parte 07 - filtros acero información técnica completa (rev. 5)

7/30/2019 Parte 07 - Filtros Acero Informacin Tcnica Completa (Rev. 5)

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THE USE OF CERAMIC FOAM FILTERS

IN HIGH TEMPERATURE CASTINGAPPLICATIONS

700 Shepherd Street

Hendersonville, North Carolina 28792 U.S.A.

Telephone: (828) 697-2411Telefax: (828) 693-1868

BRC94-02


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Page

INTRODUCTION 1

Who Is SELEE Corporation? 1

WHY FILTER? 2

Benefits to Using Ceramic Foam Filters 2

CASTING CASE HISTORIES 2

Corrosion Resistant Valve Body Casting 2

Companion Hydraulic Piston & Cylinder Castings 3

SOURCES OF INCLUSIONS IN STEEL CASTINGS 5

HOW DOES STEEL FILTRATION WORK? 5

Inclusion Separation Theory 5

Why Inclusions Can Not Be Reliably Removed In Gating Systems 5

Why Filters Are More Effective 5

How Solid Inclusion Removal Works 5How Liquid Inclusion Removal Works 8

HIGH TEMPERATURE CERAMIC FOAM FILTERS 10

Characteristics of Reticulated Ceramic Foam Filters 10

Refractory Filter Materials for Steel Casting Applications 10

SELECTING THE PROPER PORE SIZE FILTER 11

FILTER SIZING CALCULATIONS 11

Flow Rate 11

Filter Capacity 11

CONTENTS


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STANDARD SIZE STEEL FILTERS 13

FILTER INSTALLATION 15

Basic Filter Installation Design 15

Plastic Gating Components for Standard Size Filters 15

TECHNICAL SUPPORT 19

Customer Technical Support 19

Metallurgical Analysis 19

Filter Proposals 19

REFERENCES 20


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Who Is SELEE Corporation?

SELEE Corporation is a wholly owned subsidiary of

North Americas largest producer of ceramic foam fil-ters for ferrous and nonferrous foundry casting op-erations. SELEE Corporation is the only ISO 9001certified and Ford Q-1 assessed supplier for theseproducts.

Founded in 1978,SELEE Corporation is located inHendersonville, North Carolina along the edge of theBlue Ridge Mountains. Ownership of the company iscomprised of employees and three outside minorityinvestors. Included among investors are The NorthCarolina Enterprise Corporation and Leventis Over-seas Ltd. Leventis is the leading producer, bottler

and distributor of Coca-Cola in Western Africa, Ire-land, Greece and Eastern Europe.

Company facilities include 135,000 square feet ofmodern manufacturing space, a 25,000 square foot

Technology Center and a joint venture manufactur-

INTRODUCTION

SELEE's manufactur ing facility in Hendersonvi lle,

North Carolina.

ing facility in Venezuela. The Technology Center lo-cated in North Carolina is the worlds only research

facility dedicated to the development of new and im-proved ceramic foams. The company devotes almost$0.10 of every sales dollar to research and develop-ment. The state-of-the-art Technology Center isequipped with a fully analytical scanning electron mi-croscope, x-ray diffraction and a complete metallur-gical laboratory to serve both research and customerrequirements. New products introduced in 1993 in-cluded an advanced filter for single crystal superalloyairfoil casting.

The Corporate Team is made up of 130 employees.Ninteen people are dedicated to research activities

while an additional nine are utilized on full time Appli-cations Engineering efforts working with our custom-ers to help improve processes, lower costs and im-prove quality.

The 25,000 square foot Technology Center dem-

onstrates SELEE's commitment to excellence.


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The performance of ceramic foam filters in steel found-ries has been well documented in the technical litera-ture. The following examples are of two case histo-ries detailing the benefits realized by using ceramicfoam filters.

Corrosion Resistant Valve Body Casting

Filters were used to cast a 4" CN-7M valve body cast-ing in an effort to reduce extensive rework (grind/weld/heat treatment).1 Eighteen paired sets of filtered andunfiltered castings were produced and the effective-

ness of filtration was evaluated based on the numberof required inclusion weld repairs. Figure 1 is a draw-ing of the pattern plate showing the gating systemand the detailed filter installation. The casting andprocessing parameters are summarized in Table 1.

After shakeout and blast cleaning, the castings wereevaluated for visible surface inclusion material and theirnumber tabulated. These defects were then removed

WHY FILTER?

Elimination of slag inclusions

Reduced rework time and materials

Improved mechanical properties

Reduced micro-inclusion content

Improved product quality

Reduced machine shop scrap

Reduced machine tool breakage and wear

Improved machine surface quality and

integrity

Improved cosmetic surface quality

Reduced casting processing time (improvedon time delivery capability)

Benefits of Using Ceramic Foam Filters

Efficient and economical production of clean steel

castings is becoming increasingly important intodays competitive global market. The presence

of non metallic inclusions is one of the mosttroublesome problems in the production of pre-

mium quality steel castings and is a significant partof the overall processing cost. The presence of

non metallic inclusions can impair mechanicalproperties such as tensile strength, ductility, frac-ture toughness and fatigue resistance. In addi-tion the presence of surface or subsurface inclu-

sion material can significantly impair the machin-ability and pressure tightness of the casting.

