Extruder apparatus for sheathing a strand-form product, in particular a cable

Extrusion head for sheathing a strand-form product, in particular a cable, comprises a central hollow mandrel having a central bore through which the product to be sheathed passes. An intermediate mandrel surrounds the central mandrel with an annular material flow channel between forward portions of the mandrels for applying a first layer of sheathing. The intermediate mandrel has at its forward end a parti-spherical enlargement by means of which it is mounted in a socket at the forward end of a tubular guide piece with a ball and socket type joint permitting angular movement of the intermediate and central mandrels relative to the guide piece which is received in a casing mounted on a support. A second annular material flow channel is provided between the casing and the intermediate mandrel for applying a second layer of sheathing. Material is supplied to the respective annular flow channels by extruders provided at opposite sides of the extrusion head through supply tubes connected with ball-type joints to preclude lodging of sheathing material.

FIELD OF INVENTION 
The invention relates to extrusion apparatus for sheathing a strand-form 
product, in particular a cable, with a plurality of directly successively 
applied layers of plastic and/or rubber or mixture thereof, in which an 
extruder head is mounted on a machine support and in which extruders 
arranged at the sides of the extruder head are connected to the extruder 
head by special connecting pieces, supply tubes or the like, and in which 
the extruder head comprises a central hollow mandrel through which the 
product to be sheathed is led and, arranged essentially concentric 
therewith, a plurality of nozzle-forming extruder devices in the form of 
mandrels and or conducting pieces which enclose therebetween annular 
channels of which one end forms the forming nozzles while the other end is 
connected with an extruder by the supply conduit pieces. 
BACKGROUND OF THE INVENTION 
On such extrusion apparatus there is produced cable of which the core is 
led through the bore of the central mandrel and surrounded successively 
first with a thin semi-conducting layer and later with a strongly 
insulating layer of non-conducting plastic material. With this extrusion 
apparatus, the individual mandrels or conducting pieces forming the 
forming nozzles are arranged stationary exactly centered. By reason of 
tolerances of the sheathing, cable produced on such extrusion apparatus 
does not meet the requirements of modern high voltage cable. The thickness 
of the sheathing around the core is not sufficiently uniform. 
There is also known extrusion apparatus in which the mandrels formed as 
nozzles are divided and the end piece is arranged displaceably 
transversely of the axis of the mandrel. Through a displacement of the 
mandrel end piece during operation, the tolerance of the surrounding 
layers of the cable can be better adjusted, but the cable produced still 
has flaws, especially in the semi-conductive layer. This is attributable 
to the fact that the material to be extruded lodges in the adjustment 
places and here begins to polymerize or vulcanize and then during the 
operation, from time to time, is carried off by the flow of material and 
because of being already prematurely polymerized or vulcanized forms flaws 
in the semi-conductive layer. Such flaws must be cut out of the cable. 
This leads to considerable loss because not only the location of the flaws 
but also adjacent regions must be cut out. The resulting short lengths of 
the cable are frequently of limited value when they must be lengthened by 
being coupled bo other pieces of cable. 
SUMMARY OF THE INVENTION 
The invention avoids these objections. It is an object of the invention to 
provide extrusion apparatus with a precision sheathing extrusion head 
which is adjustable during operation and is so formed that in the flow 
path of the material to be extruded the material cannot lodge and be 
prematurely vulcanized or polymerized in the flow paths. 
In accordance with the invention, an intermediate mandrel surrounding the 
central mandrel is mounted in a ball joint so as to be adjustable and 
securable in adjusted position and a first sheathing material supply tube 
extending laterally from the intermediate mandrel is connected by a ball 
joint to a further sheathing material supply tube which in turn is 
connected by a ball joint to the extruder. 
