EP1754300A1

EP1754300A1 - Device for encapsulating parts of electric motors by means of resins, as well as method for using such device

Info

Publication number: EP1754300A1
Application number: EP04729189A
Authority: EP
Inventors: Aurelio Guccione
Original assignee: Mazzali Systems SpA
Current assignee: Mazzali Systems SpA
Priority date: 2004-04-23
Filing date: 2004-04-23
Publication date: 2007-02-21
Also published as: WO2005104338A1

Abstract

A device for resin encapsulation of parts of electric motors or windings or rotors, stators, coils or other similar components, of the type comprising devices for mixing and injection (13, 14) of resin for encapsulating the windings, comprises at least one piston (15) made from elastic material and having a cavity (15’) with a truncated cone cross-section with a greater diameter at the top. A cylindrical expander (18) or punch is inserted in the said cavity (15’) and its downward movement inside the said cavity (15’) of the piston (15) causes the radial expansion of the piston. The said piston can be inserted in the internal diameter (16) of the stator (17) of an electric motor.

Description

"DEVICE FOR ENCAPSULATING PARTS OF ELECTRIC MOTORS BY MEANS OF RESINS, AS WELL AS METHOD FOR USING SUCH DEVICE" TECHNICAL FIELD 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. The use of 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. BACKGROUND ART It is known that various devices and systems are used to carry out the different stages of the construction of electric motors, including the impregnation of the windings (mainly in copper) of the motors, in other words mainly of the stators and the rotors, with the use of special resins. These electric motors are mainly used in' the industrial sector, in the automobile sector, in electronics, in the sector of large motors and generators, of motors for the white goods industry, of alternate and direct current motors, servomotors, etc.. 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. In the absence of impregnation processes 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. Traditional impregnation systems use resins that solidify at temperatures and times varying from 140°C to 200 °C, making it necessary to preheat the actual windings in order to facilitate the penetration of the resin, exploiting the principle of capillarity, and to eliminate traces of humidity and of the added thinner substances from the pieces to be impregnated, before passing on to the curing (polymerization) of the resin at temperatures of around 160-180°C. 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. The advantage of 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. There are other 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 actual impregnation of the winding with resins that polymerize at high temperatures is still traditionally carried out by complete and direct immersion of the various pieces in a bath of polyester and/epoxyphenolic resins. The fundamental problem of this technique is relative to the high costs of the operations (mechanical and on machine tools) for the removal of the polymerized resin from critical parts of the various pieces (external and internal diameters, commutator segment surfaces). There are also two more sophisticated alternative techniques. The first is the so-called "roll-dip" technique, i.e. immersion up to a part of the transverse cross-section and the rotation of the stator and/or rotor around the axis of symmetry for a very precise period of time. 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). Apart from the drop by drop process, all the impregnation techniques seen so far have the common disadvantage of requiring a careful post-impregnation cleaning stage of the electrical connection contacts and of the mechanical coupling areas with special mechanical tools. In particular the brushless motors that work at high rotor rotation speeds are equipped with very delicate parts for the transmission of the torque to the motor shaft (bearings): the freedom of movement of these mechanisms cannot be impaired by traces of resin. The resin must therefore be carefully removed to restore the system to within the initial design tolerances. All this involves not only additional machining costs but also considerable risks of damage, due to the delicate cleaning stage and the production of filings that could pollute the working environment of the operators. Moreover, while, for example, the drop by drop process involves only washing waste (not cleaning/removal of the polymer) of the resin used, in the case of full immersion or roll-dip there is a high level of process waste, with consequent additional machining process costs. But as well as the problem of additional 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, for example styrene, vinyltoluene and diallyl phthalate, are volatile with a high toxicity factor for man: there is exposure to risks connected with the inhalation of their vapors in the workplaces. In addition to their low vapour pressure, which makes them dangerous for the operators, 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. As well as generating yet another additional production cost, 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. Elrom the above description it is clear that the processes currently in use for the impregnation of electric motors do not guarantee a uniform formation of the layer of insulation, are not able to ensure safety features when these motors are used in particularly difficult conditions (flameproof motors), nor even a long life in extreme conditions. It is also evident that the machining times and costs remain inevitably high in order to supply a high quality product, in which it is necessary to provide stators and rotors with features of mechanical compactness and electromagnetic insulation that are notably higher than average. DESCRIPTION OF THE INVENTION 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 dependent claims of the system for the coating and curing of resins on parts of electric motors or windings of rotors, stators and coils describe advantageous embodiments of the invention. The main advantages of this solution concern, first of all, the possibility of developing a new impregnation technique using the so- called room-temperature resins, which solidify at room temperature or just above room temperature. The main objective concerning the use .of a new "room temperature solidification" resin formulation is first of all to eliminate most of the cost due to polymerization by high temperature furnace curing, necessary for the other traditional resins. 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. In particular, to accelerate the polymerization of the resin in less time than at room temperature, a special additive with hardening features is mixed with the resin. Through an endothermic chemical reaction, 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. As regards the greater success of the impregnation process, 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 . In fact, in these cases of considerable power delivery, 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. Moreover, by maximizing the efficiency of the devices for delivery + dosage + mixing of the resin, there is no waste, except for machine down times longer than the pot-life of the mixture, before the formation of the first polymers is triggered, corresponding to the start of the gelling stage (pot-life time), beyond which it is necessary to carry out a washing operation of just the final resin mixing device in order to prevent the hardening of the resin in the relative ducts and mechanisms. Finally, 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.

