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PUNCHED BRUSHES
Technical characteristics
   
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GENERAL DESCRIPTION

The PUNCHED BRUSHES are the most traditional among the different kinds existing. They consist of tufts of bristles inserted in a backing by means of a metallic element called staple (see Figure 1.1.) fixed to the bottom of a hole previously made.
We can consider, according to the shape of the brushing surface, the following punched brushed: PLANE BRUSHES, ROLLER BRUSHES, DISC BRUSHES and HEADBRUSHES.
The main characteristic of the punched brushes is their versatility. The tufts are independent the one from the other, so that they may be disposed in a way as to make the brush assume either simple or very complex shapes.
For this reason puched brushes are particularly indicated to be manufactured in small and medium dimensions, and are indispensable when the backing has a mechanical function within the plant where the brush is installed.

 

TUFTS DISPOSITION

The tufts may be disposed in any way on the backing. When this disposition assumes regular conformation, it is called GRID. As a matter of fact there are inifinite kinds of grids, but the most common are those shown in Figure 1.2.
 
 
PL = longitudinal pitch - interaxial distance between two tufts on a row which is parallel to the longitudinal dimension of the brush.
PT= transversal pitch - interaxial distance between two adjoining rows of tufts.
a= inclination of the spiral referring to the axis of the brush (spiral grid only)

The STAGGER grid is the most frequently used, for example in the following cases:
a) brushing surface that is particularly dense
b) brushing surface that is extremely uniform.

The PARALLEL grid is used in the following cases:
a) brushing surface that is not dense
b) the brush must easily discharge particles without clogging
c) the brush must be cleaned by thin plates to be inserted between the rows of tufts
d) the brush must be cut in differents parts by the user.

The SPIRAL grid is used in the following cases:
a) the brush must convey the material being treated on one side
c) the brush must act gradually and softly on the surface to be trated.
Moreover we can find multi-start spiral grids, each start having more than one row of tufts.

 

TUFTS DIMENSIONS

The size of the tufts is very important in the planning of technical brushes. In fact the overall performance will depend also in it.
There is a precise relationship between the diameter of the tufts D and the drilling depth P.
Furthermore the depth P is limited by the thickness S of the backing (see Figure 1.3). Finally, diameter D and the minimum thickness S are strictly related, as indicated in Table 1.1 .

 

TAB 1.1

D=
2.0
2.5
3.0
3.5
4.0
4.5
5.0
5.5
6.0
6.5
7.0
7.5
8.0
9.0
10.0
11.0
12.0
P=

5.0
5.0
6.0
7.0
8.0
9.0
9.5
10.0
11.0
12.0
12.5
13.0
14.0
15.5
17.0
18.5
20.0
S=>
6.0
6.0
7.0
8.0
9.0
10.0
11.0
12.0
13.0
14.0
15.0
15.0
16.0
18.0
20.0
22.0
24.0

 
When considering thick backing the limitations illustrated in Table 1.1 are not to be considered. In determining the diameter of the tufts, we must make different considerations.
For example we will choose large tufts for brushes which are exposed to a great stress (and therefore need a good fastening) or for the brushes having bristles with large diameter. We should choose small tufts in order to obtain either very dense or very soft brushes.
   
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