a guest post by Proky
You might have heard the term Sand blasting before. Officially called abrasive blasting, it involves using compressed air to propel abrasive material against another material, effectively removing rust, paint, or other thin materials off the object. It can also be used to smooth an object.
You might think Sand blasting is a relatively new invention, but I’m here to prove you wrong! Sand blasting has actually been happening for billions of years in nature, whenever tiny bits of materials are propelled by wind, or water to create and shape the lands we know. The Grand Canyon? Blasted by sand particles beneath the surface of the Colorado River. Independence Rock? Yep, wind has blasted the rock with tiny sand particles for a very, very long time to create it’s famous smooth, round look.
While nature mastered this way of sculpting the lands with fine material billions of years ago, humans only did so in the past two hundred years or so. Legend has it that a general in the US Army during the late 1800’s, Benjamin Chew Tilghman, was stationed in a desert. He noticed a sandstorm hitting a rock wall, and some time later patented the first, primitive Sand blasting technique: using sand propelled by a stream of water or air.
The technology slowly evolved further, and in 1918, the first enclosed cabinet was created, miniaturizing the process and allowing the mass use of Sand blasting. By the 1930s, the Sand blasting business had spread rapidly and had become quite profitable.
A serious problem arose from the act of sand blasting on a commercial scale. Many of the workers in the sand blasting profession developed a lung condition called silicosis (another name for this disease is also the longest word in English language: Pneumonoultramicroscopicsilicovolcanoconiosis, although this word was invented by the National Puzzlers' League for the amusement of creating the longest word possible and is rarely if ever used by medical professionals). It is caused by the inhalation of near-microscopic dust produced by the sand blasting process, resulting in shortness of breath, a cough, fever, and bluish skin. There is no known cure for silicosis and a lung transplant is often required.
The mortality rate for silicosis is not as high as it once was, as the available safety equipment is getting more advanced and commonplace even among the poorer countries. Around forty thousand people die each year to silicosis, down from around sixty thousand in the 1980’s.
Silica sand was used for many decades, however more recently it was classified as a class-1 carcinogenic material, so many countries banned the use of this type of sand.
Sand blasting is a very dirty job as you use a fine, sandy materials for work. Depending on the size of the sand blasting area (From micro abrasive pistols to massive rooms capable to holding an entire plane), you must always wear gloves as your hands are always the closest to a working sand blasting item.
If you work with a small, enclosed sand blasting cabinet, nearly no protection is required as the sand blasting happens in a properly sealed area, but as the sand blasting area gets bigger and bigger, you are required to protect yourself. In sand blasting rooms, you must wear protective clothing made of material strong enough to withstand the constant indirect blasted of fine material. No cloth fabric can survive this for long.
You are also required to wear a helmet that covers your entire head and your upper torso. It should be made of strong plastic or other tougher but light material, so as not to strain your neck and shoulders. Air is continually delivered via an oxygen pipe connected through the back of the helmet to allow you to breathe safely.
There are several materials that can be used to blast an item. The oldest is the namesake technique of sand blasting. This involves using simple sand, propelled by compressed air to clean an object of old paint or rust, or to prepare the object for powder coating, as the material becomes more porous and the powdery paint holds better in the pores.
An alternative to using air to deliver the abrasive blasting material is water. Water blasting is much safer as the sand doesn’t contaminate the atmosphere around, lowering the risk of silicosis. However the wet blasting is not as effective against metallic materials, as it corrodes the material.
Hydroblasting is a stronger type of water blasting. The water stream is powerful enough to remove the paint by itself so does not need an abrasive medium. This technique is also more environmentally friendly, as the water can be collected and reused more easily than if it was mixed with sand and other materials.
Glass beads can also be used in blasting. It doesn’t create pores in the material, so it is used on softer materials, like ceramics, soft rocks or glass.
There is also a type of airless, waterless blasting. The items to be blasted are put into an enclosed, round barrel, along with a quantity of abrasive blasting material, and then the barrel is spun.
Steel blasting, which I am most familiar with, is a heavy duty, air-type abrasive blasting technique. We use very fine grit made of steel and iron which we blast against stronger metals, such as steel or iron. It can’t be used against aluminium, as it becomes damaged due to the heat that steel blasting generates.
Steel blasting is most commonly done in big rooms, to blast large items such as steel beams, tubes, and car parts. I start by putting steel grit into a storage container outside of the room. I don my safety equipment, and then switch on a hose made of a very thick layer of specialized rubber that can survive being blasted from the inside for a very long time (commercia hoses can stand around 2-3 months of use). If you ever held a fire hose blasting water at the strongest level, that’s about the amount of force the steel blasting hose creates.
However, the material it sprays is much more dangerous. If you ever get in direct, close contact with the propelled material, it will near instantly rip through your clothing and injure you.
Steel blasting generates a lot of heat. You cannot blast one spot for too long, as you could melt through the material. For this reason, inside corners are a particular challenge. Hosing very close to the material also creates a problem, as the grit that has contacted the material has nowhere to go. This can be partially fixed if you blast the item in very specific angles.
As I work in a large room the blasted debris is vented away through large fans around the room. The entire floor has holes that let the steel grit fall into a collecting system that is then filtered and sent back into the grit storage. Every week or so the filters need to be cleaned, as all the paint, rust and other debris can block the filtration system.
After I finish blasting the item, it is sent into a nearby powder coating room where it is sand papered to even out the porous layer I created with steel grit, then cleaned of any residual dust with a air compression piston. Finally it is coated in a electrostatic powder. Then we put it into a large oven where it stays for about 30 minutes for the paint to harden and dry.
Abrasive blasting is a dirty job that, if not protected properly, can do life-long damage to your lungs, skin, and eyes. It is a necessary job in today's modern world, as many items require a special coating that can only be properly applied if the item is blasted.
Image by Sambeawesome