Process for making a boric acid free flux

Abstract

The invention described herein pertains generally to a process for making boric acid free flux compositions in which boric acid and/or borax is substituted with a molar equivalent amount of potassium tetraborate tetrahydrate. In some embodiments, a phthalocyanine pigment is used to affect a color change at activation temperature.

Claims

1. A process of making a boric acid-free flux composition, the process comprising: combining water, potassium bifluoride, a fumed silica, potassium tetraborate and potassium fluoroborate.

2. The process of claim 1, further comprising combining the boric acid-free flux composition with boron.

3. The process of claim 2, wherein combining the boric acid-free flux composition with boron comprises combining boron in the amount of 0.1-2 weight % on the basis of the total weight of the boric acid-free flux composition.

4. The process of claim 1, further comprising combining the boric acid-free flux composition with a wetting agent.

5. The process of claim 4, wherein combining the boric acid-free flux composition with the wetting agent comprises combining the wetting agent in the amount of 0.1-1% weight % on the basis of the total weight of the boric acid-free flux composition.

6. The process of claim 1, further comprising combining the boric acid-free flux composition with a pigment comprising phthalocyanine, a wetting agent, and boron.

7. The process of claim 1, further comprising combining the boric acid-free flux composition with a pigment comprising phthalocyanine and a wetting agent, wherein the boric acid-free composition comprises approximately, on the basis of the total weight of the boric acid-free paste flux composition totaling 100 weight %: the wetting agent in the amount of 0.1-1 weight %; potassium bifluoride in the amount of 12-16 weight %; the fumed silica in the amount of 0.1-4 weight %; potassium tetraborate tetrahydrate in the amount of 26-35 weight potassium fluoroborate in the amount of 26-35 weight %; the pigment in the amount of 0.1-2 weight %; and water in the amount of balance.

8. The process of claim 1 further comprising combining the boric acid free flux composition with a wetting agent and boron, wherein the boric acid-free composition comprises approximately, on the basis of the total weight of the boric acid-free paste flux composition totaling 100 weight %: the wetting agent in the amount of 0.1-1 weight %; potassium bifluoride in the amount of 12-16 weight %; the fumed silica in the amount of 0.1-4 weight %; potassium tetraborate tetrahydrate in the amount of 26-35 weight %; potassium fluoroborate in the amount of 26-35 weight %; boron in the amount of 0.1-2 weight %; and water in the amount of balance.

9. The process of claim 1, wherein combining comprises combining, approximately, on the basis of the total weight of the boric acid-free paste flux composition totaling 100 weight %, one or more of the following amounts: potassium bifluoride in the amount of 12-16 weight %; the fumed silica in the amount of 0.1-4 weight %; potassium tetraborate tetrahydrate in the amount of 26-35 weight %; and potassium fluoroborate in the amount of 26-35 weight %.

10. The process of claim 1, further comprising combining the boric acid-free flux composition with a pigment.

11. The process of claim 10, wherein the pigment comprises phthalocyanine.

12. The process of claim 10, wherein the pigment is configured to change a color of the boric acid-free flux at an activation temperature of the boric acid-free flux.

13. The process of claim 10, wherein combining the boric acid-free flux composition with the pigment comprises combining the pigment in the amount of about 0.1-2 weight % on the basis of the total weight of the boric acid-free flux composition.

Description

DETAILED DESCRIPTION

(1) The best mode for carrying out the invention will now be described for the purposes of illustrating the best mode known to the applicant at the time of the filing of this invention. The examples are illustrative only and not meant to limit the invention, as measured by the scope and spirit of the claims.

(2) As used herein, the term approximately or about means within the stated ranges with a tolerance of 10%.

(3) The present brazing flux composition is boric acid free, provides good wetting characteristics and changes color from a color in the visible spectrum to clear at activation temperature.

(4) The invention will now be described in a series of non-limiting, but illustrative examples.

(5) Boric acid has a melting temperature of approximately 336 F. (169 C.) and melts early during heating in the brazing process. This allows boric acid brazing fluxes to begin melting at low temperatures, well before brazing temperature is reached, thereby protecting the faying surfaces from further oxidation. Additionally, this low melting temperature, coupled a boiling/dehydration temperature of approximately 532 F. (300 C.) helps to create brazing fluxes that hot rod well, that is to say that the flux will melt, then subsequently freeze, adhering to heated brazing rod. By the time boric acid reaches 842 F. (450 C.) it completely dehydrates (or decomposes releasing H.sub.2O) leaving boron trioxide, which protects the base and filler metal surfaces throughout the remaining brazing process. Replacing boric acid in a brazing flux requires the substitution of the boric acid with one or more compounds that can approximately duplicate the above properties.

