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Why Choose Morgan Equipment

Safety and Operation of Crucible

Melting Furnaces

Presentation Outline

• Fundamentals of crucible and furnace

interaction

• Electric Resistance Furnace

– Designs

– Practices and Conditions

• Gas Fired Furnace

– Designs

– Practices and Conditions

Crucible and Furnace

Interaction

Today’s more efficient iso-statically pressed cruciblesrequire equipment with uniform thermal distribution.

Melting and holding non ferrous metal in SiC (siliconcarbide) crucible furnaces is safe and reliable whileoffering the advantages of low cost, flexibleproduction and high quality metal.

Achieving this requires melting systems that aredesigned with crucible material properties in mind.

Crucible Technology

Advancements

Crucible has two functions1. Contain metal both solid and

molten

2. Act as conduit for transfer ofenergy

Type of crucible selected isapplication dependent and mustconsider:

– Mix formulations

– Forming techniques

– Engineered glazes

– High firing capabilities

Costly Obsolete Standards

Expectation of service life based on longcampaign

Furnace designs that are crucible dependent

Emphasis on energy input to achieve meltrate

In house construction

Inadequate attention to energy costs andoperation of crucible furnace

Effective Crucible Furnaces

Use the System Approach

Maximize the crucible for energy transfer – HEATSPONGE

Effective distribution of energy in the furnacechamber

Well insulated to minimize heat losses

Proper covers and temperature monitoring

Match energy input with thermal transfercapabilities

Effective controls to maintain temp

Effective Crucible Furnaces

Use the System Approach

Maximize use of

radiant energy to

transfer heat

Use crucibles that

are basin not bowl

shape

Too much energy is

wasted and can not

be transferred by

crucible material

Electric Resistance Furnaces

Important Design Considerations

1. Heating elements are arranged to offer even

heating in chamber.

2. Electrical connections are positioned so as to

minimize or eliminate current leakage.

3. Redundant fail safe systems for both electrical

and molten metal leakage.

4. Easy access for maintenance.

5. Covers, drain holes and top rings are provided.

Electric Resistance Crucible

Furnaces - Design Types

Most popular ER

furnace designs:

• Suspended coil type

• Globar

• Module

• Embedded element

design

Even Heating Prevents

Catastrophic Crucible Failure

Glaze prevents

oxidation of carbon

bond.

Even heating

prevents localized

oxidation that leads

to cracking and

weak areas on

crucible

ER Furnaces

Grounding and Wiring

Terminal connections should be protected and arranged toprevent closing circuit in event of current leakage.

Do not allow live conductors to come in contact withoperators.

Protected Unprotected

ER Furnaces

Grounding and Wiring

ER Furnaces

Grounding and Wiring

ER Furnaces

Grounding and Wiring

ER Furnaces

Grounding and Wiring

Earth Fault – Metal Leak

Crucible and molten metal are not practical to ground

to earth, so how do you protect operators?

2 ways this can be done:

RCD or residual current devise in control cabinet or

plant electrical system.

Sensing relay with rapid disconnect.

And of course always ground the metal frame work.

Example of the pin hole leak.

Pin Hole Leak

Pin hole in crucible wall.

Metal stream makes

contact with live element

wire

Operator completes

circuit while baling out

Easy Access for

Maintenance

Failed Elements should be

replaced to avoid cool zones on

crucible.

Easy access to terminal

connections and element wires to

check for loose connections and

thermal couples

Check for metal spills or splash

Changing Crucibles

Preventative Maintenance

Recommended crucible change every 6 months.

Why?

Saves energy and allows for proper maintenance

of the furnace - check connections, survey

furnace, keeps thermal transfer consistent.

In holding applications crucible campaigns of 12

months not uncommon.

Temperature Control

Critical to prevent runaway energy input andconserve energy.

Proper pyrometry shouldbe located in metal bathand furnace chamber.

Procedures should beestablished to monitor,manual or electricalcontrols.

Temperature Control

Newer Crucible

Furnaces incorporate a

temperature controller and

safety measures to prevent

temperature overshoot and

protect element

panels/wire from exceeding

use limit

Gas Fired Crucible Furnaces

Design Considerations

1. Remote ignition (manual is scary!)

2. Exhaust gas extraction that protects work area

3. Redundant fail safe systems for both burnerfailure and molten metal leakage.

4. Temperature controls to prevent temperatureovershoot and run away chamber temps.

5. Easy access for maintenance.

6. Covers, drain holes and top rings.

7. Proper insulation.

Combustion Explosion Hazards

Basic Rules to Follow:1. Establish flame immediately after air/gas mixture is

turned on and, once lit, keep it stable

2. Keep cover open

3. Never disconnect safety devices, pressure switches, inorder to keep furnace working

4. Maintain burner, paying close attention to wear

Igniting manual gas fired furnaces can be

extremely dangerous, particularly from

cold.

Redundant

Fail Safe Systems

Easy access for

maintaining burner

Drain hole with diverter

to spilt metal drainage

area

Open area to prevent

gas build up.

Typical fuel fired crucible furnaces

with brick or refractory castable linings

This furnace is

12% efficient,

consuming 4000

BTU’s to melt 1

pound of

aluminium to

pouring

temperature of

1250 F.

Furnace data exhaust stack temp 2205*F

Design Considerations –

Flue Gas

Important exhaust gases are captured and

extracted from workplace.

Previous slide shows unsafe exhausting

creating hazardous conditions for operator

from burns both direct and radiant and

from harmful emissions, such as CO and

NOX vented into the immediate work area.

Proper Venting

Specially designed exhaust

extensions that capture hot

gasses and channel them to

either an open type foundry

roof or an exhaust duct are

best. The double skin

design of the exhaust

extension presents a

surface that is not a danger

from burning

Insulating the Furnace

Low mass

thermal

lining

protects

operators

and

prevents

heat loss.

Shell temps recorded at 350 F, open drain hole

with temps recorded at 2100 F

Multiple Component Insulation Package

1. Radiant Panels – a dense refractory, panel that diffuses radiant

energy evenly through the furnace chamber

2. Thermal Ceramic – SF 607 bulk fiber compacted to 13 pcf

3. BTU Block – a microporous insulation on inside surface of steel

shell

Insulating the Furnace –

Alternative System

Radiant Panels interlock and are self supporting

Insulating the Furnace –

Alternative System

Insulating the Furnace –

Alternative System

Radiant Panels

for Gas Fired Furnaces

Additional Information

on Safety

www.morganmms.com

Go to Library section and find downloadable

version of this presentation

and the safety document:

“Metal Melting Furnaces and Ancillary

Equipment – Guidance for their Safe Use”

System Approach to Crucible and

Furnace – NO FINGER POINTING

Morganite Melting Systems22 North Plains Industrial Road Unit 1

Wallingford CT. 06492

Telephone: (203) 697-0808

Facsimile: (203) 265-6267

E-Mail: [email protected]

Dual Energy Furnace

Flexible Option

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Foundry

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