CA1124301A - Resin impregnated aromatic polyamide covered glass based slot wedge for large dynamoelectric machines - Google Patents

Abstract

47,761 ABSTRACT OF THE DISCLOSURE

An iron engaging slot wedge, for use in coil slots of dynamoelectric machines is made of a glass fiber core impregnated with a cured thermoset resin, and covered on at least two sides with a facing layer of a porous aromatic polyamide mat, impregnated with a cured thermoset resin.

Description

~LlZ43C~1 47, 76 A RESIN IMPREGNATED AROMATIC POLYAMIDE
C WERED GLASS BASED SLOT WEDGE FOR
LARGE DYNAMOELECTRIC MACHINES

BACKGROUND OF THE INVENTION
Slot wedges are strips of electrically insulating material, used to retain conductors in the coil slots of stators of dynamoelectrlc machines such as generators and motors. Prlor art slot wedge structures have included phenolic resin lmpregnated, flat, Kraft paper sheet lamin-ates. However, when subJected to temperatures on the order of 100C, after several years use, ln large generators and motors, some shrinkage o~ the Kraft paper laminates was encountered. In addition, the Kraft paper-phenollc wedges had poor interlaminar shear length, and were abra~ive to the inner surface edges of the iron stator teeth during the wedge driving operation. Asbestos-phenolic slot we~ges have found wide acceptance, having good stabllity and lubrlclty characteristlcs, but the use of asbestos ls now consldered to be a potential health hazard.
White, ln U.S. Patent 3,437,858, trled to remedy shrinkage and shear strength problems, by provlding a poly-ester resln lmpregnated, parallel glass ~lber, extruded slot wedge, havlng a core of low shear strength. This structure lncluded at each end, a metal or glass fiber tube, rod, tape or cord, having a very high shear strength. Thus, the hlghest shear strength was at the portlon of the wedge that contacted the inner surface of the stator teeth. Thls wedge was faced wlth a 5 to 30 mll ~hick tape of wrapped woven ~, glass, whleh provided a hlgh transverse bondlng strength, and allowed lncreased drlving pressure durlng wedge lnser-tion. The tape coverlng also added to the shear strength ' '' ~ ~

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~Z 43~ 1 47,76 of the wedge, since 1~2 of the glass ~lbers were transverse to the slot wedge core fibersO Such wedges would, however, still be abrasive to the lnner sur~ace edges of the iron stator teeth, during the wedge driving operation.
Balke, in U.S. Patent 3,735ll69, provided plural layers of Kapton polyimide ~ilm, or Nomex tpoly 1,3 phenylene-isophthalamlde) polyamide, high density, fibrous sheet, laminated together with adhesive, to ~orm flat composites.
These sheets, with applied adhesive, were placed ln a clamp-ing ~ixture, and then laminated, to cure the adhesive. Theyformed rigid plastic wedges, with high temperature dimen-sional stability, having the desired channel shaped slot wedge configuratlon, without using a supporting core. Such a construction, however, relies upon the thin adhesive layer ~or rigidity, and would provide wedges which could ~till allow substantial conductor displacement and vibration.
This type of wedge would be practical for small appliances, where coil forces are about 1 lb.~inch length of slot wedge, but not for large dynamoelectrlc machines, with coil ~orces of about 100 lb./inch length o~ slot wedge.
What is needed, i8 a strong wedge, able to prevent conductor dlsplacement and vibration, and resist shear stresses, shrinkage, and bowing caused by the pressure o~
the wedged conductors and heat. The wedge should, very importantly, also provide a compresæible iron engaging surface of considerable resiliency and ~ubricity, which would not abrade the inner surface edges of the laminated stator teeth during the wedge drlving operation.
SUMMARY OF THE INVENTION
The above described problems have been solved, and ~. . .

