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Патент USA US3085694

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April 16, 1963
Filed Oct. 24, 1957
mg. I
LZ 817/
?Haezbd elem
Patented Apr. 16, 1963
present invention is more especially concerned with the ex
trusion of aluminium and aluminium alloys. The method
proposed by the present invention is based on the earlier
method of preventing, by means of the relative displace
ment of mandrel and die, the development of the annular
Peter Billen, Leverkusen-Kuppersteg, Ernst Emmerich,
Cologne-Bruck, Walter Haendeler, Dusseldorf, and
Willi Linnerz, Dusseldorf-Ellen‘, Germany, assignors to
Schloemann Aktiengesellschaft, Dusseldorf, Germany
Filed Oct. 24, 1957, Ser. No. 692,230
2 Claims. (Cl. 207-10)
markings known as “bamboo rings” on extruded tubes
and cable sheaths of aluminium or other metals which are
subjected to cooling immediately they leave the die, the
said earlier method consisting in displacing the tools to
The invention relates to a method, by the relative dis 10 increase the size of the annular extrusion ori?ce when
the pressure drops and to reduce the size of the ori?ce
placement of mandrel and die, of preventing the develop
when pressure is re-applied. The method now proposed
ment of the annular markings known as “bamboo rings”
by the present invention, in which the adjustment of the
on extruded tubes and cable sheaths which are cooled
tools to increase the size of the annular ori?ce is effected
immediately they leave the die. According to an earlier
proposal (German patent application Sch 14,000 Ila/7b,
of November 20', 1953, which issued as Patent No.
1,012,892; U.S. application Ser. No. 460,961, which issued
as Patent No. 2,828,859 on April 1, 1958, of October 7,
before the standstill period begins, is primarily distin
guished from the aforementioned earlier proposal by the
fact that it is performed in a gradual manner in proportion
with the gradual contraction of the annular ori?ce due to
the cooling of the die. At the same time the simultaneous
1954; British Patent No. 765,367, published Jan. 9, 1957)
contraction of the annular ori?ce due to the gradual drop
the normal velocity of extrusion is gradually reduced to
in the pressure can likewise be taken into consideration
nil in such a way that during the standstill period the
(as proposed in German patent application Sch 14,000
cooling cable sheath and the tube-forming tools will at
lb/ 7b, U.S. patent application Ser. No. 460,961, and
no time assume temperatures likely to injure the insula
‘British Patent No. 765,367). Another feature of the in
vtion of the cable. As the temperature and the speed of
extrusion go down, the die will necessarily contract and 25 vention is that the tools are displaced in the sense of
reducing the size of the ori?ce before the press is re
reduce the size of the annular ori?ce through which the
started at the end of a standstill period. The amount of
sheath is extruded, so that the thickness of the wall of the
displacement is preferably calculated to allow for the
tube will slowly diminish. Moreover, the gradual reduc
‘degree of thermal contraction of the extruded material
tion of the normal velocity of extrusion involves a
concomitant reduction in pressure. The drop in pressure 30 which is within the region of the die during the standstill
period of the press. Allowance may also be made for
affects the pressure inside the extrusion chamber behind
contraction due to the pressure drop that precedes the
the ori?ce of the die. Consequently there is some recovery
standstill period of the press.
from the longitudinal elastic strain imposed by the normal
Yet another feature of the invention is that the further
pressure of extrusion, and this recovery likewise affects
the extrusion chamber itself. Hence, the thermal varia 35 adjustment of the tools in the sense of reducing the size
of the ori?ce until they have resumed the position which
tion of the size of the annular ori?ce due to the change
corresponds with normal extrusion velocity after the
in the temperature will be modi?ed by an elastic varia
press is re-started is gradually performed approximately
tion due to the changing extrusion pressure and the conse
in proportion with the increase in the size of the extru
quent ?uctuation of the load on the tools. The magni
tude of this elastic variation depends upon the amplitude 40 sion ori?ce due to the die again heating up.
