Press build, where to put the HP

JTknives

JTknives

Joined
Jun 11, 2006
Messages
8,651
So the plan is to get my press build over the winter. I have a rolling mill build with Salem planned in the spring/summer so I need to just bite the bullet and get it done. The press design I have mostly figured out but where I'm questioning my self is all the numbers. Tons, HP, IPS exc. I guess what I'm questioning is speed vs tons. I'm sure there is a happy medium. I can see that you could quickly build a press that is to fast. Or you could have all the tons in the world and be to slow to really work the steel efficiently. I'm going to start rounding up the parts as soon as I can nail a solid plan down.

So far my plan is to use the 10HP 3ph motor I have. I will power it with a 10hp VFD off a 50amp 220 line. I have gone back and forth between more tons and less tons trying to find a happy IPS. I'm also planning on using a single stage vane pump. The numbers I first settled on was a 5" cylinder @ 2500psi and 5.5gpm. This would give me 25 tons at 1"IPS. This still leaves alittle HP on the table according to the charts. The math says I can bump it to 3000psi and still be within the 10hp rating. This will give me 30tons at 1"IPS. I then started looking around the web and find people that seam to be getting almost this out of 5HP motors or so thy say. Or people that say thy run 10-12gpm single stage pumps on 10hp. All I have for reference is what the charts say and thy say those pumps need much more HP then 10. I found another cylinder That is 4.5" and rated to 3500psi and the pumps are rated to 3650 I think. So my next thought was run this 4.5" cylinder at 5.5g with 3000psi. This gives me 24 tons at 1.33"IPS. Or go 2000psi at 8.25gpm which gives me 16 tons at 2"IPS. But if I go in the middle between those With 2500psi @ 6.25gpm I get 20 tons at 1.63"IPS.

So as you can see there are way to many options for me to decide. And being that the only press experance I have is with my mini press and a few min on salems press I'm not quite sure what I want or need. But a question I have that I have not found an answer to is this. Say I pick a pump rated for more GPM then my motor is rated for. Will the motor slow down and the GPM drop when max pressure is reached. I guess what I'm asking is if the HP rating on the charts is x PSI with x GPM needs X HP if you want to keep X GPM constant. Or is it saying going over that GPM will lock your motor up not just slow it causing less GPM. It seams like more and more people are saying speed is more important then a bunch of tons. It does not cool the steel nearly as fast and you can work it longer. I will be mostly using it for damascus. But I will use it also for drawing out larger stock into more manageable forging stock sizes.

Thanks guys for any advise or tips you can offer. If you have a press and would or would not make changes let me know. Thank You

P.S. My motor is 1745 rpm
 
If you pick a pump where the GPM@PSI has a greater HP requirement than your motor, you will stop the motor. That's the mistake I made in my press initially, with my HP requirements calculation. If your GPM@PSI requirement is equal to your motor HP, the motor will slip a little as that PSI develops. That's how mine works now.



Because the circuit is a triangle it's helpful to ground one leg when you're planning. You have a 10 HP motor to build around, so use that as the fixed variable.

Ignore GPM and focus on displacement. GPM is simply the product of pump displacement and RPM. We'll assume you don't want to double your motor RPM with your VFD.

RPM: 1745
HP: 10

With a standard .6 cu/in pump at 3000 psi you need 9.1HP to maintain GPM at full pressure. A 4.5" cylinder will move 1.09" per second and will make 23.8 tons.

Knowing that your motor can drive that displacement at 3000 PSI, you can look at a 2 stage pump with a high pressure displacement that's similar. So a 2 stage pump with .465/1.395 displacement (22 GPM). At low pressure, 500 PSI, the 4.5" cylinder will move 2.55 IPS, and require 3.5HP in that stage. At high pressure, 3000 PSI, it will move .85 IPS and require 7 HP to move that speed at full pressure.

That 4.5" cylinder is only going to make 23.8 tons no matter how much HP or GPM you have, if your max PSI is 3000, so if you accept the above example as plenty fast, and that going over 3000 PSI gets much more costly than it's worth, if you want more tonnage you will have to sacrifice some ram speed by going to a bigger cylinder.

A 5" cylinder, with the 22 GPM .465/1.395 2 stage pump at max 3000 PSI will move the ram 2 IPS at low pressure, and at high pressure it will move .688 IPS while generating 29.5 tons. Still requires only 7hp. So you're leaving some performance on the table here, but this would be a pretty wicked press.

The next option I see is a 28 GPM 2 stage, it has the same displacement in low range as the 22, .465, but a higher low pressure displacement, 1.860. I don't know that low pressure speed over the 2 IPS above is worth the cost.

Back to the .6 cu/in single stage pump. Plug those numbers in with the same 5" cylinder and you get something that moves .88" per second all the time, at 500psi or 3000, and makes the same 29.45 tons. It uses 9.1 HP at full pressure.

I think that's actually the best option. Fast travel speed on the ram in low pressure is nice, but I think having a faster movement at full tonnage is even more useful. Both are within your HP requirements. Both make nearly 30 tons. The difference is only the importance you place on when the press is "fast." If I was building a new press around a 10hp motor I had laying around, that's what I would do. Mine works well enough for me but I didn't have a 10hp motor.
 
Also, why a vane pump instead of a gear? You can get a .61/rev Dynamic gearotor with max PSI of 3650 for about $100.
 
You know I don't know. I had thought that the cane pumps where less loud then the gear pumps. What I was wondering is my motor is rated at a 1.15 service factor which means it can run up to 11.5HP. Not full time but a press is not full time. The vfd I'm looking at is rated at 34Amp output. My motor says 24 amp draw at 230v. This leaves me to think the vfd could handle over driving the motor briefly to the 11.5HP. Which would put a 5.25" cylinder at 32.5 tons going 1.17"sec. Or go with a 5" cylinder at 3000psi and adjust the VFD speed to adjust ram speed. This way you could In fact change tons and ram speed on the fly. Want 20 tons at 2"min then bump the rpm up and drop the pressure. Or drop the rpm and up the pressure to get more tons at less ram speed. Could be the best of both worlds.
 
So the quick numbers with using a vfd are as fallows
10HP
5" cylinder
1in^3/rpm pump

At 3000psi
29.45 tons @ 1.12"/sec
1320rpm

At 1500psi
14.75 tons @ 2.24"/sec
2640rpm

Or anywhere in between. But I'm not sure how a vfd affects torque when running a motor over or under the motors rated RPM.
 
I think that at ram extend speeds of at least 1 IPS, you may find it attractive to use a single stage pump and live with the relatively slow ram speed, gaining the benefit that the ram does not slow when it hits the steel. Since you're working with a 10 hp motor this makes more sense than if you were limited to 5 hp like my press, in which case a 2 stage pump is a better option. Some higher end presses, such as Larry's, operate on this principle and it makes sense to me.
 
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