Classifications

• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
  • B29C—SHAPING OR JOINING OF PLASTICS; SHAPING OF MATERIAL IN A PLASTIC STATE, NOT OTHERWISE PROVIDED FOR; AFTER-TREATMENT OF THE SHAPED PRODUCTS, e.g. REPAIRING
  • B29C70/00—Shaping composites, i.e. plastics material comprising reinforcements, fillers or preformed parts, e.g. inserts
  • B29C70/68—Shaping composites, i.e. plastics material comprising reinforcements, fillers or preformed parts, e.g. inserts by incorporating or moulding on preformed parts, e.g. inserts or layers, e.g. foam blocks
  • B29C70/72—Encapsulating inserts having non-encapsulated projections, e.g. extremities or terminal portions of electrical components

Definitions

• This invention concerns a device for the resin encapsulation of electric motor parts or on windings of. rotors, stators, coils, or other similar components, and a procedure for the use of this device. More specifically, this invention refers to a system and to a plant for the impregnation of electric motor windings that makes use of a special resin belonging to the category of "room temperature cure” polyester resins, so called because they solidify within a few hours at room temperature, in order to encapsulate electric motors.
• This device in such a plant makes it possible to achieve a progressive infiltration of the resin inside the windings, according to a process of reascent and volumetric compression inside a special structure that exploits the principle of communicating areas, involving the use of a specific quantity of resin according to the various sizes of the motors.
• This invention can be applied in the sector of special encapsulation and potting impregnation systems for brushless motor stators and/or servomotors and/or special motors, with the use of "Room Temperature Cure" type polyester resins.
• the process of impregnating the windings is indispensable to ensure first of all the electrical and thermal insulation between the wires of the winding of both the rotor and the stator, but also, and more in general, to create a wrapping that blocks the wires so as to prevent their movement with respect to each other.
• the armature in the stator is affected by the presence of numerous Lenz forces that are established following the passage of current in the rotor. As a result, dangerous vibrations are generated on the stator windings, with the risk of short circuits and explosions.
• the impregnation machines known to background art can be of various types according to the different products to be processed, the different production lines (manual, palletised, robotised) and the different resins involved in the impregnation process.
• the impregnation process generally consists of the following traditional standardised stages: 1. the evaporation of the volatile organic substance, added as a thinner for the resin in order to reduce its viscosity and facilitate the treatment; 2. the preheating of the resin in order to trigger the process of reticulation of the chemical bonds; 3. the supply of thermal energy (either by means of a chemical agent or by direct application of heat) to ensure the formation of the long chain polymer, in other words the saturation of the reticular structure that makes the resin solid.
• the preheating stage can be carried out by thermoventilation in furnaces at a temperature of 100-130°C: in the case of motors with an overall weight varying from a few kg (4-10 kg) up to 800 kg, this stage lasts an average of 20 minutes for small sized motors up to 1 hour for the larger sizes.
• this technique is certainly the uniformity of the temperature throughout the winding, but it requires a fairly long period in the furnace for each piece.
• preheating techniques such as, for example, by passing current through the electric windings, by Joule effect: this method does not, however, allow a uniform distribution of the temperature in the various zones of the motor stator and/or rotor, causing temperature differences between the windings and the external commutator segments of the motors of up to 180-200 °G. This means a non-uniform polymerization process on the various products, compromising the quality of the finished product.
• the second is the "drop by drop” system, which in approximate terms can be described as dripping of the resin but only on the critical parts of the windings, until excellent coverage of the heads is achieved and, above all, of the inner cavities of the windings.
• the next stage is the process of gelling + polymerization which, for the resins currently in use, must take place at temperatures of around 1 0-180°C, for a period of 18-20 min., (to achieve excellent values of Bond Strength between the resin and the winding the polymerization time is extended up to 30 minutes, above all for rotor components that are stressed by the centrifugal force and temperature effects).
• the drop by drop process involves only washing waste (not cleaning/removal of the polymer) of the resin used
• the high level of process waste with consequent additional machining process costs.
• the high quantity of resin waste when traditional impregnation methods are used also involves considerable danger to the environment if one considers that the resin, being a long-chain polymer, and thus having a high degree of viscosity, usually needs to be diluted with special solvents in order for it to be handled at an industrial level.
• the solvents normally used are volatile with a high toxicity factor for man: there is exposure to risks connected with the inhalation of their vapors in the workplaces.
• the waste from the resins used in the various impregnation processes currently employed must be disposed of, respecting the regulations in force, for example by thermodestruction, thanks to which the volatile organic substances are burnt at 950°C and made inert.
