PRAXAIR AND TAFA Molybdenum (Mo) - 13T

Transcription

1 File: T Issue: Supercedes: K10320 PRAXAIR AND TAFA Molybdenum (Mo) - 13T Material Review: Molybdenum wire has not normally been sprayed with arc spray. Up until now, with inert, reducing or oxidizing atomizing gas the arc spray coating could probably be made equivalent to gas coatings with the attendant advantages of arc. Praxair and TAFA applications engineers have developed a molybdenum wire and parameters that meet or exceed aircraft and commercial specifications. Arc Spray 13T, Molybdenum wire can be sprayed with any Praxair and TAFA Arc Spray gun. Arc Spray 13T Molybdenum wire meets the following specifications: PWA For PWA Rev D, Rolls Royce MSSR9507/19 and Garrett FP5045 Type 1. CAUTION: All Praxair and TAFA wireshave been optimized for arc spraying. Use ofalternate wires usually cause problems such asexcessive tip wear, spitting and feedingproblems. We only recommend Praxair and TAFA certified wires. Application Review: Arc sprayed, molybdenum exhibits excellent adhesion to steels and is used as a bond coat where other methods of preparation are impossible or undesirable. Coating hardness can be controlled over a wide range by varying air pressure and spray distance. Coatings exhibit good bearing properties and high resistance to galling, scuffing and "pick-up" as well as good wear and abrasion resistance. Molybdenum is not recommended for use above 400 C (752 F).

2 Composition: Molybdenum 99+% Coating Physical Properties Wire Size Deposit Efficiency Melting Point Bond Strength Coating Texture 1/16" (1.6 mm) and 2 mm Percent* Approx C (4532 F) 7844 psi Variable*,** (see next page) Hardness R c Coating Density Coating Weight Shrink Adhesion Spraying: Spray Rate Coverage (wire consumption) Spray Pattern(approximate 8" standoff) Length of wire per lb gm/cc*** lb/ft 2 /mil in/in (cm/cm) Up to 5500 psi (37.9 MPa) when sprayed under the correct conditions, Molybdenum is self bonding to ferrous and aluminum based alloy. This bond is normally higher than the cohesive strength of the deposit, therefore, when tested to destruction rupture occurs within the deposit. 10 lb/hr/100 amps 1.13 oz/ft 2 /0.001 in (1.38 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 70 ft. * Depends on nozzle cap and air pressure and atomizing gas type ** 6" standoff, 40 psi , depends on air pressure - fine with high psi, average with medium psi, and rough with low psi. *** Depends on atomizing air pressure. **** Higher air pressures, smaller wire (1/16"), and lower amperage with a green nozzle cap gives smallest diameter pattern. Page 2

3 Spraying Procedure Coating Type Normal 8830/35 ArcJet 8830/35 Arc Jet Atomizing Air Pressure:Primary Secondary 50 c c 40 c 60 c 60 c 60 c --- Nozzle Cap Blue * Green Green Nozzle/Positioner (Cross=C; Slot=S) Short C ** Long C Long C Arc Load Volts a Amps b Standoff Inches Coating Thickness/Pass-mils Coating Texture-microinches aa ***Tips - Always use P/N for 13T 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 1: 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 & 9000) *** P/N Tips for Aluminum NOTE 2: In setting up the 8830 or Standard or Arc Jet, push the contact tubes forward until the back end of them with the power leads are flush with the alignment housing. This will maximize the bond strength, optimize the microstructure and give consistent results. a b c When using power lead extensions other than the normal 12 foot furnished, the voltage must be increased by approximately 3.4 volts per 50 ft. 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. Can vary between depending on size of workpiece and traverse speed. For finer finish, raise air pressure at point of finish.. Page 3

4 Finishing: Sprayed Molybdenum coatings must be finished by grinding. Where used as a bond coat no further treatment is required prior to the application of subsequent coatings. The following grinding parameters are recommended: Speeds - Wheel, SFPM: 6000 m/s: 0.29 Work, m/s: 0.37 Traverse Feed - Roughing: 1/3 wheel width per revolution Finishing: 1/7 wheel width per revolution These are starting recommendations. Diamond wheels remove stock with less wear, but will not produce better finishes for equivalent grain size. Service Limitations: Although Molybdenum has a very high melting point, one of its oxides is volatile at a comparatively low temperature. Catastrophic oxidation of Molybdenum may occur in oxidizing atmospheres at elevated temperatures and even where the atmosphere is not oxidizing. Hazards: Observe normal spraying practices, respiratory protection and proper air flow pattern advised. See AWS Publication AWS C2.1-73, "Recommended Safe Practices for Thermal Spraying" on general spray practices 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. 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