenneth J Hueston, PEng
Principal
Sturni-Hueston Engineering Inc
Edmonton, Alberta Canada

 

[GregLocock]

Agree with the general approach, but I'd use 5g for shock loads, given that this thing has no suspension. The first time a pair of wheels falls into a gutter you'll be thankful

Cheers

Greg Locock

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips.

 

[handleman]

It's sort of buried in a post in the middle of this thread, but the 1000 liter drum is not supposed to be on casters. It's a 57 liter drum that gets refilled from the stationary 1000 liter drum.

Also, the OP is looking to spec casters from a catalog, not design them from scratch. All you need to do is calculate the expected static load per caster. The caster mfr. has already taken normal use (shock loads, normal vibration, etc) into account when giving that rating. Unless your use conditions are unusually severe (high speeds, high-grit environment, extreme temperatures, severely uneven floor surface, high risk to life and limb, etc.) can you not pretty much go by the catalog rating?