Chapter 10
Interference Fit According to DIN 7190

    10.1   General Information
    10.2   Application
    10.3   Selection of Fit/Tolerances
    10.4   Automatic Dimensioning Functions (Calculator Button)
    10.5   Influence of Centrifugal Force
    10.6   Additional External Loads
    10.7   Operating Factor (Application Factor)
    10.8   Coefficients of Friction
    10.9   Stepped Hub Geometry
    10.10   Subsidence/Surface Smoothing
    10.11   Modification of Diameter
    10.12   Fretting Corrosion
    10.13   Assembly and Disassembly
    10.14   Example of Interference Fits
    10.15   How to Change the Unit of Measurement
    10.16   The Button ‘Redo’ and ‘Undo’
    10.17   Material Selection
    10.18   Message Window
    10.19   Quick Info: Tooltip
    10.20   Calculation Results
    10.21   Documentation: Calculation Report
    10.22   How to Save the Calculation
    10.23   The Button ‘Options’
    10.24   Calculation Example: Interference Fit According to DIN 7190

10.1 General Information

The interference fit is a frictional shaft-hub-connection. The joint pressure in the friction surfaces pF  that is necessary for the power transmission, is generated by the deformation of shaft and hub. According to the manufacturing method, you have to distinguish between a shrink and force fit. Shrink-fitting is a procedure in which heat is used to produce a very strong joint between two pieces of metal, one of which is inserted into the other. Heating causes one piece of metal to contract or expand on to the other, producing interference and pressure which holds the two pieces together. In a force fit of cylindrical parts, the inner member has a greater diameter than the hole of the outer member. The calculation takes place according to DIN 7190 for cylindrical interference fits. In addition, the influence of the centrifugal force, the stepped hub geometry, torque, radial force and bending moment are considered as well.

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Figure 10.1: General overview

10.2 Application

DIN 7190 defines the calculating basis for interference fits with cylindrical surfaces whose parts are made of metallic materials. This standard applies mainly for the common mechanical engineering but can be used also in other fields (e.g., precision engineering). The calculation method DIN 7190 applies for interference fits with a constant axial length of inner and outer part (see figure 1). The calculation can be used approximately for interference fits according to figure 2. Stress increases in the area of the hub edge are not considered.

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Figure 10.2: Figure 1 and 2

10.3 Selection of Fit/Tolerances

For a comfortable selection and calculation of suitable tolerances, a dialog window for the selection of fits is included. This dialog window contains the tolerance system according to DIN ISO 286 including all IT classes.

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Figure 10.3: Button ‘Selection’

In DIN ISO 286, the tolerances for the diameter are defined up to 500 mm. The desired tolerance field can be selected for hub and shaft from a listbox. An individual input of the upper and lower deviation is also possible. The lowest and highest interference as well as the fit type for the nominal diameter will be displayed. For the calculation of possible fits, the IT scope can be selected. The following IT scopes are available:

In order to find the required fit, different options are available. Based on the specified loads, the minimum interference and the maximum interference are determined. These values will be displayed automatically in the field ‘Calculation of possible fits’ and provide the basis for the dimensioning and selection of appropriate tolerances. In addition, there is the possibility to define a tolerance field for the hub and shaft. Select the option ‘Show only preferred fits’ and click the button ‘Search fits’ and all possible fits will be displayed. Then just choose the right fit.

10.3.1 Selection of Fit

Click the button ‘Selection’ in order to open the fit calculator and to let the calculation module propose a suitable fit. The fit calculator provides the tolerance system according to DIN ISO 286 including all IT classes. The upper part of the fit calculator allows to choose the tolerance field for the hub and the shaft.

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Figure 10.4: Fit calculator

For the selected tolerance the upper deviation and the lower deviation for shaft and hub will be displayed. Furthermore, the fit type as well as the highest and lowest interference will be specified.

