Field of Invention
The present invention relates to a spiral ribbed duct for telecommunications, the process of manufacturing the same and apparatus thereof used for the laying of the optic fibre under the ground.
More specifically, the subject invention relates to the manufacture of ribbed ducts adapted to receive transmission cable for telecommunication.
Prior Art
Cables are used for the transmission of communication from one place to another. These cables can be either aerially mounted or burried as per the requirements. For example it is more practical in the rural areas to bury the cables.
The installation of the transmission cables under the ground has been known for a long time. These ducts for the transmission do not have firm grip as the fibre optic cables are made of different materials like plastic, glass and metal which have different coefficients of thermal expansion.
To retain the benefits of speed and capacity of the transmission cables they should be carefully handled and should be protected from the adverse conditions like temperature, pressure and humidity. Transmission cables are usually encased within a thermoplastic sheathing. When installing sheathing must not encounter any sharp surfaces that might damage or shave it away to any substantial degree. If the plastic sheathing is damaged in any way, detrimental exposure of the fragile optic transmission cable occurs.
Previously, during underground installation , transmission cable was pulled through an inner duct. This is taught in U.S. Pat. No. 4565351, wherein smooth wall ducts have the highest coefficient of friction , and therefore require high forces to be used when pulling cable therethrough . As a result, only relatively short lengths of cable can be used before the forces build up to

the point that the cable becomes endangered. Previously, smooth wall conduits were used to hold the fiber optic cables. An example of a smooth wall approach is UK patent application GB225871 wherein an empty conduit with a detachable cable is disclosed for use in underground installation . The conduit is detachable by the release of a jacket which surrounds the conduit. The conduit, which contains the optic fiber cable , and the jacket are formed of the same material
As was disclosed in U.S. Pat. No. 5,087,153 issued to the same inventor as wherein, corrugated ducts when used alone in the standard process of burying ducted cable is very problematic. U.S. Pat.No. 5087153 disclosed that although corrugated duct i.e. transverse ribs, have a lower coeffient of friction than smooth wall ducts, corrugated ducts have relatively thin and non-uniform wall thickness. Moreover, the thin walled corrugations have a tendency to stretch or break during field installation due to their relatively low tensile strength, and wear quickly when transmission cable is pulled therethrough. The flexible nature of corrugated tubing also allowed it to rotate and shear. However, the corrugated ribs provide a very low coeffient of friction and the problems associated with its flexible nature can be overcome by using it as a liner contained within a separate distinct duct.The problems associated with these duct systems are as follows:
a. The effects of thermal expansion /contraction of the duct system.
b. The handling properties of the duct based on its mechanical design.
c. The problems associated with installation of duct under the ground.
d.The integrity of design based on the loads that will be experienced
during adverse atmospheric conditions.
One of the problems faced in the conventional duct is of thermal expansion. If not kept under controlled temperature conditions kinking of the duct at joints, corners or vertical transitions occurs.
Thus the object of the invention is to develop a ribbed duct having a firm grip which prevents the cable from slipping from the duct.

It is the object of the invention to provide a duct which has a strong adherence to the climatic conditions like temperature, pressure and humidity. It is also the object of the invention to develop a process for the manufacture of the ribbed duct overcoming the above drawbacks.
The main embodiment resides in the manufacture of a duct which has spiral ribs to make the grip stronger, provides space for thermal expansion/contraction of cable.
It is still another object of the invention to provide a duct which provides smooth passage of the transmission cables.
Summary of the Invention:-
The present invention relates to the process of making the "ribbed duct" for telecommunication. The duct is made of two layers
1) outer layer which constituting 86 to 96% of the total wall thickness of the
duct. The said outer wall consist of HDPE (high density polyethylene resin),
UVCMB (Ultraviolet Stabilized Colour Master Batch) or color master batch
with ultra violet stabilizer additive.
2) Inner layer constituting 4 to 14% of the total wall thickness of the duct. The
said inner wall consist of high density Polythene, WMB (white master batch),
Regrind (material obtained by crushing rejected ducts generated during start
up and other process rejections) and Silicore (lubricated material comentrate).
