Media Use in a Dana-Ridge Wetblast Unit.
The range of available finishes from a Dana-Ridge wetblast machine is extremely varied. Perhaps you have some carbon build-up you want to remove from a manifold, perhaps you want to remove a coating of paint from a piece and leave a nice rough surface for a new coat of paint to hold on to. Perhaps you have an alloy part that you want a nice bright finish making it look brand new. What about etching, what about removing a coating and leaving the substrate untouched, what about…?
The main variables we can control is
- Type of wetblaster used, known by names such as vapour blast, vapour hone, slurry blast, wet sandblast machine etc.
- Type of media we blast with
- Air pressure setting.
If you’ve purchased a Dana-Ridge wetblast cabinet then you’re already using the best method for getting a consistent flow and concentration to the process gun. Not all sandblasting machines operate using the same method. There’s even a variety of wet systems.
The next most important variable with any form of sandblasting or wet abrasive blasting is the choice of media. You can run pretty much any blast media through a Dana-Ridge wetblast unit except for steel shot which will ruin the pump. You can run finer and coarser media than you can through a dry sandblast unit and you can blast items that would get absolutely ruined in a traditional dry sandblasting unit too. Another advantage is there is no need for an expensive filtration unit as the water suppresses any dust.
The following is by no means an exhaustive list but let’s look at the most commonly used media.
|Sodium Bicarbonate (NaHCO₃)||Automotive such as oil galleries, carburetors, diesel pumps, injectors. Anywhere you want a matte finish or where you have an assembled part and can’t easily clean out remnant media.||2.5||Angular|
|Plastic Abrasive (several types)||Commonly used in aircraft restoration. Strips without damaging or warping the substrate.||3.5||Angular|
|Glass Bead||Provides a brighter finish. Used for blasting, peening, honing, cleaning, light deburring and Carbon removal. Used in a great variety of applications. Different sizes give different blasting properties.||4.5||Spherical|
|Crushed Glass||Cheap angular grit good for removing coatings and providing a good keyed surface. Used in many applications.||6||Angular|
|Garnet||Inexpensive angular grit good for providing a keyed surface for recoating||7.5-8||Angular|
|Aluminium Oxide||One step down from diamonds on the Mohs hardness scale, it’s a tough grit in various grades to provide a range of finishes effectively||9||Angular|
Sodium Bicarbonate (NaHCO₃)
At Dana-Ridge we often get enquiries about this blast media. There seems to be a misconception that it gives a nice bright finish. Many times, we find that glass bead is a better option. It does have some benefits however and in a wetblast machine you get 4 times the life of the media thanks to the water cushioning effect.
Advantages of Soda
- Friable – soft angular grains readily fracture into smaller particles softening the impact on substrates.
- Dissolves in water
- Safe to use on virtually any substrate, including delicate surfaces, rotating equipment and moving parts but still able to remove coatings.
- Able to be washed out of internals easily meaning no damage to moving parts.
- Unable to remove rust and scale
- Gives a matte finish (may be an advantage if it is the desired effect)
- Shorter media life
- Slightly alkaline, causing crystals to form on blasted parts (this can be neutralised in a slightly acidic solution of vinegar and water after blasting)
- In a dry sandblasting cabinet water is an issue (not in our wet system though)
The most common request for plastic media comes from aircraft manufacturers and the like. They want a media that will strip and clean but where etching of the underlying substrate cannot be tolerated. As you can imagine, aircraft manufacturers have to be very precise with their tolerances and the Dana-Ridge wetblast system can combine both the qualities of the plastic and the water cushioning aspect of the wet blast unit giving even more advantages.
Advantages of Plastic Media
- Gentle non-abrading action where no damage to the substrate can be tolerated but top coating needs removing
- As plastic impacts the blasted part the plastic breaks and creates a new cutting surface/shape
Disadvantages of Plastic Media
- Anti-static agent required in dry blasters (no need for such a thing in our wet system).
- Still a soft media and you won’t get a bright finish of a glass bead nor the aggression of an oxide or crushed glass.
- Not durable compared to other media types
An environmentally friendly spherical media providing many useful characteristics. It comes in a variety of sizes. The following table gives an idea of how to choose. The grades we supply range from the letter designations AH (very fine) through to the larger C and B grades. There are more sizes available upon request. The wetblast system gives a superior finish to dry sandblaster as the water cushion changes the way the bead interacts with the part.
Size in microns
|VS25B||420-590||Large bead gives a slight “grainy” finish compared with those below but the large mass means quick output and a more pronounced peening effect.|
|VS25C||250-420||Commonly used for carbon removal or fast processing. Bigger mass means a nice bright “satin” look and a uniform finish.|
|VS25AB||177-297||A great little all-rounder. Gives a brighter finish than C and still has enough mass to remove coatings effectively.|
|VS25AD||105-210||A nice fine media. Great for blasting uncoated alloys, aluminium etc. Will remove coatings but not as quickly as its larger counterparts but will give a great “wow factor” finish.|
|VS25AH||44-88||Has much smaller peening effect that the larger beads and less surface change. Gives a nice bright finish. Holding the beads in your hand it almost has a talc consistency. Our wet-blast units are better able to handle media this size than dry units.|
Advantages of Glass Bead
- Range of options and finishes depending on desired effects
- Stress relieving properties and peening action. More-so with the larger bead
- Typically gives the nice bright finish on blasted metal
- Not as rough as an angular grit
- More of a pushing/scrubbing action than a ripping action you get with angular grit
- Available in a range of sizes
- Environmentally friendly
Disadvantages of Glass Bead
- Peening effect with larger bead (disadvantage if not a desired outcome)
- Not as rough as an angular grit (may also be an advantage)
- Need to ensure none gets left behind in components with moving parts or close tolerances.
Crushed glass allows a cheap way of removing coatings and profiling the surface of a part. The angular nature means it is more aggressive and allows a fast processing.
Advantages of Crushed Glass
- Cheaper than glass bead and aluminium oxide
- Quick and effective for stripping coatings
- Offers aggressive surface profiling
- Made from recycled bottle glass
- Available in a range of sizes
- Environmentally friendly
Disadvantages of Crushed Glass
- Softer and not as durable as aluminium oxide
- Angular grit wears with use and becomes more rounded
A dense, tough, high performance, cost effective media that is great for providing a rough surface that will allow paint and other coatings get a grip on the freshly blasted surface.
Advantages of Garnet
- Harder than crushed glass
- Cost effective
- Good for providing a keyed surface for surface recoating
Disadvantages of Garnet
- Harsher on softer material such as aluminium
- Creates a matte finish
One step down from diamonds on the Mohs hardness scale, aluminium oxide is a sharp, dense, long lasting abrasive that is highly efficient and durable. It will clean and etch all types of surfaces and is one of the fastest cutting abrasives available. It comes in different sizes and also different quality grades, Brown, pink and white.
Advantages of Aluminium Oxide
- Tough and durable
- Creates a profiled surface
- Variety of sizes and purity levels
Disadvantages of Aluminium Oxide
Usually must be careful not to breathe the dust (not an issue in the Dana-Ridge wetblast process)
More expensive (although lasts longer)