1. Introduction
As an indispensable transmission medium in optical communication, optical fiber cable needs to be laid in a variety of environments. The addition of metal armouring layers in the structure of optical fibre cables can effectively extend the service life of optical fibre cables. Water molecules have a significant impact on the transmission performance and life of the optical fibres, and organic molecules such as polyethylene cannot resist water vapour in the air for a long time. metal armouring layer to increase
When the cable is laid in a harsh environment, one or two layers of metal armour are required to increase its resistance to lateral pressure and impact, to resist external mechanical damage and to provide a certain level of protection against insects and rodents.
The metal armouring layer of the cable is usually made of laminated steel or aluminium tape, which is wrapped longitudinally around the cable core to resist external moisture and mechanical damage. According to the standard, the cable should be water resistant in its entire section, i.e. all gaps within the cable jacket should be effectively water resistant, so that water cannot seep longitudinally through the cable core and jacket (except for the steel wire armouring part, the metal armouring layer referred to below is the steel and aluminium tape metal armouring layer). In addition, the metal armouring layer should keep the electrical conductivity in the longitudinal direction of the cable, and the metal armouring layer of the whole cable should have no broken tape phenomenon.
Through the statistical data found, optical cable in the lap of water seepage accounted for about half of the total water seepage anomaly. The metal armouring layer is generally formed in one time by using the longitudinal package forming mould, the water seepage at the lap of the armouring layer is not only related to the bonding strength of the lap of the armouring layer, but also has a great relationship with the forming of the armouring layer, that is, the reasonable or not of the metal band forming mould directly affects the quality and qualification rate of the optical cable.
At present, according to the different physical properties of steel belt and aluminum belt, each manufacturer adopts different longitudinal package forming mould, if using aluminum belt longitudinal package mould longitudinal package steel belt for a long time, it is easy to cause damage to the mould, and when using steel belt longitudinal package mould longitudinal package aluminum belt, it will produce the phenomenon of broken belt because the mould longitudinal package force is too large.
2. Aluminium strip laminating moulds
The common moulds for longitudinal wrapping of aluminium strips are, from left to right, the positioning mould, the cable core conduit, the main body of the mould and the sizing mould. The role of the positioning die is to guide the aluminium strip into the mould at a suitable angle; the role of the cable core conduit is to adjust the angle of the cable core and the aluminium strip; the main body of the mould is composed of a whole piece of sheet metal, the two sides of which are gradually curled towards the centre to form a tube. In production, the flat aluminium strip is wrapped around the cable core by the main body of the mould and then gradually curled into a tubular shape and finally pressed into shape on the sizing die, completing the longitudinal wrapping process. The aluminium strip is evenly stressed throughout the process and gradually changes into a tubular shape.
In order to meet various production requirements, different sizes of aluminium strip need to be matched with different sizes of forming moulds. If the overall size of the mould is small, it is easy to cause too much resistance to the aluminium strip and break the strip; while the overall size of the mould is larger, although the pressure on the aluminium strip is small, it is easy to appear that the crimp at the lap is not tight, resulting in water seepage at the lap.
The aluminium strip is soft and has insufficient tensile strength and is subjected to greater friction during the curling and forming process through the mould, which can easily cause the strip to break. To reduce the friction, some companies use the method of reducing the contact area between the aluminium strip and the mould by making grooves or blind holes in the inner surface of the sizing die to reduce the friction [2]; there are also methods to reduce the friction coefficient between the aluminium strip and the mould by setting a Teflon lubrication layer on the surface of the longitudinal package mould and the sizing die to reduce the friction [3], thus reducing the rate of tape breakage. In order to prevent water seepage at the lap of the aluminium strip, some companies have installed a glue dispensing device in front of the longitudinal lap forming mould, which can strengthen the bond at the lap and solve the problem of water seepage due to poor bonding of the metal strip after longitudinal lap.
3. Steel strip laminating mould
The steel strip has a certain rigidity, it is more difficult to curl and shape it, so it is necessary to use a mould with a large longitudinal force when laminating. The general steel strip longitudinal ladle forming mould consists of three parts: pre-forming mould, forming mould and sizing mould. At present, the fiber optic cable manufacturers usually use the steel belt longitudinal package mold is divided into two kinds: combined longitudinal package mold and roller type longitudinal package mold.
The structural diagram of the combined longitudinal ladle mould is from left to right, in the order of positioning mould, pre-forming mould, overlapping mould and sizing mould. The positioning die is a symmetrically mounted positioning guide roller, the pre-forming die has a conical pre-forming cavity, the overlapping die has a cone forming cavity with an open edge nozzle, and the sizing die has a conical cavity. In production, the cable core is transferred into the mould together with the steel belt, the belt positioning guide roller is adjusted to suit the width of the belt, the belt enters the pre-forming mould and curls inwards into a semi-circular arc in the pre-forming cavity, immediately afterwards the cable core is wrapped longitudinally in the overlapping mould in a cylindrical shape and produces an overlap, and finally the round belt is crimped in the sizing mould.
The role of the overlap die is to create a lap in the strip, in addition to the open lap nozzle mentioned above, there is also a pin added to the tapered end of the overlap die to create a lap in the strip.
The pin type lap nozzle is more demanding in terms of steel strip specification and the stability of the strip in production. If the width of the strip is greater than the rated width of the pin type lap nozzle, the strip will be squeezed by the pins and will easily bulge at the lap resulting in water seepage, if the strip and cable core rotate during production, the pressure at the lap will be too low and the bond will not be secure resulting in water seepage. With the open lap nozzle, the strip is not subjected to lateral resistance in the open space and the problems associated with the pin lap nozzle do not occur.
