Pattern Design. Broken Edges. Patterns are generally made from wood however they can be made from metal, plastic or any number of other materials.

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2 Sand 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.

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 All patterns must have a Taper (or Draft) this allows the pattern to be withdrawn cleanly from the mould.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

4 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 Sharp Corners Use a wax fillet on internal corners Weak Spot This can weaken the final design

5 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 from 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

6 Pattern Design Pattern 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.

7 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.

8 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 Lamp Aluminium Saucepan Aluminium Ingots

9 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

10 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

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

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

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

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

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

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

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

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

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

20 Parting Powder Again lightly dust with parting powder.

21 Sprue Pins Place the Sprue Pins in the box.

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

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

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

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

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

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

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

29 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

30 Carefully remove the pattern

31 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

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

33 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

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

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

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

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

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

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

40 When the casting has cooled open the moulding box

41 Carefully scrape the burnt sand into the bin

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

43 Use a Hacksaw to cut off the runner & riser

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

45 The End