Further casting information:
Before stopping to visit Roger and having him kindly post the sword photos, I stopped at Harbor Casting in N. Canton. A helpful shop forman there answered many of my questions about metal casting, and I observed their operation as we talked. They only cast steel, brass and bronze items of small and moderate size there. They were casting brass boat motor propellers before I arrived. The molds are made from a special fine grained grey sand, that is formed as a wet mixture over the pattern, and then kiln dried before use. The sand changes color to a cream hue during and after the pouring process. The metal is made in small batches in a small melting furnace that is heated by electric coils that have cooling water circulating through the hollow coils. The melting device is attached to a hoist for mobility and pouring. I didn't catch the name of this mini furnace, unfortunately. This technology is similiar to that used in heating small steel bar stubs prior to drop forging in other operations that I've seen. I was able to examine the sand molding material on a cooled batch of propellers, and it was fragile and crumbled easily after being fired. It was not hard as I thought that I remembered it from prior visits, but maybe that was what I saw years ago when Frankham Bronze was still in business locally. Anyway, the molten metal was poured into the flared mold 'riser'and flowed by gravity down into the 'tree', as several parts were made from multiple molds with one pouring of that heat. That is how modern sand casting is basically done today on a small scale.
Roger later connected me with a friend of his at Stark Pattern (they make mold and die patterns) who knew the technology of aluminum casting, and he graciously answered my questions about that operation. He said that it is usually done by gravity sand casting similar to steel and brass, but the riser is larger to apply more weight and pressure to fully fill the molds. Since aluminum's specific gravity is so much lighter that the other metals, some adjustments are made in the process to eliminate bubbles and air pockets, depending on size and desired quality. Sometimes aluminum is pressure cast using hydraulics in a die casting method similar to zinc casting, and another option is the use of glazed plaster-of-paris or even steel molds, in order to obtain higher detail and quality. He said that brass gravity- casts better than aluminum and that there is better detail because of the density of the heavier metal. Aluminum can also loose detail in the cleaning procedure because of its softer and more fragile characteristics. He said that most casting technology and processes in use today were also used in the 1930's.
Fred, in regards to 'Tombak', as featured in the Pack catalog, my experience with the material used by Pack & Co. is that is is not the same as the metal alloy 'Tombac', as used in Canada. I have a Pack Luft sword made of this material, and it is heafty like zinc or brass, but is obviously cast from a zinc based alloy. It can be clearly seen where the light plating finish is now gone. The Pack 'Tombak' army sword hilts are sand cast from the same zinc alloy. You can always spot them, as they have a greenish hue where the zinc impurities bleed through into the gold plating. Brass or any alloy with a very high copper content won't do that. I think that Pack was talking-up a cost cutting production alloy in their solicitations about their 'new Tombak'.
All in all, it was a very informative day. Though I could have 'Googled' the same basic information on the web, I got the info in a much more constructive way, and enjoyed the experience. I hope that you enjoy the information here as well.
