( back to top )

• Benefits of gas purging

• Operational requirements

• Types of plugs

• Wear mechanisms

• Ladle Refining station

• Oxygen removal

• Hydrogen removal

• 250 Ton ladle

• Temperature homonenizeation

• Sulfur removal

Benefits of gas Purging     ( back to top )     ( back to section 1 )

• Homogenizes the melt

• Removes contaminants

• Regulates temperature

Operational requirements for a purging plug     ( back to top )     ( back to section 1 )

Types of plugs we offer     ( back to top )     ( back to section 1 )

1. Durastir ND Plug (Non Directional)

2. Durastir DP Plug (Directional Plug)

3. We are also able to make plugs and blocks any size or composition to meet your needs.

4. We are also an agency for Special Shapes Refractory Co. which produces a plug called the stirpro

Wear Mechanisms     ( back to top )     ( back to section 1 )

Wear parameter of ladle purging plugs     ( back to top )     ( back to section 1 )

• Quantity of gas
• Pressure of gas
• Purging time
• Steel Quality (Viscosity)
• Steel Temperature
• Purging plug maintenance (Purification with O₂)
• Bottom Lining Life
• Purging Plug Type
• Ladle Circulation (Thermal Shocks)
• Infiltrations

Ladle refining station     ( back to top )     ( back to section 1 )

              Final Alloying

              Desulfurization

               Oxygen / Hydrogen removal

             Reheating

Oxygen removal - Porous plug     ( back to top )     ( back to section 1 )

Hydrogen removal     ( back to top )     ( back to section 1 )

250 ton ladle, diameter at top - 11.3 ft     ( back to top )     ( back to section 1 )

Temperature homogenization     ( back to top )     ( back to section 1 )

1. ABOVE GRAPH FOR 150 TON LADLE
2. INJECTION TIME 12 MINUTES
3. GAS FLOW 9 SCFM
4. GAS PRESSURE 49.7 PSI

• WITH BUBBLING TEMPERATURE STRATIFICATION WILL BE 50^OF OR LESS
• WITHOUT BUBBLING TEMPERATURE STRATIFICATION WILL BE 120^OF OR MORE

Standard CFM needed for sulphur removal     ( back to top )     ( back to section 1 )

Sulphur removal     ( back to top )     ( back to section 1 )

• Bottom of ladle

• Positions - Patterns - Dead zones

• Typical temperature profiles

Bottom of ladle     ( back to top )     ( back to section 2 )

Plug location = radius / 2

Measured after refractory lining is in place

Position - Pattern - Dead zones     ( back to top )     ( back to section 2 )

Typical ladle temperature profile     ( back to top )     ( back to section 2 )

• Stir plug procedures

• Flow control panel

• Comparative table for gases

• Theoretical argon gas pressure versus ladle height

Stir plug operating procedure     ( back to top )     ( back to section 3 )

1. Do not apply gas pressure to the plug exceeding 150psi.

2. Establish flow meter and back pressure reference points for your particular operation.

3. Perform a natural gas check to determine the operational readiness of the plug immediately after casting. See attached recommended procedure.

4. Between heats and after degassing, look for the safety shape change feature which will indicate when it is time for plug replacement.

5. In conjunction with the safety shape change feature, the life of the plug should be determined by accurately recording the number of stirring minutes on that particular plug. (Determining the life of a plug by the number of heats could be misleading and is not recommended.)

6. Best stirring practices do not break the slag cover. If a violent stirring practice is followed, as sometimes with desulfurizing, temperature control or vacuum degassing, follow-up with a soft stir without breaking the slag cover in order to remove impurities.

7. The major causes resulting in no stirs are:

   • Penetration

   • Skulls

   • Failure to pretest plug

   • Failure of gas supplying system

Schematic setup of the flow control panel at the steel plant     ( back to top )     ( back to section 3 )

Comparative table for gases     ( back to top )     ( back to section 3 )

Theoretical Argon gas pressure versus ladle height     ( back to top )     ( back to section 3 )

• Gunning mix protection

• Seating blocks - Pocket blocks

Gunning mix protection for replacement plug     ( back to top )     ( back to section 4 )

Seating block and pocket block     ( back to top )     ( back to section 4 )

• What to check

• The reason for plug failure

• Pipe sizing and obstructions

• Block repair and maintenance

• Leaking fittings and connections

• Checking the plug

• Brushing the plug

• Checking operational readiness

• Wear mechanisms

What to check when the plug does not work     ( back to top )     ( back to section 5 )

1. Was the plug pretested for gas flow?

2. Skull covering plug?

3. Leaks in gas supply line?

4. Check valve stuck in closed position?

5. Weak bubble?

6. Bypass gas valve left open?

7. Raw material additions piled on plug?

8. Is there solidified aluminum in the plug pipe?

9. Is the plug covered with gunning refractory?

10. Is there dirt, oil, water, etc. in the gas supply line?

The reason for the plug failure cannot be found ...

            Remove the plug and check the following:      ( back to top )     ( back to section 5 )

1. Ruptured casing

2. Was it caused by using excessive gas pressure above 150psi?

3. Steel / slag penetration

4. Was it caused by oxygen lancing?

5. Was slag forming additions, cal-sil, ferro silicon or aluminum added directly onto the ladle bottom?

6. Plug should be sectioned to observe for penetration.

Pipe sizing and obstructions     ( back to top )     ( back to section 5 )

Another common problem for gas purging are obstructions or kinks in the lines. Although these seldom affect the line pressure they can dramatically affect the volume or flow of gas to the vessel.

• Pipe sizing

  • i.e. ¾”to ½”pipe reduces volume. Try to keep consistent pipe sizing all the way.

• Bends and turns

  • every 90^o reduces volume.

