Static Friction for wheels

[gcross6]

Hello,

I am an electrical engineer but need to do a quick calculation for a new builidng that will have anchors installed in order to move large transformers and gear around in it. However I am not quite certain as to what coefficient of resistance I should use for a wheel between concrete and metal (ie: will be using trolley wheels on rollers skates to move) in order to determine the maximum force these anchors need to be withstand. If you could help me out I would really appreciate it. Thanks in advance.

 

[Lion06]

How do the anchors move the equipment around?

 

[desertfox]

Hi

Look at this site for values of rolling friction.

http://www.roymech.co.uk/Useful_Tables/Tribology/co_of_frict.htm

desertfox

 

[gcross6]

The anchors will be attached to the outside concrete column and then a winch system will be attached to pull the equipment on the roller skates.

Thanks for the website desertfox. I just have one more question though regarding the rolling friction. I was trying to remember back in my first year of school when we had to take a statics and dynamics class. There is a difference between rolling friction and the static friction before you start to get a wheel to move is there not? As I want to to make sure I will be calculating the maximum load (ie: around 100,000lbs). Thanks again.

 

[desertfox]

Hi gcross6

There is a formula for rolling friction on the link I gave you.

http://www.roymech.co.uk/Useful_Tables/Tribology/co_of_frict.htm#Rolling

Yes rolling friction is a lot less than the static friction coefficient.

desertfox

 

[gcross6]

Okay thanks. But if I used the values there for lets say rubber on concrete, will that be the total force to start it from moving or just to keep it moving after it had already started moving? I guess I'm just wondering if there is still a static value for wheels when they start at rest that I should calculate for the maximum load? Thanks again.

 

[dhengr]

Gcross6:
Google “Hilman Rollers” or whoever is furnishing your ‘roller skates,’ they will have both rolling friction and starting friction data for their particular equipment, on different surfaces. Yes, the starting force will be higher than the pulling force required once the system is in motion. The starting force has more to do with a localized bearing stress and deformation situation at the rollers, where you are almost pulling the rollers, up hill, out of a bit of a depression in the surface below. Is the 100k the weight of the load you’re moving or the approx. pulling force applied to the bldg. column. You should clear this with the structural engineer on the bldg. because he won’t have included this kind of loading in his column design; and he may care where you drill holes in his columns for your anchors. That is, load height and orientation, steel column web or flange; or reinf’g. stl. locations in conc. columns or are anchors cast-in-place? Many times, for heavy loads, riggers run steel rollers on steel plates or rails rather directly on concrete slabs, or they beat the hell out of the conc. slab.

 

[gcross6]

Thanks so much. I really appreciate it

 

[Compositepro]

Air bearing casters have almost no friction.

http://www.hovair.com/products/air-bearing-caster-modules/air-bearings-and-caster-modules.htm

 

[desertfox]

Gcross6,

The formula I gave you would be the force to get one wheel or roller moving, therefore you have to multiply that force by the number of rollers in your system assuming the total load is equally divided across the rollers.
Any additional force will be dependent on how fast you wish to move this load ie is there any acceleration? If there is acceleration then you could use the formula f=m*a where f = force, m = mass of object to be moved and a = acceleration.
Once the load is moving at constant velocity you only need sufficient force to balance the friction and to prevent the trolley from slowing down.
Finally, once the trolley is moving the dynamic friction of the trolley is usually less than the static friction.

desertfox

 

[gcross6]

Okay perfect. I calculated using the hard rubber on concrete and assumed the most the guys in the shop would use would be 4 rollers. I got a value of around 180kN or approx. 20 metric tonnes but will use a safter factor of 175% just to be safe to get around 30 metric tonnes. Does that sound like a reasonable number?

 

[dhengr]

You should really get with your shop people (millwrights, riggers) and ask them what they are going to do and what equipment they would use, rather than assume anything that you don’t have to assume, or don’t have much control over. Hard rubber wheels or rollers don’t move laterally worth a darn if you don’t have a straight shot from the bldg. wall opening to the conc. column, with the final transformer position being on that same line, and properly oriented. Half the time they skid these kinds of loads into position on greased rails or plates.

 

[gcross6]

I talked to the shop guys and they use 4 skates shown in the attachment. They are the steel rollers but I used the hard rubber on concrete for calculations because there wasn't a steel on concrete friction listed in the website that I could see so I used that for a worst case scenario. And the anchor is installed in the concrete floor, not the column that I had initially thought. I thank you guys again for your patient and help.

 

[dhengr]

Gcross6:
Regarding your steel rollers on concrete, you probably won’t find any meaningful coefficients of friction, either static or dynamic, for these units and heavy loads. The roller bearing stresses are very large and the units are no longer called heavy load skates, as you call them. At these loads they are called concrete pulverizes or crushers.

 

[gcross6]

Good to know So I should let the shop guys know they are going to need some sort of a rail system then. Thanks.