The sliding friction of the combined longitudinal ladle forming moulds on the steel belt is high and the belt is often broken in production, therefore some companies use roller longitudinal ladle forming moulds to change the sliding friction of the steel belt to rolling friction.
1: Positioning die 2: Pre-forming roller 3: Horizontal rounding roller 4: Closing rounding roller 5: Forming roller 6: Sizing roller
Rollers for longitudinal ladle moulding
As can be seen from the diagram, the roller type longitudinal ladle mould consists of a positioning die, a pre-forming roller, a horizontal rounding roller, a closing rounding roller, a forming roller and a sizing roller. The role of the positioning die is to guide the strip at a defined angle into the pre-forming rollers; the pre-forming rollers are made up of two concave and convex rollers, the role of which is to bend the edge of the strip into an arc; the horizontal rounding rollers are made up of two curved slotted rollers placed horizontally with a circular gap after fitting, the strip is pushed and rounded by both sides of the horizontal rollers when passing, the role is the same as the overlapping die described above; the lower part of the closing rounding rollers is set vertically. The lower part of the rollers is made up of curved slotted rollers set vertically and the upper part of the rollers is made up of horizontally set face rollers, the edge rounding rollers flatten and integrate the two sides of the closed strip; the forming rollers and sizing rollers are made up of the upper and lower rollers with curved slotted rollers corresponding to each other, the forming rollers integrate the strip and finally the sizing rollers shape the pre-formed strip.
The advantages of the rolling longitudinal ladle mould are: the sliding friction between the steel strip and the mould is transformed into rolling friction, which reduces the stretching force on the steel strip, ensures the rolling pattern on the strip and reduces the strip breakage rate; the mould can be adjusted in all positions, but in order to ensure a good longitudinal ladle effect, each mould needs to be installed precisely, otherwise it is easy to cause water seepage due to poor longitudinal ladle of the steel strip.
This part mainly introduces our company's integrated longitudinal ladle mould, which can be used for both aluminium and steel ladles, and the longitudinal ladle effect is good, basically eliminating abnormal phenomena such as interruptions in production. According to statistics, the number of water seepage at the lap of the metal belt accounts for less than 7% of the total number of water seepage of the optical cable each month.
The mould structure diagram has.
1: A pre-forming mould 2: Two pre-forming moulds 3: Overlapping mould 4: Forming mould 5: Sizing mould
Steel and aluminium strip integrated longitudinal cladding mould
The above parts are connected in turn by a transverse movement screw on the regulating table, which enables the movement of each part of the mould in x, y and z directions, solving the problem of matching the mould to different sizes of steel strip.
Unlike other companies, the mould shown above contains two pre-forming dies: one pre-forming die and two pre-forming dies. The two pre-forming dies reduce the resistance of the strip during the forming process, solve the problem of the strip breaking due to excessive force and increase the production speed. The two preforming moulds consist of a pair of symmetrically distributed left and right moulds, which are divided into left and right upper moulds and left and right lower moulds, the upper mould being a convex mould and the lower mould being a concave mould, with a certain gap between the concave and convex moulds to allow the strip to pass through. The structure of the left die is symmetrical with that of the right die.
One preform die. The gap between the concave and convex moulds is flat in the middle and slightly curled upwards on both sides, the size of the gap decreases with the direction of movement of the strip. The first half of the first preform is a positioning die, which guides the strip at a defined angle into the die in preparation for forming; after the strip has passed through the first preform, the sides are slightly upward to wrap the cable core.
Second preform mould. The first half of the mould is similar in structure to the first preform, but the curvature of the upper and lower gaps between the concave and convex moulds is increased and the intermediate flat distance is reduced; the second half of the mould contains only the lower left and lower right moulds, each with a tapered semi-circular hole, which are combined to form a circular hole. In production, the left and right moulds of the two preforms are placed in a figure of eight, with the figure of eight openings facing the direction of the metal strip entering the mould, so that the second half of the mould has a longitudinal wrapping force on the metal strip, which can be wrapped around the core of the cable by up to 50 per cent after passing through the two preforms.
The overlap die is similar to the overlap die described above, with a conical body with a tapered hole in the centre and an open mouth at the exit, where the metal strip is wrapped longitudinally around the cable core to create a lap.
The forming die is a cylindrical body with an equal diameter hole in the centre and the sizing die is of the same construction as the sizing die above, containing the tapered hole. The role of the forming die is to crimp the metal strip lap, the role of the sizing die is the same as above. Compared with other metal tape armouring cable, stainless steel tape armouring cable has better resistance to lateral pressure and to rodent bite and bird pecking, but the hardness of stainless steel tape is greater than the hardness of ordinary steel tape, which is more difficult to form. When using the general steel belt longitudinal wrapping molding mold, easy to damage the mold and poor molding, but the above steel and aluminum belt integrated longitudinal wrapping molding mold can complete the longitudinal wrapping of stainless steel belt, and longitudinal wrapping stainless steel belt molding effect is good, the mold will not be damaged.
5. Conclusion
At present, there are many optical cable manufacturers, in order to improve economic efficiency and market competitiveness, reduce the manufacturing cost of optical cable, optical cable manufacturing enterprises should use efficient production equipment, as far as possible to improve the production speed while ensuring the product qualification rate. According to the different physical properties of the steel and aluminium strip, manufacturers need to use the corresponding longitudinal cladding mould in production to achieve the longitudinal cladding effect.