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Figure 10.5: Deviations for the selected tolerance combination

The deviations of shaft and hub can be entered manually. In order to do so, please enable the option ‘Activate the input of user defined tolerances’.

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Figure 10.6: Own definition of tolerances

10.3.2 Calculation of Fit

You can specify the lowest and highest interference. If you have defined all data in the main mask before, the required lowest and highest interference will be entered automatically.

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Figure 10.7: Lowest and highest interference

Clicking the button ‘Search fits’ shows all possible fits. The message ‘More than 500 fits were found. Only preferred fits are shown’ may occur. Please confirm this message with ‘OK’ and choose a fit from the listbox.

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Figure 10.8: Search a fit

The option ‘Show only preferred fits’ is activated automatically and all preferred fits will be displayed in the listbox.

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Figure 10.9: Show only preferred fits

Please note: The option ‘Show only preferred fits’ is enabled by default. The list of fits is limited. Disable this option and click the button ‘Search fits’. The number of fits increases.

10.4 Automatic Dimensioning Functions (Calculator Button)

The button for the dimensioning functions is marked by a calculator symbol and is located next to the input fields. If you click on the dimensioning buttons, you get a suggestion for an appropriate input value. The calculation of the value is carried out so that the given minimum safety is fulfilled. The default value for the minimum safety is set to ‘1.2’. Clicking the button ‘Options’ allows you to change this value. A dimensioning function is available for the joint diameter, the length, the torque and the axial force.

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Figure 10.10: Dimensioning button

10.5 Influence of Centrifugal Force

The influence of the centrifugal force on the interference fit by the input of a speed is considered according to F. G. Kollmanns, Braunschweig ‘Rotierende Pressverbände bei rein elastischer Beanspruchung’ (Konstruktion 33, 1981 H.6, pp. 233-239).

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Figure 10.11: Speed

10.6 Additional External Loads

In addition to the consideration of axial and tangential forces, a radial and a bending moment can be specified. The calculation is carried out according to Mr. Prof. Gropp ‘Das Übertragungsverhalten dynamisch belasteter Pressverbindungen ...’ and Mr. Prof. Hartmann ‘Berechnung und Auslegung elastischer Pressverbindungen’.

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Figure 10.12: Axial force, radial force and bending moment

Resulting from the given loads for the bending moment and radial force, the additional external loads may be determined from the following equations:

pb = 9------Mb-------- an d  pr = --Fr--
    2 (2- QW )⋅DF  ⋅l2F            dF ⋅lF

For a too small minimum joint compression, the hub lifts off and a so-called gaping joint occurs. A gaping joint minimizes the joining surface available for the power transmission and is imperative to avoid. To avoid a gaping joint, the following condition has to be fulfilled:

pmin ≥ pr + pb

If this condition is not fulfilled, then an appropriate warning/message appears.

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Figure 10.13: Gaping joint

10.7 Operating Factor (Application Factor)

The operating factor (application factor) is determined according to DIN 3990. The following table gives some values.

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Figure 10.14: Operating factor






Application Factors KA  According to DIN 3990-1: 1987-12





Working Characteristics

Working Characteristics of the Driven Machine




of the Driving Machine

Uniform Light Shocks Moderate Shocks Heavy Shocks





Uniform

1,0 1,25 1,5 1,75





Light Shocks

1,1 1,35 1,6 1,85





Moderate Shocks

1,25 1,5 1,75 2,0





Heavy Shocks

1,5 1,75 2,0 2,25 or higher





10.7.1 Working Characteristics of the Driving Machine

Uniform: e.g., electric motor, steam or gas turbine (small, rarely occurring starting torques)

Light Shocks: e.g., electric motor, steam or gas turbine (large, frequently occurring starting torques)

