TECHNICAL INFORMATIONCONNECTORS BRAZING PROCESS

1 - INTRODUCTION
Tube brazing is an important part of the installation
procedure for both new and replacement compressors. It
is of fundamental importance that high quality brazing be
performed in order to avoid eventual reprocessing due toleakage at welded (brazed) joints.
In an effort to improve brazing techniques, this report will
cover the how to's of achieving better welds, faster welds,
and lowering the consumption of brazing materials.

2 - OXYACETYLENE BRAZINGFIG 2. - VISUAL CHARACTERISTICS OF NEUTRAL FLAME

2.2.2 OXIDIZING FLAME
The oxidizing flame is created by igniting an oxygen-richmixture of oxygen and acetylene. This flame is hotter than
the neutral flame and is recommended for brass brazing
only.

2.1 NATURE OF FLAME
The heat source is chemical in origin, formed by twogases:
comburent- Oxygen : combustion activator (comburcomburentent)- Acetylene : combustible gas
The oxyacetylene flame is obtained when the two gases(oxygen and acetylene) combine in a torch and areignited.
The maximum temperature of an oxyacetylene flame isapproximately 3100oC (5600oF), close to the tip of thebright inner cone, as shown in figure 1.

FIG. 3 - VISUAL CHARACTERISTICS OF OXIDIZING FLAME

2.2.3 REDUCING OR CARBURIZING FLAME
The reducing flame is created by sparking an acetylenerich mixture of oxygen and acetylene. It is a cooler flame
than the neutral type and it is highly recommended forbrazing copper and steel connections. The reducing flameis also used for brazing aluminum and its alloys.

FIG. 1 - COMBUSTION TEMPERATURES IN DIFFERENT FLAME
REGIONS

FIG. 4 - VISUAL CHARACTERISTICS OF REDUCING FLAME

2.2 FLAME CHARACTERISTICS

2.3 CAPILLARY ACTION

There are three (3) basic kinds of flame in theoxyacetylene brazing process:This is the phenomenon through which the filler metal isintroduced to the junction to be brazed by the attraction ofbase material molecules.

2.2.1 NEUTRAL FLAME

The liquefied filler metal always tends to flow to the hottest
point of the heated joint, however, this only happens when:

The neutral flame is created by igniting a gas mixture withequal parts of oxygen and acetylene. This flame isdestructive to the metal oxides that are usually createdduring the brazing process. This flame type isrecommended for copper to copper welds.

CODE 95040 - OCT/95 - REVISION No. 00- the brazing surface is clean- the joint clearance between the parts to be brazed iscorrect

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TECHNICAL INFORMATIONCONNECTORS BRAZING PROCESS- the faying surfaces of the parts to be brazed are hot
enough to melt the filler metal.

Figure 6 shows the different temperatures measured on asurface when the distance of the inner cone tip to thesurface changes, while using a steady carburizing flame.

2.4 TUBE JOINT CLEARANCE AND INSERTIONOVERLAPIn order to produce a high quality weld, careful attention
must be given to the joint clearance between the tubes
and the minimum insertion length. Figure 5 highlights thispoint in more detail.

(cm)

FIG. 6 - TEMPERATURE X DISTANCE FROM INNER CONE TIP TO
PARTFIG. 5 - TUBE JOINT CLEARANCE AND INSERTION OVERLAP

2.5 CLEANING OF TUBES TO BE BRAZEDTubes which are to be brazed must be free of oil, grease,oxidation, paint or any other foreign substance which
could jeopardize the bonding of materials. Special caremust be taken when flux is used to facilitate brazing. The
use of powder fluxes in the smallest possible quantity isrecommended. They, like the paste fluxes, can becomesources of contamination in the refrigeration systemcausing, for example, capillary tube blockage. This risk isgreater in systems using R 134a since the flux, like otheralkaline agents, can react with ester oil and produce salts.
These salts can then create deposits that may block flow
through the capillary tube. Brazing flux is used for thefollowing purposes:

