Patent Application
20120153650
The present invention relates to lifters used for moving horizontal-axis coils, and in particular to an electromagnetic lifter provided with shaped and adjustable polar expansions. Specific reference will be made hereafter to the moving of horizontal-axis coils, yet it is clear that the present lifter can find application also in the field of moving similar products, such as large-size rounds and tubes with a wide range of diameters.
It is known that the lifters normally used for moving horizontal-axis coils generally consist of a magnet (an electromagnet or an electropermanent magnet) with two symmetrical polarities North/South that extend along the longitudinal axis of the lifter and are arranged to the sides thereof. Said polarities are suitably spaced and involute-shaped so as to fit the largest possible number of diameters of the coils to be moved.
These known lifters have drawbacks caused by the shaping and arrangement of the polarities, which on the other hand are necessary to allow a single lifter to cover a wide range of coil diameters thus permitting the moving thereof.
A first drawback stems from the fact that the above-mentioned structure of the lifter forces it in some cases to operate with quite large air gaps and with reduced areas of contact between the polar expansions and the coil. This compels to design and manufacture lifters that are more powerful, heavier and more expensive in order to take into account these unfavourable operating conditions.
A second drawback is given by the arrangement of the polarities due to which the North-South flux lines, being arranged in planes perpendicular to the axis of the lifted coil that is in the same plane as the lifter axis, are closed tongs-like over the external turns to which the flux is linked thus producing deformations therein. In fact in the coils lifted with this type of apparatus the outermost turns of sheet undergo deformations caused by the magnetic flux, especially when the sheet thickness is <1 mm. In the case of sheet with a higher thickness said alterations remain within the elastic deformation range but they become plastic deformations in the case of lower thickness sheet.
Therefore the object of the present invention is to provide an electromagnetic lifter which is free from said drawbacks. This object is achieved by means of an electromagnetic lifter comprising polar expansions arranged perpendicularly to the axis of the coil to be lifted, divided into two halves slidable with respect to each other under the action of a suitable actuator and shaped so as to be able to penetrate each other.
The fundamental advantage of the present lifter stems from the adjustability of the polar expansions that allows them to better adapt to the different diameters of the coils to be lifted, with the result of exploiting the greatest possible useful polar section and of reducing to a minimum the operational air gap. As a consequence, the lifter need not be oversized to take into account the most unfavourable case and it results smaller, lighter and cheaper (particularly in the case of lifters with electropermanent magnets).
A second significant advantage results from the fact that, thanks to the perpendicular arrangement of the polar expansions, the North-South flux lines are arranged in planes parallel to the coil axis and therefore do not close tongs-like over the external turns to which the flux is linked thus minimizing the risk of producing deformations therein.
Further advantages and characteristics of the lifter according to the present invention will be clear to those skilled in the art from the following detailed description of an embodiment thereof, with reference to the annexed drawings wherein:
Referring first to
It should be noted that although electromagnet 1 described here is preferably bipolar said choice is not binding, since magnets with different numbers of poles properly provided with the required elements can be manufactured by the same principle.
A first novel aspect of the present lifter resides in the fact that each polar expansion 4 is divided into two halves 4a, 4b slidable with respect to each other and shaped so as to be able to penetrate each other, as it will be better described further on. Each of the two halves 4a, 4b has its active surface, i.e. the surface contacting the load, worked with a continuous radius having a value equal to the maximum radius of the coils to be lifted.
The sliding movement is achieved by means of a power-driven mechanism 5, preferably located between the two polar expansions 4, that allows the latter, which slide along dovetail guides 6, to change the profile of their shaping according to the diameter of the coil. For example, mechanism 5 can be of the hydraulic type or with motor-reducers and actuators, and it is possibly controlled by an encoder or other similar device capable of pre-setting the coil diameter and adjusting the polar expansions 4 for lifting the selected coil.
A second novel aspect of the lifter above, as previously mentioned, is the arrangement of the polar expansions 4 in a direction perpendicular with respect to the horizontal axis of the coil to be lifted, as it will be better illustrated in the following.
