Boiler musing

I stumbled on the open source lever project thread on home barista the other day. The goal of these clever people is to marry an off the shelf lever group with the thermoblock from an ascasa to make a small-footprint commercial quality lever machine. A noble goal indeed. The upsides to this idea are numerous: no pump, very fast warm up time and all of the benefits of a microcontroller. The downside, as far as I am concerned, is the inherent complexity of the microcontroller and everything that it brings with it. Call me a Luddite, but I'm not sure that I want bluetooth as an option on my espresso machine. More importantly, aside from the difficulty of recompiling the code for the replacement for the microcontroller when it fails in x years, how long is the thermoblock going to last and how long are ascasa going to continue to make it? I own an ascasa and can attest that they are great for making an espresso (but not more than one) and it burnt out in less than a year of moderate use at the office. This is an admittedly small sample, but I think that it is safe to assume that ascasa has performed some value engineering given that this is a domestic machine with a one year guarantee. How many times has the boiler failed in either of the auroras that I use? Not once, as far as I know... in thirty years.

  

With the exception of a few transistors, diodes etc inside the Gicar water level controller and the electric pressurestat, the Aurora is all industrial revolution technology. The complexity and sophistication of the engineering is expressed in the selection, sizing and form of the materials that are combined to produce its desirable and highly repeatable temperature and pressure profiles. As a result of the thermodynamic design, the grouphead temperature is stable at idle and the HX circuit balances the heat gain when pulling shots. What fails first on these machines? The controller and pressurestat. 

While I am certain that there is room for improvement in the control electronics, I think that the Aurora should remain, at heart, a steam engine.

Grouphead materials - lead in your morning coffee?

Materials - Alternatives to leaded brass used in the Aurora grouphead

The body of the Aurora grouphead is made from cast brass. Lead is added to brass to improve machinability. It acts as a lubricant and causes the chips to break into small pieces while it is being cut. Worse still, because of the way the lead crystals form as the liquid metal solidifies in the mold, the concentration of lead is highest at the inside surface - i.e. where the water comes into contact with the group body. C84400, traditionally the most popular alloy for faucets and plumbing fixtures, contains 7% lead, so it is highly likely that all vintage espresso machines help you meet your recommended daily dose of lead in the morning. This was just the way things were was until California passed its law in the early 90s. Since then, considerable effort has been made to find alternatives to leaded brass. 

Excellent guide to copper casting alloys from copper.org


From: http://www.copper.org/applications/industrial/lowlead.html

Sand-cast faucets and other plumbing components have traditionally been made from leaded red, semi-red and yellow brasses. The most common plumbing brass, C84400 (also known as 81 Metal or 81-3-7-9) contains nominally 7% lead. The most popular red brass, C83600 (85 Metal, 85-5-5-5), contains nominally 5% lead. Permanent mold and pressure die castings of plumbing components are also commonly made of the leaded yellow brass alloy C85800, which contains nominally 1.5% lead. In contrast to the red brasses, which are moderate-strength, single-phase alpha alloys, alloy C85800 is stronger at both room temperature and at elevated temperatures approaching the solidus, because of the presence of the beta phase in the alpha matrix. These improved mechanical properties are an advantage not only during casting and machining, but also in service. Alloy C85800 has a pleasant light yellow color and can be buffed to a high polish.

EnviroBrass (SeBiLOY) http://www.copper.org/environment/water/NACE02122/nace02122b.html

The idea of using a combination of bismuth and selenium as a substitute for lead was originally conceived by the ASARCO Technical Center, Salt Lake City, Utah. This was pursued by several years of research by an industry consortium which included the Copper Development Association Inc. (CDA), the American Foundrymen's Society (AFS), the Brass and Bronze Ingot Manufacturers (BBIM), the Materials Technology Laboratory of CANMET, other foundries and water product producers. The research shows that a combination of bismuth and selenium provides the same beneficial effect on machinability as does lead. In addition, pressure tightness and other casting characteristics of bismuth/selenium brasses were found to be virtually identical to those in conventional leaded alloys.

Three alloys have been developed, EnviroBrass® I, II and III, which are Alloys C89510, C89520 and C89550

Elements	Range or Max%
	EnviroBrass I C89510	EnviroBrass II C89520	EnviroBrass III C89550
Copper	86.0-88.0	85.0-87.0	58.0-64.0
Tin	4.0-6.0	5.0-6.0	0.1-1.2
Lead	0.25	0.25	0.1
Zinc	4.0-6.0	4.0-6.0	32.0-38.0
Bismuth	0.5-1.5**	1.6-2.2***	0.6-1.2
Selenium	0.35-0.75**	0.8-1.1***	0.01-0.1
Nickel (incl. Cobalt)	1	1	1.0.
Iron	0.2	0.2	0.5
Antimony	0.25	0.25	0.05
Sulphur	0.08	0.08	0.05
Phosphorus	0.05	0.05	0.01
Aluminum	0.005	0.005	0.1-0.6
Silicon	0.005	0.005	0.25

Sum of named elements 99.5

* Cu + sum of named elements, 99.5% min. 

