How big of a cylinder

[Hooked_on_HP]

I am going to put power angle on my 6' rear blade. I am trying to decide what diameter cyl. I need. It doesn't take much pressure to angle it but I am concerned with the force on it when I am moving dirt with the blade angled. Is there a rule of thumb or formula to use.
Bill

 

[AKKAMAAN]

I am going to put power angle on my 6' rear blade. I am trying to decide what diameter cyl. I need. It doesn't take much pressure to angle it but I am concerned with the force on it when I am moving dirt with the blade angled. Is there a rule of thumb or formula to use.
Bill

Go for a larger bore if you can, or better use two cylinders , one on each side, and cross connect them (blade pivot point in center??)....that will keep the hydraulic shock-pressure down if you hit a curb etc....also it will make the hook up more rigid, and it will be less risk to bend the cylinder rod....

 

[MtnViewRanch]

The factory blades that come with hydraulics usually have 4" cylinders for the angle and offset and 3 1/2" for the tilt. I doubt that you need a 4", but I would use a minimum of a 3" cylinder. In fact I am going to use a 3" cylinder for my landscape rake when I ever get around to reworking it.

Keep in mind that a longer stroke cylinder will give you better control of the angle on your blade. The factories usually use 16" stroke cylinders for their angle and offset hydraulics

 

[J_J]

I am going to put power angle on my 6' rear blade. I am trying to decide what diameter cyl. I need. It doesn't take much pressure to angle it but I am concerned with the force on it when I am moving dirt with the blade angled. Is there a rule of thumb or formula to use.
Bill

2 in cylinders should be good enough. They will push a load of 7800 lbs.

 

[MtnViewRanch]

2 in cylinders should be good enough. They will push a load of 7800 lbs.

While the 2" cylinder seems like it would be strong enough, are the rams themselves strong enough to take all of the loads that they are given? If Bill decides to use 2 hydraulics to do this, then he might be alright, but if he is going to use only one, I would not recommend it. There is a reason that the OEM guys use 4" cylinders, and I am pretty sure that none of those reasons include because the 4" hydraulics are so cheap.

 

[Brad_Blazer]

The formula is (cylinder force) = (blade tip force)*(tip distance)/(cylinder distance)
Also (cylinder force) = (hydraulic pressure)*(cylinder area)

The area of the rod has to be subtracted when calculating the cylinder retract force.
For distance in the first formula you need the perpindicular distance from the line of action of the force to the pivot point. For example let's say the 6' blade is set square and the minimum distance from the cylinder centerline to the pivot point is 10". You catch a rock with the corner of the blade and the momentary force to stop the tractor is 5000lb.

Cylinder force = 5000*36"/10" = 18000lb

When you angle the blade the distances change. At an extreme angle when the cylinder distance is very small and the leading edge of the blade starts to cut in you have an inclined plane effect adding leverage to straighten the blade even though the tip is not so far from the pivot in the direction of travel.
I would call that close to worst case. Let's say 3000lb x 36"/3" = 36000lb

These are just example numbers to get you thinking about your application. If you give the pin-pivot dimensions for each cylinder mount along with the retracted and extended cylinder lengths I can plot you a force curve.

 

[AKKAMAAN]

While the 2" cylinder seems like it would be strong enough, are the rams themselves strong enough to take all of the loads that they are given? If Bill decides to use 2 hydraulics to do this, then he might be alright....

You will need four (4) 2" bore to make up for one (1) 4" bore.....

You catch a rock with the corner of the blade and the momentary force to stop the tractor is 5000lb. Cylinder force = 5000*36"/10" = 18000lb

That was my point too, if you hit a 2" cylinder with a force that is twice the capacity, cyl can bend, also If cyl can push....also a 18000lbs (9 ton) force on a 4" bore will create 2870psi as a shock pressure, 9ton on a 2" bore will create four(4) times that that pressure, 11480psi!!!!!! Pay attention!! there is more to it than the pressure from the pump!!!!

One question that will effect the deisgn is...
"Do you need to angle the blade equallly to both sides (symmetric)???"

If not you can have blade pivot point off center, and get away with a one (1) cylinder design.

If this is a rear blade (pulled instead of pushed), you can definately go with some smaller bore, if design allows blade to "lift", when hitting an curb, rock or other.....


Using only one double action cylinder bring some problems along the path....

• 
  different force and speed on extend and retract.....

• 
  unbalanced support on the blade, cylinder have to sit on one side, which means blade need an "off center" pivot point....and that will take a long stroke cylinder.....

I am advocating two(2) cross connected cylinder because...

• it will equalize both sides of the blade......This means no differens in speed/force on each side...

• 
  makes symmetric angling possible

• 
  Give design more rigidity

Cross connected 2"x1.5"rod
extend-retract, force 5.6 ton
Double action ratio 1.0 (equal)

Cross connected 3"x1.75"rod
extend-retract, force 15.5 ton
Double action ratio 1.0 (equal)

Cross connected 4"x2"rod
extend-retract force 27.5 ton
Double action ratio 1.0 (equal)

With cross connected cylinders we can allow a larger diameter on the rod (for more rigidity) without changing the double action ratio

If you choose a one (1) cylinder design, go with larger bore, 3"+

If you choose a two (2) cylinder design, you might get away with 2" bore-1.5" rod

The rod diameter is critical on small diameter bore......thats why, sometimes, larger bore is used....

 

[dcyrilc]

The formula is (cylinder force) = (blade tip force)*(tip distance)/(cylinder distance)
Also (cylinder force) = (hydraulic pressure)*(cylinder area)

The area of the rod has to be subtracted when calculating the cylinder retract force.
For distance in the first formula you need the perpindicular distance from the line of action of the force to the pivot point. For example let's say the 6' blade is set square and the minimum distance from the cylinder centerline to the pivot point is 10. You catch a rock with the corner of the blade and the momentary force to stop the tractor is 5000lb.

Cylinder force = 5000*36"/10" = 18000lb

When you angle the blade the distances change. At an extreme angle when the cylinder distance is very small and the leading edge of the blade starts to cut in you have an inclined plane effect adding leverage to straighten the blade even though the tip is not so far from the pivot in the direction of travel.
I would call that close to worst case. Let's say 3000lb x 36"/3" = 36000lb

These are just example numbers to get you thinking about your application. If you give the pin-pivot dimensions for each cylinder mount along with the retracted and extended cylinder lengths I can plot you a force curve.

I'm not familuar with the term "cylinder centerline". Explain please.

 

[kennyd]

I am going to put power angle on my 6' rear blade. I am trying to decide what diameter cyl. I need. It doesn't take much pressure to angle it but I am concerned with the force on it when I am moving dirt with the blade angled. Is there a rule of thumb or formula to use.
Bill

I always look at how OEM's do things when I am trying to copy them...

So, I went to Land Prides web site and looked at RBT3572 hydraulic blades, found the manual (linked for you) then found the cylinder description on page 13 in section 3. It says they use a 3.5x14x1.5 cylinder for the 72", 84" and 96" blades.

 

[MtnViewRanch]

I always look at how OEM's do things when I am trying to copy them...

So, I went to Land Prides web site and looked at RBT3572 hydraulic blades, found the manual (linked for you) then found the cylinder description on page 13 in section 3. It says they use a 3.5x14x1.5 cylinder for the 72", 84" and 96" blades.

I agree, there is a reason why most if not all the OEM's make their hydraulic rear blades virtually the same. That particular design works.

One of the problems with using 2 cylinders to angle the blade is that now it is a lot harder to offset the boom. But if his blade doesn't offset anyway, then the 2 cylinder angle would work.