Spiral strip brushes
Spiral strip brushes
Generalities
Winding a strip on a cylindrical metal core produces a spiral, which together forms a roller brush. If the spiral is removed from the metal core, a flexible (spring-like) brush called a ‘free helix’ is obtained.
Spiral strip brushes are used for:
- high density rollers; very large rollers
- all-metal rollers for high temperatures
- auger brushes for material transport
- wide-pitch spirals for cleaning delicate surfaces
The helix pitch P (see figure) is the parameter that most influences the density of the strip brush. A very dense brush is not always required, however. For example, if it has to remove debris and discharge it easily, the pitch will have to be large enough to prevent the debris from accumulating between the coils.
The minimum value of P coincides with that of the base B. The maximum value, on the other hand, is a function of the winding diameter D2: the larger D2 is, the larger the maximum pitch can be.
The following limits can be set: P min = B P max = D2
There is a minimum value of D2 below which the strip cannot be wound.
This limit value depends on the base B, and is shown in the table (galvanised iron base). For stainless steel bases, the D2 min values in the table should be doubled. Regarding the maximum brush diameter D1, it is generally not possible to exceed D1=1000mm.
Winding diameter (mm)
| PLAIN TAPE | DOUBLE TAPE | ||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| B | 4 | 5 | 6 | 8 | 10 | 13 | 14 | 17 | 20 | 6 | 8 | ||
| D2 min | 12 | 15 | 20 | 25 | 25 | 90 | 90 | 160 | 160 | 30 | 50 |
In addition to defining the density of the brush, the winding pitch can be used to perform a mechanical conveying function. In fact, if P is large enough to contain all or part of the parts to be treated, the brush will behave like an auger, and the rotation will be associated with a transverse movement of the material. It is therefore important, in this case, to specify whether the winding should be right or left-handed. Finally, there may be two helixes (right and left) converging at the centre of the brush, with the effect of conveying on the middle or at either end. Translated with www.DeepL.com/Translator (free version)
The brush-coclearance solution is particularly suitable for all those cases where particularly delicate material has to be transported and for the low noise level. To design an auger brush given the amount of product to be conveyed, the following formula is very useful.
If you want to move a flow rate of material V [l /min] with a brush that rotates at n [rpm] a winding step of at least : P ≥ 4,000,000 V ∏ ne (D12 – D22) + B [mm] Where e is the auger filling factor, with e 0 at empty auger and e=1 at full auger.
Another important fact to know at the design stage is the rotational speed at which a strip roller can be driven. Unfortunately, this depends not only on the materials, but also on the load on the brush and the filament-surface friction coefficient. It is therefore necessary to calculate the limiting speed from time to time based on the known parameters. In general, a roller strip brush can be said to have a higher limiting speed than a corresponding punched brush. We are available to provide you with the necessary project data.
In the case of high speeds, a sample must be made and tested under safe conditions.
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Frequent questions
The special feature of the brush is that the work surface is made up of millions of individual elements, which are the ends of the individual filaments.
This gives the brush an adaptability that no other element, however deformable, can have.
It depends on various factors. In a nutshell, it can be said that 2 mm is a good compromise. The important thing is that the filaments of the brush work “at the tip” and not on the side.
Depending on the materials used and the dimensions, there is a tensile limit load that a single bunch can withstand.
Beyond this limit the bunch comes off, therefore the brush must be calculated according to the use. This limit can be greatly increased by building “sewn” or “tied” brushes by hand, where a continuous steel wire is placed instead of a single anchor element.
There is no single answer. Speaking for example of cylindrical brushes, the strip brush is generally cheaper when dimensions are important (e.g. over one meter in length). For small dimensions, punched brushes are certainly more suitable and convenient.
It can only happen if the brush has a manufacturing defect, like any other type of object (e.g. a roller made with silicone flakes, one of which is defective and breaks).
When it is important that no contamination occurs, it is advisable to use synthetic (non-natural) fibers with a diameter greater than or equal to 0.15 mm.
Virtually all degrees of hardness can be had, from very soft to very hard. In fact, the hardness is given by the combination between the diameter of the filament, its free length and the density of the bunches.
Of course, we can provide FDA or FOOD GRADE certifications and filament traceability.
Unfortunately not, as it is the machine + brush assembly that must be ATEX certified, not just the brush.
It is however possible to provide the materials that the certifier requires, eg. conductive bases, conductive filaments etc …
Generally speaking it is possible, but it is necessary to evaluate if it is economically convenient, and it is not always. Furthermore, in the case of a punched brush, it is not advisable to regenerate the brush more than twice in order not to reduce the holding of the bunches.
