Power Press Brakes
Power press brakes are similar to mechanical power presses in that they use vertical reciprocating motion and are used for repetitive tasks.
Press brake operation is either mechanical or hydraulic. Press brakes are either general-purpose or special-purpose brakes, according to ANSI B11.3-2002, Safety Requirements for Power Press Brakes.
General purpose press brakes have a single operator control station. A servo-system activates the special purpose brake, which may be equipped with multiple operator/helper control stations. (See Figure 25 for a power press brake operation.)
Hazards of Power Press Brakes.
As with mechanical power presses, point of operation injuries are the most common type of injury associated with power press brakes.
Here are some frequent causes of amputations from power press brakes:
• Foot controls being inadvertently activated while the operator’s hand is in the point of operation. The likelihood of this type of injury increases as the size of stock decreases and brings the operator’s hands closer to the point of operation.
• Parts of the body caught in pinch points created between the stock and the press brake frame while the bend is being made.
• Controls of a single-operator press bypassed by having a coworker activate the controls while the operator positions or aligns stock or repairs or troubleshoots the press.
• Failure to properly lockout/tagout presses during the necessary tasks of making adjustments, clearing jams, performing maintenance, installing or aligning dies, or cleaning the machine.
Case History #4
An operator was bending small parts using an 80-ton unguarded press brake. This required the employee’s fingers to be very close to the point of operation; and, consequently, the operator lost three fingers when his hand entered the point of operation. The operator on the previous shift had reported to the supervisor that the operator placed his fingers close to the point of operation, but was told that nothing could be done and that the operator should be careful.
Case History #5
An operator was bending metal parts using a 36-ton part-revolution power press brake that was foot-activated and equipped with a light curtain.
About 3-4 inches of the light curtain had been “blanked out” during a previous part run. While adjusting a part at the point of operation, the employee accidentally activated the foot pedal and amputated three fingertips.
Safeguarding Power Press Brakes
Primary safeguarding methods, such as physical guards and point of operation safeguarding devices (movable barrier devices, presence-sensing devices,
pull-back devices, restraint devices, singleand two-hand devices) can be used to effectively guard power press brakes. (Figure 26 shows a general-purpose power press brake used in conjunction with pullbacks.) Some safeguarding methods, such as presence-sensing devices, may require muting or blanking to allow the bending of material.
Always ensure that these safety devices are properly installed, maintained, and used in accordance with the manufacturer’s guidelines for the specific stock and task to be performed. Failure to do so could leave sensing field channels "blanked out" and expose operators to point-of-operation hazards as the safeguarding device’s safety distance increases when blanking is used.
In other instances, such as with special-purpose power press brakes, machines are equipped with advanced control systems that are adaptable to all forms of safeguarding concepts and devices, such as two-hand controls and multiple operator/helper actuating controls. For example, two-hand down, foot through (actuation) methods are used to safeguard employees while they operate press brakes.
With this safeguarding system, an operator uses a two-hand control to lower the press brake ram, for example, to within 1/4 inch or less of the lower die (which is considered a safe opening). The operator then has the ability to maneuver and align the work-piece within this 1/4 inch safe opening area and he or she is protected from the amputation hazard. Then the foot control is used by the operator to safely actuate the machine to produce the desired product.
Because of constraints imposed by certain manufacturing or fabricating processes, safeguarding by maintaining a safe distance from the point of operation may be acceptable. However, this is permitted only when safeguarding by barrier guard or safeguarding devices is not feasible (impossible) – that is, where the use of primary safeguarding method (such as a restraint device) is not feasible.
Additional information about a safe distance safeguarding program can be found in OSHA Instruction 02-01-025 [CPL 2-1.25] – Guidelines for Point of Operation Guarding of Power Press Brakes.
Other Controls for Power Press Brakes
The following are some secondary safeguarding methods and complementary equipment that may be used to supplement primary safeguarding or alone or in combination when primary safeguarding methods are not feasible:
- Safe distance safeguarding,
- Safe holding safeguarding,
- Safe work procedures,
- Work-holding equipment (such as back gauges),
- Properly designed and protected foot pedals, and
- Hand-feeding tools.
