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Extruder Safety
2 Extruder Safety Safety is each employee’s responsibility, ranging from the janitorial staff to company president. It is the responsibility of each associate to work safely and assist other employees to operate safely, endeavoring to eliminate all unsafe acts that lead to accidents. Of all accidents, 96% are caused by human error, carelessness, or the attitude, “It won’t happen to me.” Consequently, our personal safety plus the safety of those around us is the responsibility of each employee. It is essential to obey all work area rules and be alert for unsafe acts and conditions. Besides working safely, it is important to encourage those around you to work safely. Before a job is started, it needs to be thought through completely and determined if it can be done safely. If it cannot be done safely, do not do the job until you obtain the proper equipment or develop the proper procedure to do it safely. It is important to realize the hazards associated with each job and not take any shortcuts that might put you or your associates in the way of potential danger and serious accidents. Training new employees must include safety training plus the hazards associated with all equipment. In addition to potential equipment hazards, new employees need to know the location of all safety equipment (fire extinguishers, fire blankets, first aid, whom to contact in an emergency, etc.) and understand the correct procedures to follow in the event of an accident or injured employee. Who should be contacted? What is the procedure for reporting accidents? What is my responsibility? Where is the muster point? What do different alarms mean, and what is my response? Associates need to help one another. If you see fellow employees performing unsafe acts, help them understand the proper procedure and why what they were doing is unsafe. This is an act of caring and concern for our fellow employees, not an act to belittle or make somebody look foolish. The most important step in safety is to understand the potential hazards, realize you are not invincible, and that it can happen to you. Follow procedures and think any job through thoroughly before starting to Extrusion. http://dx.doi.org/10.1016/B978-1-4377-3481-2.00002-8 Copyright Ó 2014 Elsevier Inc. All rights reserved.
evaluate the potential for injury to yourself and others. Do not be the bull in the China shop, charging ahead without thought. If a job cannot be done safely, do not do it until procedures, methods, or equipment is available to do it safely.
2.1 Hazards Associated with an Extruder The three biggest potential safety hazards associated with extruders are burns, electrical shock, and falls. Without proper protective equipment, burns can be commonplace among employees working around extruders. Touching a hot die or handling extrudate without gloves normally causes burns. Long sleeves with properly approved thermal gloves should be worn when working around the die, changing the die, tightening die bolts, or other functions performed on the die. If insulation is placed around the die, make sure it is in good shape and properly installed. Hot extrudate from the extruder will stick to your skin. Since polymeric materials are great insulators, after sticking to the skin, they cool very slowly, continuing to burn the skin that is affected. Never stand in front of a die when a single screw extruder is starting up. Air in the extruder and possibly gas from degraded products (if the extruder has been sitting at extrusion temperature with material in the barrel for some time) can erupt from the extruder on start-up. If some polymer is left in the barrel, trapped air can be compressed, blowing the hot polymer out of the die. Standing in front of the extruder creates an unsafe condition where molten polymer can be blown out of the die, land on you, and burn you. Polymer can stick to gloves, where it holds heat for a long time, and can burn you through the gloves if the proper type of glove is not used. When removing the die and/or screw from an extruder (they are normally hot), wear the proper protective equipment (heavy duty gloves and protective thermal sleeves) to prevent burns. Dies can be heavy; therefore, a back brace or other equipment to lift and hold the die can prevent back injuries.
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The potential for electrical shock exists when improperly trained employees remove the extruder covers, thus exposing bare wires and electrical connections. Extruder heater bands are normally 220 or 440 V and can cause serious electrical shock. Check the wires to the heater bands on the die and adapters to ensure that there are no frayed, bare, or exposed wires that can cause electrical shock. In some extrusion processes, water-cooling baths are very close to the die, which can create additional electrical hazard. Unless properly trained, operators should never remove guards, exposing electrical terminals on heaters or open electrical cabinets, to solve electrical problems. The third major potential safety hazard around extruders is falls. Pellets spilled on the floor are slippery and need to be cleaned up immediately. At start-up, the extruder normally generates some scrap, which may be on the floor around the die. This creates tripping hazards that must be removed immediately. Occasionally, processing issues arise at start-up, leading to too much material on the floor around the extruder. In these situations, the extruder should be shut down, the area cleaned, and the extruder restarted. Some extrusion processes use water for cooling. Water that spills on the floor should be removed with a wet/dry vacuum or squeegeed to a drain. Wet floors are very slippery and can cause falls. The most dangerous area around an extruder is the exposed screw turning in the feed throat. Never, never stick your hands or fingers into the feed throat. If the screw is turning, it can generate incredible power that can quickly remove a finger. If the feed throat is hot, you may also get burned. The most dangerous time during extruder operation is start-up. An extruder is a pressure vessel. Material is being fed into one end with a positive conveying mechanism (screw) operating at high horsepower. If the die end of the extruder is blocked with solid plastic or contaminants, incredible pressure can build up very rapidly and blow the die off. Always start the extruder screw slowly and monitor the die pressure closely until polymer is flowing continuously. Once flow from the die is established, the screw speed can be safely increased. As mentioned previously, never stand in front of an extruder during start-up in case molten plastic is blown out of the die under high pressure. Extruders are equipped with rupture disks to prevent high pressure from blowing the die off the
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end and pressure gauges (discussed later) to monitor the pressure in and before the die. Make sure the pressure gauges are functioning properly. If the extruder does not have a rupture disk at the extruder head to relieve high pressure, it should have a pressure gauge with a feedback loop that automatically shuts the extruder down when a preset pressure is reached. Most modern extruders are equipped with both a rupture disk and a highpressure sensor that will shut the extruder down in the event of high-pressure situations. Having both the rupture disk and pressure sensor will protect in the situation where on heat-up, cold spots trap melting and expanding polymer in the head and melt pipe area. It is possible to exceed 20,000 psi in a pool of trapped polymer. Each extruder should be equipped with a fume hood at the die or vent port to remove any fumes generated.
