Casting

Casting Sand Casting is a process that has been around for over 5000 years. The process itself is fairly simple. A pattern is pressed into a sand mould to leave an impression. The pattern is then removed and the impression left behind is filled with a molten metal.

Pattern Design Broken Edges Patterns are generally made from wood however they can be made from metal, plastic or any number of other materials. When designing a pattern a number of things must be taken into consideration. Square Pattern 1. All patterns must have a Taper (or Draft) this allows the pattern to be withdrawn cleanly from the mould. This should be between 2˚ & 5˚ Sharp Edges Pattern Tapered Pattern

Pattern Design 2. Sharp internal corners should be avoided as these will focus any stresses acting on the casting and can cause it to fracture Weak Spot Sharp Corners If you leave any sharp internal edges Use a wax fillet on internal corners This can weaken the final design For a stronger casting

Pattern Design 3. Patterns should be finished with paint or varnish and sanded with fine glass paper. This will help avoid the pattern absorbing moisture form the sand and distorting. The varnish or paint will give the pattern a much finer finish and consequently the final casting will have a superior finish

Pattern Design Pattern Casting Cooling has occurred before the mould cavity has filled 4. Avoid changes in section because this may cause differential cooling (one part of the casting cooling much faster than the rest) this can lead to internal stresses in the casting. Also try to avoid patterns that are extremely thin as the molten metal can often cool before it has flowed into all areas of the mould.

Pattern Design 5. Finally remember to make the pattern slightly larger than the required casting. This will allow for any machining and for the fact that as the molten metal cools it will contract.

Casting Metals Aluminium is a lightweight, Non ferrous metal often used for casting . It is the most suitable metal for casting in the school workshop due to its low melting point (around 660˚C) Because the metal cools as it flows through the moulding box it is advisable to heat the metal to 760˚C before pouring. Aluminium Ingots Aluminium Lamp Aluminium Saucepan

Casting Metals Brass (an alloy of Copper & Zinc) is often used for casting. This yellow, non ferrous metal has many uses, mainly due to its resistance to corrosion. Brass has a higher melting point (905˚C) than aluminium and thus is generally not used as a casting material in schools. Brass Ornaments Brass Bell Brass Ingots

Casting Metals Cast Iron is a hard, ferrous metal often used by industry for casting. Cast Iron melts at about 2270˚C and consequently is not used in the school workshop. Cast Iron Gate Cast Iron Vice Cast Iron Fire place surround

The above casting equipment will be used Cope Riddle Striking Off Bar Bellows Drag Parting Powder Vent Spike Degassing Tablets Gate Cutter Rapping Iron Draw Pin Sprue Pins Rammer The above casting equipment will be used

The above Safety Equipment will be required Casting Equipment Full Face Mask Leather Apron Leather Gauntlets The above Safety Equipment will be required

Casting Pattern Drag Place the Drag face down on a board and sit the pattern in the centre

Casting Parting Powder Lightly dust the pattern and board with some parting powder (chalk dust)

Casting Carefully riddle some facing sand over the pattern until it is completely covered to a depth of 20mm

Use your fingers to lightly pack the sand around the pattern. Casting Use your fingers to lightly pack the sand around the pattern.

Casting Rammer Fill the rest of the moulding box and use a rammer to compact the sand.

Use a strike off bar to remove any surplus sand. Casting Strike Off Bar Use a strike off bar to remove any surplus sand.

Carefully turn the drag over and place the cope on top. Casting Cope Drag Carefully turn the drag over and place the cope on top.

Again lightly dust with parting powder. Casting Parting Powder Again lightly dust with parting powder.

Place the Sprue Pins in the box. Casting Sprue Pins Place the Sprue Pins in the box.

Casting Riddle more facing sand onto the underside of the pattern (about 20mm) Then fill the rest of the moulding box.

Casting Again use a Rammer to pack the sand. Take care to pack around the Sprue Pins.

Fill the Cope to the top and use the Strike off bar to level the top Casting Fill the Cope to the top and use the Strike off bar to level the top

Carefully form a pouring cup around one of the Sprue pins Casting Pouring Cup Carefully form a pouring cup around one of the Sprue pins

Gently remove the Sprue pins Casting Sprue Pins Use a finger to round over any sharp corners Gently remove the Sprue pins

Carefully separate the two halves of the moulding box Casting Pouring Cup Carefully separate the two halves of the moulding box

Carefully cut the in and out gates Casting Out Gate In Gate In Gate Carefully cut the in and out gates

Casting Draw Pin Draw Pin Rapping Iron Screw the Draw Pin into the centre of the pattern and gently tap in all directions with a Rapping Iron

Carefully remove the pattern Casting Carefully remove the pattern

Casting Use your finger to round over any sharp edges near the two gates then use the Bellows to blow away any grains of sand that have fallen into the mould

Carefully put the two halves of the moulding box back together Casting Carefully put the two halves of the moulding box back together

Casting Vent Rod Use the Vent Rod to make some holes part way through the sand on the top of the moulding box. This will help any excess gas escape

Casting Carefully lift the completed moulding box and sit it in front of the crucible furnace

Casting Heat the aluminium until it reaches the required temperature (750˚C) This can be checked with a Pyrometer

Casting Add a Degassing Tablet, this will help remove any excess gas from the aluminium and drive any impurities to the surface

Carefully skim off the impurities on the surface of the aluminium Casting Carefully skim off the impurities on the surface of the aluminium

Casting Carefully pour the molten aluminium down the runner stopping when the mould is full (when the molten metal rises up the riser)

Allow to cool (this will take a number of hours) Casting Allow to cool (this will take a number of hours)

When the casting has cooled open the moulding box

Carefully scrape the burnt sand into the bin Casting Carefully scrape the burnt sand into the bin

Remove the casting (trying not to mix the burnt sand with the rest)

Use a Hacksaw to cut off the runner & riser Casting Use a Hacksaw to cut off the runner & riser

Finally file off any excess with a Dreadnaught File Casting Dreadnaught File Finally file off any excess with a Dreadnaught File

The End