the pros and cons about melting galvanized steel charge in a silica-lined coreless induction furnace...

The Pros and Cons about Melting The Pros and Cons about Melting Galvanized Steel Charge In a Galvanized Steel Charge In a Silica-lined Coreless Induction FurnaceSilica-lined Coreless Induction Furnace

Co-AuthorsCo-Authors

Mr. David C. Williams Allied Mineral ProductsMr. David C. Williams Allied Mineral Products(Presenter)(Presenter)Mr. Saito Kiriu Corp.Mr. Saito Kiriu Corp.Mr. M. Imasaki Kiriu Corp.Mr. M. Imasaki Kiriu Corp.Nippon Crucible Ltd.Nippon Crucible Ltd.Dickinson’s Metallurgical SuppliesDickinson’s Metallurgical Supplies

Definition of the problem with Zinc-Coated Charge

Any zinc-coated charge has alwayscaused numerous infiltration ofcoreless furnace linings, especiallywhen melting iron alloys. Zinc will melt at 787F( 420C). At 1664F(907C), Zinc will turn intoa gas, easily penetrating the porosityof the sidewall. At the point of Zinc Solidification Temperature, the metal will collect in the form of a metallicfin. With conventional lining design, theZinc will reach the coil grout and copper coils, even though the copper coils are water-cooled. Eventually, “turn toturn” coil arcing will result.

Australian Foundry Institute Conference November 2004Australian Foundry Institute Conference November 2004Pros and Cons of Melting Galvanized Steel Charge Pros and Cons of Melting Galvanized Steel Charge

Corrosion Service Coatings for Steel Strip Galvanizing Alloy Zn 99.7% Al 0.3%max. Galfan Zn 95% Al 5% Galvalume Alloy Zn 55% Al 45%


Kiriu CorporationCase study of a 6MT, 50 Hz, coreless induction furnace used for melting Ductile-base iron, C 3.85%, Si 1.85%, Mn 0.25%, S 0.03%max, P 0.03% Allowable Zn 0.08-0.12%

Typical Charge: Treated Ductile Returns, Pig Iron, 20% Galvanized Steel Trim

Refractory Lining:Silica Dry Vibratable w/ Boron Oxide Bond

Total Tonnage for a Typical Lining Campaign: 3000-3500 tons, Shave Repairs every 1000 tons in Taper and Floor


©2004 Allied Mineral Products, Inc

Cross Section of Cross Section of Furnace Lining Furnace Lining

120 mm SiO2 Refractory

Heat Insulation SheetSecond Antenna0.5 mm Al

3 mm Mica SheetCoil Courtesies of Kiriu Corporation 2002



Classic Model for Finite Elemental Analysis for 6MT Coreless Furnace


HIGH ALUMINA GROUT2mm MICA 2mm MICA

120 mmSILICA


FINITE ELEMENT ANALYSIS OF 6MT CORELESS FURNACEFINITE ELEMENT ANALYSIS OF 6MT CORELESS FURNACE

120 mmSILICA

6mmINSULATING BOARD

0.5mm ALUMINUM FOIL

2mm MICA

HIGH ALUMINA GROUT

787°F419°C

1664°F907°C

2732°F1500°C

2mm MICA

2732 °F 1500 °C2472 °F 1356 °C2212 °F 1211 °C1951 °F 1066 °C1691 °F 922 °C1431 °F 777 °C1171 °F 633 °C

911 °F 488 °C650 °F 343 °C390 °F 199 °C130 °F 54 °C


Installation of Second Antenna/ Ground Detection Foil

- A metallic ring is placed against the upper portion of the furnace.-Vertical steel strips, spread apart 200 mm around the ring, will help to keep the 0.5 mm Al foil lay flat against the mica back-up. It is important to get the Al foil to lay flat without any air pockets. Air will disrupt the thermal profile through the silica sidewall and will lead to deeper zinc penetration.

Courtesies of Kiriu Corporation 2002


Dumping 125 mm of loose silica dry Dumping 125 mm of loose silica dry vibratable per layer.vibratable per layer.

Deairing 4 passes per layer.Deairing 4 passes per layer.

Add 100-150 mm of excess silica Add 100-150 mm of excess silica over desired floor thickness.over desired floor thickness.

Vibrate floor with pneumatic form Vibrate floor with pneumatic form vibrator attached to 25mm thick floor vibrator attached to 25mm thick floor plate, for a 15 minute period.plate, for a 15 minute period.

