concrete press idea

[setto]

So, I've been searching for a less expensive alternative for a hydraulic press. I thought of concrete.

What do you mean, is it strong enough?

Sorry all dimensions are in cm



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[Jekul]

Hi, have you put much thought into fatigue of the concrete? I'm sure it will be strong enough, but how will it hold up over time? Be sure to think about the heating/cooling too. I think of the concrete driveways and roads up here in the cold country, and the expansion and contraction through a 100 degree F heat cycle is extremely destructive.

[setto]

Yes,

I thought about that. The press will stay in my hobby room. No big temperature differences.

I also thought of making the concrete with fiberglass mats. Such as textile concrete. Maybe putting some steal beams inside is another solution

[doughboyshredder]

concrete is actually extremely weak. The strength comes from the rebar that needs to be embedded in the concrete. If your press is heated there will be major temp differences because of the heating of your press. Because of this you need expansion joints.

The MDF will also deform under pressure and heat when oriented in that way. I learned this the hard way.

So is it doable? Yeah, but you need to design it with rebar, expansion joints, and a surface other than mdf.

[jono]

Basically you will be making a press out of several concrete beams that will be held together by steel rods.
The stresses on the vertical concrete beams in your design would be better taken with more steel rods.
Concrete reinforced with rebar, metal mesh and lots of shredded fiberglass would probably work for the horizontal parts of your press (including the press bed).
Concrete does not seem like an ideal material for a ski press, particularly the parts of a ski press that undergo expansive forces. I would expect to see cracking from the first time you ran it through a heat and pressure cycle. On the other hand, concrete reinforced with nylon, carbon or fiberglass fibers and rebar is an intriguing idea for a press bed or other horizontal members of a ski press that undergo compression. The advantage to using concrete would be the ability to make an integrated base mold/cassette/press bed that could be internally heated and formed into any shape.
I wonder if making the horizontal members of a press with reinforced epoxy resin would work better than concrete? The resin could then be machined to any form.

[hugocacola]

Can i ask Why concret????

no big idea , concrete is very heavy...and with pressure vs temperature could blow....

[setto]

Can i ask Why concret????

thought it would be the cheapest way on making a press.

But I think it wouldnt be funny, if it broke, when I stand next to it.

[chrismp]

cheapest way to build a pneumatic press imho is using cordura like we did.

does the job nicely and the raw materials for the press frame arent really expensive since its all particle board, some formlining boards and a couple of screws.
if you have questions you can pm me in german

[Yuki_otoko]

concrete is actually extremely weak. The strength comes from the rebar that needs to be embedded in the concrete.

Almost right. It is actaully very strong. But only under compression. Reo is only used to hold it all together.

Take for example, a beam poured for construction such as a bridge etc. In ski/board construction we use laminations with the principle of compression and tensile principles. The top layer is pushed into its self, while the bottom layer is tying to be pulled apart. The middle does very little, it is only there to give distance between the top and bottom. When weight is added and things start to bend, two arcs are created. Naturally the outer arc is being pulled to a longer distance than the inner (top), while the top is being compressed. The bigger the distance between top and bottom, the more compression loaded into the top. Large spans are a testament to its strenght.

It will need to be thick and decent reo added. Dont let the reo become close to the outer as it will allow concrete to chip off, and loose all strength.

I think Snowboard Materials used to sell a hydraulic press set up with concrete molds to accomodate the complex 3D shape of board. So it could be done to make a bottom mould, but uprights definately wont work as the concrete will be used under tension.

The best way would be to use the method that Chrismp, Shopvac and others have used to complete the rest of the press. But then your half way there so you might as well make the whole press that way.

[knightsofnii]

yea concrete can be used, but not in tension or shear like you're planning in your design, throw an air bag in there and pump it up, that thing will explode.

You COULD make your MOLDS out of concrete though, I recall a wakeboard builder using concrete molds. You could basically use the concrete anywhere that is taking only a compression load.

Or you could use the concrete as the legs of the press to hold it up. But not as the internal structure itself.