Recommended Electrode Clamping Pressure
Electrode Diameter		Clamping Pressure
Inches	(mm)	Psi	MPa
28	700	109,760	757
26	650	94,640	653
24	600	80,640	556
22	550	67,760	467
20	500	56,000	386
18	450	45,360	313
Remarks: The recommended clamping pressures are provided to prevent an electrode column from slipping through the holder.

Electrode Tightening Specification
Electrode Diameter		Torque
Inches	(mm)	ft-lbs	N-m
28	700	3580 - 3840	4854 - 5206
26	650	2650 - 3350	3593 - 4541
24	600	2140 - 2390	2901 - 3240
22	550	1560 - 1810	2115 - 2454
20	500	1230 - 1480	1667 - 2006
18	450	870 - 1120	1179 - 1518
Remarks: The higher torque values are recommended for applications that use water spray rings, since the cooling effect of the water limits thermal expansion, which normally contributes to greater joint tightness. To calculate Torque: Force (lbf) = (Radius of Cylinder)² x π x Cos (angle-90) x Pressure (psi) Torque = moment arm (ft) x Force (lbf) Example: A 24 inch electrode is tightened by applying 60 psi of pressure with a 4” diameter hydraulic cylinder at an angle of 90 with a 2 foot bar. What is the applied tightening torque? Force = (2 in)² x π x cos (90-90) x 60 psi = 754 lbf Torque = moment arm x force Torque = (2 +1) x 754 = 2262 ft-lbs

Improving Electrode Performance

Inspect Lifting Plugs. Remove metal burrs that could gouge or weaken threads in
the electrode socket. When adding an electrode, check for excessive oxidation in
the electrode socket and remove any foreign material that could prevent a perfectly
tight joint.
 
Maintain Clean, Tight Joint. Poor addition practices can lead to a loose electrode joint.
Loose electrode joints are typically the result of improper addition (i.e.cross-threading
or poor thread engagement due to foreign material in the socket and end-face area),
improper torque during the add, or the use of a damaged lift plug which will cause
thread damage to the non-preset socket.
 
Ensure Bore-in Amperage is not excessive. As the electrodes seek a higher current level,
the electrode tip is in constant contact with the scrap, causing frequent current surges
and extended periods where the weight of the arm and mast rests on the electrodes
(i.e. excessive mechanical stress on the top electrode joint).
 
Minimize Electromagnetic Forces. The forces acting on the electrodes are proportional
to the square of the short circuit current. When scrap caves occur they create a short
circuit which in turn subjects the electrode column to an electromagnetic force as well
as a force caused by the weight of the fallen scrap. The higher the current spike and
the longer it lasts, the greater the chance the electrode will break. Increasing the
reactance in the circuit will reduce the short circuit current and thus reduce the force
acting upon the electrodes.
 
Ensure electrodes are not drifting downward. Electrode drift is a result of an improper
bias setting or zero offset compensation on the electrode drives.  Generally, electrode
control systems have a bias setting that controls the amount of hydraulic pressure
required to support the weight of the arms without an error signal from the regulator.
Too high of a bias setting causes the electrodes to drift up and too low of a bias
setting causes the electrodes to drift down. 
 
Ensure scrap cave limits are set properly. Determine at what amperage level the regulator
will respond to a scrap cave and initiate a fast raise response. Once the short circuit
is sensed, the up speed should be in the range of 50 ft/min.
 
Verify Pre-arc Down Speed. Pre-arc down speed should be set lower than the automatic
up/down speeds to prevent electrode tip fracture and breakage during initial contact
with the scrap. Auto up and down speeds vary from furnace to furnace but generally
perform optimally when matched at 25 ft/min or less. Pre-arc down speed should be
adjusted to approximately 10 ft/min. 
 
Non-Conductors. Ensure the regulator will sense low hydraulic pressures to avoid
electrode breakage due to non-conductors. Electrode stopping distance is proportional
to the square of the speed. The slower the pre-arc down speed the lower the chance
for electrode breaks due to non-conductors.
 
Charging Methods. Electrode breakage can be reduced by using clean, light scrap on
top of the charge.  This makes a good electrical contact and eliminates the possibility
of breakage by thrust against large pieces of scrap that might be at an angle to the electrode.
 
Roof Alignment. Electrode roof ports and cooling rings clearance on all sides.  Electrode
holders should be centered over the roof ports or binding will take place on either the
cooling rings or the refractories and electrode breakage will result.

Electrode Consumption Calculation

There are many different ways of making a seemingly simple electrode consumption calculation. The most accurate method is to weigh the columns at the start and end of some time period and then divide the weight of the graphite consumed by the tons of steel produced. The least accurate, but most commonly used method is to count electrode additions and heats produced over some time period and perform the same calculation. Daily and weekly numbers calculated using this method are almost never accurate and fluctuate wildly. The most practical yet very accurate method of calculating electrode consumption is by using the heats per add method.

Heats per add method of Calculating Electrode Consumption

Example: Calculate electrode consumption knowing the following information Average Electrode weight is 3040 lbs. Average heat size is 190 tons Phase #1: 4 electrodes consumed over 45 heats Phase #2: 4 electrodes consumed over 46 heats Phase #3: 3 electrodes consumed over 39 heats Total: 11 electrodes consumed over 130 heats Electrode Consumption (lbs/Ton) = [ Avg Electrode Weight x 3 ] ÷ [ Avg heats per add x Avg Heat Size ] = [ 3040 x 3 ] ÷ [ (130 ÷ 11) x 190 ] = 4.06 lbs/Ton