Aluminum Dip Brazing Process

1. Purpose: The Braze Joints In This Process Shall Have Complete Penetration Of The Brazing Alloy. Joints Shall Be Clean, Smooth And Without Flux Residue. The Contour Of The Outside Joints Shall Be Uniform Radius With Minimum Amount Of Excess Braze Or Flash Over The Adjacent Surfaces. The Material Used Must Conform To Mil-B-7883c.
2. General: All Burrs Must Be Removed Prior To Braze To Assure A Proper Fit. All Parts Must Be Cleaned Thoroughly Prior To Braze See Section 8 Of This Procedure.
3. Fit: The Clearance Between Mating Surfaces Of Parts Shall Not Exceed .003 Inch For Grade A, Or .006 Inch For Grade B And C, Except In Areas Of A Joint Where One Or Both Mating Surfaces Are Intentionally Beveled. In Fabrication Of Aluminum Assemblies Where Sheet Clad With Brazing Material Is Employed, The Joints Shall Make Contact If The Cladding Material Provides Sufficient Clearance.
4. Fixturing: Parts To Be Joined Shall Be Held In Position By Jigs Clamps, Supports, Or Shall Be Self Fixturing. Fixtures Used To Hold Parts And Assemblies In Alignment During Brazing Shall Be Designed To Allow Expansion And Contractions Of The Parts During Heating And Cooling. Jigs And Fixtures And Clamps Shall Be Free Of Contaminating Materials.
5. Pre-Cleaning: Prior To Brazing The Following Steps Shall Be Taken

All Parts Shall Be Free Of Oil, Dirt, And Cutting Fluids. Dirty Parts Shall Be Cleaned In A 125 To 150 Degrees F Air Agitated Soap Bath Using An Industrial Soap Such As Hurrysafe Or Equal.

Rinse Soap Water Off In Tap Water.

Dip 20 To 40 Seconds In A 5% To 10% Caustic Soda Solution At 160 To 180 Degrees F.

Rinse In Flowing Tap Water Bath.

Dip In Gilsparkel Acid Solution For About 30 Seconds.

Rinse Tap Water Acid Rinse Tank #1. Rinse Tap Water Acid Rinse Tank #2.

Dip In Deoxidizer Such As Allied Kellite # 184 Or Equal until Smut Is Removed.

Rinse In Tap Water Tank With Overflow

6. Tacking If Required:

Parts Are To Now Be Tacked Or Welded As Necessary To Hold Parts Together For Brazing.

Dip In Gilsparkel Acid Solution For About 30 Seconds.

Rinse Tap Water Acid Rinse Tank #1. Rinse Tap Water Acid Rinse Tank #2.

7. Preparation: Assemblies To Be Dip Brazed Are Now To Be Fixtured And Depending Upon The Specific Application The Form Of Braze Filler Should Be Chosen From Table Ii.

Flux Type And Material Shall Be Iaw Mil-B-7883c

Preheat Product At Temperature 25 - 100 Degrees Below The Solidus Of The Brazing Alloy, Or Preheat Iaw Specifications Or The Drawing.

Table II Alloy Filler Selection Table
Type	Source	Description
Wire	Lucas-Milhaupt	.062 Dia Alloy 718
Wire Coil	Lucas-Milhaupt	.062 Dia Alloy 716
Shim (Foil)	Lucas-Milhaupt	.003 Thick Alloy 718
Table II sizes are for reference only, substitutions on diameter or thickness is permissible

8. Brazing:

Preheat The Assemblies In A Hot Air Furnace At 1000 Degrees F Plus Or Minus 50 Degrees For Approximately 30 Minutes Or Until Adequate Time Has Elapsed For The Braze Assembly To Achieve Oven Temperature.

The Assemblies Are Then Immediately Transferred To The Brazing Bath For 1 To 4 Minutes At 1100 Degrees F Plus Or Minus Ten Degrees F.

After Removing Assembly From Salt Bath Allow Assemblies To Drain Of Salt, Tip Racks As Possible To Minimize Salt Retention In Or On The Parts.

Air Quench Parts On Cooling Rack Using Forced Air.

9. Post Braze Cleaning (May Also Be Referred On Travelers As Post Braze Cosmetic Cleaning)

Soak Parts In Air Agitated 150/180 Degrees F Hot Water Bath. Rinse Until Salt Is Completely Removed 1/2 Hour Minimum.

Rinse Salt Water Film Off In Tap Water.

Dip 20 To 40 Seconds In A 5% To 10 % Caustic Soda Solution At 160 To 18o Degrees F.

Rinse In Flowing Tap Water Bath.

Dip In Gilsparkel Acid Solution For About 30 Seconds.

Rinse Tap Water Acid Rinse Tank #1. Rinse Tap Water Acid Rinse Tank #2.

Dip In Deoxidizer Such As Allied Kellite # 184 Or Equal Until Smut Is Removed And Aluminum Is Bright And New In Appearance.

Rinse In Tap Water Tank With Overflow.

10. Passivation Of Brazed Assemblies: Assemblies That Have Been Silver Brazed Shall Not Be Given A Nitric Acid Treatment For Pasivation. Copper Or Nickel Brazing Alloys With Less Than 7% Chromium Shall Not Be Passivated.
11. Inspection:

Samples From Each Lot Shall Be Inspected To Determine Conformance To The Dimensional Tolerance Iaw Mil-Std-105 

Brazed Assemblies May Be Reworked Using Such Methods As Redipping Or Torch Per Mil-B-7883c.

Repair: When Rework Of Brazed Assemblies Is Not Possible Using An Approved Method, It Shall Be Referred To The Acquiring Activity For Disposition.

Inspect Parts Per Traveler Or Applicable Drawings For Quality Of Braze Joint. Tables V, VII, & VII Shall Be Used As An Inspection Criteria Unless Otherwise Specified By Customer And/Or Specifications.

Type of Defect	CMP0014 Grade Unless Otherwise Specified
External Voids	See Table VII
surface porosity	Acceptable
Incomplete Fusion	See Table VIII

Table VII External Void Acceptance Criteria for Dip Brazing

Joint Length (L) Inches	If L is less than 0.50 (Inches)	If L is greater than 0.50 and less than 1.00 (Inches)	If L is greater than 1.00 (Inches)
Maximum Acceptable Cumulative Void Length	0.025	0.05	0.100 Inch of Joint

Table VII Incomplete Fusion Accept Criteria For Brazed Joints

	Joint Length (L) Inches	CMP0014 GR Criteria Skip One Side Only
Braze filler alloy visible in joint	L is less than; 0.50 L> 0.50 to < 1.00 L> 1.00	Must be brazed on one side of the joint but may skip .50 per inch or substitute pressure test listed below. 1/
Braze filler alloy not visible in joint	L> 0.50 to < 1.00 L> 1.00	.125 Length Maximum .250 Length Maximum .250 Length per inch or substitute pressure test listed below 1/

1/ A Pressure Test Of 3 Psi For 1 Minute May Be Substituted For Measurement Of Incomplete Fusion (Skips) And Used For An Accept Criteria.

12. Notes: Operators Are To Familiarize Themselves With Section 6.1 Through 6.4.1 Of Mil-B-7883c And To Reference The Paragraphs For Definitions Of Symbols, Fillets And Inspection Criteria.