Field of the invention

The present invention relates to bimetallic tubes and more particularly to a method of producing a bimetallic tube.

Background of the invention

Non-ferrous metal tubes are used in tandem due to their properties such as low weight, higher conductivity, non-magnetic property or resistance to corrosion and the like. However/these non-ferrous metals are highly expensive. Hence, use of bimetallic tubes is generally preferred in engineering applications where large economical savings in non-ferrous metals are required.

The bimetallic tubes are generally made such that coating of ferrous metals is externally applied on the non-ferrous metals in order to save expensive non-ferrous metals. In comparison with the tubes that are made of a single alloy, the use of precious non- ferrous materials is reduced in the bimetallic tubes.

However, the bimetallic tubes known in the art normally have coating/ plating of ferrous metals applied externally on the surface of the non-ferrous metals. However, such external coating or plating fails to offer longer life to the end product thereby making these bimetallic tubes functionally and economically inferior.

Accordingly, there exists a need of a bimetallic tube that overcomes all the drawbacks of the prior art.

Objects of the invention An object of the present invention is to provide a bimetallic tube integrally made out of ferrous and non-ferrous metals to provide substantially high strength as well as end life.

Yet another object of the present invention is to provide a bimetallic tube that is having a firm bonding between the ferrous and non-ferrous metals.

Summary of the invention

Accordingly, the present invention provides a method of production of a bimetallic tube that is integrally made of a ferrous metal hollow and a non-ferrous metal hollow. The method of production of the bimetallic tube comprises sequential steps namely cleaning of an outer soaped surface of the ferrous metal hollow using a thinner, forming a partial cone of the ferrous metal hollow by a drawing process, positioning of the non-ferrous metal hollow over the ferrous metal hollow, carrying out a combined drawing process for obtaining an integrally formed bimetallic tube and expanding inner diameter of ferrous metal tube for the obtained bimetallic tube.

Detailed description of the invention

The foregoing objects of the present invention are accomplished and the problems and shortcomings associated with the prior art, techniques and approaches are overcome by the present invention as described below in the preferred embodiment.

The present invention describes a method of production a bimetallic tube (herein after referred to as "Bi-Metal Tube" and abbreviated as "Bi-MT") that is integrally made of ferrous and non-ferrous metals. In this one embodiment, the non-ferrous metal selected is selected from brass, copper and the like. In this one embodiment, the ferrous metal is selected from steel, stainless steel and the like. In accordance with a preferred embodiment of the present invention, the Bi-MT is produced by drawing or rolling on mandrel preferably with or without a bonding material such that a softer non-ferrous surface of the Bi-MT meets the purpose of a wearing surface and stronger steel meets the purpose of the backing material. The Bi-MT tube produced per the proposed method of production is mainly used in architectural and engineering context, preferably for use in railings, barriers, trusses, frames, bushes, and the like. The Bi-MT tube produced per the proposed method of production is having good aesthetics and strength.

In accordance with a preferred method of production, the Bi-MT is integrally made of a ferrous tube and a non-ferrous tube such that after production the outer surface of the Bi-MT tube is made of non-ferrous material and the inner surface is made of the ferrous material. The preferred method of production of the Bi-MT is a drawing process followed by a rolling process that is carried out to provide finished output size, with combination of both the non-ferrous and ferrous hollows.

In an embodiment, the Bi-MT is integrally made of a steel tube and a brass tube such that after production the outer surface of the Bi-MT tube is made of brass and the inner surface is made of steel. Accordingly, the method of production of the Bi-MT includes a first step of cleaning of an outer soaped surface of a steel hollow member by a thinner. In a next step, a partial cone of the steel hollow is formed by a drawing process followed by positioning the brass hollow over the steel hollow. The drawing of the steel (ferrous metal) tube is done to suit brass (non -ferrous metal) tube inner diameter. In a further step, a combined drawing process of both the hollows is carried out to obtain the Bi-MT tube. In the combined drawing process, the inner steel hollow is having interference fit with brass tube. It is understood here that the combined drawing process- is carried out Hengli-30 machine preferably by a cold pilgering process. In a final step, inner diameter (ID) of the Bi-MT is expanded by passing mandrel and keeping brass outer diameter same to obtain the Bi-MT tube of the present invention. ID expanding and mechanical bonding between the brass tube processes is carried out on a draw bench machine by a cold drawing process. In this one embodiment, the combined thickness of the Bi-MT ranges between 2.25 mm to 2.38 mm, wherein the overall thickness of the bimetal tube is distributed in 20% of brass and 80%> of steel. It is understood here that, a die used in the drawing process for forming the Bi-MT is preferably of ring type having a parabolic curved design. Also, a mandrel used in the drawing processes of parabolic curved design. In this one embodiment, the total reduction on brass tube and steel tube for forming the bimetal tube is about 75.6 % and 67.24% respectively.