The following is a partial list of some of the ben-efits attributed to using ceramic foam filters:

Reduced scrap rate

Reduced casting returns from customer

Increased casting yield through use ofshorter runner systems

CASTING CASE HISTORIES

by grinding followed by weld repair. After weld repairthe castings were given a solution anneal heat treat-ment. Surface defects generated by heat treatmentwere then tabulated again and weld repaired. A sec-ond heat treatment followed.

Table 2 summarizes the number of weld repairs re-quired for unfiltered and filtered castings. Table 2 showsthat prior to the first heat treatment the 18 unfilteredcastings required a total of 65 weld repairs while thefiltered castings required only one weld repair. Afterthe solution anneal the unfiltered castings required a

total of 115 additional weld repairs compared to 5 forthe filtered castings. Overall the use of filters reducedthe number of weld repairs by 96.7%. In addition 83.3%of the filtered castings could be shipped after the firstsolution anneal heat treatment compared to only 5.6%of the unfiltered castings. Further, the historical inclu-sion scrap rate was reduced from 11.5% to 0.7%.


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Figure 1: Schematic illustration of the gating systemfor the 100 mm valve body casting.

Table 1: Summary of casting processing paramatersused to produce 4" CN-7M valve body castings.

F il tered Un fi lt ered

Number of Castings 18 18

Total Number of Welds before :Heat Treatment: 1 65

Average Welds per Casting before Heat Treatment: 0.06 3.61

Total Welds after Heat Treatment: 5 115

Average Welds per Casting after Heat Treatment: 0.28 6.39

Overall Total Number of Weld Repairs: 6 180

Average Number of Welds per Casting: 0.33 10

Percent Reduction in Number of Weld Repairs: 96.7

Number of Castings Shipped after 1st

Heat Treatment: 15 1

Percent Shipped after 1st

Heat Treatment: 83.3 5.6

Finish Casting Weight: 52 lb

Casting Pour Weight: 134 lb

Pattern Size: 20 x 30

Sprue Height: 11.5

Number of Castings Per Mold: 2

ASTM Casting Specification: A744

Grade/Alloy: CN-7M 20Cr-28Ni-2Mo-3Cu

Pour Temperature: 2900 deg F

Filter Manufacturer: SELEE Corporation

Filter Type: PSZ

Filter Size: 3 x 3 x 1 Thick

Filter Pore Size: 10 ppi (coarse)

Deoxidation Practice: Zr-Si-Mn-Al-Ti +FeSe

Table 2: Summary of grind/weld repair history on a4" CN-7M valve body casting.

Companion Hydraulic Piston & Cylinder

Castings

Filtration trials were conducted on companion piston(4130) and cylinder (440C) castings for a mass transithydraulic brake system.2 Both castings highly ma-

chined (>95%) followed by plating. An initial sampleof 24 castings of each type was made without filterswhich passed visual surface inspection and met GradeB radiographic requirements. After machining the cast-ings were plated and inspected. All of the castingswere rejected for small randomly dispersed oxidemacro-inclusions.

Figure 2: Top view of the gating system for the 4130piston casting after modification to incorporate filters. Note

the absence of oxide macro-inclusions on the runner andingate surfaces confirming the effectiveness of the filters.

Figure 3: Bottom view of the gating syste for the 4130piston casting after modification to incorporate filters.

SprueWell

Side Riser

FilterPrint

FilterPrint Sprue

Well


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Table 3: Summary of casting and gating parameters for production of the companion piston and cylindercastings.

Figure 4 : Transverse slice of the gating system showingthe filter section where oxide macro-inclusions can beseen adhering to the filter.

Figures 2 and 3 show the gating system for the pistoncasting after modification to incorporate filters. Thegating system for the cylinder casting was similar. Theonly change from the existing gating system was theaddition of a vertical filter print on each side of thesprue well. The details regarding the production pa-

rameters are summarized in Table 3. After the addi-tion of filters, 200 pairs of pistons and cylinders wereproduced without any inclusion rejections following ma-chining and plating. Figure 4 shows a transverse slicetaken through both filters revealing retained oxidemacro-inclusions. EDS analysis of the inclusions re-vealed a complex mixture of alumina deoxidationclus-ters embedded in a glassyAl2O3-TiO2-Cr2O3-MnO ma-trix. The presence of deoxidation products of Al and

Ti (Al2O3, TiO2) along with Cr2O3and MnO indicatethe glassy phase formed as a result of reoxidationduring metal transfer (pouring).