Moderate Shocks: e.g., multiple cylinder internal combustion engines

Heavy Shocks: e.g., single cylinder internal combustion engines

10.7.2 Working Characteristics of the Driven Machines

Uniform: Steady load current generator, uniformly loaded conveyor belt or platform conveyor, worm conveyor, light lifts, packing machinery, feed drives for machine tools, ventilators, light-weight centrifuges, centrifugal pumps, agitators and mixers for light liquids or uniform density materials, shears, presses, stamping machines, vertical gear, running gear

Light Shocks: Non-uniformly (i.e. with piece or batched components) loaded conveyor belts or platform conveyors, machine-tool main drives, heavy lifts, crane slewing gear, industrial and mine ventilators, heavy centrifuges, centrifugal pumps, agitators and mixers for viscous liquids or substances of non-uniform density, multi-cylinder piston pumps, distribution pumps, extruders (general), calendars, rotating kilns, rolling mill stands, continuous zinc and aluminium strip mills, wire and bar mills

Moderate Shocks: Rubber extruders, continuously operating mixers for rubber and plastics, ball mills (light), wood-working machines (gang saws, lathes), billet rolling mills, lifting gear, single cylinder piston pumps

Heavy Shocks: Excavators (bucket wheel drives), bucket chain drives, sieve drives, power shovels, ball mills (heavy), rubber kneaders, crushers (stone, ore), foundry machines, heavy distribution pumps, rotary drills, brick presses, de-barking mills, peeling machines, cold strip c, e, briquette presses, breaker mills

10.8 Coefficients of Friction

The following table provides some approximate values for the coefficients of adhesion/coefficients of friction for shrink fits according to DIN 7190. The values are on the safe side and can be used for sliding in circumferential and longitudinal direction.



Coefficients of Adhesion for Shrink Fits in
Longitudinal and Circumferential Direction During Sliding


Mating of Material, Lubrication, Joining

Coefficients of Adhesion νR,νrl,νu



Steel/Steel pair



Pressurized oil assembly normally joined with mineral oil

0,12

Pressurized oil assembly with degreased surfaces joined with glycerine

0,18

Shrink fit normally after heating the outer part up to 300∘ C in an electric kiln

0,14

Shrink fit with degreased surfaces after heating up to    ∘
300 C in an electric kiln

0.20



Steel/Cast iron pair



Pressurized oil assembly normally joined with mineral oil

0,10

Pressurized oil assembly with degreased surfaces

0,16



Steel/MgAl pair, dry

0,10 to 0,25



Steel/CuZn pair, dry

0,17 to 0,25



The following table specifies the coefficients of adhesion/coefficients of friction for force fits according to DIN 7190. These values are valid for monotonic loading and are determined for inner parts made of X 210 Cr W12. They are valid for steel. After joining, the interference fits require sufficient time (24 hours is best) before first loading to assure a strong joint.








Coefficients of Adhesion for Force Fits During Monotonic Loading







Materials
Coefficients of Adhesion



Old
New
dry
lubricated



Number ν
 ll  ν
 rl  ν
 ll  ν
 rl







St 60-2 E 335 1.0060 0,11 0,08 0,08 0,07







GS-60 GE 300 1.0558 0,11 0,08 0,08 0,07







RSt37-2 S 235JRG2 1.0038 0,10 0,09 0,07 0,06







GG-25 EN-GJL-250 0,6025 0,12 0,11 0,06 0,05







GGG-60 EN-GJS-600-3 0,7060 0,10 0,09 0,06 0,05







G-AlSi12 (Cu) EN AB-44000 ff. 0,07 0,06 0,05 0,04







G-CuPb10Sn CB495K 2.1176.01 0,07 0,06 -1 -1
G-CuSn10Pb10







TiAl6V4 TiAl6V4 3.7165.10 -1 -1 0,05 -1







1 Coefficients of adhesion are unknown







The above-mentioned table means:

The coefficients of adhesive friction/coefficients of friction are dependent upon the following factors:

Due to the friction within the joint, the coefficients of adhesive friction are subject to statistical fluctuations. Therefore, the defined coefficients of adhesive friction are approximate values and are on the safe side. The values can be replaced by an experimental determination of values according to DIN 7190.