DESCRIPTION OF THE DRAWINGS Other features and advantages of the invention will become evident from reading the following description of one embodiment of the invention, provided as a non-binding example, with the help of the drawings illustrated in the attached figures, in which: - 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; - figure 10 is a schematic cross-section view of the inner punch; figures 11 to 13 are schematic views of the lower flange, the upper flange and of the spring rod, respectively; - figure 14 is a schematic view showing the type and layout of the units for mixing and pumping the resin towards the injecting nozzles. DESCRIPTION OF ONE EMBODIMENT OF THE INVENTION The system for the coating and curing of resins on parts of electric motors or windings of rotors, stators, coils or other similar components according to the invention foresees the setting up and preparation of a machine comprising a working line with a plurality of stations each of which corresponds to a respective stage for the treatment of a stator, but in the same way also of a rotor or of any electric component in which it is necessary to pot the windings in a resin bath. 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 resiή 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. 3) situated on a automated infeed line. 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. These nozzles 13 and 14 deliver quantities of product using an extremely precise mixing device, designed to dose and mix the resin and the hardener. 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. In particular, 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 ¬

appropriate sliding rod 20'. 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. In particular, to accelerate the polymerization of the resin in less time than at room temperature, a special additive with hardening features is mixed with the resin. Through an endothermic chemical reaction, 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. In particular, 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. Once the resin has been inserted in the cavity of the stator, 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. When the piston 15 reaches the end of its stroke, coming into contact with the base 11 of the pallet, the punch 18 then moves down for a certain distance in the conical housing 15' of the piston 15. The descent of the punch 18 in the conical housing of causes the radial dilation of the piston 15 and the further spreading of the resin on the walls of the stator, at the same time leaving its central part completely free. Once the compression and dilation process carried out by the piston - punch has been completed, the stator moves on towards the subsequent treatment stages, retaining the die inside it. 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. Figure 1 shows the various working stages in which the stators, moving along the conveyor belt, reach an absorption station 24, a gelling station 25, a polymerization station 26, a cooling station 27 and finally a finishing station 28. It should be noted that the expansion of the piston inside the stator makes it possible to keep the entire inner part of the stator completely free of resin, avoiding the need to remove the resin in subsequent stages (No After Work). As regards the greater success of the impregnation process, the innovative technique of compression of the resin by means of the 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 . In fact, in these cases of considerable power delivery, 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. Moreover, by maximizing the efficiency of the devices for delivery + dosage + mixing of the resin, there is no waste, except for machine down times longer than the pot-life of the mixture, before the formation of the first polymers is triggered, corresponding to the start of the gelling stage (pot-life time), beyond which it is necessary to carry out a washing operation of just the final resin mixing device in order to prevent the hardening of the resin in the relative ducts and mechanisms. Finally, 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 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. The invention is described above with reference to a preferred embodiment. It is nevertheless clear that the invention is susceptible to numerous variations that lie within its scope, in the form of technical equivalents.

Claims

1) A device for resin encapsulation of parts of electric motors or windings of rotors, stators, coils or other similar components, of the type comprising devices for mixing and injection (13, 14) of resin for encapsulating the windings, characterised in that it comprises at least one piston (15) made from elastic material and having a cavity (15') with a truncated cone cross-section with a greater diameter at the top, the said cavity (15') accommodating a cylindrical expander (18) or punch, whose downward movement inside the said cavity (15') of the piston (15) causes the radial expansion of the piston; the piston being insertable in the internal diameter (16) of the stator (1 ) of an electric motor.

2) A device for resin encapsulation according to the previous claim, characterised in that the elastic material of which the piston (15) is made consists of plastic material belonging to the Teflon family, with elastic and non-stick features.

3) A device for resin encapsulation according to the previous claim, characterised in that the elastic material of which the piston (15) is made consists of high density charged Teflon._. 4) A device for resin encapsulation according to the previous claim, characterised in that the expander cylinder (18) present inside the piston (15) comes into contact with a spring type elastic device (20), positioned on a sliding rod (20').

5) A device for resin encapsulation according to any of the foregoing claims, characterised in that, in order to cause the radial dilation of the piston (15), the downward thrust of the punch (18) is controlled by a pin (19) activated by known means.

6) A device for resin encapsulation according to any of the foregoing claims, characterised in that the piston (15) - punch (18) unit comprises other 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).

7) A procedure achieved by using the device according to one of the foregoing claims, characterised in that it foresees a first stage in which the cylindrical cavity (16) of the stator (17) is filled with a certain quantity of resin and hardener, in appropriate percentages, by the nozzles (13, 14).

8) A procedure according to claim 7, characterised in that it foresees a second stage in which, once the resin has been inserted in the cavity (16) of the stator (17), the die consisting of the piston (15) is inserted vertically into the cavity, pushing the resin down to the bottom and then upwards, distributing it on the inside of the walls of the stator and its electrical windings. 9) A procedure according to claims 7 and 8, characterised in that it foresees a third stage in which when the piston (15) has reached the end of its stroke, coming into contact with the base (11) of the pallet, the punch (18) moves down for a certain distance in the conical housing (15') of the piston (15). 10) A procedure according to claim 4, characterised in that it foresees a fourth stage in which the descent of the punch (18) in the conical housing (15') causes the radial dilation of the piston (15) and further spreading of the resin on the walls of the stator, at the same time leaving the central part completely free.