2.1.1 Hazards Associated with Takeoff Equipment The safety hazards associated with takeoff equipment depend on the extrusion process and takeoff equipment. Pinch points associated with nip rolls, pullers, and roll stacks are one potential safety hazard requiring careful operation. If two operators are running equipment containing nip rolls, they must communicate to verify that all operators are clear when nip rolls are closed. Loose-fitting clothing that can be caught in nip rolls or pullers must be avoided. Some lines have rolling knives or knives for edge slitting. These should be guarded, and operators must exercise caution when working in those areas. High-speed rotating rolls present special hazards. Guards around all rolls and nip points must be kept in place to prevent injury. Arms, fingers, and hands can easily be pulled into high-speed rolling equipment, causing severe personal injury or dismemberment. Scrap from start-up lying on the floor poses a tripping hazard. This should be picked up and disposed as soon as the line is running. If start-up problems continue and prevent cleanup, the equipment should be shut down, the area cleaned, and the line restarted. Noise >80 dB requires that hearing protection be used by all people in the area. If the noise level is <80 dB, employees may still want to wear hearing protection to prevent long-term hearing loss.
2: E XTRUDER S AFETY
Like the extruder, identify potential safety hazards associated with the takeoff equipment. Form a plan to avoid potential hazards. Know where all emergency stop buttons are and verify that they work. Do not take the approach, “It Won’t Happen to Me.” It has been reported that it takes 300 unsafe acts to cause an accident. So, if you keep doing the unsafe act, it will eventually lead to an accident.
2.1.2 Personal Protective Equipment Personal protective equipment exists to make your job safer. Determine what equipment you need to do your job safely and use it. The following is a list of some available personal protective equipment:
Safety glasses with or without side shields Safety shoes Ear protection Gloves Thermal insulated gloves for hot applications Long sleeves Hard hats Face shield Goggles Back brace Wrist brace Floor mats
2.1.3 Lockout, Tag, and Clear Procedure Anyone working on equipment should have a personal lock with his or her name on it and the only key. Before doing maintenance or other work on the equipment, turn off the power switch and lockout the switch with your personal lock. Employees working on the line must attach their own lock. After locking out and tagging the equipment before doing any work, each worker attempts to start the equipment to verify it is off and cannot be turned on. Once the maintenance or other work is completed, each worker removes his own individual lock before the equipment can be restarted. This procedure prevents somebody from getting hurt while working on the equipment when another person inadvertently starts the equipment.
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2.2 Proper Training Do not run the equipment without proper training and understanding the potential safety hazards associated with the operation. Know where you can get hurt and understand how all the equipment and controls operate. Training includes an introduction to start-up and shutdown procedures, understanding the caution or warning signs on the machines, and operating time on the equipment with an experienced operator.
2.3 Inspection and Housekeeping Before each shift, evaluate the operating area and plant in general, looking for unsafe conditions, e.g. tripping hazards, exposed wires, water on the floor, etc. Determine what you are going to do on your shift and review the operation for safety. Good housekeeping is directly related to safety. A cluttered, dirty area will lead to accidents and reflects on your attitude toward the job. A proper storage area for all tools and equipment makes the job easier and the plant a better place to work.
2.4 Material Safety Understand the materials you are using by reviewing the Material Safety Data Sheets. Improper operating conditions or purging with the wrong materials can have serious consequences. Overheating polyvinyl chloride (PVC) generates hydrochloric acid (HCl), which attacks the lungs and rusts plant equipment. Never mix acetal with nylon, PVC, fluorinated polymers, or ionomer in an extruder, as they will react and give off formaldehyde. PVC has limited thermal stability and should not be left in a hot extruder. PVC degrades in an autocatalytic reaction, generating HCl. Proper purge material should be available to remove PVC from the barrel if the extruder is going to be down for an extended time. Operators who have the flexibility to change extruder temperature profiles need to understand the upper processing limits when extruding PVC or other temperature-sensitive polymers.