Ensure that proper safeguarding and lockout/tagout procedures are developed and implemented for power press brakes. Train and supervise employees in these procedures and conduct periodic inspections to ensure compliance.
Hazards of Conveyors
Conveyors are used in many industries to transport materials horizontally, vertically, at an angle, or around curves. Many conveyors have different and unique features and uses, so that hazards vary due to the material conveyed, the location of the conveyor, and the proximity of the conveyer to the employees. Types include unpowered and powered, live roller, slat, chain, screw, and pneumatic.
Conveyors eliminate or reduce manual material handling tasks, but they present amputation hazards associated with mechanical motion. (See Figures 27 through 30 for examples of common conveyors.)
Conveyor-related injuries typically involve a employee’s hands or fingers becoming caught in nip points or shear points on conveyors and may occur in these situations:
- Cleaning and maintaining a conveyor, especially when it is still operating.
- Reaching into an in-going nip point to remove debris or to free jammed material.
- Allowing a cleaning cloth or an employee’s clothing to get caught in the conveyor and pull the employee’s fingers or hands into the conveyor.
Other conveyor-related hazards include improperly guarded gears, sprocket and chain drives, horizontal and vertical shafting, belts and pulleys, and power transmission couplings. Overhead conveyors warrant special attention because most of the conveyor’s drive train is exposed. Employees have also been injured or killed while working in areas underneath conveyors and in areas around lubrication fittings, tension adjusters, and other equipment with hazardous energy sources.
Case History #6
While removing a cleaning rag from the ingoing nip point between the conveyor belt and its tail pulley (the unpowered end of the conveyor), an employee’s arm became caught in the pulley, which amputated his arm below the elbow.
Case History #7
While servicing a chain-and-sprocket drive assembly on a roof tile conveyor system, an employee turned off the conveyor, removed the guard, and began work on the drive assembly without locking out the system. When someone started the conveyor, the employee’s fingers became caught in the chain-and-sprocket drive and were amputated.
As conveyor hazards vary depending on the application, employers need to look at each conveyor to evaluate and determine what primary safeguarding methods and energy control (lockout/tagout) practices are required. Where necessary for the protection of employees, conveyors need to have mechanical guards that protect the employee from nip points, shear points, and other moving parts, including power-transmission apparatus. Guards may include barriers, enclosures, grating, fences, or other obstructions that prevent inadvertent physical contact with operating machine components, such as point of operation areas, belts, gears, sprockets, chains, and other moving parts. A brief description of the hazards and recognized safeguarding methods is presented for common types of conveyors.
Typical Conveyor Hazards and Safeguarding Methods
Hazards: Belt-conveyor drive mechanisms and conveying mediums are hazardous as are the following belt-conveyor areas:
- conveyor take-up and discharge ends;
- where the belt or chain enters or exits the in-going nip point;
- where the belt wraps around pulleys;
- snub rollerswhere the belt changes direction, such as takeups;
- where multiple conveyors are adjoined;
- on transfers or deflectors used with belt conveyors.
Controls: The hazards associated with nip and shear points must be safeguarded. Side guards (spill guards), if properly designed can prevent employee contact with power-transmission component, in-going nip points and the conveying medium. Secondary safeguarding methods for hazard control include the use of standard railings or fencing, or safeguarding by distance (location), and installing hazard awareness devices, such as pre-start-up signals and warning signs.
Hazards: Screw conveyors are troughs with a revolving longitudinal shaft on which a spiral or twisted plate is designed. In-going nip points, of turning helical flights for the entire length of the screw conveyor, exist between the revolving shaft and trough. Since the trough is not usually required to be covered for proper operation of the conveyor and because many screw conveyors are located at or near the floor level, the hazard of stepping into the danger area is ever present. Once caught, the victim is pulled further into the path of the conveying medium.
Controls: A screw conveyor housing must completely enclose the moving elements (screw mechanism, power transmission apparatus) of the conveyor, except for the loading and discharge points. Permanently affixed grids or polycarbonate can be installed for visibility purposes to allow the operator to inspect the operation.
Alternatively, the trough side walls should be high enough to prevent employees from reaching over and falling into the trough. Open troughs can be used if covers are not feasible; but employees need to be protected by secondary safeguarding methods, such as a railing or fence.
