Morganite Crucible - Inproheatinproheat.com/sites/files/documents/care_and_use_nologo.pdfCopyright -...

Copyright - Morganite Crucible Inc 2000 1

Morganite Crucible

Care and Use of Crucibles

Website: www.morganitecrucibleinc.com e mail: [email protected]: 203-239-1624 Fax: 203-239-5829


Purpose

To promote better care and use of crucibles and extend crucible lifeTo explain what can cause short crucible lifeBasic rules of use


HandlingAvoid abrasion of the glaze - this will lead to oxidation in serviceAvoid impact damageDo not roll the crucible - glaze damage will result

Damage to glaze followedby oxidation in use

Incorrect & correct handling


Incorrect & correct storage

Stacked inside one another

Storage

Store crucibles in a warm dry place (above 20°C)Stand crucibles on pallets, never directly on the floorNever nest crucibles one inside the otherWhen stacking crucibles, separate with hardboard or similar material


Base Block

The use of a crucible base block is essential in providing uniform heating of the crucible baseThe base block should provide complete support over the whole crucible baseFor optimum efficiency - the base block must be the correct height- The base block and crucible must be installed

centrally


Correct Installation of Base Block

Correct height of stand/alignment of burnerCorrect stand support

for Morganite crucible


Use of Incorrect Base Block

Thermal stress will result if a low conductivity material is usedInadequate support will be provided if the base block is too narrow leading to distortion of the crucible baseBurner flame impingement on the crucible wall will result if the base block is too short


Use of Incorrect Base BlockGlaze deterioration from flame impingement

Distortion due to support on fire-bricks


Correct Setting In Bale-Out Furnaces

Allow 1/3”(8mm) expansion gap between top cover bricks and crucible top edge to allow for expansionPlace layer of ceramic fiber over top of lining and crucible to insulate metal top platesAllow 1/3”(8mm) expansion gap between top ring flange and crucible where applicableKeep all the labels from the crucible, in case of a claim these will be required


Correct Setting in a Bale Out Furnace

Setting of crucible

in a bale out furnace


Incorrect Setting In Bale-Out Furnaces

Insufficient expansion gap will result in lateral cracking below the top cover bricksThe upper wall of the crucible will be insulated if ceramic fiber is pushed down between cover bricks and crucible thus preventing the glaze from functioningVertical cracking will result from a tight fitting flanged top ring


Oxidised top edgesection due to insulating effect of ceramic fibre

Top edge vertical cracking due to tight fitting top ring

Incorrect Setting in Bale Out Furnaces


Correct Setting In Tilting Furnaces

Ensure stand is central and levelSpread a thin layer of refractory cement evenly over the standLower crucible onto standAllow 1/3” (6-10mm) expansion gap between crucible and grip bricks (use combustible spacer)Allow 38mm gap below spout to avoid hanging up on the spout as a result of settlementKeep all the labels from the crucible, in case of a claim these will be required


Setting of cruciblein a tilting furnace

Correct Setting of Crucible In Tilting Furnace


Incorrect Setting In Tilting Furnace

Grip bricks set to tight! Vertical cracks due to crucible expansion

Insufficient gap below spout ! Crucible hangs on refractory – 1.5” (38mm)

gap recommended below spout


Top edge vertical cracking due to tightfitting grip-brick

Crack showing gripbrick too tight

Incorrect Setting In Tilting Furnace


ChargingCharge and melt as soon as the crucible has reached red heat all overNever introduce moist charge materialCharge light scrap first to form a cushion for heavier materialUse tongs to charge ingots or large pieces to avoid crucible damagePlace ingots vertically to avoid bridging or wedging across the crucibleDo not pack metal tightly, allow room for metal to expand


Charging

Place ingots with tongs

Place ingots verticallyDo not over fill


Correct crucible charging

Charging Practice


Tightly packed charge causes ‘U-shape’ crackingBridged ingots cause inverted ‘Y-shape’ cracksIngot impacts produce cone-shape holesRe-heating frozen charge leads to bursting cracks due to metal expansion

Mechanical Damage


‘U’ orshield shape crack

‘Y’ shape crack inverted

Mechanical Damage


Cone shaped fracture

Mechanical Damage

Do not reheat frozen metal


Correct & incorrect fitting oftongs

Correct & safe use of liftingtongs

Mechanical Damage


Dross/Slag Build-Up

High expansion rate of dross causes internal pressure (approximately ten times expansion rate of crucible material)Dross has low thermal conductivity which insulates the metal thus necessitating higher furnace temperatureLeads to higher energy costsDross absorbs flux which accelerates chemical attack on the crucible


Dross accumulation in crucible leading to expansion cracking

Dross and Slag Build Up


Chemical AttackAluminum

Aluminum Applications! Excessive use of flux! Incorrect flux! Reactions are temperature dependentLeads to! External holes! Random cracking! Melting of the glaze and body material


Random Cracking

External Holes

Melting of Body and Glaze

Chemical AttackAluminum


Chemical AttackCopper Alloys

Internal corrosion by fluxes! Flux added prior to charge and not mixed ! Over fluxing and excessive time at temperature

External corrosion by fluxes! Caused by over filling, and flux running down

outside wall


Flux and slag corrosion of lowerinside wall of crucible Mouse holing due to flux attack

Chemical AttackCopper Alloys


How To Limit Chemical AttackUse minimum quantity of flux in keeping with metal qualityUse correct flux for specific operation/temperatureUse metallic sodium in preference to alkaline fluxes where applicableCarry out treatment in transfer vessel, not holding crucible where possibleEnsure crucible is kept free from dross by regular scraping and cleaning


Oxidation

Results in reduced strength and thermal conductivity, loss of material integrity

Caused By:! Glaze damage prior to use! Excessive use of ceramic fiber around top wall of

crucible! Use of excess oxygen in fuel fired furnaces! Flame impingement - glaze stripped by flame directly

contacting crucible


Cracking near top edge from bad setting followed by oxidation

Dry un-matured glaze/cracking/oxidationdue to poor furnace conditions

Oxidation


Thermal Shock

Thermal stress cracking due to rapid or localized heating ! Improperly positioned crucible! Direct burner impingement! Badly adjusted burner – short flame


Thermal stress crack across base

Thermal Shock


Summary

If a crucible experiences shorter than normal lifeCall your Morganite Sales Representative and they will advise if a claim is requiredIf it is follow the procedure detailed on the web site remembering to take pictures and retain labels so a claim can be filed properly

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