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Review Questions 1. What is the most dangerous time during extrusion and why? 2. Where are the most dangerous locations around an extruder and why? 3. What are some potential hazards associated with extrusion? 4. What is the “lockout, tag, and clear” procedure, and when should the procedure be used? 5. Why is housekeeping important? 6. What is a near miss? 7. What hazards are associated with takeoff equipment? 8. What is some personal protective equipment? 9. What materials should not be mixed with acetal in an extruder? 10. What happens if PVC is overheated? 11. How many times does an unsafe act get repeated before an accident occurs?
evaluate the potential for injury to yourself and others. Do not be the bull in the China shop, charging ahead without thought. If a job cannot be done safely, do not do it until procedures, methods, or equipment is available to do it safely.
2.1 Hazards Associated with an Extruder The three biggest potential safety hazards associated with extruders are burns, electrical shock, and falls. Without proper protective equipment, burns can be commonplace among employees working around extruders. Touching a hot die or handling extrudate without gloves normally causes burns. Long sleeves with properly approved thermal gloves should be worn when working around the die, changing the die, tightening die bolts, or other functions performed on the die. If insulation is placed around the die, make sure it is in good shape and properly installed. Hot extrudate from the extruder will stick to your skin. Since polymeric materials are great insulators, after sticking to the skin, they cool very slowly, continuing to burn the skin that is affected. Never stand in front of a die when a single screw extruder is starting up. Air in the extruder and possibly gas from degraded products (if the extruder has been sitting at extrusion temperature with material in the barrel for some time) can erupt from the extruder on start-up. If some polymer is left in the barrel, trapped air can be compressed, blowing the hot polymer out of the die. Standing in front of the extruder creates an unsafe condition where molten polymer can be blown out of the die, land on you, and burn you. Polymer can stick to gloves, where it holds heat for a long time, and can burn you through the gloves if the proper type of glove is not used. When removing the die and/or screw from an extruder (they are normally hot), wear the proper protective equipment (heavy duty gloves and protective thermal sleeves) to prevent burns. Dies can be heavy; therefore, a back brace or other equipment to lift and hold the die can prevent back injuries.
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14
The potential for electrical shock exists when improperly trained employees remove the extruder covers, thus exposing bare wires and electrical connections. Extruder heater bands are normally 220 or 440 V and can cause serious electrical shock. Check the wires to the heater bands on the die and adapters to ensure that there are no frayed, bare, or exposed wires that can cause electrical shock. In some extrusion processes, water-cooling baths are very close to the die, which can create additional electrical hazard. Unless properly trained, operators should never remove guards, exposing electrical terminals on heaters or open electrical cabinets, to solve electrical problems. The third major potential safety hazard around extruders is falls. Pellets spilled on the floor are slippery and need to be cleaned up immediately. At start-up, the extruder normally generates some scrap, which may be on the floor around the die. This creates tripping hazards that must be removed immediately. Occasionally, processing issues arise at start-up, leading to too much material on the floor around the extruder. In these situations, the extruder should be shut down, the area cleaned, and the extruder restarted. Some extrusion processes use water for cooling. Water that spills on the floor should be removed with a wet/dry vacuum or squeegeed to a drain. Wet floors are very slippery and can cause falls. The most dangerous area around an extruder is the exposed screw turning in the feed throat. Never, never stick your hands or fingers into the feed throat. If the screw is turning, it can generate incredible power that can quickly remove a finger. If the feed throat is hot, you may also get burned. The most dangerous time during extruder operation is start-up. An extruder is a pressure vessel. Material is being fed into one end with a positive conveying mechanism (screw) operating at high horsepower. If the die end of the extruder is blocked with solid plastic or contaminants, incredible pressure can build up very rapidly and blow the die off. Always start the extruder screw slowly and monitor the die pressure closely until polymer is flowing continuously. Once flow from the die is established, the screw speed can be safely increased. As mentioned previously, never stand in front of an extruder during start-up in case molten plastic is blown out of the die under high pressure. Extruders are equipped with rupture disks to prevent high pressure from blowing the die off the
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end and pressure gauges (discussed later) to monitor the pressure in and before the die. Make sure the pressure gauges are functioning properly. If the extruder does not have a rupture disk at the extruder head to relieve high pressure, it should have a pressure gauge with a feedback loop that automatically shuts the extruder down when a preset pressure is reached. Most modern extruders are equipped with both a rupture disk and a highpressure sensor that will shut the extruder down in the event of high-pressure situations. Having both the rupture disk and pressure sensor will protect in the situation where on heat-up, cold spots trap melting and expanding polymer in the head and melt pipe area. It is possible to exceed 20,000 psi in a pool of trapped polymer. Each extruder should be equipped with a fume hood at the die or vent port to remove any fumes generated.
