Ball Feet

http://www.mcmaster.com/#standard-levelers/=gax7em

Looks like 24 mm will handle 19,000 lbs ea.

Dear ozzb Sir,

Thanks for sharing the data.

I hope the thread type they have used in the levellers is ISO metric trapezoidal??

Are trapezoidal threads designated as Tr? (Ref ISO 2901:1993)

Please help

Regards

ASD23789

I wouldn't use iso threads, they would be extremely difficult to adjust and prone to failure.... Broader, stronger threads enable faster adjustments and higher load capacities than standard V-shaped threads.

Agreed - we buy in detector enclosures for radiation measurements - basically about 1000kg of lead on 4 legs. The adjusters are ISO metric M10 screws - and can be very difficult to turn to raise the height. I wouldn't like to go much heavier, particularly as an M24 will have about twice the pitch of an M10.

ASD23789, it depends how often you will adjust the feet and if they will be loaded or not during the adjustment. Standard "V" profile threads (imperial or metric) of the appropriate size will easily support your load but ACME types will be significantly easier to adjust with load on them. The ACME threads are designed to move loads repeatedly where standard threads are intended for fastening. So yes you can use standard threads but ACME will be easier to adjust.

How frequently is the Adjustment of Height required? How much ( distance) is the adjustment required ??

I think all engineering solutions should have due considerations for Cost / Benefit ratios.

The questioner obviously knows the safest solution. But he is trying to optimize on the costs ..which is always so important...with the help of this forum.

So rather than telling the obvious, we must go deeper..

Hope it helps.....

As you change height there will a time when the legs will not all be at the correct height. The whole 36 tonne vessel could (and at some point most likely will) be supported on opposite legs 1 & 3, with leg 2 only preventing it toppling, and leg 4 in the air. Legs 1 & 3 would be supporting up to 18 tonnes.

If it were my responsibility, I would design each leg to be capable of taking the full vessel weight.

Dear all,

Thanks for all the help.

The height will be adjusted only (hopefully) for one during erection, piping activities.

when the vessel is in operating condition, the load on each ball feet will be 9000 kilograms.

I am proposing to use ISO metric M60 x 3 mm thread. the minimum thread engagement length = 70 mm. Maximum height adjustment possible = 80mm.

both the bolt and nut material are made of SS 304 bar.

Due to the application in support leg (not a pressure part) the lab chemical testing will be done only (they will not ordered as per ASME specifications).

Thanks to all, waiting for your replies.

Regards

ASD23789

If both the bolt & nut are 304 you run the risk of the two parts galling together. Best to use 2 different stainless grades.

Hi,

I think you are trying to look for a sophisticated solution to a simple routine problem faced everyday by the construction engineers in the fields.

In my opinion, a simple RCC foundation with Foundation bolts grouted in position for fixing the base plate of supporting structure columns having a provision for the adjustment by putting shims will do the job. Only additional attachment you may need will be for lifting the structure for finer adjustments which can be done by providing Jack Bolts in the Base plates or by having an attachment for jacking up the individual columns by use of hydraulic Jacks.

This way we have erected numerous tanks and structures for sophisticated machines without facing any problems.

It will depend on where the tank is located. I think this can also be considered as a simple option.

How is a leveling foot more complicated than a jack bolt. It's a standard purchased item and easy to install. The OP's initial question was only about thread type.

Dear All,

Thanks for your replies.

I am now opting for Square thread M60 X 9mm pitch. (Normal Series)

Is it right to use M before major diameter for square threads?

Also the bearing pressure between Screw and nut of SS 304 material is in the range of 13 N/mm2-15 N/mm2. is it safe?

Regards

ASD23789

M60? That seems excessive for the load you specified (9 ton each leg). A standard ACME type leveling foot, p/n 6858K28 from McMaster-Carr, has a working load of 60,000 lb (30 ton) and it's 1 1/4in diameter (31.75mm).

Is the 304 stainless thread safe with 15N/mm sq pressure?...judging by that question alone, you should consider getting an engineer to work this out for you.

Dear TerraMan Sir,

In many reference books referred for the allowable bearing pressure between screw and nut, the material combination for both of them was never SS 304.

It was Bronze-cast iron,steel-cast iron,steel-bronze etc.

Also It is feared that thread galling may occur and The SS 304 screw and nut combination will seize, thus defying the purpose of ball feet.

Regards

ASD23789.

Dear asd23789 sir... You're not understanding the context of the tables and documents you are looking at! The "safe bearing pressure" you are referring to is for POWER SCREW applications meaning screws and nuts driven by gearboxes and motors. Those tables have absolutely nothing to do with leveling feet or threaded fasteners. As I mentioned before, you should consider talking with an engineer! Best regards

Dear TerraMan Sir,

Sorry for any dispespect.

I agree with your comments.

In the operating condition of the vessel load will be 9 ton on each leg.

(as per your comment regarding power screw,pair of screw and nut will be in motion, thus having different meaning for bearing pressure).

Sorry for misunderstanding.

Regards

ASD23789.

asd23789, No apology necessary. Just trying to help you. Tables and formulas for power screw applications don't apply in your case. Those were developed taking into account continuous movement between screw and nut, dynamic lubrication, longterm wear, etc. Your application is static and requires only selection of standard leveling foot based on manufacturer's stated load carrying capacity. The material selection is up to you based on environmental considerations. Yes there can be issues with SS and galling but usually that occurs when their is movement between nut and screw under load. If you adjust the leveling feet while taking weight of vessel with crane then galling should not be much of an issue. Good luck.

If you adjust the leveling feet while taking weight of vessel with crane then galling should not be much of an issue.

Would that work? I've never worked with any of these vessels but I imagine that they would settle when filled so you would need to level them under full load conditions.

I don't work with vessels either. It might be possible to take the weight of one leg as you adjust it but it may not be feasible for ASDs application...I have no idea what they are planning or what the vessel design / installation looks like. I'm just saying that SS galling should not be a problem if the leveling foot has no load on it. In any case trying to jack up 9 ton (18,000 lb) is not usually practical with a screw. You can do it but it requires a lot of torque so why bother with the effort. We typically use a simple manual hydraulic jack or cylinder (Enerpac for example) to take the load near the foot, make the adjustment, then release pressure and allow it to settle back down. It's not complicated and used in many industries all the time.

OK, that sounds like a reasonable practice, you adjust under no load conditions then see how it sits under full load.