Inlet and outlet end covers

I. Definition and Overall Function
The inlet and outlet end covers are divided into the inlet end cover and the outlet end cover.
 

They are large castings at both ends of the ball/rod mill cylinder that are sealed and pressure-bearing. They come with an integrated hollow shaft. One side is connected to the cylinder, while the other side supports the main bearing. They simultaneously perform five functions: feeding, discharging, sealing, bearing pressure, and bearing weight.

1. Seal the ends of the cylinder to form a sealed grinding chamber;
2. The hollow shaft is mounted on the main bearing, bearing the entire rotational weight of the mill;
3. The central through-hole installs a bushing to allow the material to enter and the slurry / finished product to exit;
4. Isolate the slurry and steel balls, protecting the main bearing from material ingress and bearing wear;
5. Bear the impact of steel balls, the erosion of the material, and the alternating rotational stress.
II. Structural Differences between Inlet End Cover and Outlet End Cover
1. Inlet End Cover (Feed Side)
 Equipped with a spiral feed bushing inside, with built-in double spiral blades, forcing the feed and also preventing the steel balls from flowing back into the chute;
 Mostly an extendable hollow shaft with widened shaft neck, suitable for thermal expansion and contraction;
 Equipped with end lining plates + rubber buffer pads inside, buffering the impact of the ore;
 Sealing structure: conical surface matching + gasket / O-ring, preventing the leakage of slurry.
2. Outlet End Cover (Discharge Side)
There are two types: overflow type and grid type:
 Overflow type: smooth hollow bushing, relying on the liquid level difference for self-flowing discharge of ore;
 Grid type: the inner side of the end cover is equipped with grid plates + scoop plates, first screening out large steel balls, then raising the slurry for discharge, with higher discharge efficiency;
 The blank is often common with the inlet end cover, with an inverted cover structure, reducing the accumulation of materials and wear.
III. Standard Structure Components
1. End Cover Body: an integral cast steel part (ZG270-500, high alloy wear-resistant cast steel), a circular disk body + an integrated hollow shaft neck;
2. Hollow Shaft: supporting the main bearing, with a central through-hole for material flow;
3. Bushing (Inlet and Outlet Bushings): wear-prone parts, embedded in the hollow shaft, wear-resistant, and can be replaced separately;
4. Sealing Parts: O-ring, gasket, rubber gasket, sealing the gap between the bushing and the end cover, preventing slurry leakage;
5. Wear-resistant Lining Plate: protecting the inner side of the end cover, resisting the impact of steel balls;
6. Connecting Flange: rigid locking with the mill cylinder by the outer ring bolts.
IV. Common Materials and Processes
 Main materials: cast steel, alloy cast steel, undergo quenching and tempering heat treatment for heavy-duty conditions;
 Forming: sand mold gravity casting, rough processing → fine processing → flaw detection (UT/MT) to eliminate casting pores and cracks;
 Protection: internal wall overlaying wear-resistant layer, matching wear-resistant bushings to extend service life.
V. Common Faults and Causes
1. Leakage of Slurry and Materials: too large gap between the bushing and the end cover, aging of the seal, slurry seeping into the interlayer between the hollow shaft and the bushing, continuous wear of the hollow shaft;
2. Cracking of the End Cover: casting stress, long-term alternating impact, detachment of the lining plate, local stress concentration;
3. Wear and Scratch of the Hollow Shaft: long-term erosion of the slurry abrasive on the inner wall of the hollow shaft;
4. Bearing Burnout of the Bearing: failure of the seal, slurry flowing into the main bearing, destroying the oil film.
VI. Optimization Scheme for Sealing and Leakage Prevention
1. Add O-ring slots to the cylindrical mating surface of the bushing and end cover;
2. Use stainless steel sealing welding + stress relief annealing for the mating gap to avoid cracking of the weld;
3. Add water-blocking umbrella rings on the outer wall of the end cover to prevent slurry from flowing along the shaft neck into the bearing;
4. Add rubber buffer pads at the bottom of the bushing to reduce deformation of the impact gap.
VII. Applicable Equipment
Various mining and construction mills: wet overflow ball mills, grid-type ball mills, dry rod mills, cement raw material mills, mineral grinding and beneficiation mills.