Describe in detail about the principles and various types machine guarding.

assignment 2 Q 2. Describe in detail about the principles and various types machine guarding.

ans

Fixed Guards

As its name implies, a fixed guard is a permanent part of the machine. It is not dependent upon moving parts to perform its intended 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 and permanence.

Interlocked Guards

When the interlocked guard is opened or removed, the tripping mechanism and/or power automatically shuts off or disengages, 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.

Adjustable Guards

Adjustable guards are usable because they allow flexibility in accommodating various sizes of stock.

Self-Adjusting Guards

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 that 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.

Types of Guards – Guards – Safeguarding action -  Advantages - Limitations

Fixed-
advantages---- 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 
disadvantages---- 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 - 
advantages---- Shuts off or disengages power and prevents starting of machine when 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 machine for removing jams without time-consuming removal of fixed guards.
disadvantages ---- Requires careful adjustment and maintenance. 
May be easy to disengage.

Adjustable - 
advantages ---- 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
disadvantages ---- 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 - 
advantages ---- Provides a barrier that moves according to the size of the stock entering. 
Off-the-shelf guards are often commercially available.
disadvantages ---- Does not always provide maximum protection. 
May interfere with visibility.
May require frequent maintenance and adjustment.