Analysis of Causes and Solutions for Poor Squeezing Effect of Roller Press -- Part One

1.1 One of the Causes

(1) Cause: Excessive fine powder in the material being squeezed, resulting in a small operating gap between rollers and low working pressure.

(2) Impact Analysis: As a high-pressure material bed grinding equipment, the roller press boasts high extrusion force, high grinding efficiency, and large material preprocessing capacity. In combined grinding systems, it undertakes the task of semi-final grinding. After extrusion and classification, the material entering the mill exhibits lattice cracks and microscopic defects, significantly improving its grindability, enhancing system output, and reducing grinding power consumption. However, the roller press is highly sensitive to the uniformity of the particle size of the incoming material, adhering to the principle of "squeezing coarse but not fine." When excessive fine material enters, it narrows the operating gap between rollers, reduces output, and leads to poor squeezing effect.

(3) Solution: During actual production, control the proportion of material with a particle size <0.03D (D—roller diameter in mm) to be above 95% of the total. Production experience indicates that material with a uniform particle size ranging from 25mm to 30mm yields the best squeezing effect. Screen the particle size distribution of incoming material using a nested sieve, which is simple and practical. Generally, conducting this test once every three days is sufficient. Mix different particle sizes of material to avoid feeding too much fine material into the roller press.

1.2 Second Cause

(1) Cause: Severe wear of the side baffles of the roller press, leading to edge leakage.

(2) Impact Analysis: The inherent "edge effect" of the roller press refers to better extrusion in the middle of the rollers, producing more fine powder, while the edges exhibit poor extrusion and less fine powder, i.e., bypass failure. When the side baffles at both ends wear severely, edge leakage becomes inevitable, reducing the fine powder content in the extruded material and allowing some coarse particles to enter the classification equipment, causing wear to it.

(3) Solution: Maintain a working clearance between the side baffles and roller ends at 2mm–3mm, with some enterprises using 1.8mm–2.0mm. Use wear-resistant steel plates or wear-resistant alloy castings to address this issue. Keep 1–2 sets of spare side baffles ready for immediate replacement. Before installing wear-resistant alloy castings, grind the surface burrs to facilitate installation. Measure and control the clearance during replacement using a feeler gauge and steel ruler. Implement a preventive maintenance mechanism, checking the clearance between side baffles and rollers every 7–10 days during downtime and maintaining detailed records.

1.3 Third Cause

(1) Cause: Severe wear of the dynamic and static roller surfaces without timely repair.

(2) Impact Analysis: The roller press operates in harsh conditions, and wear patterns identified by the Zhengzhou Machinery Research Institute include:

① Normal wear-induced roller surface damage;

② Roller surface hardness lower than material hardness;

③ Abnormal spalling of roller surface;

④ Overdue operation of rollers;

⑤ Losses due to roller body properties;

⑥ Local spalling caused by metal or other foreign objects entering.

Severely worn or spalled roller surfaces develop grooves, significantly reducing material crushing efficiency. Compared to flat roller surfaces, severely worn or spalled surfaces exhibit uneven extrusion force, leakage, and increased coarse particles (or even uncrushed material) in the output, affecting the potential capacity of downstream ball mills. Generally, rollers should be serviced based on wear conditions after 6000h–8000h of operation to maintain long-term and stable extrusion efficiency.

(3) Solution:

① Engage professional technicians for onsite overlay welding to restore roller dimensions.

② Replace worn rollers with spares and send them to a specialized vendor for repair.

Due to the technical measures required before overlay welding, such as flaw detection, removal of irregular wear layers, and roller surface cleaning, coupled with the high cost of wear-resistant alloy welding wire and the need to determine overlay thickness based on actual wear, overlay welding is costly.

③ Prioritize operation, usage, and maintenance in daily production. Ensure iron removal before roller press feeding to prevent roller surface damage from foreign objects.

④ Inspect roller wear during downtime, typically once to three times per week, and maintain detailed records.

(4) Case Study: The online overlay welding of worn rollers in a 120-50 roller press cost approximately 120,000 yuan.