Polymer bearings for high dump buckets

For excavator drivers and construction machinery hire companies, they are "just" a tool - but one that has to meet the highest demands in terms of load capacity and wear resistance. This is because the shovels and clearing buckets of excavators and wheel loaders that we are talking about here dig into the material with high dynamics in each individual operation and also encounter resistance like hard rock.
 
The environmental conditions during this work are unfavorable, not to say extreme: the construction machines can stand in water or remove highly abrasive material. The stress acting on the tools is very dynamic and hardly calculable, especially since the equipment is also loaded on one side and is often "misused" on the construction site.

The 8.5 m3 high dump bucket is also equipped with iglide® plain bearings. On the left: Dipl.-Ing. Sven Gasterstädt from L&K, on the right: technical igus® sales consultant Kevin Büttner.

Problem

The bearing point must be maintenance-free for a total of more than 4,000 hours in an application. Completely regardless of whether the excavator is standing in water or removing highly abrasive material. In addition, the bearing points are exposed to heavy loads and shocks. The exposure to dust and dirt is an additional challenge for the bearing positions.  

Solution

With maintenance-free and self-lubricating iglide® plain bearings, the required service life was even exceeded.  Even after 5 years of use there were no complaints or the need to lubricate or replace the plain bearings, despite the highest demands. They are also around 40 percent more cost-effective than the previously installed composite bearings.

The wide standard product range, which includes backhoe buckets of all kinds, high dump buckets and side dump buckets, is the basis for the most varied special designs. This is because the tools are always manufactured to customer specifications, and with a short lead time. Dipl.-Ing. Wolfgang Anderle, Managing Partner of L&K: "We deliver at short notice, usually within two to three weeks." The modular design of the product range contributes to this as much as the modern production with CNC machines in all areas. Another important factor for the high quality and short delivery time is the know-how of the welding specialists, who are trained and further educated by L&K in its own DVS course center.

Not all buckets and grabs from L&K are as large as these - but all are characterised by extreme load capacity and long service life.

Requirement: 4,000 hours of maintenance-free operation under harsh conditions

For about fifteen years, the basic material of the L&K tools has been the extremely resilient Hardox steels of the Swedish steel producer SSAB. Similarly resistant components must also be used on the joints that help tilt a high dump bucket or open and close the halves of a grab bucket.
 
The requirement profile for such bearings is clearly defined. Dipl.-Ing. Roland Georgi, Design Engineer and in charge of Quality Management at L&K: "The bearings must achieve the same service life as the bucket. And they must be maintenance-free."

Lightweight design counts - even for excavator buckets

Here the designers, who work with modern CAD tools, originally used metal plain bearings with a sintered-on gliding layer. Five years ago, L&K tested an alternative to this composite design for the first time and used bearings made of iglide®. The high-performance polymer with embedded solid lubricants works as a "mono-material" over the entire service life without external lubrication and is extremely resilient.
 
There are three good reasons for this choice­­: "The polymer bearings are about 40 percent more cost-effective. They require no lubrication and their mass is less than that of the previously installed composite bearings." Indeed, mass plays an important role for the design engineers at L&K: "We manufacture moving components. If the bucket becomes too heavy, the dynamics suffer. For this reason, lightweight construction is also an important trend in our company, whereby the load-bearing capacity must not be impaired."

More and more series converted

The first tests were carried out to the complete satisfaction of both the L&K engineers and the users. The ultra-light design, which is supplemented by iglide® plain bearings, is protected by a utility patent. It is used in a wide variety of applications, such as high dump buckets, which are used as salt loading buckets in the salt depots of municipal utilities, and in various designs of grab buckets and trench buckets. For a high dump bucket with a capacity of 8.5 m³, L&K has already implemented a real "XXL application" for the maintenance-free iglide® plain bearings several times.

Conversion without changing the design

The designers of L&K use bushings with diameters of 40 to 80 millimeters made of the universal material iglide® J as well as iglide® P, which remains particularly dimensionally stable under high loads and fluctuating environmental conditions including humidity.
 
Another positive aspect from the point of view of the L&K designers is that the plain bearings made of metallic composite material can be replaced 1:1 with iglide® bushings. An alteration of the surrounding structure is not necessary. Plus, both purchasing and production are satisfied with our fast delivery in small batch sizes since L&K usually only needs two bushings per tool.

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