Hi Guys,
A couple of hints from the foundry trade as a i was a greensand moulder, The correct moisture content is 4-6%water, I always tended to err on approx 5%, This was in using red mansfield sand, One soon got into a system where the feel of the sand "was just right" In the foundry i served my apprenticeship in one was left to take control over the state of their own sand I was making cast iron bronze , brass &aluminium castings
When making cast iron, the mixture was mansfield plus about 15% Scottish rock sand mixed through,, Our facing sand, was through the pan mill, or Muller
On brass bronze &aluminium, it was a straight red mansfield, Ones sand pile was used for years, and occasionally, one would add a shovelfull of new virgin sand to refresh the mix,(about once every two months) One can have the mixture too new The old moulders were meticulously careful of their sand, after casting ones moulds and knocking out the boxes, The labourer, would sprinkle some water over the sand, usually sparingly, and leave the sand for about 20 minutes till the steam permeated through the sand pile, Next the sand was flicked over using the shovel, and any lumps, were biffed with the back of the shovel, to break up the hardened /dried sand lumps, Then flicked back,
The next operation, was placing two lengths of angle iron across the bearers on the moulders sand tub, on top of these was placed a riddle with 1/4" mesh, the labourer shovelled in the sand , and yours truly or some other moulder shoved the riddle vigerously back &forward to sieve the sand into the tub This sand was left, at one end of ones tub, and one continued moulding with the sand previously left at the opposite end of ones tub till the fresh sand was cooled down (your average foundry labourer of 45 years ago, had as well as brute strength, to have a lot of common sense & skill, and a good one was a real advantage to the average moulder
Back to moulding, Ones facing sand was passed through an 1/8" sieve over ones patterns, in the moulding box, As the post has progressed on sand management, the amount of new virgin sand, is greatly dependent, on a) the metal thickness of castings being produced Heavy castings= greater sand burn as does the metal temperature
An b) some metals have a tendency to burn in to the sides of the sand mould metals such as phosphor bronze
These problems, can be greatly overcome by the application of a mould dressing, Which also gives a superior casting finish, Amongst the materials used
For cast -iron Graphite powder, or a mixture of graphite & coaldust
for bronze &brasses, peasmeal, or talcum powder
for aluminium talcum powder
Sometimes for heavy bronze greensand moulds we applied "white Blacking" No i have not taken leave of my senses! this was a mix of talcum powder &graphite powder On greensand work, all these dressings were applied by shaking the dusting powder through a muslin cloth bag, But dont go daft, Using too much.
I always used to use petrobond as a facing sand, on very delicate , &fine metal pattern moulding One application which i remember making, was the manufacture of tyre mould sections for agricultural tractor rubber tyre moulds, for the rear wheels
Unless you are making your moulds for the tiny castings a home craftsman is engaged on, a goodplan, is to scrape from your greensand mould, as much as possible when opened up,after casting Any adhering burned petrobond, as the black burned dust, forms "fines" which cloggs your greensand, and cloggs up the venting of your sand, and also repells the water for moistening.