Process of making seamless metal tube

A process for the continuous manufacture of seamless tube by confining a selected length of metal strip in the form of a tube and with at least two longitudinal abutting edges and completely melting a selected length of such tubular form to form a seamless tube and cooling the formed seamless tube. The cooling is preferably in a controlled atmosphere of nitrogen and the temperature is reduced to about 700.degree. F. before further processing takes place. In a preferred process the material is a single strip of metal formed into a tube with only one longitudinal seam and it is moved continuously through a mould heated by induction heating selectively controlled to cause the tube to preheat to a selected temperature and then be subjected to a temperature bringing the metal to its molten state to form a seamless tube and while the seamless tube is moving it is cooled downstream from the melting zone solidifying the metal and bringing it to a selected temperature before exiting the mould.

FIELD OF INVENTION 
This invention relates to a process of making seamless tube from flat strip 
stock and preferably to the process of making seamless steel tubing. 
BACKGROUND OF INVENTION 
Seamless metal tubing also known as seamless mechanical tubing has outside 
diameters ranging from 1/8 inch to 103/4 inches and wall thicknesses 
ranging from 20 gauge to 2 inches. The tubing may be oval, square, 
rectangular or other special shape in cross-section obtainable in various 
sizes and wall thicknesses. Mechanical tubing is available either hot 
finished or cold drawn but furnished (principally) cold drawn and is 
adaptable to varied treatment by expansion, cupping, tapering, swaging, 
flanging, coiling, welding and similar manipulations. Seamless metal 
tubing has a number of uses as aircraft tubing and automobile components. 
Small diameter seamless steel tubing is used by way of example on 
automotive brake lines. 
Seamless carbon-steel tubing is expensive to produce and is made in finite 
lengths principally by heating a round metal ingot, punching a hole in the 
ingot and working the so punched ingot into a tube of selected length, 
diameter and wall thickness. 
A method of making continuous seamless tubing is disclosed in DE 3034792 
dated Sept. 16, 1980. The continuous manufacturing is in a single 
production line that includes melting, casting, machining, drawing and 
shearing stations. In this process a bath of molten metal is required from 
which it can be drawn in the form of a continuous seamless tubing. 
Considerable heat is required to maintain a molten bath and from which 
there is substantial heat losses. 
Another means of forming a tube is by seam welding as disclosed in U.S. 
Pat. No. 3,248,512 issued Apr. 26, 1966 to R. A. Sommer. This patent 
discloses the use of induction heating with selective concentration of the 
heating to melt the material of abutting edges downwardly from the point 
of convergence and wherein there is pressural contact of such abutting 
edges. The end product is a welded seam tube. 
SUMMARY OF INVENTION 
An object of the present invention is to provide a process for the 
continuous manufacture of seamless tube by confining a selected length of 
metal strip in the form of a tube and with at least two longitudinal 
abutting edges and completely melting a selected length of such tubular 
form to form a seamless tube and cooling the formed seamless tube. The 
cooling is preferably in a controlled atmosphere of nitrogen and the 
temperature is reduced to about 700.degree. F. before further processing 
takes place. 
In accordance with the present invention there is provided a process for 
forming seamless metal tubing comprising confining a selected length of 
strip material having tubular form, with at least one longitudinal seam, 
between an open ended outer sleeve and an inner mandrel which together 
define a forming mould; heating a portion of said selected length to a 
selected temperature; further heating part of said portion to the melting 
temperature of the material to form a tube of molten material; causing 
relative axial movement of said forming mould and said tub to allow the 
molten material to solidify into a seamless tube while a continuing 
adjacent length of the tube is brought to its molten state and continuing 
the process until a seamless continuous length of tube of selected length 
is formed. 
In a preferred process the material is a single strip of metal formed into 
a tube with only one longitudinal seam and is moved continuously through a 
mould heated by induction heating selectively controlled to cause the tube 
to preheat to a selected temperature and then be subjected to a 
temperature bringing the metal to its molten state to form a seamless tube 
and while the seamless tube is moving it is cooled downstream from the 
melting zone solidifying the metal and bringing it to a selected 
temperature before exiting from the mould.