Scrape back any excess silica and Scrape back any excess silica and remove from furnace.remove from furnace.

Level floor surface, then set melt-in Level floor surface, then set melt-in steel form.steel form.

Set melt-in steel form into place.Set melt-in steel form into place.

Installation of the Floor Refractory



Once form has been properly Once form has been properly aligned and secured, the material is aligned and secured, the material is introduced into the sidewalls in 100 introduced into the sidewalls in 100 mm layers.mm layers.

This is followed by a leveling step.This is followed by a leveling step.

Each layer is deaired 4 passes.Each layer is deaired 4 passes.

A Netter-Cross Vibrator is then A Netter-Cross Vibrator is then placed approximately one third of placed approximately one third of the vertical form height, up from the the vertical form height, up from the bottom.bottom.

A 20 minute vibration period is used. A 20 minute vibration period is used. During this period, the silica level During this period, the silica level will drop, requiring more silica to be will drop, requiring more silica to be added. added.

Sidewall Installation using the Netter-Cross Vibrator Rig



Once the vibration sequence has Once the vibration sequence has been completed, the rig is removed been completed, the rig is removed and solid charge (i.e. grey iron and solid charge (i.e. grey iron starter blocks) is carefully stacked starter blocks) is carefully stacked inside of the form.inside of the form.

The steel plates of the furnace The steel plates of the furnace structure are attached.structure are attached.

A minimum of 3 “K” type A minimum of 3 “K” type thermocouples are placed at the thermocouples are placed at the top, the middle and at the floor, to top, the middle and at the floor, to help monitor temperature during the help monitor temperature during the sinter. sinter.

Preparation of Sintering of Lining



Inner Hot Face Surface of Conventional Silica RefractoryInner Hot Face Surface of Conventional Silica Refractory

Orange Area

Gray Area

Normal Area



Outer Cold Face Surface of the Conventional Silica Refractory Outer Cold Face Surface of the Conventional Silica Refractory

Powder Gathered on this side



Gray Area

After the penetrated silica was After the penetrated silica was removed from the taper and removed from the taper and floor, the new floor is installed floor, the new floor is installed using the Bosch vibrator tamper using the Bosch vibrator tamper method.method.

Each 125 mm layer of loose Each 125 mm layer of loose silica is deaired at least 4 silica is deaired at least 4 passes before compaction with passes before compaction with the Bosch.the Bosch.

A full sintering process is A full sintering process is followed.followed.

Shaving Floor Refractory Using Bosch Installation



Shave Repair of the Conventional Silica Refractory in the Taper Section after Penetration/Erosion


Typical lining life varies between Typical lining life varies between 900 to 1000 tons throughput.900 to 1000 tons throughput.

Relines are determined by Relines are determined by measurements in the taper and measurements in the taper and floor.floor.

Galvanized steel charge represents Galvanized steel charge represents 20 % of the charge.20 % of the charge.

This furnace was lined withThis furnace was lined with

a modified silica mix and completed a modified silica mix and completed 1436 tons throughput without repair.1436 tons throughput without repair.


The sidewalls showed minimal The sidewalls showed minimal erosion.erosion.

The taper section has eroded The taper section has eroded approximately 20-30 mm.approximately 20-30 mm.

No taper or floor shave repairs No taper or floor shave repairs performed.performed.

No zinc penetration reaching No zinc penetration reaching through the silica or reaching through the silica or reaching the Al antenna foil.the Al antenna foil.


A View of A Spent Furnace Lining after 1436 Tons Without Any Repair (Newly Redesigned Silica)



No Zinc metal penetration No Zinc metal penetration was detected in the floor was detected in the floor refractory.refractory.

Unsintered, loose silica Unsintered, loose silica refractory remained in the refractory remained in the floor.floor.

Ground Detection wires are Ground Detection wires are still intact.still intact.

Demolition of the Floor Refractory after 1436 ton campaign


Complete Demolition of the Redesigned Silica Lining


No zinc evident against the No zinc evident against the heat insulation board or on heat insulation board or on the cold face of the silica the cold face of the silica lining.lining.

No zinc was observed on No zinc was observed on the cold face of the heat the cold face of the heat insulation.insulation.

No zinc was picked up on No zinc was picked up on the Al foil in between the two the Al foil in between the two layers of mica.layers of mica.


