Understanding Tolerances for Shafts and Hub Connections per DIN 7349

Understanding DIN 7349

DIN 7349 is an important German national standard that specifies tolerances for shafts and hub connections. Properly understanding and implementing DIN 7349 is key for engineers and manufacturers working with rotating machine elements and power transmission systems.

Overview of DIN 7349

First published in 1990 by the German Institute for Standardization (Deutsches Institut für Normung or DIN), DIN 7349 establishes tolerance classes for shafts and bore holes based on their diameters. The standard applies to shafts and hub connections with diameters between 1 mm and 500 mm.

The purpose of DIN 7349 is to simplify design, ensure interchangeability of shafts and hub connections, and promote high quality manufacturing. By providing a consistent system for determining tolerances based on the connection's size, DIN 7349 makes it easier for engineers to design components that will align properly.

Key Elements and Details

DIN 7349 classifies tolerances according to "fits" - clearances between the shaft and bore hole that account for errors in manufacturing and thermal expansion. These fits are categorized into classes such as H7/h6, H7/k6, and more. The classes are denoted by symbols; for example, "H" refers to the hole while "h" refers to the shaft.

In total, DIN 7349 specifies tolerance classes for over 30 different fits. Diagrams and tables within the standard illustrate the specific tolerances and limits associated with each class of fit for different diameter ranges.

Additionally, DIN 7349 provides guidelines and calculations for determining the maximum permissible torque, service factor, and optimal engagement length based on the selected fit. It also covers topics such as surface roughness and corrections needed when using thin-walled hubs or slender shafts.

Benefits and Applications

Some of the benefits offered by properly utilizing DIN 7349 include:

• Improved machine performance from optimal shaft and hub alignments
• Straightforward system for selecting right fit class
• Interchangeability between different manufacturers/designs
• Higher power transmission efficiency
• Longer service life for rotating machinery

DIN 7349 is widely applied across many industries dealing with power transmission and rotating equipment. Some common applications include:

• Gears - connecting shafts to gear hubs
• Couplings - joining drive system shafting
• Electric motors & generators - fitting rotor shafts into housing
• Pumps, fans, compressors - transmitting torque from motor to impeller
• Machine tools - spindle connections

Implementing DIN 7349 Properly

To leverage the full benefits of DIN 7349, engineers must properly reference the standard and clearly communicate fit designations with manufacturers. Some key guidelines include:

Identify Diameter Range of Interest

DIN 7349 must be applied appropriately based on the actual diameter of the shaft and mating hole. Improperly sized fits can lead to problems with slipping, excessive stress, or interference.

Select Optimal Fit Class

Consider factors like the torque transmitted, desired contact pressure between surfaces, and allowance for thermal expansion when selecting the fit class.

Account for Special Cases

Make necessary corrections or adjustments to tolerances when dealing with slender shafts, thin-walled hubs, or other special circumstances.

Clearly Communicate Designations

Unambiguously identify fit classes (ex: H7/h6) on drawings and models to ensure correct interpretation by manufacturers.

Taking the time to properly implement DIN 7349 leads to better performing shaft and hub connections for rotating machinery. The standardized system saves time otherwise spent determining appropriate tolerances.

Conclusion

As the German national standard for tolerances of shaft and hub connections, DIN 7349 plays an important role in rotating machinery design. Understanding the classifications of fits based on diameter range within DIN 7349 is key for appropriately designing, manufacturing, and assembling shafts, gears, couplings, and other power transmission elements.

Specifying DIN 7349 fits clearly on component drawings allows for correct interpretation and quality manufacturing. When utilized properly, DIN 7349 delivers reliable, efficient and interchangeable shaft-hub connections - making it an indispensable standard for the progression of engineering and industry.

FAQs

What is the scope of components covered in DIN 7349?

DIN 7349 covers tolerances for cylindrical shafts and the mating holes they fit into. It is applied to connections with diameters ranging from 1 mm up to 500 mm.

What parameters are used to determine tolerance classes?

The tolerance class designation depends on the diameter range as well as the type of fit - clearance, transition, or interference. Classes specify boundaries for both the hole and the shaft.

Can DIN 7349 be used with both static and dynamic load applications?

Yes, the specifications in DIN 7349 are applicable to components subjected to static, dynamic, and fluctuating loads - such as in power transmission systems involving rotating machinery.

Is DIN 7349 only for new designs or can existing hardware be assessed as well?

Engineers can use the limits and guidelines provided in DIN 7349 to evaluate tolerances for existing shaft and hole connections to determine if they meet specifications.