Tools/castingcrucible/induction

Casting Crucible Induction

Some of the tools at the Hackspace are potentially hazardous to use, for these tools members are required to have an induction before they can use them. Inductions provide the most basic information on how to safely and effectively use the simpler functions of the tools, we appreciate that some members may have professional experience on some of these tools and in this case please tell your induction provider and the induction may be very reduced and just cover any risks or procedures specific to rLab. Some tools have multiple levels of induction in order to cover more advanced uses of that tool without making the basic induction take too long, higher induction levels will introduce some of the more advanced features of the tools but as with all inductions are only intended to provide basic information on the capabilities of the tools and how to use them safely. Some members of rLab may be willing to offer more detailed tuition beyond basic induction level or offer guided practice sessions in exchange for beer money or assistance on their own projects.

For all tools you are only required to take level-1 induction before use, after that you may perform any task that you feel confident you can do safely, higher levels of induction may be useful to you in performing more advanced operations but are not required before doing tasks covered in them so long as you're confident of your ability to handle those tasks without risk to yourself, others, or the tool.

PLEASE NOTE : All induction providers are volunteers who are providing inductions to the best of their ability but are NOT qualified instructors. Inductions are provided on a best-effort basis but you and you alone are responsible for your safety while using the tools and for satisfying yourself that you can operate the tools safely. There are professional training courses available from various providers in Reading and the surrounding area if you feel they are appropriate for the level of work you intend to undertake. Reading these notes is NOT a substitute for an in-person induction.

Note for wiki editors : Please do not edit induction pages unless you are one of of the people that gives that induction

equipment capabilities

• Types of casting
  • Sand casting
  • Lost-PLA casting
  • Investment (lost-wax) casting
  • Metal mold casting
• We're only going to be doing sand-casting today, procedure for others is under development
• Metals we can work with (Tin/Lead/White-metal, Aluminium, Copper/Brass/Bronze, we can't cast iron/steel)

Object designs

• How the mold is mounted to the boards, creates the cavity which can then be filled with metal, what is cope, drag and board.
• You have to be able to align the 2 parts of the mold using pins
• You have to be able to remove the mold from the sand without breaking it too badly, so allow tapers. You can't have overhangs
• Using cores if you need complex shapes but we won't cover that
• Consider how the metal will flow, small cavities are hard to fill, there needs to be a path for metal to get in and gas to get out
• Remember the shrinkage allowance, 2% in aluminium, 1.5% in brass
• What are Sprus, Gates and Risers and why you need each of them
• Design them into the mold, or cut them afterwards once you've made the sand form
• The possibility of designing, 3D printing, Casting and then finishing on the boxford.
• Printing out a mold, carving a mold from wood, high surface finish needed

Getting set up

• Casting must only be done outdoors, and only in good weather
• Getting out the casting tray
• Using the dry sand for safety
• Getting out the crucible and setting it up in the casting tray
• Choosing your metal and checking it over carefully
• Keeping the gas bottle well away from the burners
• Burners are self-lighting and have auto-shutoff

Making the mold

• Mounting the board to the cope and drag
• The sand is builders sharp-sand and bentonite clay with a small amount of water to make it stick together, too little water and it falls apart, too much and steam will prevent filling
• Screening the sand to remove lumps
• Powder the mold to help with release
• Packing the sand down hard and completely filling the drag
• First sand layer must be very fine and carefully forced into the smallest of gaps, later layers can be larger and less careful
• Leveling off to enable use of a backing board
• Flipping it over and then repeating on the cope
• Tapping and releasing the mold
• Touching up any defects, large defects mean starting again
• Cutting Sprus and risers if they weren't molded in
• Piercing gas holes to release steam and other gasses
• Reassembling the mold
• Using the pouring cup

