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Engineering Focus: Using Finite Element Analysis (FEA) in Seal Design

Finite Element Analysis  provides data to help predict how a product will function under those applied conditions and identifies areas where the design can be optimised and improved, without having to test multiple prototypes.
Here we explain how our engineers use FEA to design the optimal sealing solution for our customer applications.

What is Finite Element Analysis (FEA)?

Finite Element Analysis (FEA) is a computerised modelling method for predicting how an object reacts to forces, whether directly applied or generated by pressure, temperature effects or vibration. FEA provides data to help predict how a product will function under those applied conditions and identifies areas where the design can be optimised and improved, without having to test multiple prototypes.

Our specialist software uses mathematical models to understand and quantify the effects of real-world conditions on a part or assembly. It can be used to identify potential causes where sub-optimal sealing performance has been witnessed and can also be used to guide the design of surrounding parts, especially for products such as diaphragms and boots where contact with adjacent parts may need to be avoided. The software also allows force data to be extracted such that, for example, compressive forces for static seals and friction forces for dynamic seals can be accurately predicted to help our customers in the final design of their products.

 

 
Why do we use Finite Element Analysis (FEA)?

Our engineers encounter many sealing applications that are critical and have many complicating influences. Envelope size, housing limitations, shaft speeds, pressure/temperature ratings and chemical media are all application parameters that our engineers must consider when designing a seal.

In isolation, the impact of these application parameters is reasonably straightforward to predict when designing a sealing solution. However, when you compound a number of these factors (whilst often pushing some of them to their upper limit when sealing) it is crucial to predict what will happen in real application conditions. Using FEA as an iterative tool, our engineers can confidently design and then manufacture robust, reliable and cost-effective engineered sealing solutions for our customers.

How do we use FEA?

Starting with a 2D or 3D model of the initial design concept, produced within our advanced CAD system, we then apply the boundary conditions and constraints supplied by the customer, including pressure, force, temperatures, and any applied displacements. A suitable finite element mesh is overlaid onto the seal design, ensuring that areas of most interest have the necessary mesh size to ensure accurate results are returned for these regions whilst utilising larger mesh sizes in areas with less relevance or lower levels of displacement to minimise the computing time required to solve the model.

Material properties are then assigned to the seal and hardware components. Most sealing materials are non-linear, whereby the amount they deflect under an increase in force varies depending on how large that force is, unlike the straight-line relationship for most metals and rigid plastics, at least over the displacement range relevant to sealing applications. This complicates the material model, and extends the processing time, but we use in-house tensile test facilities to accurately produce the stress-strain material models for our compounds to ensure the analysis is as representative of real-world performance as possible.

 

What happens with the FEA data?

The analysis itself can take minutes or even hours of computing time, depending on the complexity of the part and the range of operating conditions being modelled; behind the scenes in the software, many hundreds of thousands of differential equations are being solved.

The results are then analysed by our experienced seal designers to identify areas where the design can be optimised to match the specific requirements of the application; such requirements may be for sealing at very low temperatures, a need to minimise friction levels with a dynamic seal, withstand very large pressures without extruding, or whatever sealing system properties are most important to the customer and the application.

Results for the finalised proposal can be presented to the customer as force/temperature/stress/time plots, numerical data or animations showing how a seal behaves throughout the analysis, as appropriate to their needs, and can be used as validation data in their system design process.

Case Study Project 1

Faced with very tight packaging constraints, a customer requested a diaphragm component from us for a valve application. Using FEA, we were able to optimise the design not only of the elastomer diaphragm itself, but also propose modifications to the customers hardware components that interfaced with it in order to increase the available space for the diaphragm, keeping material stress levels low to remove any possibility of fatigue failure of the diaphragm over the life of the valve.

FEA Case Study Project 2 Image FEA Case Study Project 2 Image

 

 

Case Study Project 2

A customer approached us to design a PTFE rotary lip seal that had to meet tight maximum torque requirements as their system was driven by a size-limited low power motor with modest levels of torque available.

At the same time, high seal tightness was required as leakage of the media would have caused significant problems.

By using an iterative FEA process, we produced a seal design that optimised the sealing lip geometries to provide the lowest levels of rotational friction drag whilst ensuring sufficient contact force to maintain a tight seal, and went on to provide seals that successfully passed customer validation testing.

FEA Case Study Project 1 Image FEA Case Study Project 1 Image

 

With the increased confidence in a proposed sealing solution that FEA provides, our customers can plan lower levels of physical testing and remove contingency for re-design steps, reducing their project lead times and costs, facilitating a faster and more cost-effective time to market for their new products.

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