A Large gate about to be shot blasted (before doors are closed for the process)

A Large gate about to be shot blasted (before doors are closed for the process)

What is shot blasting?

Shot blasting is a mechanical cleaning method for hard surfaces, typically metal and uses a blasting medium to remove oxides from the surface. Shot blasting is an effective method for removing the top layer of paint, debris and rust from a surface and restoring it to its original appearance. This article describes how to prepare your surface prior to applying a protective coating

Large posts after shot blasting

Large posts after shot blasting

What is the shot blasting process?

Shot blasting is widely used in the protective coatings industry as the first stage in the process.

In layman’s terms, it cleans the item that you want to coat.

It can be used on a small scale in an abrasive blast cabinet for small items, however, for most industrial operations abrasive blast systems would be installed in a large purpose-built room with ideally an auto-recovery system to recycle the blast media.

The blasting process is carried out by a trained operator wearing the appropriate PPE. The steel shot or grit used in abrasive blasting is fired out of the blasting gun with compressed air at about 110 PSi, removing any oxidised areas (Rust) and taking the metal back to its original raw state. Because there are small fragments of metal being fired at metal there is a lot of ricocheting in the closed blast room and it is mandatory that the operator is wearing the right protective gear, but also the area is not used for any other process. This abrasive blast cleaning can remove any previous powder coating or protective coatings including old galvanising, although this can be a tricky operation and take considerable time.

When powder coating, we always recommend that you start with grit (shot) blasting, this ensures that we have a clean item to start coating. Then depending on the end product, we might recommend galvanising with Hot Zinc Spray, this applies a thin layer of protective zinc to the item giving it anti-corrosion protection. Then we are ready to apply, either powder coat or wet spray.

The recover screw feeds the shot back up though a filter system for reuse

The recover screw feeds the shot back up though a filter system for reuse

What is a shot blasting machine?

There are so many different types of shot/grit blasting machines on the market, and it really depends on your needs.

In the case of most industrial powder coaters, they will have a customer build blast room with a compressed air system and recovery screw to recycle the media.

Here are just a few of the options available

  • Blast wheel machine
  • Round spring machine
  • spinner hanger machines
  • Mess belt machines
  • Trolley-type machines
  • Hanger pass through machines
Recovered and filtered shot / grit

Recovered and filtered shot / grit

This is blasting media, in this case steel grit

This is blasting media, in this case steel grit

What material is used for shot blasting?

All abrasive materials used have their own qualities. The blasting media used should suit the job at hand. In the protective coatings world, we commonly use steel grit, it’s an ununiformed shape for blasting metal to remove any oxidisation, dirt, or old coatings.

Grit blasting is commonly called shot blasting, but steel shot is actually round. At NSP coatings we mainly use grit blasting as our media of choice as it bites better on the metal and removes more of the debris and leaves a surface roughness to specification mark SA2.5 or SA3 for the new layer of the protective coating that follows.

What is shot grit blasting?

Grit blasting, shot blasting and sandblasting are all really the same thing, they are often referred to as sandblasting, but sand is not used anymore because of deadly silicosis.

These are some of the most common media used

  • Tiny Steel shot
  • Steel grit
  • Alumina
  • Silicon carbide
A close up of a shot blasted post, ready for HZS

A close up of a shot blasted post, ready for HZS

Is shot blasting dangerous?

The short answer is yes, the shot blasting process is a dangerous operation in untrained hands.

The most obvious is that theĀ force that the shot comes out of the gun could cause significant injury if it came into contact with a body part.

The less obvious is what the blasting is taking off the item, this could include lead paint,

You should ensure that a shot blast machine is only ever operated by a qualified, experienced individual and the relevant protective PPE equipment is used.

The following items should be used:

  • A filtered air fed helmet
  • Ear protection
  • A mask
  • gloves
  • Steel toe caps boots

Overview

Abrasive blasting is a very efficient way of removing old coatings or removing rust and other impairments that without removal will result in virtually no adhesion and uneven final coating finish.

We at NSP Coatings will always recommend that the base item is shot blasted, it guarantees that the coating will adhere nicely and the end result of a powder-coated finish or a wet spray finish will look its best.