Brushing resin on inside of box

[dem beats 1,223]

like i said.. then you can show us your reports from your material tester?? and you have yet to explain why it reduces it? answer me this. if the mdf become brittle. it means it became harder, but more easy to break in a stressfull situation. correct? i will aggree.. now do you honestly think that in car audio we will bend the mdf enough to fail because of this brittleness? i dont think so.. ever... so the initial hardness that the resin gives the mdf. makes it HARDER...

Testing it is super easy. It's been done. When it reaches it's failing point will delaminate and then break. The "soaking in of resin into mdf" isn't what it appears to be. This is what causes the failure. There is no bond between the resin and fiber in the MDF in the way you are thinking. The resin does not integrate with the wood fiber to result in a true composite (read matrix) type material.

Resin alone will do nothing but smell bad cost more money and time, and be a bigger mess. It probably won't weaken the MDF enough to cause failure in the thickness used in CA, but it's definitely pointless, for the application we are looking at. What M5 was saying originally was to let the OP know that it is a waste of time. Not that if he did the enclosure will break for sure.

The basic principals of why composite materials work is you are putting together both compression strength and tensile strength.

You should really calm down. I know you are passionate about what you believe, and it sounds like you have a lot of experience, but the way you are handling yourself isn't so great.

[AlanHall 6]

How am i handling myself any different? Im asking a question to support his statements and getting more smart azz replies. Im really sorry you dont enjoy the way i handle myself . back to the point... A- does the resin make it "harder" it only makes sence that it does, or else why would it be more "brittle" its yes or no.. B- is the 2 or so mm the enclosures going to push the mdf going to push to this failing point?? yes or no ..

as for dem beats i will also as you for these tests or reports? i really think you guys are thinking into the word "stronger" a little to much. no one here thinks the mdf soaks it up and its like steel. or that a single layer with resin compares to 4 layers.. But a nice heavy coat inside and out will help eliminate some flex

Edited May 22, 2009 by AlanHall

[shizzzon 461]

someone mention steel earlier. I'll be be using steel to help brace this box.

I would honestly pour small sections of concrete in it... but i do not have the weight for that.

[Tirefryr 1,742]

I don't know the specifics, but here's my experience with hardness.

I once built an enclosure out of concrete. It was very thick and it's internal airspace was round. I used an inflatable ball in the form and simply let the air out once the concrete was set. The enclosure was extremely strong and if IIRC, it weighed somewhere in the neighborhood of 320lbs. Now, we'd all agree that concrete is harder than wood correct? Well, upon trying to move this, my helped dropped his side which in turn happened to me, and the enclosure was toast. It landed straight on it's backside, from the tailgate of my pickup and "splat."

I've done this several times with MDF and plywood enclosures and none of them have been destroyed.

I don't know the physics involved, but hardness and brittleness do go hand in hand.

Contradictory to that, if I were to be stuck in a tornado, I'd rather be in a concrete and steel structure than wooden.

It's all about the type of force and how it is acting on said object(s).

Take an aluminum frame and drop it on the ground and then a steel one. Which is more likely to be more heavily damaged?

[AlanHall 6]

this is what ive been tryin to say. the brittleness the resin will give the mdf dont out wiegh the slight hardness it gives. our enlcosures wont push a piece of mdf the point where it matters that at XX amount of inches of flex it snaps sooner than no resin...

[Adrian_D 520]

this is what ive been tryin to say. the brittleness the resin will give the mdf dont out wiegh the slight hardness it gives. our enlcosures wont push a piece of mdf the point where it matters that at XX amount of inches of flex it snaps sooner than no resin...

First time you took things out of proportion. We didn't mean that it will make it break instantly when a cool breeze blows onto it

[dem beats 1,223]

Alan, what kind of testing would you like to see? You refuse to accept the experience of the others here on this forum trying to help the OP out, yet you only have your experience to fall back on. That kind of circular logic won't fly. It's beating a dead horse and expecting it to run.

