| Title of Invention | FLEXIBLE MEMBRANE GLANDPLATE |
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| Abstract | The flexible membrane gland plate according to this invention comprises a close celled cross linked polyethylene foam (XLPE) (1) as the core material and the polyurethane foam (PU) (2) of density 170 kg/m3 as the outer two stratums as shown in Figures 2a and 2b. Since the structure of PU is open celled it is prone to ingress of moisture (high permeability). To avoid this, a thin film of micro porous Polyurethane film (F), with a thickness of about 30 μm to 60 μm is bonded on the exposed area of PU foam by a process of hot lamination at 160°C. The gland plate configuration is sandwiched between two GFRP (Glass Fiber Reinforced Plastic) laminates of about 1 to 1.5 mm thickness. The cable is adapted to be inserted into the gland plate by means of guide pins having a conical edge for fixing onto the cable and inserting through the foam sandwich of the gland plate. Fig 2a |
| Full Text | Field of invention The present invention relates to a gland plate used to pass incoming or outgoing cables to and from a switchboard, specifically a flexible membrane gland plate sandwiched with GFRP laminate. Background of the Invention Gland plates are used essentially to pass incoming or outgoing cables to or from a switchboard. It provides necessary support for the cables and also protection against entry of any foreign objects. Current solutions for gland plates in switchboards enable users to pass cables through well-defined cutouts or through guide ways in the form of cable glands. Current solutions existing in the market for Type 2 enclosures impose constraints on the user under the following circumstances, when IP 30 (so as to disallow any solid objects of diameter 2.5 mm or more) has to be respected. i. Restriction is imposed against usage of same cutout locations to pass cables of different sizes at a later stage keeping ingress protection in context, ii. When plastic or sheet metal gland plates are used it is cumbersome for the user to make cutouts at any given location that the user prefers, iii. IP values would not be respected if at a later stage cables are to be removed and the hole that is formed due to cable insertion is not plugged so as to prevent ingress of foreign objects. In the present scenario various types of gland plates primarily made of sheet metal, rubber and plastics are widely used in switchboards. Figures la-lh show some of the prior art gland plates. Sheet metal gland plates (Fig lb) either have a precut for passing cables or is cut by installers as per necessity. Moreover, different types of rubber or metallic grommets (Fig 1c, Id) axe used with sheet metal to ensure required degrees of protection while passing the cables. Multi seal insert (Fig lg) is a type of rubber grommet, which is used in metal gland plates for the secure entry of several individual cables into a single cable gland. For passing cables of different diameter through a same hole stepper collar (Fig lh) is used and it is required to cut off at the required level to match the cable diameter. For passage of cables arranged in a line, two different pieces of metal gland plates are used (Fig le). Foam is provided to seal and allow passage of cables between two gland plates. Rubber gland plates (Fig la) have predefined locations for the passage of cables. The cables are passed through the hole of the corresponding diameter in the required location. Plastic gland plates (Fig If) are also similar to the rubber and metal gland plates; these have precuts to pass the cables. For all of the available solutions, either there are predefined locations or users need to cut the plate to pass cables, which becomes a difficulty. Apart from all these it is also required to respect IP values even when the cables are removed (in case of change in configuration of devices) without any insert to plug the hole formed by the insertion of the cable. US 6 323 433 discloses a grommet for engaging any of a plurality of wire or cable diameters to provide a substantially sealed interface between the wire or cable and an interconnected structure. The grommet is an integral one-piece member formed of a highly elastic material such as neoprene. US 4 504 699 discloses recoverable articles which can provide environmental sealing of elongate substrates such as connections between electrical wires. A device is disclosed for enclosing at least part of an elongate object for example one or more electrical conductors, which comprises a hollow dimensionally recoverable article which is capable of enclosing the object and which has an aperture that communicates between the interior and the exterior of the