Wood sanding - rotary brush sanding machines

I recently wrote an article about industrial sanding of wood using machines. As the subject is very broad, we talked about wood sanding in general, about abrasive materials in the form of sanding paper (a generic term that includes textile backing) and about belt sanding machines. Another category of wood sanding machines - very common in the industrial environment - includes machines with rotating brushes. Let's see why they are needed and what factors influence the quality of sanding.

What are rotary brush sanders used for

Rotary brush sanding machines are very versatile. The positioning and number of brushes, the abrasive material used and the machine's characteristics allow them to be used for different operations.

The machines can be used both for șlwhitewashing of woodas well as for sanding the primer or polishing the lake. However, the abrasive material is different for each of these operations.

The usefulness and efficiency of brushes is clearly seen in șsmoothing of profiled and carved elements. The configuration of the brushes allows the abrasive material to get into places where it is very difficult to reach with belt sanders without damaging something, which is true for both white sanding and sanding between layers. Also using brushes is De-pollution profiled elements.

Using hard brushes with a certain structure can make structuring or îforced ageing of wood. Unlike sandblastfor example, whereby one can make just ageing of the wood by partial removal of early wood, with brush sanding machines surfaces with different structures and aspects can be obtained, the appearance of old wood can be varied by using different brushes.

Using recovered wood is now very fashionable, being used for furniture, flooring and even house construction. Time spent leaves marks on wood, and it's not just the profiling but also the accumulated dirt. This reclaimed wood can be cleaned with brushes, without spoiling its old look and without removing its natural profile acquired over time.

Sanding quality on rotary brush sanders

The quality of the sanding does not only depend on the abrasive material used. There are several factors that influence the process. These factors are dependent on each other and the perfect combination must be found for each operation or object to be sanded.

Basically, the quality of the grinding is determined by the combination of the abrasive material used, the cylindrical drum (shaft) on which the abrasive is placed, the speed of rotation and the pressure on the workpiece.

The abrasive material

Sanding is done by abrasive materials mounted on a drum. These can be pieces of abrasive tape, bristles made of different materials or different textile materials that will have a different effect on the surface to be sanded.

I will not go back to the structure of abrasive tapes because we have talked about them extensively in therticle on the choice of abrasive materials. They are the same except they are small pieces, the sanding is influenced by their length and width. The narrower and shorter ones are used for flatter or rounder surfaces, while the wider and longer ones for contoured and edged surfaces.

Pieces of abrasive tape are often combined with synthetic bristles. This combination results in a perfectly sanded surface, comparable to that obtained by successive hand sanding with progressive grit abrasive paper. The length and thickness of the brushes in turn influence the sanding. Short brushes make sanding more aggressive, being used for wood, and long brushes for sanding primer, where aggressiveness is not needed.

Structuring is done with metal brushes. I won't dwell on this because it too is a large topic to be dealt with separately.

Drum rotation speed

Reels can be of different lengths and diameters depending on the machine. The abrasive material can be glued to the drum to form a common body with the drum or it can be separated, making it easy to replace the ground abrasive.

The rotational speed of the drum influences the durability of the abrasive material. The lower the speed, the longer the life of the brushes and the better the sanding quality. The speed is inversely proportional to the diameter of the hub. For example, at a diameter of 280 mm the optimum speed is between 50 and 280 rpm, and at a diameter of 50 mm the speed reaches 1200-1500 rpm.

When sanding profiled elements a very high rotational speed is not recommended. The high speed will cause flat surfaces to remain almost rough, while corners and profiles will be very rough. A slower speed will make the abrasive material not pass quickly over flat surfaces and the passage over profiles and edges will be smoother, resulting in a quality grind.

The best results are obtained with large diameter drums rotating at the lowest speed in the accepted range.

Influence of pressure

This is the pressure with which the brushes press on the material to be sanded. The optimum pressure is determined according to the object to be sanded. Basically the drum is initially fixed so that the brushes just touch the plate. Lowering it will cause the brushes to bend and determine the sanding pressure when the drum is moving.

Rotary brush sanding machines

The machines are very different and can have one or more rotating brushes. The positioning of the drums is also different. The brushes can be placed perpendicular to the belt on which the parts are, at 90º or at a smaller angle so that the "entry" into the plate is gradual, less aggressive. The combination of several brushes on the same machine results in better sanding. For example, combining two rotating brushes with different directions of rotation gives very good results for profiles. The first brush brings the wood grain in one direction and the second cuts it.

3 or 4 rotating brushes can also be combined. They can all be in the same direction of rotation or one in one direction and the others in the opposite direction. The combinations depend on the objects to be sanded and the results to be obtained.

There are also machines with an abrasive disc system whose rotation is perpendicular to the workpiece. Basically it is not the same movement for all the abrasive on the drum, but each abrasive group mounted on the disc enters gradually, sanding is much less aggressive. It is similar to the situation where the drum is not set at 90º, but multiplied several times. Very suitable for profiled doors, curved and carved elements.

The combinations that can be found on such cars are very interesting. They are machines that profile and sand at the same time. For example, with double profiling and grinding unit of the Greda, Italywhich you can find at Danibrum, profiled and sanded elements for chairs, tables or sofas can be obtained on the same machine. The machine reduces working time by combining several steps.

Rotary brush sanders are not just for large factories with complex processing lines. Like belt grinding machines, they can be stand-alone machines that can also find their place in a workshop. They don't have to be big to be complex and help you get the best results in the shortest time and using state-of-the-art technology. Sanding and structuring machine with brush and Profile grinding disc machinewhich you can also find at Danibrumare only two examples.

In conclusion, rotary brush sanders are the best solution when you need to sand profiled or carved items. The brushes have the ability to get into the most hidden corners and can sand the most diverse shapes. If profiles are part of your production such a machine certainly helps to increase the quality of the finished product.