Corrosion prevention in espresso machines

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rpavlis

#1: Post by rpavlis »

One frequently finds espresso machines, especially lever ones, that are of rather recent vintage but still have serious corrosion problems. Some machines just a few years old look ready for land fills!

The problem stems largely from the simple fact that rust catalyses the production of more rust. When iron rust contacts stainless steel even stainless can rust badly. Some metals form protective oxide coats to prevent their being further attacked by air. Iron basically does the opposite!

Copper forms a very thin oxide coat that affords protection. It dissolves away in the presence of strong acids, which is why weak acids like acetic and citric are normally used on boilers to remove carbonates. However, if one remove the protective oxide coat a new one will form, but whilst it is bare it is more vulnerable. Under some conditions chlorides can bring about a rust like reaction with copper alloys often called "bronze disease." Brass is subject to this. It is best to be overly protective and keep salt away from these materials.

The primary reason that espresso machines become heaps of rust is failure to clean them properly. When any spots of rust appear, it needs to be polished away. Even thick chrome plating can corrode if left wet and dirty. Contact with salts of all types needs to be avoided.

Brass and copper (and other copper alloys) tend mostly simply to look ugly when not cared for properly. However, it becomes more and more difficult to restore the finish to anything approaching beauty when the materials are not kept reasonably clean, however, as mentioned earlier bronze disease can happen in the presence chlorides.

It is best always to clean espresso machines after use and wipe them dry. Watch out for rust!

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drgary
Team HB

#2: Post by drgary »

Robert:

Thanks for starting this thread. What are the salts that would typically come in contact with an espresso machine, assuming we aren't throwing sodium chloride over our shoulders for good luck while standing with our backs to the machine?
Gary
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Maxwell Mooney

#3: Post by Maxwell Mooney »

Well, this is exceptionally relevant to me. Thanks for posting some stuff. I echo DrGary's question about salt(s). Do you mean a very technical definition of salt, or basic table salt, or something else all together?

Also- I've read that Muriatic acid and copper are a lethal mix. What about for other metal components?

You mentioned that any rust spots that form on chrome need to be polished away- what do you recommend for chrome polish? Metal care is something altogether unfamiliar to me.
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rpavlis (original poster)

#4: Post by rpavlis (original poster) »

There are substantial quantities of salts in many water supplies. When one lives near the sea there is also a tendency to have NaCl deposits on things. Galvanic corrosion can occur when dissimilar metals (including different concentrations of alloying metals in alloys) contact solutions with dissolved salts. Having once lived on a boat for several years I can testify to how bad a problem this can be!!! There are many special polishes for chrome finishes that seem to work well. The problem is the auto catalytic nature of rust. As I mentioned earlier in the presence of chloride copper, and especially alloys can corrode via a rather similar mechanism. When salty water evaporates it tends not to go to dryness, but leave a film of concentrated salt water that can do serious damage quickly. There are things like Simichrome polish that seem to work very well many of them leave a thin protective film.

I think it a good idea to wipe espresso machines after using them. Leaving pooled water on them is a real no no!

When I lived in the islands I generally tried to keep chrome plated things covered with a cloth cover, that was very helpful.

In reality all salts left in contact with metal are bad, and chloride salts are particularly nasty with copper and its alloys.

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hankbates

#5: Post by hankbates »

The area under the drip tray of a LP lever machine has been a source of problems since the original design, but it has been particularly so since the removable plastic drip tray was included. Basically a nice touch and improvement, inattention to keeping the space between it and the base absolutely dry can cause rapid deterioration.

Unfortunately, one of the most common configurations of these machines uses a relatively thin steel base which is chrome plated. Looks nice when new, but similar to the rusted through chrome bumpers we have all seen on 30 year old cars, the area under the tray can become a "rustbucket" in only a few years.

When the chrome layer is breached and the more reactive iron/steel layer underneath becomes exposed, it becomes a "sacrificial anode" and spends itself protecting the exposed areas whenever wet. Since small areas of iron are protecting large areas of chrome, the result is that the iron disappears, leaving a pit or worse, a hole.

