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HEXAGON Info Letter No. 47, February 1998

Copyright by HEXAGON Software 1998


FED6 - Dimensioning

The newest FED6 version can now calculate the appropriate compression spring, when the some points of the progressive spring characteristic curve are entered. You can enter up to 50 spring travels and spring forces. FED6 then calculates the appropriate cylindrical compression spring.

The picture shows a spring with a parabola shaped characteristic curve. According to the function F(s) = s▓, five points for the spring curve are entered: F(1)=1, F(2)=4, F(3)=9, F(4)=16 and F(5)=25.

FED6 - Natural Frequency

The natural frequency of a non-linear cylindrical pressure spring changes along the spring path. The new version of FED6 shows in a diagram, the natural frequency in relation to the spring path.

SR1 - Working Temperature


       TEMPERATURE
       ======================================================================
       Reference Temperature             T0       °C                20         
       ----------------------------------------------------------------------
       Working Temperature               T        °C               300         
       ----------------------------------------------------------------------
       Difference Length screw           delta LS mm             0.515         
       ----------------------------------------------------------------------
       modulus of elasticity screw       ES       N/mm▓         206000         
       ----------------------------------------------------------------------
       modulus of elasticity screw 300   ES300    N/mm▓         185000         
       ----------------------------------------------------------------------
       
       CLAMPING COMPONENTS (T = 300°C)
       ======================================================================
       i    l20 [mm]  l300 mm   E N/mm▓   E 300     d20 mm/N    d300 mm/N    
       ======================================================================
        1     60.000    60.193  210000    185000    0.218E-6    0.247E-6     
       ----------------------------------------------------------------------
        2     50.000    50.364   44000     23008    0.601E-6    1.150E-6     
       ----------------------------------------------------------------------
        3     50.000    50.126  125000    104462    0.212E-6    0.253E-6     
       ----------------------------------------------------------------------
       
       Difference Length clamping pieces delta LP mm             0.683         
       ----------------------------------------------------------------------
       Elasticity screw                  delta St mm/N        2.464E-6         
       ----------------------------------------------------------------------
       Elasticity plates                 delta Pt mm/N        1.65E-6          
       ----------------------------------------------------------------------
       yield point screw                 Re       N/mm▓            940         
       ----------------------------------------------------------------------
       yield point screw 300°C           Re300    N/mm▓            705         
       ----------------------------------------------------------------------
       Dec./inc.clamping force Work.temp.delta FM N             -40831         
       ----------------------------------------------------------------------
       assembly prestress. force 300°C   FM 300   N             290196         
       ----------------------------------------------------------------------

For differing elasticity modulus of screw and clamping plate, a higher or lower surrounding temperature causes an increase or decrease of the clamping force. Also, with high temperatures, the yield point and the E modulus decrease. SR1 calculates the temperature dependent values, these are then printed out on an additional page. The least favourable values of room and working temperatures are used in the safety margin calculation.

Yield point and E modulus as functions of the temperature, are delivered as DBF data base files. SR1 interpolates the mid-values. The data base files can be appended and altered by the user.

SR1 - FM-MA Diagram

New in our screw program, SR1, is a diagram for clamping force in relation to the tightening torque. The line for the theoretic case without thread and head friction (ŠG=ŠK=0) is also drawn. The diagram also shows that most of the tightening work is absorbed by friction. The more friction there is, the lower the target clamping force is (end of the line, yield point, screw).

HPGLMAN, DXFMAN - ARISTO Format

In the HPGL Manager and DXF Manager it is now possible to create an initialize file, which during conversion to the ARISTO plot format is automatically inserted into the ART file. Changes have also been made to the conversion of poly lines and arcs which are now drawn as a continous line.

FED1 Deviations e1, e2

The permissible deviations of the mantle curve for perpendicular and permissble deviations of the parallelity are now only given, in accordance with DIN 2089, when the spring ends are ground or forged (for pre-heated springs).

DXF with AutoCAD 14

AutoCAD 14 has been having problems with the line "$ACADVER" in the header, this is caused by the source program. For this reason, this line will no longer be included. When loading DXF files in AutoCAD, please note that DXF files (with block definitions) can only be loaded into empty documents, neither blocks or layers may be predefined!

Dutch Spring Drawing

We are now able to provide versions of the spring programs, FED1+, FED2+, FED3+, FED5 and FED6 in which the production drawings are printed out in Dutch. However, the rest of the program is still in German.

Goodman Diagram for Spring Programs

The permissible elevation stress of dynamically loaded springs can be improved by around 20% by shot blasting. This represents an increase in life expectancy of around 800%. The new versions of the program calculate with a 20% higher permissible elevation stress when there is no data for shot blasting in the data base. This replaces the message "no material data available". The warning "approx. Goodman" means that there are no exact data available in the material data base. The calculation of the no. of repetitions and life expectancy has been improved and is now only displayed with one decimal place to avoid the suggestion that they can be calculated to an accuracy of three decimal places.