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47g761 the above need met, by providing a resin impregnated, aromatic polyamide covered~ glass cloth slot wedge, adapted to be positioned in the teeth o~ coll slots in dynamoelec-tric machines. A thermoset resin impregnated, aromatic polyamide surface, on at least the two ma~or teeth contact-ing sides, provldes outstanding lubricity, resillency, tensile strength and thermal stabllity. It also has the ability to notch durlng wedge insertion, rather than abrade the edges of the stator teeth.
The aromatic polyamide is preferably in mat ~orm, about 0.005 to about 0.025 inch thick, and forms a 70% to 95% porous matrix ~or the thermoset resin. The mat is impregnated, between about 60 to about 80 wt.~, with a cured thermoset resin. The glass cloth core is about 0.2 to about 0.5 inch thick, and impregnated between about 40 to about 60 wt.%, with a cured thermoset resin. This combination pro-vides outstanding interlamlnar shear strengths of over about

2,500 lb./in. length at 100C.
J' The resin impregnated aromatlc polyamide felt mat is placed in a suitable mold cavlty, with the resln lmpreg-nated glass fabrlc superimposed thereon. Steam press platens are then used to cure the resins and laminate the , ................................................................ .- two layers, without adhesives, lnto a unitary, consolidated, composite. The organic Aramid fiber matrix, lmpregnated with cured thermoset resin, provides a resilient sur~ace layer that protects the inner surface edges of the stator , iron during the wedging operation, and allows the use of high strength glass core materials which in the past have ` been fo~nd abrasive when used alone. The winding bracing system o~ this invention, control~ stator ~orces from steady ;

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47,761 state and short circuit conditions. It is particularly useful in large generator stator applications.
BRIEF DESCRIPTION OF THE DRAWINGS
For a better understanding of the invention, reference may be made to the preferred embodlments exemplary of the invention, shown in the accompanying drawingæ ln which:
Figure 1 is a cross-sectional vlew of one type o~
stator for a dynamoelectric machine, showing the teeth of a coil slot and a slot wedge inserted therein;
Figure 2 is a cross-sectional view of one type of slot wedge encompassed by this invention,~showing the details of the core and wrapper arrangement;
Flgure 3(a) show~ one method of making the lam-inate stackup for the slot wedges of this inventiol, Figure 3(b) shows the slot wedges being formed in a two cavity mold; and Figure 4 shows a test apparatus used to determine iron abrasion in the Example.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
Referring now to Flgure 1, metal member of a dynamoelectric machine, such as a stator 1 is shown, wlth a oonventional construction, consisting of coll slots 2, contalning coil conductor windings 3, which may also contain cooling ducts. Each coil is bounded, at the top and bottom, by phenolic resin impregnated Kraft paper, or other suitable separator sheet materials 4, and surrounded by insulation 5, as is well known in the art. The insulation 5, will generally comprise a moisture resistant, elastic comblnatlon o~ thermo-setting resln and mica flakes. Slot wedge 6 is a brace for , ~ . .

43~ ~
47,761 the coil windings, and is shown disposed between the top conductor wlndings and the laminated iron stator teeth 7.
The slot wedge is lnserted between the teeth of the coil slot, and contacts the inner surface edges 8 of the stator teeth 7. The lnterior surface of the teeth is a notch in the laminated stator iron components, and can have a variety of configuratlons, such as shown at 8 or 9.
Each stator for a large dynamoelectrlc machine, co~prlses a plurallty of low-loss silicon-steel core punch-ings. ~or example, a large generator stator can be 10 ~eetin diameter and 20 feet long. It can comprise as many as 30 separate punchlngs per inch. Each lamination, before punch-ing, is coated with a high temperature inorganlc lnsulatlon, such as sodium silicate or a phosphate type insulation. The lamination is then punched, deburred and recoated.
The punched laminations havlng the cross-section of the stator coil are then stacked on bulldlng bolts and flrmly clamped together by lnsulated thru-bolts and non-magnetic finger plates, to form a stator body having coil slots and stator teeth. The insulation between each lamln-ated punching helps to prevent current losses~ at operatlng temperatures, along the outside surface of the stator.
Because of the number of indi~idual laminations~ lt is impossible to align the teeth sections to greater than a + 0.010 inch tolerance. Therefore, many of the teeth edge laminations will be "sticking out", and sub~ect to bending : or shearing by the slot wedge during slot wedge insertion.
If the teeth edge laminations are bent or sheared, they can contact each other, causing electrical short circults, and defeating the purpose of the interlamlnar insulation.