DESCRIPTION OF PREFERRED EMBODIMENT 
FIGS. 1 and 2 diagrammatically illustrate the process of the present 
invention of forming a strip of metallic material, for example, 1010 steel 
into a tube and passing such formed tube to a selectively controlled 
heating zone and forming mould to bring the seamed tube to a molten state 
and while in the mould as it moves continuously solidifying to form and 
exit as a seamless tube. 
FIG. 1 diagrammatically illustrates a coil 10 of strip metal which, for 
example, could be a 1,000 pound coil of cold roll No. 1010 steel having a 
width W of 1.6 inches and a thickness T of 0.028 inches. The strip is 
propelled by a roll former 20 producing a tube 25 having a longitudinal 
seam 26. 
FIG. 2 is a continuation of FIG. 1 downstream therefrom illustrating a 
ceramic rod 40 that extends from the former 20 and mounted in any 
convenient manner (not shown) so as to be located interiorly of the tube. 
The roll former 20 pushes the formed tube 25 through a ceramic sleeve 30 
disposed concentrically with and about the ceramic rod 40. The terminal 
end of the ceramic rod 40 is shown in broken line and identified by the 
reference 41. The thickness of the formed tubing corresponds to the space 
between the outer surface of the ceramic rod 40 and the inner surface 30A 
of the ceramic sleeve 30. 
While the formed tube is being propelled through the forming mould, which 
consists of the rod 40 and the sleeve 30, the portion of the formed tube 
within the sleeve is heated by electric induction. Heating is controlled 
along a selected length of the tube within the forming mould so that as 
the tube progresses there is initially preheating taking the formed tube 
with the metal seam to a peak temperature of about 1600.degree. F. 
Following this preheat station the heat by the induction coil is 
concentrated to increase the temperature so as to melt the tube. This 
concentration of heat can be by the addition of windings or other means 
known in the art and by way of example reference may be had to the 
teachings of the aforementioned U.S. Pat. No. 3,248,512 or the teachings 
of U.S. Pat. Nos. 2,788,426 issued Apr. 9, 1957 to G. K. Thompson; 
2,792,482 issued May 14, 1957 to J. A. Logan et al; 4,129,846 issued Dec. 
12, 1978 to Boris A. Yablochnikov and 4,560,849 issued Dec. 24, 1985 to 
Albert Migliori et al. The induction heating coil in FIG. 2 is identified 
by the reference numeral 31 having an initial preheat portion 31A followed 
by a concentrated heat portion 31B. Downstream from this is a cooling coil 
32 so that after the entire tube has been melted it is then cooled to a 
selected temperature before exiting from the forming mould as a formed 
seamless tube 60. 
The heating and cooling of the tube in the forming mould is preferably in a 
controlled atmosphere, for example, as provided by an enclosure designated 
50 shown in broken line and in which there is a controlled atmosphere of 
nitrogen. 
The drawing of the strip from the roll and forming it into a tube by the 
former 20 is pushed by such roll former 20 in a continuous manner through 
the preheat, melt and cooling stations. In the preheat station the 
temperature is taken to the peak metal temperature of about 1600.degree. 
F. Heat is concentrated by the induction coil by way of the section 31B 
thereof melting the tube and this melted tube is encapsulated on its 
outside diameter in the ceramic tube and on its inside diameter over the 
ceramic rod 40. The melting of the metal strip along the section 31B of 
the induction heating coil forms a seamless tube that is cooled down to 
about 700.degree. F. before being further processed into smaller diameter 
tubing. 
The preheat, melt and cooling takes place in a nitrogen controlled 
atmosphere and this prevents scaling of the formed tubing. The tube after 
being formed can be further worked for example by cold working to bring it 
to its desired diameter and thickness. 
While in the foregoing there is disclosed a single strip of material from 
which the tube is formed several strips could be used that are parallel to 
one another and formed into a tube providing more than one longitudinal 
seam. The strips of metal are melted along a selected portion of the 
length within the forming mould. The melt forms into a seamless tube and 
as the tube progresses in its selected path of travel there is continuous 
melting that progressively moves along the length of the tube while 
downstream from the melt there is cooling that solidifies the melt forming 
a rigid seamless tube. 
The foregoing discloses a continuous process where the tube moves relative 
to the induction heater and mould. The same principle could be used on a 
selected length of previously formed tubing (with one or more seams) that 
is held stationary while the forming mould is moved relative thereto. It 
will also be obvious the process lends itself to using many parallel 
strands of wire or parallel pieces of strip material. This process also 
permits using parallel pieces of selectively differing thicknesses 
accommodated by a mould such that the wall thickness of the seamless tube 
could be varied if so and as may be desired.