Method for producing plate packs

Plate packs are produced from a sheet-like starting product (1), which is cut to form plates, which are stacked to form a plate pack. The plates within the plate stack are joined to one another by a bonding agent. The bonding agent used is a cyanoacrylate adhesive with a high temperature stability rating. It is applied to a wetting layer (14) for the adhesive. The wetting layer (14) is formulated to a pH in a region >7. The cyanoacrylate adhesive with a high temperature stability rating is able to spread on the wetting layer (14) such that effective wetting takes place, thus achieving quick and secure joining of the plates to one another.

BACKGROUND OF THE INVENTION

The invention concerns a method for producing lamination packs in which laminations are cut from a flat starting product and stacked to the lamination pack, wherein the laminations in the lamination stack are connected to each other by a bonding agent.

In electrical machines, sheet metal packs made of stacked laminations are often used which are produced from cut electric sheets or electric strips. For cutting the laminations, usually a punch press with tool or a laser cutting machine is employed. The electric sheets/strips as starting products are in general coated with a thin electrical insulation layer whose thickness is within the μm range. These insulation layers are comprised of organic or inorganic material. Hybrid coatings are also employed which are comprised of organic and inorganic proportions. For the electrical insulation layers, varnishes are employed which are adjusted such that they have a positive effect on the cutting processes and pack assembly method, respectively.

The lamination packs are used for stators and rotors of electrical machines such as electric motors or generators. In order for the laminations lying on top of each other to be connected fixedly to each other within the lamination pack, it is known to connect the laminations lying on top of each other by means of an adhesive. Sometimes, a reliable bonding of laminations lying on top of each other cannot be ensured due to the electrical insulation layers. Sometimes, the reaction time of the adhesive is prolonged. This, for example, has an effect in a punching device in regard to the stroke rate because it depends on the curing time of the adhesive.

The invention has the object to configure the method of the aforementioned kind in such a way that a reliable adhesive connection between the laminations within the lamination pack is ensured wherein the reaction time of the adhesive remains as unaffected as possible by the starting product used for the laminations.

SUMMARY OF THE INVENTION

This object is solved for the method of the aforementioned kind in accordance with the invention in that the bonding agent is a high temperature-resistant cyanoacrylate adhesive which is applied onto a wetting layer for the adhesive that is adjusted such that its pH value is in a range >7.

In the method according to the invention, the wetting layer is applied onto the flat starting product that can be an electric strip or an electric sheet. It ensures that the high temperature-resistant cyanoacrylate adhesive can spread on the wetting layer in such a way that good wetting is achieved. It ensures a reliable and fast connection of the laminations with each other. The wetting layer is adjusted such that its pH value is greater than 7, i.e., is within the alkaline range and the HO−proportion in the wetting layer is sufficiently high. In this way, it is achieved that the curing time or reaction time of the adhesive can be kept short. When a punching device is used, for example, for cutting the laminations, very high stroke rates can then be achieved as a result of the minimal reaction times of the adhesive so that the punching device can operate with a high output. High temperature-resistant cyanoacrylate adhesives are in particular ethyl and allyl cyanoacrylates.

Advantageously, the wetting layer is comprised of dipropylene glycol, distilled and/or demineralized and/or deionized water and, as needed, at least one additive, for example, polyglycol oil. Such a composition of the wetting layer has the additional advantage that it can serve as a lubricant during the cutting process. It has a wear-reducing effect on the punching tool so that the punching tool has a long service life.

Moreover, such a wetting layer has the additional advantage that it protects the starting product against corrosion.

In an advantageous embodiment, synthetic polycrystalline diamond and/or polyglycol oil and/or corrosion protection additives and/or alkaline additives are employed as additives, for example.

The wetting layer contains between approximately 30 and 75% by weight distilled and/or demineralized and/or deionized water and approximately 25 to 70% by weight dipropylene glycol and/or approximately 0 to 20% by weight additives. By means of the proportion of water, the pH value of the wetting layer can be adjusted very easily to the respective application situation so that it can always be ensured that the adhesive will react reliably and properly within very short periods of time.

In a further advantageous embodiment, alkaline additives can assist in pH value determination or adjustment and pH value stabilization. Aqueous solutions are alkaline when the concentration of the hydroxide ions OH−surpasses that of the oxonium ions H3O+. The pH value is then greater than 7.

