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Brazing Faq's

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One needs to understand the basic fundamentals of Brazing alloys & the related procedures. In order to make the cumbersome & complex topic easy & comprehensible for readers & users, some vital questions have been dealt with in details throwing enough light on the confusing topic. Here, we are going to highlight on some of the fundamental elements which will help in answering frequently asked questions.

Q.1. What differentiates brazing, soldering & welding?
Ans. Brazing has been defined as a group of joining processes specially arranged in a manner to produce coalescence of materials. The process involves heating of these materials at a brazing temperature by using a filler metal (solder) which has a liquidus above 840°F (450°C), and below the solidus of the base metals.

In the case of Soldering, the only fact which distinguishes it from brazing is the filler metal used, since, here the liquidus is below 840°F (450°C) while it is above the solidus of the base metals.

Welding involves the process of fusion which takes place along with the melting of base metal and a filler metal.

Q.2. What is a brazing procedure?
Ans. A kind of metallurgical bond is created between the filler metal and the surfaces which are joined using the brazing procedure. The process involves application of heat directly on the base metals, thereby, the filler metal is brought into contact with the heated parts. Once the melting of filler metal takes place, capillary action is applied to draw the melted part through the joint.

Q.3. What is provided through a brazed joint?
Ans. Brazing joint process provides many properties which are namely :

Sturdy joints
Cheap temp/lower cost
Base metals integrity is maintained
Dissimilar joints are efficiently joined
well defined joint appearance
Easy acquirement of skills

Q.4. Define oxidization.
Ans: Oxidization is generally defined as a process where after the metal exposed to oxygen, the oxides form from oxygen atoms attach to the metal. Once formed, these oxides prevent the molten alloy from metallurgically joining to the metal.

Q.5. What are the filler metal form types?
Ans: Availability of filler metals in certain forms depends upon the alloy that are chosen. These firms are widely categorized as :

Wire
Strip
Powder
Paste

Mostly, the preforms are made from strip and wire.

Q.6. What does Flux mean?
Ans: When the joint surface is shielded from air, thus, preventing oxide formation after applying chemical compound, it is s is known as Flux. The metals in the process of joining are cleaned before the start of a brazing procedure, though, the flux material will dissolve and absorb oxides.

Q.7. What are the different flux forms available?
Ans: Depending upon the type of flux, flux is made available in the form of paste, slurry, liquid and powder form. Though, dispensable fluxes are found with petroleum base, the paste, slurry, and liquid fluxes are all water based. Even a torch in use is used to deliver the flux to the joint.

Q.8. How to clean a flux off of joint after brazing?
Ans: By quenching & soaking the assembly in hot water that the flux can be cleaned smoothly off the brazed joint. In order to clean a stubborn flux residue, HCl (up to 25%) can be added to the water & exclusive made cleaners can also be used for the cleaning purpose.

Q.9. What is the right process of reconstituting & thinning of flux?
Ans: In order to thin water-based flux, water is applied which is generally in the form of distilled or de-ionized meant specifically for this.

Q.10. What is a flux's shelf life?
Ans. Generally, the warranty period of a flux metal is of one year from the date of manufacture if properly stored in the original unopened container. The quality might not deteriorate even after the expiry of this period.

Q.11. What do we understand by a brazing paste?
Ans. When we talk of a brazing paste, we mean a material consisting of metal alloy in a powder form well mixed with a binder. Flux is added to this paste whenever required to provide protection from oxidization.

Q.12. What is the most feasible applications for applying a brazing paste?
Ans. The application of a brazing paste is required in functions such as :

Torch
Induction
Furnace

To make a paste formulation, flux is generally added which has an exception as well, i.e. say it has no role to play in the paste formulation when it is to be used in a vacuum or atmosphere furnace.

Q.13. What is a brazing paste's shelf life?
Ans. A warranty of 90 days is given in case of brazing paste stored in its original unopened container. The quality may not deteriorate even after the expiry of this period. The functional aspect of this paste form can be determined only by melting the paste to check if it flows or not which ultimately determines the functionality of the paste.

Q.14. In brazing, what types of joint configurations can be used?
Ans. Joints of distinct types are used in brazing where the most common of them are :

Butt joints
Lap joints
Butt lap joints

Q.15. What is the proper clearance in case of brazing?
Ans. In flux brazing, a joint clearance with a range varying from 0.002"-0.005" is there to produce a sound high strength joints. Whereas, this joint clearance should be 0.000"-0.002" in case of atmosphere and vacuum brazing. Lot of care is taken while using brazing metals with different coefficients of thermal expansion. When determining a joint clearance, the amount the materials expand has to be kept in consideration.

Q.16. What is a brazing joint's strength?
Ans. There are certain factors which determine a brazing joint's strength which are mainly :

Joining of the base metals
Joint clearance
Usage of filler metal
Use of varied base & filler metals
The gap between the two metals when being joined
Whenever there is an increment in the gap, it leads to an automatic decrement in the joint strength. But at times, the braze joint strength will equal or surpass the the strength of the base metals when used in proper conditions.

Q.17. What should be the right temperature for furnace in furnace brazing?
Ans. The temperature for furnace in furnace brazing is generally heated at 50°F-100°F above the liquidus of the filler metal being used.

Q.18. What do we mean by Handy One?
Ans. For simplification of a brazing process, a flux cored product or a Handy one is made use of. Available in the form of a brazing alloy in strip form, it is rolled around a measured amount of powdered flux. The flux gets released whenever the part is heated, thus, providing enough protection from oxidization. Handy one is found in multiple filler metals and flux combinations which joins virtually all common metals.

Tags:- Frequently Asked Questions On Brazing, Question On Brazing

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