End Plate Material - help

[Mayaki]

I know about several different materials to make end plates out of for a dry cell, but i was wondering if anyone would be nice enough to help me pick a strong enough end plate material. For the last year I've been struggling with my end plates cracking. The material I've been using is 1/2" thick polycarbonate.

I tried a clamp like design first, which was why I thought my end plates were cracking. I redesigned my dry cell to where the bolts (nylon threaded rod) that hold the cell together go through the plates, gaskets, and endplates. The end plates of the second design cracked within a week.

I’ll post pictures of the first and second design after I make this post. I can post pictures of the cracks on the end plates of the second design in a few days when I get a chance to take pictures.

My plates are arranged as follows. (19 plate cell) - 6”x5” plates
Negative: -
Positive: +
Neutral: N
End plate: |

|-NNNNN+NNNNN-NNNNN+|

I know of the following end plate materials:

Polycarbonate - This stuff is super strong, but has cracked on me every time [3 times now]
Acrylic - I used polycarbonate because it appeared to be stronger than acrylic. I’ve read that these plates crack as well.
HDPE – I’ve read mixed articles on this material absorbing moister. I’m assuming there are different grades of this material?
CPVC – I’ve heard about, but haven’t done much reading.

So my question is what type of end plate material I should use, and how thick should that material be? Also, should I be able to use two end plates for a cell with this many plates, or do I need to put in a center break plate in? Thanks.

[myoldyourgold]

Here is a link that has a chart which shows King starboard marine grade to be the best. I have not had any problem with HDPE because it never get saturated and is cheaper.

http://www.machinist-materials.com/c...r_plastics.htm

You will need some type of stiffener around the edge that is wide enough to prevent any bowing even bolts going through the plates if you are not careful. I use a full piece of 1/8" thick powdered coated mild steal on top of the HDPE.

[Mayaki]

I was thinking about trying HDPE next for an end plate. What thickness would someone recommend for a 19 plate cell? Since I've cracked numerous 1/2" sheets of polycarbonate I would assume 3/4" or thicker. Also, If i use some type of metal stiffener on the outside of the end plates, would it be necessary to use a thicker end plate?

Thanks for the link to the table.

I'm also using 1/4" threaded nylon rods that go down through my cell. Before the end plates cracked I was worried that the nylon rods would either become stripped or break. Should i drill the holes in my plates to a larger size for larger diameter rod, or is there another type of material i can use to bolt together my cell?

I will attach a picture of my latest designed cell (before it broke) once my photos are finished uploading to photo bucket. Hopefully that will help anyone diagnose the issue I've been having. Thanks.

[myoldyourgold]

was thinking about trying HDPE next for an end plate. What thickness would someone recommend for a 19 plate cell? Since I've cracked numerous 1/2" sheets of polycarbonate I would assume 3/4" or thicker. Also, If i use some type of metal stiffener on the outside of the end plates, would it be necessary to use a thicker end plate?

Thanks for the link to the table.

I'm also using 1/4" threaded nylon rods that go down through my cell. Before the end plates cracked I was worried that the nylon rods would either become stripped or break. Should i drill the holes in my plates to a larger size for larger diameter rod, or is there another type of material i can use to bolt together my cell?

I will attach a picture of my latest designed cell (before it broke) once my photos are finished uploading to photo bucket. Hopefully that will help anyone diagnose the issue I've been having. Thanks.

If you are going to put the ports on the face, 1/2 inch HDPE should work with a stiffener. If you are going to put 1/4 inch NPT on the edge then 3/4 or better yet 1 inch. If you do use 3/4 you have to make sure it is exactly in the center and straight, other wise even the HDPE will crack with 3/4" if the ports are on the edge if not centered as in my picture I posted above. That is 3/4" in the picture.

Even though I am not a proponent of fasteners through the plates the ones that are using them use stainless steel fasteners with a plastic tube to insulate them thus preventing a short. I personally find the amount of gasket around the holes on the inside and the out side is too little when you do this. The electrolyte wants to crawl under the gasket a little no mater how tight it is. Unless you take up a lot of plate area with a wide gasket there is a chance of leakage. There is two view points to this and I have just stated mine. I would though recommend going to stainless fasteners instead of plastic. You just will never be able to get them tight enough and they get loose as things heat up a little, expand and need to to be re-tightened finally striping.

[Mayaki]

Here is a picture of the cell before it cracked. Hopefully someone can learn from my mistakes. I'll see if i can find any more pictures of my previous design in the next few days.

http://img.photobucket.com/albums/v1...l/DSCN1562.jpg

http://img.photobucket.com/albums/v1...l/DSCN1561.jpg

http://img.photobucket.com/albums/v1...l/DSCN1560.jpg

http://img.photobucket.com/albums/v1...l/DSCN1557.jpg

http://img.photobucket.com/albums/v1...l/DSCN1563.jpg