Remanufacturing – the industrial reconditioning of used machines and components – offers enormous potential in tunnelling. Tunnel boring machines (TBMs) in particular, individually designed for each project and subject to heavy wear and tear during operation, are ideally suited to this form of reuse. This article shows how, through systematised processes, quality-assured standards and systematic design for remanufacturing (‘design for reman’), manufacturers can not only create ecologically and economically sustainable solutions but also speed up project execution at the same time.
Specific practical examples, such as the standardisation of bogies, illustrate how efficiency gains can be achieved and the circular economy put into practice through modularisation and targeted technical adjustments. Remanufacturing is thus further establishing itself as a forward-looking industrial strategy in mechanical engineering for tunnelling.
INTRODUCTION
Remanufacturing has long been established in the tunnelling industry: the TBMs in the field are a mix of ‘reman’ and new parts. Herrenknecht has been optionally buying back used machines from its own production on predefined terms for years. What is new now is that subsequent remanufacturing is systematically factored in at the design stage. A corresponding ‘design for reman’, i.e., the goal of parts that can be reused as easily as possible, brings efficiency and cost benefits that manufacturers can pass on to their customers.
In remanufacturing, existing, used components are systematically reconditioned in an industrial process and reassembled into a new product. Unlike a refurbishment, for example, the result achieves at least the quality level of a new product, thereby enabling another life cycle.
This has ecological, economic and social benefits: on the one hand, material consumption and negative effects on the environment can be reduced significantly; on the other, costs can be lowered. For this reason, prices for reconditioned products are generally lower than those of equivalent new products. Current economic and political conditions and trends such as sustainability and strained supply chains have meant the acceptance of remanufacturing measures has been increasing for years.
REMANUFACTURING TBMs
For several reasons, remanufacturing is particularly suitable for TBMs: firstly, they are subject to a high level of wear and tear in practical operation underground; secondly, TBMs are generally custom-built machines designed to meet specific requirements.
Herrenknecht, for example, has delivered around 1,500 machines in the 50-year history of the company because, as is widely known, TBMs are designed differently for every jobsite and requirement. So, the machine is not normally ready for use again immediately on completion of a project.
Machines used for multiple assignments without any structural changes, on the other hand, are the exception, for example when constructing identical cable tunnels for a few wind farms. But even these must be overhauled and at least partially reconditioned between deployments.
GENUINE BENEFITS
Against this background, the remanufacturing of a TBM is particularly interesting for the user and for three reasons: time savings; sustainability; and, cost effectiveness.
- Time savings: tunnelling projects are often under high deadline pressure. This makes it even more important for the TBM to be available as quickly as possible. Here, the use of existing components offers decisive time advantages, as they do not have to be laboriously manufactured and potentially delivered as well.
- Sustainability: using components multiple times reduces the ecological footprint, as greenhouse gas emissions are significantly lower. A master’s thesis carried out at the German Pforzheim University in 2021, in collaboration with Herrenknecht, quantifies this effect precisely: On average, 71.42% of emissions can be avoided per tonne of remanufactured material, compared to the production of new material. Here we consider the CO2 equivalent (CO2e). These results have since been confirmed by certifier TÜV Süd and verified in relation to the requirements of DIN EN ISO 14040:2009, DIN EN ISO 14044:2006 and DIN EN ISO 14067:2019.
- Cost-effectiveness: finally, the result of remanufacturing is cheaper than a new machine. However, given the high level of work required, these effects are not as high for TBMs as they might be for other, less complex or sophisticated products.
DEFINITION AND MINIMUM REQUIREMENTS
But what exactly does ‘remanufacturing’ mean?
At first glance, the term seems to speak for itself. A recent textbook1, for example, provides the following general definition: “Remanufacturing (refabrication) is an industrial process in which used products are restored to a condition comparable to that of a new product through disassembly, cleaning, reconditioning and testing.”
However, the exact meaning is regulated not least by industry-specific specifications and guidelines.
For machines used in tunnelling, this is the ‘ITAtech Report n° 5-V2 – Guidelines on rebuilds of machinery for mechanized tunnel excavation’ 2. This set of rules, published in 2019 by the International Tunnelling and Underground Space Association (ITA-AITES), also specifies two defined levels for TBMs, which represent different degrees of rebuild and service life extension, namely ‘refurbishment’ and ‘remanufacturing’.
- Refurbishment is the lower level. The result is a service life extension through comprehensive maintenance, repair and replacement of defective parts. The machine is made ready for use in a functional condition for similar subsequent projects without creating a completely new life cycle.
- Remanufacturing, on the other hand, is a higher value level aimed at a completely new life cycle. The machine or its components are completely disassembled, cleaned, checked, modernised if necessary and then reassembled in as-new condition. It is suitable for projects with high requirements and a long service life.
At the customer’s request, it is possible to apply different levels of reconditioning to individual assemblies within a machine. These ‘mixed applications’ allow a combination of technology, costs and risk management optimised for the specific project. For example, for a short tunnel with abrasive rock, remanufacturing of the cutterhead and screw conveyor may be necessary, while for the hydraulic system or support frame, refurbishment is sufficient.