article, and a quantity of material which, at least after the article has been recovered, seals the aperture but which can be penetrated by a probe, the material being self-sealing so that it will seal the aperture after removal of the probe. The self-sealing material may be silicone rubber or other elastomeric materials. However, these self-sealing materials have less tear strength and compression and higher indentation forces. Thus, IP 30 protection cannot be provided by said self-sealing material adopted in the above prior art. US 3 584 888 discloses a gland for electric cables comprising a grommet of resilient material having a tapered axial hole which is distended by a cable when forced into the gland so that radial pressure is exerted on the cable whereby a fluid-tight seal is formed between the grommet and the cable. The grommet has a reduced diameter portion which is encircled by a collar, which can be tightened to constrict the cable so that axial displacement of the cable is prevented. US 2007/0023198 Al discloses a gland for supporting one or more cables an annular gland body defining a hollow passage that is open at either end. A core is insertable into and removable from the passage via at least one of their ends. The core includes a resiliency deformable member that can be caused, by compression, to expand to occupy the passage. The gland body includes one or more formations to.which said cable inserted into the passage is securable thereby to permit insertion and removal of the core or components relative to the gland body without the core straining any of the cables. Another significant drawback of installing cables carrying more than 1000A current into metal sheets is that eddy current may occur and create overheating of the plate. IP30 and IP55 ratings require that all cables should be entered through one hole or each cable should be entered separately using IP55 cable glands and through non¬magnetic stainless steel plate. If the incoming cable is through a gland plate, then, in order to avoid loop effect, the gland plate should be taken in 2 parts and the cables should be placed between the two plate. The disadvantages of the above prior art patents are that there are restrictions against usage of the same cutouts to pass cables of different sizes at a later stage. Moreover, the seals mentioned therein are not strong enough to withstand ingress of foreign body while in the cable inserted position or in the cable removed position. IP values will be violated if at a later stage the cables are to be removed without using any insert to plug the hole. Therefore, there is still a need for a cable gland, which would satisfy all the above requirements, said gland is required to be having high tear and compression strength with low indentation force with flame retardant properties in case of any fire emergencies during operation. Objects of the Invention It is therefore the object of the invention to provide a gland plate to be able to pass cables of cross section of 20 mm2 to 240 mm2 in a predefined area. It is a further object of the invention to provide a gland plate to be able to use the same cutout locations to pass cables of different diameters at a later stage keeping ingress protection (IP 30) in context. It is a further object of the invention to provide a gland plate wherein insertion of cables is made with the aid of guiding pins or incisors. It is a further object of the invention to provide a gland plate wherein, even after the removal of the cables (in case of change in configuration of devices) no insertion is required to plug the hole created by the cables. It is a further object of the invention to provide a gland plate, which will prevent elements like dust or rodents from entering inside the switchboard. Brief Description of the Invention The present invention discloses a flexible gland plate for passing of incoming or outgoing cables to or from a switchboard, junction box, or other electrical devices. The invention is based on the concept of sandwich structure of foam, as it gives the necessary phenomenon to eliminate gaps at different levels during cable insertion. The behavior of each constituent material was analyzed to derive at the required combination of foam sandwich. The critical mechanical and thermal properties required to make the right combination are density, tear strength, indentation force, resilience, compression set, hardness and flammability. The interaction of these properties with each other was studied to derive at the desired solution. Six sigma tools such as GLM (Geometric Linear Modeling) and Regression Analysis come in handy to aid the design process while deriving at different combination of the foam sandwich. Based