BALL MILL MAINTENANCE

Grinding is one of the cement industry’s fundamental processes: (for the preparation of raw materials, coal grinding, and cement grinding). Cement manufacturing is a continuous process industry with very high requirements and performance rates, requiring high reliability in both the process and maintenance.

There are two basic types of ball grinding systems: open circuit and closed circuit.

In the open circuit system, the mill product has the fineness required for the next stage. In the closed-circuit system, the mill product is classified in a separator in a fine fraction that is then taken to the next step and a thick fraction that is returned to the mill for subsequent milling.

It is necessary to grind clinker, gypsum, and sometimes other additives in the proportions required at a predetermined fineness in any cement grinding circuit. The fineness is usually defined by the cement’s specific surface area measured in m²/kg or cm²/g. High-efficiency separators are normal to grind cement in a closed-circuit system due to energy consumption savings.

Safety hazards in ball mills involve numerous situations; anywhere, we can observe conditions related to process, operation, and maintenance. Ball mills can be hazardous machines if they are not operated properly. Therefore, operators should follow the essential safety and maintenance advice; as part of the course, we will cover all the safety precautions to ensure safe operation and maintenance. Operators must take certain precautions before beginning to operate a ball mill. Here is a list of the most critical safety maintenance steps that all operators must follow when using a ball mill:

• Planning: planning is essential. Operators must know precisely when to lock and stop the ball mill. Planning ensures proper coordination and cooperation between maintenance and production departments.
• Selection of the crew: it is essential to select the right maintenance team responsible for the maintenance program. Everyone should know exactly what to do before and after each operation. In case something is unclear, employees should turn to their team leaders.
• Issue Safe Work Permit: Operators must be issued a work permit before beginning work with a ball mill.
• Adequate technical knowledge: as part of the course, we will deliver adequate specialized training before starting work with a ball mill. They must fully understand how the ball mill works.
• Barricades: The best way to avoid work-related injuries is to barricade the area around the ball mill for safety reasons. It is also advisable to put up signs that prohibit entry without authorized permission. The signs also warn people of possible dangers.
• Electric Power Lockout and Tagout: Once the ball mill operation is completed, the operator must disconnect the high voltage electric power. Operators should also test the circuit once they are done with the task.

Cleaning the machine after use: A ball mill must be cleaned after each operation or at the end of the working day. Major components like the grinding tool, grinding roller, and grinding ring are prone to wear. Because of that, each part or component should be regularly lubricated and checked for damage.

Ball mill is generally used to grind material 1/4 inch and finer, down to the particle size of 20 to 75 microns. To achieve reasonable efficiency with ball mills, they must be operated in a closed system.

There is a specific operating speed for the most efficient grinding. At a certain point, controlled by the mill speed, the load nearest the cylinder’s wall breaks free, and other sections so quickly follow it in the top curves to form a cascading, sliding stream containing several layers of balls separated by the material of varying thickness. The top layers in the stream travel faster than the lower layers, causing a grinding action between them. There is also some action caused by the spinning of individual balls or pebbles and secondary movements having the nature of rubbing or rolling contacts inside the main contact line.

The mechanical elements of a tube mill could be separated into components that directly function with the grinding process (i.e., grinding media, liners, diaphragms) and into parts that can be considered individual units connected to a specific tube mill. The latter group includes:

The feed and discharge arrangement.

• The mill shell.
• The mill heads.
• The mill bearings.
• The mill drive.

In this module, we will cover all the maintenance detail, lubrication, inspection, and troubleshooting of the ball mill’s mechanical element.

The mechanical elements of a tube mill can roughly be subdivided into internal and external parts. The mill internals directly functions concerning the grinding process and include the wear parts of a mill, such as mill liners, diaphragms, and grinding media principally. We will explain how to inspect the mill liners, diaphragm, water spray system, and components as well as physical mill inspection with our checklist instruction:

• Inspection and wear trend
• Purpose
• Criterion
• Corrective measure
• Volume Loading
• Evaluating ball charge wear
• Evaluating wear parts and wear-resistant materials in mills
• Detecting a mechanical problem (breakage of a diaphragm sector)

The external parts of a standard tube mill consist of mill shell, mill heads, mill bearings, feed and discharge equipment, and the mill drive.

• Ball Main design criteria
• Critical mill speed
• Ball mill arrangement
• Types of mill drives
• Type of mill bearings
• Ball mill lubrication
• Ball mill troubleshooting
• Ball mill maintenance/Spare parts
• Effect of delayed mill maintenance

Introduction to Conveyors

This module will detail a regular sequential physical inspection of conveyors by operators and mechanical maintenance personnel. It will detail what items require inspection and what possible issues and problems the inspecting personnel should be trying to identify and rectify. It will cover each of the major components that make up a conveyor system and include the variations within different conveyor designs. The topic will cover such components as:

• Belting (handling belting, introduction to mounting, and introduction to splicing)
• Drives (tail, head, center, twin drives, boost drives, couplings, and gearboxes)
• Pulleys (drive, snub, tail, take-up, bend pulleys)
• Brakes and hold-backs
• Cleaning devices (belt scrapers and belt ploughs)
• Tensioning arrangements (gravity, screw, hydraulic)
• Idlers and rollers (impact, carry, return, anti-spank rollers)
• Chutes (feed, discharge, diverter)
• Local control stations (local control panels, emergency stop switches, safety lanyards)
• Sensors and detectors (belt drift switches, belt rip detectors, speed detectors, plugged chute detectors, weight meters, drive temperature detectors).

Fan Design and Applications

Introduction

The turbomachines used for gas compression are classified into radial, axial, or mixed flow types according to the impeller’s flow. In a radial or centrifugal machine, the increase in pressure due to centrifugal action is an essential factor in its operation. Energy is transferred by dynamic means from the impeller to the fluid. The fluid due to centrifugal action is continuously thrown outward, allowing fresh fluid to enter due to reduced local pressure.

Another characteristic feature of the centrifugal impeller is that the angular momentum of the fluid flowing through the impeller increases because the impeller’s outer diameter is significantly larger than the inlet diameter. In axial flow machines, the rotating impeller sets in motion a large mass of gas and is advanced by the blades’ aerodynamic action.

This module will cover the different types of fans used in the cement industry, applications, maintenance, and troubleshooting.

Ball Mill Dust Collector

Introduction

Dust collection systems are the most widely used engineering control technique by cement processing plants to control dust and decrease workers’ exposure to respirable dust. A well-integrated ball mill dust collection system has multiple benefits, resulting in a dust-free environment that increases productivity and process operation. The most common dust control techniques in cement plants use local exhaust ventilation systems.

In this module, we will cover:

• Basic concepts of the systems of dust collection
• Dust collector inspection
• Checklist for hood effectiveness
• Duct design
• Installation of bags and cages
• Dust collector troubleshooting (problems and possible causes and solutions)

er:

• Basic concepts of the systems of dust collection
• Dust collector inspection
• Checklist for hood effectiveness
• Duct design
• Installation of bags and cages
• Dust collector troubleshooting (problems and possible causes and solutions)