ELECTRICAL TRANSFORMER

TECHNICAL FIELD

The present invention relates to a wheel for electrical transformer and to a resin or oil electrical transformer.

BACKGROUND ART

From time immemorial is known the wheel concept, generally constituted by a element configured to rotate around an hub connected to a support, that is connected to a mean, this mean being configured to move when the rotary element rotates with respect to a surface or floor.

In many technical fields are known damping and load attenuation systems for wheels, for example the suspension of a motorcycle or the pneumatic wheels of a car.

These well-known systems attenuate the transmission of load between wheel and hub or between hub and support.

These damping or attenuation systems, generally comprise springs or pneumatic/liquid devices used for avoiding that a sudden and strong impact of the wheels with the floor comes completely to the hub, with risk of fractures or bendings.

Said damping and attenuation systems allow also to attenuate the vibrations generated by the moveable mean and transmitted to the wheels.

It's generally known the use of pneumatic wheels, made of elastomeric materials and filled with pressurized air, to reduce the mechanical loads acting on the hub by the damping effect of pressurized air.

It's moreover known the use of suspensions or shock absorbers, for example that having metallic springs, to attenuate the load generated by the mean's weight on the wheel hub.

When a moveable mean keeps still for a long period, the use of pneumatic wheels is discouraged, because they are subjected to deformation.

When a moveable mean is parked for a long period is also uneconomic to install complex and costly traditional shock absorbers .

For example, this kind of problem happens with the electrical transformer both with oil or resin. These large apparatuses are generally moved during the installation phase or during maintenance, while during the remaining periods they remain stationary connected to the electric grid.

During these long park periods, the heavy load of electrical transformer is discharged on its supports, hubs and wheels. For this reason these components are often realized, with hard and robust materials.

For example, it's well known the use of transformer wheels made of cast iron, because of its hardness and its resistance to compression.

They are also known wheels realized with nylon in order to reduce the delivery and manufacturing costs, without reducing the compression resistance and the hardness of wheel.

The wheels made of cast iron or nylon are in any case very brittles and they can easily break in case of abrupt collisions of wheels with ground.

Moreover, the hardness of the cast iron or nylon wheels doesn't allow to damp the vibrations generated by the electrical transformer during its functioning, generating consequently noise pollution.

Generally, these kind of wheels are rotary connected to the support or directly to the transformer with hubs realized with iron or steel.

The shape of these hubs is generally similar to a tube or cylindrical to allow the wheel rolling.

The solutions known in the state of the art don't allow to solve the above-mentioned problems in an economic and efficient way, in particular they don't allow to reduce the vibrations and to protect the wheels and the supports in case of collision of the electrical transformer with the ground. More particularly, the solutions known in the state of the art don't solve said problems in a manner that is both economic, safe and easy to be realized.

A long-time felt need in this technical field is that of reduce vibrations and absorb shocks between an heavy vibrating and stationary device, like an electrical transformer, and its wheels positioned on the ground.

Another particularly felt need is that of attenuate the mechanical strains between wheel and support.

DISCLOSURE OF INVENTION

An object of the present invention is to overcome the above- mentioned disadvantages occurred in prior art and to solve the problems existing in the prior art solutions.

According to a first aspect, the present invention relates to a wheel for electrical transformer comprising:

a support connected to an electrical transformer; an hub configured to be connectable to said support, comprising a metallic upper portion and a metallic lower portion coupled each other through at least an intermediate portion made of elastic material suitable for reducing the transmission of mechanical strains and vibrations between said upper and lower portions; a wheel connected to said hub in a rotary manner; wherein, when said hub is connected to said support, said upper and lower portions are respectively positioned above and below said intermediate portion with respect to the ground. In particular, the metallic upper portion, the intermediate portion made of elastic material and the metallic lower portion are joined together to form the hub.

Said hub is configured to be insertable in the support and can comprise blocking means to block the hub to the support and avoid the escape of the hub from the support.

The elastic portion is used for attenuating the transmission of loads between the upper and lower portions and for reducing vibrations.

Said hub may comprise at least a key for avoiding the rotation of hub with respect to the support.

In particular, the elastic material may be an elastomeric material, or a polyurethanic material, or an elastomeric polyurethane, having an hardness comprises between 40 and 100 shore A.

Said intermediate portion may have a minimum thickness comprised between 2 mm and 20 mm.

