PUNCHED BRUSHES - GENERAL FEATURES
PUNCHED BRUSHES are the most traditional among the various existing types. They are composed of tufts of filament inserted in the body by means of a metal element or “staple” (figure 1.1) which is lodged fully in a preformed hole. Depending on the shape of the brushing surfaces punched brushes are available in FLAT, ROLLER or DISC styles.

The main characteristic of punched brushes is their versatility. Since the tufts are reciprocally independent they can be arranged in such a way as to impart both simple or highly complex geometries to the brush. That’s why punched brushes are suitable for manufacture in any shape or size and are irreplaceable when the support performs also a mechanical function in the system in which the brush is installed.

 TUFTS PATTERN

The tufts can be arranged in any pattern across the brush body. When the pattern is regular, it is referred to as a GRID. Although the number of different grid patterns is virtually infinite, the most popular layouts are shown in Figure 1.2.




 
PL = longitudinal pitch - centre-distance between two tufts on row parallel to the longer side of the brush
PT = cross pitch - centre-distance between two adjacent tuft rows
α = Inclination of spiral with respect to the brush axis (spiral grid only)

The most widely adopted solution is the STAGGERED grid model.
This is adopted for the following requirements:
  a) very high density brushing surface
  b) very uniform brushing surface

The PARALLEL grid is used in the following cases:
  a) the brush must be able to discharge debris easily without becoming clogged
  b) mechanical parts must be able to transit between the tufts
  c) the brush must be cut into sections by the user

The SPIRAL grid pattern is used for roller brushes in the following cases:
  a) the brush is required to route treated material to one side
  b) the brush must come into contact with the workpiece surface gradually and delicately. The spiral pattern may be composed of several coils each of which composed of several rows of tufts.


 TUFTS DIAMETER

The diameter of the tufts is of key importance in the design of a technical brush. This parameter will determine the overall efficiency of the brush in operation.

There exists a relationship between tuft diameter D and hole depth P, which is effectively limited by thickness S of the support (Figure 1.3).



The table shows possible tuft diameters and relative P and S values.

When using thick supports the choice of tuft diameter is determined by non-dimensional considerations. For example, large diameter tufts are suitable for brushes subject to high stress (in which case the anchorage of the tufts must be very secure). Alternatively, small diameter tufts will produce a high density or very soft brush.

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