Such connection with ball joints assures that there are no pockets or 
projections in which, or behind which, material can lodge outside the flow 
path of the material to be extruded. However, the technical success of the 
invention is not attained through the use of such ball joints alone. The 
material supply tube must also be formed in such manner that no material 
to be extruded can lodge or be retained. This is achieved by the extruder 
apparatus in accordance with the invention. 
It is advantageous when the intermediate mandrel is inserted in a tubular 
guide sleeve having at its forward end a spherical socket which receives 
an enlarged forward end portion of the intermediate mandrel in such manner 
that the intermediate mandrel can be removed in the extrusion direction 
for cleaning. 
It is advantageous when the guide sleeve has on its rear end an annular 
parti-spherical surface against which a pretensioned ring on the 
intermediate mandrel presses and also acts as a seal. Through this ring 
there is obtained a pretensioning which presses a spherical surface on the 
intermediate mandrel into a spherical socket on the forward end of the 
guide sleeve and thereby prevents material from being pressed between 
these surfaces in the starting condition. The surface between the rear end 
of the guide sleeve and the pressing ring is formed as a parti-spherical 
surface so that there in adjustment a uniform relation is retained. 
A simple adjustment possibility is attained by providing at least three 
adjustment screws arranged between the guide sleeve and a rear portion of 
the intermediate mandrel. Furthermore, it is advantageous for favorable 
adjustability when the central mandrel is adjustable and securable 
relative to the machine support and relative to the surrounding 
intermediate mandrel. A cup-shaped object can be introduced into the 
mandrel in a similar manner. Thereby the layer to be applied can be 
adjusted precisely. A particular advantage is that in adjustment of the 
intermediate mandrel the material guide channel is not altered. 
If a further coating layer is to be provided, this is usually thin and the 
material flow is not as much of a problem as with the inner layer. 
Therefore it is advantageous when further outwardly arranged tube pieces 
of outer nozzles are arranged adjustable and securable perpendicularly to 
the inner mandrel and the support. 
In order that the supply tube conduit can move freely in an adjustment of 
the second nozzle tube it is advantageous when in the casing at the 
position of the material supply tube there is provided an opening of 
larger diameter than the diameter of the material supply tube. 
In order to secure the second nozzle tube piece in a fixed position after 
adjustment, it is advantageous when there is provided on the rear end of 
the central mandrel a flange having openings through which screws are 
inserted parallel to the axis of the mandrel. 
In order to provide a good supply of the material it is advantageous when 
there is provided a flow channel parallel to the axis between the end of 
the supply tube and a distribution channel for the material

DESCRIPTION OF PREFERRED EMBODIMENT 
The extrusion head illustrated in the drawing is mounted on a machine base 
or frame which is not shown. Two extruders, likewise not shown, are 
mounted on opposite sides of the extrusion head and are displaceable and 
securable in a direction perpandicular to the axis 7 of the extrusion 
head. 
The extrusion head illustrated in the drawing comprises a central mandrel 
1, through a central bore of which the product to be sheathed is passed 
from right to left. The central mandrel 1, has at its forward end, a 
removable and replacable section 1A, having a tapered bore ending in an 
exit opening which closely embraces the product to be sheathed. 
A likewise hollow intermediate mandrel 2, concentric with the axis 7 
surrounds the central mandrel 1, and has an enlarged forward end portion 
2A provided with a partispherical surface 4. A tubular guide sleeve 3, 
surrounds the intermediate mandrel 2 and has at its forward end a 
partispherical socket 3A, which receives the enlarged forward portion of 
the intermediate mandrel to provide a ball and socket joint. The bore of 
the guide sleeve 3 is tapered to provide between the intermediate mandrel 
2 and the guide sleeve 3 a space permitting angular movement of the 
intermediate mandrel 2, relative to the guide sleeve 3 about a center 
defined by the parti spherical surface 4 and socket 3A. 
The guide sleeve is surrounded by a casing 5, which is mounted fast on the 
machine base or frame and is provided with a removable front end portion 
5A secured by a plurality of screws 5B. A mouth piece 6 concentric with 
the axis 7 is secured on the front end portion 5A of the casing 5 by means 
of screws 8. 