The volumetric percentage of elastic material of intermediate portion, with respect to the whole volume of the hub, may be comprised between 35% and 85%.

The intermediate portion, and in particular its transversal section, may have a central thickening having a longitudinal develop.

Said upper ^' and lower portions may be connected to said intermediate portion with a joint.

Alternatively, said upper and lower portions may be glued to said intermediate portion.

Alternatively, said upper and lower portions may be vulcanized to said intermediate portion.

This solution allows to attenuate the mechanical strains between wheel and support.

According to a second aspect, the present invention relates to a method of assembling a wheel for electrical transformer comprising a wheel, a support and an hub having metallic upper and lower portions and an intermediate portion made of elastic material, said method comprising the phases of: assembling said upper and lower portions to the intermediate portion with a joint or glueing or vulcanization; inserting the assembled hub in the wheel and in the support; connecting the hub to the support for avoiding an hub disconnection.

According to a third aspect, the present invention relates to a electrical transformer comprising a plurality of wheels according to the present invention.

This solution allows to damp the strains and to attenuate the vibrations between an heavy and stationary device like an electrical transformer and its wheels.

BRIEF DESCRIPTION OF DRAWINGS

Further characteristics and advantages of the present invention will become more apparent hereinafter from the following detailed disclosure of a preferred, though not exclusive, embodiment of the invention, which is illustrated, by way of an indicative, but not limitative, example in the accompanying drawings, where:

figure 1 is a side view of an hub for wheel according to the present invention;

figure 2 is an axonometric view of an hub for wheel according to the present invention;

figure 3 is a sectional view of four different kind of hubs, wherein the section is realized transversally to the rotational axis in an intermediate position between the hub ends;

figure 4 is a side view of a wheel for electrical transformer according to the present invention; figure 5 is a schematic view of a wheel for electrical transformer according to the present invention; figure 6 is an electrical transformer equipped with wheels according to the present invention. DETAILED DESCRIPTION

The following description of some preferred embodiments of the present invention is referred to the drawings.

The following detailed description should not be regarded as being limitative, and the scope of the present invention is defined by the appended claims.

Further, the particular features, structures or characteristics of the described solutions could be combined in any suitable manner in one or more embodiments.

An object of the following described solutions is to provide a preferred embodiment for a wheel for electrical transformer, a method of assembling said wheel and an electrical transformer. With reference to the present description, the term "wheel" is used herein to refer, not only to the round rolling element 40, but also to the system 20 comprising the hub 10, the round rolling element 40 and the support 30. The number next to the term "wheel" helps to understand if the reference is made to the system 20 or to the round rolling element 40.

In a first embodiment of the present invention, there is a wheel 20 equipped with an hub 10, shown in figures 1 and 2, wherein the hub 10 is realized with two metallic portions, one is the upper portion 1 and a second is the lower portion 2, respectively connected to the opposite sides of an intermediate portion 3 made of elastic material.

The group of upper portion 1, lower portion 2 and intermediate portion 3 has an overall substantially cylindrical shape, that is typical of wheel's hub.

The hub 10 allows the rotation of a wheel 40 and is connectable to a support 30.

The support 30 is made of metal, preferably steel, and has the typical U-shaped profile with two transversal holes for allowing the insertion of the hub 10. The support 30 also comprises means for connecting it to the electrical transformer 50, 60.

The wheel 40 is made of a material resistant to heavy loads: cast iron, nylon, nylon enriched with glass fibers, nylon enriched with glass and rubber fibers or other blends of nylon.

The wheel 40 is known per se and will not be described herein in detail.

The hub 10 is connectable to the support 30 and after the connection can't slide along the hub 10 axis.

The wheel 40 is connected in a rotary manner to the hub 10 and is free to rotate within the support 30 and around the hub 10. When the hub 10 is connected to support 40, its axis is substantially parallel to the ground.

The upper 1 and lower 2 portions are preferably made of steel to resist to mechanical loads. Alternatively, said upper 1 and lower 2 portions are made of ferrous metal or other metal alloy.

The intermediate portion 3 is realized with elastomeric material, preferably rubber, more preferably SBR (Styrene Butadiene Rubber) .

Alternatively, the intermediate portion 3 is realized with polyurethane or polyurethane elastomer, preferably Vulkollan®. Vulkollan® is particularly indicated because its elasticity is similar to that of rubber and has a compact structure having a high compression resistance.

