Building a lever machine.... from scratch - Page 40

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bidoowee

#391: Post by bidoowee »

@OldNuc - many thanks for your illuminating comments on the various brazing alloys. I will pull out some sharp tools and try a gouge test on the older boilers. Note that the operating pressure that I mentioned before is actually stamped on a plate on one of my machines (along with the wattage etc). I was guessing about why this would be so and the 30 psi absolute limit for soft soldered copper plumbing seemed to be a plausible explanation. I would be curious to know if you have any suggestions for actual low silver-content cadmium-free brazing alloys that are available in Canada - perhaps SilverBrite makes something but I haven't found a distributor for them here yet.

@SamualLaw - just for you:



This is a longer test (over an hour) on a 1987 diagonal HX machine.

Methodology:

The same methods as were used for the horseshoe HX machine were used with a few minor differences.
- This machine is on 24/7 so there is no warm-up period.
- It had been at idle for at least a couple of hours.
- The same pseudo-Scace device and needle-valve was used to simulate shots.
- The period between simulated shots is generally longer and I did not repeat the faster than commercial usage of the previous test, rather, I waited for the group to recover between shots.
- At minute 3 and 32 there are cleaning flushes - i.e. pulls that were significantly larger in volume than an actual shot.
- At minute 23 a PF filled with real coffee was locked into the group and a shot pulled.
- At minute 25, the steam wand was used to foam milk for a cappuccino.
- The additional orange line that starts at minute 46 is another K-type thermocouple that was placed on top of a puck of coffee before the PF was locked into the group.


Observations:

- This machine has the same pressurestat as the horseshoe HX machine from the previous test and consequently we see the same saw-tooth wave for the boiler temperature.
- With the exception of the cleaning flushes, the brew reservoir is remarkably stable - exhibiting almost no discernable trace of the fluctuation in boiler temperature. The temperature drop for the outside of the reservoir after a shot is pulled is less than one degree and the recovery time is between two and three minutes.
- The group as a whole exhibits the same tendency as the horseshoe HX machine to gain heat with each shot.
- The recovery time for the group is a little over a minute per degree C of heat gain i.e. essentially the same as the horseshoe machine. As the groups are identical this is unsurprising.
- The shot test with real coffee plus the additional thermocouple starting at minute 46 shows a 90 C peak shot temperature and is quite likely to be accurate.
- At minute 40 I removed the PF to prepare for the next shot and the preparation time is longer than usual because I was fussing with the thermocouple. Removing the PF has a fairly significant effect on overall group temperature as the neck falls to the same 83 C that it was when the machine was at idle.

Conclusions:

- The diagonal HX is about as good as it gets as far as temperature stability of the brew water reservoir goes. The reservoir recovers from what little variation there is in less than half the time that the group takes to recover between shots.
- The slower, more realistic, pace of shot pulls in this test is illuminating. The actual temperature gain seen at the group is between 4 and 5 C per shot. This translates to a group recovery time of five to six minutes - possibly a little slow for a commercial setting, but definitely fast enough for home use and entirely manageable with a cooling strategy such as a cooling flush of a known volume.
- 1987 was better than 1982.




OldNuc

#392: Post by OldNuc »

Look to your local welding supply store. Silver braising rod is a common item and the 35% silver is the common brazing rod for HVAC. The Silver Brite 96% tin 4% silver is also used as it is much harder than soft solder. I would be very surprised to find any of these old boilers assembled with a 50/50 lead tin soft solder as it is too weak for that purpose. In the past several countries had regulations on small pressure vessels so some boilers were marked with a max pressure which was also the relief valve setting.

McMaster-Carr sells 35% silver cad free but local will be lower cost. Almost all silver solder is now cadmium free unless you specifically ask for the cadmium product.

samuellaw178
Team HB

#393: Post by samuellaw178 »

bidoowee wrote:@SamualLaw - just for you:
Thank you Thomas for the graph. I got a kick just from analyzing it. :oops: The temp of that diagonal HX brew reservoir is indeed so stable compared to the horseshoe! Though, if only the HX was made to recover slower, it would probably bring the Aurora to the next level - to balance out the rising group head. Maybe something you can explore on your reborn Aurora?

I did notice removing the portafilter allows the group to cool slightly faster, but man, that's a major difference when it's put on a plot (@40 min and @57min)!
bidoowee wrote:- 1987 was better than 1982.
I see what you're trying to do there. 8)

pizzaman383
Supporter ♡

#394: Post by pizzaman383 »

samuellaw178 wrote:Though, if only the HX was made to recover slower, it would probably bring the Aurora to the next level - to balance out the rising group head. Maybe something you can explore on your reborn Aurora?
This challenge was the main reason that I built my Double Dipper lever instead of keeping it configured as a classic dipper. I directly control the temperature of the incoming brew water and the temperature of the group head at the base of the bayonet. This brings the group head temperature recovery down to 30-45 seconds after the end of the shot. Actually, the group head temperature is back to steady state before the pressure on the puck has fully bled-off.

For the new Aurora and other dippers the rate of the heat transfer between the boiler flange and the group head determines how fast the group cools after a shot as well as at what temperature the group idles. Adjusting the gasket material and thickness can help fine tune that heat transfer. That may help get a slightly better balance.
Curtis
LMWDP #551
“Taste every shot before adding milk!”

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bidoowee

#395: Post by bidoowee »

OldNuc wrote:Look to your local welding supply store. Silver braising rod is a common item and the 35% silver is the common brazing rod for HVAC. The Silver Brite 96% tin 4% silver is also used as it is much harder than soft solder.
Many thanks. That is helpful. My welding suppliers have tried my patience ever so slightly. I switched to Linde a few years ago, but when I went there to source brazing rod, they were a) unhelpful/clueless b) wanted to charge me for supplier's catalogs. My 'rep' had also never heard of SilverBrite... I ended up ordering from McMaster and haven't had time to find out what is available here.