(6) Several compounds have attributes which would lend themselves to a boric acid replacement. These options would include, at a minimum: a combination of potassium carbonate and di-ammonium phosphate; and ammonium fluoroborate or ammonium fluorosilicate and potassium tetraborate tetrahydrate. In general, sodium salts were not considered as a likely replacement due in large part to the sodium glare encountered when heated to brazing temperatures. In addition, sodium-borate salts were further removed from consideration because they are specified in EU regulation (EC) No 1272/2008 of the European Parliament and of the Council on classification, labeling and packaging of substances and mixtures as having the same restrictions and boric acid.

(7) Potassium carbonate offers protection at temperatures exceeding 1600 F. (871 C.); and combining potassium carbonate with diammonium phosphate (DAP) would allow protection from oxidation above 302 F. (150 C.). However, while meeting some of the replacement criteria, it was determined that this combination was not practical for a dry powdered flux due to the deliquescence of potassium carbonate, the tendency of the flux to absorb moisture. The high dissociation partial pressure of ammonia from DAP require that the flux remain in a tightly sealed container when it is not in use, to preserve flux chemical and physical properties. The release of ammonia is also an issue with the ammonia fluoroborate and fluorosilicate; the release of ammonia is exacerbated when the paste flux is made due to the ready dissociation of ammonia from its anionic counterparts in an aqueous solution, though water gain is not an issue. Although these flux formulations yield an adequate performance, better alternatives were pursued based on at least two factors: (1) the unpleasant ammonia fume, from flux application to heating; and (2) the probable change in flux properties through hygroscopic update over time.

(8) Potassium tetraborate is also found in brazing fluxes. It readily dissolves metallic (not refractory) oxides at high temperature almost as well as potassium pentaborate (also another replacement option) at a fraction of the cost. It was selected as an option to consider in the replacement of boric acid. Anhydrous potassium tetraborate alone does not melt until 1500 F. (816 C.) and is hygroscopic, converting to the tetrahydrate with prolonged exposure to humidity. Hydration of powdered anhydrous potassium tetraborate fluxes causes an uncontrolled change in flux properties over time and imposes unnecessary conditions and/or processing during manufacture. Hydration is an exothermic process that causes manufacturing concerns. While anhydrous powdered potassium tetraborate flux does perform adequately, the flux does not melt until the faying surface is hot enough to form additional oxides, which will subsequently need to be removed. Additionally this flux will not hot rod well due to the high melting temperature. For all of these reasons potassium tetraborate tetrahydrate was chosen as a preferred replacement over anhydrous potassium tetraborate as a boric acid substitute.

(9) The invention will now be described by a series of non-limiting examples.

EXAMPLE #1

(10) In one embodiment of the invention, a black high temperature paste flux is described, the composition of which includes a mixture of water, potassium tetraborate tetrahydrate, potassium bifluoride, boron, UDYLITE (Udylite 62 is a product of Enthone, 350 Frontage Road, West Haven, Conn.) and fumed silica in the following weight percentages.

(11) TABLE-US-00001 TABLE I High Temperature Boric Acid Free Paste Flux Weight Component Percentage water balance wetting agent 0.1-1% wetting agent/surfactant (UDYLITE 62) potassium bifluoride 12-16% etchant/clean base metal surface (KHF.sub.2) fumed silica (SiO.sub.2) 0.1-4% emulsifying agent/plasticizer potassium tetraborate 26-35% dissolve metallic oxides and protect tetrahydrate brazing surface from oxidation (K.sub.2B.sub.4O.sub.74H.sub.2O) potassium fluoroborate 26-35% dissolve metallic oxides and halides (KBF.sub.4) and protect brazing surface from oxidation boron 0.1-2% protect surface from oxidation at high brazing temperatures Total .sup.100% (all components will total 100%)

EXAMPLE #2

(12) In another embodiment of the invention, a low temperature boric acid free paste flux will include a mixture of water, potassium bifluoride, potassium tetraborate tetrahydrate, potassium fluoroborate, pigment, UDYLITE and fumed silica in the following weight percentages.