Is there a specific empirical test that will work for you? Someone might be willing to work something out, but realistically even with amazingly sensitive and accurate measuring tools it probably won't give you an answer that will satisfy. No matter what the argument could be made "well my box wasn't like that one" or "I used a different kind of MDF" etc.

It can be proofed though. Here is a big start.

Great Explanation of how and why composite materials work.

Resin and boxes are SO popular because some people saw some other successful people use it. They don't know why it was used though or what it was doing in that application. Now if you add FG to that resin, we can start talking. However even with woven FG and resin, the flat planes of the interior do not lend itself to a strong FG type composite structure. Basically unless FG is formed in some kind of curve, it's really a poor material. Two Layers of MDF will be SO much better. Or just some simple window bracing(I would choose this approach for the most stability and rigidity).

[dem beats 1,223]

I don't know the specifics, but here's my experience with hardness.

I once built an enclosure out of concrete. It was very thick and it's internal airspace was round. I used an inflatable ball in the form and simply let the air out once the concrete was set. The enclosure was extremely strong and if IIRC, it weighed somewhere in the neighborhood of 320lbs. Now, we'd all agree that concrete is harder than wood correct? Well, upon trying to move this, my helped dropped his side which in turn happened to me, and the enclosure was toast. It landed straight on it's backside, from the tailgate of my pickup and "splat."

I've done this several times with MDF and plywood enclosures and none of them have been destroyed.

I don't know the physics involved, but hardness and brittleness do go hand in hand.

Contradictory to that, if I were to be stuck in a tornado, I'd rather be in a concrete and steel structure than wooden.

It's all about the type of force and how it is acting on said object(s).

Take an aluminum frame and drop it on the ground and then a steel one. Which is more likely to be more heavily damaged?

This is a great example in bold there. I tried to make a similar type box and I didn't even get it to hold up against it's own weight. Smart idea with the ball! Now if you would have put concrete inside an MDF the SAME thing would happen. This is because it's not a composite material. It's just one material that looks like it's connected to another material. The mechanical hold of concrete and the resin resin is AMAZING. Thermoset resin/epoxy used for FG is really amazing but it's nothing without the strength of Glass. The actual bonding, not so much. This is why resin isn't use to glue box joints together. If it could hold better it would be used, but wood glue makes for a better, for lack of a better word, glue.

Now make that same box and use some rebar. It would have broken the slab it landed on. That is an example of a composite material. Fiber reinforced concrete might have gotten it done too.

Wiki FCR page

^---just some cool info. FG isn't just used in speaker boxes and kayaks

People ALWAYS forget. Fiber glass really is glass. Silicon basically, with some other stuff in there. That is really where the strength comes from. If you like you can think of the resin as a filler, only to take up space and save weight, that also has the side benefit of giving both tensile and compression strength.

[Tirefryr 1,742]

I did use the fiber re-enforced concrete, albeit the bag type. Don't know if that makes a differnence. I also did put steel in it. No rebar, but the sheet type stuff that is commonly used in sidewalks, driveways, etc. .

[topgun 262]

If someone would be interested in sending me some MDF with resin brushed on it, I will test it in a testing frame and compare with regular MDF.

And yes, the numbers will be accurate.

[AirFramerMack 3]

So i got bored today and wanted to squash this. I took 2"x10" pieces of MDF, one with nothing(control), one with a thin layer of resin on one side, one with a thin layer on one side and one covered in resin. I let it cure for 4hours outside, in the sun at aprox 78-80degrees. Could have been longer but it was enough. The control took 12lbs of pressure to break. one with resin on top took 15lbs, with resin on bottom however took 12lbs, and covered completely took almost 18lbs. Nuff Said

[blue fury 3]

Wow I actually know a little something about this from some college classes.

I'm not going to contradict anyone who said that adding resin will make it weaker because I have no actual experience with it and have never seen any tests/plots. But it seems to me that it would lean more towards making the wood stronger.

Correct me where I'm wrong.

