materials technology in automotive recycling

- ADVANCED MATERIALS

Essay

Materials Technology in Automotive Recycling By Arnulf Frisch* and Claus Razim

1. Introduction

The growing number of disused cars and the resulting amount of waste contribute to the increasing pressure on disposal sites. Therefore, future reuse of the materials al- ready plays a major role when it comes to materials selection and the design of new motor vehicles.

Light-weight design will be increasingly applied to future vehicle generations because of the demands for enhanced fuel economy and lower fleet consumption. Materials such as plastics and aluminum, which have always provided such satisfactory service, will continue to be used in vehicle production. However, now that the aspect of recycling has to be taken into consideration, every decision in favor of these materials must include a solution for recycling these materials or material combinations.

Increasingly, the criteria applied to materials selection will be aimed at allowing the highest possible degree of recycling of complex material combinations. In addition to the technical prerequisites yet to be defined, the economic feasi- bility of material recycling plays a major role, being mainly dependent on selecting the necessary processing steps, the number of staff required, the throughput and the desired quality of the recycled material. The economic significance of material selection with particular emphasis on the cost of the reprocessed materials will be illustrated by way of con- crete examples.

Despite the efforts at material recycling, a partially dis- mantled body will eventually have to be totally recycled. Metallurgical recycling developed by Mercedes-Benz for this purpose will be described here in detail. It is a process which provides a holistic solution for vehicle recycling and allows for disposal without having to burn the residual organic materials of the body in a special-waste incineration plant.

2. General Considerations

The important requirements made of automobiles, such as safety, performance, reliability, quality, value for money, and environmental compatibility during production, during

operation, and during the disposal of disused vehicles are to an increasing degree integrated into automotive construction processes. In addition to design solutions the materials used contribute to meeting these requirements. The possibil- ity of reusing the materials contained in vehicles in the future plays an important role when it comes to selecting the materials and planning the design of new vehicles. Here, however, quality and competitiveness must not be neglected. To optimize the re-utilization of materials detailed investigations of the material-related aspects of automotive recycling are necessary with respect to technology, ecology and economy. The results contribute to the formation of guidelines both for material recycling and design planning of commercial vehicles.

3. Starting Situation: Shredder Refuse

Increasing prosperity of the population in the industrial- ized countries as well as more and more stringent environmental demands on technology have led to a continuous increase of the amount of refuse to be disposed of. At the same time the space available for refuse disposal sites is becoming more and more scarce. The increasing number of disused vehicles-in the year 1990 it was approximately two million in Western Europe-contributes to this amount of refuse. Figure 1 shows the currently practiced disposal of disused vehicles. Following the partial disassembly of the

[*I Dr. A. Frisch, Dr. C. Razim Mercedes-Benz AG D-70322 Stuttgart (Germany) Fig. 1. Disposal of disused vehicles (today).

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re-usable and re-processed components, the body of the disused vehicle moves on to the shredder in pieces the size of a fist. By means of magnetic separation and a process working according to the sink -float process, ferrous metals, non- ferrous metals and non-metallic portions are separated. Whereas the metallic parts move on to a re-utilization process, the non-metallic fraction (25 %)-mainly plastics- now as before moves on to a disposal site.

Although the shredder refuse contributes to the overall refuse quantity by only I S % , the disposal cost has increased by a factor of three to four during the 1980s, and the tenden- cy goes upwards. The overall automotive industry (including suppliers and disposal plants) is called upon to develop economic and environmentally compatible disposal concepts for disused vehicles.

Figure 2 shows the possibilities to reduce the amount of shredder refuse. They mainly refer to processing and avoiding the refuse. Processing can be achieved by means of thermal recycling, by using an improved and optimized separation technology and the recovery of chemical basic substances. The drawbacks of these processes are the high

Effecis after Effecls atler Ellecfs aller Elfecls aller Effects afler 5-6 years 10 years 15 years 2 years 2 years

Fig. 2. Recycling of disused cars: Reducing shredder waste.

energy requirement on the one hand, and, on the other, the fact that the amount of refuse would be noticeably reduced only after approximately 10 years due to the lengthy ap- proval phases and/or lengthy, but necessary new process developments.

In contrast, it is possible to reduce the amount of refuse in a much shorter time when concepts are applied which avoid the production of shredder refuse in the first place. These measures are targeted to extended material recycling, particularly in the case of plastics and/or to the increase in the metallic components in the automobile, because metals and their alloys can be recycled at almost 100% by means of re-melting.

Mercedes-Benz AG decided to use a combination of “avoiding processes” to reduce the amount of shredder refuse taking into consideration the different time effects of various technological processes. Figure 3 shows a comparison of the previous “conventional” disposal concept and the Mercedes-Benz recycling and disposal concept. Both concepts are identical including the disassembly step. Repro- cessed and re-usable components are removed and move on

*) Percenlnge of “an rocyclRbls plastics which must be dispoeed 01 by hermnl,errtgy recycling

Fig. 3. Disposal of old vehicles.