Between the central mandrel 1, and the intermediate mandrel 2 there is 
formed an annular material guide channel 9 which terminates in the mouth 
piece 6 so as to apply a first layer of sheathing material to the product 
as is passes axially through the central mandrel 1. Sheathing material is 
fed to the annular channel 9 from an extruder (not shown) at one side of 
the extrusion head through special connecting pieces which form a material 
supply tube 10. Between the intermediate mandrel 2 and the casing 5 there 
is formed a further annular sheathing material guide channel 11 opening 
into the mouthpiece 6, downstream of the annular channel 9, so as to apply 
a second layer of sheathing material to the product. A second extruder 
(not shown) on the opposite side of the extrusion head supplies sheathing 
material to the annular channel 11 through a material supply tube 12 and 
material distribution channel 13. 
In producing a cable, the cable core is led through the bore of the central 
mandrel 1 and first receives a thin layer of semi-conducting material 
which is supplied through the material guide channel 9 and immediately 
thereafter receives a thicker layer of insulating material supplied 
through the material guide channel 11. 
The intermediate mandrel 2 can be withdrawn from the guide sleeve 3 and 
casing 5 upon removal of the supply tube 10 and the end portion 5A of the 
casing together with the mouth piece 6. In order that the intermediate 
mandrel 2, after adjustment of the material guiding channel 9 can be 
secured fast with the central mandrel 1 screws 14 screwing into a flange 
2A at the rear end of the intermediate mandrel 2, secure a flange 15 which 
engages the rear end of the central mandrel 1. 
An adjustment of the intermediate mandrel 2 relative to the casing 5 and 
thereby relative to the machine base or frame, is achieved by means of at 
least three adjustment screws 16, which are screwed through radial holes 
in the guide sleeve 3 and with their inner ends engage the intermediate 
mandrel 2. Adjustment is permitted by means of the ball joint provided by 
the parti-spherical surface 4 and the socket 3A of the guide sleeve 3. 
To provide a rear seal the intermediate mandrel 2 carries on its rear end a 
flange 17, having a groove 17A receiving a resilient ring 18, for example 
of rubber, pressing on the rear end of the guide sleeve 3. The flange 17 
is removably secured on the intermediate mandrel 2 by means of set screws 
or threads (not shown). The rear end surface 19 of the guide sleeve 3, is 
of spherical curvature permitting angular movement between the guide 
sleeve 3 and the intermediate mandrel 2. 
The supply of sheathing material to the annular material guide channel 9 is 
effected by a circumferentially extending distribution channel 20, which 
is connected with the material supply tube 10 through an axially extending 
flow channel 21. The material supply tube 10 comprises an inner supply 
tube 10A which is screwed into a tapped hole in the intermediate mandrel 
2. On its outer end the inner material supply tube 10A is provided with a 
spherical cap-like enlargement 22 which receives a likewise spherical end 
piece 23 of an outer material supply tube 10B. The end of the outer 
material supply tube 10B is provided with a thread on which is screwed a 
screw cap 24, provided with an inner spherical ring surface which engages 
the spherical caplike enlargement 22 of the inner supply tube 10A. In like 
manner, the outer supply tube 10B is connected by a screw cap 25, with a 
further supply tube or with the respective extruder. The inner supply tube 
10A extends out through openings in the guide sleeve 3 and the casing 5, 
having an inner diameter larger than the outer diameter of the inner guide 
tube 10A so as to permit angular movement of the intermediate mandrel 2 
relative to the guide sleeve 3 and the casing 5. 
Channels for a temperature control medium can if desired be provided in the 
mandrels 1 and 2, the guide sleeve 3 and the casing 5. 
In the event that further sheathing layers are desired the casing 5 as 
provided with additional annular material guiding channels similar to the 
channel 11.