Inner Hot Face Surface of Heat Insulation Sheet Inner Hot Face Surface of Heat Insulation Sheet

Dark Area

Normal Area



During the demolition of the lining, During the demolition of the lining, there was no evidence of zinc there was no evidence of zinc deposition on the hot face of the Al deposition on the hot face of the Al foil.foil.

A portion of Al foil is peeled back A portion of Al foil is peeled back to show the cold face surface.to show the cold face surface.

The discoloration of the foil is due The discoloration of the foil is due to the presence of heat stored to the presence of heat stored within the lining.within the lining.


A View of the Hot Face Surface of the 0.5 mm Al Antenna Foil


The Cold Face Surface of the Second Antenna Foil The Cold Face Surface of the Second Antenna Foil

Specimen with White Powder



Hot Face Surface of the Al Antenna Foil Hot Face Surface of the Al Antenna Foil

Black Burnt Area

Less Burnt Area




Hot face of the first layer Hot face of the first layer of mica between the grout of mica between the grout and the metallic foil / and the metallic foil / antenna.antenna.

No zinc penetration was No zinc penetration was evident.evident.

Mica Layer after a 1436 ton campaign


No zinc penetration against No zinc penetration against the shunts, indication no the shunts, indication no zinc reaching the copper zinc reaching the copper coils.coils.


A View of the Shunts of the Power Coil after 1436 ton Campaign


No zinc presence on the No zinc presence on the coil or on the face of the coil or on the face of the shunts.shunts.

Clean coil with no zinc Clean coil with no zinc presence.presence.


A Close-Up View of the Power Coil and the Electrical Shunts



Old Silica New Silica


Saturation comparison: Old 50mm New 0 mm.




Saturation comparison: Old 60mm New 23mm.



Saturation comparison: Old 60-85 mm New 24mm.


Summary:

Changes were made to a conventionally designed silica dry vibratableto help minimize zinc penetration in the sidewall of a coreless inductionfurnace when using galvanize-coated steel charge.

Zinc penetration did not reach the secondary Al foil antenna, nor thepower coil. Some zinc penetration observed within the floor, the taper,and the sidewall, but was less than the conventionally-designed silicadry vibratable.

Although significant layers of slip plane and insulation was used, noZinc was found against the mica or secondary antenna.

Ultimately, lining life had improved from 900-1000 tons melted to 1436 tons melted without any shave repair. This was done while using20% of the charge as galvanize-coated steel charge.

Australian Foundry Institute Conference November 2004Australian Foundry Institute Conference November 2004Pros and Cons of Melting Galvanized Steel ChargePros and Cons of Melting Galvanized Steel Chargein a Silica-lined Coreless Induction Furnace D. Williamsin a Silica-lined Coreless Induction Furnace D. Williams

The Pros of Melting Galvanized Steel Charge in a Silica-linedCoreless Induction Furnace

Allows for more diversity in Charge and may lower melting costs. With the demand for steel charge and the subsequent shortage, this may represent a possible solution.

Using the Aluminum foil as a secondary Leak detection system,also allows the foundry to have an impervious layer to shutdownZinc permeating to the coil. It would have a similar effect towards other low temperature non-ferrous metals such as Lead, Tin or Bismuth.

Less penetrated hot face of the silica typically results in longer servicelife of the coreless furnace.

A change in the silica product is needed as well as a change in the Sintering process.


The Cons of Melting Galvanized Steel Charge in a Silica-linedCoreless Induction Furnace

Early Zinc Penetration to coil causing turn to turn electrical arcing.

The cost of the Aluminum foil

Lower Service Life due to erosion of hot face

Zinc Vapor will be collected in the pollution control system andwill cause a build-up as time progresses.


This presentation was made possible through the successfulefforts of Mr. Saito and his melt personnel, who incorporatedthe use of galvanized-coated steel charge as a viable part ofa ductile-base charge (approximately 20%) for a 50 Hz, continuous heel melting operation at Kiriu Corporation.

It has always been a challenge to successfully use galvanizedsteel in any coreless induction furnace. The problem is zincdeposition on the copper coils, leading to “turn to turn” arcing.Complete zinc infiltration of all refractories including the coil grout will often be the outcome. Kiriu Corporation has developeda method of using galvanized charge as part of a ductile-baseIron heat in a silica-lined coreless induction furnace.

Kiriu Corporation with assistance from Nippon Crucible Ltd. have successfully managed this problem for the past 2 years.


the pros and cons about melting galvanized steel charge in a silica-lined coreless induction furnace...

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