HP Forum Archive 12

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What's the history of the "Gummy Wheel"? Message #1 Posted by Steve on 10 Apr 2003, 12:46 p.m. I just repaired an 41cx card reader that suffered from a "gummy wheel". It seems like there's a lot of info on how to repair it, but now I'm wondering if anyone knows the story/history behine this problem. My understanding is that all (at least 41cx) HP card readers suffered the problem. My questions are, what caused the problem, what material was the original roller made of, why did HP use this material (they must have know it would fail), did HP make an attempt to replace the wheel once it was identified? Thanks! Steve

Re: What's the history of the "Gummy Wheel"? Message #2 Posted by glynn on 10 Apr 2003, 5:12 p.m., in response to message #1 by Steve I'm not sure *what* is behind the degradation of rubber and elastic parts at HP-- but I can tell you it is not just limited to 41cx readers. The 67 and 97 readers, the big "D" shaped tire on the 9100a, and capstan drive tape machines such as the 9144a are some of those I can directly testify have turned "mushy" with time. I have also seen this pathology on the older Colorado QIC-style tape drives, though the cases I saw were all attributed by the service tech we used to "excessive shuttling"-- where the tape used might have a block that can't be read properly, so the drive might forward and reverse the tape over and over to try to read it. It was guessed that these machines, doing unattended backup and verify, were "shuttling" all night. The equivalent of "driving the tires off" a car. I am darn sure that my 9100a reader was never used that way; ditto, I would think, for the card reader on my 97. It seems just age did it in those cases. Heat is often blamed, but I am not so sure about that. My car has PLENTY of rubber that never has melted, though it has lived most of its life in this part of the southern U.S. we affectionately call Hell. On the other hand, you would expect that an office wallflower like the 97 would neither be exposed to, nor generate, enough heat to make a difference to its parts. Why would heat particularly be a problem in the cardreader? Other possibilities people have mentioned: 1. Air. Some rubber products oxidize, and thus breakdown. Surely you know that your reader was only intended for use in a complete vacuum? :-) 2. Some microbes attack and eventually eat natural-based rubber. Witness the foam pads on your eight-tracks. (The "Andromeda Strain" theory) 3. Aerosols and vapors from solvents are attracted particularly to this rubber. Your cologne was too strong. 4. HP used a supplier with an inferior formulation of rubber (this in comparison with TI, who never seems to have this happen) 5. The lack of use of the parts is the problem-- because they get hardly any exercise, the "soft" polymers dry out of the piece, leaving porous compounds that disintegrate on use. (This is the "Armor-All" theory; supposedly, adding polymers in will keep these parts "new"). I don't know what validity can be assigned to any of this. (My bet is on #4). I DO know that it's a problem, for sure.

Re: Deteriorating Rubber Message #3 Posted by Paul Brogger on 10 Apr 2003, 5:38 p.m., in response to message #2 by glynn We tried using the kids' pacifiers for Christmas ornaments -- kind of a nostalgic, family-oriented thing . . . After a couple of years, the "sucky" parts turned gooey, sticky, and started falling apart. Ditto for the yellowish nipples on the old resuable baby bottles. It seems deterioration of rubber components is a problem in many areas. (One might suspect that it had a part in having the kids in the first place, but let's not go there . . . )

Paul has the answer! Message #4 Posted by glynn on 10 Apr 2003, 6:54 p.m., in response to message #3 by Paul Brogger The clue was -- >>> After a couple of years, the "sucky" parts turned gooey, sticky Now I understand: HP also made "sucky" parts. :-)

Re: Deteriorating Rubber Message #5 Posted by Ellis Easley on 12 Apr 2003, 8:43 a.m., in response to message #3 by Paul Brogger Ozone is well known for causing rubber to deteriorate, and I recently heard a news report that pine trees are responsible for putting a lot on nitrogen oxides in the air, and as I understand it, the reason nitrogen oxides in car exhaust is bad is because it leads to the generation of ozone - the NOx acting as a catalyst, I guess.