** Experience favors Bi:Se ≥ 2:1. 

*** Bi:Se ratio ≥ 2:1.


Federalloy - http://www.concast.com/green-alloys.php

Federalloy is a patented alloy in which lead is replaced with bismuth to create pressure-tight plumbing fittings and fixtures. It has excellent machinability. Concast has been the only foundry in the nation licensed to produce the Federalloy series of lead-free copper alloys. We joined forces with Federal Metal Company, who developed the Federalloy group of alloys, such as C89831 and C89835.

C89831 is a replacement for C84400

Chemical Composition
Alloy	Cu%	Sn%	Pb%	Zn%	Fe%	Ni%1	Sb%	P%	S%	Al%	Si%	Bi%
C89831
	91-87	3.7-2.7	0.1	4	0.3	1	0.25	0.05	0.08	0.005	0.005	3.7-2.7
1Ni value includes Co.
Note: Cu + Sum of Named Elements, 99.0% min. Single values represent maximums.

EcoBrass - C69300 (wrought) / C87850 (cast)


http://en.coppercanada.ca/pdfs/CCMagazinePDFs/E157b.pdf

The two most common types of lead-free alloys in commercial use today are the silicon brasses (of which ECO BRASS®
 is one) and the bismuth containing bronze alloys. It is noteworthy that ECO BRASS® melts at temperatures about 150°C
(300°F) lower than the bismuth alloys, and it is 7% less dense. This means that for the same size component, the manufacturer can reduce the casting weight by 7%.

ECO BRASS® can be used in all potable water applications incorporating extruded rod, forgings and castings. Some examples are faucets, fire protection devices, ball valves, shower valves and water meter bodies.

Element
	Cu(1,2)	Pb	Sn	Zn	Fe	P	Ni(3)	Mn	Si
Min (%)	73					0.04			2.7
Max (%)	77	0.09	0.2	Rem	0.1	0.15	0.1	0.1	3.4
(1) Cu value includes Ag.
(2) Cu + Sum of Named Elements 99.5% min.
(3) Ni value includes Co.

C89833 Copper Bismuth Alloy - source lbfoundry.com

Alloy C89833
Cu%	Sn%	Pb%	Zn%	Fe%	Ni%	Sb%
86.00-91.00	4.00-6.00	0.09	2.00-6.00	0.3	1	0.25
P%	S%	Al%	Mn%	Si%	Bi%
0.05	0.08	0.005	N/A	0.005	1.70-2.70

Update 2016 3 2

Excellent database of properties of copper alloys.
http://www.copper.org/resources/properties/db/basic-search.php

_________

First quote back from a foundry in China. They seem to be suggesting casting in CuZn40 alloy which is C28000 aka Muntz Metal. C85800

This is both odd and not desirable as:

The UNS designations for wrought brasses includes C20500 through C28580, and C83300 through C85800 for cast brasses.


Certain brasses can corrode in various environments. Dezincification can be a problem in alloys containing more than 15% zinc in stagnant, acidic aqueous environments. Dezincification begins as the removal of zinc from the surface of the brass, leaving a relatively porous and weak layer of copper and copper oxide. The dezincification can progress through the brass and weaken the entire component

http://www.copper.org/resources/properties/microstructure/brasses.html _________

LEAD FREE COMPLIANCE

With the legislation passed in California (AB1953) and Vermont S152) serving as a catalyst for a national interest in the lead free regulations for potable water, a National Lead Free Bill was signed by President Obama in January 2011. This Senate Bill S.3874 (aka: Reduction in Lead in Drinking Water Act) that was signed will reduce the lead content in faucets, fittings and valves from 8% to no more than a weighted average of 0.25% maximum lead when used with respect to the wetted surface of pipes, plumbing fittings and fixtures or other potable water applications. This law will go into effect nationally January 1, 2014.

__________

Interesting reading:

Metal Casting: A Sand Casting Manual for the Small Foundry, Volume 2
By Steve Chastain


____________________

Update 2016 3 3

Excellent site and white paper on the comparison of lead-free copper alloys.

__________________


Update 2016 3 20 - Dezincification - slay the beast you cannot see

Finding an appropriate brass alloy in China is proving to be complicated. Further reading is required.

General discussion of brass types 

http://admin.copperalliance.eu/docs/librariesprovider5/publication-117/117-section-6-types-of-brass.pdf

A note on the dezincification of brass and the inhibiting effect of elemental additions - 1993 

http://www.copper.org/applications/rodbar/pdf/7013.pdf

Excellent explanation and analysis of dezincification 

https://cdn.chasebrass.com/wp-content/uploads/2016/11/Dezincification-Web-Class-ver-5-11-17.pdf

Some Conclusions

15% is the limit for zinc content to avoid the problem (mostly).

Arsenic, phosphorus, antimony, aluminum, silicon are used to inhibit corrosion in brasses of up to 35% zinc composition. 

Annealing redistributes the vulnerable beta phase in duplex brasses into localized pockets as opposed to strings thus reducing the effects of dezincification.