Advantageously, only distilled or only demineralized or only deionized water is employed for the wetting layer. When all types of water are employed for the wetting layer, then their total proportion is within the specified range of approximately 30 to approximately 75% by weight.

The proportion of the additive or additives in the wetting layer can be between 0 and approximately 20% by weight. When only one additive is employed, then the proportion of water and/or the proportion of dipropylene glycol or of the other additives can be reduced appropriately in accordance with the proportion of the additive.

In an advantageous embodiment, the wetting layer is applied by a spraying method onto the starting product. In this way, it is ensured that the wetting layer is applied uniformly onto the starting product. In this context, the starting product itself is not stressed.

The wetting layer can be applied also by brushing onto the starting product. By means of brushing, the surface of the starting product can be cleaned to a certain degree so that a reliable reaction between the wetting layer and the adhesive is ensured.

The wetting layer can finally also be applied by polishing onto the starting product.

By means of a solid additive, for example, diamond, in the liquid, the surface can be smoothed by means of polishing or brushing. In an advantageous method, only the surface peaks of the insulation layer are removed in the micro range. The insulation effect of the insulation layer is maintained.

It is advantageous when the wetting layer is applied onto the entire surface of starting product. Then the entire starting product is covered by the wetting layer so that an optimal corrosion protection, an excellent lubrication during the punching process as well as an optimal wetting by the adhesive are ensured.

When the wetting layer is applied onto both faces of the flat starting product, the corrosion protection of the starting product is optimal. Also, it is possible in this way to apply the adhesive selectively onto one of the two faces of the starting product.

In an advantageous embodiment, the wetting layer is applied onto the starting product in the advancing direction of the starting product upstream of a punching device or a corresponding cutting device. The subsequent application of the adhesive can then be realized in a simple way and without impairment by application of the wetting layer. In particular, the corresponding application units for the wetting layer and for the adhesive can be configured in a constructively simple way because they are arranged spatially separated from each other.

There is also the possibility to apply the wetting layer onto the starting product by means of at least one application unit which is located in a punching tool. In this case, the facility used for performing the method can be constructed to be relatively compact. In this context, it is also provided that first the wetting layer is applied before subsequently the adhesive is applied onto the wetting layer.

The application unit provided for the adhesive can be provided advantageously at the punching tool. This is advantageous in regard to the short reaction times of the adhesive because only a minimal period of time is required between the application of the adhesive and cutting the lamination and arranging it on the lamination pack. In this way, it is ensured that the adhesive reacts only once the lamination with the applied adhesive is pushed onto the lamination pack.

With respect to high numbers of cycles when producing the laminations, it is further advantageous when the adhesive and the wetting layer are applied onto the lamination immediately prior to or after cutting from the starting product.

In case of a strip-shaped starting product, an advantageous process resides in that the wetting layer, in advancing direction of the starting product, is applied onto the starting product after coating and prior to winding onto a coiler. This has the advantage that only the adhesive must be applied during the cutting or punching process.

In another advantageous process, the wetting layer, when a strip-shaped starting product is employed, is applied in advancing direction of the starting product prior to splitting the strip.

The subject matter of the application results not only from the subject matter of the individual claims but also from all specifications and features disclosed in the drawings and the description. Even if they are not subject matter of the claims, they are claimed as being important to the invention insofar as, individually or in combination, they are novel relative to the prior art.

Further features of the invention result from the additional claims, the description, and the drawings.

DESCRIPTION OF PREFERRED EMBODIMENTS

FIG. 1shows in schematic illustration a device with which laminations2are cut from an electric strip1or an electric sheet in a known manner (FIG. 5). In an exemplary fashion,FIG. 5shows a punch3of a punching device11with which the laminations2are punched from the electric strip1. They are stacked to a lamination pack5in a chamber4of the punching device11. The chamber4extends through a bottom die6of the punching device11. As is known, a braking unit7is located in the chamber4which is of an annular configuration and exerts on the laminations2or the lamination pack5a radial braking force8in the known manner. This braking force is so high that the punch3can push the respectively punched lamination2with sufficient pressure onto the lamination pack5located in the chamber4so that the laminations2lying on top of each other can be fixedly connected to each other in a way to still be described. InFIG. 5, it is shown in an exemplary fashion that, between neighboring laminations2within the lamination pack5, adhesive dots9are located by means of which the laminations2lying on top of each other are fixedly connected to each other.