Dr. Arnulf Frisch is 33 years old and studied Materials Science at the Aachen University of Technology from 1981 to 1986. In 1987 he moved to the Powder Metallurgy Laboratory of the Max Planck Institute for Metals Research in Stuttgart to work on his Ph.D. on defect healing mechanisms during hot isostatic pressing of polyphase materials. In addition he worked on the joining of metals to ceramics for high temperature applications. In November 1991 he moved to the Mercedes-Benz AG in Stuttgart, where he became the assistant of the Director for Production Technology And Environment. In December 1994 he took over the unit for the Management of Innovations in the Department for Advanced Development at Mercedes-Benz.

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Essay ADVANCED. MATERIALS

to a recycling process; for further exploiting this method, new recycling procedures and processes have recently been investigated.

Following the partial disassembly, the body of the disused vehicle is compressed into bales, cut in pieces using a scrap cutter and subjected to the steel production process of metallurgical recycling (see Section 6).

4. Environment, Recycling, and Economy

The additional consideration of quality requirements, particularly with respect to safety, leads to a conflict in materials technology between the components of lightweight construction, safety, environment, resources and costs (Fig. 4). The

Safety

Light-weight design

Environment and resources

costs

Fig. 4. Conflicts of materials technology in the automotive industry

arrangement of the cost components in the form of a trian- gular pyramid shows the mutual interdependencies. For this reason it must be the objective of a future material development to comply with all requirements to the same extent, in order to produce high-quality, environmentally compatible and competitive products. In the following, the conflicts between environment/recycling and economy will be explained by the example of the lightweight materials plastic and aluminum.

4.1. Plastics

The use of plastics is inevitable for lightweight construction and safety. At Mercedes-Benz, however, they are used only in places where they offer functional advantages. There are specific challenges as far as the recycling and the re-use of plastics are concerned. One major reason for this is that these materials have a cascade of properties which are particularly distinct when it comes to recycling, and which require high-energy and high-cost processing steps in order to repro- duce a component with the same quality.

Figure 5 uses the example of a bumper to show an excerpt of the processing steps from the component to the ground

plastlc components

plastic material

to be ground

Fig. 5. Plastic recycling: Costs of the processing stages from the component to the material to be ground.

material. An important prerequisite for re-use is that the material is free of impurities and has been segregated in advance; this means that after the initial crushing the metal parts and impurities must be separated. The high-energy grinding processes lead to high processing costs which can be as high as DM 100/tonne.

After the generation of the ground stock, the material is further processed into granulate. This process, as well, con- tains several stages, such as plastifying, granulating and dry- ing processes which can generate costs of up to DM 100iton- ne for each process.

The fuel tank is used as an example to compare the re-processing costs with the costs required to produce a tank from new materials (Fig. 6). Since similar processing steps are required for the production of the bumper, the costs for the recycled component are more than 50 % higher than for the

Processlng ground materlal 0.72 DM/kg

Regrnnulation 0,72 DM/kg

0,W DM/kg Logistics

Overheads and profit 0.59 DM/kg

Removal tram scrap vehicles 2.20 DM/kg

The processing cost of 2,93 DM/kg is clearly higher than the cost of higher-quality new material

( c: 1 Fig. 6. Processing costs of a plastic fuel tank.

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same component made from new material. When the disassembly cost of the disused tank is added, the processing costs reach a level of 2.5 times as high as the costs for new material.

These examples make it obvious that re-processing of plastics must be carefully assessed, both for economical and ecological reasons. A condition for the re-use of plastics is the marketability in terms of cost, suitability for use, and the demand on the part of the customers. Taking into consideration the boundary conditions explained, Mercedes-Benz is investigating a large number of plastic components for their re-usability together with suppliers and raw material manu- facturers jn several recycling projects. However, if these conditions do not prevail, plastic portions should be utilized as an energy medium in thermal and metallurgical recycling processes. In the future, plastic refuse should be dumped on disposal sites only as a last resort.

4.2. Aluminum

Accumulated expertise and the use of sophisticated com- puter equipment have made it possible to optimize lightweight design. This provides a further chance to reduce weight. For various reasons aluminum is a suitable material for lightweight construction. Moreover, it has a high resis- tance against corrosion which results in a long service life. In the automotive industry aluminum is used in the form of wrought alloys and high-strength wrought alloys for body parts and bumpers and as cast alloys for engine parts and blocks (Fig. 7).

Fig. 7. Aluminum-recycling

At a first glance aluminum is regarded as a light alloy which is particularly easy to recycle. Although the energy required for the production of secondary aluminum is only 12 9’0 of the amount needed to produce primary aluminum, it becomes obvious at a second look that especially the cost

for logistics and disassembly steps can make aluminum recycling more expensive than recycling steel which is the main material component in automobiles.

An important prerequisite for aluminum recycling is the segregated use of aluminum components in the above-men- tioned aluminum alloy groups. If this segregation is not SUC-

cessful, the aluminium alloys can only be re-used as cast alloys. In addition, only one alloy group is allowed to be used for an aluminum component which can be disassembled.