Generally, the preferred elastic material for realizing said intermediate portion 3 has an hardness comprised between 40 and 100 shore A, more preferably comprised between 60 and 95 shore A, wherein shore A hardness is a measured value obtained with a type A durometer in accordance with ASTM D2240 standard.

In a particular embodiment of the present invention, the intermediate portion 3 is realized with a plurality of layers (not shown) overlapped to each other and having different hardness, to form the intermediate portion 3.

In a further particular embodiment, said layers are alternated with additional layers (not shown) , preferably made of metal, to form a sandwich structure that is both rigid and elastic. The upper 1, lower 2 and intermediate 3 portions are glued together, or vulcanised together, or jointed together.

In the last case, the intermediate portion 3 has a shape complementary to that of upper 1 and lower 2 portions.

For example, it could be used a dove-tail shape joint, as shown in figure 3D, wherein the intermediate portion 3 has a transversal section having a double dove-tail and wherein the upper 1 and lower 2 portions have transversal sections complementary to said dove-tails, in order to interlock the hub portions together.

In particular, to interlock the hub portions, the upper 1 and lower 2 portions slide on the intermediate portion 3 until they are completely overlapped.

In case of glueing of portions, it can be used cyanoacrylates or epoxy glues.

In a simplified version of the hub 10, the intermediate 3, upper 1 and lower 2 portions are kept joined by means of the support. When the three portions are assembled, and the hub is inserted and coupled with the support, the support itself maintains the portions 1, 2, 3 connected, without glueing, vulcanization or a joint

With particular reference to figures 1, 2 and 3, the hub 10 comprises blocking means 4a, 4b and 4c for avoiding the escape of hub 10 from the support 30.

In particular, due to the vibrations of electrical transformer, the hub 10 can slide and escape from the support 30, generating damages to the system.

For avoiding this inconvenience the hub 10 comprises a rib 4a at a first end, and a blocking system 4b, 4c at the other end. In particular, the blocking system could comprise a nut 4b screwed on a threaded end 4c of the hub 10, as shown in figures 1, 2 and 4.

An alternative blocking system is a gudgeon pin (not shown) coupled to the hub 10 by means of an hole or a groove realized on hub 10.

The first end of the hub 10 can be realized without rib 4a and can be clinched against the support 30 for guaranteeing a permanent coupling. In a particular embodiment, also the other end of hub 10 can be clinched against the support 30.

Furthermore, for avoiding a rotation of the hub 10 with respect to the support 30, the hub comprises one or more key/s 5 insertable in corresponding recess/es of the support 30.

Alternatively, the key/s can be realized on the support 30 and the recess/es on the hub 10.

Preferably the support 30 comprises a recess or a notch (not shown) configured to receive the key 5 and avoid a rotation of the hub 10 with respect to the support 30.

In a particular embodiment at least one end of the hub 10 can be squared while the central body remains cylindrical to allow the rotation of the wheel 40 around the hub 10.

In correspondence of the squared end, the support 30 can have the same shape, in order to create a connection that prevents an hub rotation with respect to the support 30.

In this way, the upper portion 1 remains upward and the lower portion 2 remains downward with respect to the ground. The intermediate portion 3 is substantially maintained parallel to the ground.

The intermediate portion 3 can have transversal sections having different shapes, as shown in figure 3, for providing different damping effects.

A first preferred shape is when the intermediate portion 3 has a substantially flat shape and its section is substantially a rectangle, as shown in figure 3A.

In this case the upper 1 and lower 2 portions are obtained from a metallic cylinder conveniently cut in two parts for receiving the intermediate portion 3.

When the intermediate portion 3 is flat, its thickness is between 2 and 20 mm, in function of wheel 20 diameter and of the loads applied on the hub 10.

Alternatively, as shown in figure 3B, the section of the intermediate portion 3 comprises a central hump that develops longitudinally along the hub 10. Said central hump has a shape substantially proportional to the radial pressure profile acting on the hub 10. In this case, the section of the intermediate portion 3 has two lateral parts having thickness between 2 and 20 mm, while the thickness increases gradually moving toward the centre of the hub 10 section.

As shown in figure 5, when the wheel 20 is assembled and a load 60 is applied over the support 30, the weight of load 60 is discharged from the support 30 to the hub 10 and then from the hub 10 to the wheel 40 and finally from the wheel 40 to the ground.

Since the pressure profiles generated by the contacts hub- support and hub-wheel, acting on the hub 10 in static condition, are arc-shaped, the intermediate portion 3 has a cylindrical shape with two lateral wings as shown in figure 3B.