Oxide Macro-

inclusion

Casting Parameter Piston Casting Cylinder Casting

Alloy Type: AISI 4130 AISI 440C

Mold Pour Weight: 84 kg 71 kg

Individual Casting Weight: 9 kg 8 kg

Number of Castings/Mold: 4 4

Type of Mold: No-bake No-bakeMold Pour Time: 20 seconds 20 seconds

Filtration Parameters

Filter Manufacturer: SELEE Corporation SELEE Corporation

Filter Type: PSZ PSZ

Number of Filters: 2 2

Filter Size: 50 x 75 x 25 50 x 75 x 25

Pore Size: 10 ppi 10 ppi

Gating Parameters

Sprue Area: 645 mm sq 645 mm sq

Runner Area: 1,658 mm sq 1,658 mm sq

Filter Area

entrance:

exit:

7,742 mm sq

5,439 mm sq

7,742 mm sq

5,439 mm sq

Ingate Area: 3,871 mm sq 3,871 mm sq

Gating Ratios, As:Ar:Af:AIG: 1:2:6:8:4:6:0 1:2:6:8:4:6:0


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Figure 5: Scanning electron photomicrograph of a typicaloxide macro-inclusion extending below the casting sur-face. EDS analysis indicated silica sand grains embed-ded in a glassy MnO-Al

2O

3-SiO

2matrix which formed due

to reoxidation during pouring.

SOURCES OF INCLUSIONS IN STEEL CASTINGS

the mold cavity, and during pouring, entrained silicasand grains present in the gating system. Uponentering the mold cavity the inclusions float to thecope casting surface resulting in an embedded sur-face defects.

Sources of non-metallic inclusions in steel castingsinclude eroded molding sand, ladle/furnace slag and/or refractories, deoxidation and reoxidation productsas well as oxide macro-inclusions. The mosttroublesome type of inclusion in steel castings is theoxide macro-inclusion or ceroxide (ceramic ox-ide). In commercial steel castings ceroxides areobserved to range in diameter from 1/8" to greaterthan 2" and form surface depressions as deep as 1/4" or more. These defects are nearly always locatedon either the cope casting surface, or beneath a coredsurface (Figure 5). The formation of oxidemacro-inclusions has been the subject of numerousinvestigations over the last 35 years. (3-8) Studiesby the Steel Founders Society of America (SFSA)and researchers at Union Carbide produced findings

on the problem which warrant review.(5,7,8)

Figure 6: Composition of oxide macro-inclusions identi-fied in commercial and experimental steel castings plot-ted on a pseudo SiO2-Al

2O

3-MnOFeO ternary phase dia-

gram.5

Two other significant conclusions were reached; 1. Ox-ide macro-inclusions will be generated as long as oxy-

gen is present in either the air or in the refractory ma-terials which come in contact with molten steel, and2. Their elimination would involve mechanical removalin the gating system prior to the mold cavity.

The mechanism of formation of both deoxidation andreoxidation inclusions was studied by workers at UnionCarbide. They established that the large oxide inclu-sions were the result of reoxidation during pouring.(7)

In addition they concluded that reoxidation productsare significantly larger than deoxidation products andare rich in the weaker deoxidizers of silicon and man-ganese. The initial reoxidation inclusions formed in

aluminum deoxidized steel were large alumina clus-ters. As reoxidation further proceeded, the inclusioncontained smaller quantities of aluminum and increas-ing amounts of manganese and silicon. Figure 7 illus-trates the proposed mechanism for the formation ofboth reoxidation and deoxidation inclusions in alumi-num deoxidized steel. One of the conclusions reachedwas that the solution to the problem would be of amechanical nature rather than chemical. Changing

SFSA sponsored work in the early 1960s at BattelleMemorial Institute established the primary source ofoxide macro-inclusions to be oxidation of the moltensteel during pouring and fluxed ladle refractories.(5)

Figure 6 shows the composition of ceroxides fromboth commercial and experimental test castings plot-ted on a pseudo SiO2-Al2O3-MnO+FeO ternaryphase diagram. The chemical composition was ob-served to be strongly influenced by the base steelcomposition (primarily the Mn/Si ratio) and the addi-tions of strong deoxidizers (Al, Ti, Zr). It was con-cluded that oxide macro-inclusions formed outside

Casting Surface

Glassy

slag phase

Slica Sand

i 2

MnO &FeO

Al O2 3

20

40

60

80 20

40

60

80

Commercial steel casting with Al addition.Experimental castings without Al addition.Experimental castings with Al addition.


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the deoxidation practice would alter the compositionof the reoxidation inclusion, but not prevent its forma-tion.

A recent industry sponsored investigation by SFSAestablished once again that reoxidation was still the

major cause of oxide macro-inclusions in steel cast-ings. (8) Investigation of commercial and test platecastings poured in production foundries establishedthat reoxidation was the source of 83% of oxidemacro-inclusions. Figure 8 shows the distribution and

origin of the various oxide macro-inclusions identifiedby this investigation.

