Heat exchanger tube precursor and method of producing the same
A heat exchanger tube precursor that allows manufacturing a heat exchanger having high corrosion resistance after brazing treatment is provided. The heat exchanger tube precursor includes: an Al alloy tube; and a flux layer including a Si powder, a Zn-containing flux, a Zn-free flux, and a binder, the flux layer being formed on an outer surface of the Al alloy tube.
1. A heat exchanger tube precursor comprising: an Al alloy tube; and a flux layer including a Si powder, a Zn-containing flux, a Zn-free flux, and a binder, the flux layer being formed on an outer surface of the Al alloy tube,
wherein the Si powder has a particle diameter distribution such that 99% particle diameter (D 99 ) is 5 μm or more and 20 μm or less, and an amount of coarse particles having diameters of not smaller than 5 times (D 99 ) is less than 1 ppm by volume, wherein (D 99 ) denotes a critical diameter defined such that cumulative volume of particles not larger than (D 99 ) constitute 99% by volume of all the particles,
an amount of the Si powder applied on the Al alloy tube is in a range of 1 g/m 2 to 5 g/m 2 ,
an amount of the Zn-containing flux applied on the Al alloy tube is in a range of 3 g/m 2 to 20 g/m 2 , and
50% particle diameter (D 50 ) of the Si powder is (D 99 )×0.05 or more and (D 99 )×0.7 or less, (D 50 ) denoting a critical diameter defined such that cumulative volume of particles not longer than (D 50 ) constitute 50% by volume of all the particles.
2. The heat exchanger tube precursor according to claim 1 , wherein the Zn-containing flux contains at least one selected from ZnF 2 , ZnCl 2 , and KZnF 3 .
3. The heat exchanger tube precursor according to claim 1 , wherein the Zn-free flux contains at least one selected from LiF, KF, CaF 2 , AlF 3 , SiF 4 , KAlF 4 , and KAlF 3 .
4. The heat exchanger tube precursor according to claim 1 , wherein the Al alloy tube is constituted of an alloy containing Si of 0.05% or more and 1.0% or less by weight, Mn of 0.05% or more and 1.2% or less by weight, and the balance being consisting of Al and inevitable impurities.
5. A method of producing a heat exchanger tube precursor, the method comprising the steps of:
classifying a pre-classification Si powder to obtain a post-classification Si powder in which 99% particle diameter (D 99 ) is 5 μm or more and 20 μm or less, an amount of coarse particles having diameters of not smaller than 5 times (D 99 ) is less than 1 ppm by volume, and 50% particle diameter (D 50 ) of the Si powder is (D 99 )×0.05 or more and (D 99 )×0.7 or less;
preparing a coating material including the post-classification Si powder, a Zn-containing flux, a Zn-free flux, and a binder; and
applying the coating material on an Al alloy tube, wherein an amount of the Si powder applied on the Al alloy tube is in a range of 1 g/m 2 to 5 g/m 2 , an amount of the Zn-containing flux applied on the Al alloy tube is in a range of 3 g/m 2 to 20 g/m 2 , (D 99 ) denotes a critical diameter defined such that cumulative volume of particles not larger than (D 99 ) constitute 99% by volume of all the particles, and (D 50 ) denotes a critical diameter defined such that cumulative volume of particles not larger than (D 50 ) constitute 50% by volume of all the particles.
6. The method of producing a heat exchanger tube precursor according to claim 5 , wherein the Zn-containing flux contains at least one selected from ZnF 2 , ZnCl 2 , and KZnF 3 .
7. The method of producing a heat exchanger tube precursor according to claim 5 , wherein the Zn-free flux contains at least one selected from LiF, KF, CaF 2 , AlF 3 , SiF 4 , KAlF 4 , and KAlF 3 .