A number of ribs are provided on the inner layer of the duct as per requirements. The typical height & the spacing between the ribs is fixed. The ribs are spiral in nature and pitch is as per the requirements. For identification

purposes different color of ducts with different stripe combinations can be provided. Number of stripes will depend upon the requirements.
The said equipments used for the said process are the blender, Extruder A & B, color feeder, Extruder C (striper Extruder), cross arm die head and Die connectors, spiral pitch controller spiral pin assembly, vacuum tank, cooling tank, puller, printer, flame treatment, process control system, red drive.
Accordingly the present invention relates to a spiral ribbed duct for holding the optic fibre transmission cables used in telecommunication comprising :
an outer layer of high density polyethyene (HDPE) and compounding
agents such as Ultraviolet Stabilized Color Master Batch (UVCMB)
constituting 86% to 96% by weight of the total duct;
an inner layer made of high density polyethylene (HDPE), Silicore and
compounding agents such as White Master Batch (WMB) constituting
4% to 14% by weight of the total duct;
a plurality of spiral ribs provided in the inner core of the said inner
layer having a pitch of 1.0 M to 1.3 M +/- 0.2 M to .4 M to provide a
firm grip to the optic fibre transmission cables.
A spiral ribbed duct for holding the optic fibre transmission cables used in telecommunication has an outer layer made of 97-99% High Density Polyethylene and 1-3% compounding agents, the inner layer made of 82-85% of High Density Polyethylene and 15-18% silicore and compounding agents with spiral ribs of the hieght of 0.3 to 0.9 mm with the number of the ribs ranging from 30 to 35.
Accordingly the present invention also relates to a process for manufacturing a spiral ribbed duct comprising steps of:
i. blending HDPE with regrind upto maximum of 10% and loading in the hopper of the first extruder by means of automatic vaccum loading

system wherein Ultravoilet Stabilised Color Master Batch doses the said material through color feeder installed on the said extruder for extruding the outer layer of the said duct;
ii. blending HDPE, Silicore and White Master Batch in a blender, loading the said mixture in the hopper of the second extruder by means of automatic vaccum loading system and extruding the inner layer of the said duct;
iii. blending polymer and White Master Batch or Ultravoilet Color Master Batch in the desired proportion and extruding the said blended material to form the material of stripes;
iv. controlling the stripper extruder temperature of each of the barrels and die of each extruders by means of heater and thermocouples mounted on the said extruder;
v. co extruding the materials in a cross arm die pin assembly wherein HDPE material with UVCMB are fed on one side of the assembly and the layer comes out from the said side of cross arm die pin assembly to form an outer layer, feeding the lubricator from the other side of cross arm die pin assembly at an elevated temperature enabling the inside layer at the outlet fused to the said outer layer, feeding the outer layer fused with an inner layer to a spiral pitch controller provided with a pin insert to obtain a spiral of the desired configuration in the spiral pitch controller, treating the duct surface with flame torch and printing the desired message on the duct.
A process for manufacturing a spiral ribbed duct wherein the programme variable frequency drive is provided with a suitable value of RPM for obtaining the corresponding pitch of the spiral pitch controller and on starting the spiral pitch controller drive, gear motor starts rotating at the RPM programmed in

the drive, which in turn rotates in the shaft as well as the pin insert provided in the said spiral pitch controller.
In the process for manufacturing a spiral ribbed duct the said pin assembley provides grooves in the said pin insert to form ribs on the inside surface of the duct and spiral effect given by the rotating shaft wherein the bush of the spiral pin assembly acts as a journal bearing and helps in smooth rotation of the shaft.
The duct is then passed through a tank fitted with a pair of vaccum pumps to maintain vaccum in the compartments containing chilled water at 10 to 12 deg. C which is fed continuously to the chamber to cool the drawn duct and further through the open cooling tank having overflow holes and drain holes at the front and rear side and a water inlet at the center wherein chilled water is circulated to cool the drawn duct through the tanks having 4 to 8 nylon rollers of desired size mounted on tank having the duct provided on the center and pulled with a puller at a desired speed via the printer and flame treatment for inprocess check of the finished ribbed duct.