WN1 Micro sliding


       ---------------------------------------------------------------------
       Shearing modulus                  G        N/mm▓  82692      82692
       ---------------------------------------------------------------------
       Shearing stress, shaft            tau I    N/mm▓       24.5
       ---------------------------------------------------------------------
       Shearing stress for slipping      tau R    N/mm▓       4.9
       ---------------------------------------------------------------------
       Transfer.torque for slipping      T R      Nm          795.7
       ---------------------------------------------------------------------
       Rotation, hub                     phiA     ░           -0.0011
       ---------------------------------------------------------------------
       Rotation, shaft                   phiI     ░           0.0284
       ---------------------------------------------------------------------
       Torque limit, drift               Tgrenz   Nm          137.7
       ---------------------------------------------------------------------
       Safety again. micro slipping      Tgr./T               0.229
       ---------------------------------------------------------------------
       Stress concentr.coeff.            alpha kt             1.061
       ---------------------------------------------------------------------

For large alternating torques micro sliding can occur in the seam surface due to differing rotations of the shaft and hub. This causes fitting corrosion, which drastically reduces the life expectancy of the pressed fit. The calculation is documented in the German book "Shaft/Hub Joints" by Kollmann (Publisher: Springer). The following measures are recommended for driftless transfer:
  • When the E modulus of the shaft and hub is the same, the diameter ratio value, QA=DA/DF, of the hub, should not exceed ▀.5.
  • When materials with different E modulus are select, the shaft must have the greater shearing modulus.
  • For predefined dimensions, strive for increased seam pressure.

    WL1/WL1+ Bearing Rigidity

    Until now, WL1/WL1+ have calculated with an infinitely great rigidity for the bearing positions. The deflection at the bearing positions was zero. In the new version you can, alternately, enter the spring rate [N/mm] of the bearing position. Then, WL1/WL1+ will take bearing bending into account. The bending line of the bearing position then no longer goes through zero, but is equal to w=F/c. The bending critical torque is therefore reduced.

    WL1/WL1+ Quick Output

    The bending critical torque has been added to the quick output.

    WL1/WL1+ SchemaWL1/WL1+ Bending Critical Torque

    The bending critical torque can now be calculated for 3, 4 and 5 mounted shafts. Until now the bending critical torque has been calculated according to the Kull and Dunkerley method (Literature: Bohl, Str÷mungsmachinen 2, Publisher: Vogel). The method according to Kull is usually more accurate and requires less calculation time, for this reason the Dunkerley method can now be dropped.

    WL1+, LG1 - Roller Bearing Rigidity

    Approaching step by step, the bearing rigidity can be calculated from the overstrain of the rolling element and the bearing bush. It is not constant, but dependent on the bearing force. For smaller supporting forces, the rolling bearing rigidity is low. This can lead to problems with low-loaded fast moving shafts because the critical speed is very low. By pre-stressing the rolling bearing, or using rolling bearings with negative clearance, the bearing rigidity can be increased. For later versions of WL1+ and LG1, we are planning calculation of bearing rigidity for the selected rolling bearings in relation to the load.

    WL1/WL1+ 50 Shearing Forces

    The maximum number of radial forces has been increased from 20 to 50. This means that up to 50 mass forces can be calculated according to Kull for the critical speed. The error message "Kull: m>20" has been dropped.

    LG1/WL1+ Skew-Angle Roller Bearing

    LG1 and WL1+ now include calculation, data base and drawing creation for skew-angle roller bearings.

    LG1/WL1+ Bearing Play

    For grooved ball bearings the creation of reference load from the bearing play is dependent upon the ball bearing used. The selected bearing type (bearing play normal, C3, C4 or user defined) is now printed out as well.

    WL1/WL1+ Accepting shaft sections as additional mass

    Under Edit->Calculation you can automatically accept shaft sections as additional mass for the calculation of the critical speed. For the calculation of the critical speed, the program calculates with point masses which lie in the x-coordinates of the additional mass or take effect at the center of gravity of the shaft section. For long shaft sections, or non-stepped shafts, this is too inaccurate. By dividing the shaft up into several equal sectons, you can increase the accuracy of the critical speed calculation. The same applies for additional mass. When additional mass is distributed over a relatively long distance, or passes through a supported position, there is the danger of inaccuracy during calculation of the critical speed. You must imagine that the center of gravity for an additional mass is exactly at the support position. The deflection is then zero, this causes the spring constants and natural frequency to be infinitely large. Realistic values can be obtained by dividing the additional mass into two sections taking affect to the left and the right of the support.

    WL1/WL1+ Dynamic Bending Line

    Due to the static deflection of the shaft, additional forces develop caused by the unbalance of the shaft mass with
    F = m * omega▓ * r
    
    with omega = 2*PI*n
    
    with
    F: dynamic radial force
    m: mass in Kg
    omega: rotation frequency
    n: shaft rotational speed 1/s
    r: deflection at the mass center of
    gravity.
    
    After recalculation, the increased deflection due to unbalance can be used for the calculation of F dyn, until balance is attained.

    WL1/WL1+ Resonance and Damping

    By taking the transfer function into account, the dynamic bending line in the resonance range is increased, and weakened in the area the other side of the natural frequency. The degree of damping is around 0.1 to 0.2 for steel shafts.

    A diagram can be created which shows the deflection at any x coordinate on the shaft in relation to the shaft rotational speed, also taking the critical speed and damping into account.

    WL1+ Locking ring

    For the groove position of a locking ring in accordance with DIN, it is now possible to enter the x position on the shaft, determining whether it is to the right or the left of the groove.
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