Transcript NEW DEVELOPMENTS IN BRAZING FLUXES

NEW DEVELOPMENTS IN
BRAZING FLUXES
DR. Y. BASKIN
SME BRAZING AND SOLDERING
TECHNOLOGIES CONFERENCE
ORLANDO, FLORIDA
FEBRUARY 7-8, 2002
February 7, 2002
SME Brazing and Soldering
Technologies Conference
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DEVELOPMENT OF A FLUORIDE-FREE
FLUX WAS DRIVEN BY ENVIRONMENTAL
AND SAFETY CONCERNS
Cleaner Plant Water Effluents
 Better Workplace Air Quality
 Improved Safety in Brazing Operations

February 7, 2002
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THE PAST DECADES HAVE WITNESSED
THE ELIMINATION OF HAZARDOUS
METALS AND CHEMICALS
 Cadmium from brazing filler metals
 Lead from plumbing soft-solders
 CFC solvents in all applications
 Hydrazine from different
formulations
 Asbestos from insulation
February 7, 2002
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PRIMARY REASONS FOR CONTINUED
USE OF FLUORIDE BEARING FLUXES



Fluoride-bearing brazing fluxes perform
consistently in many applications, giving little
reason for change.
There was an almost universal conviction that it
was impossible to develop an acceptable
fluoride-free brazing flux, leading to little R&D
efforts.
Environmental and health studies concentrated
on other sources that exhibited greater
dangers, such as CFCs, lead, and other
elements.
February 7, 2002
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COMMON INGREDIENTS OF
CONVENTIONAL BRAZING FLUXES





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Boric Acid
Boron Oxide
Elemental Boron
Organic Additives
Potassium Bifluoride
Potassium Fluoborate
February 7, 2002






Potassium Fluoride
Potassium Pentaborate
Potassium Tetraborate
Silicon Dioxide
Sodium Tetraborate
Water
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COMPOSITIONAL AREA
OF COMMON BRAZING FLUXES
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FLUX ACTIVATION TEMPERATURE AS A
FUNCTION OF B/F RATIO
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EFFECT OF TIME ON FLUX
ACTIVATION TEMPERATURE
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FLUX EXHAUSTION TEMPERATURE
AS A FUNCTION OF B/F RATIO
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THE HAZARDS ASSOCIATED WITH
FLUORIDE-BEARING FLUXES CHANGE
DURING DIFFERENT BRAZING
OPERATION STAGES

Working with raw flux

Brazing at elevated temperatures
when HF and BF3 gases are released

Discharging raw flux and flux residues
into plant effluent, and entry into
water system
February 7, 2002
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EXPOSURE LIMITS AND HAZARD LABELS
FOR FIVE FLUORIDES
FLUORINE
COMPOUND
ACGIH
TWA-TLV
OSHA
TWA-PEL
NIOSH
TWA-REL
OSHA
LABEL
D.O.T
LABEL
Boron Trifluoride
1ppm
1ppm
1ppm
-
Poison
Hydrogen Fluoride
3ppm
3ppm
3ppm
Toxic
Corrosive
Potassium Bifluoride
2.5 mg/m3
2.5 mg/m3
2.5 mg/m3
Toxic
Corrosive
Potassium Fluoborate
2.5 mg/m3
2.5 mg/m3
2.5 mg/m3
Toxic
-
Potassium Fluoride
2.5 mg/m3
2.5 mg/m3
2.5 mg/m3
Toxic
-
February 7, 2002
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POTENTIAL HEALTH HAZARDS FROM USE
OF FLUORIDE-BEARING FLUXES


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Irritation to skin and fingernails by the
raw flux.
Irritation of the eyes, mucous membranes,
and respiratory system by gases and fumes
generated during brazing.
Calcium depletion (sclerosis) of the bones and
mottled teeth from long-term exposure to
fluoride gases and fine fume particles.
Potential health hazards from discharge of
untreated flux and flux residues into the water
supply.
February 7, 2002
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EQUIPMENT
Thermolyne 1500 Furnace – Maximum
Temperature: 1,200°C
 Calibrated Pyrometer with Surface
Probe. Maximum Temperature: 1,300°C
 30 Tempilstik Temperature Indicators.
Temperature Range: 400-1,200°C
 Brookfield Viscometer
 Hot Plate
 Timer
 Balance

