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Innovations in Pretreatment:Advanced Non-Phosphate Pretreatments
Suresh Patel Chemetall
FABTECH Canada 2014
Outline Overview of Advanced Pretreatments (APs)
What are Silanes?
What are Phosphonates?
Practical application‒ Choosing the right pretreatment
‒ Successfully making the transition
‒ some practical lessons/case studies
Final Comments
FABTECH Canada 2014
Advantages Environmentally friendly…no zinc, no/low phosphorous
Energy savings……….operate at ambient temperature
Less capital investment……….fewer stages needed
Smaller bath initial charge………smaller tank used
Simple, robust operation………….‒ Wide operating windows
‒ No scale
‒ Almost no sludge
‒ Simple waste treatment
Versatile……… work with most substrates, paints
Match paint performance of process replaced
Advantage: Cost savings
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SilanesUp Close
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Silane Pretreatments What are they?
‒ Organic: Organofunctional silanes
‒ Inorganic: Unregulated metals such as zirconium
How do they work?1. Metals form ionic bond to substrate
2. Silane forms covalent bond to substrate
3. Silane cross-links
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Silane Pretreatment Organic Plus Inorganic
OO O O O O O
Si
CH2CH2
Si
OH
O
HOO
O
O
O
O
OHO
Si
Si
Si
Si
Si
Si
CH2 CH2
CH2
CH2
CH2CH2
CH2CH2
CH2
CH2
OH
HOO
HO
HOO
SiSi
Si O
O
OO O
CH2
CH2
O
CH2CH2
Si
Si
SiSi
Si
Si
O
O
CH2CH2
CH2
CH2
CH2
Si
Si
Si
Si
OH
OH
O
HO
OH
OO
ZrHO
OO
ZrHO
OO
CuHO
OO
ZrHO
OO
ZrHO
OO
ZrHO
OO
Mn
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What Does the Coating Look Like?
SEM
Zinc Phosphate
FEG-SEMSample preparation: Induced crack initiation with liquid nitrogen
Silane
60 nm
6 μm
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New Silane Developments High-performance applications
‒ Accelerator
‒ Unique silane molecules
• better e-coating on mixed metal
• better corrosion performance
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New Silane Developments
Touch-Up, manual wipes For repair of spot defects
Sand Defect Wipe on Silane Ready for Paint
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New Phosphate-Free Developments
Three-stage process Cleaner-coater
Rinse
Rinse
Economical
Three-stage process Alkaline cleaner
Rinse
Silane coater
Good for more difficult soils
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PhosphonatesUp Close
FABTECH Canada 2014
Phosphonate Pretreatments What are they?
‒ Organic: Phosphonate
‒ Inorganic: Unregulated metals zirconium and titanium
‒ Proprietary activating ingredients
How do they work?‒ Covalent bonding of Phosphonate to substrate
‒ Ionic bonding of metals to substrate
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Phosphonate Pretreatment Organic Plus Inorganic
O
P
OO
R3
R2R1
Substrate
OO O OO
ZrTi P
OO
R3
R2R1
FABTECH Canada 2014
Practical Application
FABTECH Canada 2014
Good Cleaning is Essential
Organic soils (oils, metalworking fluids)‒ Alkaline cleaning
Inorganic soils (rust, scale, welds)‒ Mechanical: grinding, blasting, etc.
‒ Pickling: acid followed by neutralization
Advanced Pretreatments use less heat and weaker acids than phosphates, so they don’t help with cleaning.
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Good Rinsing is Essential Alkalinity
‒ Can precipitate active ingredients in AP
Complexant from cleaner‒ Complexes active ingredients in AP
Phosphorous from cleaner‒ False reading in phosphonate bath check
Contaminants in general ‒ Can react with active ingredients in AP
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How to Control the Rinses Conductivity limit: 200 μS/cm (150 ppm TDS)
Automatic conductivity controller
Exit fresh water halo
Drip water conductivity
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Product Selection 1) Washer considerations?
‒ Stainless Steel or Plastic‒ Mild Steel‒ Number of stages‒ Rinsing
2) Water quality?‒ DI or RO‒ Tap water
3) Phosphorous discharge limits?