A new base for one of these machines costs around $100 in chrome, and more than double that in brass. It might be worth it to go for the brass if you intend to keep the machine for a long while (most of us do, I think). If you don't like the color mismatch, be prepared to keeping the area under the tray very dry.

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drgary
Team HB

#6: Post by drgary »

Isn't the brass finish more delicate than the chrome? Christopher Cara cleans the chrome on the boiler and group with a very fine steel wool. Keeping the base dry is easy as long as you dry the base and the bottom of the drip tray. And if it ever starts to pit you can treat it with a little Rustoleum since the base is hidden under the drip tray.
Gary
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rpavlis (original poster)

#7: Post by rpavlis (original poster) »

Brass is much softer than steel, and hence brass is easier to scratch and dent than steel. However, brass is also much more resistant to corrosion. Brass does, however, need to be kept away from chlorides.

A serious issue in espresso machines, it seems to me, comes from the practice of plating brass and copper. The plating tends to peal and blister eventually, and then it is absolutely ugly. It is not just a little ugly, really hard core ugly. Had the brass or copper part been left bare this ugliness would have been avoided, and the part could simply polished with a good brass polish.

I have a genuinely brass 1999 Europiccola. About the only plated part on it is the group handle shaft. I do take care to avoid scratching the solid brass base. (I think the brass base became truly brass in the mid 1990s, but I am not sure.) When I got the machine it was coated with a protective polymer, except for the boiler and all of the brass soldered to it. Even though 13 years old the polymer has held up well. I use brass polish on the boiler about every six weeks to two months. A serious advantage of brass is that it is easy to machine brass modifications and have them look perfect when the machine is already brass!

Chrome plated steel is much more resistant scratching, but dramatically less resistant to chemical attack and rusting. When the plating peels away it looks bad, and the only real way to have it look decent again is to have the whole part replated.

Corrosion often begins around fasteners. Putting a bit of grease under fasteners when they are replaced or reinstalled tends to protect the metal underneath them. Otherwise installing it tends to scratch the plating and liquid water tends to stay there longer and corrosion follows. The screw in the centre of La Pavoni drip wells from about 1982 to 2005 tends to be an unfortunate example of this!

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rpavlis (original poster)

#8: Post by rpavlis (original poster) »

There is another point:

Once iron or steel objects are covered with rust there is a technique that can remove every trace of the rust. This method involves submerging the object in an alkaline solution. I always used about 3% sodium hydroxide when I did it many years ago, but many people these days use 5% or more sodium carbonate. It is a much less nasty material. DO NOT USE SODIUM CHLORIDE. DO NOT TRY THIS WITH COPPER ALLOYS. Use a polyethylene or glass container.

Connect a wire to the object and connect this wire to the NEGATIVE terminal a direct current power supply. A 4 to 10 amp 12 volt battery charger is idea. Take a waste chunk of stainless steel (it will be destroyed in time by the process) or a chunk of graphite and connect a wire to this. Run this second wire to the positive terminal.

Immerse the object and the waste stainless or graphite piece in the solution so that they do not touch and turn on the current. Typically rusty parts will be completely stripped of all rust in just a few hours. This leaves absolutely BARE metal. IF ONE REVERSE THE wires to the power supply it will quickly DESTROY the object instead of remove its rust!!!!!!

IMMEDIATELY after removing the part from the alkaline solution it MUST be washed with lots of clean water, and IMMEDIATELY dried, and then coated with something to protect the now totally bare metal. (Rust prevention paint comes to mind!)

I never tried this with chrome plated materials. I would test with a small unimportant object first.

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drgary
Team HB

#9: Post by drgary »

Robert, that's a gem! What's the name of this process?
Gary
LMWDP#308

What I WOULD do for a good cup of coffee!

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rpavlis (original poster)

#10: Post by rpavlis (original poster) »

We just called it electrolytic rust removal. Some of the people in archaeology at the University of the Virgin Islands often did this on artifacts that had been recovered from the sea. On really badly rusted objects the result was amazing. Much of the rust is loose so it gets stripped off by the evolving hydrogen, but some of the rust seems to get "unrusted" by being reduced back to iron.

Aluminium, by the way, reacts rapidly with alkaline aqueous solutions, so one must make sure that there is no aluminium on anything immersed when doing this.