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47,7~1 There~ore, it ls essential that the slot wedge exterior be of substantial lubricity, and of a type construction able to be scraped by the stator teeth laminations, without bending the laminations, while still maintaining its structural integrlty.
When the insulated conductor windings and the separators are inserted into place in the coil slots, then a plurallty of slot wedges 6 are driven into place by a suit-able drivlng means such as a block and mallet. Friction contact occurs between the slot wedge iron engaging exterior surface, and the stator iron laminated punchings, at teeth edge contact points 8, on the side and bottom of the slot wedge. In general, the slot wedge assembly has a length equal to that of the coil slot, and usually consists of a plurality of wedges approximately 6" in length. Therefore, a 20-~oot long stator would contain 40 slot wedges per slot.
The slot wedges of this inventlon are easlly molded to various conflgurations and are easily machlnable.
A preferred type of slot wedge 6 is shown in detall in Figure 2. The slot wedge 6, consists of a glass fiber core 20, such as glass fabric or cloth. The glass ~lber oore may be in machlned sheet form, but is pre~erably ln spiral, i.e., wound or rolled form, as shown. A rolled core is particularly useful, since it increases the inter-laminar shear strength of the core by 10% to 20%. Thus, : B exteriorf edges 21 of a rolled core can withstand a greater outward force from the coils held in the coll slots. The - slot wedge core is impregnated with a thermoset resin such aæ, for example, a phenolic resin or an epoxy resin, both of which are well known in the art. These resins can contain a . .

.. , ,~, .

43~
47,761 variety of well-known curing agents 3 accelerators and inhibitors.
The glass cloth used in the core will have a thickness o~ about 0.003 to 0.01 inch. After overlaying or rolllng, and curlng in the mold, the glass cloth will pro-vide a core having a thickness of from about 0.200 to about 0.500 inch. It will be impregnated with about 40 to about 60 wt.% of a cured thermoset resin, based on resin plu5 glass cloth weight. Thicknesses below 0.200 inch and resin loadings below 40 wt.% will allow voids to seriously impair the core strength.
The glass fiber core is covered, on at least two sides, by an aromatic polyamide mat, i.e., felt, facing, which has at least a 70% porous structure~ general~y about 70% to 95% porosity, before resin impregnation. This low density allows very high resin loading, within a tough Aramid matrix having exceptlonal tensile strength. The covering ls integrally lamlnated and bonded to at least the teeth facing, iron engaging side ~urfaces 21 of the core, and generally, for ease of application, to the top surface 22 and the iron engaging edge part of the bottom surraoe at 23 as well. This provides a slot wedge having a top sur~aoe 24, a bottom coil ~acing sur~ace 25, the iron engaglng edges 26 which will contact the teeth of the stator, and two primary iron engaging teeth contacting sides 27.
This covering must consist of a resin lmpregnated aromatic polyamide mat. Many other materials, such as aromatlc polyimides are difficult to bond to the glass core surface. The coverin~ must not be in film form, since this type of coverlng will have a tendency to shear from the , . . . . . ..