All of the above cited investigations into the origin ofoxide macro-inclusions identified reoxidation as themajor cause. Whenever molten steel is poured

through an atmosphere containing oxygen the for-mation of reoxidation inclusions will be unavoidable.Changing the deoxidation practice would therefore notprevent its formation, only the chemical composition.Therefore filtration in the runner system is an at-

tractive and technically sound technology for

eliminating the troublesome problem of oxide

macro-inclusions in steel castings.

Figure 7: Schematic illustration of the mechanismof formation of deoxidation and reoxidation inclusionsin steel castings.7 Figure 8: Sources of oxide macro-inclusions in car-

bon and low alloy steel castings.8

Oxygen

Alumin um

Silicon

Manganese

Alumin a Galaxy

Oxygen

Alumin um

Silicon

Manganese

DE XIDATI

REOXIDATION

Large Alumina Galaxy Multiphase Globule Single Phase

Globule

1st Stage 2nd Stage 3rd Stage

100

90

80

70

60

50

40

30

20

10

Reoxidation

MoldingMaterial

Slag

Refractor

Deoxidation

1%1%2%

14%

83%

PercentofCa

rbonandLow

AlloyMacro-Inclusions,395Total


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HOW DOES STEEL FILTRATION WORK?

wall is usually less than 1/16". This short separa-tion distance combined with the tortuous flow path ofceramic foam filters provides a high level of filtration

efficiency.

INCLUSION SEPARATION THEORY

The separation of inclusions from molten steel is a

two step process:9

1. Transport of the oxide inclusion to an interfacesuch as the refractory ladle walls, the ladle slag,or any surface within the gating system (sprue,runner, filter, ingate).

2. Separation of the inclusion at the interface.

The key to effectively removing inclusions from mol-ten steel is to have a very short separation distance.Separation of inclusions in traditional runner systemsrelies on inclusion particle transport to one of the run-ner surfaces. Filtration relies on the flowing metal tobring the inclusion close to the filter structure wherecontact can occur.

WHY INCLUSIONS CAN NOT BE RELIABLY

REMOVED IN GATING SYSTEMS

Traditional gating systems are designed to removeinclusion material in the runner system by flotation.However, due to restriction of the flask size, yield con-siderations, as well as sprue and ingate locations,

runner systems are often very short. The combina-tion of short runner bars, relatively high runner ve-locities and highly turbulent flow conditions make ef-fective inclusion separation by flotation difficult, par-ticularly for very small inclusions.

WHY FILTERS ARE MORE EFFECTIVE

Figure 9 schematically illustrates the filtration pro-cess where inclusion particles smaller than the cellor pore openings are retained in the depth of the filterstructure.

The primary reason filtration is more effective thanflotation is the small separation distances betweenthe inclusion and filter surface. The inclusion separa-tion distance in runner bars is typically on the orderof .75 to 2.5", which given the high metal velocitiesand short runner lengths makes effective inclusionseparation difficult to impossible to achieve. Filtra-tion is very effective because the separation d is-

tance between an inclusion particle and the filter

Metal Flow Direction

Figure 9: Schematic illustration of inclusion particleretention in a ceramic foam filter.

HOW SOLID INCLUSION REMOVAL WORKS

When a solid inclusion comes in contact with the in-ternal filter wall there must be a mechanism for theinclusion to adhere, otherwise subsequent release

may occur. Whether an inclusion will adhere to afilter wall is dependent on the interfacial energy rela-tionship between the molten metal (m), the inclusion(i) and the filter (f): (15)

G = if- mf- mi (1)

where G =Gibbs free energy

=interfacial energy


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Filter

HOW LIQUID INCLUSION REMOVAL WORKS

The removal of liquid inclusions relies on a high workof adhesion ((WA)IF) between the liquid inclusion (i)and the filter (f):17,18

(WA)if=mi(1 +cosfi-im) (2)

where (WA)if= work of adhesion

mi=interfacial energy between the meltand the liquid inclusion

cos()fi-im=contact wetting between theliquid inclusion and the filter

Figure 12: Backscattered electron image showing aneroded silica sand particle adhering to the filter surface.Note the capillary withdrawal of molten metal from the in-terstitial contact area between the silica sand grain andthe filter.

Figure 10: Schematic illustration showing the shape

of a liquid droplet on an oxide substrate for non wet-ting ( >900) and wetting conditions ( 90 DEG.

< 90 DEG.

S

M

SM

S SM

M

Filter Substrate

Solid InclusionParticle

Region of LiquidMetal Withdrawal


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Figure 15: Backscattered electron image showing an oxidemacro-inclusion with silica sand grains embedded in manga-nese-silicate matrix which has wetted to the filter. Mold Mate-rial: green sand

clusions have low contact wetting angles on refractoryoxide surfaces indicating that they can readily be re-

moved by filtration.(9) Figures 14 - 18 show examplesof various types of liquid inclusions, including oxide

macro inclusions, which have wetted and adhered topartially stabilized zirconia foam filters.

