 The
recommended maximum length of the compression limiter is
the minimum thickness of the plastic component. The compression
of the compression limiter at the recommended tightening
torque assures that there will always be some compression
on the plastic component.
The recommended
minimum length of the compression limiter is the maximum thickness
of the plastic component, minus the maximum allowable compression
of the plastic components, plus the compression of the compression
limiter at the proof load. Stated in formula mode:
Where:
Lc min - is the minimum length of the compression
limiter
Lp max - is the maximum
thickness of the plastic component
d - is the maximum
allowable compression of the plastic component
determined as follows:
Where:
 -
is the allowable compressive stress, and
Ep - is the modulus of
elasticity, of the plastic specified
c - is the compression
of the compression limiter at the proof load, as
noted in the Spirol specifications
Example:
The plastic component is 14mm +.01/-0.0 thick, made from ABS 30%
glass filled with a maximum allowable compression strength
of 140 MPa and a modulus of elasticity of 5,500 MPa.
The
bolt used is a M6x1 class 5.8
The
compression limiter is BUSH M6 x 14 BK CL200, which
is a non-heat treated steel split seam compression
limiter. The length tolerance is +0.0/-0.15
d=
140 MPa x 14.1mm / 5,500 Mpa = 0.359 mm
c=
14mm x 0.0018 = 0.025mm
Lc
min = 14.1 - 0.359 + 0.025 = 13.77mm
Since
the standard length tolerance of +0.0/-0.015mm
for a split seam compression limiter is less than
the -0.03mm allowable compression, the standard
length tolerance meets the requirements of this
application. |
A
further determination needs to be made to verify that at the
recommended clamping load, the head of the bolt, or washer
if one is used, will seat itself against the compression limiter
at the maximum tolerance condition. Stated in the formula mode:
Where:
Lc mind - is the minimum
length of the compression limiter
Lp max - is the maximum
thickness of the plastic component
Pclamp - is the recommended
clamping load
Ap - is the stress
area of the plastic component calculated as follows:
Where:
D1 - is the minimum hole
in the plastic component
D2 - is the maximum
bearing surface diameter of the bolt head, compression
limiter head, or washer
Ep - is the elastic
modulus of the plastic
Example:
The plastic component is 14mm + 0.1/-0.0 thick made of ABS 30%
glass filled with a maximum allowable compression strength
of 140 MPa ands a modulus of elasticity of 5,5000 MPa.
The
bolt used is a M6x1 class 5.8 with a head diameter
of 12mm. The recommended clamping load for this
bolt is 5.73kN which is 75% of the proof load.
The
compression limiter is a BUSH M6 x 14 BK CL200, which
is a non-heat treated steel split seam compression
limiter. The minimum recommended hole for this compression
limiter is 9.0mm. The length tolerance is +0.0/-0.15.
The
assembly will require a compression
limiter with a length tolerance<+0.0/-0.2
to assume seating of the bolt against
the compression limiter. A standard
14mm +0.0/-0.15 compression limiter
will meet the needs of this application. |
|
RoHS compliant 