TI's have plenty of gum. Stuck to the case.... Message #6 Posted by Michael Meyer on 15 Apr 2003, 12:19 a.m., in response to message #2 by glynn The TI's I've rebuilt: half a dozen SR-52's and a dozen or more TI-59's have all had deteriorated rollers. I opened up a batch of SR-52's that had a wad of gum melted to the back of the case! Why would anyone put gum (or putty) into the calculator? But wait... there's no rubber roller! It's not gum afterall! Good thing I didn't try to chew it.... None of the HP's I've seen were that bad.... to the point of dripping to the back of the cases..... The TI-59's and SR-52's work fine now. I used plumber's washers glued onto the shaft and "lathed" down to the perfect size. I'll wager that the plumbing washers will last more than 20 years. Michael

Re: TI's have plenty of gum. Stuck to the case.... Message #7 Posted by glynn on 15 Apr 2003, 3:22 a.m., in response to message #6 by Michael Meyer Well, I suppose I should be happier knowing it isn't just HP's fault. I'd been told by a TI fan that they had no such difficulties. The consensus seems to be that if there is a roller or belt or other product, it may turn to goo with time, smog or whatever, and probably grow fungus if it can. I think the jury is out and we'll simply have to wait and see about model-airplane or surgical tubing. Maybe five, ten, fifteen years? This is discouraging. Is there no known formulation of rubber/urethane/other synthetic which would do what the HP materials can do, WITHOUT inevitable liquification or cracking, guaranteed?

a spiritual answer ... Message #8 Posted by Ellis Easley on 15 Apr 2003, 8:56 a.m., in response to message #7 by glynn ... not in this world

Re: What's the history of the "Gummy Wheel"? Message #9 Posted by David Smith on 10 Apr 2003, 5:59 p.m., in response to message #1 by Steve The rubber wheel is NOT actually rubber. It is a polyurethane that HP chose for its ability to grip and pull a card that had been soaked in oil through the reader. This compound consists of a synthetic rubber cured with an isocyanate curative. Their choice of materials was not stable with time and the polymer chains break down into their primodial goo. If you have a reader that has not been rebuilt, just wait. You WILL soon experience the joy of goo.

Re: What's the history of the "Gummy Wheel"? Message #10 Posted by ToddG. on 10 Apr 2003, 10:08 p.m., in response to message #9 by David Smith Dave is correct regarding the material. My understanding is that this polyurethane will oxidize over time, and thus turn to goo. I seem to recall reading that they used the best material available at the time, but it was not impervious to ozone attack from the air (oxidation). Some of the folks on this board have repaired many of the readers in the 65, 67, and 41, and they use more modern materials (e.g., surgical tubing) that may be more resistant to oxidation.

Re: What's the history of the "Gummy Wheel"? Message #11 Posted by Paul Brogger on 12 Apr 2003, 2:38 p.m., in response to message #9 by David Smith Whatever the material was, its breakdown is dramatic! I'd just recently resurrected my HP-97 after several years in (warm, indoors) storage, and just fixed the card reader yesterday. The wheel was not so much a "wheel" at all, but a gummy, waxy build-up! It had no more hint of its original form than the fact that it was wrapped around the metal hub. Goo indeed!

Re: What's the history of the "Gummy Wheel"? Message #12 Posted by David Smith on 13 Apr 2003, 5:24 p.m., in response to message #11 by Paul Brogger Wait till you find one that some fungus has decided is quite tasty... the wheel can sprout all sorts of white furry growths.

Mine was like this... Message #13 Posted by Vieira, Luiz C. (Brazil) on 14 Apr 2003, 1:58 a.m., in response to message #12 by David Smith ... after about nine years resting inside a shoes box (the same box I stored my "spread-around" HP41C). The goo sort of "cracked" in many small parts and in between them was the mentioned white furry. I did not take a picture, but it is quite a site... Luiz C. Vieira - Brazil

Re: Mine was like this... Message #14 Posted by James M. Prange on 14 Apr 2003, 2:03 a.m., in response to message #13 by Vieira, Luiz C. (Brazil) I hope that the shoes (and your feet) didn't develop the same problem. Regards, James

Re: Mine was like this... Message #15 Posted by Ellis Easley on 14 Apr 2003, 5:19 a.m., in response to message #14 by James M. Prange Another thing made of polyurethane is toothed timing belts. I have an old HP chart recorder with such a belt on the chart drive. I left it in the garage for a couple of years and when I tried it out one day, the paper didn't move. I opened it up and the only thing left of the belt was the loop of fabric that made up the outer surface - even the printing on the fabric was legible. Also a small pile of polyurethane crumbs and a couple of empty cockroach egg cases. Apparently, two generations of cockroaches were weaned on that belt! I'm amazed by the wisdom of mothers. I rented a storage unit that I didn't enter for a number of years and when I finally moved my stuff out, I found that some of it was infested with termites which got in through cracks in the concrete foundation. Wherever there was the sand that the termites bring up to build their tunnels, I found lizard eggs. I'm sure Momma lizard put them there knowing the babies would be able to snack on termites as soon as they came out of their shells!

Re: Mine was like this... Message #16 Posted by Vieira, Luiz C. (Brazil) on 14 Apr 2003, 5:55 a.m., in response to message #14 by James M. Prange Tell me about it...

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