Author Topic: Solvent welding a crack in WECo hard plastic  (Read 4480 times)

Offline cihensley@aol.com

  • Hero Member
  • *****
  • Posts: 653
Solvent welding a crack in WECo hard plastic
« on: August 11, 2011, 02:46:05 PM »
This is a continuation of test I described in: http://www.classicrotaryphones.com/forum/index.php?topic=5059.0

I think I mostly solved the gas bubble problem in crack repair with a different technique. Previously, I used dissolved plastic the consistency of syrup. I found that a very thin mixture is better - around 10 parts of MEK to 1 part plastic. I use a small natural bristle artist brush. I groove the crack with a diamond bit in a Dremel tool. I then paint the groove and about 1/16 of the area around the groove with MEK (It starts dissolving the plastic immediately so no wait time like earlier repairs). I use the brush (The plastic mixture is in a small glass bottle) and dab, not paint, the liquid into the groove and surrounding area. When the mixture dries (about 4 hours) it will have shrunk a lot because it is mostly MEK. I repeat this 5 or 6 times until the dry groove is filled. Sand level with wet 400 grit wet/dry. Low spots can be seen because they are shiny. Fill the low spots and re-sand. Repeat as many times as necessary.

The pictures show the repaired crack (The bottom of the crack started where the pen point is) and the back side of the crack. I cut a groove in the finished piece of shell to show what I started with. The piece was sanded with a detail sander using all grits of micro-mesh, followed by a spray of MEK. The slightly matted finish of MEK polishing can be seen by comparing the side with other portions of the piece of shell. Perhaps dipping the shell fully in MEK will solve the matte appearance from spraying. I will try this in a future test.

Chuck

Offline JorgeAmely

  • Hero Member
  • *****
  • Posts: 2162
  • SC from 1973
Re: Solvent welding a crack in WECo hard plastic
« Reply #1 on: August 11, 2011, 03:26:08 PM »
Impressive, to say the least.
Jorge

Offline cihensley@aol.com

  • Hero Member
  • *****
  • Posts: 653
Re: Solvent welding a crack in WECo hard plastic
« Reply #2 on: August 12, 2011, 05:19:51 PM »
First test of solvent polishing by MEK "dipping"

The flat side of the piece of blue shell on the left was sanded with all grits of micro-mesh. Then one-half of the piece was dipped into a container of MEK. You can see the difference in texture. The piece of blue shell on the right is original - unpolished - for comparison. The MEK dip was insertion and removal. It was not held stationary in the solution. The matte finish that results from spraying MEK is not evident - it is smooth. Held up to the light shows that the MEK eliminated even the minutest of scratches. I removed the piece slowly from the MEK to see if there was any tendency to run, which was a concern going into the test. No runs developed. The next step will be try the process on complete components - shell, handset, caps, etc. I will be looking to see if there is any color transfer to the MEK. There was none in this test. But, because it will take about 5 gallons of MEK to cover fully a shell any color transfer, necessitating fresh MEK for each polishing job, would make the process uneconomical.

Chuck

Offline HarrySmith

  • Hero Member
  • *****
  • Posts: 5268
  • 1937 302
Re: Solvent welding a crack in WECo hard plastic
« Reply #3 on: August 13, 2011, 04:27:28 PM »
Looks very nice! And only a dip, not hours of sanding & polishing!
If there is no color transfer why is it necessary to use fresh solvent?
Harry Smith
ATCA 4434
TCI

"There is no try,
there is only
do or do not"

Offline cihensley@aol.com

  • Hero Member
  • *****
  • Posts: 653
Re: Solvent welding a crack in WECo hard plastic
« Reply #4 on: August 13, 2011, 05:11:30 PM »
HarrySmith:

There was no color transfer in this test. When I do a larger component, we shall see. If there is no color transfer with larger components there will be no need for fresh solvent.

Chuck

Offline Bill

  • Hero Member
  • *****
  • Posts: 594
Re: Solvent polishing and color correction
« Reply #5 on: August 14, 2011, 09:25:27 AM »
I started thinking about solvent welding and polishing at about the same time that Chuck first mentioned it. I havenít done anything with welding, but I headed down the same road as Chuck on polishing, and after conferring with him, decided to post some tentative results here.

A while ago, I picked up a red 500. The shine was pretty good, though not perfect. I was tired of sanding, since I had just sanded a black 554 into oblivion without any really good results (still learning). Since I had a gallon of MEK on hand, I decided to try it on the red phone, rather than sanding. I hadnít thought about dipping Ė that is Chuckís idea. Instead, I got a paper towel, folded it over several times, saturated it dripping wet with MEK, and pulled it lightly over the surface of the case, ONCE, to thoroughly wet the plastic.  As Chuck has reported, it did a lot of good for the small scratches and improved the finish a lot. Sadly, it also left some drag marks in the softened finish, so I envisioned having to sand anyway.

But this phone also had a problem with the color. I described it to Chuck as slightly ďblotchyĒ, but that word wasnít conveying anything useful, so I tried to photograph it. In the attached photo of the handset, you may be able to see that at the right hand end of the back of the handset, the color and shine are pretty good. But as you move an inch down toward the middle of the handle, there is something else, an irregular cloud-outline. This is something within the plastic Ė it is not on the surface. It could undoubtedly be removed by a few days of sanding, but as I said, Iím tired of sanding, at least on cheap phones. I decided to try the towel-drag approach to see if it would correct the color problem. So as above, I loaded up a towel, dragged it ONCE over the back of the handset, and let it dry for an hour. The shine was improved, but the color problem was still there, confirming that it was not something on the surface. Having nothing to lose, I loaded up a new towel, dragged it once, then loaded it again and dragged it a second time, before the first application dried. Eureka! The first drag did not pull up any color, but the second drag did Ė the towel had a lot of red on it. And when it dried, I had both good gloss and good color Ė the blotchiness was gone. As expected, though, it left some drag marks in the softened finish, so again I envisioned having to sand.

