Distorded molds

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mammuth
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Joined: Tue Oct 28, 2014 3:48 am
Location: somewhere in the alps

Distorded molds

Post by mammuth »

How are your mdf molds? Do you get distortion on the width axis (concave or convex)?

Mine did this, im not sure where to look for the problem. Part of the problem i had nailed down but it seems the mdf gets compressed during pressing (i press with 4-5 bar)
Tom
skidesmond
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Post by skidesmond »

I've never had distortion, but I don't press that high. I'm usually around 40-45psi (3 bars) . How much support do you have under you mdf molds? Are they security bolted or bonded together?
mammuth
Posts: 449
Joined: Tue Oct 28, 2014 3:48 am
Location: somewhere in the alps

Post by mammuth »

Main problem where my bladders which are too wide for my boards. Thats why i had more pressure on the edges (or even more outside) then on the center (its a 2 bladder system). Could see the problem looking trough the cattrack ... it did bend a little bit.

This problem i address now with smaller bladders .. for a 3 bladder system my boards are too narrow (18-24cm).... the cattrack and bladders where 38cm wide

I think/hope this was the main part of the problem.

Bottom of the press is level (with leveling compound) and doesnt move, otherwise i would see cracks here. I will add a 15mm steel plate and screw it to the I beams to be on the safe side. Together with the leveling compound it should be bombproof .. hopefully

The molds where made out of 19mm mdf standing stripes, bolted together with 10mm threaded rods, the later versions glued and bolted together.

Under the molds i had 19mm mdf laying flat, even these are little bit concave now. Thats what puzzles me.

Were talking here about a few 10ths of a millimeter ... just enough to make the grinding of the board much more time/edge consuming.

I will do the 15mm steel plate and make new molds, this time cnc with flat (laying) centerpiece. Will also do the molds more narrow (board width + 2-3cm) Hope it solves my problem. But if the mdf will have compression i will propably run into the same problems.
Tom
Dtrain
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Post by Dtrain »

What kind of levelling compound did you use? I'm thinking about trying to level my presses 2 lower beams. One has a section that is a sniff lower than the other.
mammuth
Posts: 449
Joined: Tue Oct 28, 2014 3:48 am
Location: somewhere in the alps

Post by mammuth »

It was a self leveling compound for floors. Basically its a type of concrete with mixed in resin for 1-30mm thick applications. When mixed it has low viscosity (almost like water) and very fast cure time (20 min pot life, 3 hours to walk on, 24 hours to drive on). I pressed the first board on the next day.

But ... i used this cause i needed a solution on the same day and its cheap (about 1.30 euros/kg)

I did a 5mm thick layer, thats enough to have a nice level surface.

When i have to redo it i will probably use a low viscosity casting epoxy with a glasfibre mat inside (to make it removable so i can disassemble the press when i move). Disadvantage: 25 euros/kg, Advantage: flexible, doesnt crack
Tom
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