Figure 13: Sessile drop of a liquid inclusion on a filter substrate.The contact wetting angle between the filter and liquid inclusion isdenoted by .....

Figure 14: Backscattered electron image showing an oxidemacro-inclusion with silica sand grains embedded in a man-ganese alumino-silicate matrix which has wetted to the filter.Mold Material: green sand

Oxide Macro-inclusion

Filter

Filter

Oxide Macro-inclusion

Metal

Filter

Figure 16: Backscattered electron image showing an oxide

macro-inclusion with silica sand grains embedded in a man-ganese-silicate (2MnOSiO2) matrix which has wetted to the

filter. Note the capillary withdrawal of metal at the inclusionfilter interface. Mold Material: green sand.

Filter

Figure 17: Large oxide macro-inclusion which has wetted thefilter structure. EDS anslysis at high magnification indicatedthe inclusion to be alumina clusters embedded in a manga-nese silicate (2MnOSiO

2) matrix. Mold Material: green sand

Reoxidation

Inclusion

Filter

Filter

Liquid Ca

Aluminates

Liquid Ca

Alumi nates

Figure 18: Backscattered electron image showing calciumaluminates which have wetted to the filter structure. EDSanslysis indicated the inclusion to be a mixture of 3CaOAl

2O

3

and 12CaO7Al2O

3. Deoxidation: Al +Ca wire injection

The work of adhesion is defined as the amount of work

required to physically separate a liquid inclusion fromthe filter surface and create new metal/filter and metal/

inclusion interfaces. Equation 2 shows that maximumliquid inclusion adhesion to a filter will occur at a low

contact wetting angle (). In other words maximum in-clusion adhesion is obtained when the liquid inclusion

wets the filter (Figure 13). Generally liquid oxide in-

Filter

Metal

Sand

Sand

2-phase Oxide

Macro-inclusion

Filte

LiquidInclusion (I)

Metal

IM

MF

IIF


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Figure 19: Scanning electron photomicograph showingthe three-dimensional structure of a reticulated foam filter.

CHARACTERISTICS OF RETICULATED CERAMIC

FOAM FILTERS

Figure 19 is a scanning electron photomicrographshowing the three dimensional interconnecting poly-hedral cell structure of a reticulated foam filter. Formolten metal to flow to an adjacent cell it must passthrough an aperture which is characteristically onethird the cell diameter. As a result, the flow from onecell to the next dramatically reduces the inclusionparticle transport distance for removal. The intercon-necting three-dimensional cell structure creates a tor-tuous flow path further increasing the probability ofinclusion contact and adhesion to the filter surface.Ceramic foam filters are available in a range of stan-dard pore or cell sizes. Figure 20 shows the relative

pore size of No. 10, 15, and 25 foam filters which arecommonly used for steel casting applications.

REFRACTORY FILTER MATERIALS FOR STEEL

CASTING APPLICATIONS

The molten environment encountered in steel sandcasting applications is quite severe in terms of therefractory filter material requirements. The refrac-tory filter material must be able to withstand the initialmetallostatic priming head and thermal shock with-out spalling of filter fragments or breaking down. Thefilter material must have extremely high thermal shockresistance to withstand the nearly instantaneous 2800- 3100 F thermal transit encountered in steel sandcasting applications where the filter can not be pre-heated. In addition, the filter must have sufficient hightemperature strength, creep resistance and resistanceto corrosive attack by both the molten steel and slag.

Partially stabilized zirconia (PSZ) using magnesia(97% ZrO2-3% MgO) as a stabilizer offers the bestcombination of hot strength, creep resistance, ther-mal shock resistance and resistance to chemical at-tack. The combination of these properties allows forfabrication of low density filters which will easily primewithout excessive superheat or filter preheat.

Pure zirconia exhibits a martensite phase transfor-mation at approximately 1000C. This phase changeresults in a 9% volume increase during cooling in thefiring process, thereby initiating microcrack toughen-

ing. Partial stabilization of the high temperature tet-ragonal phase to the appropriate level (60% mono-clinic, 40% tetragonal) with magnesia (MgO) resultsin high strength and increased resistance to crackpropagation, while the dispersed monoclinic phasecontributes to the high thermal shock resistance ofthe filter.

HIGH TEMPERATURE CERAMIC FOAM FILTERS

No. 15 No. 25No. 10

Figure 20: Relative pore size of No. 10, No. 15 and No. 25 ceramic foam filters.