In a particular embodiment the intermediate portion 3 is a cylinder of elastic material. In this solution the upper 1 and lower 2 portions are two semitubular caps disposed oppositely over the elastic cylinder to form the hub 10. In this case, both caps have individual connection means with the support 30, to avoid their rotation.

These last two solutions dampen the load acting on the hub 10 in a more efficient way, since the intermediate portion 3 has an higher thickness where the load is more concentrated. Preferably,, the intermediate portion 3 separates horizontally and completely the upper portion 1 from the lower portion 2. In another preferred embodiment, shown in figure 3C, the section of the intermediate portion 3 has a Z or S shape, for increasing the contact surfaces between upper 1 and lower 2 portions and intermediate portion 3. An increasing of the contact surface allows a better adhesion of surfaces in case of glueing or vulcanization.

In a particular embodiment of the wheel 20, said upper 1 and lower 2 portions are also connected to each other by means of a metallic strip (not shown) , preferably disposed at one end of the hub 10 or at both ends.

According to the present invention the volumetric percentage of elastic material of the intermediate portion 3 with respect to the whole volume of the hub 10 is comprised between 35% and 85%, more preferably between 50% and 60%.

Another aspect of the present invention is the method of assembling a wheel 20 for electrical transformer 50 having an hub 10 according to the present invention.

Said method of assembling comprising the phases of: assembling the upper 1 and lower 2 portions to the intermediate portion 3 with a joint or glueing or vulcanization in order to obtain an hub 10 configured to be insertable in a support 30 and to receive a wheel 40; inserting the assembled hub 10 in the wheel 40 and in the support 30; connecting the hub 10 to the support 30 for avoiding an hub 10 disconnection.

The hub 10, the support 30 and the wheel 40 are assembled together to form the wheel 20.

The phase of assembling said three portions permits to obtain a single-body hub that is similar, for shape and dimensions, to the common hubs for wheels.

In particular, said phase of assembling with glueing can foreseen a preventive phase of superficial treatment of upper and lower surfaces of intermediate portion 3, and a superficial treatment of bottom surface of upper 1 portion and of above surface of lower 2 portion.

Said superficial treatment can comprise a sandpapering of said surfaces in order to improve their ruggedness and consequently the contact surface extensions useful for adhesion.

Alternatively, the phase of assembling with a joint can foreseen the sub-phases of cut the upper 1, lower 2 and intermediate 3 portions, in order to make them complementary and consequently joinable.

As shown figure 5, an electrical transformer 60 (not completely shown) having wheels 20 discharges its weight W and its vibrations on the hub 10 through the support 30. The hub 10, thanks to its intermediate portion 3 amortizes the weight W and damps the vibrations transmitted, while the upper 1 and lower 2 portions give strength and stiffness to the hub 10.

Similarly, the strains transmitted from the hub 10 to the wheel 40 are reduced and the wheel 40 is less stresses, avoiding possible fractures of wheel 40.

In case of an unexpected increasing of weight force , for example due to the landing of an electrical transformer on the ground, the upper 1 and lower 2 portions move .them closer and the intermediate portion 3 is compressed absorbing at least part of extra weight force, that otherwise it would be completely discharged on the wheel 40.

A further aspect of the present invention is an electrical transformer 50, shown in figure 6, comprising a plurality of wheels 20 according to the present invention.

The wheels of said electrical transformer 50 are preferably four, but can be more.

Being the electrical transformer 50 an heavy and vibrant device, due to its conversional activity, vibrations and weight are completely discharged on wheels 20.

In a particular embodiment of the electrical transformer 50, the wheel 40 is connected directly to the transformer 50, without the typical U-shaped support.

In this particular version, the hub 10 is connected, by means of a flat support (not shown) , to the electrical transformer 50, and the wheel 40 is inserted on the hub 10 embossed with respect to the transformer body.

The present invention overcomes the shortcomings of the prior art by using elastic materials for damping vertical forces and vibrations, and introducing the elastic material directly in the hub, without modifying dimensions or conditions of use of the hub, wheel and support.

It is clear that the wheel for electrical transformer, the method of assembling and the electrical transformer so conceived can be susceptible of various modifications and variations, all covered by the scope of the invention; furthermore all the details are replaceable by elements technically equivalent. In practice, the materials used and the dimensions may be any according to the technical requirements .