on the above research, the gland plate according to the present invention comprises a close celled cross linked polyethylene foam (XLPE) as the core material and the polyurethane foam (PU) of density 170 kg/m3 as the outer two stratums as shown in Figures 2a and 2b. Since the structure of PU is open celled it is prone to ingress of moisture (high permeability). To avoid this, a thin film of micro porous Polyurethane film, with a thickness of about 50yum is bonded on the exposed area of PU foam by a process of hot lamination at 160°C. The use of this film also helps in giving the foam sandwich a good appearance on the exposed area besides providing protection to PU foam against any environmental hazards. The use of PU foam increases the temperature withstand capability of the foam upto about 120°C. Besides it ensures easy insertion of cables and also guarantees the required degree of protection even when the cables are removed due to its remarkable resilience. The XLPE foam as the core material provides the necessary stiffness and better permeability against water and air. To prevent the membrane from any damages due to rodents the PU foam can be added with a special additive mixture of NEWARC grade Master batch Anti rodent granules. The invention also discloses guiding pins designed to the required cable sizes. These guiding pins have conical edge that can be fixed and then directed through the foam sandwich. Brief Description of the drawings Fig la to lh shows the gland plates used in the prior art Fig 2a shows the exploded view of the various layers of the gland plate according the present invention Fig 2b shows the assembled view of the various layers of the gland plate according to the present invention. Fig 3a and 3b shows the gland plate sandwiched between two layers of GFRP laminates. Fig 4 shows the guiding pins that are used for easy entry of the cables onto the foam sandwich. Fig 5a, 5b and 5c show the schematic of the assembly of the gland plate of the present invention along with cables and guide pins onto the switchboard. Detailed Description of the Invention Referring now to the drawings wherein the showings are for the purpose of illustrating a preferred embodiment of the invention only, and not for the purpose of limiting the same, The concept of sandwich structure of foam gives the necessary substrate property to eliminate gaps at different levels during cable insertion. The suitable foam material for a gland plate is desirable to have high mechanical strength (tear strength, hardness); low compression set, flame retardant property and high temperature withstand capacity. But the material with low compression set cannot have higher mechanical strength. Table A below shows the material properties of different elastomers and foam materials, which could form as one of a constituent material in the foam sandwich. TABLE A : Individual material Properties of different elastomers and Foam General Properties Natural Rubber Neoprene Nitrite Urethane Rubber Ethylene Propylene Silicone Polyethylene Foam ACTIFOAM Hardness (Shore A) 20-90 10-95 20-95 10A-80D 30-90 10-85 40-60 40 Specific Gravity (Base Material) 0.93 1.23 1.0 1.06 0.86 1.1-1.6 0.18±0.03 0.35-0.40 Tear Resistance Good Good Fair Excellent Good Poor Good Excellent Compression Set Good Fair to Good Good Good Good Fair Good Excellent Flame Retardant Property Fair Low Good Good Fair to Poor Fair Good Excellent Temperature Range (°C) -55 to +90 -40 to +100 -40 to +100 -25 to +100 -50 to + 150 -60 + 200 -40 to +105 -40 to +160 After analyzing the individual material properties, a combination of seven different configurations of foam sandwich were fabricated and tested as per ASTM D-3574 standards. The seven combinations are as follows Configuration details A. PU Film (50jum) + Pofyurethanel70 + Polyethylene!70 + PolyurethaneHO + PU film (50(im). B. Nitrite + PolyurethanellO + Nitrite C. PolyurethaneHO + Polyethylene Fire grade 120D + PolyurethanellO D. Nitrite + Polyethylene60 + Nitrite E. Nitrite + Polyethylene40 + Nitrite F. Nitrite + Conductive Ethylene Vinyl Acetate 70 + Nitrile G. Nitrile + Actifoam + Nitrile The test results of all these seven combinations are shown in Table B. It is evident as per the results tabulated in Table B that the configuration with the least indentation force, high tear strength and compression set with optimum hardness would be most desirable. For configuration C the compression set is less, which may not be sufficient enough to give a required IP30 protection after removal of cable. Also, for these two configurations hardness number is comparatively less to give enough stiffness to withstand the cable weight and cable bending force. In case of configuration D, E and F the