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# Electric Motors/Crane repair, hoist repair, crane construction, crane parts, crane maintenance

Question

Crane Design
QUESTION: Dear Will

http://en.wikipedia.org/wiki/Crane_(machine)

Cranes are designed to lift and move specific loads capacity in tons. What are the input parameters in terms of mechanical, electronic, electrical components considered for Crane Construction
in terms of its ability to lift more loads ?

i.e. Electrical Power, Pulleys, Shafts, Ropes, Levers, Crane Height etc.

Example :

Some Cranes can lift a load of 100 ton, while some cranes can lift say a load of 500 ton. So in the second case, what are the parameters considered for designing the crane which can lift more loads.

Thanks & Regards,
Prashant S Akerkar

ANSWER: Well you ask a lot of good questions,   I could write for days on this,   is there something in particular you are looking to find or resolve?

You can google cranes and hoists and get tons of engineering data, history, so on,   so not sure what to reply with,

But let me give you a bit on the example,    of course the distance out from the supporting structure is critical. Like a load off the end of a shaft is often called overhung load,   so the farther out, the more support in the structure itself,

Lets look at a hand operated chain hoist,    say it is a 1 ton capacity,     many hoist can be double by double sheaving  or using twice the chain and reconfiguring the way it is attached to the lifting gear or pulley,   whatever the mechanism.

As to you larger overall question,  it is how they measure horsepower,  how much weight a horse, can lift up a straight cliff,  if you will,  with a some sort of rope attached,

Now it is going to vary on several things,  size of the horse,  versus the amount of weight,  say the weight is hard on a small horse  but the horse can still pull it up,   without injury, [or in the mechanical sense failure]  by going slower,   where a large horse can lift the same load but do it faster,   so then you are talking torque and horsepower,

It i fairly linear,  from 500 tons to 100 tons,  if it takes a five foot wide beam to hold 100 then it will take about five times that to lift the 500.

In that example speed is not in the equation,  either the boom is strong enough or it fails,

The closer in to the lifting device reducing the overhung distance will allow for more weight to be lifted,

In passenger elevators,  they do a lot of engineering to the sheaves and ropes to get to the proper weight lifting ability,

One thing you might find interesting is an elevator,  uses more power to go  DOWN THAN UP,

The reason is the counter weight is always [or most always] heavier than the car, and heavier than the car full of people,     so if in the rare rare chance the lifting shaft would break at once totally,  the counter weight would go down, and the car would go up,

I can tell you we have repaired and installed about every kind of hoist or lifting device in existence,  we really don't get into heavy equipment,  as in your photo,  but any other hoist or crane including many tons of cab operated cranes to a simple chain hoist,  we deal with those.

Another quick bit of information,   testing of cranes,  is quite the experience,   in able to test something that lifts say   20 tons,   it is normally tested at 25% over capacity,  as a rough rule,  so we have to get 20 tons [and the test weight has to be certified]  so we use everything from formed concrete blocks that can be attached together to get the desired weight,  water bags,   [we know what the bag weighs, how much water weighs, and if we are accurate on the amount of water or number of gallons,  we have an exact test weight]

We also prefer to do dynamic testing when possible,   static testing would be like attaching your hook to a giant stake in the ground, and by watching the dyno or scale in between  we know we stress the scale it will read in some form of weight,     if all holds we are good,

The better test is dynamic where we actually lift the weight  making the lift wheel, gear or whatever turn and bring the chain or rope, again whatever,  over the lifting component itself,   this is a more a complete test than just static,  but if nothing else is possible static will work,

You can imagine trying to haul all this test weight to a specific site,  it can be a huge expensive job, but it is critical all lifting devices be tested on a regular basis,  stresses,  unseen stresses or cracks in the metal  before manufacturing can show up years into service,  but only if tested,  and hopefully before the test is a dropped load,

I had noticed lately,  a large amount of reports of these large construction type cranes,  failing, falling over,  causing all kinds of destruction,   not sure what that was all about, maybe just a period of time when many failed but it did seem odd there for a while,    about oh  10 or less years ago, it seemed every few months some huge crane fell.

But,

I really need something specific,   just too much science and engineering to explain here,  but if you have an idea you are working on,  or a problem that you need help with,   let me know and I will do my best to help,

Again  googling hoists,  cranes,  theory of,   that kind of search will give you years of reading if you want to go that far,

You can use my shop email   repair@mearservice.com,   or our shop phone 816-650-4030  anytime, if you have a specific problem or issue,  always happy to try and figure out if we can help over the phone or by email  to resolve something quickly and accurately,  but as far as all the parameters you have asked about,  just way to broad a subject,

You might even start by reading up on basic HP  and how it is measured,  and torque,  so when you have a good grasp of the basics,  then maybe the issues of cranes and lifting will be more easily understood.

