A cold rolling mill consists of a working mechanism and a drive system. The working mechanism applies pressure to the metal and controls its cross-sectional dimensions, while the drive system supplies power to the rolls.
The equipment described here is a gantry-type horizontal dual-drive rolling mill used for producing cold-rolled ribbed steel bars. It consists of two active rolling stands with the same basic structure. Each stand is installed horizontally and driven independently through a motor, reducer, and universal shaft assembly.
Main structural components of the cold rolling mill
Working mechanism
The working mechanism is the main part of the rolling mill that performs material deformation. Its main components include the mill housing, rolls, roll bearings, roll adjustment mechanism, guide equipment, and mill base.
Mill housing
The mill uses a gantry-type housing to support and position the rolls. The housing provides a rigid frame for the roll assemblies and maintains their alignment during rolling.
Rolls and roll ring assembly
The roll rings are mounted on the main roll shafts and secured with nuts. Bearing housings are fitted at both ends of each roll shaft and installed inside the gantry frame.
The bearing housings fit into the housing structure to hold the rolls in a horizontal position. The upper and lower roll assemblies use the same basic mounting arrangement.
Roll bearings
The bearings support the roll shafts and allow them to rotate under rolling loads. The bearing housings also maintain the correct roll positions and help keep the roll gap stable during operation.
Roll adjustment mechanism
The adjustment mechanism changes the clearance between the upper and lower rolls. By adjusting the roll gap, operators can control the deformation of the incoming steel bar and produce different product diameters and cross-sectional profiles.
Guide equipment
The guides direct the steel bar into the rolling stands and maintain its correct position during processing. A twisting guide is installed between the two rolling stands to rotate the rolled material by 90° before it enters the second stand.
Mill base
The mill base supports and secures the rolling stand. It provides the mounting reference for the gantry housing and drive components and helps maintain equipment alignment during operation.
Drive system
The drive system supplies power to the rolls and consists mainly of the electric motors, reducers, connecting shafts, and couplings. Depending on the equipment configuration, a gear stand may also be included.
The dual-drive mill described here consists of two active horizontal rolling stands with the same installation arrangement and structural design.
Each stand uses the following drive configuration:
Motor → Reducer → Universal shaft → Rolling mill
The motor supplies power to the reducer, which lowers the rotational speed and increases the output torque. The universal shaft then transmits torque to the roll shaft.
The main equipment specifications are as follows:
| Parameter | Specification |
|---|---|
| Housing type | Gantry-type |
| Rolling stand arrangement | Horizontal |
| Drive arrangement | Reducer drive |
| Main motor quantity | 2 units |
| Main motor power | 75 kW / 2 units, as specified in the original equipment data |
| Reducer ratio | i = 7.5 |
The original motor specification is recorded as 75 kW/2 units. Whether this refers to 75 kW per motor or 75 kW for both motors combined should be confirmed against the motor nameplates or equipment documentation.
Working principle of the cold rolling mill
The motor drives the rolls through the reducer and universal shaft. The rotating rolls grip the steel bar through friction and feed it through the roll gap. The upper working roll and lower supporting roll apply pressure to the material from opposite sides, reducing its cross-sectional dimensions and forming the required rib profile.
In the described equipment, the lower supporting roll and upper working roll perform different functions.
Lower supporting roll
The lower supporting roll is located closer to the mill base. It supports the steel bar during rolling and carries the reaction force generated by the rolling operation.
The roll surface also works on the lower side of the steel bar. According to the roll profile used in this machine, it helps form the ribs on the lower surface.
Upper working roll
The upper working roll is positioned above the supporting roll, farther from the mill base. It applies rolling pressure to the upper surface of the steel bar while the lower roll supports the material.
The corresponding roll profile forms the ribs on the upper surface. The upper and lower rolls work together to produce the required cross-sectional shape.
Two-pass rolling process
The two active rolling stands perform different operations during production.
The first stand reduces the incoming material and compresses it into an oval cross-section. After the first pass, the twisting guide rotates the oval-shaped material by 90° before feeding it into the second stand.
The second stand performs the forming operation. Its roll profiles shape the material and produce rib patterns on both sides of the steel bar, resulting in the finished ribbed product.
The roll gap must be adjusted according to the required product dimensions. Different roll gaps and roll profiles are used to produce different steel bar sizes and cross-sectional shapes.
Maintenance and operating requirements
Regular inspection and maintenance help keep the rolling mill in proper working condition and reduce unexpected equipment failures. The following checks should be carried out before operation and during routine maintenance.
Pre-start inspection
Check the electrical control system and confirm that the motors, control components, and related equipment are in normal condition.
Check the oil levels in all oil tanks and confirm that they meet the equipment requirements.
Inspect the lubrication points and ensure that the required lubrication has been supplied.
Check the incoming material and confirm that the feeding position and material condition are suitable for rolling.
Inspect the roll guides and confirm that they are correctly installed and aligned.
Check the fasteners and connections on the moving components for looseness.
Routine equipment maintenance
Keep electrical components and control cabinets clean. Dust and other contaminants should be removed using appropriate methods after the equipment has been safely stopped and isolated.
Inspect moving parts regularly for loose fasteners, abnormal wear, and other mechanical problems.
Check the operating condition of the bearings, transmission components, and lubrication system.
Monitor the equipment for abnormal noise, vibration, overheating, or other signs of malfunction.
Inspect the guides and roll surfaces regularly to maintain stable material feeding and product quality.
Operating limits
The rolling mill must operate within its specified load and process limits. Excessive rolling loads or incorrect roll gap settings can damage mechanical components and shorten equipment service life.
Operators should follow the specified rolling standards and process parameters when adjusting the roll gap and feeding material. If abnormal operating conditions occur, the equipment should be stopped and inspected before production resumes.
Maintenance work involving electrical equipment and moving mechanical components must be carried out under safe shutdown and isolation conditions. Stored mechanical or hydraulic energy must also be released before components are dismantled.