tear strength is high but indentation force and hardness number are also very high which can create difficulty to pierce the gland plate while passing the cable. So these configurations cannot be selected. In configurations A and G, harness, tear strength and indentation force is optimum to give required strength and compression set is good enough to give IP30 protection. After analyzing these results, which included cost analysis it was concluded that configuration G is the best to satisfy all requirements for an IP30 gland plate. Experimentally, it has been observed that it can give the required protection even after removal of cables. Configuration A also holds good to meet the required compression set and strength. It is not very efficient like configuration G but it is also a potential cost effective solution to meet the requirements of an EP30 gland plate. Hence configuration A and configuration G are selected solutions and explained in detail in the remaining part of this specification. Configuration A This configuration of the gland plate according to an embodiment of the invention is illustrated in Figure 2a of the accompanying drawings. The said configuration of the gland plate comprises a close celled cross linked polyethylene foam (XLPE) (1) as the core material and the polyurethane foam (PU) (2) of density 170 kg/m3 as the outer two strarums as shown in Figures 2a and 2b. Since the structure of PU is open celled it is prone to ingress of moisture (high permeability). To avoid this, a thin film of micro porous Polyurethane film (F), with a thickness of about 30 jj, m to 60 // m is bonded on the exposed area of PU foam by a process of hot lamination at 160°C. The use of this film (F) also helps in giving the foam sandwich (1, 2) a good appearance on the exposed area besides providing protection to PU foam (2) against any environmental hazards. The use of PU foam (2) increases the temperature withstand capability of the foam upto about 120°C. Besides it ensures easy insertion of cables and also guarantees the required degree of protection even when the cables are removed due to its remarkable resilience. The XLPE foam (1) as the core material provides the necessary stiffness and better permeability against water and air. To prevent the membrane from any damages due to rodents the PU foam can be added with a special additive mixture of NEW ARC grade Master batch Anti rodent granules. Adhesive (modified acrylic special sensitive adhesive) cold lamination process has been used to bond the layers XLPE foam (1) and PU foam (2) as shown in Figure 2b. The overall thickness of the flexible membrane gland plate (G) has been achieved after analyzing the effect of key functional parameters of each configuration with variation in thickness. The thickness of the XLPE foam (1) layer is about 4-6 mm and the thickness each of the top and bottom layers of the PU foams (2) is about 11-14 mm, thereby giving a total thickness of about 15 to 20 mm. Also, the constraints imposed by the technical specification have been considered during optimization of membrane thickness. Significantly, the PU foam (2) can be mixed with a special antirodent additive, for instance, Masterbach antirodent granules, to prevent the membrane from any damages due to rodents. The above-mentioned gland plate configuration is now sandwiched between two GFRP (Glass Fiber Reinforced Plastic) laminates of about 1mm thickness. Figures 3a and 3b shows the details of the GFRP sandwich panel. The thickness of the GFRP Laminate (5) was fixed at 1mm after performing a structural analysis based on the maximum loading conditions under which the panel could be subjected to. The said GFRP laminate (5) act as reinforcement for the gland plate (G). Such a reinforcement material is a bi-directional woven E-glass fiber with an ultraviolet isopthalic polyester based resin forming the matrix material, fabricated in a 60-ton compression-molding machine. After the post curing process the laminates are marked with necessary dimensions and cut to required profile. The laminate is cut to the required profile to ensure enough surface contact for bonding the GFRP and foam sandwich. Subsequently the two faces are bonded with the aid of Epoxy based adhesive capable of transmitting shear and axial loads to and from the sandwich core. The entire panel is then allowed to cure under room temperature. For bulk manufacturing, Resin Transfer Molding (RTM) process can be adopted as it proves to be more economical and have good control over reinforcement orientations. Open edges on sandwich panels can be sealed to prevent moisture and dust ingress, to enhance appearance or permit subsequent fixings. In this case an edge filler method has