- -  AGRICULTURE CORE CURRICULUM - - 

(CLF2000) Advanced Core Cluster: AGRICULTURAL MECHANICS

 (CLF2250) Unit Title: Oxyacetylene WELDING

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 (CLF2255) Topic:   Oxyacetylene BRAZING          Time     Year(s) 
                                                   5 Hours  1 / 2 / 3 / 4
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         Topic Objectives: Upon completion of this lesson, the students
                            will be able to:

         Learning Outcome #:

             (F-4) - Use the oxyacetylene equipment to braze mild steel.

             (F-7) - Select welding rods and fluxes appropriate for the
                       job.

         Special Material and Equipment: Oxygen and acetylene cylinders, 
                       regulators and hoses, torch, tips, open-end wrench, 
                       striker, goggles, gloves, flux, bronze filler rods, 
                       sheet metal, mild steel plate

          References: Cooper, Elmer L. (1987). AGRICULTURAL MECHANICS:
                         FUNDAMENTALS AND APPLICATIONS. Albany, NY: Delmar
                         Publishers.
                       Phipps, Lloyd J., & Reynolds, Carl L. (1990).
                         MECHANICS IN AGRICULTURE (4th ed.). Danville, IL:
                         Interstate Publishers.

           Resources: Deere & Company. (1987). WELDING (6th ed.) 
                         (Fundamentals of Service (FOS) Series). Available 
                         from: John Deere Technical Services, Dept. F, John 
                         Deere Road, Moline, IL 61265 (Available in
                         Spanish)

          Evaluation: Quiz by instructor.

TOPIC PRESENTATION: Oxyacetylene Brazing

A. Brazing 

   1. Brazing is the bonding (adhesion), rather than fusing (melting),
       of two metal objects.

   2. This adhesion connection is made with a minimum of alloy (bronze) 
       which melts above 800 degrees Fahrenheit and flows by capillary motion 
       between close-fitting metal.

   3. Brazing differs from braze welding in the following ways:
           1) Brazing requires a very thin joint, as when overlapping sheet 
               metal.

           2) Braze welding joints resemble those of fusion welding; there 
               is more bonding metal at the joint as compared to brazing. 

   4. Brazing can be used to join dissimilar metals.

   5. Brazing can be used to join thin pieces of metal in order to decrease 
       the danger of melting through.

   6. Brazing can be used on most commercial metals, where oxyacetylene 
       welding may have limitations.

B. Brazing Equipment

   1. Brazing uses the same welding apparatus as oxyacetylene welding.

   2. Flux required for bronze or brass brazing is usually a borax type
       consisting of sodium borate with other additives. (Flux is any 
       substance or mixture used to promote the fusion of metals or minerals, 
       for example, alkalies, borax, lime, fluorite, etc.)

       a. Flux removes all oxides from the metal surfaces to be welded.

       b. Flux forms a protective coating over the heated metal surfaces 
           that prevents oxidation.

       c. Flux floats the oxides and their impurities with which it combines 
           to the top of the molten metal.

   3. Bronze filler rods come in different sizes and have a lower melting
       point than the metal being bonded depending on their alloy 
       composition.

       a. Silicon bronze is used for copper sheet and mild steel.

       b. Nickel bronze is used for mild steel, cast iron, and wrought iron.

C. Operating the Oxyacetylene Equipment to Braze and Braze Weld

   1. Basic Brazing Technique:

       a. Set up the metal pieces to be joined.

       b. Select the appropriate torch tip.

       c. Adjust the torch to the appropriate gas pressures.

       d. Put on appropriate protective goggles and gloves.

       e. Light the torch with the striker and adjust the flame to slightly 
           oxidizing.

       f. Heat the bronze filler rod with the torch flame and and dip it in 
           the flux so that it becomes coated with flux.
       g. Heat the area on the metal to be bonded to a cherry red color and 
           "tin" it by applying a light coating of fluxed filler rod.

       h. After "tinning," finish the braze or braze weld by filling in the 
           joint with a non-fluxed filler rod.

   2. Brazing and Braze Weld Demonstrations

       a. Overlap Joint (Brazing)

           1) Overlap two pieces of sheet metal by approximately 1/4 inch.

           2) Using the proper gas pressure and flame adjustment, "tin" the 
               joint.

           3) After "tinning," go back over the joint with a non-fluxed
               filler rod to smooth the joint.

       b. Fillet Joint (Braze Welding)

           1) Set up the two pieces of sheet metal at right angles.

           2) Using the proper gas pressure and flame adjustment, "tin" the 
               joint.

           3) After "tinning," go back over the joint with a non-fluxed 
               filler rod to smooth the joint.

         _________________________________________________________
         ACTIVITY:

         1. Bond sheet metal by brazing.

         2. Bond mild steel plate by braze welding.
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