Technical background

 

Fitting

In one go you can fit two pointers, as these are linked. The looks is equal as the standard pointers, and disruption is indicated Immediately. The height is 7 mm equally as our standard pointer, such that retorquing while fitted is an option.

Stages of tightening.

During the fitting process of a wheel, usually the nuts are rotated by hand such that the wheel won’t fall of. Furthermore pneumatic tightening tool is used up to around 400 Nm, which with most trailers is an angle of around 55 degrees from the starting point that all play is disappeared between nut, wheel and hub.

Using the torque wrench up to the advised torque level (for example 630 Nm) the angel of 55 degrees will be enlarged up to around 90 degrees, and the required clamping force is reached.

Wobbling wheels / Clamping force.

Without clamping force between the wheel and the hub, the wheel starts wobbling, usually followed by shearing of the nuts or snapping the studs with wheel detachment as the final outcome.

Therefore the presence of clamping force is essential to keep wheels attached.

The clamping force is the direct result of the pull back/elasticity of the steel stud, as the stud is stretched /elongated by tightening the nuts.

The maximum elasticity level of the steel is indicated as the Yield point. Commonly the fasteners are designed to stretch the stud up to 75% of it’s limit.

Beyond this point the elasticity fades away and so does the clamping force. Permanent deforming takes place, elements becomes fatigue and leading to failure.

The graph shows the linear properties of the material up to the Yield point. For those reasons

over torqueing and additional stress can lead to dangerous situations.

Relative movement of wheel and hub and loosening torque

Under the circumstances that the wheel and the hub are relative moving, the stud is under stress and bends, with the possibility to create a loosening torque on the wheel nut. In addition the additional stress can make the stud fatigue.

Tests with our Wheel nut loosening machine based on the Junkers principle, did show that the actually loosening torque is a relative constant share of the tightening torque in the range of 5 to 8 %. So tightened at 630 Nm, the loosening torque at that moment can be as big as 30-50 Nm.

When the tightening torque drops due to loosening rotation of the wheel nut, the loosening torque reduces an equal share.

So after a loosening of approximal a 90 degrees rotation the clamping force/loosening torque is completely gone starting at 630 Nm, and over an angle of 55 degrees is fastened only with the pneumatic tool.

Twindicator

During the loosening/rotation of the nut/pointer the bridge under the pointers will be stretched and elongated over an angle of around 50 degrees. The increasing counterforce becomes constant

when the maximum indication angle of 50 degrees is reached.

Further rotation of the nut pushes the mating teeth of the Twindicator ring to the outside, till the hexagon nut slips/rachets to the next set of 6 teeth clamping the nut again and still indicating.

Retaining function

As soon as a balance arises between the loosening torque and the counterforce by the Twindicator, the loosening rotation comes to a stop.

Due to the presence of loosening torque, being a share of the

tightening torque/clamping force, clamping force is present and wobbling of the wheel is prevented.

This is the retaining function of the Twindicator.

Will it retain for ever? That is hard to warrant and very unlikely to do so. Heat development, wear of the stud holes, the stud fitting, all kind of elements and more can influence the circumstances, and the wheel needs maintenance.

Interparts Automotive 21-10-2019