Tyre protection chains have been an integral part of the operation of many hard rock quarries around Australia for decades. As new quarries open and the current tyre shortage environment continues to drive operators to source solutions to the occurrence of tyre-related ‘unplanned downtime’, we will take a look at the use of tyre protection chains as an answer.
First, let’s look at the applications for tyre protection chains in the modern quarry environment. Tyre protection chains were first used in the 1950s. As mechanised earthmoving equipment developed, demands by quarrymen and miners for higher productivity meant larger machines, with higher horsepower and in turn larger tyres.
As the tyre size increased, so did the replacement costs. Premature tyre failure and poor service life became more than simply an inconvenience, significantly impacting on bottom line profits. Sudden tyre failure meant operating costs of large wheeled machines became unacceptable in many applications.
Also developed in Europe, the existing non-skid snow chain (also known as traction chain) was the genesis for the creation of tyre protection chains; the concept was taken to the next level and the first crude chains were born.
Jump ahead to today and after five decades of continual development in tyre chain design, metallurgy and heat treatment technology, we can now manufacture chains suitable for the world’s largest wheel loaders. Today’s chains far out perform those of the past in terms of strength, wear resistance (service life) and consistency of quality.
When you consider the power, loadings and tractive forces of modern hi-tech wheel loaders used in quarrying and mining, it becomes obvious that it takes tested and proven design, together with the highest quality materials and manufacturing processes, to produce a product that can handle the forces generated by these machines.
Tyre protection chain design and manufacture
The production of tyre protection chains requires specialist facilities and technical capability. RUD/Erlau chains are manufactured in a state-of-the-art works located in southern Germany. Due to the high capital costs and production volumes required to make fabrication economically viable, there are no local manufacturing facilities or capability in Australia – so all of the products used here are imported.
Tyre protection chains essentially consist of three main sections – the inner and outer sidewalls and the centre net. Each of these areas is constructed of variations of basically only two main components – the mid-ring (also known as the connecting ring), and the forged wearing (vertical) link. (See Fig. 1.)
The mid-ring (Fig. 2) is the basic component which classifies the chain size, and determines the design to suit to a particular machine and tyre size. For instance, on most quarrying wheel loader tyre sizes of up to 35/65-33, the material diameter of the mid-ring is usually 16mm, while for larger tyres of up to 45/65-45 it’s typically 18mm. For larger mining machines, 22mm mid-rings are used.
The metallurgy involved in a chain’s manufacture is relatively advanced, using a CrNiV alloy which is then case hardened to between 61 and 68 Rockwell C. This provides a component equipped with the core tensile strength and ductility needed to withstand the high forces generated by the machine and tyre, and yet also have the level of hardness needed to provide a long service life, typically up to 30,000 hours (or higher) in low abrasion rock types such as limestone.
In a “close” mesh protection chain, four vertical links are attached to each mid-ring. The vertical wear link is also manufactured from a CrNiV alloy, drop forged to provide maximum toughness and then also heat-treated to between 61 to 68 Rockwell C. It is the vertical wear link which provides the protection against cuts and staking in the tyre tread area, and how this component is designed and manufactured directly translates to the amount of protection the tyre receives (percentage of coverage), and the length of service life the chain delivers in the application.
The global tyre shortage
Long before the relatively recent advent of earthmover tyre unavailability, tyre protection chains have been well accepted in the hard-rock quarrying and mining sectors as being a proven means of reducing tyre operating and replacement costs, and eliminating unplanned downtime resulting from sudden tyre failure due to cuts and penetration.
Now, over three years into the tyre shortage, and tyre protection chain viability is no longer just assessed on purely operating cost terms. It is often now a matter of “What can I do to preserve my available stock of tyres?” Unavailability of tyres has been the catalyst for many previous ‘skeptics’ to take a different perspective, and trial the product. In almost every instance, once the product has been in service for a short time, the many benefits that chains deliver show through:
? Machine availability (reduced downtime due to tyre damage/repair).
? Improved productivity (due to reduced digging cycle times).
? Better traction.
? Lower fuel burn.
? Significantly extended tyre service life.
If we consider the economics of just the last point alone, we can quickly see the results in the table on page 84. Note: The data is based on typical tyre costs prior to the impact of shortage and subsequent cost escalations. If you add to these figures the cost impacts of unplanned downtime on productivity, and the economic benefits can quickly be multiplied many-fold.
Installation and maintenance
Fitting of tyre chains on a quarry size machine takes on average about 1.5 to 2 hours per wheel.
Chains can be fitted to any tyre type – bias, radial or slick, new or worn – as long as the case is in good condition. And there is no change to the normal operation of the machine – tyre pressures and tramming speeds and distances remain virtually unchanged, even load and carry is still viable. The one thing to consider is maximum recommended speed for machines with chains is 25 km/h, but tramming distances of several kilometres each day are commonplace in many of today’s open-cut mines and large quarries.
Maintenance of modern chains is much reduced. With some routine attention to basic daily checks, normally done by the operator, ensuring the chains are maintained and tensioned within the operating parameters will provide long and trouble-free service life.
When necessary, parts replacement is simple and can be done in only a few minutes, and with no requirement for special tools. And if the occasional component breakage does occur, consider this: if a high tensile, case-hardened piece of alloy steel has been broken due to rock impact, imagine what would have happened to the tyre if the chains were not fitted – $45 for a repair link versus possibly $25,000 (or these days, much more) for a new tyre. Now, just how long will those chains last?
The service life of a chain is determined by many parameters, most of which are site and application specific. These include machine travel speeds and distances, abrasiveness of the rock/ore, wet or dry floor conditions etc. So there is no stock standard answer to the question. Typical chain service life in quarry applications in Australia varies from as low as 5000 hours in abrasive granites, to more than 35,000 hours in hard limestones.
In high abrasion applications (eg granite), a heavy-duty design is recommended. A chain with a large wearing-link presents the largest possible surface area (and wear volume) to the ground, providing both maximum protection of the tread area, due to the small mesh opening, coupled with the longest wear life for the chain, due to a large wearing link mass.
For lower abrasion rock types, a chain design with a lower wearing mass will reduce the initial outlay while still delivering exceptional service life. Various derivatives of vertical link shape and profile together with mesh pattern can result in a reduced purchase price, yet delivering excellent traction characteristics. It’s really “horses for courses”, and that’s why the application and product experience of your chain supply/service partner can assist you in the correct selection of the chain that will offer the best value and performance in your specific situation.
The combination of modern design, quality product and in-field expertise will lead to results which will ensure most quarry operators will ultimately say: “I can’t believe how well those chains have lasted, and how much money I’ve saved.”
Irrespective of the service life you can achieve with tyre chains in your particular application, the facts are clear. Tyre protection chains have been around for more than five decades now, and tyre shortage or no tyre shortage, the proven benefits obtained will ensure that while every rock can cut rubber, and tyres need air, chains will be going around, and around, and around for a long time to come.
Source: RUD Chains