 In the mining industry, ball mills are used for grinding various minerals, such as coal, limestone and iron ore. In the cement industry, ball mills grind raw feed and clinker. From time to time, people must work inside the mills to do maintenance or inspect and service the machines. But before entering the mills, certain precautions must be taken and specific procedures must be followed. This video program outlines those precautions and describes the proper procedures for servicing and maintaining grinding mills. We'll be going in number three finished mill sometime this morning, and we would like for you, if you can, to run some tests in the atmosphere. Sure will, John. We would appreciate it. Here is a list of the procedures needed to safely and efficiently perform ball mill maintenance and repair work. Planning. Selecting and briefing the crew. Issuing safe work permit. Barricading. Locking out the electrical power. Removing the hatch. Safeguarding access to the mill. Providing lighting. Providing ventilation. Providing respiratory protection. Safeguarding welding and cutting. Performing other maintenance work. Reinstalling the hatch. And cleaning up. Planning is needed to ensure close cooperation and coordination between the production and maintenance departments. And to maintain the safety and efficiency of the task at hand. Mark? Yeah, this is John. Yes, we're going to shut down number three finished mill last schedule. Right. Yes, we'll need you to drive the pins in, run the belts empty, and then grind the mill out for 30 minutes. Yes. And we'd like to have it down about nine o'clock. Okay, John. We'll have it emptied out and shut down by nine. All right, sir. Thank you. A timely completion of maintenance and resumption of production depends on proper planning. The mill must be stopped at a precise time. The maintenance crew must be selected and told what to do during the shutdown. And parts and supplies needed for the job must be readily available. Rick, if you have any questions, you work directly for John or Dave or myself. Take your orders directly from them. That way we'll know that you will not get hurt. If you have any questions, then get back to one of your crew leaders or me and we'll answer them the best we can. We're going to take number three finished mill down. We suspect it's got the discharge grate stopped up. It's been a little low on production. While we're in there, we'll also check the ball charge and correct that if needed. Since we're going to be working in a confined area, we must follow procedures that are itemized on this safe work permit. If you have any questions while I'm filling these out, do not hesitate to ask them, because that's what this is concerning, a safe mill operation. A safe work permit is needed for all jobs to be performed in confined spaces. The checklist includes questions such as these. Will hot work be involved? Are qualified people assigned to the job? Have they been adequately briefed prior to entry? And if contractors are involved, are they also briefed on procedures, including pre-entry atmospheric testing and emergency rescue? And is the necessary safety equipment including all personal protective devices on hand before the work is started? Jim, you and Rick go to the tool room and get the necessary tools. Dave, you and John get the barrier tape and barricade the bottom of the side of the mill off to make it safe. And I'll be able to directly post the safe permit and then we'll start our work. After the supervisor has inspected the mill area and determined that all conditions of the safe work permit have been met, he will sign and post the permit at the job site. Only then will the maintenance work begin. Most grinding mills are located above the mill house floor. It is therefore necessary to barricade the immediate area around the mill and put signs for bidding entry of unauthorized personnel. After it is emptied, the operator will kill the power to the mill. The plan calls for sufficient time to allow the cooling of the mill. The electrical department is summoned to disconnect the high voltage electrical power. If the power has been disconnected, the circuit is tested. Then the electrician sets the transfer switch from the normal run position to the spotting position. This will enable the maintenance crew in the mill to spot the hatch for entry. The ball mill manhead is spotted at the 12 o'clock position to allow for easier access into the mill. To complete the lockout, the electrical supervisor and the maintenance crew shall place their personal locks on the tongs. This is to ensure that the mill cannot be re-energized until maintenance is complete and all personnel are outside the mill. In terms of safety, electrical lockout of the machinery is the single most important step in this procedure. After the equipment has been properly spotted, de-energized and locked out in the plant, the maintenance crew proceeds to the central control room to tag out the appropriate switching equipment. Hatch removal is one of the most difficult and dangerous jobs