In addition, combined configurations are often used, in which reconditioned machines are combined with new components. The new components are defined and documented either by the customer, the planner or the machine supplier. Typically, the customer’s request for new parts concerns safety-critical or wear-intensive components, such as the main drive, bearing and sealing systems, the shield or the cutterhead.
New parts can also be unused original parts from stock that were initially intended as spare parts. For components sensitive to aging (such as seals, hydraulic hoses), the remaining service life is required to be at least twice as long as the planned project duration.
DEFINED PROCESSES
Both refurbishment and remanufacturing follow defined processes, on which the ITA guidelines are also based. Accordingly, the restoration of functionality takes place in four steps and the establishment of a new product life cycle in six.
Specifically, refurbishment involves the complete maintenance and repair or replacement of defective functions or components. This is followed by a complete functional test with documentation, but without redefining the product life cycle. The corresponding process steps are:
- Cleaning.
- Partial disassembly to replace defective components or wear parts.
- Assembly and painting.
- Functional test.
The remanufacturing process, on the other hand, is closely aligned with original production and consists of six core steps, accompanied by a quality assurance process:
- Disassembly: all components are disassembled down to individual part level. Worn or non-reusable parts are sorted out. Seals and other disposable components are removed.
- Cleaning: this involves removing soil residues, grease, liquids and rust as well as the old paintwork. If previously used in problematic (e.g., contaminated) soils, additional protective measures may be required.
- Inspection: depending on the component, visual inspections, dimensional checks or special tests (such as crack testing, leak testing) are carried out. The parts are then divided into three categories: ‘directly reusable’; ‘can be reconditioned’; or ‘to be replaced’.
- Reconditioning: reconditioning is carried out in the same way as the production steps for a new part. Technical improvements, upgrades or reinforcements can also be integrated.
- Reassembly: final assembly corresponds to initial production. The final testing and documentation are also carried out following the same criteria as for new machines.
- Functional test: the tests are based on the OEM’s testing processes and specifications.
EFFICIENCY POTENTIAL THROUGH STANDARDISATION AND MODULARISATION
Herrenknecht expands on the ITA specifications to create a high-level approach. This includes as standard, for example, complete measurement and functional testing on an individual test basis in accordance with manufacturer specifications and in close cooperation with the respective OEMs.
The result of such remanufacturing is a machine that is practically indistinguishable from a new one in terms of performance and appearance. The warranty, including CE or other specifications required in the country of use, is also the same as for a new machine.
The prerequisites for this are created with a dedicated site for rebuild services at the German Rhine port of Kehl. There are 140 experts employed at the site, which has more than 100,000 m2 of production and storage space. They process around 15,000 components per year. The remanufacturing strategy not only pursues a high technical standard, but also consistently focuses on efficiency to offer customers the optimal solution at the best price.
The company increasingly relies on standardised and modularised components. In this context, standardisation and modularisation mean standardising processes and components to streamline the processes and exploit synergies.
CURRENT EXAMPLES: BOGIES
A current example of this approach is the standardisation and modularisation of bogies. These bogies are components in a TBM’s back-up system that ensure the correct travel of the back-up. They must tolerate high mechanical loads while precisely maintaining the position of the machine but otherwise have no complex tasks to perform. Nevertheless, there have been many different designs in the past, such as right-hand and left-hand welded variants. Accordingly, standardisation here promised great potential for improvement.
Design changes were therefore carried out to standardise the structural steelwork of the bogie and make it uniform. Instead of left- and right-hand versions, adaptation to different tunnel diameters is now achieved using Vulkollan tyres with different correction profiles. This means the bogies can be modular – from 2-axle to 8-axle versions.
These modules can be adapted according to needs and customer requirements. This makes the bogies more flexible and universally usable. ‘Old’ versions are retrofitted to the current design before being used again.
This ‘design for reman’ concept has been implemented in the area of bogies for around two years. The greatest effects of the new standardised and modularised solution are reduced design effort, low rebuild costs and the ability to use a higher proportion of used parts. This represents a first strategic step toward a longterm circular economy. Further components are now to follow successively.
CONCLUSION AND OUTLOOK
The remanufacturing of TBMs has established itself as a sustainable strategy that combines technical, ecological and economic benefits. Defined processes and qualityassured standards enable a new product life cycle, saving time, significantly reducing the carbon footprint and promoting the reuse of valuable resources. With a systematic ‘design for reman’ approach, the company is demonstrating how standardisation and modularisation – for example of bogies – can unlock further potential for efficiencies without sacrificing flexibility.
In the future, remanufacturing will gain even more significance in tunnelling. Given growing demands for sustainability, supply chain resilience and economic efficiency, there is an increasing focus on the principle of the circular economy. The systematic roll-out of ‘design for reman’-capable components and even closer integration with digital tools – for example for service life monitoring – offer additional potential. The goal is to further establish remanufacturing as an industrial standard.
REFERENCES
- Ebel, K.-D. & Spath, D. (Hrsg.): ‘Refabrikation – Produktaufarbeitung als Schlüsselstrategie der nachhaltigen Produktion’ (Springer Vieweg, 2015)
- ITAtech Report n° 5-V2 – Guidelines on rebuilds of machinery for mechanized tunnel excavation (2019)7
