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49 

Types of flame change based on the proportion of propane and oxygen. 
[Neutral Flame] 
Perform brazing with this flame 
(This is a flame when oxygen and propane are mixed at proper proportion, and has lesser effect on the brazed 
metals) 

 

 

 

[Carbide Flame] 
When propane is excessive, the flame has white color flame in between the white core flame and outer flame. 
(This is due to the lack of oxygen and the proportion of unburned propane is excessive. 
The black carbon created during the brazing work may contaminate the surface of the brazed metal). 

 

 

 

[Oxidizing Flame] 
Oxygen is more compared to the neutral flame. Although the flame size is small, this has the highest flame heat. 
However, due to the excessive oxygen contained in the flame, the brazing point gets oxidized. (This flame may cause 
holes, due to the high heat. The pipe may get melt） 

 

 

[In case of short break] 
1.  Close the “propane valve” of the torch. 
2.  Close the “oxygen valve” of the torch. 
[In case of finishing work] 
1.  As above, close the flame following the procedure of “In case of short break”. 
2.  Completely close the valves of oxygen and propane cylinders. 
3.  Release the remaining gas inside the hose by opening the “oxygen valve” and “propane valve” of the torch. 
Confirm the 1

st

 and 2

nd

 side gauge pressures of “oxygen” and “propane” cylinder pressure adopter are “zero”. 

 
 
 
 
 
 
 
 
 
 
 
 

White core flame

10 ~ 15 mm

Outer flame (Light orange color)

White core flame

Pale white

Outer flame (Blue color)

White core flame

Outer flame (Blue orange color)

50 

Use BAg brazing material (silver solder) to increase the welding performance. 
 

Category 

JIS 

Standard 

Number 

Composition of ingredients (%) 

Temperature (°C) 

Tensile strength 

(Reference) 

Characteristics 

and 

applications 

Ag 

Cu Zu Cd  Ni  P 

Solidus Liquidus

Brazing

temp 

Kgf•cm

2

 

Base 

material 

BAg 

BAg •

 

1A 

49.0 

~ 

51.0 

14.5 

~ 

16.5 

14.5 

~ 

18.5 

17.0 

~ 

19.0 

—

 

—

 

approx.

625 

approx.

635 

635 

~ 

760 

45.5 

 

S20C 

Liquidity is good at

low temperature, 
it is preferable to 

a small junction of 

the gap in the 

universal form. 

BAg •

 

1 

44.0 

~ 

56.0 

14.0 

~ 

16.0 

14.0 

~ 

18.0 

23.0 

~ 

25.0 

—

 

—

 

approx.

605 

approx.

620 

620 

~ 

760 

45.5 S20C 

It has similar 

performance to the

BAg •

 

1A, and 

suitable for every 

base material 

except the light 

weight metal. 

BAg •

 

2 

34.0 

~ 

36.0 

25.0 

~ 

27.0 

19.0 

~ 

23.0 

17.0 

~ 

19.0 

—

 

—

 

approx.

605 

approx.

700 

700 

~ 

845 

45.5 S20C 

It is a brazing 

filler metal in 

universal form, 

suitable for a 

slightly larger gap 

junction. 

BAg •

 

3 

48.0 

~ 

51.0 

14.5 

~ 

16.5 

13.5 

~ 

17.5 

15.0 

~ 

17.0 

2.5 

~ 

3.5 

—

 

approx.

630 

approx.

690 

690 

~ 

815 

35 

~ 

70 

SS 

~ 

SUS 

It has good 

corrosion 

resistance in 

stainless 

steel-based 

brazing, suitable for

brazing tungsten 

carbide, aluminum

bronze and copper.

BCuP 

BCuP-2 

—

 

remain

—

 

—

 

—

 

6.8 

~ 

7.5 

approx.

710 

approx.

785 

690 

~ 

815 

21 

~ 

24.5 

Cu 

Good liquidity, 

suitable for brazing

copper tube. 

BCuP-3 

4.8 

~ 

5.2 

remain

—

 

—

 

—

 

5.8 

~ 

6.7 

approx.

645 

approx.

815 

720 

~ 

815 

21 

~ 

24.5 

Cu 

Suitable for brazing

when the joint 
spacing is not 

constant 

BCuP-5 

14.5 

~ 

15.5 

remain

—

 

—

 

—

 

4.8 

~ 

5.3 

approx.

645 

approx.