2.1.1 Hazards Associated with Takeoff Equipment The safety hazards associated with takeoff equipment depend on the extrusion process and takeoff equipment. Pinch points associated with nip rolls, pullers, and roll stacks are one potential safety hazard requiring careful operation. If two operators are running equipment containing nip rolls, they must communicate to verify that all operators are clear when nip rolls are closed. Loose-fitting clothing that can be caught in nip rolls or pullers must be avoided. Some lines have rolling knives or knives for edge slitting. These should be guarded, and operators must exercise caution when working in those areas. High-speed rotating rolls present special hazards. Guards around all rolls and nip points must be kept in place to prevent injury. Arms, fingers, and hands can easily be pulled into high-speed rolling equipment, causing severe personal injury or dismemberment. Scrap from start-up lying on the floor poses a tripping hazard. This should be picked up and disposed as soon as the line is running. If start-up problems continue and prevent cleanup, the equipment should be shut down, the area cleaned, and the line restarted. Noise >80 dB requires that hearing protection be used by all people in the area. If the noise level is <80 dB, employees may still want to wear hearing protection to prevent long-term hearing loss.
2: E XTRUDER S AFETY
Like the extruder, identify potential safety hazards associated with the takeoff equipment. Form a plan to avoid potential hazards. Know where all emergency stop buttons are and verify that they work. Do not take the approach, “It Won’t Happen to Me.” It has been reported that it takes 300 unsafe acts to cause an accident. So, if you keep doing the unsafe act, it will eventually lead to an accident.
2.1.2 Personal Protective Equipment Personal protective equipment exists to make your job safer. Determine what equipment you need to do your job safely and use it. The following is a list of some available personal protective equipment:
Safety glasses with or without side shields Safety shoes Ear protection Gloves Thermal insulated gloves for hot applications Long sleeves Hard hats Face shield Goggles Back brace Wrist brace Floor mats
2.1.3 Lockout, Tag, and Clear Procedure Anyone working on equipment should have a personal lock with his or her name on it and the only key. Before doing maintenance or other work on the equipment, turn off the power switch and lockout the switch with your personal lock. Employees working on the line must attach their own lock. After locking out and tagging the equipment before doing any work, each worker attempts to start the equipment to verify it is off and cannot be turned on. Once the maintenance or other work is completed, each worker removes his own individual lock before the equipment can be restarted. This procedure prevents somebody from getting hurt while working on the equipment when another person inadvertently starts the equipment.
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2.2 Proper Training Do not run the equipment without proper training and understanding the potential safety hazards associated with the operation. Know where you can get hurt and understand how all the equipment and controls operate. Training includes an introduction to start-up and shutdown procedures, understanding the caution or warning signs on the machines, and operating time on the equipment with an experienced operator.
2.3 Inspection and Housekeeping Before each shift, evaluate the operating area and plant in general, looking for unsafe conditions, e.g. tripping hazards, exposed wires, water on the floor, etc. Determine what you are going to do on your shift and review the operation for safety. Good housekeeping is directly related to safety. A cluttered, dirty area will lead to accidents and reflects on your attitude toward the job. A proper storage area for all tools and equipment makes the job easier and the plant a better place to work.
2.4 Material Safety Understand the materials you are using by reviewing the Material Safety Data Sheets. Improper operating conditions or purging with the wrong materials can have serious consequences. Overheating polyvinyl chloride (PVC) generates hydrochloric acid (HCl), which attacks the lungs and rusts plant equipment. Never mix acetal with nylon, PVC, fluorinated polymers, or ionomer in an extruder, as they will react and give off formaldehyde. PVC has limited thermal stability and should not be left in a hot extruder. PVC degrades in an autocatalytic reaction, generating HCl. Proper purge material should be available to remove PVC from the barrel if the extruder is going to be down for an extended time. Operators who have the flexibility to change extruder temperature profiles need to understand the upper processing limits when extruding PVC or other temperature-sensitive polymers.
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Review Questions 1. What is the most dangerous time during extrusion and why? 2. Where are the most dangerous locations around an extruder and why? 3. What are some potential hazards associated with extrusion? 4. What is the “lockout, tag, and clear” procedure, and when should the procedure be used? 5. Why is housekeeping important? 6. What is a near miss? 7. What hazards are associated with takeoff equipment? 8. What is some personal protective equipment? 9. What materials should not be mixed with acetal in an extruder? 10. What happens if PVC is overheated? 11. How many times does an unsafe act get repeated before an accident occurs?