Crucible question - The Home Foundry

I was BS'ing with OCD recently about crucibles. And he brought up an interesting point I missed. Everyone is aware of the importance of conducting a proper heat cycle with a brand new crucible. Somewhere he uncovered a flux treatment as part of that procedure! I believe it was from Morgan too! We all know flux tears down crucibles, but I seem to remember reading this somewhere too and just dismissed it. Of course I can't find it now on Morgans site. What got me thinking about this was seeing Roberts crucible in his bike thread. I see some crucibles with a nice even crust on them and then I see this. It appears some of the metal has removed some of his crucible material. The question is where does that go? Does that initial flux prevent this? Why do some crucibles I see have nice even coating on them? Obviously, the end goal is maximum service life, no failures and no mystery material ending up in stuff we pour.

Here is a helpful page from Morgan, but it's not on it. http://www.morganmms.com/media//maximising-crucible-service-life-mgam.pdf




For comparison....Look at this crucible, notice the even coating?

I have to agree with HT1, there is a lot of misinformation about crucible types, metal suitability, temperature ratings, etc.

I have researched some of the Morgan crucibles.

Below are first-use tempering instructions for a Morgan Salamander-Super.
As I understand it, the tempering sets the coating on the exterior of the crucible, making it durable, and also drives out any moisture that may be in the crucible.



Here is some info I have gathered over the years regarding Morgan crucibles:

Note that the clay-graphite Salamander Super is "ferrous-metal-rated", and the silicon-carbide Excel and Himelt are designed for non-ferrous metals with lower casting temperature ranges.

If you plan on doing iron work, I would recommend a Salamander-Super.
If you are only going to do non-ferrous work, a silicon-carbide crucible may last longer, depending on the quality of the crucible.

A poorly made crucible will fail with whatever metal you use; I have seen some supposed "iron-rated; 'its what the salesman told me' " crucibles fold up like a wet waffle as they approach the melt temperature of iron; thus the reason I stick with the Morgan Salamander-Supers.

There are other quality brands beside Morgan, but these are the ones I have used and am familiar with.

A Morgan "SALAMANDER SUPER" is a graphite crucible.
It can be used with both ferrous metals such as gray iron, as well as non-ferrous alloys such as aluminum, brass, and bronze.
Typical metal casting temperatures are F - F (850 C - C).
Color is black.
The PREHEATING / FIRST USE instructions for fuel-fired furnaces is as follows (per Morgan):
A new crucible shold be preheated empty in order to minimize the termperature gradient across the crucible wall. If there is a risk of the crucible having absorbed some moisture, then the furnace should be initially heated slowly up to approximately 392 F (200 C) and held at this temperature until all moisture has been driven off.
A new crucible should initially be heated slowly and evenly to F (600 C) on low power, avoiding local impingement of flame on the curcible. Subsequently the full heat input rate should be utilized to achieve a uniform bright red condition over the whole crucible at approximately F (900 C) at which point the crucible should be charged immediately, taking care not to packing metal tightly or bridging ingots across the crucible.

Morgan "EXCEL" and "HIMELT" crucibles are made from silicon carbide, and are designed for use with non-ferrous metals (not iron).
Typical metal casting temperatures for these crucibles are:
EXCEL: F - F (850 C - C)
HIMELT: F - F ( C - C)
The color is red.
The PREHEATING / FIRST USE instructions for fuel-fired furnaces is as follows (per Morgan):
A new crucible shold be preheated empty until they reach a uniform bright red color (approximately F (900 C) in order to pre-condition the glaze. The preheating time will depend o the size of the crucible (can be up to one hour for a large crucible). Avoid direct flame impingement on the crucible surface.

Below are photos of Morgan Salamander-Super (on left) and Morgan Salamander Hi-Melt.
Very confusing nomenclature since you would thing they are rated for the same temperatures and metal types since they both are labeled "Salamander" (they are not).
The black one (clay-graphite) is ferrous-metal rated, the red one (silicon-carbide) is not ferrous-metal rated.

The red one (Hi-Melt) is Morgan's best and longest lasting crucible for non-ferrous metals.
The black one (Salamander-Super) will work with iron, and will also work with non-ferrous metals.
The red one (Hi-Melt) is not rated for iron work.

They both have glazing on them that needs to be tempered prior to use.

I have standardized on the Salamander-Super for all crucible sizes and metal types, and it seems to work well if tempered correctly and not abused, jammed, overloaded, over-fluxed, etc.