---------- FOLLOW-UP ----------

QUESTION: Dear Will

Thank you.

http://en.wikipedia.org/wiki/Hydraulic_cylinder
http://en.wikipedia.org/wiki/Hydraulic_motor

Hydraulic Cylinder Design could be one of the important factors for lifting more load in Crane Construction ?

Thanks & Regards,
Prashant S Akerkar

OK a bit more specific,  but still fairly general.  The simple answer is whatever that were used to build the 100 ton crane,  use the same components five times larger.

Maybe this would be of help:

http://www.terex-training.com/elearning.aspx

This a very inexpensive training program for technicians, which explains every component you mentioned,    it is not an engineering program,   BUT I can promise you that those who repair and work on any device,  with enough formal or required training, or maybe even on the job training,  plus relative experience can keep up with most engineers.

I am not formally trained as an engineer, but have no problems communicating with any engineer on any electrical mechanical device.

For the low investment this company commands for this online program it might be money well spent,  depending on your end goal.

As to the sub question of:

Hydraulic Cylinder Design could be one of the important factors for lifting more load in Crane Construction ?

ABSOLUTELY. however hydraulics is not my strong suit,  I repair fork lifts and other hydraulics,  have rebuilt cylinders,  understand the accuracy of the internal components,  have been a guest at a large cylinder rebuilding company,  [all they do is hydraulic cylinders]

All sizes and types,   and there is so much to the simple design in everyday use.  The concept is fairly simple, but obtaining the optimum pressures, with moving components, preventing wear, the cylinder itself must be structurally intact,  has a high degree of tolerance as to the straightness, interior finish,  so on.

This is where a lot of motor shops fail,  looking at a basic motor,  you see four bolts on each end,  two end housings,  a rotating element, and a stationary set of laminated steel, with magnet wire of some type configured around to make electromagnets that produce rotation, torque and horsepower,     what is overlooked is the absolute need for very close tolerances on the housings,  the bearing fits, the straightness of the shaft and rotating element,  can be easily overlooked.

A few thousandths of an inch,   on the size of the housing bore,  when extended out to and through the output shaft,  is huge,

Heat relief,  where considerations for thermal growth are also overlooked,    when a bearing warms up,  it expands,  in the assembly design process,  considerations and tolerances for this expected thermal growth must be properly acknowledged, and applied,

Imagine two bearings on a simple shaft, held in two housings,   if the bearings are installed in such a way,  that they are captured,  when the thermal growth occurs there is no room for movement and then binding begins,

How it happens,   both bearings are fit in the housings, the housings are just a tiny bit over tolerance,   so the repair includes a drop of loctite glue to hold the outer race from spinning,   but both housings are just a touch oversized,    now the glue is used on both ends,   now more considerations come into play,  the size of the outer race of the bearing when manufactured, all have tolerances,  in other words nothing is perfect, and repetitive,  so they allow tolerances

So take the motor with the over sized housings,   off a chart they know this, so glue is used, now the new bearing are purchased,  both bearings are on the HIGH side of the manufacturing tolerances,  making them on the large size when measuring the outside diameter,   just fractions of an inch,

Now we have locked bearings,   bearings that are tight anyway,  both glued to try and prevent the outside race from spinning, and the thermal growth when the bearing expands  REALLY HAS NO WHERE TO GROW,  crushing the rotating elements into their paths,   a huge mechanical problem will develop,

Same with cylinders,  heat is a consideration, thermal growth,  straightness of the bore, on and on,  very simple things.

But yes the better the internal components,  the materials,  the precision of the assembly, all will have a huge effect on the capability and service factor of the cylinder.

Hydraulic power has been used for a long time, and for good reason.

I think you will find the site below very interesting,  lots of history, formulas,  discussions of mechanical advantages,   so on.

http://www.lowtechmagazine.com/2010/03/history-of-human-powered-cranes.html

It appears you are staying with this 100 versus 500 ton capacity,  and how to get from the 100 to 500 maybe without an entire new crane.

The cylinder will be a huge component, but the force from the cylinder will have to be handled by every other component down the line.

