Cardboard Crusher

Pressure is an easy physical measure - just reduce the area over which the force is applied....

Take a sheet of cardboard, and press it down with a pencil end. Does it go flat? What force did you apply? What is the cross-section of the pencil end? Area times force is pressure.

NOW you start looking for useful cylinders to apply a decent margin over that pressure..

Get the picture?

Brian Whatcott Altus OK

I understand the calculations that is simple. However, given the size of the corrugations in cardboard, I don't think a pencil is a large enough sample size to get any reliable data. With a large enough sample size to get good numbers I don't think I could exert enough force in a measurable way with out building some apparatus. I am trying to avoid doing that. I do have an air cylinder that with some 1.5 ID tubing, a little machining and welding, I could use the air cylinder to do some tests if I can't find more data from the net.

I am trying to wean you away from looking for net inputs, in favor of easy, easy tests.

If you don't like a pencil, then choose a bigger punch tool.

I looked around my study: what is round and flat about 3/4 inch diameter? Ah, here's one, a plastic bottle top.

Gather a cardboard sample, a bottle with a measured top diameter, and a bathroom scales.

1) Place cardboard on scales. 2) Press down on cardboard with bottle top. 3) Read scales. 4) Measure force to flatten cardboard (F lbs). 5) From bottletop diameter D in, calculate its area A sq in A = pi X D X D /4 (pi = 3.142) 6) From bottletop area A and force on scales F calculate the pressure to flatten the cardboard F/A psi

Then, if you have a ram on hand and a pressure source, you can work out your available crushing force You can calculate the crushing head diameter to achieve the crushing pressure you worked out above.

You can do this. It is not hard.

Brian Whatcott Altus OK

What you are measuring is the flat crush resistance of the corrugated board. That will vary with flute size (A,B,C,F,micro-flute, etc.), flute paper weight, liner weight, single-wall vs. double-wall vs. triple-wall construction. And flat crush resistance is only useful if you are trying to compress a nice flat stack of corrugated boxes (cardboard is actually a misnomer).

If you are trying to compact boxes at random (as in a garbage masher) then you also need to consider the edge crush resistance of the corrugated box. This is defined as the resistance to crush when loaded perpendicular to the flutes. This is a measure of the corrugated board's stacking strength and is expressed in psi. 44psi is a very typical target ECT (Edge crush test) value for quality boxes (i.e. not the cheap crap that stuff from China coms in); the actual would typically err on the high side. Actual crush strength would depend on the size of the box (square inches of corrugated board) and the loading. Strenth will be much higher if the load is applied perfectly perpendicular than if there is a lateral component to the loading.

As for how tightly you can compress it, try a little experiment. Take an ordinary piece of paper and crush it as hard as you can into a little ball. Notice how it springs back a little? Notice also that as hard as you crush it, that one lousy piece of paper is probably thicker than a stack of 25 sheets. Corrugated boxes behave the same way, only the spring-back is worse. It is a remarkably resilient material.

If you really want to fit as much corrugate into as small a space as possible, your best approach is to try to cut it up into flat pieces so that you can attempt to approach the theoretical minimum size, which is basically the thickness of all the layers of paper in the box.