KISSsoft Tutorial: Keyway/Key 1 Starting KISSsoft K ISSsoft Tutorial ...

KISSsoft Tutorial: Keyway/Key
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For release 10/2008
kisssoft-tut-003-E-key.doc
Last modification 23.10.2008 14:42:00
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KISSsoft Tutorial 003: Keyway/Key
1.1 Starting the software
1 Starting KISSsoft
Start KISSsoft using „Start/Programme/KISSsoft 10-2008/KISSsoft“. The following window will
appear:
1.2 Select calculation
Figure 1.1-1: Start KISSsoft, KISSsoft main window.
Using the Module tree window Tab “Modules”, select the keyway/key calculation:
Figure 1.2-1: Selecting calculation module “Keys”.
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2.1 Task
2 Analysis of a key
A key is to be analysed with the following key/load data (see DIN 6892, example 1):
Shaft diameter
120mm
Outer diameter hub D1 200mm*
Outer diameter D2
270mm
Width for diameter D2
within the carrying length, c 17mm
Distance a0
96mm
Key
DIN 6885.1 A32x18x125
No. of keys 1
Chamfer shaft
None
Chamfer hub
0.8mm
Nominal torque
4’000Nm
Maximal torque
15’000Nm
Application factor 1.50
Frequency of peak load 10’000
Frequency of change in sense
of rotation 250’000
Slowly alternating torque,
Material hub
GG25
Material key
C45
Material shaft
C60
Carrying length ltr
125-32=93mm
* Since ther are 10 holes in part 1 (64mm diameter) to accommodate the elastic elements of the
coupling, the hub is less stiff under torsion. Hence, for the calculation, the pitch diameter is used
and not the outer diameter of the hub.
There are two analysis methods available in KISSsoft for keys:
- DIN 6892, Method C
- DIN 6892, Method B
Method C according to the DIN standard is a simplified method and will not be considered here.
Hence, DIN 6892, method B should be selected under the “Module specific settings” after starting
the module:
Figure 2.1-1: Selecting, DIN 6892, method B as analysis method.
The following material properties are to be used:
Yield strength Re [MPa]
Ultimate strength Rm [MPa]
EN-GJL-250 (GG25 brittle) 130 200
C45 K (cold drawn) 430 680
1C60 N (normalised) 310 600
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Figure 2.1-2: Assembly of the connection, with the left half of the connection to be analysed.
2.2 Entering the data
This data is to be entered as follows:
Figure 2.1-3: Definition of D2, D1, a0 and c.
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Important:
Selection of
calculation method
Key form to be
selected, details of
geometry are
defined
automatically with
the shaft diameter,
see Figure 2.2-3.
Choose „Own
Input“ for the
materials, see also
Figure 2.2-4
Figure 2.2-1: Input window - Definition of loads and main dimensions.
The detailed geometry as shown in Figure 2.1-2 is to be entered as follows:
Figure 2.2-2: Input window, group: ‘geometry’ - Definition of geometry of hub with different outer diameters.
The value for width of outer diameter D2 over in the carrying length c, can be specified by the
setting the flag in the “Checkbox” for this.
The geometry of the key is shown using the “Plus button”, see marking in Figure 2.2-2:
The detailed geometry of the key is defined from the
type of key selected and the shaft diameter. It is also
possible to define own key geometry.
Figure 2.2-3: Information on the key selected.
The material data has to be defined using the “Plus button” to the right of the selection list (Select
“Own Input” first).
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Definition of key material. Define
ultimate and yield strength. The value
for the permissible pressure is only
relevant for the calculation method
according to Niemann.
Material type is to be chosen correctly.
Since this is a brittle material, the
permissible stresses will be calculated
based on the ultimate strength of the
material and not on the yield strength.
Definition of shaft material
2.3 Execution of analysis and protocol
Figure 2.2-4: Defining the materials.
Pressing in the Tool bar the icon “Ó” (or the button F5) in the main window starts the calculation
and some results are shown in the lower section of the main window (such as resulting pressures
and safety factors). Note the status bar shows “Results are consistent”. This shows that the input
data and the results shown correspond.
The analysis of the key is according to DIN 6892. The calculation is especially suitable for static
loads, but also for pulsating and alternating loads. However, usually the shaft is the critical element
of the connection. The shaft has to be checked in the shaft analysis, see section 3.
