METHOD AND AN ARRANGEMENT FOR MANUFACTURING ELONGATED GROOVED ELEMENT

Abstract: The invention relates to a method and arrangement for manufacturing an elongated grooved element, in which method the grooved element is manufactured by extruding plastic material onto a base element and by forming open grooves (2) on the surface of the plastic material along the length of the grooved element. To reduce defects in forms, the grooved element is manufactured in two stages (3, 4): in a first stage, a pre-grooved support structure is formed and, in a second stage, the actual grooved surface is formed onto the pre-grooved support structure.

Description: METHOD AND AN ARRANGEMENT FOR MANUFACTURING ELONGATED GROOVED ELEMENT The invention relates to a method for manufacturing an elongated grooved element, in which method a grooved element is manufactured by extruding plastic material onto a core element and by forming open grooves on the surface of the plastic material along the length of the grooved element and in which method the grooved element is manufactured in two stages. The invention also relates to an arrangement for manufacturing an elongated grooved element. Methods and arrangements of this kind are currently known for example at cable manufacture. Among the cables that such methods and arrangements may relate to are telecommunications cables where the core element is provided with open grooves into which conductor elements are positioned. The conductor elements may comprise for example insulated metal wires, coated optical fibres, ribbon conductors made of optical fibres, etc. Cables of this type are often referred to as slotted-core cables. One of the methods and arrangements used in the manufacture of such slotted-core cables is disclosed in US Patent 5,830,516. The described solution is based on the use of a calibration device, which causes problems with regard to line speed, for example. A further problem in this solution is that it can only be used for manufacturing helical grooved elements, SZ grooved elements cannot be manufactured using the solution of US Patent 5,830,516. Another example of the prior art is the solution disclosed in US Patent 4,548,567. JP A 4-56810 and US 4,814,133 describe solutions in which an elongated, ground element is manufactured in two stages. A drawback in prior art solutions, including those disclosed in the above publications, is that the portions between the grooves of an elongated grooved element tend to bend in the circumferential direction of the element and, in the worst case, they may even fall, which means that the desired shape of the profile cannot be maintained. This drawback relates to the behaviour of plastic material at the extrusion head of an extruder when the grooved element is being formed and/or during the subsequent cooling phase. Attempts have been made to solve the problem by means of material technology, i.e. by trying to develop materials that allow the above described phenomenon to be eliminated. Also, low line speeds have been used in an attempt to solve the problem. These measures have not, however, been successful in eliminating the shortcomings involved. It is an object of the present invention to provide a method and an arrangement that allow the drawbacks in prior art to be eliminated. This has been achieved with the method and arrangement of the invention. The method of the invention is characterized in that in a first stage a pre-grooved support structure is formed and in a second stage the actual grooved surface is formed onto the pre-grooved support structure. The arrangement of the invention in turn is characterized in that a first extrusion head is arranged to form a pre- grooved support structure and a second extrusion head is correspondingly arranged to form the actual grooved surface onto the pre-grooved support structure. A major advantage of the invention is that it allows the bending and falling of the portions between adjacent grooves in the elongated grooved element to be prevented, the invention thereby improving the dimensional accuracy of the groove profiles and, thereby, the entire grooved element. A further advantage of the invention is its simplicity, which makes the invention economical to introduce and to employ. In the following the invention will be described in greater detail in connection with a preferred embodiment and with reference to the accompanying drawing, in which Figure 1 is a schematic view of a conventional core element of a slotted-core cable; Figure 2 is a schematic view of an arrangement of the invention; and Figure 3 is a schematic, longitudinal view of an elongated grooved element manufactured using the method of the invention. Figure 1 is a schematic view of a conventional elongated grooved element, which in the case of Figure 1 is a core element of what is known as a slotted-core cable. The element in Figure 1 is manufactured by extruding plastic material onto a base element 1 and by forming open grooves 2 on the surface of the plastic material along the entire length of the grooved element. The extrusion of the plastic material and the forming of the grooves 2 can be carried out using a suitable extruder means, which may comprise for example a rotating extrusion head, etc. The above description is fully apparent to a person skilled in the art, and therefore the matter will be not discussed in greater detail in this context but a reference is made to the US publications 4,548,567 and 5,830,516 mentioned earlier. Figure 2 is a schematic view of the arrangement of the invention, and Figure 3 is a longitudinal view of the elongated grooved element manufactured using the arrangement of the invention. An essential idea of the invention is that the grooved element is manufactured in two stages. In the first stage of the manufacture, a pre- grooved support structure is formed and in the second stage the actual grooved surface is formed onto the pre-grooved support structure, i.e. on the element provided with pre-formed grooves. A preferred method for carrying out the above measures is that an extruder means, for extruding plastic material onto the base element 1 , is formed of two rotating extrusion heads 3, 4 located at a distance from each other. The rotating extrusion heads 3, 4 can be any rotating extrusion heads known per se. Seen in the direction of travel of the base element 1 , the first extrusion head 3 is arranged to form the pre-grooved support structure 5 and the second extrusion head 4 is correspondingly arranged to form the actual grooved surface 6 onto the pre-grooved support structure 5. The pre-grooved support structure 5 and the actual grooved surface 6 are particularly clearly shown in Figure 3. The grooves in the actual grooved surface 6, i.e. the grooves into which the conductor elements are to be positioned, are shown with reference numeral 2 in Figure 3. Consequently, one of the basic ideas of the invention is that the grooved element is manufactured in two stages. The manufacture can advantageously take place as a continuous process as disclosed above. This is not, however, the only alternative; a grooved element according to the basic idea of the invention can also be manufactured in two separate production runs, either on the same production line or on different lines, etc. The pre-grooved support structure 5 provides a structure that effectively supports the final structure of the elongated element, a layer providing the actual grooved surface 6 being then formed onto the structure. An advantage of the solution is that the amount of molten plastic material is reduced and, thereby, fewer defects appear in the form of the grooved element and in the profiles of its grooves than in prior art. The invention also allows for shorter cooling distances and considerably higher line speeds than before. The advantages of the invention become evident particularly in the manufacturing processes of SZ cables and grooved element cables of a large diameter, i.e. over 15 mm. In the manufacture of large grooved element cables in particular, problems have often emerged because the amount of plastic material needed may be large and in connection with large material amounts, above mentioned defects in forms caused by shrinkage occur easily. Various measures can be carried out between the first extrusion head 3 and the second extrusion head 4. One of these is the cooling of the pre-grooved support structure 5 which can be implemented for example using a cooling device 7. The pre-grooved support structure 5 can also be heated, if necessary, before the second extrusion head 4. The manufacture of the elongated groove element takes place in two stages, as shown in Figure 2, for example. These stages, i.e. the extrusion of the plastic material carried out using the first extrusion head 3 and the extrusion of the plastic material carried out using the second extrusion head 4, are conducted as a continuous process where the separate stages are carried out as a continuous synchronized process. The synchronization allows the rotation of the extrusion heads to be arranged in such way that the grooves of the pre-grooved support structure 5 and those of the actual grooved surface 6 coincide as shown in Figure 3. The synchronization of the extrusion heads can be implemented for example by means of a suitable monitoring means 7 that is used for controlling the rotation of the second extrusion head 4. The monitoring means 7 can be for example a mechanical or optical groove follower. The control function is schematically shown in Figure 2 by means of arrow N. The above described example of an embodiment is in no way meant to restrict the invention, but the invention may be freely varied within the scope of the invention. It is therefore apparent that the arrangement of the invention or its details need not be exactly like those shown in the Figures, but other solutions are also possible.

