Mechanical power shears contain a ram for their shearing action. The ram moves a non-rotary blade at a constant rate past the edge of a fixed blade. Shears may be mechanically, hydraulically, hydramechanically, pneumatically, or manually powered and are used to perform numerous functions such as squaring, cropping, and cutting to length.
In the basic shear operation, stock is fed into the point of operation between two blades. A hold-down may then be activated that applies pressure to the stock to prevent movement. One complete cycle consists of a downward stroke of the top blade until it passes the lower fixed blade followed by an upward stroke to the starting position.
Shears can be categorized as stand-alone manual shears, stand-alone automatic shears, and process-line shears.
§ Stand-alone manual shears. An operator controls them from a control station. The operator feeds the shear either by hand or the automatic loading mechanism and activates the equipment using hand or foot controls or a tripping device on the back side of the shear. An example is an alligator shear.
§ Stand-alone automatic shears. These feed and stroke automatically and continuously. The operator uses hand-activated or foot-activated controls to initiate the operation requiring limited additional operator interaction. An example is a guillotine shear.
§ Process-line shears. These are integrated into an automated production process and are controlled automatically as part of the process. Examples include crop shears and cut-to-length shears.
The primary hazard associated with shears is the shearing action at the point of operation. Amputations may occur in the following situations:
§ The foot control inadvertently activates while the operator’s hands are in the point of operation. Such amputations usually relate to foot-activated, stand-alone manual shears that require the use of both hands to feed the stock.
§ A tripping device located on the back side of the shear’s mouth operates the shear but does not prevent the operator from reaching into the hazard area. Such tripping devices, commonly found on stand-alone manual shears, may increase productivity but must be used in conjunction with appropriate safeguards.
§ When there is no hold-down and stock being fed into a stand-alone manual shear kicks out and strikes the operator’s hands or fingers.
§ The shear is not equipped with either a full-revolution or a part-revolution clutch. Even after it is shut down, a shear that is not equipped with either type of clutch continues to cycle until its energy is exhausted.
| Case History | An employee was cutting material with a 50-inch guillotine shear equipped with two buttons to prevent employees from reaching into the blade area. He had taped up one of the buttons and used his knee to trip the other button. With both hands under the blade he inadvertently hit the free button with his knee. This activated a stroke of the blade, which amputated both of his hands just below the wrists. Source: OSHA IMIS Accident Investigation Database |
Because shears have a wide variety of applications, safeguarding methods must be determined individually for each machine based on its use. A number of different safeguarding methods may be necessary to adequately protect the operator as well as other workers nearby. For example, you will need to consider the machine size, operating speed, size and type of material, length of production runs, required accuracy of the work, methods for material feeding and removal, operator controls, and clutch type.
Here are some engineering controls you should use:
§ Use automatic-feeding devices such as conveyors with stand-alone manual shears when the material is uniform in size and shape.
§ Equip mechanical shears with either a part-revolution or full-revolution clutch. Methods of safeguarding depend on the type of clutch in use. Shears equipped with full-revolution clutches used in single-stroke operations must be equipped with an anti-repeat feature.
The following recommendations apply to safeguarding the shear’s point of operation during feeding activities at the front of the machine:
§ Install a fixed or adjustable point of operation guard at the in-feed of the shearing machine to prevent operator contact with the shear’s point of operation as well as the pinch point of the hold-down. The guard’s design should prevent the employee from reaching under or around it.
§ Install a safety trip control device — such as a pressure-sensitive body bar, safety tripod, or safety tripwire cable — at the in-feed section of the shear.
§ Install a presence-sensing device, such as a light curtain, near the in-feed area of a stand- alone automatic or process-line shear.
§ Install hold-down devices that prevent the work piece from kicking up and striking the operator.
§ Install and arrange two-hand trips and controls so that the operator must use both hands to initiate the shear cycle. Two-hand trips and controls should be designed so they cannot be defeated easily. The ANSI B11.4 Safety Requirements for Construction, Care, and Use of Shears standard recommends the installation of additional safeguarding when two-hand controls are used on part-revolution shears, based on the nature of the shearing operation. ANSI specifies the use of guards on full-revolution shears.
§ Use restraints for stand-alone manual shears when other guarding methods are not feasible or do not adequately protect employees. These devices may not be appropriate if the job requires employees mobility.
§ Install guarded operating stations at a safe distance from the shear’s point of operation to prevent inadvertent activation.
§ Mount guarded foot pedal controls at a safe distance away from the point of operation to prevent accidental activation.
The following recommendations apply to safeguarding for operations performed at the rear of the shear:
§ Install fixed guards on the back side of shears.
§ Install an awareness barrier guard with an interlocking gate, a presence-sensing device (light curtain), or a safety trip control (safety tripwire cable or safety tripod) on the back the shear.
Here are some work practices and administrative controls for shearing machines you can follow:
§ Develop and implement safe operating procedures for shearing machines and conduct periodic inspections to ensure compliance.
§ Instruct operators to use distancing tools when their hands might reach into the point of operation because of the size of the material being cut.
§ Instruct employees to perform routine maintenance on the clutch and braking systems.
§ Instruct employees to inspect all guarding to ensure that it is in place properly before the machine is operated.
§ Instruct supervisors to ensure that operators keep their hands out of the shear’s point of operation at all times while the machine is energized and not properly locked out.
§ Instruct employees not to perform activities on the back side of a shear while it is operating or still energized.
§ Prohibit employees from riding the foot activation pedal.
§ Ensure that all operators receive on-the-job training under the direct supervision of experienced operators until they can work safely on their own.
§ Require workers to perform servicing and maintenance activities under an energy control program in §1910.147.
3 comments:
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