@samuelLaw

I thought you might like that. I think that it is safe to conclude that the group is the limiting factor here, not the HX. And "limiting" is a very strong word - both versions are essentially already entirely temperature stable if you allow five minutes between shots. As I once heard a London Underground train driver say to passengers trying to get onto an already overfull train at rush hour: "The next train will be here in five minutes. If you can't wait five minutes, walk."
Maybe you can explore something on your reborn Aurora
Watch this space!

OldNuc

#396: Post by OldNuc »

McMaster has it all but is not the most economical place to shop but they do ship fast and it is all in stock. They get a lot of my money.

I do not know if this outfit ships into Canada but this is were I buy those products. http://www.weldingsupply.com/cgi-bin/ei ... ND:brazing This is the silver braze flux page and the rest is close.

feitz

#397: Post by feitz »

samuellaw178 wrote:Thomas (and others),

Any chance we can tell what material/techniques were used on the joints, just by looking at them? There seems to be two kind of techniques used on vintage Aurora from what I can see? This thread has been so educational thus far, thanks Thomas!

Images from Kaffee-netz after some kind of treatment (sand blasting/polishing?)

<image><image>

Note that the brass neck (brew reservoir) was joint to the boiler using the grey material. That part will see about up to 4 bar max. :?

<image>
The technique used for cleaning the boiler is called 'Gelbbrennen' in German, 'pickling' in English.
-> https://en.wikipedia.org/wiki/Pickling_(metal)
The greyish colour of the brazing probably stems from the chemical process.
Best regards from Munich
Claus

LMWDP #527

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bidoowee

#398: Post by bidoowee »

OldNuc wrote: this is were I buy those products
Awesome. I will definitely look into that. Suppliers are the more than half the battle on this project.
feitz wrote:The technique used for cleaning the boiler is called 'Gelbbrennen'
That was my suspicion - I was going to guess acetic acid as it is fairly easy to get and somewhat safer than the hydrochloric and sulfuric alternatives (fun for the whole family)!
pizzaman383 wrote:This challenge was the main reason that I built my Double Dipper
Those are impressive numbers! I'm sure I've looked at your build before, but I couldn't find it with a quick search in the forums. Trail of breadcrumbs?
pizzaman383 wrote:For the new Aurora and other dippers the rate of the heat transfer between the boiler flange and the group head determines how fast the group cools after a shot as well as at what temperature the group idles
I have started doing some thermodynamic modelling of the boiler, brew reservoir and the group assembly and I had begun to lean towards the conclusion that the water in the brew reservoir in conjunction with the bolts that connect the group to the brew reservoir flange (i.e. the boiler flange) play a more significant role in terms of heat transfer from the boiler to the group than the gasket istself. I use asbestos substitute 'sanitary' gaskets that are between 2-3mm in thickness. I'm not sure what they are made of, but my guess is some kind of treated paper or cellulose. The thermal conductivities of the materials in question:

k - (W/m K)
Stainless 12-45
Water 0.591
Asbestos 0.15
Paper 0.05

I haven't done any area calculations, but certainly the water surface in contact with the group is similar to the area of the gasket which would suggest it is transferring heat at a higher rate than gasket itself. Similarly, even if the cross-sectional area of the bolts is (e.g.) a tenth of the size of the gasket, they would still be transferring roughly an order of magnitude more heat; if, of course, my assumption that the gasket has similar properties to paper and/or asbestos is correct and/or I'm not out to lunch.

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bidoowee

#399: Post by bidoowee »

I imagine everyone remembers the story of Goldilocks and the Three Bears?



Illustration: Arthur Rackham. I love the painterly references on the wall - a Degas ballerina on the left, an old master on the right, an enameled reproduction of a Greek vase in blue? But I digress.

Apart from carrying a wee bit of Freudian baggage, it is also perhaps not the most pertinent of fairy tales for our times (how would you react if you came home and found someone sleeping in your kid's bed?).

Anyways, what I wanted from it for today's post is the porridge. You know, the three kinds of porridge that are too hot, too cold and just right? You see where I'm going with this...

Except that in my story there are four bears, or rather three bears and no bear, but neither of those versions scan very well, so we are going to stick with the original title.

First up is Papa bear's porridge.



This is one of the first temperature profiles that I took of the prototype machine. The methodology is very similar to the tests on the Brugnettis that I posted previously. As always, the Scace-values are not terribly useful except for comparison.
A reminder of the colors:
Blue - boiler wall
Red - brew reservoir
Purple - group neck
Green - PF receiver on the group
Yellow(ish) - Scace puck

Observations:
- The boiler temperature curve is sinusoidal as opposed to saw-tooth and has a delta of 0.7 C between minima and maxima. This performance was obtained using only the P term of the algorithm. It could probably be improved with some additional tuning, but I haven't bothered because it is already pretty good.
- Brew reservoir temperature is stable at idle and shows no trace of the boiler temperature variation.
- Recovery times for a shot are about 2 minutes per degree for the group and 1 minute per degree for the brew reservoir.
- Group temperature at idle (~70 C) is quite a bit lower at idle than the Auroras (~80 C and ~83 C for the horseshoe and diagonal versions respectively).
- Don't touch the probes.

Conclusions:
- Job (pretty much) done on the PID boiler control.
- Plenty of room for improvement on the brew reservoir temperature stability which is gaining too much heat after a pull.
- The whole shebang has to be hotter.

Next up: Mama bear and No bear.

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pootoogoo

#400: Post by pootoogoo »

What about the center painting ? :lol:
Can't wait to see the two other bears reaction.