Using KISSsoft, the load carrying length of the key is always used as the load carrying length
(ltr=93 mm). The frictional torque has to be calculated in another module (e.g. in the interference fit
module). If it is not known, it should be set to zero. The safety factors shown are the minimal safety
due to nominal torque (fatigue strength) and peak torque (static strength). Note that the application
factor is used only for the nominal load.
Using in the Tool bar the icon to the right of “Ó” (or F6) a report containing all input data, analysis
parameters, and results is written. This report includes all input data, analysis parameters (see also
section 2.5) and results. It can easily be included in a formal strength report.
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2.4 Calculation of maximum permissible torque
In a second step, the permissible nominal torque is to be calculated such that a minimal safety factor
of 1.20 is reached. For this, the required safety factor of 1.20 is defined in the module specific
settings, (see Figure 2.4-1). Then, the “Sizing button” to the right of the nominal torque field is to
be pressed and the maximum permissible nominal torque is calculated to be 3305Nm. If then “Ó” is
pressed again, the resulting minimal safety factor will be 1.20, see marking in Figure 2.4-2.
Figure 2.4-1: Set the required safety factor in the module specific settings.
2
1
(1)By Pressing the
“sizing button” the
result is for
permissible
nominal torque is
shown.
(2) After
recalculation
results in safety
factor being equal
to the required
safety factor (3).
3
2.5 Remarks on the report
Figure 2.4-2: Calculation of maximum permissible nominal torque.
Some remarks on the parameters listed in the report:
- Equivalent torque: Teq=KA*Tnenn , KA according to DIN3990
- Circumferential force from torque: Feq=Teq/r , Fmax=Tmax/r
- Definition of load carrying length, ltr and depth, ttr
- Pressure from circumferential force, contact area and load factor Kv: depending on number
of keys used; maximum of two keys accepted in analysis, Kv=0.75 (higher for pressure
under peak load (deformation of key assumed), Kv=0.9)
- Load distribution coefficient K l , uneven load distribution over the length of the key
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- Friction factor K R : Accounts for torque transmitted by means of interference fit (for peak
torque only)
- Do not use brittle materials for hubs if using interference fit
- Load direction changes coefficient f W : considers the frequency of changes in load direction,
different for abrupt or slow changes
- Frequency of peak load factor f L : factor considering the frequency of peak loads, different
for brittle or ductile materials
- Support factor f S : Higher strength of materials loaded under pressure, depending on material
- Hardness influence coefficient f H : for hardened surfaces
- Permissible contact stress calculated from ultimate (brittle materials) or yield strength
(ductile materials) and above factors
- For temperature range of -40°C to 150°C
3 Shaft analysis
3.1 General
From the research conducted on keys, it is known that usually it is the shaft which is the critical part
of the connection. Shearing of the key is uncommon and happens only under peak loads. The
corrosion effects shown in a number of fatigue tests due to alternating bending action (and resulting
micro movement between the members of the connection) is known to be the prime damaging
mechanism in the connection. The complete proof of strength of the connection not only includes
the proof against permissible contact stresses as shown above, but also the proof of strength of the
shaft and the hub. However, the latter rarely is a problem except for very thin-walled hubs. In the
KISSsoft key analysis, proof is only carried out for contact stresses. The proof against fatigue
failure of the shaft should be obtained using the KISSsoft shaft analysis.
3.2 Notch factors for shaft analysis
Since the damaging mechanism (especially for the shaft) is a combination of notch stresses and
corrosion, it is not sufficient to use a notched shaft for the determination of notch factors. Hence, for
the determination of notch factors for a key connection, experiments using the complete connection
are necessary. In these experiments, a wide range of parameter has to be investigated. Therefore, the
notch factors given in the literature differ and are usually defined only in a range.
It remains the responsibility of the engineer to carefully review the notch factors used in the shaft
analysis.
See for example
- DIN 6892, Passfedern, Berechnung und Gestaltung
- U. Oldendorf, Lebensdauer von Passfederverbindungen, VDI Bericht 1790
- E. Leidich, Einfluss des Schwingungsverschleisses auf die Tragfähigkeit von Welle-Nabe-
Verbindungen, VDI Bericht 1790
- DIN 743, Tragfähigkeit von Wellen und Achsen
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