Ceramic material has self-healing effect

New spreader roll in the spotlight

2015-10-06 - EvoStretch is Voith’s new spreader roll for the paper industry. The roll features a bearing that is offered exclusively by Voith. In this interview, Thomas Holzer and Thomas Weisshappl explain the special features and benefits of the EvoStretch spreader roll.

Why is Voith launching a new spreader roll on the market?

We want to extend our spreader roll technology for the paper industry and at the same time reinforce our position as a one-stop-shop. With EvoStretch we can now offer our customers a high-quality product that is also technologically unique.

And what is unique about this roll?

What is special about it are its ball bearings, which incorporate some ceramic balls to extend service life.

Can you explain this please?

Gladly! For the EvoStretch we developed a new ball bearing in collaboration with SKF, a leading manufacturer of bearings. What is special about our new ball bearing is that as well as the usual steel balls one or two ceramic balls are integrated into each bearing. This gives the bearing a kind of self-healing effect.

How can we visualize this self-healing effect?

Ball bearings in conventional spreader rolls are made entirely of steel. During operation, extremely tiny particles detach from the bearings due to the millions of rolling movements and these can gradually damage the contact surfaces. These can in turn cause roll vibrations. Once this stage is reached the roll bearings have to be replaced.

In the EvoStretch, the ceramic balls assume a kind of polishing function. Ceramic is harder than steel and therefore is capable of smoothing the contact surfaces. As a result, the total service life is longer than in conventional rolls.

Are these kinds of bearings really only available from Voith?

Yes, the bearing is manufactured exclusively for us by SKF.

Is the new bearing already being used in the industry?

We have already upgraded some third party rolls in our service center and fitted them with the new bearings. On the test rig in the service center and during various field trials on paper machines the bearings were and are still running according to expectations. Very thorough laboratory tests at SKF also showed that the bearings offer distinct advantages over standard bearings. The contact surfaces also take considerably longer to show signs of wear.

Is Voith also installing the new bearing into rolls from other manufacturers?

At our service center we can retrofit the bearing to any spreader roll regardless of its manufacturer. We can also convert rolls built in the imperial system to the metric system, which offers the great advantages of shorter delivery times and lower costs.

Is this kind of rebuild worth it?

It pays off for paper mills after just the second service following the rebuild. And speaking of service, with our StretchUp Service we are now also offering a service package especially for spreader rolls that can be carried out in our roll service centers in Asia and Europe. Another innovation is our SolarStretch polyurethane sleeve for spreader rolls. It offers certain benefits over rubber sleeves and can also be supplied and mounted at our service centers.

In what respects is the polyurethane sleeve superior to the standard rubber sleeves?

The tests that we performed on SolarStretch clearly demonstrated that the abrasion resistance of polyurethane is twice as high as that of rubber. SolarStretch also performed better in respect of tear resistance and dynamic properties. Thanks to the polyurethane, the generation of heat during the dynamic load is kept to a minimum.

Read more about EvoStretch and StretchUp Service