(13) TABLE-US-00002 TABLE II Low Temperature Boric Acid Free Paste Flux Weight Component Percentage water balance wetting agent 0.1-1% wetting agent/surfactant (UDYLITE 62) potassium bifluoride 12-16% etchant/clean base metal surface (KHF.sub.2) fumed silica (SiO.sub.2) 0.1-4% emulsifying agent/plasticizer potassium tetraborate 26-35% dissolve metallic oxides and protect tetrahydrate brazing surface from oxidation (K.sub.2B.sub.4O.sub.74H.sub.2O) potassium fluoroborate 26-35% dissolve metallic oxides and halides (KBF.sub.4) and protect brazing surface from oxidation pigment (phthalo- 0.1-2% active temperature indicator cyanine) Total .sup.100% (all components will total 100%)

(14) Copper Phthalocyanine Green No. 7 was employed in several compositions as a visual indicator of activation temperature. It decomposes in the range of temperature form 1022 F. (550 C.) to 1650 F. (900 C.), depending on the level of accessible oxidizing agents. Testing revealed reliable correlation between the color change of the low temperature (green) brazing fluxes from green to clear and brazing temperature, at the faying surfaces. Furthermore this color change did not appear to be dependent on the level of pigmentation.

EXAMPLE #3

(15) In another embodiment of the invention, a high temperature boric acid free powder flux will include a mixture of potassium tetraborate tetrahydrate, potassium fluorosilicate, potassium fluoroborate and boron in the following weight percentages.

(16) TABLE-US-00003 TABLE III High Temperature Boric Acid Free Powder Flux Weight Component Percentage potassium tetraborate 44-54% dissolve metallic oxides and protect tetrahydrate brazing surface from oxidation (K.sub.2B.sub.4O.sub.74H.sub.2O) potassium fluoro- 1-3% wetting agent/surfactant silicate (K.sub.2SiF.sub.6) potassium fluoroborate 44-54% dissolve metallic oxides and halides (KBF.sub.4) and protect brazing surface from oxidation boron 0.1-2% protect surface from oxidation at high brazing temperatures Total .sup.100% (all components will total 100%)

EXAMPLE #4

(17) In another embodiment of the invention, a low temperature boric acid free powder flux will include a mixture of potassium tetraborate tetrahydrate, potassium fluorosilicate, potassium fluoroborate and a pigment in the following weight percentages.

(18) TABLE-US-00004 TABLE IV Low Temperature Boric Acid Free Powder Flux Weight Component Percentage potassium tetraborate 44-54% dissolve metallic oxides and protect tetrahydrate brazing surface from oxidation (K.sub.2B.sub.4O.sub.74H.sub.2O) potassium fluoro- 1-3% wetting agent/surfactant silicate (K.sub.2SiF.sub.6) potassium fluoroborate 44-54% dissolve metallic oxides and halides (KBF.sub.4) and protect brazing surface from oxidation pigment (phthalo- 0.1-2% active temperature indicator cyanine 500-600 C.) Total .sup.100% (all components will total 100%)

(19) As described above, the phthalocyanine pigment is an aromatic macrocyclic compound that forms coordination complexes with many elements of the periodic table. These complexes are intensely colored which facilitates the color transformation at temperatures employed in the reaction. As described above, the phthalocyanine pigment is an aromatic macrocyclic compound that forms coordination complexes with many elements of the periodic table. These complexes are intensely colored which facilitates the color transformation at temperatures employed in the reaction from colored in the visible spectrum to essentially colorless at temperature. The phthalocyanine macrocyclic compound is illustrated below, and wherein a metallic ion would be coordination bonded to the nitrogen atoms, typically within the 5-membered rings.

(20) ##STR00001##

(21) The above compositions are useful for the brazing of metallic materials based on copper, silver, nickel and iron based alloys. Without being held to any one theory or mechanism of operation, the flux is used to remove the oxide layer and enable the wetting of the base materials. The activated flux creates a layer on the workpiece and removes any surface oxides. The color change at activation temperature is a distinct characteristic not seen when compared to fluxes commercially available for purchase.

(22) Compositions and combinations of the above fluxes were tested and met all AWS A5.31M/A5.31:2012 testing standards for water content, particle, adhesion, fluidity, fluxing action, flow, life and viscosity.

(23) The boric acid free fluxes described in Tables I-IV deliver excellent performance, standing on their own as brazing fluxes. As discussed below, the boric acid free fluxes deliver results often superior to commercially available standard fluxes that are not boric acid free.

