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The Pros and Cons about Melting Galvanized Steel Charge In a Silica-lined Coreless Induction Furnace Co-Authors Mr. David C. Williams Allied Mineral Products.

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Presentation on theme: "The Pros and Cons about Melting Galvanized Steel Charge In a Silica-lined Coreless Induction Furnace Co-Authors Mr. David C. Williams Allied Mineral Products."— Presentation transcript:

1 The Pros and Cons about Melting Galvanized Steel Charge In a Silica-lined Coreless Induction Furnace Co-Authors Mr. David C. Williams Allied Mineral Products (Presenter) Mr. Saito Kiriu Corp. Mr. M. Imasaki Kiriu Corp. Nippon Crucible Ltd. Dickinsons Metallurgical Supplies

2 Definition of the problem with Zinc-Coated Charge Any zinc-coated charge has always caused numerous infiltration of coreless furnace linings, especially when melting iron alloys. Zinc will melt at 787F( 420C ). At 1664F( 907C ), Zinc will turn into a gas, easily penetrating the porosity of the sidewall. At the point of Zinc Solidification Temperature, the metal will collect in the form of a metallic fin. With conventional lining design, the Zinc will reach the coil grout and copper coils, even though the copper coils are water-cooled. Eventually, turn to turn coil arcing will result. Australian Foundry Institute Conference November 2004 Pros and Cons of Melting Galvanized Steel Charge

3 Corrosion Service Coatings for Steel Strip Galvanizing Alloy Zn 99.7% Al 0.3%max. GalfanZn 95% Al 5% Galvalume AlloyZn 55% Al 45% Australian Foundry Institute Conference November 2004 Pros and Cons of Melting Galvanized Steel Charge

4 Kiriu Corporation Case 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 % 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: tons, Shave Repairs every 1000 tons in Taper and Floor Australian Foundry Institute Conference November 2004 Pros and Cons of Melting Galvanized Steel Charge ©2004 Allied Mineral Products, Inc

5 Cross Section of Furnace Lining 120 mm SiO 2 Refractory Heat Insulation SheetSecond Antenna 0.5 mm Al 3 mm Mica Sheet Coil Courtesies of Kiriu Corporation 2002 Australian Foundry Institute Conference November 2004 Pros and Cons of Melting Galvanized Steel Charge ©2004 Allied Mineral Products, Inc

6 Classic Model for Finite Elemental Analysis for 6MT Coreless Furnace Australian Foundry Institute Conference November 2004 Pros and Cons of Melting Galvanized Steel Charge HIGH ALUMINA GROUT 2mm MICA 120 mm SILICA ©2004 Allied Mineral Products, Inc

7 FINITE ELEMENT ANALYSIS OF 6MT CORELESS FURNACE 120 mm SILICA 6mm INSULATING BOARD 0.5mm ALUMINUM FOIL 2mm MICA HIGH ALUMINA GROUT 787°F 419°C 1664°F 907°C 2732°F 1500°C 2mm MICA ©2004 Allied Mineral Products, Inc

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

9 Dumping 125 mm of loose silica dry vibratable per layer. Deairing 4 passes per layer. Add mm of excess silica over desired floor thickness. Vibrate floor with pneumatic form vibrator attached to 25mm thick floor plate, for a 15 minute period. Scrape back any excess silica and remove from furnace. Level floor surface, then set melt-in steel form. Set melt-in steel form into place. Installation of the Floor Refractory Courtesies of Kiriu Corporation 2002 Australian Foundry Institute Conference November 2004 Pros and Cons of Melting Galvanized Steel Charge

10 Once form has been properly aligned and secured, the material is introduced into the sidewalls in 100 mm layers. This is followed by a leveling step. Each layer is deaired 4 passes. A Netter-Cross Vibrator is then placed approximately one third of the vertical form height, up from the bottom. A 20 minute vibration period is used. During this period, the silica level will drop, requiring more silica to be added. Sidewall Installation using the Netter-Cross Vibrator Rig Courtesies of Kiriu Corporation 2002 Australian Foundry Institute Conference November 2004 Pros and Cons of Melting Galvanized Steel Charge