10.9 Stepped Hub Geometry

For the stepped hub or/and shaft (see figure below), there is a larger joint compression on the thick-walled segment than on the thin-walled segment for the same fit. Hence, widely different stress and deformation ratios occur on each segment. In that case, the total length LF  has to be used. The hub can be considered as composed of separate discs of different diameters. From it, the mean joint pressure for the interference fit is determined. Because the stresses and deformation cannot change abruptly from one segment to another segment, this method of segmentation presents an approximation. The effort to define the matching conditions or to determine the joint compression by using FEM calculation is just useful for critical cases.

The calculation is determined according to the algorithm in Prof. Hartmanns ‘Berechnung und Auslegung elastischer Pressverbindungen’.

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Figure 10.15: Stepped hub

Click on the button ‘stepped’ next to the input field ‘Outer diameter hub’ to consider the stepped hub geometry. Any number of segments can be defined.

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Figure 10.16: Button ‘Stepped’

The figure (see figure 10.15) shows how the segmentation has be specified. A segment can contain a constant outer hub diameter and inner shaft diameter. If a shaft bore extends over two outer hub diameters of different size, then two segments has to be defined with a different outer hub diameter and equal inner shaft diameter. In case there is a stepped shaft bore within a constant hub outer diameter, then use this method, too (a definition of two segments with equal outer hub diameter and different inner shaft diameter).

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Figure 10.17: Definition of geometry

Place a checkmark in order enable and use the stepped hub geometry.

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Figure 10.18: Enable stepped hub geometry

Now you can start to define the segments. Enter the number of segment and add the segment length, outer hub diameter and inner shaft diameter.

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Figure 10.19: Define segments

Clicking the ‘OK’ button applies your input values and the diagram button will be enabled.

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Figure 10.20: Button ‘Diagram’

That diagram shows the compressive stress along the fit length. Move the mouse over the diagram to see the values for the lowest (pK), highest (pG) and mean (p) compressive stress due to the lowest, highest and mean interference.

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Figure 10.21: Diagram

10.10 Subsidence/Surface Smoothing

Due to the smoothness of asperity peaks during the joining, only the interference Uw  is available. Unless there are experimental values, the equations according to DIN 7190 for force and shrink fits are:

U = Uo - s and  s = 0,8(RzA + RzI)

where s is the subsidence that results from the determined surface roughness Rz  of inner and outer part. Uo is the lowest, highest and mean interference.

If the values of the surface roughness for the arithmetic mean value of the profile coordinates Ra  (formerly the arithmetical mean deviation of the roughness profile Ra  ) are specified according to DIN EN ISO 4287, then the determined mean values according to DIN 7190 can be used for the surface roughness Rz (see table below). Select the entry ‘User defined’ from the listbox ‘Surface’. Now the input field next to the listbox is enabled and you can enter a value for the surface roughness Rz .

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Figure 10.22: Own input of surface quality






Comparison of Mean Roughness Ra  and Average Roughness Rz





Ra  in μm
Ra0,8 Ra1,6 Ra3,2





Rz  in μm from 3,15 6,3 12,5




to 10 20 31,5





Average surface roughness Rz  in μm
Rz6,3 Rz12,5 Rz20





10.11 Modification of Diameter

The calculation of the modification of diameter at the inner and outer diameter of shaft and hub takes place according to Niemanns ‘Maschinenelemente’ volume 1 pp.789, 3rd edition 2001. There, the modification of the diameter is considered by the joint pressure and centrifugal force. The influence of temperature on the modification of diameter is considered on the outer diameter of the shaft and on the inner diameter of the hub by the modified interference and joint pressure.