In the tests where the resin+mdf failed quicker, the resin layer was probably like 1/16" to 3/8" right? Again, without seeing any tests, the main reason I could think of for this would be that the resin (still in liquid form) soaked into the MDF and ended up making the mdf less dense. So in doing this, it took away from the distance between the neutral axis of tension and compression © and moment of inertia (I) making the yield strength of the MDF panel less. If this was compensated by making the resin layer much thicker, (.75" - 1"), then I would think that there would be a definite rise in the yield strength of the MDF panel. But since this isn't practical (And especially since the properties of a MDF are better suited for 'panel-like' situation), another panel of MDF is added. Plus I don't know the mechanical propertied of a sheet or panel of solid resin, so this may be false.

agree?

Now adding rope and other stuff to the panel to add resin to will make it stronger, just like adding another piece of wood roughly the size and shape of the rope. This changes the I of the panel, thus changing the yield strength. You all know it, that's why you brace toward the empty area of the panels.

[blue fury 3]

So i got bored today and wanted to squash this. I took 2"x10" pieces of MDF, one with nothing(control), one with a thin layer of resin on one side, one with a thin layer on one side and one covered in resin. I let it cure for 4hours outside, in the sun at aprox 78-80degrees. Could have been longer but it was enough. The control took 12lbs of pressure to break. one with resin on top took 15lbs, with resin on bottom however took 12lbs, and covered completely took almost 18lbs. Nuff Said

To be most accurate, I suggest proportional sizes. I'm not sure that a 2"x10"x.75" mdf covered in resin will hypothetically produce the same results as 20"x10"x.75" (a smaller common enclosure panel). If you change the size of the piece, that you would have to change the layer of resin to the same proportions as well as the thickness of the MDF.

Edited May 24, 2009 by blue fury

[Nightshade 0]

I can tell you from my own personal experiences with resin in enclosures they are louder with resin opposed to without. I will tell you why this is. Since all mdf is is compressed saw dust held together by glue it "leaks" air if you will. By applying the resin to the inside walls of the enclosure it stops air from leaking out the surface of the mdf. Resin if done right is also almost as slick as glass and the reduced drag on the airflow inside the enclosure also helps to be louder.

These numbers are completely accurate and you can take them for what you want. I did this test with my last enclosure in my car and here are the results that I came up with.

1. Bare box with no resin, only sealed at the seams of the enclosure with liquid nails did a 146.8 db on the dash

2. I applied 2 coats of resin to the inside of the box only and then tested and got a score of 147.1 db

3. I added 45 degree angles inside the box made of resin and went to 147.6 db

4. I then applied 2 coats of resin to the outside of the enclosure and achieved a score of 147.8db

So you can clearly see by applying resin and resin only I gained exactly 1 db. I've already explained why and that is to reduced drag inside and outside the enclosure's surface area, and also keeping the mdf from "breathing" and releasing pressure.

I urge those of you that are non believers to do the same test and please post your results. I'm not saying that you will achieve the same gains as myself, but I'm sure that there will be a significant increase in the enclosure over the same enclosure without resin. You have to make sure when doing resin to the outside of the box that you do not put carpet over it because that will increase drag more than the bare surface let alone a resined outer surface.

[AirFramerMack 3]

So i got bored today and wanted to squash this. I took 2"x10" pieces of MDF, one with nothing(control), one with a thin layer of resin on one side, one with a thin layer on one side and one covered in resin. I let it cure for 4hours outside, in the sun at aprox 78-80degrees. Could have been longer but it was enough. The control took 12lbs of pressure to break. one with resin on top took 15lbs, with resin on bottom however took 12lbs, and covered completely took almost 18lbs. Nuff Said

To be most accurate, I suggest proportional sizes. I'm not sure that a 2"x10"x.75" mdf covered in resin will hypothetically produce the same results as 20"x10"x.75" (a smaller common enclosure panel). If you change the size of the piece, that you would have to change the layer of resin to the same proportions as well as the thickness of the MDF.

regardless of size my "data" i guess you could call it proves it made it stronger. so a bigger piece of wood will just yield higher break weights. Point in case, it did strengthen it

[Tirefryr 1,742]

There are way too many variables for us to test this accurately.

