Spreaders fixed

The first type of furnace was the spreader stoker, in which a mechanical shovel moved between a fuel hopper and the fixed grate, spreading the coal onto the burning zone (Chapter 14). Later improvements in ash handling and coal feeding, however, have made this early stoker design obsolete. 

For spreading prefabricated solutions in roll-to-roll processes, spreader bars and doctor blades are very common. The former is a thin rod (a few millimeter in diameter) on which a thin wire with a fixed... 

A doctor blade is simply a smooth bar or blade which is held a fixed distance from the substrate. The blade is then moved relative to the substrate and film precursor to spread the solution. As with a spreader bar, the velocity, rheology of the solution, interfacial energy between blade, solution, and substrate are important process parameters. Clearly the distance between the substrate and the doctor blade is important as well. 

The body of a spreader tmck is fixed on wheels. It ensures lengthways transportation of a fabric roll above a spreading table (see Figure 9.3). After laying the fabric to a specified length the spreader stops and then moves in the opposite direction. The speed of the spreader can be adjusted according to the fabric type and properties. 

The fiiUy automated spreading process is driven and controlled by an encoder. Using a special belt with metal denticles fixed to one side of the spreading table, the encoder system counts the number of denticles and recalculates them in the distance (metres inches) from the start point. This defines the placement coordinates of the spreader truck on the spreading table at a given moment. 

Ladders must not be tied or fastened together to create longer sections unless they are specifically designed for such use. A metal spreader or locking device must be provided on each stepladder to hold the front and back sections in an open position when the ladder is being used. Two or more separate ladders used to reach an elevated work area must be offset with a platform or landing between the ladders, except when portable ladders are used to gain access to fixed ladders. 

There are two types of coihniercial motor-driven apparatus at present. In one, the spreader trough is carried over the row of plates by a motor drive (Firms 15, 35) in the other, the trough is fixed and the plates are passed beneath it using motor-driven rubber rollers (Firms 33, 54). A further development of the Stahl automatic apparatus permits the rational preparation of gradient layers [675] (Firm 44). This apparatus will have automatic devices for delivery, removal and stacking of plates so that they can be dried. 

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