10.12 Fretting Corrosion

According to Niemann ‘Maschinenelemente’ volume 1 p. 800, 3rd edition 2001, the torque is transmitted also during repeated load by elastic transformation (i.e., without slip), if the torque T is smaller than the maximum torque TE . For a solid shaft, disk-shaped hub with LF ∕DF > 0,25  and shaft and hub with equal E modulus, it is expressed as:

         T ⋅S
TE ≤ ∘-------R---L--
       (1-8Q2A) ⋅2⋅DFF

T⋅Sr is the slipping torque against fretting corrosion. This results in remedial measures agaisnt fretting corrosion. The joint pressure, coefficient of adhesion in terms of circumference, the joint diameter or the safety against sliding can be increased in order to avoid micro sliding/fretting corrosion. A rotating bending may cause fretting corrosion. If the mentioned conditions for a possible determination of the maximum torque are given, the maximum torque is calculated for the minimum, mean and maximum interference.

10.13 Assembly and Disassembly

10.13.1 Shrink fits

In shrink fits, the outer member is heated or the inner part is cooled, or both, as required. The calculation of the temperatures to cool the inner part or to heat the outer part is dependent upon the chosen minimum fit. Additionally, a mating clearance for joining has to be kept to avoid adhesion. For an individual production, it is recommended to use the following mating clearance

U   = 0,001 ⋅D
 sϑ          F

For the individual production the risk of premature adhesion of the joining parts is covered before the assembly process is completed. By using joining devices, the above recommended mating clearance can be fallen below. Click on the button ‘Options’ to define the mating clearance. Two possibilities are available. On the one hand, the mating clearance can be specified dependent upon the joint diameter, on the other hand a mating clearance can be entered directly in μm .

In general, the room temperature as well the joint temperature of the inner part are set. The required joint temperature is calculated as follows:

ϑAerf = ϑR + --UF---+ αI-⋅(ϑI - ϑR )
             αA ⋅DF   αA

The button ‘Options’ allows to change the room temperature and the joint temperature of the shaft (see section 10.23 ‘The Button Options’). The highest joint temperature may not exceed the required work piece features of the heat-treated parts.

In the following table, the data according DIN 7190 valid data are specified for the maximum joint temperatures dependent on the material of the outer part and the heat treatment.



Joint Temperature


Material of the Outer Part (Hub) Joint Temperature ∘ C Maximum


Structural steel lower strength
Cast steel 350
Modular cast iron


Hardened and tempered steel or cast steel 300


Surface layer hardened steel 250


Case-hardened steel or high-tempered structural steel 200


The following table provides the coefficients of linear thermal expansion for inner and outer part.








Poissons Ratio, Elastic Modulus, Coefficient of Linear Thermal Expansion







Materials Material Poissons Elastic Modulus
Coefficient of Linear
No. Ratio N ∕mm2
Thermal Expansion α
ν ≈
  -6
10∘C--
≈
Heating ≈ Supercool







MgAl8Zn 3.5812 0,3
AlMgSi 3.2315 0,34 65 000 to 75 000 23 -18
AlCuMg 3.1325 0,33 to 0,34







GG-101 0.6010 70 000
GG-151 0.6015 0,24 80 000 10 -8




GG-201 0.6020 105 000
GG-251 0.6025 0,24 to 0,26 130 000







GGG-50 0.7050 0,28 to 0,29 140 000 10 -10







Malleable cast iron 0.25 > 90 000 to 100 000 10 -8







C-steel low alloyed 0,3 to 0,31
Ni-steel 0,31 200 000 to 235 000 11 -8,5







Bronze 0,35 16 -14





Red brass 0,35 to 0,36 80 000 to 85 0000 17 -15





CuZn39Pb3 2.0401 0,37
CuZn37 2.0321 0,36 18 -16







1 Not allowed for system engineering in metallurgy/rolling mills







Liquid nitrogen (ϑI = - 195,8∘C)  is used to cool shrink fits. Liquid nitrogen shrink fitting is one of the safest assembly methods. In some cases CO2  dry ice (ϑI = - 78,4∘C)  is also used as a coolant. Based on the maximally permissable temperature of the hub, it must be decided whether the cooling process is necessary or not.

