lift capacity vs. breakout force

[carpenter383]

This may seem like a dumb question, but while researching tractors I've noticed some loaders have a breakout force that is basically double the lift capacity. While other loaders' rated lift capacity is only say 400 lbs shy of the breakout force. So is the rated lift capacity simply what the manufacturer feels is safe, based on a given tractor? Am I missing something?

 

[Eagleview]

The breakout force is the amount the bucket can exert in it's crowd back function ie. tearing out a tree root while rolling the bucket back , as opposed to trying to lift it with the loaders lift arms (lift capacity).

 

[carpenter383]

I thought that was "roll back" force

 

[CHDinCT]

I believe that break out force to some degree is dependent on how far out the front edge of the bucket is from the bucket cylinders; therefore, two buckets of the same capacity but with different dimensions would have different breakout numbers. The farther out the front edge is, the less breakout force it will have. This is one factor, but I believe there are others such as the size of the bucket cylinders.

 

[J_J]

This may seem like a dumb question, but while researching tractors I've noticed some loaders have a breakout force that is basically double the lift capacity. While other loaders' rated lift capacity is only say 400 lbs shy of the breakout force. So is the rated lift capacity simply what the manufacturer feels is safe, based on a given tractor? Am I missing something?

I believe that they build or order a certain bucket, and then figure the cylinder size that will give a reasonable breakout before the bucket is destroyed. You can over power a bucket real easy by using the wrong cylinder. You will probably rip out your mounting brackets, or warp your bucket. Other things to consider is the front to back length. A shorter bucket on the same frame, will have a greater break out force, due to mechanical advantage. The same thing applies to the lift cylinders also. You could go to a larger cylinder, but you might place your front axles at risk, by overload. Just enough is what they settle on.

If you built a super strong bucket, and your front pins can take it, you could go to a larger cylinder. I am sure that someone put some kind of measuring device on the bucket and curled the bucket back to see what break out force they can give the bucket.

 

[carpenter383]

Well It makes more sense now, I thought breakout force was at max psi when the pressure relief valve opens thanks for the info guys

 

[john_bud]

Lift is obviously how heavy of an object you can lift "at a particular location" with respect to the loader. Some (unscrupulous) companies will give that rated at the lower pivot point. That's beyond the back of the bucket (closer to the tractor) and the number is worthless. A better one is "bucket center" as that is where you will have a load. An even better one is to have it at 500mm forward of the bucket edge. That is where a chained on load like a large log is often located. Heck, I'd be happy if they would just certify how many pounds of heaped dirt can be picked up to full height!

Break out is the upward force generated at the bucket lip. It is larger than the lift as the bucket can be on the ground and there is some "pry" action occurring with some down force transferred to the back of the bucket. Some will refer to it as the "roll back" force and that's a good description. JJ is correct that you can over power the bucket and bend it if you go too big on the cylinder. That's fairly rare as they match the cylinders to the bucket nowadays pretty well.

 

[schmism]

i physcally can not get a larger cylinder on my roll back function on the bucket due to geometry. The fat end of the cylinder (when fully extended) only sits about 1/4" above the loader arm. Course I have the older loader design that pins the cylinder directly to the bucket and not to a 2nd linkage.

 

[john_bud]

i physcally can not get a larger cylinder on my roll back function on the bucket due to geometry. The fat end of the cylinder (when fully extended) only sits about 1/4" above the loader arm. Course I have the older loader design that pins the cylinder directly to the bucket and not to a 2nd linkage.

Can not???? Always took that to be a challenge...

Sure you can. Cut off the old ears, weld on new ones that give a larger cylinder some room to breath.

 

[Eagleview]

Large loaders use a "Z" linkage on the bucket . The ram is then able to push out on the "Z" linkage which reverses the direction of thrust so the bucket rolls back which gives a greater breakout force . A ram has more push power than pulling power because of the piston area that the oil can work against is less on the ram side than the other side . As a rough example , there may be 5 square inches on the piston face . Say 2,000psi working pressure , 5X2,000psi=10,000lbs pushing force . On the other side that has the ram bar attached you may only have 3 square inches of piston surface area because the ram bar takes up the extra room . So you have 3X2,000psi=6,000lbs pushing force .

 

[KentT]

Large loaders use a "Z" linkage on the bucket . The ram is then able to push out on the "Z" linkage which reverses the direction of thrust so the bucket rolls back which gives a greater breakout force . A ram has more push power than pulling power because of the piston area that the oil can work against is less on the ram side than the other side . .

Yep, the Power Tracs use that design -- and some of us have bent or broken the linkage... and then there's me who's done both...

I'm amazed at the force that 2500 PSI hydraulics can generate. I can't conceive what true HIGH pressure hydraulic systems can do...

 

[Eagleview]

Yes , it still blows me away too . This is my excavator which i use for pulling out trees . It just drags them out of the ground . When you look at how short the top of the dipper stick is (vertical arm) from it's pivot point compared to how long the arm is overall , it's hard to imagine how much push that top ram must have .

 

[J_J]

Yes , it still blows me away too . This is my excavator which i use for pulling out trees . It just drags them out of the ground . When you look at how short the top of the dipper stick is (vertical arm) from it's pivot point compared to how long the arm is overall , it's hard to imagine how much push that top ram must have .

That is one nice machine.

I would guess you are only using about 20 % of available push power. You will get the most power when the push side length is equal to the other side of the pivot.

