Double-Roll Welded Tubing



Applicable to braking tubing, fuel tubing, air supply tubing, motor fuel tubing and machine oil tubing systems for automobile manufacturers, we can provide Zinc coating, Zinc-Aluminum alloy coating, and Aluminum-Zinc alloy coating service according to clientĄ¯s requirement. In addition, white and olive green passivation, PVF and PVDF coating services are available.

First, the deep impact extrusion steel BHG2 which is made in Shanghai Bao Steel Co., Ltd is cold rolled to precision steel strip, and then the precision steel strip is converted to a copper coated steel strip on a continuous copper coating line. This copper coated steel strip is the base material of double roll welded tube.

Technical Standard for Double Roll Welded Tubing used Steel strip

Copper Coating & Cutting Technical Standard for Double Roll Welded Tubing used Steel Strip

Chemical Composition

Tension Test (Standard Length 50 mm)

C

Si

Mn

P

S

Yield Strength

TensileStrength

Elongation Rate

MPa

%

0.03-0.035

≤0.02

0.1-0.2

<0.02

≤0.01

≥160

≥300

≥40


Diagram of Double Roll Welded Tube Fabrication Process:




Double Roll Welded Tube Sketch


The fabrication process of double roll welded tube is as follows: first, the copper coated steel strip is rolled to double layer by a forming roller (the overlapped strip between inner and outer strip is among 1.0-1.5mm), and then sent to a continuous heating furnace which is filled by a protection gas to be brazed, so the double layers of copper coated tube are strongly welded to a single layer seamless tube. The brazing temperature of 1180o C in continuous heating furnace is higher than copper melting point, but is lower than melting point of BHG2 steel strip. Thus, this process can make copper fully melt without tube deformation and failure.

The fabrication process of double roll welded tube is as follows: first, the copper coated steel strip is rolled to double layer by a forming roller (the overlapped strip between inner and outer strip is between 1.0-1.5mm), and then sent to a continuous heating furnace, filled by a protection gas, to be brazed, so that the double layers of copper coated tubes are strongly welded to become a single layer seamless tube. The brazing temperature of 1180o C in the continuous heating furnace is higher than the copper melting point, but lower than the melting point of the BHG2 steel strip. Thus, this process makes the copper fully melt without tube deformation or failure.


Technical Standard of Plain Double Roll Welded Tubing

Double Roll welded tube is made of low carbon steel, and then rolled and brazed; its heat transfer coefficient is about 70. Normally the heat transfer coefficient of low carbon steel is about 30, and the heat transfer coefficient of copper is 60. As a result, double roll welded tube is an ideal tube for radiators, electrical heaters and condensers.

Double roll welded tube has better vibration resistance, yield strength, and pressure resistance than a pure copper tube, so it is ideal for automobiles, refrigeration compressor, hydraulic components and hydraulic tube connections.

Tubing Category

Specification

Main property & Data

outside diameter (mm)

wall thickness (mm)

Minimum Blowup Pressure (MPa)

surface smoothness (mg/m2)

allowable pressure (MPa)

Elongation Rate (%)

σb

(MPa)

σs

(MPa)

Double roll welded tubing

4.76

0.70

110

≤166

35

≥25

≥290

≥190

6.0

85

6.35

78

8.0

67.5

25

10.0

55