10.13.2 Force Fits

The required pressing force for joining is determined from:

Fe = π⋅DF  ⋅lF ⋅ϑll ⋅pmax

The ‘Option’ button allows to define the coefficients of adhesion νll  for pressing in and pressing out (see also section 10.23 ‘The Button Options’). The table (see table 10.8) specifies the coefficient of adhesion νll  . The maximum joint pressure pmax  is determined for the highest interference. In case the joining surfaces are not lubricated with grease, larger coefficients of friction and larger longitudinal and tangential forces occur. There is a risk of scuffing for joining surfaces that are not lubricated, in particular for a elastic-plastic dimensioning. Before joining, the joining surfaces should be lubricated with oil.

Furthermore, the following information has to be considered for the engineering design according to DIN 7190:

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Figure 10.23: Force fits

The values for the edge length le  are specified in the following table. The measurement is indicated in mm.







The Edge Length le






D
F
D
  F
over to le  over to le






50 80 4 400 630 8






80 160 5 630 800 9






160 250 6 800 1000 10






250 400 7 1000 - 10






During the manufacturing process of interference fits by force fitting, the joining area is provided with a thin oil film over the entire surface. A jamming of the assembled parts must be avoided. The slip-stick effect can be avoided by the press-in speed and discharge speed of approx. 50 mm/s and sufficient pressing force (2,5x extraction force). Force fits requires sufficient time (24 hours) before first loading, then the complete adhesive force is reached (only 70% immediately after pressing).

10.14 Example of Interference Fits

The following section gives some guidance on selecting fits according to E. & K. Felber. There are features that can be expected in general during the assembly. The assembly rules specify the character of the fit and all features correspond to the mean value of fits. The list contains fits that are used frequently. Almost all fits can be formed in quality (e.g., from H8/u8 to H8/u7 to H6/u6). In general, the standard fits (e.g., H8/u7) can be used. According to the function, you have to select fine qualities (e.g., H6/u6) for larger requirements (requirements for accuracy and uniformity). The following examples are taken from the mechanical engineering and cannot to be considered as complete in any detail.

Examples for interference fits: H8/u8; U8/h7; H8/s7; S7/h6; H7/r6; R7/h6

Features, assembly rule: The parts are assembled and tightened and have a strong interference. The parts are pressed together or assembled into position while hot and cooled. In general, a safety device against torsion or shifting in lengthwise direction is not necessary.

Examples: Spur gears that are mounted tightly on a shaft, couplings, collar rings, press rings, wheel rims, bearing bushings in housings, bushings in gear hubs, tight pivots, bushings made of synthetic resin pressed material, parts which cannot be loosened by large forces.

10.15 How to Change the Unit of Measurement

Use this function if you want to change the unit of measurement quickly. Just a right-click on the input field where you want to change the unit. The context menu contains all available units. The two arrows mark the current setting. As soon as you select a unit, the current field value will be converted automatically into the chosen unit of measurement.

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Figure 10.24: Change measurement unit

10.16 The Button ‘Redo’ and ‘Undo’

The button ‘Undo’ allows you to reset your input to an older state. The button ‘Redo’ reverses the undo.

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Figure 10.25: Button ‘Redo’ and ‘Undo’

10.17 Material Selection

Clicking the button ‘Material’ opens the material database. In case there is no material that will fulfill the design requirements, then simply define your individual material. You will find the entry ‘User-defined’ in the listbox. If you select this option, the input fields will be enabled, so that you can enter your own input values or add a comment. Please select the material from the list. You will get detailed information on the material. The two cursor keys ‘Up’ and ‘Down’ of your keyboard allows you to navigate through the material database, so you can compare the different material properties with each other.

