Feature

Normal (sintering volatiles)

Abnormal (precursor of failure)

Smoke color

Faint white / light blue, thin

Thick yellow, brownish-yellow or black, continuous plumes

Duration

Appears within 30–90 min after slipping and gradually weakens

Persists for hours without dispersing, or even worsens

Accompanying signs

No irritating odor, no drips

Paste oil seeping from the electrode shell, pitch dripping from the lower edge, irritating odor or open flame

Electrode condition

Slipping normal, current steady

Difficulty in slipping, paste column not moving, electrode sliding down or current fluctuation

No.

Cause

Mechanism

Troubleshooting and handling

1

Volatile matter mismatched with furnace operating conditions

High volatile matter in the paste (e.g., high-volatile pitch used by mistake or too much coal tar blended in), so light components escape in bulk during sintering

Sample and test the volatile matter; check the formulation with the supplier; adjust the paste's volatile matter if necessary

2

Excessive slipping amount

A single slip too long moves the unsintered section quickly into the high-temperature zone; large amounts of uncarbonized pitch heat up, smoke or even cause "paste leakage"

Practice "slip little and often", no more than 200 mm per slip; power off for 10–20 min of balance after slipping

3

Insufficient electrode cooling

Water / air cooling at the top of the electrode shell fails, the softened section becomes too long, and the paste softens and flows prematurely in the low-temperature zone

Check the cooling fans and the shell jacket water circuits; measure the shell wall temperature (it should be below the pitch softening point)

4

Paste column too low

The top of the paste column is too close to the sintering zone; a top temperature above 110℃ makes the newly added paste soften and volatilize early

Measure the paste column height (generally 2.5–3.5 m) and top up in time

5

Electrode shell damage / paste leakage

The shell burns through or a weld cracks; liquid paste seeps out and smokes or ignites directly at high temperature

Immediately reduce load and cut power; inspect the shell; slipping below the leak point is prohibited

6

Furnace condition fluctuation, abnormal burden-surface temperature

Charge collapse and slag turnover cause a sudden rise in furnace-mouth temperature, over-baking the lower section of the electrode

Stabilize burden distribution; restore the normal burden height after treating the burden surface

7

Paste quality problem (softening point too low)

Pitch softening point below the process requirement (e.g., low-temperature pitch used where 85–105℃ is required), so the paste softens prematurely inside the shell

Test the softening point (ring-and-ball method); keep samples for third-party testing