Removing and Replacing GTA Furnace Electrodes

Answer

This Information Applies To: Agilent GTA 120, 240/280 GTA Furnace

Issue

Over time, the electrodes may become pitted or eroded and users may see a decrease in precision or begin to experience the "Tube fault" error when new tubes are installed. If any of these instances occur, the electrodes should be replaced.

Requirements

• Replace electrodes in pairs. Single electrode replacements are not recommended. 
  
• Always remove the electrode on the right first, then the left electrode. 
  
• Always replace the left electrode first, then the right electrode. 
  
• Remove both electrodes first before attempting to fit the replacement electrodes. 
  
• When using the tool kit, follow the instructions exactly to avoid damage to components.
  

Items Required

• Both electrodes, press-fitted to their housings.
• Electrode extractor tool (p/n 9910031200)

Steps to Follow

Removing the Furnace Electrodes

Warning: Ensure that the control unit is switched off and unplugged. Ensure that the workhead has been allowed to cool completely before proceeding.

Before replacing the electrodes, disassemble the GTA Furnace workhead.

Figure 1. Direction of removal

1. 1. Pass the draw bolt of the tool kit through the right side electrode from the outside of the workhead. The threaded portion should extend past the electrode. (Figure 2).
      

      
      
      Figure 2. Passing the draw bolt through the electrode
      
      

   2. Place the spacer over the other side of the electrode. It should fit onto the inner face of the housing.  
   3. Place the shoulder face of the collar on the spacer, followed by the PTFE washer (Figure 3).
      

      
      
      Figure 3. Placing the spacer over the electrode, follow with the collar and washer on top of the spacer
      
      

   4. Place the textured nut onto the washer and twist until the head of the bolt is against the electrode. This can be seen from the outside window of the furnace. Ensure the head of the bolt fits onto the electrode (Figure 4). 
      

      
      
      Figure 4. Placing the textured nut
      
      

   5. Draw the electrode into the spacer by rotating the textured nut clockwise using the wrench included in the kit (Figure 5).
      

      
      
      Figure 5. Placing the wrench onto the nut and twisting
      
      

   6. Continue to turn clockwise until the electrode and tool kit are drawn fully through the spacer (Figure 6).
      

      
      
      Figure 6. Drawing the electrode through the spacer
      
      

   7. Once the electrode is drawn out, remove the nut from the bolt and dismantle the tool kit. Discard the used electrode (Figure 7).
      

      
      
      Figure 7. Removing the nut and dismantling the tool kit
      
      

8. Repeat steps 1 through 6 on the left side electrode (Figure 8)

   

Figure 8. Repeating steps 1 through 6 on the left side electrode

Replacing the Furnace Electrodes

Caution: Always replace the left side electrode first.

     

Figure 9. Direction of installation.

Warning: Hot Surface Contact with hot furnace atomizer surfaces can cause serious burns. Always switch off the control unit, disconnect the power supply cable, and allow time for the workhead to cool to a safe handling temperature before handling.

1. 1. 1. Fit the adapter onto the bolt of the tool kit, so that the bolt fits into the slot. The adapter protects the electrode during the procedure (Figure 10). See Figure 9 for direction of installation.
         

         
         
         Figure 10. Fitting the adapter onto the bolt
         

      2. Place the new electrode over the bolt thread, with the thinner side of the electrode into the adapter, until the electrode sits inside the adapter (Figure 11).

         
         
         Figure 11. Placing the new electrode over the bolt thread
         
         

      3. Hold the bolt, adapter, and electrode, and position the electrode against the inner side of the electrode housing. Ensure that the electrode is straight and seated in the adapter so that it will enter the housing aligned (Figure 12).

         
         
         Figure 12. Installing the bolt, adapter, and electrode into the electrode housing
         
         

      4. Fit the shouldered face of the collar onto the bolt from the outside of the furnace, followed by the PTFE washer. Fit the textured nut on the washer and thread onto the bolt (Figure 13).

         
         
         Figure 13. Fitting the collar and washer onto the bolt
         
         

      5. Using the wrench provided in the kit, rotate the nut onto the assembly until it is held into position. The shouldered face of the collar fits into the window on the outside of the electrode housing (Figure 14).

         
         
         Figure 14. Rotating the nut onto the assembly
         
         

      6. Rotate the nut until the electrode is pulled into the housing evenly (Figure 15).

         
         
         Figure 15. Electrode is pulled into the housing evenly 
         
         

         Caution: Once you feel resistance, stop tightening the nut. Over-tightening the nut will crack or damage the electrode.

      7. Remove the nut from the bolt and carefully remove the tool kit (Figure 16).

         
         
         Figure 16. Removing the nut and tool kit

      8. Repeat steps 1 through 7 on the right side electrode (Figure 17).

                 
         
         Figure 17. Repeating steps 1 through 7 on the right side electrode

         Tips: To ensure that the electrodes are fitted correctly, place a graphite tube between the two electrodes. Without the center block (the shroud) in place, clamp the electrodes together. You should be able to turn the graphite tube with your fingers. If there is too much resistance, the electrodes may need to be pushed into the furnace bore further

The workhead can now be re-assembled. See Removing the GTA Furnace Workhead.