Braze gap size and dimensions for weld fittings
Braze gap size
The braze gap is limited by three dimensions (see Figure 3). The most important dimension is the gap width "b". For gap widths in the range from 0.05 mm to 0.2 mm the term "gap" is retained, whereas gap widths above 0.2 mm up to max. 0.5mm are generally designated "groove". Gaps (0.05 to 0.2 mm) are particularly well suited for mechanized or automated brazing. Grooves (0.2 to 0.5 mm) are generally brazed manually.
Dimensions of the braze gap for brazed joint
In cases of brazing joints tubes, the larger pipe tolerances and the peculiarities occurring in pipework construction will not always allow to achieve a braze gap width of b U ð 0.5 mm . This is particularly so with pipes/tubes above 70 mm outside diameter and brazing joint types A3, A5, A6, A7, B3 and B6 (see Table 5, page 10). Generally, the optimum strength of the brazed joint is not achieved in such cases.
The gap length "l" depends on the shape of the parts to be joined and can rarely be influenced by design measures. The gap depth "t" depends on the gap length and the force which has to be transmitted by the brazed joint and can be determined with the help of the mammogram, Figure 4, page 5, or calculated (see page 5). The mammograms apply only to brazed joints on parts which transmit tensile and compression forces, but not torques
Example for determining the gap width with the aid of the mammogram, Figure 4, page 5:
Example a) Given: Metal plate thickness s 1 = 5.3 mm;
Tensile strength Rm = 500 N/mm 2
Required: Gap depth t
Solution: Draw a vertical line from the abscess "plate thickness s 1 " (plate thickness s 1 = 5.3 mm) to the intersection point with the straight line for the tensile strength (Rm=500N/mm 2 ). Connect intersection point and ordinate with a horizontal line and read off the gap depth t = 27 mm.
Example b) Given: Pin diameter d 1 = 14 mm;
Tensile strength Rm = 600 N/mm 2
Required: Gap depth t
Solution: Draw a vertical line from the abscisse "pin diameter d 1 " from point d 1 = 14 mm to the intersection point with the straight line for the tensile strength Rm=600N/mm 2 . Connect intersection point and ordinate with a horizontal line and read off the gap depth t= 21 mm. Example c) Given: Tube dimensions 28 x 2.5;
Tensile strength Rm = 400 N/mm 2
Required: Gap depth t
Solution: Draw a horizontal line from the ordinate "tube outside diameter d 2 " from point d 2 = 28 mm to the curve for the wall thickness s 2 = 2.5 mm. From here draw a vertical line to the intersection point with the straight line for the tensile strength Rm=400N/mm 2 . Connect intersection point and ordinate with a horizontal line and read off the gap depth t = 11.9, rounded up to 12 mm.
