The sandpaper is defined as material that incorporates a hard abrasive, capable to tear mechanically part of substrate/ material that is applied, the condition to produce this mechanical tear is that the hardness of the abrasive that contains the sandpaper is greater than the hardness of the substrate / material on which it is applied.
In the area of paint, sandpaper are used in the following processes:
Removal of material - The highly abrasive grit of the sandpaper are used for removal material as mechanical treatment, thanks to the abrasives sandpaper can remove oxide layers, remove old paints, eliminate metal parts, etc…
Adhesion Promoter - Sandpapers with a medium-high abrasive power are used to scratch the surface of the substrate in order to create rough surfaces favoring the anchorage and adhesion of future coats.
Smooth surface – Sandpapers with high-medium abrasive power are used for deburring and smoothing of the fillers or putty.
Surface preparation before application of the final paint layers – Sandpapers with medium-low abrasive used to smooth and eliminate defects (especially in paints or sealers) before applying of the final coating of paints, enhancing the aesthetics.
Repair of paint defects – Sandpapers with low abrasive power are used during the process of repair some defects such as orange peel, dust inside the paint, pinholes, etc ...
Sandpaper is composed of the following elements:
Support of sandpaper
The support of the sandpaper is the element by which the grains abrasive are placed, there are different types of materials supports as paper, fiber, plastic, foam and mesh.
The choice of the sandpaper support depends on the type of work to be done, if we want to smooth flat surfaces use sandpaper made with paper due its economy, if we want sanding rounded surfaces we will use sandpaper with foam support due its high flexibility suitable for working with bends, otherwise if we want remove metal parts, welding beads or remove surface oxides, we need sanding with polyamide fiber sandpapers due to its high resistance to abrasion.
Adhesive of sandpaper
The adhesive or glue is the material that allows to fix the abrasive grain on the support, while maintaining the abrasive grains bonded together, that is the reason why the adhesive or glue sandpaper is applied in two layers:
Layer 1 - Synthetic adhesives like phenolic or epoxy are used which are highly resistant to temperature and mechanical stresses, these types of adhesives are used to fix the grains to the support.
Layer 2 - Natural adhesives are used which are less resistant than synthetic adhesives, these types of adhesives are used to keep the grains together, if the sandpaper is used for removing metal synthetic adhesives are used in order to withstand the high pressures and temperatures at which the abrasive is subjected.
Abrasive of sandpaper
Abrasive sandpaper is the element which performs tear of material on the surface it is applied. Depending on the origin of the abrasive that contains the sandpaper, we can classify the wide range of minerals in the market as:
Natural abrasives such as silica, emery, garnet or diamond
Synthetic abrasives such as corundum or silicon oxide and silicon carbide
For work performed at the paint area generally always used corundum (aluminum oxide) as abrasive material on the sandpaper, for the treatment of materials such as marble or stone is used abrasives of silicon carbide, diamond abrasives are used for working with a high hardness metals.
In order to be able to indicate for each job and the type of sandpaper to use, the abrasives are encoded as PXXXX where P indicates the sandpaper and XXXX is a numeric value between 16 and 4000 indicating the abrasive grain size and abrasive power of the sandpaper.
Lower number indicates high abrasion power, so for sanding surfaces with filler or putty we use rough P80 sandpaper and to repair defects such as orange peel we used ultrafine sandpaper P3000.
Now that you know the sandpaper, Did you know the origin of the word comes from the name of fish called "Sand"?, The first human civilizations used the rough skin of this animal to make the functions of sandpaper.
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