11 Once the vibration sequence has been completed, the rig is removed and solid charge (i.e. grey iron starter blocks) is carefully stacked inside of the form. The steel plates of the furnace structure are attached. A minimum of 3 K type thermocouples are placed at the top, the middle and at the floor, to help monitor temperature during the sinter. Preparation of Sintering of Lining Courtesies of Kiriu Corporation 2002 Australian Foundry Institute Conference November 2004 Pros and Cons of Melting Galvanized Steel Charge

12 Inner Hot Face Surface of Conventional Silica Refractory Orange Area Gray Area Normal Area Courtesies of Kiriu Corporation 2002 Australian Foundry Institute Conference November 2004 Pros and Cons of Melting Galvanized Steel Charge

13 Outer Cold Face Surface of the Conventional Silica Refractory Powder Gathered on this side Courtesies of Kiriu Corporation 2002 Australian Foundry Institute Conference November 2004 Pros and Cons of Melting Galvanized Steel Charge Gray Area

14 After the penetrated silica was removed from the taper and floor, the new floor is installed using the Bosch vibrator tamper method. Each 125 mm layer of loose silica is deaired at least 4 passes before compaction with the Bosch. A full sintering process is followed. Shaving Floor Refractory Using Bosch Installation Courtesies of Kiriu Corporation 2002 Australian Foundry Institute Conference November 2004 Pros and Cons of Melting Galvanized Steel Charge

15 Shave Repair of the Conventional Silica Refractory in the Taper Section after Penetration/Erosion Courtesies of Kiriu Corporation 2002 Typical lining life varies between 900 to 1000 tons throughput. Relines are determined by measurements in the taper and floor. Galvanized steel charge represents 20 % of the charge. This furnace was lined with a modified silica mix and completed 1436 tons throughput without repair. Australian Foundry Institute Conference November 2004 Pros and Cons of Melting Galvanized Steel Charge

16 The sidewalls showed minimal erosion. The taper section has eroded approximately mm. No taper or floor shave repairs performed. No zinc penetration reaching through the silica or reaching the Al antenna foil. Courtesies of Kiriu Corporation 2002 A View of A Spent Furnace Lining after 1436 Tons Without Any Repair (Newly Redesigned Silica) Australian Foundry Institute Conference November 2004 Pros and Cons of Melting Galvanized Steel Charge

17 Courtesies of Kiriu Corporation 2002 No Zinc metal penetration was detected in the floor refractory. Unsintered, loose silica refractory remained in the floor. Ground Detection wires are still intact. Demolition of the Floor Refractory after 1436 ton campaign Australian Foundry Institute Conference November 2004 Pros and Cons of Melting Galvanized Steel Charge

18 Complete Demolition of the Redesigned Silica Lining Courtesies of Kiriu Corporation 2002 No zinc evident against the heat insulation board or on the cold face of the silica lining. No zinc was observed on the cold face of the heat insulation. No zinc was picked up on the Al foil in between the two layers of mica. Australian Foundry Institute Conference November 2004 Pros and Cons of Melting Galvanized Steel Charge

19 Inner Hot Face Surface of Heat Insulation Sheet Dark Area Normal Area Courtesies of Kiriu Corporation 2002 Australian Foundry Institute Conference November 2004 Pros and Cons of Melting Galvanized Steel Charge

20 During the demolition of the lining, there was no evidence of zinc deposition on the hot face of the Al foil. A portion of Al foil is peeled back to show the cold face surface. The discoloration of the foil is due to the presence of heat stored within the lining. Courtesies of Kiriu Corporation 2002 A View of the Hot Face Surface of the 0.5 mm Al Antenna Foil Australian Foundry Institute Conference November 2004 Pros and Cons of Melting Galvanized Steel Charge

21 The Cold Face Surface of the Second Antenna Foil The Cold Face Surface of the Second Antenna Foil Specimen with White Powder Courtesies of Kiriu Corporation 2002 Australian Foundry Institute Conference November 2004 Pros and Cons of Melting Galvanized Steel Charge

22 Hot Face Surface of the Al Antenna Foil Black Burnt Area Less Burnt Area Courtesies of Kiriu Corporation 2002 Australian Foundry Institute Conference November 2004 Pros and Cons of Melting Galvanized Steel Charge