Accordingly the present invention also relates to an apparatus used in the process for manufacturing a spiral ribbed duct comprising :
a blender, an extruder having a barrel and a screw wherein the barrel has 4 to 8 zones driven by a DC motor and having a temperature controller, die head and die connector coupled with the said extruder;
means for feeding color master batch dosing unit installed on the extruder consisting of DC motor, screw & the feed section;
means coupled with said main die head for providing stripes to the said duct;

means for co extrusion of materials HDPE with UVCMB when fed from one side, while lubricating material is fed to the said die on the other side fusing the inside layer with the outside layer;
means for connecting simultaneously the main extruder & the co-extruder to the cross-arm die head;
means to control the pitch of the spiral driven by a AC source;
spiral pin assembly comprising a pin, bush, shaft and pin insert threaded on to the said shaft having grooves corresponding to the number of desired ribs in the inner core;
means for cooling the duct with chilled water at 10 to 12 deg.C with at least 3 compartment tank fitted with a pair of vaccum pumps;
means for cooling the duct in an open tank fitted with a minimum of 4 to 8 nylon rollers of desired size mounted on the said tank to keep the duct fully immersed in water;
means to draw / pull the duct at a desired speed from the said control.
The said apparatus used comprises color feeder as the means for feeding color master batch to the extruder, cross arm die head & die connectors as the means for coextrusion of material, striper extruder as the means for connecting simultaneously the main extruder and the co-extruder, spiral pitch controller as the means to control the pitch of the spiral, vaccum tank and cooling tanks for cooling the duct and finally the puller for pulling the duct.
BRIEF DESCRIPTION OF THE DRAWINGS
Fig. 1 illustrates the cross sectional view of the " spiral ribbed duct".

Fig. 2 illustrates the flow chart of the process of preparation of the spiral ribbed duct.
Fig. 3 illustrates the manufacturing set up and the process of the " spiral ribbed duct"
In the Fig. 3 the parts of the manufacturing set up can be well described with the following numerals:
1 - Stand, 2 - Geared Motor, 3 - AC Drive, 4 - Extended Shaft, 5 - Chain Drive, 6 - Pin, 7 - Die Head, 8 - Bush, 9 - Shaft, 10 - Pin Insert.
DETAILED DESCRIPTION OF INVENTION
The present invention relates to the process of making "ribbed duct" for telecommunication comprising the materials and the equiments used.
The said materials used are the HDPE used for outer and inner layer of the Duct, UVCMB is used for outer layer of the Duct, Silicore and WMB are used for inner layer of the Duct. The outer layer constitutes 86-96% of the total wall thickness of the duct. For identification purpose different color of ducts different stripe combination can be provided. No. of stripes and color of stripes will depend upon the customer requirements.
The inner layer constitute 4 to 14% of the total wall thickness of the duct. Number of ribs are provided on the inner layer as per requirement of the customer. These ribs are spiral in nature and pitch is as per the requirement of the customer.
The said equipments used are the blender in which the polymer (HDPE), silicone and WMB are blended and taken to extruder B, the polymer (HDPE) and regrind are blended and taken to extruder A.
The extruder A & B consist of a barrel and a screw. The barrel has 4 to 8 zones depending on the size of the extruder. Heaters are used to heat these barrel zones and blowers are provided on the zones for the purpose of

cooling. The temperature controllers control the temperature of the zones by heating/cooling as required. Additional temperature controllers are provided on the extruder for controlling the temperature of auxiliary equipments like screen changer, Die head, Die connectors etc. The screw is coupled to a gearbox at the rear end. This gearbox is driven by a DC motor through a belt drive. A DC drive provided on the extruder panel controls the speed of the DC motor. An screen "changer assembly (SC) is mounted on the front side. Temperature of this SC is maintained using heaters, thermocouples mounted on it and temperature controllers mounted on the Extruder panel. The colour master batch of the required color gets mixed the HDPE at Ext. A. Molten mass from extruder forms the outer layer and molten mass from Ext. B forms the inner layer of the Duct.
Ext. C (striper extruder) is a smaller version of above extruders used for providing stripes, if required, onto the duct. This extruder is coupled to the main die-head.
