Retaining Compound Joint Strength Considerations


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Calculation of Bonded Slip Fits and Press or Shrink Fits Augmented with Adhesive Bonding.

Henkel has developed an extensive library of data on the adhesive performance of retaining compounds. This data has been consolidated to provide predictive tools that can be used to estimate the load capacity of bonded slip fit and press or shrink-fit joints
augmented with adhesive bonding.

These calculations can be performed by trained Henkel staff using our proprietary RetCalc+ software, created specifically for retaining applications. The following explains these calculations and applies them to a practical example.

The strength of a bonded joint and the torque that can be transmitted are calculated with the following equations. The strength of a press or shrink fit, augmented with adhesive bonding, is the sum of the strength calculated for the bonded joint plus the strength value of the press or shrink-fit joint without adhesive bonding.

View formula here.

Key

RC strength is the compressive shear strength of the retaining compound in N/mm2 measured in accordance with ISO 10123. This value is reported on the Technical Data Sheet for each retaining compound.
ftotal represents the sum of these Joint Design and Retaining Compound factors.

Joint Design Factors

f1 = Type of joint
f2 = Materials
f3 = Clearance
f4 = Surface finish
f5 = Engagement ratio
f6 = Load

Retaining Compound Factors

f7 = Cure method
f8 = Operating temperature
f9 = Operating environment
SAMPLE CALCULATION:
Fitting a Gear to a Clutch


This assembly is made in two parts in order to permit cutting of the gear teeth. The original design required positioning three dowels equally spaced on the joint between the two contacting surfaces to transmit the torque, since the wall thickness was too small to accommodate a keyway. The gear wheel has helicoidal teeth, and is subjected to different tangential and axial loads, depending on the direction of rotation, but the torque load never exceeds 18 N.m (159 in.-lb.). As torque transmission was the driving design factor, calculations only concern this load.

The dowels used present many disadvantages, causing distortion and rejected assemblies due to the thinness of the parts. Loctite® 648™ was suggested to replace the dowel pins, to simplify the assembly process and improve quality.

Dimensions of the bonded surface between the steel gear and the cast iron clutch:

Component Factors
Diameter = 32 mm
Engagement length = 15 mm
RC Strength = Loctite® 648™ has a strength of 29 N/mm2

Joint Design Factors
f1 = 1.0 for bonded slip fit
f2 = 0.8 for cast iron
f3 = 1.0 for a clearance of 0.025 mm
f4 = 1.0 for surface finish
f5 = 0.7 for a L/D ratio of 0.5 and a shaft diameter of 32 mm
f6 = 0.5 for alternating movement

Adhesive Design Factors
f7 = 1.0 for room temperature cure (no activator)
f8 = 1.3 for 150°C operating temperature
f9 = 1.0 for ambient air operating environment

The sum of the joint design and adhesive design factors is

ftotal = f1 x f2 x f3 x f4 x f5 x f6 x f7 x f8 x f9 = 0.36

Substituting these values in the formula: View formula here.

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