Acrylic Expansion 2

[MECH8T4]

I am working on a drive thru design involving the use of acrlyic on internal panels which will be exposed to temperatures up to 70 degrees C.
I know acrylic will take the heat if expansion clearance is allowed for in a frame, but I don't know if less bowing will occur if thicker as apposed to thinner material is used. I.E will .060 acrylic boy more than .125 material if both were installed in frames?

Also, if I am bonding two pieces of acrylic together with a t molding to leave a gap between them, with the expansion of this assembly be impacted if I use one sheet at .060 and one at .125"? In other words, do I need to made both parts with the same thickness to ensure the assemble expands and contracts correctly?

ANy help on this would be great.

 

[MikeHalloran]

Especially if there's a temperature gradient through the thickness, the thicker material should warp less.

Whether the thickness change at the splice would be objectionable depends on the details and the adjudicator.


Mike Halloran
Pembroke Pines, FL, USA

 

[dhengr]

The coefficient of expansion and contraction is a material property, so a long as the two sheet thicknesses and the joining Tee are of the same material they should move at the same rate. Buckling or oil canning are dependant on the sheet thickness, with thicker being less prone to buckling. I would allow for movement in both directions in the plane of the sheet.

 

[MECH8T4]

Thank you both for the feedback.
The two panels ans the T are both made out of acrylic and it sounds like all should be good with that in terms of movement.

I will be setting up some heat lamps to try to simulate the heat gain for summer motnhs to see how much oil canning will occur.

We normally produce units with .080 thick acrylic, but in this application we are trying to keep the weight down to make it easier to cahnge panels.

We are alos hoping that having the T bond the panel on three sides will help reduce the oil canning from possibly happening.

 

[dhengr]

If weight is a problem, how big are these sheets? What prevents them from being blown out or sucked out by the wind? This will determine the max. panel size, then you study this for expansion and contraction affects. That’s pretty flexible mat’l. when it’s that thin, and under any lateral loading it will tend to deflect enough to pull out of its frame. It will deflect and act like a tension field or tension net, being pulled out of the frame, but held in by the gaskets. As long as you pay attention to the total potential expansion and contraction, with some sort of a gasketed joint which can move fairly freely at the structural frame you should not have much problem with oil canning. If the gasket pinches the sheet to tightly it will put the sheet into compression, all around, and that will cause the buckling or oil canning. I wouldn’t use heat lamps, they provide to concentrated a heat source. I would mount a structural frame with this mat’l. in it, in a wall or a box, and just heat one side, vs. ambient temp. on the other side, enough the represent the max. swing in temps. and watch and/or measure the deflection. What is this bonded Tee joint you are talking about? Show some sketches of how this joins two different thickness sheets on three sides. I don’t see this as improving sheet buckling much.

 

[MECH8T4]

The sheets are about 42"x25" and are held in an aluminum frame. The frame is open on one of the long sides to access graphics that slides in between the two panels. The panels are bonded with the acrylic "T" on three sides. The T is used to close the edges on the 3 sides and at the same time leave a .080 gape btween the sheets for the graphics.

I can get some detials on this on Monday to better show what this is.