Then Chuck mentioned the idea of dipping, and I think this is going to be the answer. My guess is that a quick dip, as Chuck mentioned, will remove surface roughness and scratches, and restore gloss. It appears that a quick dip will not pull up any color, so the MEK in the dip tank will be re-usable. On the other hand, if there is a color problem, the wipe approach (using a lot less MEK) will correct it, followed by a dip in the tank to correct the marks left by the wipe.

A great idea, Chuck. Iím very encouraged. If I have more results, Iíll post, and Iím sure you will as well. The dripping-rag approach wastes a bit of MEK, but MEK is cheap and easily available, so you may have found a real winner here.

Bill
« Last Edit: August 28, 2011, 05:34:21 PM by Bill »

Offline HarrySmith

  • Hero Member
  • *****
  • Posts: 5268
  • 1937 302
Re: Solvent welding a crack in WECo hard plastic
« Reply #6 on: August 14, 2011, 01:27:25 PM »
OK, these are promising results. I appreciate you guys sharing them with us. I have been saying since I started working on phones that there must be a way to chemically resurface them rather than sanding.
I HATE sanding >:(
Harry Smith
ATCA 4434
TCI

"There is no try,
there is only
do or do not"

Offline Bill

  • Hero Member
  • *****
  • Posts: 594
Re: Solvent welding a crack in WECo hard plastic
« Reply #7 on: August 15, 2011, 11:17:34 AM »
It seemed too easy, and it was. The "drag" corrected the color, but left drag marks. The drag marks were NOT corrected by a dip. In my previous correspondence with Chuck, he predicted that this would be the case, and he was right. Unless there is a way to make smaller (MUCH smaller) drag marks, some sanding will be needed. Oh, well.

Chuck, you are better at this than I am, and I know you were planning to run similar experiments. We are anxiously waiting for your results.

Bill
« Last Edit: August 15, 2011, 11:20:52 AM by Bill »

Offline TelePlay

  • Global Moderator
  • Hero Member
  • *****
  • Posts: 7232
  • Available by PM
    • . . . the times they been a'changing
Re: Solvent welding a crack in WECo hard plastic
« Reply #8 on: August 07, 2013, 11:29:29 PM »
Just wanted to pass along this link to a tool I have found very useful and handy to apply dissolved plastic to a phone repair, be it a crack or a hole. It's a Jarit 285-380 Freer Elevator. Seems to be a $25 item that is going for $15 in used condition.

http://www.re-owned.com/itemcode--92wu64-c3

It's a surgical tool/instrument but works nicely for applying either thin or thick portions of dissolved plastic to a phone. It can be used on end to apply a very thin amount or it can be used like a spatula to apply and smooth pea sized chucks of softened plastic. I've been using it with acetone as the solvent and am amazed at how handy it is for applying and modeling plastic in a phone repair. It is also a very good mixing tool when dissolving the plastic before application.

Being stainless steel, it won't rust and it is easily cleaned up with a paper towel while the plastic solution is just damp. Or a towel with a bit of acetone on it to get dried plastic off of it.

This picture is just about actual size which is 7.75 inches long.
« Last Edit: August 10, 2013, 01:22:05 AM by TelePlay »
            John . . .

              

Offline TelePlay

  • Global Moderator
  • Hero Member
  • *****
  • Posts: 7232
  • Available by PM
    • . . . the times they been a'changing
Re: Solvent welding a crack in WECo hard plastic
« Reply #9 on: September 01, 2013, 09:23:01 AM »
Using the above Jarit tool as a very nice spatula for applying dissolved plastic, I've come up with another useful tool for rough sanding and shaping the applied plastic down to pre-polishing levels - nail files found at Sally in grits of 100/180 (black), 220/320 (blue) and 400/600 (pink). They are about 3/4" inch wide, 7" long and 1/8" thick. They are washable (reusable) and can be used for wet sanding. I use the 220/320 the most.

Got a 302 with a broken corner and instead of tossing it, made it a project shell. Per this forum, backed the large hole with stiff blister pack, dissolved some black ABS plastic in acetone and patched it into the opening. Let it sit for about a week and went to work on it with the 100 grit file, moving up to 600.

When getting it smooth, found plenty of pits associated with acetone trapped in the plastic so went to the recommended thinner plastic solution to spatula it into the pits and re-sanded with the files (at least 3 or 4 times to get the pits out).

The photos follow and the only problem I see is the ABS black does not exactly match the 302 shell black. I hope to remedy that by applying a few thin coats of plastic from the shells inner ribs.

While the repair has a long way to go, just wanted to mention that these washable nail files, for about $1.19 each, work very well on flat surfaces and for rounding corners.
« Last Edit: September 01, 2013, 10:11:24 AM by TelePlay »
            John . . .

              

Offline cihensley@aol.com

  • Hero Member
  • *****
  • Posts: 653
Re: Solvent welding a crack in WECo hard plastic
« Reply #10 on: September 01, 2013, 10:23:58 AM »
TelePlay:

Thank you for the hints on spatula and files. The spatula, in particular, will be very useful.

Chuck