In addition to the adhesive connection, the laminations2lying on top of each other can also be connected with form fit to each other, for example, by means of raised portions pushed out of the lamination or partially punched-out tongues which engage corresponding recesses or cutouts of the neighboring lamination, respectively.

The lamination pack5is employed for producing rotors and/or stators of electric motors as well as of generators also.

As can be seen inFIG. 1, the electric strip1is coiled on a coiler10that is rotatable about its axis. The electric strip1which is decoiled from the coiler10is guided through a straightening apparatus (not illustrated) by means of which the electric strip1is straightened for the subsequent punching process. Downstream of the straightening apparatus, the electric strip reaches the punching device11in which the laminations2are punched in the described way from the electric strip1.

Also, two or more electric strips1can be guided adjacent to each other into the punching device11so that the laminations2can be punched simultaneously from the individual electric strips1. Furthermore, it is possible to punch the laminations2in the electric strip1not only in one track but, for example, also in two tracks.

The punching device11is provided with one or a plurality of corresponding punching tools in the form of the punches3. The laminations2which are punched by them reach in the described way the chamber4into which the laminations2are pushed by the punch3immediately after punching. The chamber4forms the receptacle for the lamination pack5. The braking unit7ensures that the laminations2are contacting with their edge with friction the inner wall of the chamber4so that they cannot fall out of the chamber4. For each punching stroke, the respectively punched lamination2is pushed downwardly onto the laminations which are already located within the chamber4. A support plunger (not illustrated) is projecting into the chamber4and the laminations2are stacked on it to the lamination pack5. With each punching stroke, the support plunger is moved step-by-step in downward direction so that the respectively punched lamination2can be moved so far downwardly into the chamber4that the subsequent lamination2to be punched can be reliably pushed into the chamber4.

In case of a plurality of electric strips1guided simultaneously through the punching device11, it is advantageous when each electric strip1has correlated therewith one chamber4so that in the punching device11a plurality of lamination packs can be stacked adjacent to each other at the same time. However, there is also the possibility to provide in the punching device11only one chamber4into which the laminations2which are punched from different electric strips1are transported by means of a transport device, for example, a rotary unit, into the area above the chamber4and then are pushed into the chamber4. Such a transport device is in particular advantageous when the laminations2are punched in adjacently positioned tracks from an electric strip1. Then, the adjacently positioned laminations2can be transported with such a transport unit into the only chamber4.

Within the lamination pack5, the laminations2lying on top of each other are fixedly connected by a bonding agent. In the exemplary embodiment according toFIG. 1, the bonding agent is applied by means of an application unit12onto the electric strip1in a known manner, still prior to punching the laminations2. The bonding agent can be applied in different ways onto the electric strip1, for example, contactless by spraying but also by application by means of a drum, a roller and the like. In this context, the bonding agent can be applied areally but also only in dots or strip-like onto the electric strip1. Depending on the size of the lamination2, a different quantity of bonding agent is required in order to connect the laminations2fixedly to each other within the lamination pack5. Preferably, the bonding agent is applied in dots onto the electric strip1.

As a bonding agent, high temperature-resistant cyanoacrylate adhesives are employed. Ethyl or allyl cyanoacrylates are conceivable as such adhesives. They are solvent-free, cold-curing 1-component adhesives which quickly polymerize and cure within a short period of time. These cyanoacrylate adhesives have a high temperature resistance which reaches at least 130° C., preferably up to approximately 150° C. and higher.

Allyl cyanoacrylate can be exposed to even higher temperatures at minimal loads for short periods of time. After approximately two hours, the adhesive connection reaches a temperature resistance up to 250° C. Ethyl cyanoacrylates can also be used for short periods of time at higher temperatures when the loads are minimal.

The electric strip but also electric sheets used for producing the laminations2are provided with a coating13(FIG. 6a) which forms an electrical insulation layer and is present at both faces of the electric strip1. The electric insulation layers13have only a very minimal thickness which is within the μm range. The insulation layers13are comprised preferably of purely organic or purely inorganic materials. However, hybrid coatings can be used also which are comprised of organic and inorganic proportions. Such insulation layers for electric strips1or electric sheets are known and are therefore not explained in detail. For forming these insulation layers13, varnishes are applied onto the electric strip1, which may exhibit different properties that have a positive effect on the cutting methods as well as the pack assembly or stacking of the laminations2.

