Premature track failure on skid steer loaders.
Over the last six years we have been involved in the problem solving to early failure on several model skid steer loaders of the rigid frame type and offer the following comments.
Several years ago I was involved in discussion with Japanese manufacturer over claims by resellers to the track life on this type of unit being 1000 hrs or greater.
It was where the life on several sizes was rated between 500 – 700 hrs with the following conclusion.
A rubber track excavator has a rated track life of around 2000 hrs, with the conclusion that 25% of these hours would be walking. This with the blade being used to fill open drains gave the rated walking life of around 500 – 700 hrs to that type of track.
On the skid steer there are several contributing causes to early failure and I list for your consideration.
- The track loader when used with the weight on the bucket and down force, places all the weight to the rear idler and the track then is without recoil protection with the track being in its higher tension between the rear idler and the engaged sprocket teeth. This is noticed when the machine is reversing and the greater movement of the front idler in recoil is due to the forced pull from the sprocket to the front idler over the whole top length of the track. The recoil spring rarely moves when pushing.
- The type of track used is more common on tracked dumpers and it must be remembered that the drive on a dumper is always at the front in direction of travel. The recoil idler is at the rear and the tension is pulling along the top of the track allowing affective recoil.
- The diameter of the loader rear idler when compared to other applications is much smaller in diameter and this when the track is pulled around its circumference, sets up a rocking motion of the pin plate like a see saw inside the track which is accentuated when the idler radius becomes smaller. The average diameter of an excavator sprocket or idler is greater than this rear idler as used and the rocking of the plate is not as severe. In the rocking of the pin plate it wears against the insulator layer covering to the wire cording and in all my examination of failed tracks it is very obvious that this contributes to the early failing when the pin plate eventually starts a direct contact to the wire cords. This early failing appears on many tracks around 500 hrs. You will also notice that the track never wears its tread before the failing occurs and it is always a cord failure that ends the track life. This life varies in application and is with earlier failing occurring to a machine which is constantly changing direction.
My conclusion to the problems:
This type of machine is where the manufacturer advises its intended use as a tool carrier for use on sand, soil and turf. The three point turning method is recommended with avoidance to trash or aggregate ingestion in the rail from on the spot turning. When a load is carried in the bucket the weight is on the front idler and therefore allows some recoil movement.
The operator tends to use this machine, turning as they did with a wheel skid steer. Recoil forgiveness is only designed for loose material and not aggregate or trash.
The track in its design needs shorter pin plates to allow its radial curve to be as the smaller rear idler on this type of machine is designed, the insulator layer needs to be increased and the cording size increased also to allow for the extra recoil tension. Several manufacturers are currently working on this change although they make no claim to fault in their existing design. They claim the machine manufacturer has used an existing track and the track manufacturer is working to modify its new intended use. The fault is the small radius of the rear idler when compared to the pitch of the track and the length of the plate. I.e 100 mm pitch around 400 mm wheel.
The manufacturer of these machines under estimated the intended use of this machine in our market and applications it was sold into and we need to request their assistance in obtaining better tracks. Another common failure we have experienced is to the compound being too hard and again the elasticity of the outer layer has been a problem when pulled around the smaller radial surface of the rear idler. Manufacturers have softened the compound as they again found the need.
My experience is where I have been an Advanced Qualified engineer for 45 years ,fitted the first rubber track in 1974 and I sell around 250 pieces per Month. My website dtn.com.au will give reference to our company and I am available to discuss points of this letter at any time.