Just bought a HP-67 calculator at an auction

[teenix]

(08-25-2020 03:20 PM)Chr Yoko Wrote:  This "gummy wheels" issue seems to come from the material degradation over time.

Look at your engine bay and you will see plenty of long lasting engineered application specific rubber materials ;-)

Yes, but aren't we talking 50 years or so, what manufacturer in their right mind would create products to last that long even if they could, especially in the cheap throw away world of today. The fact the many old calculators of that era are still working surely says a lot about the manufacturing standards. I don't know how long the engineers expected the devices to last especially with rapid technology advances, but I would doubt this long.

I don't imagine looking under the hood of a 50 year old car that is used daily and still has original rubber hoses and the like, let alone seat coverings, paint etc, and although better materials nowadays, modern car parts don't always last either - usually when the warranty expires ;-) I guess long lasting materials don't do much for the environment either after they are discarded.

I fly 50 year old aircraft daily in conditions that would make the designers cringe so I'm glad in this instance they did a good job :-)

cheers

Tony.

[SlideRule]

The Publisher Summary for Handbook of Environmental Degradation of Materials, 2005, Chapter 7 - Chemical and physical aging of plastics {pgs. 153-163}

" This chapter distinguishes between chemical aging and physical aging of plastics. Chemical aging or chemical resistance is simply the effects of chemicals on the plastic. Various examples of chemical aging, including … another type of chemical aging—that is, environmental stress cracking and crazing. Environmental stress cracking is a type of failure that occurs through surface interactions … The effects of physical aging on the failure behavior of a typical brittle polymer, polystyrene, are discussed. Properties examined are creep rupture lifetimes, fatigue lifetimes, and environmental stress cracking … "

In its' entirety, a most excellent read.

BEST!
SlideRule

[pinkman]

Impressive, as usual.

My questions would be:
Did HP, in the 70’s, have the opportunity to use a better plastic for an acceptable price?
Did they know “physical aging” was as bad?
Did they avoid using more expensive plastics for some reason (financial or other)?

[SlideRule]

(08-26-2020 12:05 PM)SlideRule Wrote:  The Publisher Summary for Handbook of Environmental Degradation of Materials, 2005, Chapter 7 - Chemical and physical aging of plastics {pgs. 153-163}

" This chapter distinguishes between chemical aging and physical aging of plastics … "

Thermal degradation / aging is also a candidate process.

BEST!
SlideRule

ps:don't forget to include reversion.

[[kby]]

(07-30-2020 01:13 AM)teenix Wrote:  

(07-29-2020 11:20 AM)Harald Wrote:  Well, if the card read has NEVER been used, maybe there is a chance it still works. I suspect the deterioration of the wheel is triggered by contamination. Maybe it gets contaminated by the cards, but maybe just air getting in is enough. Would be interesting to find out...

Hard to say. HP says it had to use a "special" polyurethane compound to provide reliability over many operating factors, so it may degrade at different rates to other polyurethane types. I don't know much about chemistry but it appears these can degrade due to many factors including temperature, location (sea-side etc) and residue or hungry little microbes which might get transferred from your fingers to the cards to the wheel.

Maybe if the calculator survived packed in its box in a cool and dry environment over the years, the wheel might still be ok.

cheers

Tony

From the generally available literature at the time, HP's principle criteria for the HP-65 pinch rollers was the "grippiness" of it even under adverse conditions (oily cards and low temperatures are the examples they talk about). As such, while I'm sure they wanted it to last the expected "life of the calculator", longevity probably wasn't as important, and something that might have been too hard to optimize on top of the other two criteria, especially with 1970s era polymer chemistry. It's still a bit of a black art, but things we can can control much better now than then.
I don't know what TI used for their rollers as I've never owned let alone disassembled a TI calculator.
Regular rubber pinch rollers are susceptible to oxidative damage primarily by ozone, so that would mean it depends on how polluted your local air is. The other major killer is often UV light, but that should not be an issue for the pinch roller.

Oddly I have one -65 (which is assembled from the best parts I had from several), but the machine the reader came from appeared to have never had the roller replaced. It wasn't one of the usual things (tubing, washers, etc.). I also recall the label on the back of t he machine the reader came from (can't remember if it was actually a -67 or a -65) did not appear to have ever been removed (I know that can be hard to tell if it's really done well, but usually there are some tell-tale signs if you know what to look for). Additionally, this roller is black; the original ones are a pale translucent yellow.

Interestingly enough some person on TAS sells pinch rollers for TEAC open-reel tape decks made of the urethane because they are softer and do grip better; the original ones get glazed and hard sooner than one likes. However, although i initially thought this seemed like a good idea, I quickly remembered that the HP-65 pinch rollers were also polyurethane, and, recalling all of my experiences with the gummy wheel, decided they were a really bad idea for quarter-inch quarter-track magnetic tape. Cleaning the goo off of the cards without damaging the card is much easier than it would be for flimsy tape.

[calc-calcs]

(08-25-2020 11:12 PM)teenix Wrote:  

(08-25-2020 03:20 PM)Chr Yoko Wrote:  This "gummy wheels" issue seems to come from the material degradation over time.

Look at your engine bay and you will see plenty of long lasting engineered application specific rubber materials ;-)

Yes, but aren't we talking 50 years or so, what manufacturer in their right mind would create products to last that long even if they could, especially in the cheap throw away world of today. The fact the many old calculators of that era are still working surely says a lot about the manufacturing standards. I don't know how long the engineers expected the devices to last especially with rapid technology advances, but I would doubt this long.

.....///...

EXACTLY. Nuff said I would think.

[Kostas Kritsilas]

(10-04-2020 12:03 PM)calc-calcs Wrote:  

(08-25-2020 11:12 PM)teenix Wrote:  Yes, but aren't we talking 50 years or so, what manufacturer in their right mind would create products to last that long even if they could, especially in the cheap throw away world of today. The fact the many old calculators of that era are still working surely says a lot about the manufacturing standards. I don't know how long the engineers expected the devices to last especially with rapid technology advances, but I would doubt this long.

.....///...

EXACTLY. Nuff said I would think.

HP was using silicone rubber for probe insulation in the 1960s. I don't have the background in plastics/polymers to say for sure, but silicone rubber seems to be an ideal material for this application. I don't see it as costing any more than the polyurethane that they used.

HP engineering for most of the time the company existed was superb. Not just good, superb. They were the equal of any aerospace company, and came up with products that were mind-blowingly good. Take a look at the HP 3325 Frequency Sunthesizer some time, or the HP 3458 multimeter. All from the 1970s and 1980s, and so good that they haven't been surpassed. The 3458a is still in production. The point of all this, is that HP, back then (in the same era as the red LED calculators) didn't think about whether the product was supposed to last 3 years, or 300 years; they just made the best possible product. And in many cases, the product might go obsolete before it would break down.

They simply missed the boat on the card reader wheel material. Happens.