Eccentric pipe sections

Details Eccentric pipe sections Eccentric pipe sections

2001-08-09

2003-06-24

Tolan, Ed (Department: 3725)

Metal deforming

By extruding through orifice

Utilizing internal forming means

C072S260000, C072S265000

Reexamination Certificate

active

06581431

ABSTRACT:

BACKGROUND OF THE INVENTION
The present invention relates to an extrusion press device for manufacturing eccentric pipe sections—in particular pipe sections with circular outer and inner contours—from extrusion blocks, in particular extrusion billets. The extrusion device features a container with a chamber with longitudinal axis M
R
which accommodates the extrusion block, an extrusion stem which is introduced into the container chamber, and features a dummy block, a mandrel body forming the inner wall of the pipe-section, and a die with an opening with longitudinal axis M
M
forming the outer wall of the pipe section. The invention further relates a process for manufacturing seamless, eccentric pipe sections, and the use thereof.
Pipe sections produced by means of extrusion processes are characterised by way of an outer and inner wall or an outer and inner contour of round cross-section. The outer and inner contours usually exhibit the same shape as viewed in cross-section.
The production of concentric pipe sections with a wall thickness which is essentially uniform, by means of extrusion, is known. Also known are extrusion processes which permit seamless concentric pipe sections to be produced. The expression “concentric” indicates that the geometric middle points of the outer and inner contours as viewed in cross-section coincide with each other, with the result that when the outer and inner contours are of the same shape, the wall thickness over the whole cross-section is constant.
The production of seamless, concentric pipe sections is based on the principle of so-called extrusion over a mandrel. A mandrel body with mandrel arm and mandrel tip is advanced from a stem body, in the form of a hollow stem, into the container chamber and penetrates completely the extrusion block introduced into the container chamber. The mandrel tip is advanced up to or into the die opening immediately following the container chamber. The mandrel body does not have any points anchoring it to the die with the result that the extrusion block material is able to flow over the whole of the outer contour of the mandrel and into the die opening without forming a seam. In this process, because of the high flow stresses, the mandrel body cannot always be held exactly in the central position, the resultant pipe section is often not exactly concentric, as is desired, but instead slightly eccentric.
“Eccentric” means that the geometric middle points of the outer and inner contours—as viewed in cross-section—do not coincide, but instead lie a distance apart from each other and, accordingly, the thickness of the section wall varies over the cross-section.
The eccentricity of seamless, extruded pipe sections that are intended to be concentric is however very small, amounting to 0-10% of the average cross-sectional wall thickness of the section.
The eccentricity corresponds according its definition to the direct distance d between the two geometric centres of the outer and inner contour of the pipe section in cross-section.
For certain applications on the other hand use is made of pipe sections which are purposefully eccentric in cross-section. The eccentricity of such pipe sections is however, generally much greater than the process-related eccentricity values achieved with concentric designed pipe sections.
It is known to produce eccentric pipe sections by extrusion methods employing multi-chamber dies. The mandrel body is incorporated as a mandrel part in a die plate. The material to be extruded is fed to a welding chamber via a plurality of inlets under arms of the mandrel and, forming weld seams, passes around a shape-forming mandrel and through the die opening. Pipe sections manufactured by this process contain so called extrusion weld seams. This process is, however, suitable only for easily extrudable alloys exhibiting low mechanical strength values.
If the outer and inner contours have the same geometric shape, in particular that of a circle, then the eccentricity can be expressed by the following equation:
E
=
S
max
-
S
min
2
(
1
)
where S
max
represents the maximum and S
min
the minimum thickness of the wall of the pipe section. The average wall thickness S
av
of the eccentric pipe section in question can be calculated as follows:
S
av
=
S
max
+
S
min
2
(
2
)
The magnitude of S
av
also corresponds to the wall thickness of a concentric pipe section with the same outer and inner contour measurements as the eccentric pipe section.
To compare the eccentricities of pipe sections of various sizes, i.e. such sections with different outer and inner contour measurements, the so called relative eccentricity E
R
is calculated as follows:
E
R
=E/S
av
  (3)
Whereas the continuous manufacture of seamless extruded concentric pipe sections is practised on an industrial scale, the production of seamless, eccentric pipe sections with constant eccentricity along the length—allowing for a tolerance range—has not yet been solved satisfactorily.
Trials aimed at the production of seamless, intentionally eccentric pipe sections by extrusion over a mandrel, result in the mandrel arm usually being deflected towards the middle of the die opening as a result of the different flow pressures over the cross-section. This results in pipe sections with eccentricity values that deviate significantly from the intended values and non-uniformly along the length of the section; these eccentricities lie far beyond the normal inaccuracy of 0 to 10% of the average wall thickness. The deflection of the mandrel arm towards the centre of the die opening can, furthermore, lead to parts of the extrusion press device being damaged. Also, eccentric pipe sections manufactured this way tend to bend and curve when they emerge from the die. This means that the final length of pipe section bends off to one side on leaving the die.
SUMMARY OF THE INVENTION
The object of the present invention is to propose an extrusion press device and an extrusion process for manufacturing seamless, eccentric pipe sections having as constant as possible eccentricity along their length.
That objective is achieved by way of the invention in that the mandrel body, when in the position for extrusion, is a mandrel arm of longitudinal axis M
D
with a mandrel tip that can be pushed out of the dummy block through the extrusion block up to or into the die opening, such that the material of the extrusion block can flow in a seamless manner around the mandrel arm, through the die opening. The mandrel arm is arranged eccentric in cross-section with respect to the container chamber and with respect to the die opening, and the die opening is arranged eccentric in cross-section with respect to the container chamber. The longitudinal axis M
D
of the mandrel arm and the longitudinal axis M
R
of the container are a distance apart and lie essentially parallel to the longitudinal axis M
K
of the die opening, in such a way that the longitudinal axis M
K
of the die opening in cross-section lies between a pair of straight lines g
1
and g
2
each passing through the mandrel arm longitudinal axis M
D
and the container chamber longitudinal axis M
R
of as well as perpendicular to lines p connecting the mandrel arm longitudinal axis M
D
and the container chamber longitudinal axis M
R
.
The container chamber longitudinal axis M
R
, the mandrel arm longitudinal axis M
D
and the die opening longitudinal axis M
K
are so called middle axes which in cross-section pass through the geometric middle point of the elements of the device.
The mandrel arm longitudinal axis M
D
, the container chamber longitudinal axis M
R
and the die opening longitudinal axis M
K
are preferably parallel to each other.
In a preferred version the eccentric arrangement of the mandrel arm with respect to the container chamber and the die opening, and the arrangement of the die opening with respect to the container chamber are chosen such that the container chamber longitudinal axis M
R
, the mandrel arm longitudinal axis M
D
and the die opening longitudinal axis M
K
lie on a common plane

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