Extension Spring Component Generator dialog box - Calculation tab

Sets parameters for calculation of an extension spring.

Access:

Ribbon: Design tab Spring panel Extension and click the Calculation tab.

Type of Strength Calculation

Extension Spring Design	Designs dimensions of the extension spring for the specified spring load.
Spring Check Calculation	Calculates assembly dimensions and an extension spring strength check for the specified load and spring dimensions.
Work Forces Calculation	Calculates the forces induced by the extension spring of the specified dimensions.

Calculation Options

Select the options for spring calculation.

Design Type	Note: This option is available only if you select Extension Spring Design in the Type of Strength Calculation area.
	F, Assembly Dimensions d, L 0 , n, D, Hook	Designs suitable wire diameter, number of coils, spring diameter, and hook size for the specified load F 1 , F 8 and assembly dimensions L 1 , L 8 , H of the extension spring.
	F, Assembly Dimensions, Hook d, L 0 , n, D	Designs suitable wire diameter, number of coils and spring length and diameter for the specified load F 1 , F 8 , assembly dimensions L, L 8 , H, and hook shape of the extension spring.
	F, D d, L 0 , n, Assembly Dimensions, Hook	Designs suitable wire diameter, number of coils, length, assembly dimensions L 1 , L 8 , H of the spring and hook size for the specified load F 1 , F 8 , and the extension spring diameter.
	F, D, Hook d, L 0 , n, Assembly Dimensions	Designs suitable wire diameter, number of coils, length and assembly dimensions L 1 , L 8 , H of the spring for the specified load F 1 , F 8 , extension spring diameter and hook shape.
	F 8 , D, Assembly Dimensions, Hook d, L 0 , n, F 1	Designs suitable wire diameter, number of coils, spring length and required force F 1 in the pre loaded state for the specified working force F 8 , diameter, assembly dimensions L 1 , L 8 , H and hook shape of the extension spring.
Method of Stress curvature correction	Use the drop-down list to select the method of stress curvature correction.
	With helical springs, the stress appearing in the spring coils at the given loading is calculated for simple torsion. Additional bending stress appears in the coil due to its rounding. Therefore, the stress is corrected in the calculation using a correction coefficient. As several different coefficients are commonly used, choose from the list the correction coefficient which meets your local usage or recommendations of standards.
	Note: From the view of strength check of a spring exposed to static loading, using the correction coefficient from Gahner gives the best results.
	Hint: With springs exposed to static loading, corrections are not executed.

Loads

The edit fields are enabled if you select Work Forces Calculation in the Spring Strength Calculation area.

Dimensions

Enter or measure the spring dimensions.

Note: The availability of the edit fields depend on the selected option in the Type of Strength Calculation area.

Spring Prestress

Cold formed extension springs are preferably produced with pre-stressing, with close-coiled active coils. The spring pre-stressing has a considerable effect on increasing the loading capacity of the spring. For deformation of the spring to the appropriate length, use a higher loading than with springs without pre-stressing. Pre-stressing appears in coils of the spring in the course of coiling of the spring wire, and its size depends on the used material, spring index and the manner of coiling. Pre-stressing of the spring is significantly lower with springs coiled on automatic spring coiling machines.

Free State Stress

Enter the free stress value. Click the arrow to open the Initial Extension for Specified Diameters dialog box where you can set the value. Note: The edit field is enabled only if you selected Free Pre-stress option from the previous drop-down list.

Spring Material

Select the spring material and its properties. Click to open the Material Database where you can select the appropriate material.

Warning: Strength parameters of material are determined empirically and reflect minimum values applicable for a group of materials. Although these values are close to the values obtained using measurement of particular materials, it is recommended in cases of final calculations to use the parameters of material according to the material sheet or specifications of the producer.