23 Courtesies of Kiriu Corporation 2002 Hot face of the first layer of mica between the grout and the metallic foil / antenna. No zinc penetration was evident. Mica Layer after a 1436 ton campaign Australian Foundry Institute Conference November 2004 Pros and Cons of Melting Galvanized Steel Charge

24 No zinc penetration against the shunts, indication no zinc reaching the copper coils. No zinc penetration against the shunts, indication no zinc reaching the copper coils. Courtesies of Kiriu Corporation 2002 A View of the Shunts of the Power Coil after 1436 ton Campaign Australian Foundry Institute Conference November 2004 Pros and Cons of Melting Galvanized Steel Charge

25 No zinc presence on the coil or on the face of the shunts. No zinc presence on the coil or on the face of the shunts. Clean coil with no zinc presence. Courtesies of Kiriu Corporation 2002 A Close-Up View of the Power Coil and the Electrical Shunts Australian Foundry Institute Conference November 2004 Pros and Cons of Melting Galvanized Steel Charge

26 Courtesies of Kiriu Corporation 2002 Old Silica New Silica Australian Foundry Institute Conference November 2004 Pros and Cons of Melting Galvanized Steel Charge Saturation comparison: Old 50mm New 0 mm.

27 Courtesies of Kiriu Corporation 2002 Old Silica New Silica Australian Foundry Institute Conference November 2004 Pros and Cons of Melting Galvanized Steel Charge Saturation comparison: Old 60mm New 23mm.

28 Courtesies of Kiriu Corporation 2002 Old Silica New Silica Saturation comparison: Old mm New 24mm. Australian Foundry Institute Conference November 2004 Pros and Cons of Melting Galvanized Steel Charge

29 Courtesies of Kiriu Corporation 2002 Australian Foundry Institute Conference November 2004 Pros and Cons of Melting Galvanized Steel Charge

30 Courtesies of Kiriu Corporation 2002 Australian Foundry Institute Conference November 2004 Pros and Cons of Melting Galvanized Steel Charge

31 Courtesies of Kiriu Corporation 2002 Australian Foundry Institute Conference November 2004 Pros and Cons of Melting Galvanized Steel Charge

32 Summary: Changes were made to a conventionally designed silica dry vibratable to help minimize zinc penetration in the sidewall of a coreless induction furnace when using galvanize-coated steel charge. Zinc penetration did not reach the secondary Al foil antenna, nor the power coil. Some zinc penetration observed within the floor, the taper, and the sidewall, but was less than the conventionally-designed silica dry vibratable. Although significant layers of slip plane and insulation was used, no Zinc was found against the mica or secondary antenna. Ultimately, lining life had improved from tons melted to 1436 tons melted without any shave repair. This was done while using 20% of the charge as galvanize-coated steel charge. Australian Foundry Institute Conference November 2004 Pros and Cons of Melting Galvanized Steel Charge in a Silica-lined Coreless Induction Furnace D. Williams

33 The Pros of Melting Galvanized Steel Charge in a Silica-lined Coreless 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 shutdown Zinc 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 service life of the coreless furnace. A change in the silica product is needed as well as a change in the Sintering process. Australian Foundry Institute Conference November 2004 Pros and Cons of Melting Galvanized Steel Charge in a Silica-lined Coreless Induction Furnace D. Williams

34 The Cons of Melting Galvanized Steel Charge in a Silica-lined Coreless 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 and will cause a build-up as time progresses. Australian Foundry Institute Conference November 2004 Pros and Cons of Melting Galvanized Steel Charge in a Silica-lined Coreless Induction Furnace D. Williams

35 This presentation was made possible through the successful efforts of Mr. Saito and his melt personnel, who incorporated the use of galvanized-coated steel charge as a viable part of a 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 galvanized steel in any coreless induction furnace. The problem is zinc deposition 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 developed a method of using galvanized charge as part of a ductile-base Iron 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. Australian Foundry Institute Conference November 2004 Pros and Cons of Melting Galvanized Steel Charge in a Silica-lined Coreless Induction Furnace D. Williams


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