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Machine Guarding
Introduction

Guards are barriers which prevent access to danger areas. There are four general types of guards:


Fixed
As its name implies, a fixed guard is a permanent part of the machine. It is not dependent upon moving parts to function. It may be constructed of sheet metal, screen, wire cloth, bars, plastic, or any other material that is substantial enough to withstand whatever impact it may receive and to endure prolonged use. This guard is usually preferable to all other types because of its relative simplicity.
Safeguarding Action Advantages Limitations
  • Provides a barrier
  • Can be constructed to suit many specific applications

  • In-plant construction is often possible

  • Can provide maximum protection

  • Usually requires minimum maintenance

  • Can be suitable to high production, repetitive operations
  • May interfere with visibility

  • Can be limited to specific operations

  • Machine adjustment and repair often require its removal, thereby necessitating other means of protection for maintenance personnel


Interlocked
When this type of guard is opened or removed, the tripping mechanism and/or power automatically shuts off or disengages, the moving parts of the machine are stopped, and the machine cannot cycle or be started until the guard is back in place. An interlocked guard may use electrical. mechanical, hydraulic, or pneumatic power or any combination of these. Interlocks should not prevent "inching" by remote control if required. Replacing the guard should not automatically restart the machine. To be effective, all removable guards should be interlocked to prevent occupational hazards.
 
Safeguarding Action Advantages Limitations
  • Shuts off or disengages power, stops the moving parts and prevents starting of the machine when the guard is open; should require the machine to be stopped before the worker can reach into the danger area
  • Can provide maximum protection

  • Allows access to the machine for removing jams without time consuming removal of the fixed guards
  • Requires careful adjustment and maintenance

     
  • May be easy to disengage 



Adjustable
Adjustable guards are useful because they allow flexibility in accommodating various sizes of stock.
 
Safeguarding Action Advantages Limitations
  • Provides a barrier that may be adjusted to facilitate a variety of production operations
  • Can be constructed to suit many specific applications

  • Can be adjusted to admit varying sizes of stock
  • Hands may enter danger area - protection may not be complete at all times

  • May require frequent maintenance and/or adjustment

  • The guard may be made ineffective by the operator

  • May interfere with visibility


Self-adjusting
The openings of these barriers are determined by the movement of the stock. As the operator moves the stock into the danger area, the guard is pushed away, providing an opening which is only large enough to admit the stock. After the stock is removed, the guard returns to the rest position. This guard protects the operator by placing a barrier between the danger area and the operator. The guards may be constructed of plastic, metal, or other substantial material. Self-adjusting guards offer different degrees of protection.
 
Safeguarding Action Advantages Limitations
  • Provides a barrier that moves according to the size of the stock entering the danger area
  • Off-the-shelf guards are often commercially available
  • Does not always provide maximum protection

  • May interfere with visibility

  • May require frequent maintenance and adjustment

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