Material	Specifies material values you enter or select from the Material Database.
	If a material is selected from the Material Database, its values are inserted automatically into the following edit fields, and the edit fields are locked. To unlock the field clear the box.
Allowable Torsional Stress	Enter the value.
Modulus of Elasticity in Shear	Enter the modulus of elasticity of the spring material.
Density	Enter the density of the spring material.
Utilization Factor of Material	Enter the utilization factor of the spring material. Click the arrow next to the edit field where you can set the value.
	The coefficient gives a relation between the torsion stress of a spring in the fully loaded state and the allowable torsion stress, such as u S » τ 8 / τ A . If a greater value is selected, less material is needed for spring production, the spring dimensions and the space for mounting are less, but the securing of spring stability during its function is lower, and vice versa. Therefore this coefficient is a reciprocal value of the safety rate. For common operational conditions, the value of the utilization factor of the material is recommended to be within the u S = 0.85 ... 0.95 range. Lower values can be used for springs working in aggressive surroundings, at high temperatures or loaded with impacts.
	The value of the utilization factor of the material is selected in a dialog box where a range of recommended values is designated.

Assembly Dimensions

H, L 1 L 8	Calculates the length of a fully loaded spring for the specified working deflection and the length of the pre loaded spring.
H, L 8 L 1	Calculates the length of a pre loaded spring for the specified working deflection and the length of the fully loaded spring.
L 1 , L 8 H	Calculates the working deflection for the specified lengths of a pre loaded spring and a fully loaded spring.

Spring Coils

Rounding of Coil Number	Set the value for rounding the coil number value.
Active Coils Number	Specify the spring number of active coils.

(More)

Displays additional options for spring design. To display the More Options area, click More in the right lower corner of the Calculation Tab.

Design of Working Deflection
Note: Available only if you select Extension Spring Design in the Type of Strength Calculation area, and these options in the Design type drop-down list: F, D d, L 0 , n, Assembly Dimensions, Hook or F, D, Hook d, L 0 , n, Assembly Dimensions.
Not Specified	Designs suitable spring working deflection for the specified load and spring diameter.
Minimum Working Deflection	Designs suitable spring working deflection that is larger than the minimum allowable value Hmin, for the specified load and spring diameter.
Maximum Working Deflection	Designs suitable spring working deflection that is smaller than the maximum allowable value Hmax, for the specified load and spring diameter.
Deflective Range	Designs suitable spring working deflection that is the nearest to the demanded deflection H', for the specified load and spring diameter.
Design of Spring Diameter
Note: Available only if you select Extension Spring Design in the Type of Strength Calculation area, and these options in the Design type drop-down list: F, Assembly Dimensions d, L 0 , n, D, Hook or F, Assembly Dimensions, Hook d, L 0 , n, D.
Not Specified	The smallest suitable spring diameter is designed for the specified load and spring assembly dimensions.
Minimum Diameter	The smallest suitable spring diameter larger than the minimum allowable value D2min is designed for the specified load and spring assembly dimensions.
Maximum Diameter	Designs suitable spring outside diameter smaller than the maximum allowable value D1max for the specified load and spring assembly dimensions.
Diameter Range	Designs suitable spring diameter nearest to the demanded diameter D' for the specified load and spring assembly dimensions.

Results

To display the Results area on the right side of the Calculation and Design tabs, double-click the double line on the right or click the chevron.

Displays the calculated dimensions values such as Correction Factor or Spring Mass. Values are calculated when the Calculate command is pressed.

Following output parameters are displayed in the Results pane:

• Wahl Correction Factor (K _w )
• Spring Constant (k)
• Length of Coiled Spring Part (L _z )
• Theoretic Limit Length of Spring (L ₉ )
• Min. Load Spring Deflection (s ₁ )
• Total Spring Deflection (s ₈ )
• Limit Spring Deflection (s ₉ )
• Limit Test Length of Spring (L _minf )
• Initial Extension (F ₀ )
• Spring Limit Force (F ₉ )
• Min. Load Stress (τ ₁ )
• Max. Load Stress (τ ₈ )
• Natural Frequency of Spring Surge (f)
• Deformation Energy (W ₈ )
• Developed Wire Length (l)
• Spring Mass (m)

Note: For further description of the calculated parameters in metric or English units, see Engineer's Handbook.

Summary of Messages

Displays the reports about calculation. To open the Summary of Messages area at the bottom of the Calculation and Design tabs, double-click the double line at the bottom of tabs or click the chevron at the bottom of the tabs.

Toolbar Commands