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Figure 10.26: Material selection

10.18 Message Window

The calculation module provides a message window. This message window displays detailed information, helpful hints or warnings about problems. One of the main benefits of the program is that the software provides suggestions for correcting errors during the data input. If you check the message window carefully for any errors or warnings and follow the hints, you are able to find a solution to quickly resolve calculation problems.

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Figure 10.27: Message window

10.19 Quick Info: Tooltip

The quick info feature gives you additional information about all input fields and buttons. Move the mouse pointer to an input field or a button, then you will get some additional information. This information will be displayed in the quick info line.

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Figure 10.28: The quick info

10.20 Calculation Results

All important calculation results, such as the lowest, highest and mean interference, will be calculated during every input and will be displayed in the result panel. A recalculation occurs after every data input. Any changes that are made to the user interface take effect immediately. Press the Enter key or move to the next input field to complete the input. Alternatively, use the Tab key to jump from field to field or click the ‘Calculate’ button after every input. Your entries will be also confirmed and the calculation results will displayed automatically. If the result exceeds certain values, the result will be marked red.

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Figure 10.29: Calculation results

10.21 Documentation: Calculation Report

After the completion of your calculation, you can create a calculation report. Click on the ‘Report’ button.

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Figure 10.30: ‘Report’ button

You can navigate through the report via the table of contents that provides links to the input values, results and figures. This calculation report contains all input data, the calculation method as well as all detailed results. The report is available in HTML and PDF format. The calculation report saved in HTML format, can be opened in a web browser or in Word for Windows. You may also print or save the calculation report:

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Figure 10.31: Calculation report

10.22 How to Save the Calculation

When the calculation is finished, you can save it to your computer or to the eAssistant server. Click on the button ‘Save’.

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Figure 10.32: ‘Save’ button

Before you can save the calculation to your computer, you need to activate the checkbox ‘Enable save data local’ in the project manager and the option ‘Local’ in the calculation module. A standard Windows dialog for saving files will appear. Now you will be able to save the calculation to your computer.

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Figure 10.33: Windows dialog for saving the file

In case you do not activate the option in order to save your files locally, then a new window is opened and you can save the calculation to the eAssistant server. Please enter a name into the input field ‘Filename’ and click on the button ‘Save’. Then click on the button ‘Refresh’ in the project manager. Your saved calculation file is displayed in the window ‘Files’.

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Figure 10.34: Save the calculation

10.23 The Button ‘Options’

Click the button ‘Options’ in order to change the default settings. The button ‘Options’ allows you to define the minimum safeties, the mating clearance, the temperatures at joining (room temperature and shaft temperature) as well as the coefficient of friction at joining for pressing in and pressing out for a force fit. Additionally, there is the possibility to enter the number of decimal places for the output of the numerical values in the report.

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Figure 10.35: ‘Options’ button

Here are the default settings that you can modify:

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Figure 10.36: Options

10.24 Calculation Example: Interference Fit According to DIN 7190

10.24.1 Start the Calculation Module

Please login with your username and your password. Select the module ‘Interference fit’ through the tree structure of the project manager by double-clicking on the module or clicking on the button ‘New calculation’.

10.24.2 Calculation Example

A cylindrical interference fit has to be dimensioned against sliding. Enter the following values:

Joint diameter = 50 mm

Length = 20 mm

Outer diameter hub = 95 mm

Inner diameter shaft = 30 mm

Torque = 80 Nm

Axial force = 125 N

Speed = 2.000 min/-1

Operating temperature = 25∘ C

Operating factor = 1.2

Coefficient of friction axial = 0.15

Coefficient of friction circumference = 0.15

Material shaft = 20MnCr5

Surface shaft = N6

Material hub = C45 hardened and tempered

Surface hub = Rz = 6

10.24.3 Start the Calculation

Please start to enter the values into the input field. All important calculation results will be calculated during every input and will be displayed in the result panel. A recalculation occurs after every data input. During the input of the values it can happen that the results will be marked in red. Nevertheless, please continue to input the data as usual.