430 ~
47,761 glass core during the wedging operation. The aromatic polyamide mat is preferably in a single layer, non-woven form, about 0.005 to about 0.025 inch thick after molding.
The mat provides a matrix of about 5 to 30 volume percent of theoretical density, i.e., 70 to 95 percent porosity, ~hich is impregnated with about 60 to about 80 wt.% of a cured thermoset resin, based on resin plus mat weight. The thermoset resin can be, for example, a phenolic resin or an epoxy resin, which can contain a variety of well-knwon curing agents, accelerators and inhibitors.
Thicknesses of the molded polyamide resin mat below 0.005 inch, will not provide a sufficient thickness to allow facing compression, and to allow thè rough teeth edge surfaces to score and scrape the wedge as it is being driven. Thicknesses below 0.005 inch will reduce the resil-iency of the facing and cause possible rupture or telring of the mat, and contact of the iron teeth laminations with the abrasive glass cloth core. Resin loading below 60 wt.% wlll seriously impair the adhesion of the covering to the core, 2~ since some of the resln used in the covering seeps into the core during high pressure lamination, provlding outstandlng bonding of the two comPonents of the laminate wlthout use o~
adhesives. Less than 60 wt.% resln would also decrease the lubricity of the covering and its ability to absorb the mechanical scraping and scoring of the teeth punchings.
An all aromatic polyamide slot wedge is not useful for large dynamoelectric machines because of excessive creep , and shrinkage at operating temperatures. The preferred thickness ratio of impregnated glass fiber core layer:impreg-nated aromatic polyamide facing layer is between about 10:1 ~lZ4361 47 ,76 g.
to about 100:1. A ratio less than 10:1 will cause shrinkage problems. A ratio over 100:1, i.e., very thin covering layer, will cause possible abrasion problems.
Aromatic polyamlde, in yarn, paper~ mat and fiber form are well kncwn in the art, and comprise aromatic rings united by carbonamide links .~ .
- C - NH - .
Such aromatic nylon materials have a wide range of chemical and physical properties, and have excellent thermal stabi-lity. They can be prepared by reacting an aromatlc diaminewith an aromatlc diacid chloride in an aqueous system. A
; complete description of their properties ànd synthesis can be found, for example, ln U.S. Patents 3, 671, 542 and 3,240,760, herein incorporated by reference. These Aramids are used in this invention in the form of high molecular weight ~ilament mats. These fibrous mats comprlse substantially round fiber filaments havin~ an approximate average diameter of between about 0.0001 to 0.0008 inch. The mat may also contain fibrid binder particles. The mat has about 90% to 100%
resilienoy against compactiOn, i.e., it will absorb impact easlly and return to its original shape. Such reslliency i~
retained to a great degree even when the mat ls loaded with resin.
The most preferred aromatic polyamide i8 a poly , (phenylenephthalamide) having a tenslle strength of over about 90,000 and preferably over about 250,000 lb./sq.in., and a tensile modulus of over about 2.0 x 106 and pre~erably over about 10 x 106 lb./sq.in. One example of this type of ~aterial consists essentially of recurring units of poly : , , ~L~2436)1 47,761 (1,4-phenyleneterephthalamide):

~ NH ~ N~ - C ~ C ~ ,`

described as Kevlar by Gan et al, in Vol. 19 o~ the Journal 0~ Applied Polymer Science, pp. 69-82 (1975). These tensile properties will provide a reasonably close match with the glass in the core, which has a tensile strength of approx-imately 200,000 to 400,000 lb./sq.in., and a tensile modulus o~ about 10 x 106 lb./sq.in.
By closely matching the values of the two com-ponents of the laminated composite, there~wlll be lesschance of delamination under the coil pressures and temp-eratures encountered ln large dynamoelectric machlnes, which can be about 75 to 150 lb./inch length of ~lot wedge at about 75C to 125C. Also, no adhesive need be used to bond the Aramid and glass together. The aromatic polyamides, when in porouæ mat form provide a matrix of about 5 to 30 volume percent density for the thermoset resin. The impreg-nated, cured mat is resilient, flexible and has lubricating properties, allowing it to absorb soraping contact with rough surfaces.
Figure 3(a) shows the aromatic polyamide felt 31, lmpregnated with resin and a roll of impregnated glass ~abric 32. They are placed in the mold 35 with associated P/Q ~ens LJ steam patternE 36, shown in Figure 3(b~.

EXAMPLE l . .
; Several resin impregnated aromatic polyamide faced glass based slot wedges were made. A style #7628 glass cloth strip, 2-3/8" wide, and 0.010" thick, was impregnated .. . . . .

43~ 1 47,761 with an acetQne solution of a bisphenol A epoxy res~n, having an epoxy equivalent weight of 450 to 550, (sold commercially by Shell Chemical Co. as EPON 1001) using trimellitic anhydride as a catalyst. This impregnated strip was passed through a treating tower at 140C, to evaporate the acetone solvent. This provlded a B staged, non-tacky strip, with about 50 to 55 wt.% resin loading, whlch was cut to a 60" length.
A 75% porous, i.e., 25 vol.% dense strip of hlgh modulus aromatlc polyamlde non-woven felted mat, havlng a weight of 7 oz./sq.yd., a tensile strength of about 300,000 to 400,000 lb./sq.in., and about g5% resiliency (described as primarily poly 1,4-phenlyleneterephthalamide, sold com-merclally as Kevlar 29 by E.I. DuPont De Nemours & Co.)

