Basic Information - ALFRA TML 500 Mode D'emploi

BASIC INFORMATION CONCERNING THE HANDLING OF MAGNETIC
LIFTING GEAR, IN PARTICULAR TML
The magnetic surface is located on the underside of the lifting magnet incorporating multiple magnetic poles
which generate the magnetic holding force 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 deep penetrating magnetic field similar to tree
tap roots, and require a large material thickness to achieve maximum holding force. The compact magnetic
field of the TML magnets is similar to a shallow root and achieves maximum holding force even when used on
thin materials(see table 2 in this operating manual).
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 alow carbon material. Steels with high carbon content or
whose structure has been changed by heat treatment have a lower 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 table1.
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
Most stainless steels, aluminium, brass
Surface quality
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 a kind of "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, or an air gap, between work piece and lifting
magnet. An increase in surface roughness or unevenness also has an adverse effect on the magnetic holding
force. Reference values can be found in the performance table of your lifting magnet.
Load dimensions
When working with large workpieces such as girders or plates, the load can deform 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. Hollow objects or those smaller than the magnetic surface will also result in less holding
power being available.
Load alignment
During load transport, care must be taken that the lifting magnet is always at the center 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 breakaway force perpendicular in relation to the surface, and the maximum rated load-bearing
capacity is achieved with the 3:1 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 will begin to lose their magnetic properties
irreversibly from a temperature of more than 80°C (180°F), 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 or in the
operating manual.
Magneticforce in %
100
90-95
90
45
11
0
19