When referring to preheating in refrigeration, where tube
brazing is usual, it is easily noticed that the conventional
torch is not convenient for brazement quality andproductivity. In this case, the use of torch like the one
shown on figure 7 is recommended. Besides a better
productivity, the use of this type of torch presents thefollowing advantages:• faster heating or preheating• less torch movement during brazing• higher fluidity and therefore better filler metal
joint penetration- to clean the area to be joined- deoxidize the area to be joined- facilitate flow of filler metal
2.6 PREHEATING
To provide a more efficient brazing homogeneity, thecontact surfaces of the two parts to be connected should
be preheated. In particular, pay close attention to theareas around the insertion depth region. For flat surface,preheating is performed by circular movements of theflame on the entire surface to be brazed.

CODE 95040 - OCT/95 - REVISION No. 00

FIG. 7 - A MORE ADEQUATE TORCH FOR TUBE BRAZINGIMPORTANT: The brazing of compressors with copper
connectors requires additional care as well as a specificprocedure concerning preheating. More information isavailable in item 3.2.2.

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TECHNICAL INFORMATIONCONNECTORS BRAZING PROCESS

3 - TUBE BRAZING PROCESSES INREFRIGERATION SYSTEMS

3.1.2.5 When the filler rod begins to melt, apply the torchfrom point A to point B and vice versa until the filler metal
penetrates between the tubes. (Fig. 9)

3.1 COPPER PLATED STEEL CONNECTORS WITH
COPPER OR COPPER PLATED STEEL TUBES
3.1.1 FILLER METAL / BRAZE FLUX AND FLAME
ADJUSTMENTFor this type of brazing, high fluidity silver-base filler rods
are used with a silver content varying from 50% to 25%.
This type of connection requires the help of brazing flux.
However, it must always be remembered that the amountof flux should be minimized and preference must be given
to the powder type, as fluxes constitute a form ofcontamination in the refrigeration system.
This kind of brazing requires a carburizing or reducing
type of flame (with a small excess of acetylene).

FIG. 9IMPORTANT: Never put the flame into direct contact withthe filler metal rod. Let it liquefy through heat transmission
from the tubes.

3.1.2 BRAZING SEQUENCE
3.1.2.1 Make sure that the tube to be brazed is free ofgrease, oil, paint, oxides or any other foreign substancewhich could jeopardize the bonding of the materials.

3.1.2.6 Remove the flame and leave the filler rod for someseconds on the joint, then remove it.
3.1.2.7 The appearance of the connection must be inaccordance with figure 10.

3.1.2.2 Before heating the tubes apply the flux on thebrazing joint.
3.1.2.3 With the torch, heat both the male and female
tubes, from point A to point B and vice versa. Remember
to avoid putting the flame into direct contact with the part
coated with flux. (Fig. 8)
NOTE: Heat the steel tube at a slightly higher temperaturethan that used with the copper tubes.

FIG. 10 VISUAL CHARACTERISTICS OF A GOOD-LOOKING
BRAZEMENT.

3.1.2.8 Should porosity be suspected or identified in thebrazement, heat joint again, moving the torch from point A
to point B and vice versa (see fig. 9). If necessary, add theleast possible amount of filler metal.
3.2 COPPER CONNECTORS WITH COPPER TUBES
FIG. 83.1.2.4 Immediately after preheating the tubes and after
flux liquefying, apply the tip of the filler rod (preheated) tothe brazing joint.
NOTE: Do not force the filler rod. Simply touch it to the joint
to be brazed and let it melt until it flows completely
throughout the joint.

CODE 95040 - OCT/95 - REVISION No. 00

3.2.1 FILLER METAL / BRAZING FLUX AND FLAME
ADJUSTMENT
For this kind of brazing, use silver-base filler rods with asilver content of 15% to 5%. Copper-Phosphorus filler
metal rods, with high fluidity characteristics can also beused. It is not necessary to use fluxes for this kind ofbrazing. The flame type recommended for this weld is theneutral flame.

