THE SHOW
Well, this is the business end of the operation. The following is a description of preparing the moulds through to the finished casting. Another great site to view the moulding and casting operation in more detail is at Steve Hoerner's FOUNDRY 101 web page.
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The job that I'm doing this morning is to cast two small compressor units for steam Loco's. One will be a two cylinder unit, the other will be a single cylinder unit. Both jobs will involve simple cores to produce the bores.
The above shot shows the flask ready to fit to the pattern. Note the long dowels that fit through the blocking plate to align with it's mating flask.
Flask fitted and ready to ram up. The great thing about using these wooden flasks is that they can be easily modified to suit various patterns and situations. In this case they needed to have a height increased, a length of 3/4" square a couple of nails and glue and instant height change.
Lightly dust the pattern with parting dust to assist removal of the sand mould. The are many different types of dusting powders that are specifically designed for this job. I use el cheapo "no name brand" talcum powder in a small bag made up from an old bed sheet. No mess no fuss and to cap it all off, it smells nice.
I'm using Petro Bond moulding sand for this job, the process for Green Sand is identical. I firstly ram the corners and around the sides, then work inwards ramming around the base of the pattern.
I continue to add sand in layers and ram in an up and down direction followed by side to side. I prefer to ram the mould firmly and then vent well to ensure high definition with a fine surface finish.
When the ramming is complete, scrape of the excess sand to leave the top flush with the flask.
Before removing the sand mould from the pattern I spike down to the pattern to assist with venting gasses when the molten metal is poured. In most cases I find this negates the need for risers and further disturbance of the mould.
These particular patterns had very little draft to work with, particularly in the fins so removing was very tricky
After ramming the runner is cut. I like to make these as large as practically possible to feed the casting whilst it's cooling.
The feeding gates are then cut to feed metal from the runner to the mould.
This is a selection of the tools that I use for working the sand.
The core sticks are selected for the job. These are purchased from a specialist core maker and depending on size cost around $1.00 each.
All cored up and ready to go. The cores are easily cut to length with a hack saw before fitting.
Before beginning the casting operation, consideration must be given to the most important tools of the job, personal safety gear. No matter how small or how quick the operation is, I don't start until I'm suited up from top to bottom. Firstly, I wear leather safety boots with spats, the apron is made from Kevlar and coated with a heat shield, I wear a safety helmet fitted with a full face shield including a chin return to prevent splashes up my neck, a thick woollen jacket and lastly leather gloves with a woollen liner.
I've heard of, and seen to many horrific burns that people have received to be complacent. I treat each cast as if their will be a mishap and plan for the worst case scenario. A few minutes of planning could save months of pain having skin peeled off my backside and attached to my arms, legs, chest and face. THINK ABOUT IT.
The set-up, not ideal, but it will do until I have a more permanent facility (coming soon). From left, - gas bottle and regulator, furnace, temperature controller, pouring shank and tongs, long handled pliers and spoon for skimming, moulds sitting on a steel tray. The moulds are set off the ground to assist venting and are clamped to prevent separation during the pour.
The metal I'm working with is Silicon Bronze. Before pouring, the molten metal is skimmed to remove impurities that have floated to the top.
With the crucible set in the pouring shank the hot stuff can be introduced to its new shape. Pouring temp 1200 deg C. The crucible being used is a #6 silicon carbide.
Once the job is complete any excess is poured into a hollow sand mould.
Jobs done and the vents are smokin.
Four hours later the moment of truth, the grand opening.
Final result, no flaws, an extremely fine finish and one happy customer. Not bad for a mornings work.
Special thanks to my working men (alias my two youngest son's)
Matthew ("Macca") to the right
Michael ("Spud") To the left
As an addition to the casting process I have begun to include a number of set-up and procedural changes to better ensure that a first time every time approach becomes the norm. To this end I now include the addition of a filter to the runner along with a deep 'basin' cut into the drag to assist with the entrapment of impurities during the pour.
To further protect the metal properties of the bronze I now add a spoon full of broken glass together with a tea spoon of Borax Brazing Flux into the crucible before beginning a melt. The glass when melted forms a skin over the top of the melt to protect it from oxidization, the borax assists with cleaning the molten bronze bringing impurities to the surface adhering to the glass.
Below is a description of the use of two types of filters.
This is a mould for a small plumber block used in the construction of a small stationary steam engine. The brown woven gauze like patch on the mould is the filter. This is purchased as a sheet 900mm wide by any length, it can easily be cut to any shape with scissors. Note the pouring basin in the drag.
View showing the filter sitting over the basin.
View showing the cope fitted to the drag with the filter between the two.
This is another type of filter I've used in the past. Its a ceramic block which is like a sponge in structure to trap impurities. Also shown is a small length of pipe used to set the filter block together with the wooden former. I use this former on larger moulds to form the basin to trap any solids or dirt.
View showing the pipe rammed up with sand with the wooden former to allow the filter to be fitted.
View showing the pipe sealed with sand around its base to prevent any chance of a metal run out. Note the filter in the pipe runner, this lines up with the runner cut in the cope.