Basic Information - ALFRA TMH 50 Manual De Instrucciones

BAsic inFORMATiOn cOnceRning THe HAndLing OF MAgneTic
LiFTing geAR – in pARTicuLAR TML / TMH
The magnetic surface is located on the underside of the lifting magnet incorporating different magnetic poles
which generate the magnetic holding force through magnetic flux when activated. The maximum holding
force that can be achieved depends on different factors which are explained below:
Material thickness
The magnetic flux of the lifting magnet requires a minimum material thickness to flow completely into the
load. Below this minimum thickness of material, the maximum holding force is reduced subject to material
thickness. Conventional switchable permanent magnets have a deeply penetrating magnetic field similar to
tree tap roots, and require a large material thickness to achieve maximum holding force. The compact magnetic
field of TML and TMH magnets is similar to a shallow root and achieves maximum holding force even when
used on thin materials (see performance data in table 2).
Material
Every material reacts in a different way to penetration of the magnetic field lines. The load-bearing capacity
of the lifting magnets is determined using an S235 material. Steels with high carbon content or whose
structure has been changed by heat treatment have a low holding force. Foamed or porous cast components
also have a lower holding force, so that the given load-bearing capacity of the lifting magnet can be
downgraded on the basis of the following table 1.
Table 1
Material
Non-alloyed steel (0.1-0.3% C content)
Non-alloyed steel (0.3-0.5% C content)
Cast steel
Grey castiron
Nickel
Stainlesssteel, aluminium, brass
surfacequality
The maximum holding force of a lifting magnet can be achieved in case of a closed magnetic circuit in which
the magnetic field lines can connect up freely between the poles, thus creating a high magnetic flux. In contrast
to iron, for example, air has very high resistance to magnetic flux. If an air gap is formed between the lifting
magnet and the work piece, the holding force will be reduced. In the same way, paint, rust, scale, surface
coatings, grease or similar substances all constitute a space(i.e. an air gap), between work piece and lifting
magnet. Furthermore, an increasein surface roughness or unevenness has an adverse effect on the magnetic
holding force. Reference values for your TMH 50 can be found in table 2.
Load dimensions
When working with large workpieces such as girders or plates, the load canpartly become deformed during
the lift. A large steel plate would bend downwards at the outer edges and create a curved surface which no
longer has full contact with the bottom of the magnet. The resulting air gap reduces the maximum load-
bearing capacity of the lifting magnet. In contrast to this, nor should objects be hollow or smaller than the
magnetic surface, as otherwise the entire power of the lifting magnet will not be used.
Load alignment
During load transport care must be taken that the lifting magnet is always at the centre of gravity of the work piece
and that load, or lifting magnet respectively, is always aligned horizontally. In this case, the magnetic force of
the lifter acts with its full pull-off strength at right anglesin relation to the surface and the maximum rated load-
bearing capacity is achieved through the 1:3 standard safety factor. If the position of work piece and lifting magnet
changes from horizontal to vertical, the lifting magnet is operated in shear mode and the work piece can slip
away to the side. In shear mode, the load-bearing capacity decreases dependent upon the coefficient of friction
between the two materials.
Temperature
The high-power permanent magnets installed in the lifting magnet irreversibly lose their magnetic properties
from a temperature of more than 80°C, so that the full load-bearing capacity is never reached again even after
the magnet has cooled down. Please note the specifications on your product and in the operating manual.
Magneticforce in %
100
90-95
90
45
11
0
15