Sandblasting
When steel touches oxygen, it oxidizes in time.With rain and sea water, some acids make oxidation faster.We simply call it corrosion.However, corrosion can’t be underestimated.Rust unzips the steel and causes it to corrode.When every object made of iron and steel corrodes, it becomes useless after a while and it goes to scrapyard.To use the material we have effectively for years we must prevent that material’s touch with oxygen.For this there are some ways.
1. The material must be chromed or galvanized.It is a very expensive way and it can be only applied on small pieces.Can you chrome a ship or a bridge made from steel?
2. The material must be painted.This is the easiest way in the world today and cheap.
HOW TO PAINT?
The most important thing to do before an object made from steel which can be a ship, carcass made of steel construction, container, storage or silo made from metal sheet, fuel or water tank, even garbage containers and construction equipment, briefly everything made from iron-steel is painted is to clear all kinds of oil, rust and paint residuals on the surface that will be painted properly.
HOW TO CLEAN THE SURFACE PROPERLY?
The most ideal way to clean an object made from steel is sandblasting.Rubbing down or cleaning with wire brush also work in small pieces but when compared with sandblasting these two methods are technically quite inadequate.
WHAT IS SANDBLASTING AND HOW TO PRACTISE IT?
Sandblasting is practised basically with special materials named sand,that is similar to sand but different from the sand we know produced specially for this process, that has types such as silica, basalt and grid and different usage areas.Silica sand which has quite thin types is generally used in thin sheet metals when sandblasting is practised in mild intensity.Basalt whose dust emission is little is generally used in indoors and the places where sand can be used recycled.Grid is the sand type whose dust emission is the lest and sandblasting power is the best.It is actually iron cinder not sand.
PRACTISING OF SANDBLASTING PROCESS
Sandblasting is hitting the sand which is described above to the metal surfaces with high pressure air.While sand corrodes the metal surface at micron level during this hitting process, it scratches and cleans all kinds of unwanted substance on the surface at the same time.
TYPES OF SANDBLASTING
Sandblasting process has generally two types.
1. Automatic Sandblasting
2. Manuel Sandblasting
1.AUTOMATIC SANDBLASTING
Steel construction elements which aren’t generally welded or cut and steel material which is welded and cut partially sandblasted in automatic machines.The advantage of this system is the fast and economic sandblasting of a material whose size is big enough to fit in machine.The disadvantage is that big materials can’t be sandblasted.For example; you can’t sandblast a construction equipment, fuel tank, container, steel bridge or other big materials that have to sandblasted on site in sandblaster.
2.MANUEL (MOBILE) SANDBLASTING
Manuel sandblasting can be practised all kinds of materials (generally big materials) everywhere with high pressure producing compressor, sandblaster, hoses etc.However, the disadvantage of this method is dust formation.It is possible to sandblast without dust formation.For sandblasting without dust watery (wet) sandblasting is done.Because watery sand is sandblasted on a sandblasted material with a special method in this system there is no dust formation.Watery (wet) sandblasting is performed more in marines, harbour launches and to fiber or wooden boats.The purpose is sandblasting to boat without disturbing people with dust.Also, watery sandblasting is prefered in cities, constructions or buildings when plaster is removed and scarified, walls are cleaned (paint scratching-removing) and aging is performed on marble or natural stone surfaces similar to marble.Actually it is also possible to perform watery sandblast on steel surfaces but because special paint that has to be applied to the surface immediately after sandblasting is quite expensive it isn’t prefered on steel surfaces.
RATING OF SANDBLASTING
Sandblasting process is rated according to how unwanted formations on steel’s surface are cleaned and how the surface is corroded.There are some standart ratings about this.In Turkey “Swedish Standards For Ground Vibrations And Airblast” SA 1, SA 2, SA 2,5 ve SA 3 ratings which are Sweedish standarts are used.These rating measurements were accepted on 08.04.1999 exactly as TS EN ISO 8501-1 by TSE institution.
SA 1: It is a quite superficial cleaning rating.It is a quite superficial cleaning rating on rusted surfaces and named as ‘’sweeping’’ in the market.
SA 2: It is a sandblasting rating at which steel is cleaned quite well and surface is scratched considerably.It is classified in American SSCP measurement scale as commercial, in British BS 4232 measurement scala as 3rd quality 80% whole surface.
SA 2,5: It is the most prefered sandblasting rating in the market at which steel surface is scratched quite well, the unwanted formations are cleaned almost completely and the specific color of steel is easily seen.It is classified in American SSCP measurement scale as ‘’Near White’’, in British BS 4232 measurement scale as ‘’2nd quality %95 whole surface’’.
SA 3: It is a sandblasting rating at which steel surface is scratched quite well, the unwanted formations are cleaned completely, the specific color of steel appear completely.It isn’t prefered in the market because practising time and cost is quite expensive.It is classified in American SSCP measurement scale as ‘’White Metal’’, in British BS 4232 measurement scale as ‘’1st quantity 100% whole surface’’
Sandblasting process must be performed and finish in dry weather as soon as possible and then painted because steel is more vulnerable against corrosion after the rust and unwanted formations are cleaned.If the weather is humid sandblasted steel starts to fade out and corrode immediately.
PAINTING PROCESS
After steel is sandblasted first ground coat must be applied, then the actual paint must be applied.The area where steel is used is very important.For example; the paint that will be applied to a ship and to a container are different.Also, how thick the paint applied will be must be decided by taking into account the conditions steel will be exposed to.This topic is so critical an important that, for example, the factors such as in which sees a ship will cruise more, (because saltness and temperature rate will change) and how fast it will travel constantly (because the friction rate will change) must be considered.It is also important that with which painting tool paint will applied. The most convenient method is using airless paint machines because airless paint machines stick the paint with high pressure without mixing the paint with air.If airbrushes are used as it used to before air bubbles at micron level stay between the paint’s grain and the quality of painting process decreases.Lastly, we can say that steel has a very large usage area and is one of the most robust material against time and other factors but only if it is sandblasted, its surface is cleaned and prepared properly and painted.