EXAMPLES

EXAMPLE- 1 :

A brass hollow having dimensions 50.0mm x 1.2mm was taken. Brass tube reduced to 46.7x1.49x43.75. A steel tube was of having dimensions 44.45 mm x 4 mm with 1020 grade was taken and reduced to 43.4x3.4x36.2. The steel hollow was soaped and cleaned by thinner only on an outer surface thereof. The brass hollow and the steel hollow were rolled on Hengli-30 machine by a cold pilgering process wherein a partial cone of steel hollow was formed in pilgering process and then the brass hollow was inserted over the steel tube. A combine pilgering of both hollows were done with strokes of 45 - 50 strokes and feed rate 2.00mm. A firm mechanical bonding between the brass and the steel hollows was established by cold pilgering process brass and steel tube together and expanding the outer diameter of the steel tube to achieve more interference fit and mechanical bonding. The finished output size of the Bi-MT, rolled with combination of both hollows, was 29.00 mm x 2.25mm wherein the finished tube outer brass tube was having dimension 29 mm x 0.45mm and the inner steel tube was having dimension 28.3 mm x 1.80mm. An overall dimension band was ranging from 28.85 mm to 29.00mm. A combined thickness observed was ranging between 2.25 mm to 2.38mm. Overall thickness of the Bi-MT was distributed in 20% of brass and 80% of steel. The Bi-MT so obtained was passed for internal diameter expansion. A die used in the drawing process was of ring type with curve design with an incoming size 50.8 mm and an outgoing size was 29.4 mm. A mandrel used was of curved design having dimension 33.00 mm x 23.75mm.lt was observed that, the total reduction on brass tube was 75.6 % and the total reduction on steel tube was 67.24%.

EXAMPLE-2

A brass hollow having dimensions 50.8mm x 1.2mm was taken. A steel tube was of having dimensions 44.45 mm x 4 mm with 1020 grade was taken. The steel hollow was soaped and cleaned by thinner only on an outer surface thereof. The brass hollow and the steel hollow were rolled on Hengli-30 machine by a cold pilgering process wherein a partial cone of steel hollow was formed in pilgering process and then the brass hollow was inserted over the steel tube. A combine pilgering of both hollows were done with strokes of 45 - 50 strokes and feed rate 2.00mm. The finished output size of the Bi-MT, rolled with combination of both hollows, was 32.00 mm x 2.25mm. Overall thickness of the Bi-MT was distributed in 20% of brass and 80% of steel. A die used in the drawing process was of ring type with curve design with an incoming size 50.8 mm and an outgoing size was 29.4 mm. A mandrel used was of curved design having dimension 33.00 mm x 24.5mm.

EXAMPLE- 3 : Chemical Analysis of the Bi-MT tube

The Bi-MT tube produced per the preferred method of the present invention was tested to analyze and ascertain that the chemical components are within prescribed limit. Accordingly, the Bi-MT tube, having an outer diameter of 83.00 mm, an inner diameter of 75.00 mm and a length of 4.15 meters, was taken for the chemical analysis.

Table 1: Chemical analysis data components

Specification

(Max.) 0.22 1.6 0.55 0.025 0.025 — —

Specification

(Observed) 0.165 1.270 0.090 0.0040 0.0130 — ^■ 0.0450

It was observed that, the Bi-MT tube produced per the method of the present invention was having observed specification well below the maximum specification limits. Accordingly, the chemical component stability of the Bi-MT tube was ascertained EXAMPLE- 4: Dimensional Analysis of the Bi-MT tube

The Bi-MT tube produced per the preferred method of the present invention was analyzed to ascertain that the dimensional components of the Bi-MT tube were within prescribed limit. Accordingly, the Bi-MT tube, having an outer diameter of 83.00 mm, an inner diameter of 75.00 mm and a length of 4.15 meters, was taken for dimensional observations.

Table 2: Dimensional analysis data

It was observed that, the Bi-MT tube produced per the method of the present invention was having observed specification well within the minimum-maximum specification limits. Accordingly, the dimensional stability of the Bi-MT tube was ascertained EXAMPLE- 5 : NDT / ECT testing of the Bi-MT tube

The Bi-MT tube produced per the preferred method of the present invention was tested for no destructive testing (NDT)/ eddy current testing (ECT). Accordingly, the Bi-MT tube, having an outer diameter of 83.00 mm, an inner diameter of 75.00 mm and a length of 4.15 meters, was taken for the testing. Accordingly, various tests such as Hardness, Flaring Test, Flattening Test, Crushing Test, Yield Strength, Tensile strength and % Elongation were carried out.

Table 2: Mechanical properties data

It was observed that, the tube undergone 100% NDT (ECT) testing and conforms to the standard.

The foregoing descriptions of specific embodiments of the present invention have been presented for purposes of illustration and description. They are not intended to be exhaustive or to limit the present invention to the precise forms disclosed, and obviously many modifications and variations are possible in light of the above teaching. The embodiments were chosen and described in order to best explain the principles of the present invention and its practical application, to thereby enable others skilled in the art to best utilize the present invention and various embodiments with various modifications as are suited to the particular use contemplated. It is understood that various omission and substitutions of equivalents are contemplated as circumstance may suggest or render expedient, but such are intended to cover the application or implementation without departing from the spirit or scope of the present invention.