With parquet - regardless of the type - the quality of the surface is of great importance. Sanding therefore plays a central role in production. There are several sanding processes at different points in the production process, each of which is carried out by a wide belt sanding machine. It is possible to cover all sanding processes with a single powerful model with many sanding units. In addition to conventional longitudinal and transverse sanding units, calibration planing units or a brush unit are also conceivable. Alternatively, several smaller machines can be used.
Calibrating
The aim of calibration is to level both the top and the bottom of the workpiece and, above all, to ensure a constant thickness. Calibration is carried out on a wide belt sander with coarse sanding belts (grit 80, 120, 160). When producing two-layer parquet, it may be necessary to calibrate the top layer before pressing. This is particularly the case with wide blanks or when a hard carrier material is used, e.g. Plywood or HDF. After pressing, the board is sanded again to a uniform thickness.
Pre-sanding / filler sanding
A flat surface is created during pre-sanding. This is necessary for solid planks: here, after filling, excess filler residues are removed; this is also known as filler sanding. There is a similar sanding process for laminate flooring, especially for PDL (Printed Direct Laminate): As a preparation for printing, a filler is first applied to the carrier board, which then has to be sanded. In order to achieve a good printing result, it is particularly important to carefully remove the sanding dust with a brushing machine. In the production of two-layer parquet, depending on the type of wood and the quality of the cutting process, it may be necessary to remove burn marks from the lamellas caused by the sawing process before sorting.
Fine wood sanding
In order to achieve a perfect surface when painting, the wood surface must first be sanded with fine grain. This process is also known as fine wood sanding. Widebelt sanders with several units are used for this. A cross sanding unit (transverse to the feed direction) at the beginning removes protruding wood fibers and ensures an optimal surface. A wide belt sander with cross sanding unit is also called a cross sanding machine. Several longitudinal units with graded grit remove the traces of grinding of the cross sanding unit and remove any unevenness. After all, it is important to clean the sanded surface of sanding dust. For this purpose, a brush unit or even a dedicated brushing machine is used immediately after the sanding machine.
Intermediate varnish sanding
When making parquet, not only the wood but also the lacquer must be sanded once or even several times. The dried surface has fine unevenness after each application of varnish: Wood fibres that have been raised as a result of the varnishing process, or the surface of the varnish layer itself. In addition, the sanded surface increases the adhesion between the two layers of paint. After priming, therefore, a sanding process (intermediate sanding) is necessary before each further paint application. The intermediate sanding of the lacquer is done with a fine grain (e.g. 320). Only the surface of each lacquer layer should be smoothed. Under no circumstances should it be sanded through, i.e. removed completely. This process places high demands on the precision of the wide-belt sanding machine used.
After sanding, the sanding dust must always be removed by brushing or other measures so that the quality of the next painting process is not affected. For this purpose, a brushing unit is used in the wide belt sander or a brushing machine which is located directly behind the wide belt sander. The last layer of paint, which is applied as the top layer, is not sanded.
