Our business associate CLEMCO INTERNATIONAL GMBH is the European headquarter of Clemco Industries the world's largest manufacturer of air-powered blast equipment used to clean, deburr, shot peen, remove coatings, finish or otherwise improve the surface being blasted
Surface Preparation
Blasting equipment
Compressor (Air requirement)
Pressure pots
Remote valves
Blast hose
Blast nozzles
Protective clothing & helmet
Abrasives
Types of abrasives
Abrasive recovery system
Blasting is a process in surface preparation for cleaning metal objects free oil and rust and leaves the surface ready for painting or bonding.
Types of Blasting
Centrifugal blasting
Wheel type
Pressure blast or pot blast
Open blasting
Closed blasting
Surface Preparation
Roughness – anchor profile
Cleanliness
Anchor Profile Coating requires specific profile to ensure adhesion and complete protection of the substrate. The abrasive particles cut into steel to form tiny peaks and valleys. The depth of the profile is controlled by the size, type & hardness of the abrasive used.
For instance in ship repair the etched surface or “anchor profile” required will be about 125 microns using the grit size of 0.5 to 2.5 mm.
Cleanliness The steel structures painting council (SSPC) has established four degree of cleanliness for blasting for removal of contaminants and loose materials on the surface
White metal blast. - SA -3
Near white metal blast. - SA – 2.5
Commercial blast. - SA – 2
Brush – off blast. - SA - 1
BLAST NOZZLES
AREA OF COVERAGE FOT SA – 2 ½ FINISH
1
6 mm Nozzle
10 Sq Mt / Hr
2
8 mm Nozzle
15 Sq Mt / Hr
3
9.5 mm Nozzle
22 Sq Mt / Hr
4
11 mm Nozzle
32 Sq Mt / Hr
5
12 mm Nozzle
40 Sq Mt / Hr
Chemical Pre-treatment
Quality Criteria - proper cleaning is the single most important aspect of a paint/powder finishing system should you decide to maximize paint/powder performance. Most people in manufacturing assume painting/powder coating automatically increase the important physical properties associated with coating. This is not true.
The following items are directly related to the type and quality of the pretreatment on the metal substrate that will be paint/powder coated:
Shot Blasting
Dry – film adhesion
Cross hatch adhesion
Impact testing
Zero T bends
Post forming
Accelerated humidity testing
Accelerated salt spray testing
All of these properties can be improved with paint/powder, but only when proper cleaning, rinsing, conversion coating and drying takes place prior to any substrates entering the paint/powder booth.
Spray pretreatment
Dip pretreatment
Soil Characterization Chart
Cleaning Difficulty
Type of Soil
Very difficult
Chlorinated/sulfurized oils
Stearates – diecast release agents
Buffing/polishing compounds
Heavy duty rust proofers
Cured paint
Carbon smut
Medium difficult
Mill oil
Hydraulic oils
Straight oils
Lapping compounds
Waxy inhibitors
Metal oxides
Usually easy
Soluble oils
Water soluble
Emulsified oils
Synthetic oils
Light machine oils
Conversion Coatings Selection Chart
Metal
Iron
Zinc
Chrome
Chrome
Type
phosphate
phosphate
phosphate
oxide
Iron/Steel
X
X
Galvanize
X
X
X
X
Aluminium
X
X
X
X
What is a clean surface?
There are many degrees of cleanliness that can be achieved on a substrate surface and just as many ways of checking the surface for cleanliness. The following is a list of these conditions of cleanliness and checking methods.
Clean surface– one which is free of oil and other unwanted contaminants. The degree of cleanliness required is dependent on the operation, or process, which the part of product must pass to. Obviously manufacturers utilizing the cell cleaning concept or work station cleaning, are typically cleaning between process steps. Situations like these usually do not require the degree of cleanliness needed for final pre-paint preparation.
Water break-free surface – this condition tells you that you have removed all organic soils. The parts exiting the last pre-treatment or rinse stage prior to drying will show a uniform sheeting of the rinse water indicating an organically clean surface. The water break-free surface has been the long-standing rest for cleanliness. The key to this test is using fresh uncontaminated rinse water. Detergent additives or rinse aids, used in a final rinse may hide poor cleaning. Additionally, contaminated rinses, due to poor overflow, may also mask poor cleaning due to the surfactants’ wetting ability.
Water break surface– this condition tells you that you have not sufficiently cleaned the substrate surface and that there are residual organic soils still present. The part will exhibit a surface which would resemble a freshly waxed car surface after a good rain. You will not see uniform sheeting of the water, but you will see beads of water. Normally poor cleaning is most often found on or near weldments, or in areas which receive poor spray impingement to the part.
White towel test– wiping a white towel across clean and dry surfaces will indicate the effectiveness of inorganic soil removal. Check flat surfaces and those areas most likely not to receive direct spray impingement.
Tape pull test– applying scotch tape to a clean and dry surface will also indicate the effectiveness of inorganic soil removal. This method of checking surface cleanliness is accomplished by first applying the tape on the substrate surface, then removing and placing the tape on a white piece of paper. The contrast of the white paper allows for easy identification of remaining soils.
Ultraviolet (UV) detection– this method requires soiling the substrate surface with fluorescent oil, and cleaning and inspecting this surface under ultraviolet light.
P.A.T. – photo acoustical technology, quantified the degree of cleanliness by a numbering system. This is accomplished through photo electron emission or reflectance. The higher the reflectance, the cleaner the surface.
Rinsing
A part is no cleaner than the quality of the rinse water used. The purpose of effective rinsing may be one or all of the following :
Flush remaining wetted soils from the substrate.
Neutralize, or dilute, remaining alkalinity after cleaner stages
Maintain a wet substrate between stages
Flush non-adherent phosphate, or conversion coating from substrate
Cleanse excess water hardness, and salts, prior to dry-off.
Proper and adequate rinsing is critically important in pretreatment for paint/powder, when an accelerated corrosion specification is required. The key considerations and factors which affect sound rinsing are:
Quality of the original water
Volume of the water supply tank in the pretreatment system
Method of application (immersion or spray)
Quantity of water coming into contact with the part surface (flooding)
Part configuration or design
Time of contract (duration) of the water
Raw water cost
Raw water conservation
Drain vestibule length within the pretreatment system.
Water Comparison
Raw
Softened
D.I./R.O.
Impurities
varied amounts of
varied amounts of
practically none
Minerals including
minerals depending
Hardness depending
on the water source,
On the water source
low calcium and
Magnesium
TDS
dependent on
somewhat higher
Near zero
Source
than the raw water
Advantages
Least corrosive,
no scale/scum
No scale/scum
Lowest cost.
Problems
problems. No
Residue after
Drying
Disadvantages
Scale and soap
slightly more
most corrosive
Scum, residue
corrosive than
(by itself).
After drying
the raw water,
Highest cost
Less visible
Residue after
Drying
Water Preferences
Alkaline Cleaner
Raw if scale/scum are not a problem
Blend D.I./Raw
Intermediate Rinse
Raw (lowest cost, scale/scum should not be a problem here)
Phosphatizing
Distilled/R.O.
Raw
Blend D.I./Raw
Seal Rinse
Distilled/R.O. Raw is second choice, never softened
