ZIRCAR Ceramics: Low Mass Castertips for Generation Now Twin Roll Casters

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Newly Developed Low Mass Castertips for Generation "Now" Twin Roll Casters

Abstract

With the trend in continuous twin roll aluminum strip casting heading ever wider and thinner, greater performance will be required from the castertips employed on such systems. Several varieties of ceramic fiber based castertips exist that have been part of establishing what in many instances are record production levels. New production efficiencies on these wider and thinner casters will come with advances in castertip technology including but not limited to: improved cleanliness (lack of shot - to reduce inclusions), reduced deflection over unprecedented widths and less reactivity with alloying elements. This paper discusses a variety of recently developed low-mass castertip products. Presented are data on the physical characteristics and properties of recently developed group of castertip products. Castertips made of alumina-silica fiber and NON RCF Soluble fiber are discussed.

Introduction

When first developed twin roll continuous aluminum strip casters used, among a list of materials, calcium silicate asbestos cement castertips , nozzles, trough liners and floats. Asbestos cement products enabled the production of what certainly amounts to billions of tons of strip. As asbestos cement fiber products were regulated out of commercial availability other type of filled cement boards took their place. Today calcium silicate cement products are still widely used in numerous metal contact continuous casting applications.

Pictured above is a modern twin roll caster along
with a schematic layout of a strip casting line.¹

Over time continuous casting of aluminum strip has evolved to the point where gauges of strip are thinner than ever before. Widths of coils are also expanding almost annually. With these evolutions have come tighter demands put on the castertip material used. Less thermal mass in the amount of molten aluminum being brought to the nip has meant lower thermal conductivity is required in the tip material. Thinner strip gauges have brought huge roll diameters requiring castertip assemblies to become thinner and much deeper. Although calcium silicate cement products can be machined into such finely tapered tip assemblies, thermo mechanically they do not work well on generation now roll casters.

Castertips made of ceramic fibers and inorganic refractory binders were found to possess useful thermal conductivities and strengths and in the middle 1970s were being used on a majority of twin roll casters. Manufacturers of ceramic fiber based tips saw the requirement for a 45 pcf density "hard" ceramic fiber castertip soar with the release of its products - several to gain and defend their status as industry standards for nearly two decades.

Discussion
This paper presents data obtained from a variety of castertip products now being produced or under development by ZIRCAR Ceramics Inc. When available, data on "the industry standard" castertip will also be provided for comparison. Castertips containing ceramic fiber, filler and silica binder are called ZIRCAR Castertip Type Z-450. Castertips made of NON RCF fiber are known as castertip Type Z-SOL. Varieties of Type Z-450 and Type Z-SOL which are reinforced with inorganic high temperature glass fibers are known as Z-450 R and Z-SOL R respectively.

Caster Tip	Density	Major Constituents	Other Feature/attributes
ZIRCAR Z-450	45 pcf	Washed Ceramic Fiber, Inorganic fillers & Silica binder.	Recently accepted as equivalent to "industry standard by several casthouse operators.
ZIRCAR Z-450 R	45 pcf	Washed Ceramic Fiber, Inorganic fillers & Silica binder.	A developmental reinforced castertip designed to exhibit high stiffness.
ZIRCAR Z-SOL	45 pcf	NON RCF Fiber, Silica binder	A developmental castertip product designed to give casthouse operators a choice of NON RCF products.
ZIRCAR Z-SOL R	45 pcf	NON RCF Fiber, Silica	A developmental reinforced castertip product designed to enhance the application of NON RCF castertip products.
"INDUSTRY STANDARD"	42-48 PCF	RCF Fiber/Silica	Accepted and used in a majority of casthouses around the world.

ZIRCAR Z-450 castertips have smooth fully reinforced surfaces and edges and are trimmed to precision final dimensions on a CNC router.

Castertips Type Z-450 R and Type Z-SOL R have a layer of very strong high temperature reinforcing fiber integrally formed into them.

The industry standard has been a silica bonded ceramic fiber board with a hard exterior and a less rigidly bound interior.

Typical Properties and Characteristics
Castertip Type	Composition	Hardness Surface (Durometer Type A Model 306L)	Hardness Edge (Durometer Type A Model 306L)	MOR, Mpa (psi)
ZIRCAR Z-450	31.7% Al₂O₃67.6% SiO₂	94	85	800
ZIRCAR Z-450 R	31.7% Al₂O₃67.6% SiO₂	94	85	ND
ZIRCAR Z-SOL	76% SiO₂8.3% MgO 15% Al₂O₃	94	85	450
ZIRCAR Z-SOL R	Ibid.	94	85	NA
"Industry Standard"	68% SiO₂32% Al₂O₃	96	50	650

Deflection and Elasticity
Deflection and elasticity are terms that can be applied when discussing the stiffness of a castertip. Deflection refers to the distance a castertip will bend under its own weight as well as under loaded test conditions. Elasticity refers to the degree to which a deflected castertip regains its natural deflection after the loaded condition is removed.

