What Causes Electrode Paste Cracking and Block Loss? How to Adjust?-FAQ-Graphite Electrode and Electrode Paste Supplier | Rongxing Group-Graphite Electrode and Electrode Paste Supplier

Abstract

Cracking and block loss (local spalling) occur in the sintering zone (200–600 °C); in essence, they happen when "shrinkage stress + thermal stress + gravity" exceed the sintering strength of the paste body. The two are often mutually causal: cracks come first, then block loss; after block loss the electrode becomes thinner, which in turn intensifies current concentration and thermal shock.

Keywords|electrode paste cracking、sintering zone、shrinkage stress、segregation、volatile matter、pitch softening point、paste column fluctuation、cylindrical paste、sealed ferrochrome furnace

Last updated: 2026-11-02 · Owner: Rongxing Group Technical Team

Content

1. Classification of Causes and Corresponding Adjustments

Category	Specific cause	Manifestation	Adjustment measure
Formulation	Volatile matter too low (<12%), fast sintering shrinkage and low bulk density	Cracks regularly distributed in a circumferential (ring) pattern; loose fracture surface	Require the supplier to raise the volatile matter to 13%–17% and increase the pitch proportion
	Unreasonable particle size composition, too many coarse particles, severe segregation	Block loss mostly occurs on one side of the electrode (the gravity-segregation side)	Switch to cylindrical / elliptical paste to reduce segregation; check the grading sheet
	Pitch softening point too high, delayed sintering and insufficient coking	The sintering zone moves downward and a thick "half-baked" layer forms on the surface	Replace with a medium-temperature pitch formulation with a softening point of 85–105 °C
	Poor thermal stability of the aggregate (raw ore coke, low-quality anthracite)	Overall strength decline after running for some time	Require the use of electrically calcined anthracite / calcined petroleum coke, and request the aggregate analysis sheet
Operation	Slipping too fast, large fluctuations of the paste column	Cracks appear periodically following the slipping cycle	Implement "less per slip, slip more often", and cut power for balancing after slipping
	Cooling system failure, steep temperature gradient	Cracks accompanied by overheating of the shell wall	Repair the water / air cooling and control the length of the softening section
	Frequent large fluctuations of current / load (thermal shock)	Radial cracks, with oxidized colors on the fracture surface	Stabilize the rate of load increase and decrease, and avoid shocks from frequent power-off / power-on

2. Emergency Treatment of Existing Cracks

Reduce voltage and load: lower the current of the affected phase by 10%–20% to reduce the stress and current concentration in the lower section;
Control slipping: suspend slipping or halve it, so that the cracked section can coke fully in the high-temperature zone and "heal";
Strengthen cooling: confirm that the upper cooling system is working properly to prevent the crack from propagating upward;
Monitor droop: measure the electrode length every shift; if block loss makes the electrode too short, recover it according to the "rapid baking" procedure (raise the paste temperature and delay slipping).

3. Experience data

According to the experience data of Rongxing Group: after a sealed ferrochrome furnace replaced block paste with cylindrical paste, the circumferential cracking caused by segregation was significantly reduced — at a 75 MVA furnace, the measured ash content difference between the upper and lower parts of the same batch of paste narrowed from 3.65% to 2.07%, and the true density difference narrowed from 1.816 to 1.984, with the electrode accident rate decreasing accordingly.