Preparing metal for paint
Before painting metal products, you need to prepare the surface properly. Preparing metal for paint may be carried with the help of different technologies. But all of them are removing the rust, essentially.
According to the degree of destruction corrosion is classified into several levels
- corrosion spots (small penetration depth)
- pitting (little dots, penetrated deep into the body of the material)
- rust (loss of the part of the material)
- deep corrosion (rust lesions are formed under the surface of the coating)
Preparing metal for paint can be carried out by the following methods:
- mechanical treatment
- chemical treatment
- thermal treatment
The mechanical method of removing corrosion has established itself as the most effective one. It is done with your own hands using a power tool.
There are several ways to remove rust mechanically:
- Clean the surface with wire brushes to remove small pockets of corrosion, to clean the welds and for the primary treatment of surfaces coated with a thick layer of rust.
- Abrasive processing of metal by means of grinding discs. It is used for small areas of corrosion. If you use high-quality discs, the result will be quite good.
The method has two serious drawbacks in terms of handmade work:
- consumption of high-quality materials
- requirements for certain skills of work
- Sandblasting installation: the bombing of the centers of the sand jet corrosion filed under pressure. It is the so-called metal sandblasting. The main elements of sand plants are a container with sand and sandblasting gun. For sandblasting installation use a small compressor.
Removing the rust with sand
Before the use, sand must be thoroughly dried. The sand can be recycled after sifting - the cleaning efficiency decreases in this case, but, of course, it will take you much more time. Sandblasting removes not only all rust, but also the layers of the old paint. In the treatment of the joints, for example, this method is the only one possible.
- Waterjet machining metal provides the rust removal under the action of the water jet and abrasive mixture.
The intensity of distinguished waterjetting:
- under super high pressure - completely removes all corrosion coatings applied previously to the work surface;
- under high pressure – removes most of the old coating and corrosion, but there may be areas of highly durable coating and black oxides;
- under low pressure – the most economical way against the abrasive flow, but after the drying the secondary rust traces usually remain.
This method is based on the removal of rust under the influence of chemically active substances. A related species is an electrical-chemical treatment. The formulations are applied to the surface using a brush or a spray.
Means for removing rust are divided into two main categories:
A disadvantage of such compositions is that while contacted with water there can be new sources of corrosion on the treated surface. So, after the washing the materials should be quickly and thoroughly dried and treated with high quality anti-corrosion agents. It is 21st century, but there is still no ways to save the metal from water!
5% aqueous solution of sulfuric or hydrochloric acid also removes rust in a very effective way. But it is definitely added to a corrosion inhibitor - a substance that slows the chemical reaction. Most often it is used as an inhibitor of methylamine. It is necessary to add it in an amount of 0.5 g per liter of solution. Without an inhibitor you can not use acid solutions – otherwise it will dissolve not only corrosion, but also the material.
Quite an interesting result is provided by means of phosphoric acid. Apply 15-30% solution of phosphoric acid onto the treated surface, it will become a durable coating. This is possible because the chemical reaction produces iron orthophosphate, which creates a protective film on the surface. For the best effect an alcohol solution may be added (4 ml per liter of solution) or tartaric acid (15 ml per liter of solution).
Surfaces with the deep corrosion must be treated with a mixture of:
- lactic acid - 50 g
- paraffin oil (100 ml)
This solution converts rust into a soluble salt inside of vaseline oil - the iron lactate.
For the heat treatment you should used oxy-acetylene torch. As a result of exposure of flame, the rust is removed virtually all mill scale. Unfortunately, not all types of rust areas burns well, so this method is almost never used in modern paint systems.
Galvanized surfaces should be prepared correctly: carefully wash away the dirt, grease, debris. Use alkaline solutions (for example, usual washing powder) to wash salts, dirt and grease. Remnants of detergent are thoroughly rinsed with clean water - preferably under pressure – and then well dried. After careful preparation of the surface of the surface you may start painting.
We will be glad if you were able to get all the necessary information on preparing rusty metal for paint and preparing galvanized sheet for paint right here!