Praxair and TAFA Arc Spray Bond Wire79B

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1 File: Issue: Supercedes: B I11229 I10816 Praxair and TAFA Arc Spray Bond Wire79B Material Review: 79B wire, a unique nickel-aluminum alloy for use in arc spray systems, is available from Praxair and TAFA. The wire produces superior bond coats that are dense and resistant to high temperature oxidation, thermal shock and abrasion. The material is equally suitable as a one-coat system; for example, a finish of five (5) microinches is attainable. This wire is manufactured exclusively for wire arc spraying. The unusual self-bonding ability of the alloy is attributed to the exceptionally high temperatures the nickel-aluminum reaches and which on impact with the base material, forms a strong bond. Measured bond strengths have been determined to be 55 percent higher than those formed by exothermic reactions of nickel and aluminum mixtures -- the previous materials available to demonstrate such self-bonding characteristics. One of the major problems in achieving high quality, well bonded coatings in any thermal spray process is the costly, extensive preparation of the substrate. 79B eliminates the problem. The coating, through extensive testing, has also been found to be superior to exothermic materials in sharp edge and impact loading. 79B wire is self-bonding to a broad range of smooth metal surfaces including annealed or hardened carbon steels, annealed or hardened alloy steels, stainless steels, aluminum, nickel, cast iron, titanium and tantalum. It is not self-bonding to copper based alloys or tungsten. 79B wire can be sprayed with any Praxair and TAFA arc spray gun. Praxair and TAFA's 79B meets the following specification = Rolls Royce Omat #3/90A CAUTION: All Praxair and TAFA wires have been optimized for arc spraying. Use of alternate wires usually cause problems such as excessive tip wear, spitting and feeding problems. We only recommend Praxair and TAFA certified wires. Application Review: Arc spray coatings from to inch (0.01 to mm) can be readily applied in one pass. Thicker coatings up to inch (6.3 mm) have been applied by continuous spraying. Thus, in some cases, 79B can be used as a one-coat system. Coatings can be machined to a rough finish with tungsten carbide tools or ground to smooth finish with aluminum oxide or silicon carbide wheels. 79B wire can be sprayed directly on a smooth, chemically clean surface without conventional blasting, turning or roughening, thereby, eliminating the need for expensive preparation equipment and the associated labor and quality control. However, where possible, the surface should be prepared by rough cutting (thread), rough grinding, grit blasting (24 mesh steel shot or aluminum oxide at 80 psig pressure blast) or using a clean coarse emery cloth since this increases bond strength by an additional 600 psi. In any case, note that the surface to be sprayed must be clean, freshly exposed metal. Since 79B coatings look like stainless steel, it is cosmetically acceptable to many end users as a finish coat. Typical properties of the Praxair and TAFA nickel-aluminum arc spray coating when sprayed on a clean but unroughened (unprepared) steel surface include: bond strength psi; with a typical coating hardness of R b.

2 Composition: (Typical) Nickel Al 80 percent 20 percent Coating Physical Properties: Wire Size Deposit Efficiency Melting Point Bond Strength Tensile Coating Texture (as sprayed) Hardness Coating Density Coating Weight Magnetic Properties Abrasion Resistance Impact, Sharp Edge and Bend Resistance Coefficient of Thermal Expansion Electrical Resistivity Heat Resistance 1/16 in (1.6 mm) 70 Percent 2642 F (1450 C) 9,000 psi blasted Variable b (see next page) R b 7.4 gm/cc c lbs/ft 2 /mil Non-magnetic, slight magnetic susceptibility Good Excellent 7 x 10-6 in/in F (1000 F) 220 micro ohm cm (approximate) Good d Spraying: Spray Rate Coverage (wire consumption) Spray Pattern c (approximate 8 inch standoff) Length of wire per lb 10 lbs/hr/100 amps (4.5 kg/hr/100 amps) 0.9 oz/ft 2 /0.001 in (1.10 kg/m 2 /100 microns) Cross Nozzle/Positioner - 1 in (2.5 cm) vertical height x 1-3/4 in (4.4 cm) width Slot Nozzle/Positioner - 2 in (5 cm) vertical height x 1 in (2.5 cm) width 84 ft. (1/16 in) a b c d e Values are for steel substrates according to ASTM C inch standoff, 40 psi , depends on nozzle cap, air pressure - fine with high psi, average with medium psi, and rough with low psi. Density depends on air pressure - 80 percent "Bond Coat" setting, 90 percent subsequent buildup. No evident nickel alloy/substrate scaling with inch coating after: five 1000, three 1800 F, F Higher air pressures, smaller wire (1/16), and lower amperage with red nozle cap gi ves smallest diameter pattern. Page 2