The color feeder is a color master batch dosing unit installed on extruder A to feed the color master batch in the HDPE of the outer layer of the Duct. It consists of a DC motor, screw and the feed section. This unit works on a DC drive. The cross arm Die head and Die connectors is a special die head meant for co-extrusion of materials. HDPE material UVCMB is feed on one side, this material comes out through the die as outside layer. Lubricated material is feed to the die on the other side (opposite to the HDPE material feed) and this material comes as inside layer at the outlet fused to the outer layer. Heater bands and thermocouples are mounted on the die. These heaters and thermocouples are connected to the temperature controllers provided on the extruders and the die temperature is maintained with the help of these controllers as desired.
Metal Die Connectors are used to connect the main extruder (Extruder A) and the co-extruder (Extruder B) to the cross arm die head. Temperature of these
connectors is maintained using heaters, thermocouples mounted on it and temperature controllers mounted on the extruder panel.
The spiral pitch controller controls the desired pitch of the spiral. It consists of a stand on which AC geared motor is mounted which is driven by an AC drive. This drives the extended shaft by means of chain drive.
The spiral pin assembly consists of the pin which is a conical piece made of EN-19 and fitted on to the main die head, a bush which is made of brass and fitted onto the pin. This acts as a journal bearing and helps in smooth rotation of the shaft, a shaft is made of SS - 304 material. This passes through the pin and bush. It further gets coupled to the extended shaft of the spiral pitch controller. A pin inert is threaded on to the shaft. It consists of No. of grooves corresponding to the No. of ribs specified by the customer.
This unit controls the formation of spirals and pitch of the spiral can be precisely adjusted by adjusting the controls in this unit. In this the extrusion of "ribbed duct" is started like a normal duct. After achieving the required line speed and required parameters of the duct, enter suitable value of RPM into the programmed variable frequency drive. This value of RPM corresponds to the pitch of spiral required. The pitch of special in meters is equal to RPM of shaft per line speed in meters per minute. At the press of the "start" button on the drive, gear motor starts rotating at RPM programmed on the drive. This motor in turn rotates the shaft as well as the pin insert. The grooves provided into the pin insert from ribs on the inside surface of the duct and spiral effect is given by the rotating shaft.
The vacuum tank is a tank with 3 compartments or chambers. A sizing sleeve along with lub plate of desired size is mounted in the front. Rubber gaskets with desired size bore are mounted between first and second compartment, second and third compartment and at the rear end of the tank. This tank has two vacuum pumps, the first pump is used to maintain the vacuum in the first chamber and the second pump is used to maintain
vacuum in the second and third chamber. Chilled water at 10° to 20° C is feed continuously to the chamber to cool the drawn duct passing through the tank.
The cooling tank is an open tank with an over flow holes and drains holes at the front and the rear side and a water inlet at the center. Rubber gaskets with desired size bore are mounted at the front and the rear end. Chilled water is circulated to cool the drawn duct through these tanks. 4 to 8 nylon rollers of desired size are mounted on the tank so as to position the duct at the center of the tank. The over flow holes are positioned so as to keep the duct fully immersed in water.
The puller is the unit used to draw/pull the duct at the desired speed. It consists of a dual belt conveyor driven by a chain drive, reduction gearbox and an DC motor. A DC drive controls the speed of the DC motor. The top belt conveyor is mounted on a slid and is controlled by a pneumatic cylinder.
The inkject printer is used to print logo and other Alphanumeric messages on the duct. This printer used MEK based ink black die ink or pigmented white or yelow ink. Ducts are marked at every meter. Printing message consists of product description with size, manufacturer's logo and name and any other matter specified by the customer.
The flame treatment is given to the part of surface of the duct meant for printing, by LPG flame torch with a nozzle. This helps in improving the adhesion of the ink onto the duct surface. The process control system ("gravitol" or "co-expert") is used to control the process automatically. This system is based on "weight-loss" priciple. Weight hoppers with load cell are installed on both the extruders to monitor the flow of raw material. Speed sensing system is installed on the puller. All these three units are synchronized through a PC based system, which achieves correct weight per meter of the duct and the required wall thickness.