(24) In addition, the following tests were performed on an additional series of fluxes synthesized using the compositions identified in Tables 1-6 with the performance criteria identified and defined below being characterized in Tables 1a-6a.

Oxide Removal

(25) All of the boric acid free fluxes dissolved all oxides from the base metal surface.

Activation Range

(26) All of the boric acid free fluxes are fully active, removing oxides, throughout the range of 1050 F.-1600 F. (566 C.-871 C.) and 1050 F.-1800 F. (566 C.-982 C.), for the low temperature (green) flux and the high temperature flux (black) respectively.

Hot Rodding

(27) Hot Rodding is the coating of a piece of brazing rod (filler metal) by dipping a hot end into a powdered flux. This is applicable to powder fluxes only. Both powder fluxes hot rodded extremely well.

Flux Flowability in Activation Range

(28) A flowability test was performed per AWS A5.31M/A5.31:2012. Flowability was good for both the boric acid free powders and the pastes.

Brazing Odor and Fumes

(29) There was very little objectionable odor and fumes throughout the brazing process for all of the boric acid free fluxes.

Activation Indicator

(30) The pigmented fluxes of Tables 2 & 4 were the only fluxes that had a visual indicator of activation temperature actually tested.

(31) In judging the performance of brazing flux formulations seven criteria were chosen: (1) Hot RodThe ability of a powder brazing flux to adhere to a hot brazing rod/wire. (2) Flux FlowHow well the molten flux spreads, or wets out, across the heated surface of the base-metal(s)more specifically, how well the molten flux flows along the brazing joint capillary and the immediately adjacent faying surfaces; (3) Metal FlowMetal flow is an arbitrary measure of the brazing flux's ability to lower the surface tension of the molten filler metal at the base-metal surfaceit is in general measured by how well the molten filler metal spreads, or wets out, across the heated surface of the base-metal(s)more specifically, how well the molten filler metal flows along the brazing joint capillary and the immediately adjacent faying surfaces; (4) Acrid OdorThe quantity of fumes and smoke emitted and how irritating, sharp or pungent they are; (5) Flux CompositionThe homogeneity and ease of application; (6) Flux ResidueThe ease with which flux residue is removed; and (7) Hot CleanThe ease with which flux residue is removed using hot water alone.

(32) Each criterion is evaluated for the flux formulation as having a subjective value between one and five, where 1 (one) is not desirable and 5 (five) is desirable.

(33) In the following examples, testing was performed on eight powdered and three paste flux test formulations of varying components and/or combined in varying ratios. Of these formulations six contained boric acid to establish several benchmarks. SSP-4 was chosen as our baseline for powdered flux (Tables 1 & 1a) and SSWF as the baseline for the paste flux (Tables 2 & 2a). None of the initial testing was for boron-containing (high temperature) fluxes. The assumption was made that a successful low temperature flux can be used as a basis for a high temperature flux. Experience with prior art compositions bear this out. Furthermore, the green phthalocyanine pigment was not included in the functional tests of the low temperature fluxes, as it is present in levels deemed too low to be of any significance to the performance of the flux, other than to provide visual indication to the operator.

Initial Powder Fluxes

(34) TABLE-US-00005 TABLE 1 Composition (% mass) Test No NH.sub.4BF.sub.4 (NH.sub.4).sub.2SiF.sub.6 H.sub.3BO.sub.3 C.sub.6H.sub.8O.sub.7 K.sub.2SiF.sub.6 (NH.sub.4).sub.2PO.sub.4 K.sub.2CO.sub.3 KBF.sub.4 KF K.sub.2B.sub.4O.sub.74H.sub.2O SSP-1 22 5 9 64 SSP1-a 21 6 10 63 SSP1-b 22 12 13 53 SSP-f 5 22 9 64 SSP-16 10 30 10 20 30 SSP-28 10 10 60 20 SSP-6 15 5 20 10 50 SSP-4 20 10 10 50