3 Spraying Procedure: Coating Type Normal Arc Jet Arc Jet / / Atomizing Air Pressure:Primary Secondary 50 c c --- Nozzle Cap Green * Green Green Nozzle/Positioner (Cross=C; Slot=S) Long C ** Long C Long C Arc Load Volts a Amps b Standoff Inches Coating Thickness/Pass-mils Coating Texture-microinches aa a When using power lead extensions other than the normal 12 foot furnished, the voltage must be increased by 3.4 volts per 50 foot of extension; i.e., add 3.4 volts to the recommended voltage setting for a given wire if the extension is increased to a 50 foot length. b Can vary between depending on size of work piece and traverse speed. c For finer finish, raise air pressure at point of finish. Using excessive voltage reduces quality of coating. Voltage should be adjusted to give minimum noise and smooth arc operation. Excessive voltage causes larger particles and poor spray pattern. Too low a voltage will cause popping. Be sure not to overheat substrate even if this means stopping to allow cooling, use air jet cooling if greater speed is required. Note that on some applications where preheating is tolerable, preheating work to 300 F can improve bond and deposit efficiency. NOTE: Standard air caps and positioners can be used in 8830 or 9000 systems. * P/N Arc Jet Air Cap ** P/N Arc Jet Modified Short Cross (8830 & 8835) Finishing: An exceptionally good finish can be achieved by turning: Surface Speed Traverse Speed Depth of Cut 1.27 m/s (250 fpm) 38 cuts/cm (96 cuts/in) ( in) 250 micon (0.010 in) for first few cuts then 125 micron (0.005 in) to finish Tungsten carbide tools can be used to obtain a rough finish and grinding to obtain a good smooth finish. Use light cuts for roughing and finishing. Dress frequently and do not permit coating to overheat. High nickel alloys are difficult to finish. If a grinding wheel is used, it may tend to load up which in turn tends to smear the coating or increase pull-out. If a cutting tool is used, even a ceramic or diamond tool, pull out may be a problem on the very hardest coatings. However, it is fairly easy to generate a 20-microinch finish using the correct grinding wheel and grinding technique. A 15-microinch finish can be obtained with care. Secondary finishing is required below 10 microinch. Grinding must be taken in stages, working down in finish with successively finer finishing surfaces. Page 3

4 A typical grinding wheel specification obtained from Norton and others could be: Silicon carbide 37 C I hardness 8 porosity Vitrified open wheel Typical Grinding Setup: Wheel rpm: Med/High Shaft rpm: Low SFPM: High with the work running opposite the wheel Amount removed per pass Use very light pressure and clean wheel. Secondary finishing with either silicon carbide or diamond cloth using a mineral base (non-sulfur) 5 to 10 weight hydraulic oil or kerosene can produce finishes below 10 microinches AA. Typically, it is a good idea to start with a 240 grit paper, then progress to 320, 400 and perhaps to 600, 1200, even If diamond cloth is selected, one should use a 9 to 15 micron particle size (obtained from 3M or others). The objective is to use the 240 cloth to completely remove the grinding marks from the 37C wheel. Then, use the 320 cloth to remove the marks from the 240 cloth. Then use the and so on. If one switches to the finer cloths too soon, a high polish will result on the "high spots", but many of the original deep grinding marks will remain. Patience is the secret to the art. A series of a 1/2" diameter shafts were finished at Praxair and TAFA following these principles. The finish on the 79B coated shafts was judged to be "approaching 8 microinches"; i.e., definitely better than 16, but clearly not as good as 4. Speeds & Feeds Dry Grinding Wet Grinding Wheel Speed SFPM Work Speed SFPM rough Wheel Traverse IPM 7 rough finish In Feed (inches) rough finish Coolant -- Water Sol, 1-50 Note: See Bulletin for aircraft rear turbine case machining recommendations ( SFM, 0.008" feed). Hazards: Observe normal spraying practices, respiratory protection and proper airflow patterns advised. For general spray practices, see AWS Publications AWS C2.1-73, "Recommended Safe Practices for Thermal Spraying and AWS TSS-85, "Thermal Spraying, Practice, Theory and Application." Thermal spraying is a completely safe process when performed in accordance with proper safety measures. Become familiar with local safety regulations before starting spray operations. DO NOT operate your spraying equipment or use the spray material supplied before you have thoroughly read the Praxair and TAFA Instruction Manual. A Material Safety Data Sheet will be sent with each initial purchase and updated as required. DISREGARDING THESE INSTRUCTIONS MAY BE DANGEROUS TO YOUR HEALTH. The Information provided herein is believed to be accurate and reliable; however, results may vary with workpiece preparation and operator technique. Praxair and TAFA warrants only that the wires are free of defects in material and workmanship. No other warranty is expressed or implied. Page 4

5 Copyright 2000 Praxair Technology, Inc. All rights reserved Telephone: Fax: Praxair, the Flowing Airstream design and Making our planet more productive are trademarks or registered trademarks of Praxair Technology, Inc. in the United States and/or other countries. Other trademarks used herein are trademarks or registered trademarks of their respective owners. Printed in the United States of America Telephone: Fax: TAFA is constantly improving its products, therefore specifications are subject to change without notice TAFA Incorporated is a Praxair Surface Technologies company. Page 5