In order for the cyanoacrylate adhesive to ensure a reliable connection of laminations2lying on top of each other in the lamination pack5, a wetting layer14is applied onto the insulation layer13. It is configured such that a good wetting action is achieved with the cyanoacrylate adhesive, the pH value at the surface is >7, and the OH−proportion in the water is predominant. Due to the good wettability of the wetting layer14, the adhesive drops do not form individual drops but spread areally on the wetting layer14. In this way, it is ensured that the laminations2within the lamination pack5are connected reliably and fixedly to each other.

The wetting layer14in the embodiment according toFIG. 1is applied in the region between the coiler10and the punching device11on both faces of the electric strip1by means of an appropriate application unit15. The application can be realized by spraying, by brushing, or by polishing with the corresponding medium.

For producing the wetting layer14, a lubricant is employed that contains dipropylene glycol as well as distilled and/or demineralized and/or deionized water. A preferred composition of the lubricant is:30 to 75% by weight distilled and/or demineralized and/or deionized water 25 to 70% by weight dipropylene glycol.

Depending on the application situation, the lubricant can contain additionally polyglycol oil whose proportion can amount to between 0 and 20% by weight. When polyglycol oil is contained in the lubricant, the proportion of dipropylene glycol and/or of distilled and/or demineralized and/or deionized water can be reduced correspondingly.

As polyglycol oils, in particular polyethylene glycols (PEG), polyalkylene glycols (PAG), and polypropylene glycols (PPG) are conceivable. The pH value of the polyglycol oils is within the alkaline range, i.e., above 7. Since the pH value of the wetting layer14is in the alkaline range, not only proper bonding of neighboring laminations2can be achieved in connection with the good wettability but also a very short curing time. In this way, high numbers of units can be achieved in the production of the laminations2or the lamination packs5. Due to the use of the wetting layer14, curing times of approximately one second can be achieved.

The additional lubricant has moreover further advantageous properties. For example, it can be used for increasing the tool service life in the punching process. Moreover, the lubricant serves for cooling the punching process.

In combination, the use of the described lubricant thus results in an effective wear reduction of the punching tools and in an improvement of the energy efficiency in the punching process due to the cooling action.

The described lubricant is water-soluble so that it is easy to handle. The wetting layer14also acts to inhibit corrosion. The electric strip1or also the electric sheet exhibits no corrosion even after weeks.

The described lubricant has moreover an excellent viscosity index. The viscosity of the lubricant decreases only minimally with increasing temperature so that it ensures constant properties even at higher temperatures.

In the described way, the lubricant contains deionized or also demineralized water. Also, a completely desalted water can be employed. Demineralized water can be obtained in a simple way from normal tap water by means of ion exchangers.

When completely desalted water is employed as an additive to polyglycol oil, the degree of purity is measured by measuring the conductivity. The conductivity measuring devices required for this are known. The lower the conductivity, measured in S/cm or μS/cm, the fewer contaminants are contained in the water.

In order to achieve an optimal corrosion protection as well as excellent lubrication properties, the electric strip1is advantageously covered across its entire top and bottom faces by wetting layers14. Due to the areal application, the punching tool of the punching device11is lubricated and cooled by means of the wetting layer14. During the punching process, the wetting layer14is distributed by the corresponding punching tool across the cut surface in the electric strip1or in the electric sheet so that the cut surface is protected against corrosion.

FIGS. 7a, 7band 8a, 8bshow in a schematic illustration wetting layers14which comprise abrasive and fillers or solid bodies16, for example, diamond grains. The fillers16are provided in distribution in the wetting layer14. In addition to the described advantages of the wetting layer14, an optimization, i.e., a reduction of the surface roughness of the laminations2, is obtained by addition of the fillers16. This optimization or reduction is the result of the punching process, as will be explained in more detail with the aid ofFIGS. 9 to 10. In the embodiment according toFIG. 7a, 7b, the fillers16project slightly past the wetting layer14(seeFIG. 7a) while in the embodiment according toFIG. 8a, 8bthey are embedded completely in the wetting layer14(seeFIG. 8a).

FIG. 9shows schematically a guide plate of a tool top part as well as a tool bottom part18of the punching device11. Both tool parts17,18each have a flat pressure side19,20.

