Grommet properties#
This section describes the properties of grommet as modelled in DAVE.
MBL#
The typical configuration of a grommet and terminology is shown below:
The MBL of a grommet is referred to a twice that of the parts (IMCA defines the breaking load as 12 times that of the unit ropes and a correction for spinning losses). This is the MBL of a grommet “when used in standard configuration”. This means it is 2 times the MBL of rope that is it made off, neglecting friction.
Bending losses and losses due to friction are not considered in this definition. DAVE does account for those when determining the maximum allowed (bending losses) and occuring (friction) tension in the rope.
References:
IMCA defines the MBL (CRBL) as 12x that of the unit-ropes. This corresponds to 2x the CRBL of the parts (each have 6 outer unit ropes). For the WLL, IMCA considers the bending factor which depends on the application.
BS/EN defines the MBL / SWL as 2x that of a the parts
Length and length definition#
The length of a grommet is defined either by its “ultimate length”, “nominal length” or “Circumference length”
Length of slings and grommets is measured by inserting pins in both ends and pulling the item taut (under a low tension).
The nominal length is then the distance between the insides of the eyes or the outside of the pins.
The ultimate length is the distance between the insides of the eyes or the outside of the pins for a hypothetical situation where the pin radius (r) is zero.
The circumferential length is the length as measured over the centerline of the grommet.
Nominal length#
For nominal length the diameters of the pins are prescribed in the IMCA and EN13414 standard and are copied below for convenience:
Cable diameter [mm] |
Pin diameter [mm] |
|---|---|
60…150 (EN) |
300 |
151…250 |
500 |
251…375 |
750 |
376…500 |
1000 |
Note that these pin sizes are a recommendation only. Supplier/manufacturer and purchaser may decide to deviate from these values.
Circumference length of grommets#
According EN-13414 the length of a grommet may also be defined as “The length of a grommet shall be the length of its circumference, measured along its centreline”.
Note
When performing length variations, for example as required for DNV, DAVE applies the variation on the ultimate length for slings or circumference length for grommets.
Splices, mass and stiffness#
DAVE assumes that the whole grommet rope has the same properties. A spliced section is not accounted for.