Our objective is to provide our customers with the best value;for optimum performance at the lowest installed cost. To achieve this objective, our sales strategy focuses on the application engineering approach.
Starting with an analysis of your needs and objectives, our application engineers determine the best Spirol ® COMPRESSION LIMITER for the application. Consideration is not only given to the compression limiter but also to the specifications of the components to be assembled and potential assembly problems.Recommendations and samples are provided for your evaluation.The versatility of the Spirol ® COMPRESSION LIMITER makes it the ideal component part to meet the specific eng
ineering and economic objectives of plastic assemblies. Our range of standard compression limiters is designed to meet most requirements. If a special diameter, length, duty, material, tolerance or configuration
is needed, we are ready to assist you.
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THE SPIROL CONCEPT
THE FUNCTION OF A COMPRESSION LIMITER
Compression Limiters are designed to protect the plastic components of an assembly from the compressive loads generated by the tightening of bolts.
The objective is to keep the compressive stresses below the elastic limit of the plastic. In practice, as the bolt is tightened the plastic compresses and the stress in the plastic increases until the head
of the bolt, or washer if one is used, comes into contact with the compression limiter. Thereafter, the compression limiter and plastic
will compress at the same rate. The compression limiter will absorb additional clamping loads without further significant compression
and increased stress in the plastic material.
A properly designed bolted joint must meet the following criteria:•The head of the bolt, or washer if one is used, should
always seat against the compression limiter under load.
This will prevent deterioration of the bolted joint resulting
from diminished clamping load due to plastic creep.
•The compression in the plastic component should not
exceed its elastic limit, when compressed to seat the bolt
against the compression limiter in the worst-case tolerance
condition of the assembly.
•The proof load of the compression limiter should be equal
to or greater than the proof load of the bolt to assure that
the compression limiter will not yield prior to the bolt under
excessive clamping loads.
•The clearance between the maximum bolt diameter and
the minimum installed inside diameter of the compression
limiter should be sufficient to compensate for normal
misalignment.
Standard Spirol® COMPRESSION LIMITERS meet these criteria. The clearance between the bolt and the inside diameter of the
installed compression limiters is adequate to meet normal misalignment. The length and length tolerance is application dependent. The standard tolerance is sufficient to meet most needs, but verification is recommended. Spirol engineering is available to assist in this process. If it is determined that a special compression limiter is required, a documented recommendation
will be provided.
The Spirol range of compression limiters includes both the split seam and solid knurled designs.The
split seam type is produced from carbon steel in heat-treated and non-heat-treated versions. The solid knurled type is produced from brass. Since these compression limiters are designed to meet specified proof loads, the dimensional specifications are different. The split seam design has a lead to facilitate insertion. The solid design has a
pilot, allowing it to stand freely in the hole prior to complete installation.
DETERMINING LENGTH
AND TOLERANCE
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
component, plus the compression of the compression limiter
at the proof load.Stated in formula mode:
Lc min = Lp max – d + c
Where:
Lc min is the minimum length of the compression
limiter
Lp max is the maximum thickness of the plastic
component
d is th
e maximum allowable compression o
f the
plastic component determined as follows:
σ x Lp max
Ep
Where:
σis 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
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 formula mode:
Pclamp x Lp max
Ap x Ep
Where:
Lc min is the minimum length of the compression塑料件的
设计 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:
π
4
Where:
D
1
is the minimum hole in the plastic
component
D
2
is the maximum bearing surface diameter
of the bolt head, compression limiter
head, or washer
Ep is the elastic modulus of the plastic
d =
Lc min = Lp max -
Ap = x ( D
2
2 - D
1
2 )
VERIFICATION OF BOLT SEATING AT RECOMMENDED CLAMPING LOAD
Verification of the seating of the bolt head or washer against the compression limiter at the recommended clamping load is the final assurance that the minimum length tolerance for the compression limiter will meet the recommended bolted joint requirements.Stated in formula mode:
Tmax x Ap x Ep
Lp max
Where:Pc is the load required to assure contact between
the bolt head or washer and the compression limiter
Tmax is the maximum tolerance condition of the
assembly, calculated as the maximum thickness of the plastic component (Lp max) minus the minimum length of the compression limiter (Lc min)
Ap is the stress area of the plastic component as
calculated in the previous element
Ep is the elastic modulus of the plastic Lp max is the maximum thickness of the plastic
component
Pc =
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