Question 1: Problems & Countermeasures of Grooveless Rolling
(1) Instability of rolled pieces
Without constraint from groove side walls in grooveless rolling, rolled stock is prone to square distortion and offset. Larger reduction leads to worse stability and interruptions to rolling.
Solutions: Install double-row rolling guides at mill entry; equip the first stand with grooved rolls to stabilize the workpiece in the first pass and maintain steady rolling throughout the whole process.
(2) Sharp edges of rolled stock
Repeated flat rolling creates extremely sharp edges that easily form metal folds. Fast temperature drop at edges triggers cracks on certain alloy steels. Bar mills feature heavy reduction per pass, forming natural barrel shapes on stock and eliminating sharp edges automatically.
Question 2: Why Rolling Guides Adopt Oil-Air Lubrication or Grease Lubrication Separately
- Oil-air mixed lubrication for rolling speed above 25m/s
Bearings run at ultra-high rotating speed under high-speed continuous rolling. Lubrication parameters: oil consumption 2×0.230 cm³ with 1–2 injection cycles per minute; air consumption 2×50 standard liters per minute.
- Grease lubrication for rolling speed below 25m/s
Grease consumption ranges from 2×2 cm³/h to 4×4 cm³/h.
Question 3: Advantages of Horizontal-Vertical Alternating Mill Trains vs All-Horizontal Mill Trains
- Eliminate rotary twisting guides between stands, reduce steel biting impact and stabilize rolling status;
- No stock twisting between passes, minimal dimension fluctuation especially at head and tail ends;
- Avoid rolling defects and twisting cracks caused by twist rolling, ideal for alloy steel production;
- Uniform mechanical properties along full length of finished products without twisting deformation.
Question 4: Core Advantages of Cantilever Rolling Mills
- Simple operation: No housing, bearing chocks or complex adjusting screws for easy calibration. Short stand distance simplifies pass and guide alignment greatly.
- Simplified components: Eliminate transmission coupling shafts, cutting component quantity by nearly half compared with conventional mills.
- Ultra-fast roll change: Roll replacement time reduced by 75%.
- Lower maintenance workload.
- Cost-saving & high operation rate: Save 20% building investment and 30% foundation cost; shorten installation & commissioning cycle by 25%; cut equipment investment by 10%. During production, downtime for groove change drops by 75%, interval time for rolling program switching decreases by 15%, and mill availability rises by 5%–7%.
Question 5: Maintenance Requirements for Cantilever Rolling Mills
- Transmission system: Regularly inspect motor operating load, gear coupling lubrication and gear tooth wear condition.
- Reducer & gearbox: Periodically open inspection ports to check gear abrasion and bearing lubrication status.
- Lubrication system: Keep pipelines unobstructed with stable pressure and flow.
- Regularly inspect and replace lip seals, eccentric flanges, static and dynamic labyrinth seals.
Question 6: Structural Features of High-Precision Pre-Stressed Rolling Mills
This mill adopts half-housing frame design with the following merits:
- Ultra-high mill rigidity & superior dimensional precision
Pre-stressed mill housing columns are much shorter than traditional designs, shortening stress line by 75%. Higher rigidity controls dimensional tolerance within ±0.06mm at both head and tail of stock, supporting negative tolerance rolling for section steel.
- Compact layout & light weight
Under identical allowable rolling force, the mill features smaller footprint and lower overall cost.
- Easy disassembly, installation and maintenance
Roll change including preloading and unloading takes only 10–15 minutes, lifting mill operation rate.
- Welded construction for easy manufacturing, costing only 60% of cast steel frames.
Question 7: Characteristics of Closed Housing Rolling Mills
Multi-groove two-high closed mill is the most common small rolling mill model. Modern designs place screwdown devices between housing top beam and top bearing chocks to preserve housing integrity and boost rigidity. Supporting technologies include hydraulic top roll balance, manual worm gear axial adjustment, hydraulic trolley roll change and mill traversal to fix rolling line position. Multi-groove rolls reduce roll change frequency and downtime loss. Closed two-high mills serve as reliable roughing and intermediate stands, widely adopted in standard finishing trains.
Single-groove closed mills have emerged globally in recent years, equipped with short barrel rolls assembled with single-pass centrifugally cast high-strength wear-resistant ductile iron collars. Compared with conventional closed two-high mills: total equipment weight cut by nearly half; constant rolling line without pass alignment devices; short double-support roll barrels deliver high rigidity to bear heavy rolling load; smaller floor space and simpler operation. Vertical cantilever versions feature lightweight, simplified structures.
Question 8: Definition & Features of Short Stress Line Rolling Mill
Stress line refers to the closed force circulation path on all load-bearing components of mill housing under rolling force. A short stress line mill optimizes structural layout to minimize this force circulation path for higher rigidity.
Key strengths: compact size, light weight, high rigidity and extended bearing service life. Widely used in small intermediate and finishing rolling lines. Online rapid roll change devices eliminate full stand replacement and lower total investment, expanding its application scope. Not recommended for roughing mills with large stock cross-section, as stock thrust or tension may damage connections between stand and base.
Question 9: Main Characteristics of Compact Rolling Mills
Compact mills belong to high-reduction rolling equipment with below features:
- Narrow stand spacing. The upstream stand pushes stock into the downstream stand to realize forced biting and high-reduction rolling;
- Train composed of 4, 5 or 6 horizontal-vertical alternating stands;
- Short roll barrel with only one single pass groove or flat rolling surface;
- High reduction performance reduces total stand quantity by 1–2 sets versus standard two-high mills under equal output;
- Stand frames adopt short stress line or cantilever structures;
- High reduction brings high risk of steel piling between stands if improperly adjusted; narrow stand spacing complicates on-site adjustment and fault handling;
- Individual drive for each stand with precise, rigid transmission control. Torsion-free and loop-free rolling, full PLC/microcomputer automation control with high intelligent level.