In this process, the HDPE required for outer layer of duct is blended with regrind of the same color upto maximum of 10% (if available) and loaded in extruder 4 hopper by means of automatic vaccum loading system. UVCMB is dosed in this material through color feeder. Material required for inner layer is blended separately in the "Blender" with required percentages of HDPE, silicone and WMB and loaded in extruder B hopper by means of automatic vacuum loading system. The material required for strips is blended separately in the "Blender" with required percentages of HDPE and white or color master batch and loaded in the extruder C hopper manually. It is confirmed that the required temperatures are attained in the extruder barrel zones and die head before starting the extruders.
The extruders and puller are now started from the control system panel and molten material is joined to the Starter pipe which is previously passed through the cooling tanks, vacuum tank and the puller. Vacuum in the tank and extruder outputs are adjusted till desired quality of ducts obtained in terms of dimensions and surface finish. If stipes are required, striper extruder is started at this point. The suitable value of RPM is entered into the programmed variable frequency drive. This value of RPM corresponds to the pitch of spiral required.
At the press of "start" button on the spiral pitch controller device, gear motor starts rotating at RPM programmed in the drive. This motor in turn rotates the shaft as well as the pin insert. The grooves provided into the pin insert from ribs on the inside surface of the duct and spiral effect is given by the rotating shaft for the required spiral pitch. The flame torch is started and duct surface to be printed is treated. The printer is started with required printing message to be printed onto the duct. The quality of print is checked before coiling. The duct is wound on a collapsible reel with the help of reel drive to form the coils of required length. Before this operation the duct is subjected to online inspection.

We claim :
1. A spiral ribbed duct for holding the optic fibre transmission cables used in telecommunication comprising :
an outer layer of high density polyethyene (HDPE) and compounding agents such as Ultraviolet Stabilized Color Master Batch (UVCMB) constituting 86% to 96% by weight of the total duct;
an inner layer made of high density polyethylene (HDPE), Silicore and compounding agents such as White Master Batch (WMB) constituting 4% to 14% by weight of the total duct;
a plurality of spiral ribs provided in the inner core of the said inner layer having a pitch of 1.0 M to 1.3 M +/- 0.2 M to .4 M to provide a firm grip to the optic fibre transmission cables.
2. A spiral ribbed duct for holding the optic fibre transmission cables used
in telecommunication as claimed in claim 1 wherein the said outer layer is
made of 97-99% High Density Polyethylene and about 1-3% compounding
agents.
3. A spiral ribbed duct for holding the optic fibre transmission cables used
in telecommunication as claimed in claim 1 wherein the inner layer is made
of 82-85% of High Density Polyethylene and about 15-18% silicore and
compounding agents.
4. A spiral ribbed duct for holding the optic fibre transmission cables used
in telecommunication as claimed in claim 1 wherein the height of the said
spiral ribs is 0.3 to 0.9 mm.
5. A spiral ribbed duct for holding the optic fibre transmission cables used in telecommunication as claimed in claim 1 wherein the number of the ribs in cross sectional view ranges from 30 to 35.
6. A process for manufacturing a spiral ribbed duct as claimed in claim 1 comprising steps of:
i. blending HDPE with regrind upto maximum of 10% and loading in the hopper of the first extruder by means of automatic vaccum loading system wherein Ultravoilet Stabilised Color Master Batch doses the said material through color feeder installed on the said extruder for extruding the outer layer of the said duct;
ii. blending HDPE, Silicore and White Master Batch in a blender, loading the said mixture in the hopper of the second extruder by means of automatic vaccum loading system and extruding the inner layer of the said duct;
iii. blending polymer and White Master Batch or Ultravoilet Color Master Batch in the desired proportion and extruding the said blended material to form the material of stripes;
iv. controlling the stripper extruder temperature of each of the barrels and die of each extruders by means of heater and thermocouples mounted on the said extruder;
v. co extruding the materials in a cross arm die pin assembly wherein HOPE material with UVCMB are fed on one side of the assembly and the layer comes out from the said side of cross arm die pin assembly to form an outer layer, feeding the lubricator from the other side of cross arm die pin assembly at an elevated temperature enabling the inside layer at the outlet fused to the said outer layer, feeding the
outer layer fused with an inner layer to a spiral pitch controller provided with a pin insert to obtain a spiral of the desired configuration in the spiral pitch controller, treating the duct surface with flame torch and printing the desired message on the duct.