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Figure 10.37: Input of the values

Please note: Please note the section ‘Selection of fit’ for the specification of the tolerances. With the definition of the surface quality of the hub, you have to notice that the given value (Rz=6) has to be entered by the ‘User defined’ input. Select ‘User defined’ in the appropriate listbox and enter the desired value into the input field next to the listbox.

Selection of Fit / Calculation of Possible Fits

The button ‘Selection’ allows you to open the dialog window for selection of fits. Here you can choose the possible tolerances or the appropriate fits can be suggested.

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Figure 10.38: Button ‘Selection’

Enable ‘Show only preferred fits’ and click the button ‘Search fits’.

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Figure 10.39: Activate preferred fits

Two fits will be recommended to you.

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Figure 10.40: Recommended fits

Select the fit H7/s6 and click the button ‘Ok’.

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Figure 10.41: Select the fit H7/s6

Automatic Dimensioning of the Maximum Torque

Due to the fit calculation, a safety close to the given minimum safety has been determined. By the help of the comfortable dimensioning functions, other values can be checked and optimized regarding the use of the minimum safety. So the maximum torque can be defined using the given minimum safety against sliding (SR=1.2) . The button ‘Options’ allows you to specify the minimum safety. Click on the dimensioning button (‘calculator symbol’) next to the input field for the torque.

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Figure 10.42: Automatic dimensioning function

The maximum torque is determined.

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Figure 10.43: Minimum safety

Here the maximum torque is ‘83.60 Nm’. If you enter now a higher value than ‘83.60 Nm’, the safety against sliding is fallen below.

The calculation result is marked in red. You will get an appropriate information in the message window.

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Figure 10.44: Result panel

Now click on the calculator symbol again, then the maximum torque is determined (83.50 Nm) and the minimum safety of ‘1.2’ is fulfilled. The specifications of the results is given for the lowest, highest and mean interference. If the minimum safety is not fulfilled, then the safety is marked in red.

10.24.4 Calculation Results

All important calculation results, such as the lowest, highest and mean interference, will be calculated during every input and will be displayed in the result panel. A recalculation occurs after every data input. Any changes that are made to the user interface take effect immediately. If the result exceeds certain values (e.g., the minimum saftey), the result will be marked red.

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Figure 10.45: Calculation results

10.24.5 Documentation: Calculation report

In case you have finished your calculation, please click on the button ‘Report’.

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Figure 10.46: ‘Report’ button

The calculation report contains a table of contents. You can navigate through the report via the table of contents that provides links to the input values, results and figures. The report is available in HTML and PDF format. Calculation reports, saved in HTML format, can be opened in a web browser or in Word for Windows.

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Figure 10.47: Calculation report

You may also print or save the calculation report:

10.24.6 How to Save the Calculation

When the calculation is finished, you can save it to your computer or to the eAssistant server. Click on the button ‘Save’.

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Figure 10.48: ‘Save’ button

Before you can save the calculation to your computer, you need to activate the checkbox ‘Enable save data local’ in the project manager and the option ‘Local’ in the calculation module. A standard Windows dialog for saving files will appear. Now you will be able to save the calculation to your computer.

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Figure 10.49: Windows dialog to save the file

In case you do not activate the option in order to save your files locally, then a new window is opened and you can save the calculation to the eAssistant server. Please enter a name into the input field ‘Filename’ and click on the button ‘Save’. Then click on the button ‘Refresh’ in the project manager. Your saved calculation file is displayed in the window ‘Files’.

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Figure 10.50: Save the calculation

Our manual is improved continually. Of course we are always interested in your opinion, so we would like to know what you think. We appreciate your feedback and we are looking for ideas, suggestions or criticism. If you have anything to say or if you have any questions, please let us know by phone +49 (0) 531 129 399-0 or email eAssistant@gwj.de.