(35) TABLE-US-00006 TABLE 1a Base Hot Flux Metal Acrid Flux Flux Hot Test No Metal Rod Flow Flow Odor Comp Residue Clean SSP-1 Copper 1 4 3 2 5 4 5 Stainless 1 3 3 2 5 4 5 SSP1-a Copper 1 3 3 2 5 4 5 Stainless 1 3 3 2 5 4 5 SSP1-b Copper 1 3 4 1 4 3 4 Stainless 1 3 3 2 4 3 4 SSP-f Copper 2 3 3 2 3 3 5 Stainless 2 3 4 2 3 3 4 SSP-16 Copper 1 4 4 4 5 5 5 Stainless 1 4 4 4 5 5 5 SSP-28 Copper 5 4 4 4 4 4 4 Stainless 5 4 4 4 4 4 4 SSP-6 Copper 3 5 3 2 5 4 5 Stainless 3 5 3 2 5 4 5 SSP-4 Copper 4 5 3 3 5 4 5 Stainless 4 5 3 3 5 4 5

Initial Paste Fluxes

(36) TABLE-US-00007 TABLE 2 Composition (% mass) Udylite Test Copper No H.sub.3BO.sub.3 Wetting (NH.sub.4).sub.2PO.sub.4 KHF.sub.2 K.sub.2CO.sub.3 KBF.sub.4 KF Water SSP- 10 20 10 10 20 30 Bal- 11 ance SSP- 20 20 10 10 20 20 Bal- 12 ance SSWF 41 0.03 18 18 Bal- ance

(37) TABLE-US-00008 TABLE 2a Base Hot Flux Metal Acrid Flux Flux Hot Test No Metal Rod Flow Flow Odor Comp Residue Clean SSP-11 Copper N/A 4 3 3 5 4 5 Stainless N/A 4 3 3 5 4 5 SSP-12 Copper N/A 5 3 2 5 4 5 Stainless N/A 5 3 2 5 4 5 SSWF Copper N/A 5 3 4 5 4 5 Stainless N/A 5 3 4 5 4 5

(38) Potassium tetraborate is a common component in brazing fluxes. It readily dissolves metallic (not refractory) oxides at high temperature; this makes it a natural consideration for replacement of boric acid; for these reasons it was actually the chemical of first choice. Anhydrous potassium tetraborate alone does not melt until 1500 F. (816 C.) and is hygroscopic, converting to the tetrahydrate with prolonged exposure to humidity. Hydration of powdered anhydrous potassium tetraborate fluxes causes an uncontrolled change in flux properties over time and imposes unnecessary conditions and/or processing during manufacture. Hydration is an exothermic process that causes manufacturing concerns. While anhydrous powdered potassium tetraborate flux does perform adequately, the flux does not melt until the faying surface is hot enough to form some additional oxides, which will subsequently need to be removed; additionally this flux will not hot rod well due to the high melting temperature. For these reasons potassium tetraborate tetrahydrate was chosen as a preferred embodiment over anhydrous potassium tetraborate. Boric acid in both the powder and paste fluxes was replaced with potassium tetraborate tetrahydrate. This replacement was approximately a 1:1 molar ratio of borate content for both fluxes initially, and then adjusted against the wetting agent(s) to achieve the optimal performance.

Testing of Low Temperature (Green) Powder Boric Acid Free Flux Formulations

(39) TABLE-US-00009 TABLE 3 Composition (% mass) Test No K.sub.2SiF.sub.6 KBF.sub.4 K.sub.2B.sub.4O.sub.74H.sub.2O SSP-2 18 57 25 SSP2-a 18 52 30 SSP2-b 20 40 40 SSP2-c 14 43 43 SSP2-d 10 45 45 SSP2-e 8 46 46 SSP2-f 6 47 47 SSP2-g 2 49 49

(40) TABLE-US-00010 TABLE 3a Base Hot Flux Metal Acrid Flux Flux Hot Test No Metal Rod Flow Flow Odor Comp Residue Clean SSP-2 Copper 2 4 4 2 5 4 5 Stainless 2 3 3 2 5 4 5 SSP2-a Copper 2 4 4 2 5 4 5 Stainless 2 3 3 2 5 4 5 SSP2-b Copper 2 4 4 2 5 4 5 Stainless 2 3 3 2 5 4 5 SSP2-c Copper 2 4 4 2 5 4 5 Stainless 2 3 3 2 5 4 5 SSP2-d Copper 3 4 4 2 5 4 5 Stainless 3 3 4 2 5 4 5 SSP2-e Copper 3 4 4 3 5 4 5 Stainless 3 3 4 3 5 4 5 SSP2-f Copper 4 4 5 4 5 4 5 Stainless 4 4 4 4 5 4 5 SSP2-g Copper 5 5 5 4 5 4 5 Stainless 5 5 5 4 5 4 5