Safety equipment and hazards

• Hazards
  • Any water getting into molten metal WILL EXPLODE, so we can't cast on days with even the slightest chance of rain. Drinks must be kept well away from the crucible. Check your metal stock carefully for liquids or voids as voids will also explode on heating. Check the sand in the casting tray is dry
  • Sand tends to make melt stop and set, it'll run long distances on other surfaces and start fires at considerable distances
  • Burns are an obvious hazard, basic information about burns treatment and when to call an ambulance
  • Fumes coming from metal are both acutely and chronically toxic
  • Beware of concrete and stone spalling in case of spill
  • Fire hazard, does everyone know how to use extinguishers?, remember - NO WATER!
    • Get extinguishers out and ready
    • Check all gas equipment for any leaks
  • Sudden temperature changes causing cracking/shattering, Cold metal should never directly touch hot, pre-warm stuff
  • Risks of bystanders - Let people at rLab know, only people directly involved should be within 5m of the casting equipment
• Safety equipment
  • Overalls required - NON-SYNTHETICS ONLY!!
  • Jeans are good
  • Shoes Leather or natural fabric, NO SYNTHETICS, Steelies preferred. - Trainers NOT acceptable
  • MIG Welding gloves should be used, nothing else, no others have sufficient insulation and are non-melting
  • Googles AND face shield when pouring, remember face-mask will burn if there is an accident
  • Dust masks
  • You can get specialized foundry versions of all of this kit, all of which are very effective and very expensive

Starting to melt

• How the burner works, it's self-lighting, the crucible tips to pour and the burner goes out.
• The burner forms a flame vortex around the crucible to heat the metal
• The crucible is made of clay/graphite composite, it's expensive (£100) and delicate and only lasts a few casts, so we ask for contribution to cover cost of replacement.
• Inspect the crucible before starting, a cracked crucible will be become very dangerous on heating
• Remember metal expands as it heats, that will break the crucible if it's packed in tight or gets sideways inside it
• When cold metal touches hot it can cause local freezing of the hot metal, that can cause large forces that will break the crucible
• This means that before metal goes into the crucible it must be pre-warmed around the outside of the forge, and then only added in small amounts so it doesn't radically cool the crucible. Little and often is the way to add metal.
• Additions must be made carefully to avoid splashing.
• The maximum capacity of the crucible is about 3Kg of aluminium, or 10Kg of copper. That equates to the crucible being about 75% full.

Making the Pour

• Positioning the casting box under the spout and fitting the pouring cup
  • Getting the box level
  • Making sure the cup is accurately over the spru
  • Consider where splashing and run-off will go
  • Weighting the box down if pouring lead, brass, or other dense metal. Not always needed for Aluminium
• Possibility of using dross filters
• Checking temperature of the melt using the thermocouple
  • 750ºC-800ºC for Aluminium
  • 950ºC-1050ºC for Brass
  • For other metals consult your supplier
  • High end of the range for small castings or fine detail, lower end for bulk castings with rough surfaces
• Degassing
  • Using the degassing flux to get trapped gasses out of aluminium otherwise your cast will have voids and porosity
  • It's very concentrated, you don't need much
  • Pre-warm the plunger
  • Use it to press the flux down to the bottom of the crucible
  • Keep it there till the bubbling stops
• Skimming
  • Using a tool to skim off the oxides that will have formed
  • Must be done immediately before pouring
• Pouring
  • Full safety gear required!
  • Final temperature check to make sure we're still in the right range
  • The burner will cut off as the crucible begins to tip and re-light when it's replaced
  • Warn everyone not directly involved to clear the area
  • Pour in one smooth motion, no stopping and starting, try to maintain the pour rate to keep the pouring cup half full
  • Gasses and possibly flames will come from the risers and vent holes, this is expected behavior
  • "Bumping" or "Burping" that's forceful enough to overflow the pouring cup is NOT expected and indicates a problem, STOP
  • The pour is finished when either
    • There's metal visible in all risers
    • Metal stops draining from the casting cup into the mold
  • Metal still in the pouring cup is likely to overflow out of the risers, let this happen, fight fires with sand
  • Sprinkle dry sand onto the top of the pouring cup for insulation
  • Be aware that the burner will re-light once the crucible is returned to the upright position, do not allow the metal in it to become overheated.

• Letting cast cool a bit

• Pouring off surplus

• Full cooling of cast

copied over from old wiki

contents 3 Cleaning Up

cleaning up Pour any remaining aluminium into the ingot mold and let it cool down. Let the crucible cool down as well and unplug it from the mains, and turn off the butane.

Once everything is cool, put the crucible away on the shelf, and then put the sand back into the bin. Put away the tray tidily and sweep any spilt sand up.