The electropermanent magnet version of the above-mentioned lifter is illustrated in
In practice, the only differences of lifter 1′ consist in a yoke 2′ having a slightly different shape that houses the conventional magnetic bicomposites 7, 8 respectively formed by Alnico and strontium ferrite or Alnico and rare earths (preferably neodymium). Two solenoids 3′, of copper or anodised aluminium or the like, orientate the two Alnico masses forming the so-called reversible magnetic blocks 7 to switch the electropermanent magnet 1′ between the active state and the rest state.
The adjustment of the polar expansions 4 will now be illustrated in greater detail with reference to
The surface in the central region of the polar expansions 4 starting from the longitudinal axis of the lifter is discontinuous in that each of the two halves 4a, 4b is comb-shaped with equal teeth and a constant pitch. The first half 4a has a shape substantially symmetrical and corresponding with the second half 4b, which has its teeth offset by one pitch so that it can perfectly penetrate the first half 4a.
The sliding movement of the two halves 4a, 4b of the North polarity, which is synchronous with that of the two halves of the South polarity, allows them to adapt to the different diameters of the coils to be moved. The fully extended position of
The total sliding run of the two halves 4a, 4b of each polar expansion 4 is indicatively of the order of 150-250 mm (75-125 mm for each half) in the case of large-size magnets.
The operation of the present lifter is therefore quite simple and effective and is readily understood from the description above and from
The polar expansions 4, after adjustment of the position of the two halves 4a, 4b according to the diameter of the load L to be lifted, get into contact with the horizontal-axis, coil and, upon activation of solenoids 3/3′, the flux lines link to load L as shown in
This novel arrangement assures a coupling between the active surface of the lifter and the coil such that the difference between the maximum and minimum active surface is quite low, namely of the order of 15-20% (maximum useful polar section 100%, minimum 80-85%). This means that the force of the magnet at the extremes of the lifter operating range changes about by the same percentage (15-20%), and the amount of said percentage change is much lower than the amount of the percentage change of known lifters in which the difference in useful polar section can be of the order of 70-80% (max. 100%, min. 20-30%).
As a consequence, a lifter according to the present invention can be designed to have on one hand much higher performance and on the other hand a significantly lower weight and therefore cost. To support this statement, some indicative figures of the quantities being treated are given hereunder to perform a comparison with prior art lifters.
The coils of ferromagnetic steel sheet are produced in a very wide range of characteristics, size and weight, with sheet thickness from 0.2 to 20 mm, external diameter of the coil between 900 and 2600 mm and weight between 2 and 45 t (it should be noted that to the decrease of the coil diameter does not correspond an indicatively quadratic decrease of the weight).
In order to guarantee a safe moving of such a range of coils with a conventional lifter it is necessary to design and manufacture a lifter with polar expansions increased about by 50%, considering that the electromagnet must have an anchorage force equal at least to twice the maximum considered load according to the EN 13155 standard.
This results in a lifter that when designed according to conventional knowledge, for example in the electromagnet version, requires about 15 kW of applied power at 220 V and weighs about 8 t. A similar lifter according to the present invention requires a power of about 12 kW and weighs about 6.5 t, i.e. a 20% decrease both in required power and weight. It should also be noted that the oversizing required to the conventional electromagnet not only proportionally increases the costs but it increases as well the problem of the deformation of the external turns of the coil.
The improvement in performance achieved by the new structure and arrangement of the polarities allows an extremely significant decrease in size and weight, which is particularly useful in the application of the present lifter to automatic storage systems. This fact also allows to build a magnet suitable to move coils of different diameter with absolute safety without being compelled to size the magnet for the most unfavourable case (usually consisting of rather small coils yet with a high weight).
It is clear that the above-described and illustrated embodiment of the lifter according to the invention is just an example susceptible of various modifications. In particular, the exact shape of the two halves 4a, 4b can be different from the above-illustrated comb shape as long as the two parts are complementary, for example the teeth could not all be identical and with constant pitch, and also guides 6 could have a different shape (e.g. T-shaped or the like), while the relevant actuator mechanism 5 could be located at a different position.
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/IT2009/000393 | 9/1/2009 | WO | 00 | 2/29/2012 |