Nightshade, your testing is great, but it doesn't prove that the resin or angles helped. A slight change in volume from adding the resin and angle could also be the reason for this. A difference in air temp, driver temp, slight power increase or spike, etc, could have easily accounted for your gains as well. There is no way to accurately pinpoint the resin or angles and being the sole factors for the increase in SPL.

Let's shoot this one to the Mythbusters team. Ha Ha.

[blue fury 3]

So i got bored today and wanted to squash this. I took 2"x10" pieces of MDF, one with nothing(control), one with a thin layer of resin on one side, one with a thin layer on one side and one covered in resin. I let it cure for 4hours outside, in the sun at aprox 78-80degrees. Could have been longer but it was enough. The control took 12lbs of pressure to break. one with resin on top took 15lbs, with resin on bottom however took 12lbs, and covered completely took almost 18lbs. Nuff Said

To be most accurate, I suggest proportional sizes. I'm not sure that a 2"x10"x.75" mdf covered in resin will hypothetically produce the same results as 20"x10"x.75" (a smaller common enclosure panel). If you change the size of the piece, that you would have to change the layer of resin to the same proportions as well as the thickness of the MDF.

regardless of size my "data" i guess you could call it proves it made it stronger. so a bigger piece of wood will just yield higher break weights. Point in case, it did strengthen it

For those sizes, yes. The proof is definitely not there yet since the resin layer is NOT proportional. Next semester, I'll see if I can use an actual machine with commonly sized panels.

I want to clarify that I am not saying it is or isn't stronger, just throwing some important factors out there.

Edited May 24, 2009 by blue fury

[shizzzon 461]

hey, is that possible? send to mythbusters?

[Thorshammer 1]

Zack very well put!

I've done similar tests and always saw a gain once resin was applied. In my most recent box without the resin it breathed like no tomorrow, Hideous sounding.

Once I glassed the box it eliminated that breathing and solidified the sound.

Guess this one just boils down to either you've tested this for yourself or your just talking theoretically.

I will always glass my boxes.

[shizzzon 461]

when u say glass, is this a mixture of Fg and resin or just resin and how much?

[topgun 262]

hey, is that possible? send to mythbusters?

I can do the testing on panels. Its part of what I do as a job.

[dem beats 1,223]

Tirefryr, I thought fiber crete had to be sprayed(not that I have any damn clue why that would be) to work. You used the sheet steel with holes punched in it?

I'm really impressed either way.

[Tirefryr 1,742]

Tirefryr, I thought fiber crete had to be sprayed(not that I have any damn clue why that would be) to work. You used the sheet steel with holes punched in it?

I'm really impressed either way.

No, not mesh. It's the screen stuff that comes in the rolls. . . I don't know the proper term for it. As for the 'crete, I don't know why it would have to be sprayed. I've never seen concrete sprayed before. Pumped, yes, but it's essentially the same as a pour. The foundation in my old man's pole barn was poured with fiber-reinforced concrete and that has had no problems yet. I just used the stuff you buy in a bag at Lowes.

This is the stuff:

http://www.quikrete.com/ProductLines/Fiber...ConcreteMix.asp

[topgun 262]

Tirefryr, I thought fiber crete had to be sprayed(not that I have any damn clue why that would be) to work. You used the sheet steel with holes punched in it?

I'm really impressed either way.

Never seen it sprayed before. I do not know of what you are referring to, but the stuff I've seen does not have to be sprayed, although I have seen fiber reinforced, stuff with glass beads in it, and lightweight stuff, but I know for a fact I haven't seen nearly all of it when referring to concrete.

[dem beats 1,223]

no clue why I thought it had to be sprayed. Anyway, this is how I have seen concrete sprayed.

http://en.wikipedia.org/wiki/Gunite