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TECHNICAL INFORMATIONCONNECTORS BRAZING PROCESS

3.2.2 SPECIAL CARE IN BRAZING COPPER
CONNECTORSe must be
When brazing copper connectors, special carcare
taken to avoid any damage to the weld joining thecopper connector to the compr
essor housing
compressor
housing. Damage
to this weld, as well as any other system joint, will cause
refrigerant leakage and eventual rework.
For this purpose, the flame has to be directed away fromthe compressor and must be more intense at the very endof the female tube (the final 6mm is recommended), as
shown in figure 11. The flame-type must be neutral and thefiller metal rod should be as described in item 3.2.1. Thus,
avoid direct flame over the brazing spot on thecompressor housing and carry out connector preheating
only on the area close to its tip.

NOTE: Do not force the filler rod. Simply touch it to the joint
to be brazed and let it melt until it flows completelythroughout the joint.
IMPORTANT: Do not direct the torch flame directly on tothe filler rod. Allow it melt through simple contact with thetube.
3.2.3.4 Remove the flame and leave the filler rod for someseconds on the joint, then remove it.
3.2.3.5 Should porosity be suspected or identified in thebrazement, heat joint again, moving the torch from point A
to point B and vice versa (see fig. 9). If necessary, add theleast possible amount of filler metal.
3.3 COPPER CONNECTORS TO STEEL TUBESFiller metal, brazing flux and flame adjustment follow thesame information as stated in item 3.1. However, special
care must be taken when brazing copper connectors (seeitem 3.2.2).

m6m

4 - USUAL FAILURES IN BRAZING
4.1 INSUFFICIENT JOINT PENETRATION

FIG. 11 - SPECIAL CARE IN BRAZING COPPER CONNECTORSIMPORTANT: Avoid stress in the tubes to be brazed. Under
these conditions there is a high probality of cracks
occuring in the copper tube as well as in the material to beadded.

This kind of failure is generally found when the torch isdirected only to the joint itself without heating the adjacentareas. Tubes inadequately heated impair brazing
capillarity and the filler metal liquefies only where theflame was applied (Fig. 13).

3.2.3 BRAZING SEQUENCE
3.2.3.1 Make sure that the tube to be brazed is free ofgrease, oil, oxides, paint or any other foreign substancewhich could jeopardize the bonding of the materials.
Preheating of the connector must follow recommendations
as set down in the above item 3.2.2.
3.2.3.2 Heat male and female tubes uniformly up to theideal brazing temperature moving the flame from point A topoint B and vice versa. (fig. 12)
3.2.3.3 Apply the filler rod tip to the area to be brazed.

FIG. 13 - INSUFFICIENT BRAZING JOINT PENETRATION

4.2 TUBING OBSTRUCTION
This failure occurs by the excessive use of filler metal andis generally accompanied by excessive joint clearance,
insufficient insertion overlap and/or inadequate heat
distribution (Fig. 14).

FIG. 14 - TUBE OBSTRUCTION
FIG. 12CODE 95040 - OCT/95 - REVISION No. 00

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TECHNICAL INFORMATIONCONNECTORS BRAZING PROCESS

4.3 CRACKING, BRITTLENESS AND POROSITY
These three failures are generally caused by excessive
heating of the tubes to be brazed.

These aspects result in a poor-looking brazement, as wellas base metal brittleness and porosity.
For correct flame adjustment and its application to eachkind of material to be brazed, see item 2.2.
IMPORTANT: Excessive application of filler metal does not
improve welding resistance at all. It only increases theconsumption of filler metal, oxygen and acetylene andfurther reduces brazer productivity.

FIG. 15 - POROSITY

4.4 USE OF INADEQUATE FLAME
This item is very important and has a big influence on thebrazing results.
Bad flame adjustment can result in an inadequate
preheating, melting of base metal, bad heat distribution,
low fluidity and bad adherence of the filler metal.

FIG. 16 - BRAZING WITH EXCESS OF FILLER METAL

Should you require further information, please contact our sales team at the following telephone /fax numbers:

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2232 Northmont Parkway
Duluth, Georgia - USA 30096
Phone: +1 770 814-8004+1 800 549-9498
Fax: +1 770 622-4620+1 800 462-1038

CODE 95040 - OCT/95 - REVISION No. 00

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Phone: +55 47 441-2430
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