I get a lot of "inventors" that are bound and determined to reconfigure a device, mostly electrical motors,  so that they operate perpetually,     or by adding flywheels and other gadgets some how create power,  without supplying more energy,

One rule,  power is converted not created, in the most simple explanations I can provide,

Here is where advantages come from, and could easily impact your sub question on cylinders,

Real rough,    a combustion engine,  can be rule of thumb rated at 40 to 50% efficient,  meaning the power applied   by the time is it converted,  looses half the applied power through mechanical considerations of friction, windage, [in the example of a motor, losses in the motor core, developing the electro-magnet]

in the example of a combustion engine,  even more  friction over 4.6.8 cylinders,  friction form cam shaft, and main shafts,   burning of the fuel, many more components and associated losses before the output power is delivered to the output

Where a three phase vanilla motor can produce 93% and above efficiency,  so for every watt of energy used,  93% IS AT THE MOTOR SHAFT IN A ROTATIONAL DIRECTION,  AT THE END OF A COMBUSTION ENGINE,   AT THE DYNO,  ONLY HALF THE POWER IS OUTPUT FROM THE FUEL USED,

Hard to keep this simple,   but for electric vehicles,  the advantages are in the efficiencies of the power plant,     without improved efficiencies,   then the manufacturer is forced to place attention on other areas of the vehicle,  reduced weight,  materials with strength but lighter,    the inefficiencies are still there,     the gas mileage improvement are gained by pushing less load down the road,

Hydraulics like any power manipulation should have a goal,   matching whatever power input to the needed load,

If you look at electric motors,   they come in horsepower ratings like this,   5,  7.5, 10, 15, 20, 25. 30, 40. 50 60, 75, 100   NEMA VANILLA MOTOR Horsepower,

So you have a crane and want to pick 100 tons,  for talking points let's say it takes 100 HP to pick 100 tons,   what if you want to pick 80 tons?

Do you stretch a 75 HP into it's service factor,  [sf is the amount of over nameplate the motor can withstand on a consistent basis,   many motors have 1.0  which is just nameplate,  many others have up to 1.25  with the median being 1.15]

Or do you use a 100 HP  now the 100 HP is going to handle the 80 tons, but when running, the efficiency obviously are going to be reduced,

You see the huge gaps in motor HP rating,  so the problem is, using just the bare minimal input to get the same output     this is efficiency and I NEVER HEAR THAT DISCUSSED with all the world fuel problems,  but you can see how difficult sizing a motor install is,   matching the driver with load.

Now to hydraulics,  most hydraulics are powered by some kind of electrical motor,  now that the technology of frequency control is becoming a main stay,   there can be some savings using that route,

But the more efficient the cylinder in conveying a pressure type energy into a mechanical type energy the more efficient the entire system can become.

And if a cylinder is more efficient,  everything being equal,  cylinder is 4 inches diameter, all the same,   but the mechanical energy on the output side is more,  with the same physical size,    this is done as above,  with precision materials,  tight tolerances,  so on.

I think you have even more specific needs,  so if you wish let me know what they are,  my personal email is wbwill@sbcglobal.net     glad to talk this over from there,    if it is some sort of proprietary idea,    and we can communicate in even more privacy if that is the case, and often it is on here,

Hope this moves you forward a bit more,   again I am here to keep helping until I am out of help but I have a huge association of people who are experts in many fields I can turn to for more help,

But the more efficient your cylinder is,  then we can look to a somewhat smaller structure assuming all other components will handle the stresses of lifting 500 tons, and all the possible angles and locations,

Are you looking for a repetitive lift of the same amount over and over again?  Or looking for being able to get to 500 tons if needed?

That is a big question,  no sense making things variable if the load is consistent,  hydraulic work good, with the various types of pumps,   some can be huge overkill,   but hydraulics allows flexibility in the motion under various loads to a certain overall limit.

Goo luck and again if you want to get more specific you have my address,
Questioner's Rating
 Rating(1-10) Knowledgeability = 10 Clarity of Response = 10 Politeness = 10 Comment Dear Will Thank you. Thanks & Regards, Prashant S Akerkar

Electric Motors

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#### Will

##### Expertise

Three phase/ AC DC single phase motors, controls, any problems or failures, motor installation, performance issues, connections. All other electric motors/gearboxes/apparatus. Specialty repair concerns, obsolete motors and solutions. Other mechanical or specialty equipment. See my profile under Home/electrical at this site

##### Experience

30 plus years in the electrical motor and apparatus repair industry. VP level management of repair facilities, current owner of my own specialty repair and consulting firm.

Organizations
EASA, IBEW [retired], other specialty organizations, Lubrication, Vibration EDI, Tribo-electric Councils

Publications
Currently fielding concerns at this site under "Home Electrical"

Education/Credentials
4 year technical, College level specific courses, EASA repair courses, vibration analysis electronic and electrical trade school.