Timken Super Precision Bearings for Machine Tool Applications

A
ENGINEERING
DUPLEX BALL BEARINGS
Back-to-Back Mounting, DB or (“O”)
(Contact angles diverging toward shaft centerline)
Before mounting, there is clearance between the two adjacent
inner ring faces. After mounting, these faces are clamped together
to provide an internal preload on each bearing. This arrangement is
well-suited for pulleys, sheaves and other applications where there
are overturning loads and also all floating positions where thermal
expansion of the shaft occurs. It also provides axial and radial
rigidity and equal axial capacity in either direction when used in
a fixed location. Back-to-back is the most commonly used of all
duplex arrangements. Timken pairs for back-to-back mounting
should be ordered as DU. Example: 2MM207WI-DU. Also available
as two single flush-ground bearings, e.g., -SU (two bearings).
DB
Marked faces
of outer rings
together
method of assembly or disassembly occurs from its use. Timken
pairs for face-to-face mounting should be ordered as DU. Example:
2MM212WI-DU. Also available as two single flush-ground bearings,
e.g., -SU (two bearings).
Tandem Mounting, DT
Before mounting, the inner ring faces of each bearing are offset
from the outer ring faces. After mounting, when an axial load is
applied equal to that of twice the normal preload, the inner and
outer ring faces are brought into alignment on both sides. This
arrangement provides double axial capacity in one direction only.
More than two bearings can be used in tandem if additional axial
capacity is required. Timken pairs for tandem mounting should be
specified as DU. Example: 2MM205WI-DU. Also available as two
single flush-ground bearings, e.g., -SU (two bearings).
DT
One marked and
one unmarked
outer ring face
together
Clearance
between
inner ring faces
Inner ring faces
clamped together
These inner and
outer ring faces
are flush
Inner and
outer ring faces
not flush
on either side
Under axial load
equivalent to
twice the normal
preload. Inner and
outer ring faces
are flush
on both sides
Before Mounting
Mounted
Fig. 83. Back-to-back bearing assemblies before and after mounting.
Face-to-Face Mounting, DF or (“X”)
(Contact angles converging toward shaft centerline)
Before mounting, there is clearance between the two adjacent
outer ring faces. After mounting, these faces are clamped together
between the housing shoulder and cover plate shoulder, providing
an internal preload on each bearing. This arrangement provides
equal axial capacity in either direction as well as radial and axial
rigidity. Since the face-to-face mounting has inherent disadvantages
of low resistance to moment loading and thermal instability, it
should not be considered unless a significantly more convenient
DF
Unmarked faces
of outer rings
together
Before Mounting
Mounted
Fig. 85. Tandem bearing assemblies before and after mounting.
Other Mountings
Flush-ground (DU) pairs may be mounted in combination with a
single flush-ground bearing as a “triplex” (TU) set shown below.
Also shown below is a “quadruplex” (QU) set where three bearings
in tandem are mounted back-to-back with a single bearing. These
arrangements provide high capacity in one direction and also a
positively rigid mounting capable of carrying a moderate amount
of reverse thrust.
Clearance
between
outer ring faces
These inner and
outer ring faces
not flush
Inner and
outer ring faces
clamped together
Faces flush
on both sides
TU
QU
Fig. 86. Typical triplex and quadruplex bearing mountings.
Before Mounting
Mounted
Fig. 84. Face-to-face bearing assemblies before and after
mounting.
98 TIMKEN MACHINE TOOL CATALOG