been used to close the edges. This additional operation of edge closure would not be required when adopting RTM technique. The exposed area of the sandwiched foam in the GFRP panel forms the zone for cable entry. This panel can be installed along with a base column either on the top or bottom of the switchboard or any Low and Medium voltage enclosures employing cable insertion for connecting devices. Figures 4a and 4b show guide pins (4) that aid in easy entry of the cable. The cables are fixed onto the guide pins, which are made for the required cable sizes and these guiding pins, having a conical edge (4a), can be fixed to the cable and then directed through the foam sandwich. Figure 5a to 5c show the assembly of the cable onto the gland plate according to the present invention. The cable (3) is inserted into the guide pin (4) and they are together pressed into the flexible membrane gland plate (G) comprising the GFRP plate (5) and the foam sandwich (6). The closed cell structure of the XLPE foam (1) aids in reducing the permeability of air and moisture. Fig 5c illustrates the assembly of the gland plate onto a switchboard frame (F). It should be noted that on removal of the cable from the gland plate (in case of change in configuration of devices) no insertion is required to plug the hole created by the cables since no hole is created due to the inherent property of the flexible membrane of the gland plate which has excellent indentation force withstanding capacity. Thus IP30 parameters are respected and the said assembly overcomes all the limitations of the prior art as mentioned earlier in the specification. The invention also foresees the use of a core material, which has a negative Poisson ratio that would yield extraordinary results in achieving the functional requirements. Negative Poisson ratio occurs when the material expands laterally when stretched and contract when compressed. WE CLAIM 1. A flexible membrane gland plate for the entry of incoming or outgoing cables wherein said gland plate comprises: a layer of closed celled cross linked polyethylene foam; said closed celled cross linked polyethylene foam layer being sandwiched between top and bottom layers of polyurethane foams; and a thin film of micro porous polyurethane film in the thickness of 30^m to 60 /J. m is bonded on the exposed area of said polyurethane foam.. 2. The flexible membrane gland plate as claimed in claim 1, wherein the thickness of the gland plate is 15-20 mm. 3. The flexible membrane gland plate as claimed in claim 2, wherein the thickness of the closed celled cross linked polyethylene foam is 4-6 mm and the thickness each of the top and bottom layers of the polyurethane foams is 11-14 mm. 4. The flexible membrane gland plate as claimed in claim 1, wherein the said gland plate is sandwiched between at least two layers of GFRP laminates for purpose of entry of the cable either from top or bottom of the switch board. 5. The flexible membrane gland plate as claimed in claim 4, wherein the GFRP laminate has a thickness of 1-1.5 mm. 6. The flexible membrane gland plate as claimed in claim 5, wherein the reinforcement material is a bidirectional E-glass fiber with an ultraviolet isopthalic polyester based resin forming the matrix material. 7. The flexible membrane gland plate as claimed in claim 5, wherein the cable is adapted to be inserted into the gland plate by means of guide pins, said guide pins having a conical edge for fixing onto the cable and inserting through the foam sandwich of the said gland plate. 8. The flexible membrane gland plate as claimed in claim 1, wherein the said polyurethane foams is mixed with an antirodent additive to prevent the gland plate from any damages due to rodents. 9. The flexible membrane gland plate as claimed in claim 8, wherein the antirodent additive is preferably a Masterbach antirodent additive. |
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| Patent Number | 269418 | ||||||||||||
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| Indian Patent Application Number | 1562/CHE/2008 | ||||||||||||
| PG Journal Number | 44/2015 | ||||||||||||
| Publication Date | 30-Oct-2015 | ||||||||||||
| Grant Date | 20-Oct-2015 | ||||||||||||
| Date of Filing | 26-Jun-2008 | ||||||||||||
| Name of Patentee | SCHNEIDER ELECTRIC INDUSTRIES SAS | ||||||||||||
| Applicant Address | 35 RUE JOSEPH MONIER,F-92500 RUEIL MALMAISON | ||||||||||||
Inventors:
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| PCT International Classification Number | H01M 027/26 | ||||||||||||
| PCT International Application Number | N/A | ||||||||||||
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PCT Conventions:
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