in the maintenance operations. Hatches fit tightly and must be loosened by pounding in order to open. In most cases, lugs temporarily or permanently attached to the outside shell are used to anchor a porta-power or jack in a position where pressure can be applied to the hatch. A cherry picker, mobile crane or similar equipment can be used for removing and reinstalling the hatch. Bridge cranes are not suitable because they lack a precise control and a powerful bridge crane can break the cable or sling from which the hatch is suspended. Sharp blows to the hatch will release it into the mill. The hatch can be allowed to drop into the mill or be lowered with an overhead crane or other hoisting device. To prevent the fall of persons from the top of the mill during maintenance operations, a safe access tune and a secure work area on top of the mill is needed. Safety belts and lanyards are attached to a cable stretched above the top of the mill. This serves as a tie-off point for people working at the hatch. Adequate lighting is needed for maintenance operations. To safeguard against electrical shocks, use low voltage illumination. If low voltage is not available, use protected rough service balls, along with three-wire drop cords which have functional ground protection. The work area inside the mill must be ventilated. In case of emergency shutdown, a substantial amount of material may be left in the mill. In such instances, workers must wear individual respiratory protective devices. The mill should be emptied as much as possible prior to shutdown. Otherwise, material remaining inside will make the work area very dusty. Dampers on the dust collector can be positioned from the central control room to control the flow of air through the mill at a rate that will not stir up the dust still remaining in the mill. Sometimes the dust collector is not adequate for maintaining a flow of fresh, dust-free air inside the drum. In such instances, fans or air horns are used to provide ventilation in the mill. When toxic substances are present, special air monitoring equipment must be available. If all other measures fail to provide proper ventilation, crew members who may be exposed must wear respiratory devices which can protect them from toxic substances. In some cases, self-contained breathing apparatus or supplied air respirators may be required. Also, each employee entering the mill must wear a safety belt that can be attached to the tagline. A safety harness must be available for emergency rescue in the event a worker is injured and must be lifted out of the mill. Fire extinguishers of the proper type must be within easy reach. Where dust and heat are a problem, appropriate protective clothing must be worn. It is very important that during welding and cutting operations, exhaust fans and respirators are used to keep the air free from toxic substances. Compressed gas cylinders needed for welding should never be taken into the mill. It may also be necessary to shut down the dust collector in order to protect the bags from sparks and slag generated during cutting and burning operations. Some plants use white iron balls for grinding. Excessive heat applied to these grinding balls can cause them to explode. Particularly dangerous are balls two and a half inches in diameter or larger. During maintenance, when such balls are in the mill, where sources of high heat are present, such as from cutting torches, the balls must be protected from the heat to prevent possible injuries to workers inside. Maintenance inside the mill involves a variety of tasks such as discharging the medium, recharging the mill, changing the liners and maintenance of separators. When the work is completed, all tools are taken out and the job is inspected. Precautions and safeguards used in reinstalling the hatch are similar to those used in its removal. A cherry picker or mobile crane is most suitable for this work. Prior to turning the unit back to the production crew, make sure that all equipment, pig pens, medium containers and barricades are removed and the area around the mill is cleaned. Have the maintenance crew members remove their locks from the switches, after which the electricians can reconnect and turn on the power. Then required lubrication and other routine pre-starting procedures can be performed. Finally, remove the lockout tags and the safe work permit before turning over the operation of the mill to the production crew. Mark, this is John. Number three finished mill has been checked out, reconnected and it's ready to go. All maintenance procedures have been completed. The mill is now ready for production. Okay, thank you. Supervisors, mill operators and repairmen are responsible for the planning and execution of special safety procedures and safeguards, which relate to the maintenance of the ball mills. This special emphasis on organizing and briefing the crew members in safe procedures while closely adhering to all safeguards will go far in ensuring the safety of mill personnel and the completion of the work with a minimum of downtime.