• these processes cause atmospheric pollution and the emission of these substances, in closed and open environments, must respect precise regulations delegated mainly to the regional authorities.
• This invention proposes to provide a system for the coating and curing of resins on parts of electric motors or windings of rotors, stators, coils, or similar, that can eliminate or at least reduce the disadvantages described above.
• the invention also proposes to provide a system for the coating and curing of resins on parts of electric motors or windings of rotors, stators and coils that is easy to carry out so as to prove economically advantageous. This is achieved by means of a system for the coating and curing of resins on parts of electric motors or windings of rotors, stators and coils whose features are described in the main claim.
• the system for encapsulating stators is designed to perform a gradual infiltration of the resin inside the windings, according to a process of reascent and volumetric compression inside a special structure which exploits the principle of communicating tanks and involving the use of a specific quantity of resin according to the various sizes of the motors. All this is possible thanks to an appropriate system of airtight encapsulation of the part being impregnated, achieved by inserting a piston in the internal diameter of a normal stator, whose subsequent radial expansion allows uniform penetration of the resin even in the most hidden cavities, totally eliminating process waste.
• the system therefore foresees various stages for the various working cycles and resin treatments in controlled temperature environments, thus helping to improve the process in terms of reducing process times and of quality of the finished product.
• a special additive with hardening features is mixed with the resin.
• this hardener provides the mixture with the heat necessary to considerably reduce the polymerization time from _ of an hour to just over half an hour.
• the system according to the invention foresees two successive working stations, in which the mixture for the casting and filling of the relative zone is prepared in the first, and the right conditions needed to further reduce the polymerisation, based on slight increases of the temperature with respect to room temperature, are achieved in the second stage in special furnaces.
• the machinery will be equipped with a device for extremely precise mixing, designed for the dosing and mixing of the resin and the hardener, providing a resin that be polymerized in just over half an hour, if placed in environments at a temperature of 40-45 °C at the most, extremely limited compared to the temperature involved in traditional impregnation processes.
• the polymerization process is then speeded up in environments at a temperature only slightly higher than room temperature, with much lower industrial costs for temperature control, both in the preheating stage and the subsequent cooling stage. This cooling stage can be carried out in much less time than when starting from temperatures of around 180°C, as is the case with traditional techniques.
• the innovative technique of compression of the resin by means of a sort of conical die that expands radially offers numerous possibilities of improvement in the quality of the finished product. Thanks to a deeper infiltration of the resin in all the microcavities and even in those of the stator commutator segments, the entire structure acquires greater protection against mechanical stress and a better degree of saturation of the entire space in which the windings are housed, favouring a better thermal exchange with the exterior of the motor, fundamental in extreme working conditions, and thus a considerable production of heat from inside the motor itself .
• a further advantage of the expandable die device is that, even when the dimensions of the stators to be treated vary, the number of necessary dies is considerably reduced thanks to the features of reversibility to the deformation of the material chosen for the die piston: a material which as much as possible, in fact, must resist the deformation suffered at each stage of the process.
• - figure 1 is a schematic plan view of the overall system according to the invention
• - figure 2 shows a cross-section of the pair of nozzles designed to deliver the quantity of resin and of solvent in the stator windings
• - figure 3 is a schematic view of the stator in which the resin is about to be injected
• - figure 4 is a schematic view of the same stator in which, at a subsequent stage, the die is inserted
• figure 5 is a schematic view of the stator and of the radially expanded die
• - figure 6 is a schematic view of the part according to the detail Z in figure 5
• figure 7 is a schematic view of part of the pallet
• - figure 8 is a schematic cross-section view of the insertor body assembly
• - figure 9 is a schematic cross-section view of the insertor body
• the system according to the invention uses a special resin, belonging to the category of "room temperature cure” polyester resins, which have the feature of solidifying in the space of a few hours at room temperature, to carry out the Potting and Encapsulation of electric motors.
• the system used to encapsulate the stators foresees the progressive infiltration of the resi ⁇ inside the windings, according to a process of reascent and volumetric compression inside a special structure that exploits the principle of communicating tanks. This structure involves the use of a specific quantity of resin according to the various sizes of the motors.
• the system comprises a station 10 (fig. 1) for the manual insertion of the stators in a vertical position and their clamping on an appropriate fixed base 11 of the pallet (fig.
