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Tools/castingcrucible/induction: Difference between revisions
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{{inductioninfo}}
The [[Tools/castingcrucible|casting crucible]] is one of the most useful but also most hazardous items of equipment rLab has. Because of this people seeking induction will have to provide more safety equipment than is usual, inductees must have
equipment capabilities▼
* Cotton or other non-synthetic overalls required
* Heavy trousers, Jeans are good
* Leather shoes - NO SYNTHETICS, Steelies preferred. - Trainers are NOT acceptable
* If wanting to cast lead or other hazardous metals then a mask rated for FFP3 and metal fume. For Aluminium and copper castings then we have masked rated FFP3
Casting can only be done outdoors and absolutely must be kept dry. This limits the times when inductions can occur to Sundays when the forecast indicated no possibility of rain. Sundays because that's the only time the carpark is likely to be empty and when dry because of the risk of explosion if the crucible is rained on.
* Types of casting
** Sand casting
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* 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 [[Tools/boxford|Boxford CNC Mill]].
* Printing out a mold, carving a mold from wood, high surface finish needed
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* Using the dry sand for safety
* Getting out the crucible and setting it up in the casting tray
* Selecting which crucible to use - Aluminium reside in the default crucible
* Choosing your metal and checking it over carefully
* Keeping the gas bottle well away from the burners
* Mounting the regulator
** Left-hand thread on the regulator
** Do not use PTFE tape on the thread
* Burners are self-lighting and have auto-shutoff
** Turn the blower on first and off last
* Selecting suitable metal
** Reused old castings are cheapest, but have increased risk of voids, porosity and poor strength
** Virgin metal of an approved casting alloy will give the best results but at the highest cost
** Choose depending on budget and mechanical loads the part must withstand
Making the mold
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* 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. This is approx 1.5l of liquid metal.
Making the Pour
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** 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.
After the Pour
* The cast needs a little time to cool before it can be moved or it'll distort
** How long depends on the size of the thickest part of the cast, from a few seconds up to several minutes
* Once the cast has cooled a little then move the casting box away from the crucible
** Position a mold under the spout, either a trough or the baking tray and pour out the remaining metal
** Do not let metal cool in the crucible, it'll be very hard to remove later
Unmolding
* The cast needs to cool down a lot before it can be unmolded
* Times are likely to vary from as little as 5 minutes for a small cast up to an hour for a very large one.
▲* Pouring off surplus
* Once cool take the casting box over to the table and break out the sand to reveal the casting
** Wear welding gloves! Parts of the casting and the sand may still be several hundred degrees
* Collect the sand and riddle it, returning all unburnt sand to the store
* Burnt sand goes in the bin
3 Cleaning Up▼
Casting Flaws
* Examine your finished casting for flaws
** Poor Surface finish - Mold not packed well, mold of poor surface finish, failure to talc the mold, metal too hot, lack of gas vent holes
** Small bubbles in the casting - Poor degassing, sand too wet, metal too hot
** Sunken areas - Spru too small, bad part geometry
** Sand inclusions - Mold not packed well
** Slag inclusions - Poor skimming, bad pour control
** Unfilled areas - Insufficient gating
** Cold joints - Bad gating design, metal had to flow too far through small passages
** Excess flashing - Mold not clamped tightly
* Letting everything cool properly, this may take several hours, allow time for this.
* Examining crucible, discard if visibly cracked and arrange order of new one
* Returning casting equipment to proper location
* Sand into the suitable boxes
* Sweeping up everything
* Putting the casting tray back
* Returning unused metal to store
* Dust masks to bin, they cannot be re-used
* Re-order any PPE that was damaged
[[Category:Inductions]]
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