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SELECTING THE PROPER PORE SIZE FILTER

The selection of the optimum pore size filter requiresa decision involving a trade-off between product qual-ity (melt cleanliness) and the size and cost of the fil-

ter required. In addition metal fluidity has to be care-fully considered. Aluminum deoxidized carbon andlow alloy steels have limited fluidity requiring coarse(No. 10), low density (L grade) filters to be used in

FLOW RATE

To obtain the proper mold fill time it is essential tocalculate the proper size filter. The effective filter area

(AF) must be large enough so the filter does notchoke the flow of molten metal or become blockedwith retained inclusions prior to the end of the pour.Filter sizing models have been developed based ona Bernoulli mechanical energy fluid flow model usingfilter pressure drop curves. Figure 21 shows themetallostatic pressure drop curves for 10, 15 and 25ppi filters. Figure 22 shows the influence of the filterarea/choke area ratio on the percent of the originalunfiltered flow. These curves were calculated fromthe metallostatic pressure drop curves in Figure 21.At small filter area/choke area ratios (AF/AC 6), the choke inthe gating system controls the rate of mold fill. Fig-ure 23 shows that for finer pore size filters additionalsurface area is required to maintain the same moldfill rate. Table 4 contains the minimum recommendedfilter area to choke area ratios based on achieving90% of the original unfiltered flow rate.

To determine the minimum filter size which will main-tain at least 90% of the original unfiltered mold fillrate, multiply the appropriate AF/AC ratio in Table 4by the choke area of the gating system. For instancefor a gating system with a choke area of .75 in2wherea No. 15 ppi pore size filter has been selected, theminimum filter surface is calculated as follows:

Filter Area =8 X .75 in2 =6 in2

order to reliably prime. Finer pore size filters offersignificantly higher filtration efficiency and improvedcasting cleanliness, but larger surface areas are re-

quired to offset their higher flow resistance.

FILTER SIZING CALCULATIONS

FILTER CAPACITY

The second sizing factor to consider is whether thefilter will become blocked or plugged with retained

inclusion material prior to the end of the pour. Theamount of molten steel a filter will pass is dependenton the filter pore size and steel cleanliness. The quan-tity of steel which will pass through a filter is highlydependent on deoxidation practice. Deoxidation prac-tices utilizing strong deoxidizers (Al, Zr, Ti) which formoxide galaxies or clusters will eventually cause thefilter to block with retained inclusion material. Tables5 and 6 provide guidelines for the quantity of metalthat various size filters can be expected to pass de-pending on the type of deoxidation practice.

After calculating the filter size based on both flow rate

and blockage, the larger of the two values should beused.

Table 4: Minimum recommended filter to choke arearatios to obtain a minimum of 90 percent of the origi-nal unfiltered flow rate.

Filter Pore

Size Number

Minimum Recommended

Filter to Choke Ar ea Ratio

(AF/AC)

10 6

15 8

25 9


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Table 5: Filter sizing guidelines for steels deoxidized with either Al, Ti or Zr.

Table 6: Filter sizing guidelines for steels not deoxidized with either Al, Ti or Zr.

Figure 21: Metallostatic pressure drop across thefilter as a function of the filter approach velocity (V

F)

for 10 (coarse), 15 (medium) and 25 (fine) ppi foamfilters.

Figure 22: Influence of the filter area to choke arearatio (A

F/A

C) on the percent of the original unfiltered

flow rate.

0

20

40

60

80

100

0 2 4 6 810

12

14

16

18

20

FILTER AREA/CHOKE AREA RATIO

PERCENT

OFORIGINAL

FLOWR

ATE

10 ppi

15 ppi

25 ppi

0

10

20

30

40

50

60

70

80

90

0 40 80 120 160 200

FILTER A PPROACH VELOCITY

FILTERPRESSUREDROP-MMOFFe

10 ppi

15 ppi

25 ppi

SELEEPart Number

FilterSize

Maximum RecommendedPour Weight

Maximum RecommendedChoke Area

Single Filter Double Filter Single Filter Double Filter

FESZ20201007L 2x2x.75 45 kg 91 kg 310 mm sq 619 mm sq

FESZ203010L 2x3x1 68 kg 136 kg 452 mm sq 910 mm sq




SELEEPart Number

FilterSize

Maximum RecommendedPour Weight

Maximum RecommendedChoke Area

Single Filter Double Filter Single Filter Double Filter

FESZ20201007

FESZ20201007L2x2x.75 182 kg 364 kg 310 mm sq 619 mm sq

FESZ203010

FESZ203010L2x3x1 273 kg 545 kg 452 mm sq 910 mm sq

FESZ303010


FESZ304010


FESZ404010



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Tables 7 and 8 list standard size partially stabilized zirconia (PSZ) filters produced by SELEE Corporationalong with their dimensional specifications. The suffix L refers to the low density variant which should beused with carbon and low alloy steels or any other application where the filter priming is a concern.