4) Performance?‒ Varies with paint‒ Varies with substrate
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Before Charging the Tank Plan, Action item list Baseline current process Write operating manual and log sheet Washer modifications
‒ Exit halos‒ Counter-flows
Order all titration supplies Order all automation equipment, feed pumps Chemically descale and rinse all stages Align nozzles
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Clean Rinse Rinse RinseCoat
Fresh WaterH
alo
Halo
Halo
Waste Treatment Was Iron Phosphate
Was Rinse(smaller)
Cascades and halos cut
water use in half
Converting a Typical 5-Stage Washer
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Charging the Tank Post, read and understand MSDSs
Use proper PPE
Circulate water, then check conductivity
Charge and adjust baths
Retain bath samples and panel samples
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Appearance on Cold Rolled Steel
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Appearance on Other Substrates
Steel Electrogalvanized Aluminum
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Checking the bath Photometric methods
‒ Zirconium
‒ Titanium
‒ Phosphonate
‒ Silane
pH
Conductivity
Free or Total Acid?Hach DR/890
Portable Colorimeter
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Coating reaction and drag-out causes‒ conductivity to fall
‒ pH to rise
Sensor detects this change Pumps feed at assigned ratio
‒ Inorganic component
‒ Organic component
Pulsatron Pumps
Automation: Conductivity or pH
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Once the Line is Running
Operator Training Verify performance
‒ Bath analysis in lab‒ Coating weight‒ Adhesion‒ Corrosion testing
Routine line audits Log SPC Data, Chart it, Post it 15
20
25
30
35
30-May 1-Jun 3-Jun 5-Jun 7-Jun 9-Jun 11-Jun 13-Jun
LCL
UCL
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A Transition Success Story
When the winds of change blow, some people build walls and others build windmills.
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The Situation, 2006
Utility vehicle manufacturer Nine-stage zinc phosphate process Two-step powder coat Chemical cost increases: phosphate, zinc, nickel Needs:
‒ Counter rising, chemical costs with other savings.
‒ More environmentally-friendly process for ISO 14001
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Actions Taken, 2006 - 2007
Panels and small part tested Baseline established Cost savings calculated Decision to transition made Plan with timeline formulated Washer, counter-flows, exit risers re-plumbed Washer chemically descaled Line started-up Operators trained
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The Results, 2008 - 2012
Salt spray results equal to zinc phosphate 30% reduction in water usage 90% reduction in sludge generation Environmentally-friendly process Stable process
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Another Transition Success Story
Do not be afraid of going slowly; be afraid of standing still.
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The Situation, Prior to 2009 Off-road, snowmobile, motorcycle, military vehicle
manufacturer Six-stage iron phosphate process E-Coat primer and powder topcoat Needs:
‒ Reduce overall pretreatment costs
‒ Reduce waste treatment costs
‒ Maintain excellent paint performance
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Actions Taken, 2008
Panels tested Baseline established Cost savings calculated Decision to transition made Plan with timeline formulated Washer chemically descaled Line started-up Operators trainedyesterday
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The Results, 2009-2013 $72,000 annual energy savings 40% savings in waste treatment sludge 35% savings in waste treatment cost 15% reduction in pretreatment cost overall Salt spray results equal to iron phosphate + seal Environmentally-friendly process Stable process with wide parameters
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Some Real World
Lessons
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“This never happened before…”
Cause: Drips from the conveyor loadbars
Spots that bleed through the paint
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Meanwhile, at another facility
Paint adhesion failure
Cause: HRS mill scale was softened by acid pickle
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Baseline
Important to baseline thoroughly‒ Paint performance
‒ Understand the whole process
Changing from phosphate to non-phosphate didn’t change‒ Conveyor configuration
‒ Substrates, acid pickle, and etc.
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Some Final Comments Communicate clearly, form a team, carefully plan with:
‒ Equipment supplier
‒ Pretreatment supplier
‒ Paint supplier
Performance requirements
Limitations‒ Cost
‒ Substrates
‒ Water quality
‒ Paint
‒ Equipment Materials of construction
Number of stages