The accompanying drawings are axial sections of parts
of the pressure ?uctuation that occurs in the space con—
of three extruded aluminium cable sheaths showing the
taining the tools. If the pressure of extrusion is abruptly
inequalities (bamboo rings) in the conformation of the
relaxed, then a pronounced annular depression will form
sheaths at the points which correspond with the standstill
on the extruded tube, known as a “bamboo ring.” If the
drop in pressure is gradual, then the resultant marking will 45 periods of the press. The sheath shown in FIGURE 1
is produced without any displacement of the extrusion
not be pronounced. Whereas rapid cooling causes the
tools and therefore exhibits the development of a pro
diameter of the die to become smaller by radial contrac
nounced bamboo ring. In the production of the sheath
tion and hence entails a reduction in the wall thickness
shown in FIGURE 2 the size of the annular extrusion
of the cable sheath, the withdrawal of heat from the tool
ori?ce was increased as the pressure fell at the end of the
head by the cooling of the tube when the standstill periods
extrusion stage before the standstill period began and it
are long causes a shrinkage of mandrel and die also in the
was reduced again when pressure was re-applied. FIG
axial direction. This axial shrinkage involves an enlarge
URE 3 illustrates the method of controlling the extrusion
ment of the annular extrusion ori?ce and hence tends to
ori?ce as proposed by the present invention.
thicken the wall section of the extended tube.
In the method illustrated in FIGURE 1 the pressure
It has already been disclosed that the depression which
of extrusion is gradually reduced before the point 1,
forms part of the bamboo ring and which is due to elastic
which corresponds with the standstill period, is reached,
changes in the size of the extrusion ori?ce at the end of a
‘ so that the wall thickness “d” of the extruded sheath will
pressure period can be prevented from forming by a
likewise diminish from the left to the right towards
displacement of the mandrel, i.e. by an adjustment of
point '1. During the standstill period the die cools and
the size of the ori?ce, i.e. a variation of the distance
'therefore radially contracts, thus pressing a bamboo
between mandrel and die. The object taken in view by the
ring, in the form of a notch-like annular groove, into the
present invention is to eliminate the eifect of changes in
the size of the extrusion ori?ce due to causes that had
> wall of the sheath. For re-starting the press a high pres
not heretofore been considered, namely those due to
' sure is then applied, which causes the size of the ori?ce
extruding aluminium, the temperature ?uctuation that
tube wall slowly increases to assume its original value
“d” at about the point 3. The resultant confonnation of
changes in temperature. When extruding lead sheaths 65 to increase and the tube wall to thicken abruptly at the
point 2. During the ensuing pressure stage the tempera
these temperature variations do not produce considerable
ture of the die gradually rises and the thickness of the
and particularly troublesome changes. However, when
must be controlled covers a range of several hundred
degrees C. and this is rapidly traversed owing to the high
rate of cooling the process requires, which therefore pro
duces very sensible thermal shrinkage effects. Hence the
the wall, as shown in FIGURE 1, is therefore non-uni
form and unsatisfactory.
In the method illustrated in FIGURE 2, which is an
improvement on that of FIGURE 1, the wall thickness
likewise gradually diminishes from its normal value “d”
on the left to a smaller value “til” at the standstill point
4- owing to the gradual pressure drop during this period.
However, when the press stops, at the point 4, the tools
are adjusted in the sense of increasing the width of the
ori?ce. This adjustment therefore compensates the im
pending reduction in wall thickness due to the contrac
tion of the die. When the press is re-started, at the point
5, the pressure of the extruded material rises again and
may not always be as pronounced as shown in the draw
ings, the individual sections are nevertheless easily detect
able when the cable sheath has been completed.
Since in actual practice it is very rarely possible by ad
justing the tool to compensate with entire precision
shrinkage due to changes in temperature as well as elastic
changes due to fluctuations in pressure, it is preferred in
making the adjustments to be somewhat generous in the
positive direction i.e. in the sense of an increase in the
thickness of the sheath wall beyond its thickness in other
regions, and at points 7 and 11 not to effect the adjust
the thickness of the wall tends to increase, but this is now
ment abruptly but gradually whilst the sheath still slow
compensated by a readjustment of the tools, in the sense
ly moves through the die. A small and uniform tem
of decreasing the ori?ce, at point 6. In other words, the
porary increase in the wall thickness throughout the con
tools are ?rst displaced, at the point 4, to increase the
ori?ce, and they are then readjusted, at the point 16, to re 15 trolled length of the cable is an advantage when, as is
frequently necessary, the standstill periods are long, be
duce the ori?ce. This method is better than the method
cause the increase will then offset the effect of metal
illustrated in FIGURE 1, because there is now no abrupt
lurgical changes due to cooling, which would otherwise
reduction in wall thickness as at 1 in FIGURE 1, but
rather a short increase in thickness. The further course
of the extrusion process from point 6 corresponds with
that shown in FIGURE 1, and the original wall thickness
d will therefore be re-established.
