When Sly Agri, the UK specialist agricultural machinery manufacturer, was looking for a set of bearings that would assure reliability in the field, with constant knocks, shimmies and shakes and whole load of mud thrown in, without any maintenance, head engineer Toby Kilham turned to igus for advice. Kilham turned the finished track system from a conceptual idea into a working product in just two months.
Tractors have been on tracks for years; the first rubber tracked tractor came about in 1986. Since then there has been a growing tendency towards tracks over tyres, to help minimise deep soil compaction. Soil compaction is a major problem within farming and, with larger, heavier machinery being used, there can be some serious damage to the fields, which can be costly to put right and have a huge impact on crop yields if not done. The irony is that the tractor might weigh anything from 12 - 20 tonnes. The grain cart, on the other hand, can weigh close to 50 tonnes, when fully laden - over twice the weight of the tractor, yet traditionally the carts are not on tracks.
“We already had a lot of experience servicing and maintaining these rubber tracked machines, so the logical route was to develop our own undercarriage to go onto other machinery,” said Kilham. Sly Agri first conceived the idea of the single trailed track system back in 2011. At this time the engineering design was only in a conceptual form with no prototype to build and test. Last year, however, the company was approached by Perard, the French agricultural machinery manufacturer. It initially wanted Sly Agri to supply it with a track and some rollers to enable it to build its own, but soon realised it was unable to hit the target build cost. Perard asked Sly Agri to design and build a track system; this was in April and it wanted delivery in June.
“Bearing in mind, at this stage, the design was fairly conceptual and not into the required detail to carry out its function,” continued Kilham. “The next two months were a coffee fuelled blur, from my perspective – trying to finalise the design, check the loading, co-ordinate the integration onto the grain cart chassis, as well as arrange manufacture of all components at local machine shops.”
EU regulations mandate brakes on trailers and to make contour following much better in the field an integrated suspension. “From our experience of seeing the US track machines, we knew that without a suspension it would crack and shake itself to pieces in a few seasons,” explained Kilham. “The idea of our system was to prevent that from happening, by cushioning the impacts from rocks and ruts. We use hydraulic cylinders with accumulators and have a number of pivoting points in the system, which is where the igus bearings are used.”
Before choosing bearings, Kilham did look at the obvious choice of metal bronze bearings and using grease, but due to the high level of maintenance required, it wasn't an option. “Usually the person driving the chaser tractor is young and often isn’t concerned too much about maintaining the machinery, perhaps only greasing once a week instead of daily,” he explained. “During harvest season time is of the essence and, quite often, tractors are brutalised. I know this because I am a farmer’s son and I've seen machinery treated badly; as an engineer, I have sympathy because I know how much effort is required to try and make them bullet proof!”
Sly Agri had experience working with igus on the cultivator side of its business. The plastic bushes suited this application because they are easy to install, require no maintenance and, although much smaller, have to deal with similar conditions.
Kilham highlighted that product selection and using the online catalogues and download tools were of particular use: “As a design engineer, I can simply grab a 3D model and drop it into the CAD programme in minutes, rather than having to create parts from dimensional drawings. The information is also very clear on hole-sizing, etc. Also, when we gave Paul Smith, who is our local igus representative, the information on loading, frequency of oscillation, etc., we got all of the bearing life calculations back very quickly, which was what we needed given the time constraints – letting the experts do this takes a significant risk away from us.”
All bushes were from the iglidur range, which was recommended for the application to prevent the ingress of water and dirt. “On stripping down after the season, the condition of the bearings was almost as good as new – that’s after a few hundred hours of constant abuse,” noted Kilham.
Sly Agri’s next challenge is to implement power assist steering using hydraulic motors to enable to track system to drive itself, or at least assist the tractor.
About the track system
The track system is a standalone undercarriage that can be mounted up to almost any chassis and effectively transfers the weight on the machine onto the ground in a far more controlled manner than tyres. The deep compaction on the soil is greatly limited, saving costs and improving yields. The system also rides smoothly over bumps and ruts due to the multiple pivoting nature of the suspension.
It is designed to operate at speeds of up to 40kph with loads of up to 50 tonnes and uses 18 pivoting axles in total over both sides to follow the ground and absorb the loads. There is a main central shaft, which gives the overall front to rear pivoting motion, with front and rear frames that can oscillate along with double-acting bogeys that move in the lateral and longitudinal directions to reduce point loading on the system and make the machine ride much smoother.
It was an engineering challenge to ensure all the components were capable of this loading in the types of conditions they would experience - often submerged in water and running all day long means good seals and resistant bushes are required.