 

[Soundguy]

i physcally can not get a larger cylinder on my roll back function on the bucket due to geometry. The fat end of the cylinder (when fully extended) only sits about 1/4" above the loader arm. Course I have the older loader design that pins the cylinder directly to the bucket and not to a 2nd linkage.

Get you a fancy one like this and you got plenty of room for the cyl.. ( it's back on the backside of the upright portion of the mast.. uses a rocker arm and rod to xmit the power. )

 

[IslandTractor]

Lift is obviously how heavy of an object you can lift "at a particular location" with respect to the loader. Some (unscrupulous) companies will give that rated at the lower pivot point. That's beyond the back of the bucket (closer to the tractor) and the number is worthless. A better one is "bucket center" as that is where you will have a load. An even better one is to have it at 500mm forward of the bucket edge. That is where a chained on load like a large log is often located. Heck, I'd be happy if they would just certify how many pounds of heaped dirt can be picked up to full height!

While I agree the use of different measurement points is confusing to new buyers, I'd actually prefer to have the pivot point number to compare loaders. Yes, you will never actually lift anything directly at the pivot points but it tells you more about comparative loader lift than mid bucket especially if you are intending to use a grapple or forks for example. 500mm forward of pivot point (not bucket edge) is also useful for the same reason. Bucket sizes vary however so "mid bucket" lift just favors companies that put shallow buckets on the loader.

Given that we usually do not lift heavy loads to full height, what I'd really like to be able to compare is 1) max volume of gravel or dirt you could lift to full height as you pointed out and 2) max load you could lift to a traveling height, say 2ft off the ground. and 3) "breakout force". Again, it is more useful if that number reflects either pivot pins or 500mm unless you intend only to use the stock bucket.

Regarding the initial question: what is breakout force?....I have always thought it was the combined max force generated by using both lift and curl cylinders simultaneously when the bucket/grapple is on the ground. That is somewhat different (higher) than just curl force at front lip of the bucket.

 

[jinman]

This is my excavator which i use for pulling out trees . It just drags them out of the ground .

My apologies for being totally off topic, but what kind of tree is that in your picture? The bark looks like a sycamore, but the leaves do not look large or solid like sycamore leaves. Sycamores also have lots of large roots (4" to 6" dia) running out very shallow in the ground for sometimes 8' from the trunk. The root ball on that tree looks small, but it could just be my perspective.

 

[john_bud]

Regarding the initial question: what is breakout force?....I have always thought it was the combined max force generated by using both lift and curl cylinders simultaneously when the bucket/grapple is on the ground. That is somewhat different (higher) than just curl force at front lip of the bucket.

If one were to look up the technical specs on how breakout force was measured, one wouldn't have to think about it.... . By the way, I didn't specify which cylinders were used to generate the upward force at the bucket lip.


SAE J732 is written for larger wheel and track loaders, but should also apply to skid steers and compact track loaders. Breakout force is one of the specifications defined, and here is how it is measured;

1. Loader on hard surface, transmission in neutral
2. All brakes released
3. Unit at standard operating weight, rear of loader not tied down
4. Bottom of cutting edge parallel to ground, no more than .75" above the ground
5. If tilt circuit is used, bucket hinge pin must be specified as pivot point, and lift arms should be blocked under bucked hinge pin to minimize linkage movement.
6. If lift circuit is used, pivot point should be specified as lift arm hinge pin, and front axle should be blocked to minimize tire deflection.
7. If both circuits are used, the dominating pivot point must be specified.
8. If the circuit causes the rear of the machine to leave the ground, the force required to lift the rear of the machine is the breakout force.

This is all listed in the Caterpillar Performance Handbook in the wheel loaders section. In the skid steer section, both lift and tilt breakout forces are listed separately. SCUT, CUT and even UT's often don't list which break out is published and some even fail to follow the specs exactly -- resulting in what I call "marketing numbers" that have little to do with what the machine can do.

Your comment on the lift being affected by the size of the bucket is valid, but the manufacturer should list lift and breakout for each bucket as it it part of the spec. Personally, I only want to know how much the machine I'm on with bucket that it has attached can lift. The pivot point number fails to give me a feel for that as it can be hugely different. But, that's just me, YMMV.


jb

 

[IslandTractor]

If one were to look up the technical specs on how breakout force was measured, one wouldn't have to think about it....

There you go ruining a perfectly good TBN thread with data. We could have dragged this out for days.

I understand your point about individual buckets but the manufacturers don't make it easy to find out which bucket they used. I fully appreciate that we don't lift things by the pivot pins but it is at least an easily understood reference point. Actual lift capacity precision is probably not all that useful anyway as our loads are difficult to precisely quantify so for me it is the comparison of one loader to another that is most useful. As few loaders share the same bucket, either the pivot pins or 500mm measurement seems easiest to use.

 

[Eagleview]

My apologies for being totally off topic, but what kind of tree is that in your picture? The bark looks like a sycamore, but the leaves do not look large or solid like sycamore leaves. Sycamores also have lots of large roots (4" to 6" dia) running out very shallow in the ground for sometimes 8' from the trunk. The root ball on that tree looks small, but it could just be my perspective.

It is a Red Gum , one of our Eucalypt's .

They have been wised up about the forces of the wind pushing at them but are new to the concept of this gadget pulling them straight up .

This photo may give you a better idea , that is a full size trail bike beside it . Also you may be able to see the stubs of the larger roots that get broken off and left behind when the tree is extracted .

 

[IslandTractor]

Ironhorse, aren't you guys down under supposed to still be asleep at this hour?