• Long runs

  • every 10 feet of run reduces volume. Try to keep the runs short and straight.

• Hose reels

  • each loop around a hose reduces volume. Make sure the line is out when purging.

• Quick disconnects

  • many have a small ball valve that greatly reduces volume. i.e. many have only a ¼”opening.

• Check valves

  • same as above.

• GENERAL

  • Use common sense and follow the system from beginning to end. Do not enter closed gas-containing spaces without proper safety equipment, i.e. sniffers, etc. Inert gasses are odorless and can be very deadly.

Pipe sizing and obstructions     ( back to top )     ( back to section 5 )

These are placed in plugs to tell when the useful or safe life of the plug has been used. Do not ignore these warnings. Always remember – WHEN IN DOUBT -TAKE IT OUT! Either take the ladle out of service, change the plug, or gun over the plug, but do not use a plug that has worn to the indicator.

Block repair and maintenance     ( back to top )     ( back to section 5 )

As a rule, blocks that have worn to ½ the length of the plug should be replaced. Replacement plugs should be gunned up level with the floor immediately after installation. Minor cracks should be repaired from the cold face before installing the plug. Again, do not take chances. If you doubt the integrity of the block, take it out.

Leaking fittings and connections     ( back to top )     ( back to section 5 )

One of the most common problems found in gas purging are leaks which waste expensive gas, lead to weak or no stirs, and can create a venturi effect, clogging off the plug completely. While welded connections are preferred, this is not always possible, so the system should be checked periodically for leaks.

• One way is to listen

  • listen for high pressure leaks and hisses while the Argon or Nitrogen lines are hooked up. This is not always practical because of noise and the mill environment.

• The fittings can be soap tested, or one could use his hand to run over the connection to feel for leaks. Again, this works best for the high pressure gasses, and is not usually practical because of the time constraints.

• Odor

  • the smell of natural gas should immediately tell you there is a leak somewhere. Again, this is not a practical way to check for leaks. However, do not ignore this smell.

• Bag Test

  • Many mills use this to immediately show them if they have leaks. After the face of the plug is lanced and opened, a flame is then run along the piping while connected to the gas supply. A flame will indicate where there are leaks. All leaks should be eliminated as quickly as practical to save gas and insure stir performance. Some people actually use lit bags, others use rosebuds or torches, and others use lit rags on the end of an old lance pipe. If this method is used, it should only be used where the ladle is clearly accessible, and never in a pit or closed-in area. As always, safety equipment, including face shields, should be worn.

• GENERAL

  • Whichever method is used, make sure it can be done safely and quickly. While most mills have low natural gas pressures, there are some exceptions.

Checking the plug     ( back to top )     ( back to section 5 )

To achieve 100% stir performance a plug should be checked after each cast flow. Different plants use different methods to achieve the same goal.

• Back pressure

  • some us back pressure gauges to tell if they have flow. However, leaks in the system will give false readings.

• Bubble gauges

  • where the plastic ball bounces around with flow. Again, leaks will distort this reading.

• Flame test

  • Natural gas is connected to the plug and the face of the plug is observed for flame.

• GENERAL

  • While all of these have merit, the plug and surrounding block should always be looked at for excessive wear or use. Never ignore the safety or wear indicators.

Brushing the plug     ( back to top )     ( back to section 5 )

If the plug does not show flow, it may not stir with the next heat. One option is to change the plug but this is not always feasible. The second option is to brush the plug.

• Nitrogen

  • High-pressure nitrogen is applied to the plug and the hot-face of the plug is gently washed or brushed with oxygen until sparks are observed being blown back from the plug.

• Natural gas

  • Natural gas is applied to the plug, and the hot-face of the plug is gently washed or brushed until a flame is observed coming from the plug.

• Gradall

  • The face of the plug is scraped after each heat.

• GENERAL

  • When brushing a plug, try to stay 12”or more off the hot face of the plug and use a sweeping or brushing pattern. Oxygen is usually at very high pressures and will clog the plugs and prematurely wear out refractories if held too close. Always wear protective clothing and equipment when performing this function.

Checking the operational readiness of the porous plug after completion of casting    

                                                                                                         ( back to top )     ( back to section 5 )

After each casting, the operational readiness of the bubbling system should be checked for the next service period. Immediately after emptying the slag, natural gas or coke oven gas is hooked up to the porous plug. There will be ignition since the brick is still very hot. A flame indicates that gas flow exists (Figure 1 below).

If this is not the case, while leaving the gas in a turned on position, the porous plug must be cleaned of slag and steel residue from the inside of the ladle. This is done carefully with an oxygen lance having a very soft flame (Figure 2 below).

A black pipe with a 1” I.D. is recommended for the oxygen lance when used to clean plugs installed in ladles 100 ton or larger. For ladles 100 ton or smaller, a black pipe ½”– ¾” I.D. is suggested. Applied oxygen pressure should range 70-100psi.

The red glow will be seen during the period when the oxygen lance is burning off solid metal. Once the metal covering the plug is gone, the red will disappear and the color will turn dark or black to indicate oxygen cleaning completion.

If no gas flow can be achieved, the plug should be replaced.

Should the mentioned gas types not be available, it is possible to run a check with argon or nitrogen. However, there will become markedly darker in comparison to its surrounding. A heavy shower of sparks will indicate renewed operational readiness.

Using compressed air may be risky since the oxygen content may attack the steel casing.

The gas flow test must be conducted carefully and accurately since the service life and safety of the bubbling system will depend a great deal on these work procedures. It is consequently suggested that one employee per shift be assigned responsibility for this work.

Gas purging cone pretest procedure

Wear mechanisms     ( back to top )     ( back to section 5 )

Bubble formatin (depending on purging gas quality)