Most cement companies attribute frequent brick falling from rotary kilns, short refractory lifespan, and localized red-hot kilns solely to the quality of refractory materials and masonry techniques, neglecting the core hidden equipment hazard of excessive kiln ellipticity. Kiln ellipticity continuously damages the refractory lining, leading to a series of problems such as refractory material detachment, unplanned downtime, and increased clinker production costs. This article, based on practical experience from a 5000t/d new dry-process production line, concisely analyzes the pathogenesis, core causes, graded rectification plans, and long-term control measures for excessive ellipticity, helping companies achieve stable production and cost reduction from the root of the equipment issue.
I. Core Understanding: The Hidden Root Cause of Brick Falling and Kiln Redness is Kiln Body Out-of-Circle The ellipticity of the rotary kiln cylinder, i.e., the difference between the maximum and minimum radii of the kiln cylinder during one revolution, is a key indicator for measuring the structural stability and stress balance of the kiln. Industry standard: Generally, the ellipticity of the cylinder should be ≤0.2% of the kiln diameter, and the ellipticity at the tire position should be ≤0.15% of the kiln diameter. Values ​​exceeding 0.3% will continuously induce equipment failure.

When the kiln body ellipticity exceeds the standard, the refractory bricks will be repeatedly subjected to alternating compressive and tensile stresses with each revolution, causing the bricks to loosen, crack, and fall off, significantly shortening the service life of the refractory materials. This also leads to mechanical problems such as abnormal wear of the tire pads, creep bulging of the cylinder, overheating of the support roller bearings, and kiln body imbalance, ultimately causing localized kiln redness, shutdown, and increased maintenance costs and safety risks.

II. Four Core Causes of Excessive Kiln Ellipticity
Excessive ellipticity is the result of multiple factors, including equipment assembly, high-temperature operating conditions, daily maintenance, and construction defects. The core causes can be categorized into four types:

(I) Mechanical Stress Imbalance
This is the primary cause of excessive ellipticity. Uneven load distribution among the three-stage support rollers and overloading of the cylinder by a single roller can cause permanent flattening of the cylinder at the tire; kiln centerline deviation and skewed running trajectory cause continuous uneven load deformation of the cylinder; uneven wear and tilting angle deviation of the support rollers lead to disordered stress points, further amplifying the elliptic deviation of the cylinder.

(II) Abnormal Fit Between Tire and Pad
The industry standard fit clearance is 3-6mm. After long-term operation of the production line, the pad wears and thins, causing excessive clearance between the tire and the cylinder, resulting in localized suspension and loss of constraint and support. The kiln's own weight and material pressure will flatten the cylinder, forming an out-of-round shape that is "flattened vertically and spread horizontally," a frequent cause of failure in older production lines. (III) High-Temperature Thermal Deformation and Operating Damage The kiln shell steel plates are highly sensitive to high temperatures. Red-hot kilns and refractory material detachment expose the steel plates directly to the high-temperature flame, causing irreversible high-temperature creep, resulting in collapse and bulging deformation. Frequent start-ups and shutdowns of the production line and drastic fluctuations in kiln temperature generate alternating thermal stress, exacerbating shell deformation. Alkali and chlorine corrosion from AFR alternative fuel combustion accelerates refractory material wear, indirectly inducing high-temperature deformation and worsening the problem of excessive ellipticity.

(IV) Defects Left Over from Construction and Maintenance Processes Uneven welding stress in the shell butt welds, improper rounding after overhauling and replacing sections, and excessive misalignment; failure to reserve standard expansion joints in the refractory brickwork, and the inner lining compressing the shell during high-temperature operation, all contribute to inherent or acquired roundness loss of the kiln body.
III. Tiered Rectification Solutions Based on the degree of ellipticity exceeding the standard, differentiated rectification plans will be formulated, balancing production continuity and treatment effectiveness.

(I) Minor Exceeding Standard (0.2%-0.3%): Online Non-Stop Optimization
Applicable Conditions: Stable equipment operation, no obvious red kiln, no large-area brick falling. The kiln centerline will be re-measured and corrected using laser equipment, the roller tilt angle will be adjusted, and the equipment load will be balanced; the calcination temperature inside the kiln will be stabilized, and start-up, shutdown, and kiln drying operations will be standardized to reduce thermal shock stress on the cylinder; refractory materials will be regularly inspected and repaired, and expansion joints will be constructed in a standardized manner to curb the continued deterioration of ellipticity.

(II) Severe Exceeding Standard (>0.3%): Complete Overhaul and Rectification After Shutdown
Applicable Conditions: Problems such as red kiln, frequent brick falling, cylinder bulging, and high temperature of rollers exist. First, replace and thicken the wear pads, strictly controlling the tire-to-cylinder clearance within the standard range of 3-6mm. Second, use hydraulic tools to correct out-of-roundness cylinder sections and replace sections with permanent creep or crack damage. Third, calibrate the kiln body straightness and the horizontal parallelism of the support rollers, ensuring the tire-to-support roller contact area is ≥70%. Fourth, standardize refractory brickwork, precisely reserve expansion joints, select alkali-resistant and low-creep refractories, and restore the lining's protective capabilities.

IV. Long-Term Prevention and Control System

1. Establish a regular inspection mechanism: Conduct a comprehensive inspection of the kiln centerline, support roller load, and tire clearance annually, and conduct a quarterly special inspection of the cylinder ellipticity to proactively identify and fine-tune potential hazards.

2. Strictly control high-temperature operating risks: Prevent prolonged localized red-hot kilns; immediately adjust parameters upon the appearance of minor high-temperature anomalies; optimize raw material and fuel ratios, strictly control harmful components such as sulfur, alkali, and chlorine, and reduce kiln corrosion and operating condition fluctuations.

3. Standardized Operation and Maintenance: Unify kiln start-up, shutdown, drying, and maintenance procedures to eliminate rough handling; regularly maintain transmission, lubrication, and cooling systems to ensure stable equipment operation.

4. Enhanced Construction Quality Control: Strictly inspect and accept processes such as cylinder welding, refractory lining, and pad replacement; strictly control key parameters such as cylinder section roundness, misalignment, and expansion joints to eliminate potential problems left over from maintenance.

V. Core Value of Implementation and Rectification: After the entire solution is implemented, the kiln body ellipticity can be stably controlled within the industry standard range, completely solving core pain points such as refractory material damage and kiln shutdowns. Actual measurement data shows that after rectification, the service life of refractory materials increases by 20%-30%, the cost of refractory materials per ton of clinker decreases by 0.3-0.8 yuan, and the frequency of unplanned shutdowns decreases by more than 60%, effectively improving the operational stability of the kiln system and achieving improved quality, reduced costs, stable production, and safe operation of the production line.