February 7, 2002
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BASE METALS
February 7, 2002

Copper

Mild Steel

Brass C-260 (70%Cu/30%Zn)
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FILLER METALS
AWS
CLASSIFICATION
COMPOSITION
LIQUIDUS
TEMPERATURE
BAg-28
40% Ag
30%Cu
28%Zn
2%Sn
710°C/1,310°F
BAg-36
45%Ag
27%Cu
25%Zn
3%Sn
688°C/1,270°F
BCuP-4
87.5%Cu
6%Ag
7.25%P
718°C/1,325°F
February 7, 2002
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PHYSICAL PROPERTIES OF FLUORIDEFREE FLUX
Form
Color
Specific Gravity
Viscosity @ 22°C/72°F
Fluorine Content
Flash Point
Freezing Effects
Heating Effects to 50°C/122°F
Active Temperature Range
February 7, 2002
Creamy Paste
White
1.4
225,000 ± 20,000 cps
< 100 ppm
None
None
Minimal
670-870°C/1,235-1,600°F
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TEMPERATURE RANGES FOR FLUXES
AND FILLER METALS
FLUX
ACTIVATION
TEMPERATURE
MAXIMUM
RECOMMEND
TEMPERATURE
Average Fluoride-Bearing
Fluoride-Free
570°C/1,050°F
670°C/1,235°F
870°C/1,600°F
870°C/1,600°F
FILLER METAL
MAXIMUM
LIQUIDUS
TEMPERATURE
RECOMMENDED
TEMPERATURE
BAg-28 (40%Ag)
BAg-36 (45%Ag)
BCuP-4 (6%Ag)
710°C/1,310°F
688°C/1,270°F
718°C/1,325°F
802°C/1,475°F
785°C/1,450°F
785°C/1,450°F
February 7, 2002
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Technologies Conference
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FILLER METAL SPREAD AS A FUNCTION
OF BASE METAL AND FLUX
BASE
METAL
Brass
Copper
Mild Steel
BAg-28
FILLER METALS
BAg-36
BCuP-4
Fluoride-Free
Excellent
Excellent
Excellent
Fluoride-Bearing
Excellent
Excellent
Excellent
Fluoride-Free
Moderate
Moderate
Moderate
Fluoride-Bearing
Excellent
Excellent
Poor
Fluoride-Free
Moderate
Moderate
Poor
Fluoride-Bearing
Moderate
Moderate
Poor
FLUX
FURNACE TEMPERATURE: 785°C/1,450°F
EXCELLENT SPREAD: > 2.0cm2
POOR SPREAD: <0.5cm2
February 7, 2002
TIME IN FURNACE: 60 Seconds
MODERATE SPREAD: >0.5cm2<2.0cm2
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BENEFITS OF USING
FLUORIDE-FREE FLUX

Greater Operator Safety

Better Workplace Air Quality

Cleaner Plant Water Effluents
February 7, 2002
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Technologies Conference
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PRIMARY SKIN IRRITATION STUDY
FLUORIDE-FREE
FLUX
Primary Dermal
Irritation Index
(PDII)
Classification
February 7, 2002
2.3
Not a primary irritant.
Non-corrosive to skin.
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FLUORIDE-BEARING
FLUX
5.9
A primary irritant
Corrosive to skin.
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APPLICATIONS FOR
FLUORIDE-FREE FLUX

COPPER-TO-COPPER

BRASS-TO-BRASS

COPPER-TO-BRASS

BRASS-TO-MILD STEEL

COPPER-TO-MILD STEEL

MILD STEEL-TO-MILD STEEL
February 7, 2002
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