* XX denotes filter pore size

STANDARD SIZE STEEL FILTERS

Table 7: Standard Size Square and Rectangular Partially Stabilized Zirconia (PSZ) Foam Filters Producedby SELEE Corporation and Product Code Numbers.

Filter Size,Inches

SELEE ProductCode Number*

A/max,mm

A/min ,mm

B/max,mm

B/min,mm

T/max,mm

T/min,mm

2 x 2 x .75FESZ2020XX07

FESZ2020XX07L51.00 48.00 51.00 48.00 20.70 17.50

2 x 3 x 1FESZ2030XX

FESZ2030XXL51.00 48.00 76.20 73.00 27.00 23.80

3 x 3 x 1 FESZ3030XXFESZ3030XXL

76.20 73.00 76.20 73.00 27.00 23.80

3 x 4 x 1FESZ3040XX

FESZ3040XXL76.20 73.00 102.00 98.00 27.00 23.80

4 x 4 x 1FESZ4040XX

FESZ4040XXL102.00 98.00 102.00 98.00 27.00 23.80

4 x 4 x 1.25 FESZ4040XX125

FESZ4040XX125L102.00 98.00 102.00 98.00 33.40 30.20

5 x 5 x 1FESZ5050XX

FESZ5050XXL127.00 122.90 127.00 122.90 27.00 23.80

5 x 5 x 1.25FESZ5050XX125

FESZ5050XX125L127.00 122.90 127.00 122.90 33.40 30.20

4 x 6 x 1FESZ4060XX

FESZ4060XXL102.00 98.00 152.00 147.00 27.00 23.80


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Table 8: Standard Size Round Partially Stabilized Zirconia (PSZ) Foam Filters Produced by SELEECorporation and their Product Code Numbers.

Filter Size,Inches

SEEE ProductCode Number

D/max,mm

D/min,mm

T/max,mm

T/min,mm

2 OD x .75FESZ20RDXX07

FESZ20RDXX07L51.00 48.00 20.70 17.50

3 OD x 1FESZ30RDXX

FESZ30RDXXL76.00 73.00 27.00 23.80

4 OD x 1FESZ40RDXX

FESZ40RDXXL102.00 98.00 27.00 23.80

4OD x 1.25 FESZ40RDXX125

FESZ40RDXX125L102.00 98.00 33.40 30.20

5 OD x 1FESZ50RDXX

FESZ50RDXXL127.00 123.00 27.00 23.80

5 OD x 1.25FESZ50RDXX125

FESZ50RDXX125L127.00 123.00 33.40 30.20


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BASIC FILTER INSTALLATION DESIGN

Filters should be installed in the runner system for

the best results rather than in the pouring basin ordirectly under the sprue. Figure 23 shows the rec-ommended filter installation where filter(s) are in-stalled vertically in the gating system directly adja-cent to the sprue well. A slightly over sized anddeeper sprue well is utilized in order to maintain asufficient thermal mass to prevent premature freez-ing of the steel until sufficient metallostatic pressureis obtained to prime the filter. With low density (gradeL) partially stabilized zirconia filters, carbon steel willreadily prime the filter at casting temperatures downto 2850 F. This system is normally utilized withunpressurized gating systems where the ingates are

located in the cope in order to keep the gating sys-tem full of molten metal during the entire pour to mini-mizing air entrainment.

Table 9: Available plastic filter prints and matching runner dimensions.

FILTER INSTALLATION

Figure 29: Plastic filter prints for standard squareand rectangular size filters for single and double run-ner bar systems.

PLASTIC GATING COMPONENTS FOR

STANDARD SIZE FILTERS

To simplify the pattern modifications, plastic filterprints are available which can be easily mounted onthe pattern board or plate. Figure 29 shows some ofthe plastic filter prints which are available for bothsingle and double runner systems. The part num-bers for available plastic filter prints and the match-ing runner size requirements are given in Table 9.

Filter Size,Inches

SELEE PartNumber

RunnerHeight,

mm

Runner Width,Bottom, mm

Runner Width,Top, mm

Part Number or PlasticGating Components

2 x 2 x .75 FESZ2020XXFESZ2020XXL

25.4 25.4 22.7 ACFD0043Single

ACFD0044Double

2 x 3 x 1FESZ2030XX

FESZ2030XXL31.8 45.7 40.1

ACFD0030

Single

ACFD0031

Double

3 x 3 x 1FESZ3030XX

FESZ3030XXL44.5 44.5 36.7

ACFD0032

Single

ACFD0033

Double

3 x 4 x 1 FESZ3040XX

FESZ3040XXL50.8 50.8 41.9 ACFD0034

Single

ACFD0035

Double

4 x 4 x 1 FESZ4040XX

FESZ4040XXL50.8 50.8 41.9 ACFD0036

Single

ACFD0042

Double


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Figure 23: Schematic illustration showing vertical method of filter installation for single and double runnersystems for steel sand casting applications.