Claims: CLAIMS 1. A method for manufacturing an elongated grooved element, in which method a grooved element is manufactured by extruding plastic material onto a core element and by forming open grooves (2) on the surface of the plastic material along the length of the grooved element and in which method the grooved element is manufactured in two stages, characterized in that in a first stage (3) a pre-grooved support structure (5) is formed and in a second stage the actual grooved surface (6) is formed onto the pre-grooved support structure (5). 2. A method according to claim 1, characterized in that the two manufacturing stages (3, 4) of the groove element are carried out as a continuous, synchronized process. 3. An arrangement for manufacturing an elongated grooved element, the arrangement comprising a rotating extruder means which is arranged to form a plastic material layer provided with a grooved surface onto a base element, whereby the rotating extruder means is formed of two rotating extrusion heads (3, 4) located at a distance from each other, characterized in that the first extrusion head (3) is arranged to form a pre-grooved support structure (5) and the second extrusion head (4) is correspondingly arranged to form the actual grooved surface (6) onto the pre- grooved support structure (5). 4. An arrangement according to claim 3, characterized in that the rotation of the second extrusion head (4) is synchronized with that of the first extrusion head (3) by means of a monitoring device (7).

Inventors: HILLBERG JUKKA, KOSTIAINEN MIKKO, HILLBERG, JUKKA, KOSTIAINEN, MIKKO
Applicants: HILLBERG JUKKA, KOSTIAINEN MIKKO, NEXTROM HOLDING SA, HILLBERG, JUKKA, KOSTIAINEN, MIKKO, NEXTROM HOLDING S.A.
Application year: 2000
Main classification: B29C47
IPC codes: B29C47, B29K101, B29L15, G02B6