Test Method for Determining Deflection and Elasticity
To quantify deflection and elasticity a simple test procedure was established. The castertips analyzed were studied in two groups all EXHIBITING the same cross section. The first set of tips measured 1740mm (68.5") long x 394.25mm (13.75") wide with a body thickness of 15.25mm (0.6"). A second group of tips 2337mm (92") long were also tested. The profile for all of these test tips is shown in the sketch below.

Pictured above is the profile of Z-450 used in the deflection and elasticity testing on 1730mm long tips²

Definitions

Natural Deflection: To begin each castertip was supported on opposite ends by blocks of wood and allowed to span the blocks without any additional support. The tips were supported by 150 mm high blocks. Each tip's natural deflection was obtained by measuring the distance between the bottom of the sagging tip and the test table and subtracting that distance from the height of the support blocks.
Loaded Deflection: After the natural deflection is measured a 1 kg (2.2 Lbs.) weight is placed on the centerline of the tip. Loaded Deflection was obtained by measuring the distance between the bottom of the sagging tip and the test table and subtracting that distance from the height of the support blocks.
Elasticity: Elasticity is the measure of how close a tip returns to its natural deflection after unloading. After Loaded Deflection numbers are obtained, the 1-kg weight is removed. Elasticity is measured by subtracting the distance from the bottom of the now unloaded tip from the tip's natural deflection.

Shown above is test apparatus used with the 1740mm wide tips.

The image to the left show how each tip was supported from the test table at its ends. Its natural deflection was then measured. The next step as shown in the center image was to place a 1Kg weight on the center of the tip and to determine its loaded deflection. The tip's elasticity was determined by measuring how much it returned to its natural deflection.

Data Obtained

The fist set of data was obtained by taking the average of the results of measuring at least a few specimen tips of each type. The spreadsheet below compares ZIRCAR's Z-450 and Z-SOL with the "industry standard".³

Deflection and Elasticity Set One
	Industry Standard	Z-450
Length of tip	1740mm (68.5")	1740mm (68.5")
Weight of tip	4050g	4037g
Natural Deflection	17mm	15.9mm
Loaded Deflection	26.5	22.1mm
Elasticity	0.5mm	0.1mm

The second set of data was obtained from analyzing 2337mm wide single piece castertips. No data is provided for an "industry standard" as castertips of this length are currently unavailable from other.

Deflection and Elasticity Set Two
	Z-450	Z-450 R	Z-SOL	Z-SOL R
Length of tip	2337mm	2337mm	2337mm	2337mm
Weight of tip	7844g	7844g	7844g	7890g
Natural Deflection	55mm	9mm	83mm	70mm
Loaded Deflection	65mm	25mm	105mm	45mm
Elasticity	0mm	0mm	3.2mm	1mm

Conclusion

ZIRCAR Ceramics has developed a line of low mass castertip products which include ceramic fiber based as well as NON RCF fiber based varieties. These products exhibit densities and thermal conductivities required in thin aluminum strip casting. ZIRCAR's Z-450 castertips exhibit greater stiffness and elasticity than "industry standard" castertips. ZIRCAR's Z-SOL shows promise as a NON RCF alternative castertip. Reinforced varieties of both these castertips show increased stiffness and elasticity. ZIRCAR's new castertips could become the new Industry Standard For Generation Now Casters.

Addendum:

In addition to castertips other recently developed casthouse products developed by ZIRCAR include: Baffle Boards and End Dams in Z-450 and Z-SOL compositions; Boron Nitride and other ceramic coatings for enhanced non wetting performance; Ceramic Fiber and NON RCF coating papers. See ZIRCAR's website at www.castertips.com for complete company and product information.

References:
1) Pechiney Aluminum Engineering, Vorrepe France, from their website.
2) Fata Hunter, Milano Italy, from castertip assembly drawings provided.
3) Raoul Aubry, Eurofoil S.A. Luxembourg, September 21, 2000.

By David Hamling, Vice President, ZIRCAR Ceramics, Inc. Florida, NY.E-mail dph@zircarceramics.com. Website www.zircarceramics.com

Co Author: Phil Hamling, President, ZIRCAR Ceramics, Inc. Florida, NY.E-Mail pdh@zircarceramics.com. Website www.zircarceramics.com.