Why and How Grid is used in Blow room?

In the final analysis, it is the grid or a grid-like structure under the opening assembly that determines the level of waste and its composition in terms of impurities and good fibres. Grids are segment-shaped devices under the opening assemblies and consist of several (or many) individual polygonal bars or blades (i.e. elements with edges) and together these form a trough. The grid encircles at least 1/4, at most 3/4 and usually 1/3 to 1/2 of the opening assembly.

Two-part Grid
Two-part Grid

The influence of the grid on cleaning efficiency?
The grid has a major influence on the cleaning effect via:
• the section of the bars;
• the grasping effect of the edges of the polygonal bars;
• the setting angle of the bars relative to the opening elements;
• the width of the gaps between the bars;
• the overall surface area of the grid.

Elements of the Grid?
The following elements can be used in the grid:
• slotted sheets (a): poor cleaning;
• perforated sheets (b): poor cleaning;
• triangular section bars (c): the most widely used grid bars;
• angle bars (d): somewhat weak;
• blades (e): strong and effective. 

Elements of the Grid

These elements can be used individually or in combination. Modern grids are mostly made up of triangular bars. They are robust, easy to manipulate and produce a good cleaning effect. The same is true of blade-grids. Blades have been used as grid elements for a long time (the mote knife), almost always in combination with triangular section bars. 

What are the Grid adjustments?
Three basic adjustments:
• Distance of the complete grid from the beater;
• Width of the gaps between the bars (a=closed, b=open);
• Setting angle relative to the beater envelope.

Grid adjustments

What are the general factors influencing opening and cleaning performance?
Degree of opening, degree of cleaning and fibre loss are influenced by-
- Type of opening roller
- Speed of the opening roller
- Degree of penetration
- Type of feed
- The spacing of the feed from the opening device
- Type of grid
- Area of the grid surface
- Grid settings
- Airflow throw the grid
- Condition of pre-opening
- The thickness of the feed web
- Material throughput
- Position of the machine in the machine sequence.

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