Feed loading and discharge points can usually be guarded by providing enclosures, screening, grating, or some other interruption across the openings which will allow the passage of the material without allowing the entry of a part of the employee’s body into the moving part(s).
Hazards: Nip points occur when a chain contacts a sprocket, such as when a chain runs around a sprocket or when the chain is supported by a sprocket or when a shoe above the chain precludes the chain from lifting off the sprocket. Nip points also occur at drives, terminals, take-ups (automatic take-ups may also have shear points), and idlers. Employee clothing, jewelry, and long hair may also get entangled and caught in the moving chain conveyor.
Controls: Sometimes, moving chains cannot be enclosed without impairing the functioning of the conveyor. However, in some cases, barrier guards may be installed around the moving parts for hazard enclosure purposes or, in other instances, nip and shear points may be eliminated by placing a guard at the nip point or shear point. Other secondary safeguarding options include safeguarding by distance (location) and the use of awareness devices.
Hazards: Roller conveyors are used to move material on a series of parallel rollers that are either powered or gravity-fed. Powered roller conveyors have the hazard of snagging and pulling objects, including hands, hair, and clothing into the area between the rollers and the stationary components of the conveyor.
In-going nip points generally exist between the drive chain and sprockets; between belt and carrier rollers; and at terminals, drives, take-ups, idlers, and snub rollers.
Controls: Roller conveyors need to, where feasible, have permanent barrier guards that can be adjusted as necessary to protect the employee from nip and shear points. For example, the unused section of rollers closest to the employees needs to be guarded when transporting small items on a roller conveyor that do not require the use of the entire roller width. Also, conveyor hazards may be reduced by eliminating or minimizing projections from the roller and through the use of pop-up rollers. Other secondary safeguarding options include safeguarding by distance (location) and the use of awareness devices.
Other Controls for Conveyors
The following are some secondary safeguarding methods, work practices, and complementary equipment that may be used to supplement primary safeguarding or alone or in combination when primary safeguarding methods are not feasible:
- Safeguarding by safe distance (by location) — locating moving parts away from employees toprevent accidental contact with the hazard point—is one option for safeguarding conveyors. It is particularly difficult, however, to use this method when employees need to be at or near unguarded moving parts.
- Use prominent awareness devices, such as warning signs or lights, to alert employees to the conveyor operation.
- Allow only trained individuals to operate conveyors and only trained, authorized staff to perform servicing and maintenance work.
- Visually inspect the entire conveyor and immediate work area prior to start-up to determine that the actuation will not cause an employee hazard.
- Inspect and test conveyor safety mechanisms, such as its alarms, emergency stops, and safeguarding methods.
- Do not use any conveyor which is unsafe until it is made safe.
- Forbid employees from riding on conveyors.
- Prohibit employees working with or near conveyors from wearing loose clothing or jewelry, and require them to secure long hair with a net or cap.
- Install emergency stop devices on conveyors where employees work when they cannot otherwise control the movement of the conveyor. This recognized safety feature provides employees with the means to shut off the equipment in the event of a hazardous situation or emergency incident.
For emergency stop devices, you will need these engineering controls:
- Equip conveyors with interlocking devices that shut them down during an electrical or mechanical overload such as product jam or other stoppage. Emergency devices need to be installed so that they cannot be overridden from other locations.
- When conveyors are arranged in a series, all should automatically stop whenever one stops.
- Equip conveyors with emergency stop controls that require manual resetting before resuming conveyor operation.
- Install clearly marked, unobstructed emergency stop buttons or pull cords within easy reach of employees.
- Provide continuously accessible conveyor belts with emergency stop cables that extend the entire length of the conveyor belt to allow access to the cable from any point along the belt.
- Ensure that conveyor controls or power sources can accept a lockout/tagout device to allow safe maintenance practices.
- Perform servicing and maintenance under an energy control program in accordance with the Control of hazardous energy (lockout/tagout), 29 CFR 1910.147, standard. For example, instruct employees to lubricate, align, service, and maintain conveyors when the conveyor is locked or tagged out if the task would expose them to an area of the conveyor (or adjacent machinery) where hazardous energy exists.
[Content with recognition to OSHA]
Specific Machine Hazards Part 1