SPInduwedge – Technical evaluation

Technical evaluation of the properties of SPInduwedge

On the Vienna University of Technology an investigation was carried out to prove the stability of SPInduwedge and to compare the mechanical data with conventional magnetic slot wedges.
The results of this investigation are shown in the diagrams of this folder and in an descriptive 23-page booklet (Technical Report), which can be ordered from ASPIN.

The superiority of the mechanical properties of SPInduwedge can be seen when looking on the values of delamination load which corresponds to the force of inserting the wedge with a hammer (diagram 1), flexural strength (diagram 2) and module of elasticity (diagram 3). Moreover SPInduwedge react different to forces which normally damage the wedge, which can be seen in picture 1 to 3. These very pictures proves the superiority of SPInduwedge.

Conventional slot wedge

Conventional slot wedges show tearing on the cleavage test, sometimes the tear is propagating on the whole length of the wedge and the glass cloth is laid open. Subsequently this leads to complete destruction.


The fundamental difference of the slot wedges SPInduwedge to other wedges is not only the fact that they endure the highest cleavage forces (see values of delamination load in diagram 1) but also that a damage by a cleavage force leads to a completely different kind of fracture. The force effect, as seen in the picture, is deviated nearly in a right angle to the side. This means that the damage is limited to a small area and that the internal structure of the wedge remains intact. So the stability remains almost unaltered.

Laminated slot wedge

In the picture you can see a laminated magnetic slot wedge with poor adhesion between the layers, so that even small forces lead to delamination.

Diagram 1: Delamination Load

Delamination load obtained by cleavage test according to DIN 53464. In this diagram you can see the values of 4 different conditions: unaged and aged wedge at room and elevated temperature (23°C and 155°C).
Condition (1) is relevant when inserting the wedge with a hammer, condition (2) is relevant in an operating system. For comfortable interpretation the bars are starting at a force of 1000 N, so that values below 1000 N are bars pointing down. SPInduwedge shows the highest values at all conditions and therefore has the best cleavage protection, not only because of the high values of delamination load but also because of the different behavior to cleavage forces.

Diagram 2: Flexural Strength

SPInduwedge shows the highest values for flexural strength at elevated temperature. Only competitor 4 shows good flexural strength at room temperature too, but the values decreases to 54 MPa at 155°C, which is not satisfying. Data is obtained by bending test according to ISO 14125.
The advantage of SPInduwedge is obvious, especially when you compare figures of non-magnetic material (e.g. EP GC 203/ G-11/ HGW 2372.4 or similar): SPInduwedge F HP is in the range and even surpasses some non-magnetic materials in mechanical properties.

It can be seen that ageing (heating at 210°C for 14 days) does barely influence the mechanical properties at room temperature, but very well at elevated temperatures. At 155°C all materials shows – as expected – in general lower mechanical properties compared to room temperature, but due to a post curing effect the aged material shows improved properties at this temperature except for materials of competitor 4, where properties decrease extremely for some reason.

Diagram 3: Module of Elasticity

When looking on the figures of module of elasticity the interpretation is analogical to previous diagram 2: Good values at room temperature are not proving good values at elevated temperature. But in many data sheets values for elevated temperature are not given. SPInduwege slot closure keys are they only one showing a module of elasticity above 15.000 MPa at 155°C, some competitors are not reaching this value at room temperature.