• the system foresees two successive working stations, in which the mixture for the casting and of the relative area is prepared in the first, and then the conditions appropriate to further reduce the polymerization time, based on slight increases of the temperature with respect to the room temperature are achieved in special furnaces.
• the system according to the invention is equipped with an injection station 12 which comprises a pair of nozzles 13 and 14 for the injection of the mixture consisting of amounts of resin combined with amounts of solvent or reagent.
• the nozzles 13 and 14 comprise spiralled end tubes that form the end part of the mixing heads.
• This mixing device provides quantities of resin that can be polymerized in just over half an hour, if placed in environments at a temperature of 40-45 °C at the most. All this is possible thanks to an appropriate airtight system of encapsulation of the part to be impregnated, achieved by the insertion of a piston 15 (figs. 3 and 4) in the internal diameter 16 of a normal stator 17.
• the piston 15 is made from a sufficiently elastic material to allow its subsequent radial expansion, which on one hand permits correct penetration of the resin even in the most hidden cavities, and on the other allows the total elimination of process waste.
• the piston 15 is made from a plastic material of the Teflon family, which is a considerably elastic material with non-stick features and according to a preferred embodiment of the invention this piston is made from high density charged Teflon.
• the piston 15 presents a cavity 15' with a truncated cone cross-section with a greater diameter at the top so as to accommodate a cylindrical expander 18 or punch.
• Figures 8, 9 and 10 clearly show the conformation and arrangement of the piston 15 and punch 18 components.
• the downward thrust of the punch 18, controlled by a pin 19 activated by known means, causes a radial dilation of the piston 15.
• the expander cylinder 18 present inside the piston 15 is located against an elastic spring type device 20 or similar, positioned on an - In ⁇
• the piston 15 - punch 18 unit comprises further structural components including an upper flange 21 and a lower flange 22, while the upper part of the punch is closed by a flange 23 with a central threaded hole for the screwing in and fixing of the control pin 19.
• the system therefore foresees various stages in which the various work cycles and treatment of the resin are carried out in controlled temperature environments, helping to improve the process in terms of reducing the process times and of the quality of the finished product.
• a special additive with hardening features is mixed with the resin.
• this hardener provides the mixture with the heat necessary to considerably reduce the polymerization time from _ of an hour to just over half an hour.
• the impregnation process consists of the following stages: 1. evaporation of the volatile organic substance, added as a diluent for the resin in order to reduce its viscosity and make the process treatment easier; 2. preheating of the resin due to the triggering of the process of reticulation of the chemical bonds; 3. provision of thermal energy (either by a chemical agent or by direct application of heat) to ensure the formation of the long chain polymer, i.e. the saturation of the reticular structure that makes the resin solid.
• the process according to the invention for application of the resin in the stator windings foresees a first stage in which the cylindrical cavity 16 of the stator 17 is filled with a certain quantity of resin and hardener, already mixed in appropriate percentages by the nozzles 13 and 14.
• the die consisting of the piston 15 is also inserted into the cavity, pushing the resin down to the bottom and then upwards, distributing it on the inside of the stator walls and of the electrical windings.
• the punch 18 then moves down for a certain distance in the conical housing 15' of the piston 15.
• the entire structure acquires greater protection against mechanical stress and a better degree of saturation of the entire space in which the windings are housed, favouring a better thermal exchange with the exterior of the motor, fundamental in extreme working conditions, and thus a considerable production of heat from inside the motor itself .
• the dissipation of heat has a great effect on the performance: the better the thermal exchange with the exterior, the lower the temperature inside the motor and the greater the performance that can be obtained from the motor.
• Figure 14 shows the type and layout of the units for mixing and pumping the resin towards the injecting nozzles.
• the pumping units comprise planetary roller type peristaltic pumps 29 and 30 which, connected in groups of 2 for each component, are staggered in the working position of the rollers. This ensures continuous delivery even in the presence of minimum quantities to be pumped.
• the mixing heads positioned in correspondence with the injectors 13 and 14 are made from special plastic material and are designed to keep the two pumped components separate until they come into contact and start to be mixed in the spiralled end tubes which form the end part of the mixing heads.

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• Chemical & Material Sciences (AREA)
• Engineering & Computer Science (AREA)
• Composite Materials (AREA)
• Mechanical Engineering (AREA)
• Manufacture Of Motors, Generators (AREA)

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• 2004
  • 2004-04-23 EP EP04729189A patent/EP1754300A1/de not_active Withdrawn
  • 2004-04-23 WO PCT/IT2004/000229 patent/WO2005104338A1/en not_active Ceased

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