MACHINE GUARDING Identification Jennifer Byrne 2020 1 Jennifer
MACHINE GUARDING & Identification Jennifer Byrne 2020 1
Jennifer Byrne 2020 2
Ø Any point other than the point of operation at which it is possible for a part of the body to be caught between moving parts, between moving and stationary parts, or between the material and moving parts of a machine tool. Jennifer Byrne 2020 3
Ø Ø Ø Any guard selected should not itself present a hazard such as trapping or shear points, rough or sharp edges or hazards likely to cause injury. Moveable guards should not need tools to adjust them. Moveable guards should be adjusted to enclose as much of the cutter as possible. Jennifer Byrne 2020 4
Ø Guards should be designed and constructed with the object of preventing any part of the body from reaching a danger point or area. Ø They should take account of the physical characteristics or the people involved, and in particular their abilities to reach through openings, and over or around barriers or guards. Jennifer Byrne 2020 5
Ø If the hazard is on a part of the machinery which does not require access, a guard should be permanently fixed to the machinery. Ø These types of guards must require tools for removal. The fixed guards must be able to: – withstand their operating environment – contain projectiles where necessary – not create hazards by having, for example, sharp edges. Ø Fixed guards may have openings where the guard meets the machinery or openings due to the use of a wire mesh type enclosure. Jennifer Byrne 2020 6
Ø Ø Where it is not practicable to use enclosing guards, barriers may be used to prevent people reaching the danger point. These rely on a combination of height and distance to achieve their purpose Jennifer Byrne 2020 7
Ø Ø Ø Wherever there is a danger of an operator getting into trouble on a machine there must be a facility for fast access to an emergency stop device. The e-stop device must be continuously operable and readily available. Operator panels should contain at least one e-stop device. Additional e-stop devices may be used at other locations as needed. Jennifer Byrne 2020 8
Ø E-Stop devices come in various forms. Pushbutton switches and cable pull switches are examples of the more popular type devices. Ø When the e-stop device is actuated, it must latch in and it must not be possible to generate the stop command without latching in. Ø The resetting of the emergency stop device must not cause a hazardous situation. A separate and deliberate action must be used to re-start the machine. Jennifer Byrne 2020 9
Ø Ø Emergency stop devices are considered complimentary safeguarding equipment. They are not considered primary safeguarding devices because they do not prevent access to a hazard nor do they detect access to a hazard. What are the guards on this Machine? Jennifer Byrne 2020 10
Ø The usual way of providing this is in the form of a redcoloured mushroom-headed push button on a yellow background which the operator strikes in the event of an emergency. Ø They must be strategically placed in sufficient quantity around the machine to ensure that there is always one in reach at a hazard point. Jennifer Byrne 2020 11
Ø These devices use a steel wire rope connected to latching pull switches so that pulling on the rope in any direction at any point along its length will trip the switch and cut off the machine power. Ø The cable pull switches must detect both a pull on the cable as well as when the cable goes slack. Slack detection ensures that the cable is not cut and is ready for use. Ø Cable distance affects performance of the switch. For short distances, the safety switch is mounted on one end a tension spring mounted at the other. Jennifer Byrne 2020 12
Ø The use of two-hand controls (also referred to as bi-manual controls) is a common method of preventing access while a machine is in a dangerous condition. Two controls must be operated concurrently (within 0. 5 s of each other) to start the machine. Ø This ensures that both hands of the operator are occupied in a safe position (i. e. , at the controls) and therefore cannot be in the hazard area. Ø Machine operation must cease when either of the controls are released, if one control is released, the other control must also be released before the machine can be restarted. Jennifer Byrne 2020 13
Ø The physical design spacing should prevent improperation (e. g. , by hand elbow). Ø This can be accomplished by distance or shields as the examples shown below. Jennifer Byrne 2020 14
Ø When access to the machine is frequent, movable guards are preferred. Ø The guard is interlocked with the power source of the hazard in a manner which ensures that whenever the guard door is not closed the hazard power will be switched off. Ø This approach involves the use of an interlocking switch fitted to the guard door. The control of the power source of the hazard is routed through the switch section of the unit. Ø The power source is usually electrical but it could also be pneumatic or hydraulic. When guard door movement (opening) is detected the interlocking switch will initiate a command to isolate the hazard power supply either directly or via a power contactor (or valve). Jennifer Byrne 2020 15
Ø Tongue operated interlocks require a tongue-shaped actuator to be inserted and removed from the switch. Ø When the tongue is inserted, the internal safety contacts close and allow the machine to run. Ø When the tongue is removed, the internal safety contacts open and send a stop command to the safety related parts of the control system Jennifer Byrne 2020 16
Ø Ø Some interlocking switches also incorporate a locking device that locks the guard door closed and will not release it until the machine is in a safe condition. For the majority of applications the combination of a movable guard an interlock switch with or without guard locking is the most reliable and cost effective solution. Jennifer Byrne 2020 17
Ø An interlock provides the connection between a guard and the control or power system of the machinery to which the guard is fitted. Jennifer Byrne 2020 18
Ø These devices are used to provide guarding of a floor area around a machine. A matrix of interconnected mats is laid around the hazard area and pressure applied to the mat (e. g. , an operator's footstep) will cause the mat controller unit to switch off power to the hazard. Jennifer Byrne 2020 19
Ø Perimeter access control is often used to detect access along the outside edge of a hazard area. Light curtains used to detect perimeter access have resolutions that detect full bodies. This can be accomplished by a couple different ways: – Multi-beam light curtains consisting of two or three beams – Single beam device that is reflected off mirrors to create a dual beam pattern are regularly used. Ø Ø In either case, the lowest beam should be 300 mm off the ground, and the highest beam should prevent a person from simply climbing over the light curtain. Mirrors can be used to deflect the light beam around a cell. Jennifer Byrne 2020 20
Ø Ø Safety light curtains consist of an emitter and receiver pair that creates a multi-beam barrier of infrared light in front of, or around, a hazardous area. The emitter is synchronized with the receiver by the photoelectric beam nearest one end of the housing. Jennifer Byrne 2020 21
Ø Ø Use safety tags to ensure your employees and visitors are protected against hazards and potentially dangerous situations. It requires that hazardous power sources be "isolated and rendered inoperative" before any repair procedure is started. Jennifer Byrne 2020 22
Ø Adam Thull was building a checkout counter for a local bookstore when he noticed a wood panel falling off the edge of his table. As he lunged to catch it, his right forearm got caught on the blade of his Ryobi table saw – and the machine quickly cut completely through one of his forearm bones and a nerve. Ø http: //www. youtube. com/watch? v=c. TUOh. Ycw 4 ZY Jennifer Byrne 2020 http: //fcir. org/2013/05/16/power-tool-industry-circles-the-wagons-as-disabling-saw-injuries-mount/ 23
Ø Ø Ø Outline the FOUR main categories of guards and safeguarding devices that may be used to minimise the risk of contact with dangerous parts of machinery. Where should emergency stops be situated on a machine? Should moveable guards need tools for adjusting? Why/why not? Why is distance needed between two hand controls? What happens if a laser beam is broken on a machine? Jennifer Byrne 2020 24
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