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Motor size for hydraulic press


Caleb Gant

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I am currently in the process of building a press from I beam and the hydraulics from a log splitter. The log splitter I'm looking at picking up has a 6 hp  gas motor that is broken. I don't know if it's repairable or not but I'm assuming not. The splitter is rated for 25 tons.

With all that prefacing out of the way here is my question: is 6 gas hp enough? most presses  I've seen use a 5 hp electric motor which if what I've read is right would be a 15 hp gas motor. Does this mean that most log splitters run at a lower psi (due to lower torque) or am I missing something. 

Thanks

-Caleb 

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Log splitters are rated by tonnage not horsepower so if it's rated 25 tons and has a 6hp gas engine that's what it is.  If you put an eight HP motor on it it MIGHT have more push but I can't say for sure. 

Log splitters do stall on a tough block so there is a set psi above which it escapes over bypass. If the bypass valve says 25tons worth of psi is ALL YOU GET!:angry: Then that's it, a larger engine won't make more tonnage though you can under power it with to small an engine.

You shouldn't have any trouble coming up with an engine for not much, they're everywhere.

Frosty The Lucky.

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Good Morning,

Most Log Splitters are manufactured with huge safety margins. Engine governors are not set to max speed, relief valves are set to lower than max. Is the pump a high pressure / low volume, low pressure / high volume (a 2 stage pump). If it is a 2 stage pump, you don't need a high HP engine. I built a log splitter that I also use for a press. i used a 1200 VW engine because that is what I do. I used a 2 stage pump and the creaking a groaning was spooky at first.

Neil

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thanks for the replies. I did not do a good job of asking this question but I was more wondering if the equivalent electric motor hp (2 hp) would be enough to get the same tonnage from the splitter. I am very happy with 25 ton so I am not looking to get any more power out of it just to maintain the same power rating and not under power it. Iam not sure if the pump is 2 stage or not but i can probably find out.

thanks

-caleb

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Remember that the two main factors of a forging press are PRESSURE and SPEED. You can be putting out 25 tons of force, but if your ram is only travelling at 1/4" per second, the workpiece will cool faster than you can forge it.

It's good that you have a cylinder rated for 25 tons. What you need to do is find out the speed of the pump in gallons-per-minute (particularly the high pressure/low speed setting, if it's a two-stage pump) and the diameter of the piston inside the cylinder. The latter will give you the area of the piston. From this, you can calculate how big a motor you need.

To do this, you need to calculate the fluid pressure and then the horsepower. You calculate the fluid pressure by dividing 50,000 pounds (25 tons) by the area of the piston in square inches (radius of the piston in inches, squared and multiplied by pi). You then calculate the horsepower by multiplying the fluid pressure by the pump volume in gpm and dividing by 1714.

Here's an example. Let's assume your cylinder's piston is 5" in diameter and your pump is putting out 4 gpm. That gives a piston area of about 19.63 square inches. 50K pounds divided by 19.63 is about 2,545 psi. 2,545 psi x 4 gpm = 10,180; 10,180/1714 = 5.9 HP. Call it a 6 HP motor.

Now to calculate the ram speed. To do this, you need to calculate how far the pump's speed in gpm will displace the piston in one second. You already have the area of the piston in square inches, so an equal number of cubic inches will move the piston one inch. What you need to do now is to multiply the pump gpm by 231 (cubic inches to a gallon), divide by the area of the piston to get piston speed in inches-per-minute, and divide by 60 to get inches per second.

Going back to our earlier example, your 4 gpm pump will move 924 cubic inches per minute. Your five-inch piston will need 19.63 cubic inches to move one inch, so 924/19.63 = 47 inches per minute. 47/60 = 0.78 inches per second. That's a bit slow, but acceptable at with that tonnage.

All this depends on the work you want to do, of course. To quote IFI member Ric Furrer, "I do some work where 24 ton is too much force and others where 1,000 ton is too little."

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a 5hp gas engine will have a slightly lower power output than a correctly rated 5hp electrical motor. This is due to gas engine hp ratings not taking into account the internal friction losses, Also electrical motors are rated at full output which they can do  nearly forever and is calculated as volts times amps, Gas motors are rated for continuous duty not peak, which due to many factors, are not the same for gas powered motors and are calculated at a specific RPM (3600), even tho they can run at various PRMs.

Most motors can put out a lot more maximum horsepower than they can sustain continuously in addition the rated HP for electric motors is based on the torque  that the motor can be ran continuously without exceeding the temperature that the windings break down. whereas with gas motors the torque values are based on 3060 RPM and their Hp are based on 3600 to confuse things even more

 

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After reading your message at least 3 times I think I under stand what you're saying. 1 the actual peak hp output of a gas motor will be slightly less than its rated for due to friction and 2 a gas motor will not be running constantly at its peak hp like an electric motor would be and 3 whoever decided how to label motors wanted to make everything harder for everyone. I think that I am going to get either a 4 or 5 hp electric motor to replace the broken gas motor if I cant fix it. if I get really impatient maybe ill hook and old 17 hp riding lawnmower engine haha ;-)

Thanks

-Caleb

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One would hope this doesn't need to be said, but don't run ANY gasoline powered motor inside unless you have a dedicated exhaust system that will clear every bit of CO from the building.