7. A process for manufacturing a spiral ribbed duct as claimed in claim 6
wherein the programme variable frequency drive is provided with a suitable
value of RPM for obtaining the corresponding pitch of the spiral pitch
controller.
8. A process for manufacturing a spiral ribbed duct as claimed in claim 6
wherein on starting the spiral pitch controller drive, gear motor starts rotating
at the RPM programmed in the drive, which in turn rotates in the shaft as well
as the pin insert provided in the said spiral pitch controller.
9. A process for manufacturing a spiral ribbed duct as claimed in claim 6
wherein the said pin assembley provides grooves in the said pin insert to form
ribs on the inside surface of the duct and spiral effect given by the rotating
shaft wherein the bush of the spiral pin assembly acts as a journal bearing
and helps in smooth rotation of the shaft.
10. A process for manufacturing a spiral ribbed duct as claimed in claim 6
wherein the drawn duct is then further passed through a tank fitted with a pair
of vaccum pumps to maintain vaccum in the compartments containing chilled
water at 10 to 12 deg. C which is fed continuously to the chamber to cool the
drawn duct.
11. A process for manufacturing a spiral ribbed duct as claimed in claim 6
wherein the drawn duct is again passed through the open cooling tank having
overflow holes and drain holes at the front and rear side and a water inlet at
the center wherein chilled water is circulated to cool the drawn duct through
the tanks having 4 to 8 nylon rollers of desired size mounted on tank having
the duct provided on the center.
12. A process for manufacturing a ribbed duct as claimed in claim 6
wherein the puller pulls the duct at a desired speed via the printer and flame
treatment for inprocess check of the finished ribbed duct.
13. An apparatus used in the process for manufacturing a spiral ribbed
duct as claimed in claim 1 comprises of:
a blender, an extruder having a barrel and a screw wherein the barrel has 4 to 8 zones driven by a DC motor and having a temperature controller, die head and die connector coupled with the said extruder;
means for feeding color master batch dosing unit installed on the extruder consisting of DC motor, screw & the feed section;
means coupled with said main die head for providing stripes to the said duct;
means for co extrusion of materials HDPE with UVCMB when fed from one side, while lubricating material is fed to the said die on the other side fusing the inside layer with the outside layer;
means for connecting simultaneously the main extruder & the co-extruder to the cross-arm die head;
means to control the pitch of the spiral driven by a AC source;
spiral pin assembly comprising a pin, bush, shaft and pin insert threaded on to the said shaft having grooves corresponding to the number of desired ribs in the inner core;
means for cooling the duct with chilled water at 10 to 12 deg.C with at least 3 compartment tank fitted with a pair of vaccum pumps;
means for cooling the duct in an open tank fitted with a minimum of 4 to 8 nylon rollers of desired size mounted on the said tank to keep the duct fully immersed in water;
means to draw / pull the duct at a desired speed from the said control.
14. An apparatus used in the process for manufacturing a spiral ribbed
duct as claimed in claim 13 wherein the means for feeding color master
batch is color feeder.
15. An apparatus used in the process for manufacturing a spiral ribbed
duct as claimed in claim 13 wherein the means for coextrusion of material is
cross arm die head & die connectors.
16. An apparatus used in the process for manufacturing a spiral ribbed
duct as claimed in claim 13 wherein the means for connecting
simultaneously the main extruder and the co-extruder to the cross arm die
head is striper extruder.
17. An apparatus used in the process for manufacturing a spiral ribbed
duct as claimed in claim 13 wherein the means to control the pitch of the
spiral is spiral pitch controller.
18. An apparatus used in the process for manufacturing a spiral ribbed
duct as claimed in claim 13 wherein the means for cooling the duct are
vaccum tank or cooling tank.
19. An apparatus used in the process for manufacturing a spiral ribbed
duct as claimed in claim 13 wherein the means for pulling the duct is puller.
20. A spiral ribbed duct for holding the optic fibre transmission cables
used in communication substantially as herein described with reference to
accompanying drawings.
21. A process for manufacturing spiral ribbed duct as substantially as
herein described.
22. An apparatus used in the process for manufacturing spiral ribbed duct
substantially as herein describer with reference to accompanying drawings.