Thread: 55t press

here is another drawing, end view, of the head. Missing the holes and also the top plate that will bridge over the top of each PFC....

Top and bottom flange of 250PFC are 16mm thick. Web is 8mm thick. At this stage the 2 - 250PFC beams will be bolted to the uprights, which will also bolt angle (say 100x100x12) to the inside of each web. Then a end plate of say 250 high x 340 Long x 12 thick will be bolted to each angle. This fixing the beams together

note I have added some 30x12 flat to the top outside edges of the ram mounting plate. Im thinking to bolt these to it with M10 socket caps. These 30x12 will act as lock in rails, with only a small gap between them and the beam. Doing this on the top also should help the beams stop deflecting when the press is in use...

open to any ideas on size of material, design and bolt sizes.

looking at some bolts today, I doubt I can get any more than 150mm centers on the bolts in the PFC's. When you take into account the head size, the flange thickness and the radius from flange to web....

Originally Posted by uninformed

so maybe one of the engineering types can tell me if 250 PFC will be strong enough for a basic 55t H frame press. It will be 2 peices top and 2 peices for the table. 100x16 flat for the verticals, 2 each side with 200mm speration. Im thinking a 32mm dia hole/pin for the table height adjustments. I can box in the 250 PFC if needed. Frame width will be approx 840 clear between the 100x16 flat bar verticals

I don't have my steel structures code (AS4100), steel sections books, safe load tables, or steel design software with me, otherwise it would only take a few minutes to check properly. That also means I can't check in accordance with the code so I will do a rough back of an envelope check here to see if it is in the ball park.

With what you want to do I expect the shear capacity of the 250 PFC (parallel flange channels), not bending to be what determines the capacity of the press structure.

Now with beam sections used like like this, most of the vertical shear is carried by the web (most of the bending is carried by the flanges). So we can quickly check the shear stress using just the web area, Aweb = 250mm x 8mm = 2000mm^2 – note I haven't subtracted the area of holes in the web so we may have to address that later.

The vertical shear load on the 250 PFC is greatest when 55 Tonne is applied close to the supporting uprights, so assume 27.5 T on each PFC at the support.
Now 27.50 T results in a load of approx 275 kN (kilo Newton)
Use 1.5 live load factor (for simplicity I'm ignoring dead loads (weight of members, etc.) here)
Then factored live load is V = 1.5 x 275 kN = 413 kN approx
Then shear stress = 413 kN / 2000mm^2 = 207 MPa (unsatisfactory).

The shear capacity of 250 PFC is too low when the ram is used to press 55 T at one end. Restrict the use of 55 T to when the ram is close to the mid span. When the ram is near the supports about 30 T should be OK. Holes in the web will reduce the capacity unless you weld some compensation at least equal to the hole area onto the web.

Web stiffeners will be required at the support and load locations. These are required to prevent the web from buckling – usually for a 250 PFC they would be 75 x 10 (or 75 x 8) flat bar extending between the flanges with one edge welded to the web and the ends welded to the flanges.

PFC (and angle) sections are not symmetrical so their shear centre is offset, resulting in torsion when load is not applied through the shear centre. For a 250 PFC the shear centre is about 30 mm from the back of the web. For this reason you should arrange the pair of PFC's so their toes are pointed out, i.e. ] [ You will also have to restrain the PFC's to resist twisting – weld something between them, near the supports at each end, and if it can't extend for the 250 depth, then it should at least tie them together at the top and bottom.

For the 100 x 16 FB uprights: the cross sectional area is 1600 mm^2
For a load of 413 kN, the tensile stress is 413 kN / 1600 mm^2 = 258 MPa (unsatisfactory).

Like the 250 PFC's the capacity of these members is too low unless you restrict the use of 55 T to when the ram is close to the mid span. When the ram is near the supports about 30 T should be OK. Holes in the uprights will reduce the capacity unless you weld some compensation at least equal to the hole area.

For 32 mm diameter pins the cross sectional area is 804 mm^2, so you would need 3 pins each side (or use high tensile strength material) to match the shear capacity of the 250 PFC web.

Originally Posted by uninformed

Is this more for bolts in true shear? say like the bolts holding the head beams to the flat bar uprights? 32mm dia will work in the 100mm flat and be within your rule.

I was looking at the bolts in my driveflanges and thinking no way 1.5 rule. But they are creating a friction fitting so shouldnt see shear (in a perfect world) right?

where Im concerend about material left outside the bolt hole is bolting the 75x12 to the 100x16. The bolt passes through the 75 and will be going into the 16. These bolts are clamping and im not quite sure what forces they will see. The 75x12 is used to help stop the 100x16 buckling (my guess) below the table the uprights would be in compression and above it they would be in tenstion....when the press is in use??? In Dave's press he has used 3/8th bolts at 8 inch spacings passing through the 75 into his 19 (he has used 100x19, I had already ordered 100x16)

If I use the 1.5 rule in 16mm I can use a 5.333333333 mm bolt. I was thinking 5/16 but may have to go to 6mm. Any smaller and I was thinking it to small to be any good??

The rule I gave before is the edge distance required by the Steel Structures Code, i.e. 1.5 x bolt diameter for flame cut or sheared edges or 1.25 x d for machined or rolled edges (for simplicity I have ignored the revision to AS4100 that changed the wording a little to increase it to account for clearance between bolt and hole). The code considers all types of failure of the joint.

The above was not specifically for distance from threaded holes per your original question, and I had little idea of what you had in mind.

I will have to digest more about what has been posted since to try and understand what you are wanting to do and form some idea of the loads, etc. For the moment my thinking is leaning toward recommending you need to change your design - unless the bolts don't carry much load, in which case the question is, why are they there?

It could be a few more days before I can reply.

Hi John.

Isn't the 55ton load supported by four sections of 250PFC in shear?

From what I understand of John's calculations, he is considering the load case where the ram is located hard against one side of the frame. In this case most of the load is placed on only 2 sections of the 250PFC and one upright. If the ram was located in the centre of the span, the load would be spread evenly across both uprights, and hence 4 sections of the 250PFC. Having it hard against one of the mounts is the most extreme load case which can/should occur, so that's what he's designing for.

I'm only a student engineer, we're learning some of this stuff at the moment, so that's about all I feel qualified to say. Also, feel free to correct me if I'm wrong!

-Martin

Originally Posted by turkeybrain

From what I understand of John's calculations, he is considering the load case where the ram is located hard against one side of the frame. In this case most of the load is placed on only 2 sections of the 250PFC and one upright. If the ram was located in the centre of the span, the load would be spread evenly across both uprights, and hence 4 sections of the 250PFC. Having it hard against one of the mounts is the most extreme load case which can/should occur, so that's what he's designing for.

I'm only a student engineer, we're learning some of this stuff at the moment, so that's about all I feel qualified to say. Also, feel free to correct me if I'm wrong!

-Martin

Reading it for the third time, I think you're right. I hadn't considered that situation as all the presses I've used had the ram fixed dead-centre.

Nice work Serg! I have only just seen this thread.

Guess I shouldn't tell you what a chinese 50t press sold for at the glenfords sale over here...

I picked up a 12T for <$100 which should be enough for my needs...