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I haven't been there since the late 60s but there was a salvage yard in Burbank Cal. that had the coolest surplus and salvage anywhere. There were a number of engines from the Saturn V. Sitting in an apollo capsule wasn't in the offing, it was sitting on the heat shield on a stand and I couldn't lift myself high enough to get in, the interior was pretty stripped though. I did crawl into an Gemini capsule and still wish I hadn't. They are NOT designed to crawl around in laying on their side. 

There were stacks of: rocket engines, old sea mines, who knows what space gear. The salvaged computers from JPL were state of the art for the day they had transistor motherboards and a garage sized bank was probably 256kb!

I liked visiting that salvage yard better than Disneyland. Dad hauled me along to help carry what he got, he was usually looking for special alloys for the shop. 

This is the salvage yard the TV series "Salvage 1" was based on. 

Frosty The Lucky. 

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I will have to check out big dog forges video.Thanks for the suggestion. Frosty that must have been so cool. I hope to one be an astronaut so I would to get to see something like that. JHCC dont worry ill wear a mask while I produce carbon monoxide inside with all the doors closed. I mean what could go wrong?

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Horsepower is force x velocity. 1hp is 550 lb*ft/s

That's a quick way to figure out how much power you need to drive a cylinder a desired speed.

Using the same numbers as JHCC above of 50000 pounds at .78 inch/sec ; 50000 lb*.065 ft/s / 550 lb*ft/s = 5.9 hp. The same number he calculated from pressure and gpm.

If you had a 8 hp motor how fast would that push it?  8 * 550/50000 = .088 ft/s, or 1.06 in/s

That 1200 VW at peak 40 hp?  40*550/50000 = .44 ft/s, 5.28 in/s

 

 

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3 hours ago, Boondoggle said:

Horsepower is force x velocity. 1hp is 550 lb*ft/s

If electrical energy were converted into mechanical energy with no loss, it would take 746 watts to lift 550 lbs. One foot in  one second. 

Pnut

I copied this directly from Industrial Hydraulics by Richard W. Vockroth

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A 3HP electric motor will replace a 5 hp petrol engine, so a 3.5 hp electric motor is what you need. 

Of course if you buy a Chinese motor, all bets are off, their rating has a creative component. 

otherwise 3.5 should do it.

 

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Whether or not the motor is Chinese has nothing to do with it. What's critical is to look at the continuous HP rating, which is the true measure of a motor's power. Many less-expensive motors are rated with peak horsepower, which is the maximum power a motor can reach for short periods of time. That's basically a marketing gimmick, allowing sellers to advertise motors at a higher hp than they really are. The thing to look out for is "SPL" next to the hp rating. Officially, that's short for "SPeciaL", but I read somewhere that it really means "Someone's Probably Lying". 

I just bought a Chinese motor for my hydraulic press. It's rated to draw 22 amps at 230 volts with an 80% efficiency. Using an online FLA-to-horsepower converter, I find that that gives me a true continuous HP of 5.4.

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8 hours ago, Boondoggle said:

Horsepower is force x velocity. 1hp is 550 lb*ft/s

That's a quick way to figure out how much power you need to drive a cylinder a desired speed.

Using the same numbers as JHCC above of 50000 pounds at .78 inch/sec ; 50000 lb*.065 ft/s / 550 lb*ft/s = 5.9 hp. The same number he calculated from pressure and gpm.

If you had a 8 hp motor how fast would that push it?  8 * 550/50000 = .088 ft/s, or 1.06 in/s

Not quite. For a hydraulic press, your calculations ALWAYS need to include the size of the cylinder and the capacity of the pump, because the speed of the ram depends on the volume of fluid being moved in a given amount of time.

The math happens to work in this case because the 5.9 hp was based on a 5" cylinder and a 4 gpm pump. If you change that to a 6" cylinder and keep the motor and the pump the same, the tonnage actually increases to about 35, but the speed goes down to 0.54 inches/second. If you want to get 25 tons at 0.78 inches/second out of a 6" cylinder and a 5.9 hp motor, you need a pump that puts out 5.72 gpm, while if you want that same tonnage and speed from a 6" cylinder and a 4 gpm pump, you need a motor that puts out a little over 4 hp. 

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  • 1 year later...

I just did what you are talking about...I converted a 22 ton 11gpm 2 stage log splitter that had a 6 hp engine...I used a new 5 hp electric motor with everything else the same...The  4 inch ram works fast enough.  Working indoors is why I switched to electric...It moves metal BUT the biggest issue is the press dies had to be made smaller as the larger dies sucked out the heat too quick..dropped from 2" round to 1/2" rounding dies to lengthen the billet.  I may change out the ram and pump at some point but it does work right now.

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