In the method now proposed by the present invention,
which is illustrated in FIGURE 3, the pressure again
gradually diminishes from the left to the standstill point
adversely affect the ?exural properties of the cable.
What is claimed is:
1. A method of controlling the thickness of a sheath
or tube of aluminium or other metal produced in an ex
trusion press in which the thickness is determined by the
distance between one end of the mandrel and the end
face of the die aperture and in which the extruded prod
uct is cooled immediately after leaving the die, compris
sion. The e?ect of cooling would therefore be to dimin
ing the steps of reducing the extrusion pressure gradual
ish the wall thickness accordingly. However, according
ly when a stoppage is to be effected, progressively adjust
to the invention it is proposed to counteract this gradual
ing the relative axial spacing of the mandrel and die from
decrease from the very beginning by displacing the tools 30 the beginning of the reduction in pressure and during its
at the point 7, where the reduction of pressure begins in
continuance to the extent necessary to compensate for
with a concomitant reduction in the velocity of extru
the sense of progressively increasing the ori?ce so that
the wall thickness will not actually diminish at all but
the reduction in the annular gap that would otherwise re
sult from the variation of the load on the mandrel and
will maintain its original value “d” until the standstill
die caused by the changing extrusion pressure, continu
point is reached, or may even be slightly increased. Dur 35 ing the adjusting of the mandrel and ‘die to compensate
ing the standstill period of the press, which begins at
point 8 the tools are re-adjusted at the point 9 for the
further enlargement of the extrusion ori?ce to compen
sate for the thermal contraction of the die. During the
for the reduction in the annular gap that would other
wise be caused by the cooling and consequent contraction
of the die, and progressively re-adjusting the mandrel
and die when extrusion is resumed, to the extent neces
possibly prolonged standstill period the extrusion ma 40 sary to compensate for the thermal and elastic expan
terial in the vicinity of the ori?ce will cool so that, rough
sion of the die resulting from the increase in temperature
ly expressed, it will lie between the tools with play, thus
and pressure.
tending to give rise to a sudden considerable increase in
wall thickness when pressure is re-applied. To prevent
this from happening it is proposed by the invention to
re-adjust the tools at the point 10 during the standstill
period in the sense of reducing the ori?ce.
When pressure is resumed at the end of a prolonged
period of standstill the increase in wall thickness, in
dicated at points 9 and 10, will therefore be only slight '
(wall thickness greater than or equal to d) and this is
then compensated up to point 11 by the further adjust
ment of the tools to constrict the ori?ce, thus at the same
time continuously compensating the increase in wall
thickness that will be caused by the rise in the tempera
ture of the die, and therefore operating to maintain the
wall thickness d. Hence, besides preventing the develop
ment of depressions, the present invention will also re
duce any undesirable thickening of the wall. If the ad
justment of the tools is skillfully controlled and per 60
formed, any thickening of the wall may even be entire
ly avoided. However, whenever such thickening does oc
cur, the transitions will not be abrupt, a factor which will
tend to impart to the tube or sheath a much greater
flexural strength on the bending machine than when
changes in wall thickness are well de?ned and abrupt.
Although the variations in the thickness of the walls
2. A method of controlling the thickness of a sheath
or tube of aluminium or other metal produced in an ex
trusion press as claimed in claim 1, further comprising
the step of reducing the size of the extrusion gap before
the press is re-started after a standstill period to the ex
tent necessary to compensate for the thermal contrac
tion of the cooling extrusion material in the vicinity of
the die during the stand-still period.
References Cited in the ?le of this patent
Greenall ____________ __ Sept. 27, 1938
Anderson ____________ __ Oct. 31, 1939
Norman ____________ .._ Feb. 26, 1957
Emmerich ____________ .._ Apr. 1, 1958
Great Britain _________ __ Sept. 8, 1932
France ______________ __ Oct. 10, 1942
Germany ____________ __ Apr. 15, 1954
“Advanced Fluid Mechanics,” vol. 1, by R. C. Binder,
Prentice-Hall, Inc., Englewood Cliffs, N.J., @ 1958, pp.
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