3-1/2" wide and 0.125" thlck, was lmpregnated wIth a methanol solution of a phenol-formaldehyde resin. This impregnated strip was passed through a treating tower at about 140C, to evaporate the solvent. This partly cured the resin in the strip, and provided a dry pre-preg, with about 70 to 75 wt.%
-of phenolic resin in a 25 vol.% Aramid matrix. The strip was then cut to 6" lengths.
The epoxy-glass strip was rolled into a 20 layer thick tube and superimposed on the phenolic-Kevlar covering strip, as shown in Figure 3(a) of the drawings. ~he phenolic-glass tube was pressed flat and the ends of the phenolic-Kevlar strips were bent over the flattened tube top. No adhesives were used. This lay up was placed in a mold ;: - ' ' -cavity, as shown in Figure 3(b), ~nd heat and pressure consolidated between hot press platens at 155C for 1/2 hour at l,OOO psi. The composite was allowed to cool, and then .

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47,761 removed, to provide a consolidated, bonded, laminated slot wedge. The molded composite had a resilient, lubricating, aromatic polyamide facing on the short face side,the two teeth contacting edge sides and on the edges of the bottom side, as shown in Figure 2 of the drawings. The aromatic polyamide covering was compressed to a thickness of about 0.015", and the aromatic polyamide matrix was loaded with about 70 wt.% resin. The glass cloth core was about 0.361' thick, and was loaded with about 50 wt.% resin. There appeared to be excellent bonding of the two adhesiveless layers .
Tests were then run on this composite for strength and stability. The wedge was placed, face down, in a hollow steel test fixture having a simulated stator surface. Here, the beveled side edges rested on steel in the fixture, and a steel pressing bar simulating conductor winding pressure in ~; a stator, was pressed against the coil bracing back of the slot wedge. A 30 ton Amsler Universal testing machine was used in con~unction with a Baldwin microformer unit to measure deflection. The test assembly was operated in an oven with a thermometer attached to the specimen. The interlaminar wedge shear strength at 100C was measured to be 3,510 lb./inch length of slot wedge. This iæ over 230%
above the usual 75 to 150 lb./inch length coil pressure -found in most large dynamoelectric machines and well above the 1,500 lb./inch length typical of phenolic resin Kraft paper sheet slot wedges.
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A similar slot wedge was tested at 100C and 150 psi for 48 hours. This test simulated actual dynamoelectric machine operating conditions. The % thickness shrinkage, ~`Z ~3~
47,761 and % bowing o~ the slot wedge after removal was not measu-rable. This is a dramatic improvement over the 2% to 4%
shrinkage for phenolic resin Kraft paper sheet slot wedges, and 5% shrinkage for an all Kevlar wedge impregnated with phenolic resin. The observed shrinkage of ~evlar requires its use in combination with a glass core, in order to be useful in large dynamoelectric machines.
Abrasion tests were run using a machined, solid Aramid slot wedge and a test fixture, shown in Figure 4 of the drawings. The test fixture 40 comprised a 5" long stack of laminated punchings, each insulated from each other by a phosphate type insulation. There were 30 punchings per inch of fixture length. The slot wedge consisted of a molded block of sheets of phenolic resin impregnated Kevlar aromatic polyamlde. The molded block was about 0.04" thick, 7.5"
long, and provided a 25 vol.% aromatic polyamide matrix loaded with about 75 wt.% phenolic resin. The color of the wedge was pale yellow. The block was machined to a length ~ -of 0.976 + 0.015 inches with a 0.031 radius at its ends, as shown at 40 in Figure 4. A slmllar wedge was machlned from a 0.04" thlck molded block of epoxy resin impregnated glass cloth. Both wedges were machined to exactly matching dimen-sions. The distance between the deepest portion 41 of the teeth 42 of the fixture was 1.0 inches. Bolts 43 holdlng the laminated punchings of the test fixture together are shown as 44.
The abrasion test was a short, mechanical push-pull stroke, applying 150 psi force between the wedge and the iron that moved each wedge through the punchings. New punchings were used for each test fixture. Testlng was ~L~L24301~1L
47,761 conducted at 25C. This test very closely slmulated actual wedge insertion conditions for generator stators. Both the phenolic-aromatic polyamide wedge and the epoxy-glass cloth wedge were moved through their test fixtures, engaglng the lron for 1,000 cycles. Iron deposits were found on the contacting surfaces of the epoxy-glass cloth wedge. The phenolic-aromatlc polyamide wedge appeared to have less effect on the punchings and dld not have any appreciable lron deposits on the contacting sur~aces. The phenolic-aromatic polyamide wedge showed much more wear. Scanning electron micrographs of the punchings of each test flxture were examined and the punching edges in contact wlth the phenolic-aromatic polyamide showed much less wear than the punching edges in contact with the epoxy glass cloth wedge.
Water absorption tests were run according to standard ASTM
D-570, which involves immersing samples in 25C water for 24 hours. The results showed very good results of 1.1% water absorption by weight for the phenolic-aromatic polyamide-epoxy glass cloth wedge.
Phenolic-aromatic polyamide ~aced, epoxy-glass cloth slot wedges, made as described above were tested in approximately 6" lengths, as a stator winding wedge system, in the slots of a stator in a large two pole steam turbine generator 20KV, 669 Megawatt, with outstanding results.
These slot wedges were easily driven into the slots, did not harm the iron edge laminations they contacted, insuring the i magnetic integrity o~ the stator core assembly. The slot wedges also maintained radial pressure on the coils, holding `~ the pressed coils tightly in place to prevent vlbration.