800 

705 

~ 

815 

21 

~ 

24.5 

Cu 

When brazing of 

copper and copper, 

it is used without a

flux, but not 

possible for brazing

basic materials 

 
Caution 
BCuP (phosphorus copper wax) is easy to react with sulfur, and makes a brittle compound water soluble, and causes 
gas leakage. In hot spring areas, use other brazing materials or paint the surface for protection. 

Use flux to protect the base materials. 
1.  Remove impurity and oxide film on the metal base, and improve the flow of the brazing material. 
2.  Prevent oxidation of the metal surface in brazing. 
3.  Reduce the surface tension of the brazing material. 

In order to prevent oxidation in the pipe, perform the brazing operation in nitrogen gas flow. 
Flow rate 0.05 m

3

 / h, or pressure reducing valve at 0.02 MPa (0.2kgf / cm

2

) below. 

 
 
 
 
 
 
 
 
 

51 

1.  No impurity on the brazing point 

If dirt or oil is attached on the brazing point, the 
brazing filler metal does not reach to junction, and 
it may cause poor welding. 

 
 
 
 
2.  Adequate gap space in the brazing point 

The advantage of capillary current situation is 
used in brazing. If the gap space is too large, this 
phenomenon may not occur and it may cause 
poor welding because brazing filler metal does not 
flow to join the front part. 

 
 
 
 
3.  Appropriate size for insertion 

The guideline for pipe insertion dimensions is to 
three times the diameter of the base material, but 
you need to decide the insertion size in 
consideration of the clogging of the brazing 
material. Generally, for thin pipes, you need to 
increase the insert size, and for thick pipe vice 
versa. 
 
 
 
 

4.  Brazing material to flow from top to bottom 

Brazing filler metal will easily flow to the 
connecting portion by capillary action. 
Further, by bending the brazing portion of [dryer 
side] of the capillary tube at 15 mm from the tube 
top to the angle of about 120°, you can prevent 
the damage of dryer inside and the clogging of 
brazing material caused by the excessive insertion 
of capillary tube. 
 

 

 

 

 

 

 

1.  Place the flame to a pipe which has more heat 

capacity in order to let the brazing material melt by 
the pipe heat. Heat the pipe up to the melting 
temperature of the brazing material, but when it is 
overheating, assess the temperature by pipe color 
in order not to melt the pipe. 

 

 
 
 

 

 
The pre-heating is to heat the base material until the melting temperature, and requires certain training to distinguish 
the color of the heated base material in order not to melt the material. 
The color and temperature of copper tube 

  Becoming red color • • • • • • • 480°C 

  Dull red • • • • • • • 650°C 

  Cherish red • • • • • • • 760°C 

  Brightening cherish red • • • • • • • 870°C 

 

Gap 0.025 ~ 0.05 mm

Insert diameter 10 ~ 25 mm

Inner diameter ø6.45

Outer diameter ø6.35

Brazing material

(Runny)

Brazing material

(Hard to flow)

Dryer

15 mm

120°

Filter

(Wire mesh)

Capillary

tube

Burner

Burner

Brazing

material

Brazing

material

52 

(Reference) 
Melting temperature of copper • • • • • • • Approx. 1083°C 
Maximum temperature obtained in propane and oxygen • • • • • • • Approx. 1083°C 
The important point is to heat the bonding part uniformly within a short period of time until reaching to the brazing 
temperature in the following manner. 
2.  Apply the flame on to the side with better heat transmission. If the pipe thickness is consistent, by heating like 

30% iron and 70% copper, the copper pipe inside reaches to brazing temperature. 
Iron pipes have low heat transmission and only the part the flame is applied get high temperature, and this 
causes oxidization of the pipe. The flow of the brazing filler is affected negatively. 

 
3.  Apply the flame on to the side of larger heat 

capacity. 
When brazing a thin tubes such as capillary tube 
and dryer, etc., caution has to be taken to apply 
the flame to the dryer side (thick pipe side), in 
order to prevent burn out by the heat. 
 

4.  When brazing the compressor connection pipes 

(suction and discharge), remove the sound 
insulation plate and the fan, and place the 
compressor stand vertically (to prevent the 
leakage of compressor refrigerating machine oil), 
and apply the flame from the compressor body 
side. 

 

 

Pin holes → Small holes are generated on the surface of the brazing metal. 
Wet temperature → Liquidus temperature at which the brazing material starts flowing out by heating, generally it is  
                                the liquidus-line temperature. 
Blow holes → Hollows made by gas in the brazing material of brazing portion (gas reservoirs). 
Pits → As a result of blow holes, small dents generated on the outside surface of welding. 
Voids → The blazing material does not reach completely to the brazing part. It cannot be identified from outside.