DOWNSPRUE

VERTICAL FILTER PRINT

COPE INGATE

SPRUE WELL

DRAG RUNNER

BOTTOM VIEW

SCHEMATIC ILLUSTRATION OF

DOUBLE FILTER/RUNNER SYSTEM

SCHEMATIC ILLUSTRATION OF

SINGLE FILTER/RUNNER SYSTEM

BOTTOM VIEW

SIDE VIEWSPRUE WELL

DRAG RUNNER

COPE INGATE


DOWNSPRUE

SIDE VIEW


Figure 24: Installation drawing for 2" x 2" x .75" filters for single and double runner systems.

PLASTIC GATING PIECE PART NUMBER: ACFD0043 PLASTIC GATING PIECE PART NUMBER: ACFD0044


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Figure 25: Installation drawing for 2" x 3" x 1" filters for single and double runner systems.





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PLASTIC GATING PIECE PART NUMBER: ACFD0042PLASTIC GATING PART NUMBER: ACFD0036


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CUSTOMER TECHNICAL SUPPORT

SELEE Corporationhas a staff of Metallurgical and

Applications Engineers to provide full technical sup-port for their filtration products. Technical assis-tance is available for filter sizing and installationdesign, metallurgical analysis of casting defects,inclusion identification and spent filter analysis.SELEE Corporationmaintains a complete metallo-graphic facility including a fully analytical scanningelectron microscope with light element capabilityand x-ray diffraction for structural analysis. In ad-dition CAD design services are available for filterinstallation/gating system design. Technical sup-port can be obtained by:

Writing:SELEE Corporation700 Shepherd StreetHendersonville, North Carolina 28792U.S.A.

Phone: 1-800-438-7274(828) 697-2411

FAX: (828) 693-1868

email: [email protected]

METALLURGICAL ANALYSIS

Metallurgical analysis of casting defects and spentfilters is available. When submitting samples thefollowing information should be included along withthe sample:

1. Description of the problem or objective of theanalysis

2. Description of sample

3. Alloy Type/Designation

4. Deoxidation practice

5. Description of melting/refining/practices

6. Name and address of the individual request-ing the report

TECHNICAL SUPPORT

FILTER PROPOSALS

Complete CAD filter installation design proposals areavailable. The following information is required toprepare a detailed engineering proposal:

1. Pattern or Casting Identification Number

2. Alloy Type/Designation

3. Pouring Practice

4. Deoxidation Practice

5. Pouring Temperature

6. Mold Pour Time

7. Mold Pour Weight

8. Casting Weight

9. Number of Castings

10. Existing Gating Designa. sprue dimension & heightb. Number and size of runners (cross section)c. Number and size of ingates (cross section)d. Engineering drawing of existing gatingsystem showing sprue, runner and ingatelocations.


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1. A. Friesel, R. J . Karamon and L. S. Aubrey; Filtra-tion of High-Alloy, Corrosion Resistant and Nickel-Base Valve Body Castings,AFS Transactions, vol.

100, 1992, pp 209 - 219

2. L. S. Aubrey, J . R. Schmahl and M. A. Cummings;Application of Advanced Reticulated Ceramic FoamFilter Technology to Produce Clean Steel Castings,AFS Transactions, vol. 101, 1993, pp 59 - 69

3. C. A. Sanders, One Answer to the Snotter Prob-lem, Modern Castings, (May 1956)

4. H. Blosjo, Ceroxide Defect-What it is and How itsIncidence can be Reduced, J ournal of Steel Cast-

ings Research, Steel Founders Society of America,Number 7, pp 1-4 (J an 1957)

5. W. S. Lyman, F. W. Boulger,An Investigation ofFactors Producing the Ceroxide Defect on Steel Cast-ings; Part I--Composition and Sources, SteelFounders Society of America Research Report No.48, (Feb 1961)

6. R. A. Flinn, L. H. Van Vlack, G. A. Colligan,Macroinclusions in Steel Castings, AFS Transac-tions, Vol 69, pp 485-512 (1966)

REFERENCES

7. J . W. Farrell, P. J . Bilek and D. C. Hilty,InclusionsOriginating from Reoxidation of Liquid Steel, Elec-tric Furnace Conference Proceedings, AIME, Vol 28,

pp 64 (1970)

8. J . A. Griffen, C. E. Bates, R. W. Monroe and J .Svoboda, Appearance and Composition of OxideMacro-Inclusions in Steel Castings, AFS Transac-tions, Vol 87, pp 187-202

9. A. W. Cramb, Caster Related Product Defects:Causes and Cures, Presentation at the IMIS Steel-making Symposium, Monterrey, Mexico, (Nov 1989)

10. A. W. Cramb and I. J imbo, Interfacial Consid-erations in Continuous Casting, Iron and

Steelmaker, pp 43-55, (J une 1989)

parte 07 - filtros acero información técnica completa (rev. 5)

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