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Claims (12)

47,761 We claim:

1. An iron engaging slot wedge adapted to be positioned in the coil slots of a dynamoelectric machine comprising a glass fiber core impregnated with a cured thermoset resin, and covered, on at least two sides, with a facing layer of a mat of aromatic polyamide fiber, impreg-nated with a cured thermoset resin.

2. The slot wedge of claim 1, having an inter-laminar shear strength of over about 2,500 lb./in. of length at 100°C.

3. The slot wedge of claim 1, wherein the glass fiber core is in spiral form, and the facing layer covers the iron engaging sides of the wedge.

4. The slot wedge of claim 1, wherein the facing layer is a single layer in non-woven form and the thickness ratio of glass fiber core:facing layer is between about 10:1 to about 100:1.

5. The slot wedge of claim 1, wherein the glass fiber core is between about 0.2 inch to 0.5 inch thick and impregnated between about 40 wt.% to about 60 wt.% with a cured resin selected from the group consisting of epoxy resin and phenolic resin.

6. The slot wedge of claim 1, wherein the facing layer is between 0.005 inch to about 0.025 inch thick, im-pregnated with a cured resin selected from the group con-sisting of epoxy resin and phenolic resin, and the aromatic polyamide consists essentially of a poly (phenylenephthalamide) having about 95% to 100% resiliency against compaction.

47,761

7. The slot wedge of claim 6, wherein the facing layer consists essentially of a poly (phenylenephthalamide) having a tensile strength of over about 250,000 lb./sq.in.

8. The slot wedge of claim 6, wherein the aromatic polyamide consists essentially of poly (1,4-phenylenetere-phthalamide).

9. The slot wedge of claim 6 wherein the core resin impregnant is an epoxy resin and the facing layer resin impregnant is a phenolic resin.

10. A generator comprising a stator containing a plurality of slot wedges having the construction of claim 6.

11. In the coil slot of a dynamoelectric machine, a laminated, slot wedge facing wound coils consisting essen-tially of a glass fiber core impregnated between about 40 wt.% to about 60 wt.% with a cured thermoset resin, and covered, on at least two sides, with a resilient facing layer consisting essentially of a poly (phenylenephthalamide) fiber matrix of at least 70% porosity impregnated with about 60 wt.% to about 80 wt.% of a cured thermoset resin, said slot wedge having an interlaminar shear strength of over about 2,500 lb./in. of length at 100°C.

12. The slot wedge of claim 11, wherein the facing layer consists essentially of poly (1,4-phenylene-terephthalamide), the core resin impregnant is an epoxy resin, the covering layer resin impregnant is a phenolic resin, the thickness ratio of glass fiber core:facing layer is between about 10:1 to about 100:1; and the thickness of the core is between about 0.2 inch to about 0.5 inch.