There are two major possibilities to ensure segregated use: first, specific disassembly with the appropriate segregation, which, however, requires high personnel costs. Owing to the low degree of purity of materials from the conventional sink-float process only cast alloys can be reproduced. Sec- ondly, automatic material sorting using the process of laser detection is currently still being tested, but it constitutes a considerable technical challenge when it comes to achieving the required degree of purity during sorting.

Figure 8 shows a comparison of the costs required to recycle a steel body according to the Mercedes-Benz concept with

Steel Aluminium Fig. 8. Cost estimate for recycling: Steel body and aluminum body (incl. logistics costs).

those required to recycle an aluminum body. With aluminum recycling the application of the metallurgical process is impossible so that the “shredder solution” has to be cho- sen which involves high-energy cutting followed by thermal processing of the shredder residues. In addition, steel recycling does not require the segregated separation into alloy groups. According to estimates, the costs needed to recycle an aluminum body are almost three times as high as those needed to recycle steel.

5. Environmentally Compatible Design

The results of the recycling projects carried out so far, explain that on the one hand a considerable amount of (man- ual) work is required for the disassembly of re-usable parts

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Essay ADVANCED. MATERIALS

and the segregation of material groups, and on the other hand high-energy recycling processes have to be applied in some cases. For these reasons, the evaluation of the projects resulted in guidelines relating to “environmentally compatible designs” which allow easy disassembly, applicable for future vehicle generations. They are summarized in Figure 9.

Fig. 9. Guidelines for “environmentally compatible design”.

They comprise modifications in joining technology, such as the development of connecting parts which are easy to disas- semble and the reduction of components with full-face adhe- sion, simplification of the draining of service fluids and the central arrangement of electronic components as often as possible. To facilitate the segregation of plastic types during recycling, Mercedes-Benz marks all plastic parts which are heavier than 100 g. In addition the reduction in the variety of materials facilitates the recycling of the disused vehicle.

Figure 10 shows the variety of plastics which are used in the E-class (mid-range series) of automobiles. Whereas almost 75% of the plastic is comprised of five plastic types (PVC, PUR, ABS, PP and PA), the remaining 25 % are di-

rt

Fig. 10. Application o f plastics in the Mercedes-Benz Executive-class.

vided into ten further types of plastic. Here it seems to be reasonable to reduce the variety of types.

In order to arrive at an economically and ecologically optimum energy and materials balance during production, it is necessary to use the most suitable materials holding them in the cycle as long as possible by the use of appropriate recycling methods. This leads to a holistic consideration ; i.e. balancing and evaluating the consumption of energy and raw materials, the benefit, recyclability and environmental compatibility.

The complex way of drawing up an ecological balance, which may be accompanied by numerous insecurities, imponderabilities and subjective assessments is shown in Figure 11. When drawing up such a balance the recycling

Fig. 11. Steps for the life cycle a5sessment

process must be weighed against the production of new material. The investigations and results presented show that material recycling is not free of cost. Similar to the production process, it requires energy and auxiliary material and causes emissions and residues. For this reason it does not make sense to go for recycling at all costs; rather, the in- stalled recycling systems need to work at minimum losses (cost-wise) .

6. Metallurgical Recycling

Taking into consideration the equal ranking of economic and ecological aspects, metallurgical recycling was developed at Mercedes-Benz to dispose of pre-treated and partially disassembled disused vehicles (Fig. 12). This recycling process is a steel production process during which a pre- disassembled disused vehicle from which all re-usable components, units, service fluids and materials were removed, is compressed into bales, cut in pieces using a scrap cutter and is then moved on to a melting furnace for steel production. An emission control system downstream of the melting process avoids the recombination of pollutants owing to an adapted temperature control. The advantages of this system

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Disassembllng are that environment-polluting substances are avoided, the energy contents of the organic substances remaining in the body of the disused vehicle are utilized (saving primary energy of up to 30%), their carburization effect, and that the inorganic components are used as a flux for making slag.

The utilization of the materials which cannot be recycled results in an additional protection of raw materials and resources. With this process which was further developed and prepared for large-scale technical implementation in cooper- ation with Voest Alpine Stahl AG as part of a research com- pany, the loop of disused vehicle disposal can be closed avoiding environment-polluting residues and refuse.

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Fig 12 Metallurgicdl recycling

MortimeG R. J./Monk, P.M. S./Rosseinsky, D. R.

Elec trochromism Principles and Applications

Publication date: All aspects of electro- June I995 chromism from funda-

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references round off this first in-depth treatise on the topic.

From the Contents: Electrochromism and the Scope for Electrochromic Displays/ Electrochromic

Operation, Kinetics and Mechanisms/ Construc- tion of Electrochromic Displays/ Electrochromic Systems/ Metal Oxides/ Phthalocyanine Systems/ Prussian Blue Systems/ Other Inorganic Systems/ B ip yridinium Salts/ Conducting Polymers/ Other Organic Systems/ Photo-Electrochromism/ Poly- electrochromisd Electrochromism via Colloid Deposition

C H E M I S T R Y

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materials technology in automotive recycling

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