Testing of High Temperature (Black) Powder Boric Acid Free Flux Formulations

(41) TABLE-US-00011 TABLE 4 Composition (% mass) Test No Boron K.sub.2SiF.sub.6 KBF.sub.4 K.sub.2B.sub.4O.sub.74H.sub.2O SSP2-h 5 5 50 40 SSP2-i 4 6 48 42 SSP-j 3 3 46 46 SSP-k 2 3 47 47 SSP-l 2 3 48 48 SSP-m 1 3 48 48

(42) TABLE-US-00012 TABLE 4a Base Hot Flux Metal Acrid Flux Flux Hot Test No Metal Rod Flow Flow Odor Comp Residue Clean SSP2-h Copper 1 2 3 3 5 3 5 Stainless 1 2 3 3 5 2 4 SSP2-i Copper 2 2 3 3 5 3 5 Stainless 2 2 3 3 5 2 4 SSP-j Copper 3 2 3 3 5 3 5 Stainless 3 2 4 3 5 3 5 SSP-k Copper 3 3 3 3 5 4 5 Stainless 3 3 4 3 5 3 5 SSP-l Copper 4 4 4 4 5 4 5 Stainless 4 4 4 4 5 4 5 SSP-m Copper 5 5 5 4 5 4 5 Stainless 5 5 5 4 5 4 5

Testing of Low Temperature (Green) Paste Boric Acid Free Flux Formulations

(43) TABLE-US-00013 TABLE 5 Composition (% mass) Udylite Fumed Copper Test No SiO.sub.2 Wetting KHF.sub.2 KBF.sub.4 K.sub.2B.sub.4O.sub.74H.sub.2O Water SSP-48 2 1 23 23 28 Balance SSP48-A 2 1 20 23 30 Balance SSP48-B 1 0.75 15 30 31 Balance SSP-C 1 0.05 15 32 32 Balance SSP-D 1 0.5 14 32 32 Balance

(44) TABLE-US-00014 TABLE 5a Base Hot Flux Metal Acrid Flux Flux Hot Test No Metal Rod Flow Flow Odor Comp Residue Clean SSP-48 Copper N/A 2 3 2 4 4 3 Stainless N/A 2 2 2 4 4 3 SSP48-a Copper N/A 3 3 2 4 4 4 Stainless N/A 2 3 2 4 4 4 SSP48-b Copper N/A 3 3 2 4 4 4 Stainless N/A 3 3 2 4 4 4 SSP-c Copper N/A 4 4 3 4 4 5 Stainless N/A 4 3 3 4 4 5 SSP-d Copper N/A 5 5 4 5 4 5 Stainless N/A 5 5 4 5 4 5

Testing of High Temperature (Black) Paste Boric Acid Free Flux Formulations

(45) TABLE-US-00015 TABLE 6 Composition (% mass) Udylite Test Fumed Copper No Boron SiO.sub.2 Wetting KHF.sub.2 KBF.sub.4 K.sub.2B.sub.4O.sub.74H.sub.2O Water SSP- 4 2 2 25 38 28 Bal- 50 ance SSP50- 3 2 2 23 36 29 Bal- a ance SSP50- 2 1 1 17 35 30 Bal- b ance SSP50- 1 1 0.75 15 33 31 Bal- c ance SSP50- 1 1 0.5 14 32 32 Bal- d ance

(46) TABLE-US-00016 TABLE 6a Base Hot Flux Metal Acrid Flux Flux Hot Test No Metal Rod Flow Flow Odor Comp Residue Clean SSP-50 Copper N/A 3 3 2 4 4 4 Stainless N/A 2 3 2 4 4 4 SSP50-a Copper N/A 3 3 3 4 4 4 Stainless N/A 3 3 3 4 4 4 SSP50-b Copper N/A 4 4 3 4 4 5 Stainless N/A 3 4 3 4 4 4 SSP50-c Copper N/A 4 5 4 5 4 5 Stainless N/A 4 4 4 5 4 5 SSP50-d Copper N/A 5 5 4 5 4 5 Stainless N/A 5 5 4 5 4 5

(47) The invention has been described with reference to preferred and alternate embodiments. Obviously, modifications and alterations will occur to others upon the reading and understanding of the specification. It is intended to include all such modifications and alterations insofar as they come within the scope of the appended claims or the equivalents thereof.