The electric strip1or also the electric sheet with the wetting layers14applied to both its faces and the fillers16contained therein is resting on the pressure side20of the tool bottom part18. The tool top part17is spaced from the electric strip1. It is moved in the direction of arrow21(punching direction) downwardly in the direction toward the tool bottom part18. The fillers16in the wetting layer14secure during the punching process the electric strip1. As can be seen inFIG. 10in greatly enlarged illustration for the tool bottom part18, this is caused in that the fillers16which project partially past the top side of the wetting layer14get hooked in the pressure side20of the tool bottom part18as a result of the roughness of the pressure side20. In the same way, also the fillers16get hooked in the roughness peaks of the pressure side19of the tool top part17.

The described guide plate of the tool top part17can be provided in the punching tool itself. In principle, there is also the possibility of providing the guide plate separate from the punching tool in the punching device11.

In the process according toFIG. 1, by means of the application unit15the wetting layer14is applied onto both faces of the electric strip prior to adhesive application. The additional lubricant polyglycol oil of the wetting layer14ensures that the good lubrication properties are effective in all punching operations. By means of the wetting layers14on both faces of the electric strip1, a reproducible and reliable reaction of the cyanoacrylate adhesive as a result of the alkaline wetting layer14is also ensured. The cut surfaces which are produced during the punching process at the electric strip1are covered by the wetting agent in the described way so that these cut surfaces are protected against corrosion.

While in the embodiment according toFIG. 1the application unit12for the adhesive is provided at the punching tool, the application unit15for the wetting layer14is also provided, together with the application unit12for the adhesive, at the punching tool in the embodiment according toFIG. 2. By means of the application unit15, the wetting layer14is applied onto both faces of the electric strip1that is decoiled from the coiler10. The application of the material of the wetting layers14is realized prior to the adhesive application. In this way, it is ensured that the cyanoacrylate adhesive can react reliably.

FIG. 3shows schematically a further embodiment in which the application of the wetting medium and of the adhesive is carried out within the braking unit7of the punching device11. In this case, onto the punched laminations2first the wetting layer14is applied and subsequently the adhesive is applied. The wetting layers14provide a high corrosion protection, also of the cut surfaces that are produced at the lamination by punching. On the wetting layers14, the cyanoacrylate adhesive can react reproducibly and reliably. InFIG. 3, the application units12and15for the adhesive and the wetting layer material are again only schematically illustrated. The electric strip1is decoiled from the coiler10.

FIG. 4shows in schematic illustration the lamination pack5which is located within the braking unit7. In the braking unit7, at least one cooling circuit22is accommodated by means of which a cooling medium23is conveyed in order to cool the lamination pack5. The cooling medium is located in a tank24. Since the lamination pack5is formed in the braking unit7in the described way, there is sufficient time available in order to cool the laminations2or the lamination pack5and also to activate the cyanoacrylate adhesive. When the lamination pack5is removed from the braking unit7, the laminations2are fixedly and reliably connected to each other.

FIG. 11shows in schematic illustration a device with which the wetting layer14can be applied to the electric strip1. The electric strip1is supplied coiled onto a coiler10′. The electric strip1is guided through a schematically illustrated straightening apparatus25with which the electric strip is straightened in the known manner. The electric strip1reaches subsequently a coating device26in which the coating13(FIG. 6) is applied onto the electric strip1on both faces. In advancing direction of the electric strip1downstream of the coating device26, at least one application unit15is provided with which the wetting layer14is applied onto the coating13in the described way. The application unit15is provided such that it applies the wetting layer14to both faces of the electric strip1. Subsequently, the electric strip1with the coating13and the wetting layer14is wound onto the coiler10. It is then moved to the punching device11with which the laminations2are punched and stacked to the lamination pack5in the described way.

FIG. 12shows schematically a device in which the electric strip1is decoiled from the drum10′ and guided through a splitting device27. The electric strip1, in contrast to the embodiment according toFIG. 11, is already provided with the coating13. The electric strip1in advancing direction upstream of the splitting device27is provided by means of an application unit15with the wetting layer14. In the splitting device27, the electric strip1is split across its length in the known manner. The thus produced electric strips are coated on both faces, provided with the wetting layer14and are wound onto the coiler10, respectively. The coiler10is then moved to the punching device11, with which the laminations2are punched and the lamination packs5are produced in the described way.