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TT
(Thrust & Torque Mounts)
General
The TT mounts are especially developed for the high-powered / low
weight, close coupled engine I gearbox combinations. The unique
mounting design characteristics enables to transmit both Thrust
and Torque forces whilst ensuring excellent vibration isolation.
The TT mounts have a linear stiffness over a wide load range varying
from compression H to extension (+ I necessary to maintain the optimum
isolation properties of the Mass-Spring system formed by engine
/ gearbox and mounts. The close-coupled gearbox reduces the engine
rpm's and as a consequence, magnifies the engine torque. The reaction
torque is being transferred over the TT mounts to the foundation
as additional compression or extension forces which requires the
TT mounts unique linear (compression I extension) stiffness to maintain
the same high degree of isolation.
Specification
The stiffness ration from Vertical (Z) to longitudinal (X) is selected
such to minimize displacements of the installation and connected
equipment in this direction, which for instance is beneficial for
shaftseals. The thrust capacity per mount, related to the actual
mount load (Fl) can be taken from the capacity curves. The height
adjustable TT mounts are produced in a lightweight, seawater resistant
aluminum and among others feature slotted / threaded holes to secure
the mounts during transportation and, or alignment of the engine
installation. The castings are designed such as to protect the interchangeable
rubber inserts from contamination. The central threaded stud enables
easy installation and in the case of a thrust transferring application
of the TT mounts; the recommended tightening torques should be kept.
The TT mounts have an integrated limiter, which limits the displacements
in the vertical direction to +3.1 and -11.5 mm for the TT-I mount
and +3.3 and -6.3 mm for the TT-2 mount. In the horizontal direction
the TT I mount is limited to + or -5 mm and the TT-2 mount to +
or -3 mm. The standard rubber mix NR39 is available from 45°
Sh.A up to 70° Sh.A and can be used up to 90° C continuous
and 110° C peak temperature, furthermore it will ensure low
creep values. The NR 11 mix is available in 45° to 75° Sh.A,
which can be used up to 70° C continuous and 90° C peak
temperature and will ensure higher load capacities. All TT mounts
are marked with the rubber hardness derived from the individual
stiffness test on one side of the top casting.
Technical
Data
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Typical Creep
The
typical creep rate of the TT mounts will vary with compound, rubber
hardness, dynamic loads, thermal loads, and strain. The typical
value for the NR39 compounds will be 3% of the static deflection
increase per decade. For the NR 11 compounds this value will be
4%. 48 hours after loading more than half of the total creep figure
over 20 years will be achieved.
- Thermal
Expansion
The typical thermal expansion rate of the TT mounts will be approximately
0.01 mm / °C increase in height depending on compound, rubber
hardness and strain. The expansion rate is directly related to
the temperature of the rubber element.
- Thermo
Shock
Every temperature exceeding the latest achieved peak temperature
will cause a permanent set of the mount of approximately 0.01
mm / °C in the range from 20° to 90° C. For instance
the first thermal load from surrounding temperature to normal
working temperature will cause an extra set of the deflected height
next to the normal creep. Every time the mount temperature is
raised to the normal working temperature, no extra set will occur.
Once the normal working temperature is exceeded, an extra set
will occur again. The permanent set is directly related to the
temperature of the rubber element.
Download
TT-1 Dimension Specifications
PDF Drawing of mount
Download
TT-2 Dimension Specifications
PDF Drawing of mount
Download TT-3
Dimension Specifications
PDF Drawing of mount
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