JEC Group have brought together the international community of composites leaders and executives in our Composites Circle as an unique networking opportunity to meet with both peers and future partners.
For three years now, I have been following the rapid expansion of the carbon-fibre industry and how carbon fibre is penetrating more into volume applications, especially in the industrial, automotive and aerospace segments. The increase in demand has led to fibre shortages, especially of the low-count tows (1K – 6K), and their prices have soared. To meet the greater demand, almost all low-count tow producers are investing heavily in new production facilities. This, of course, is a conventional approach to remedying the shortage.
(Published on March 2006 – JEC Magazine #23)
BY HENRIK OLOFSSON, BUSINESS DEVELOPMENT MANAGER, OXEON AB, SWEDEN
Apart from the greater demand, the inflexibility of carbon fibreto- fabric converting technologies is another factor that reduces the availability of carbon fibre from the existing capacity and leads to fibre price increases.
Carbon-fibre manufacturing is a very complex, expensive process. It is slow, and it requires constant and careful supervision. Therefore, any production stoppage is very costly. In these circumstances, to maximise cost-effectiveness a fibre producer would wish to produce just one standard tow size all year round. Unfortunately, this ideal situation is not practicable, because tows of several different counts – for example, from 1K to 24K or more – are required to satisfy 1) the requirements of producing fabrics of different areal weights and 2) the materialinput requirement for today’s most employed yarn-to-fabric converting equipment, i.e. the conventional weaving loom.
Because it takes the same time and effort to produce a 1K tow as it does for a 24K tow, the output in terms of weight is drastically reduced, especially for low-count tows like 1K, 3K and 6K. The lower output is also compounded by a certain amount of production loss due to downtime for machine resetting when new tow counts are to be produced. These factors contribute to increased fibre cost.
Carbon fibre production loss
Production output for carbon fibre is usually calculated on the plant’s installed capacity. This corresponds to the plant’s maximum theoretical capacity when producing only 12K tow at 100% activity rate. To obtain a practical picture, it is possible to calculate output on “mix load” capacity. This would correspond to the actual capacity to produce the complete range of tows (1K, 3K, 12K, etc.) at 100% activity rate. As a rule of thumb, the mix load capacity is taken to be 70% of the installed capacity . In 2005, the global installed capacity for low-count tows (1K-24K) was about 25,000 tons.
The mix load capacity would thus correspond to about 17,500 tons. Seen differently, the industry could have produced an extra 7,500 tons of 12K tow from the installed capacity if the low-count tow counts (1K, 3K and 6K) had not been produced. The annual loss for not producing the extra 12K tow is estimated to be 150 million euros.
How has this come about? Can it be changed? There are no immediate answers, although different ideas could be discussed. The main reason the industry is in its present situation is that 3K and 6K tows of most fibre grades are certified for aerospace use, and to avoid costly recertification processes, they are used automatically. These low count tows are also the only ones available for producing low-arealweight fabrics (200g/m2 or less).
A fibre producer, of course is very keen to get a big contract with the aerospace industry. This is often a long-term contract involving large volumes on a steady yearly basis. However, a consequence of such a contract is that the fibre producer will have difficulty in supplying other markets, such as the recreational industry.
Bringing in new production flexibility
Whereas a fibre producer would like to gain by producing one standard tow count all the time, preferably a heavy tow count such as 12K or 24K to maximise output in kilo terms, the market is demanding low-areal-weight fabrics.
These orders cannot be ignored, but they cannot be produced using heavy tow counts, either. It is difficult to produce satisfactory fabrics below 300g/m2 using 12K tows. The situation is paradoxical, as the most expensive production step in the carbonfibre value chain is called upon to satisfy most demands in a flexible way.
Clearly, if carbon fibre is to compete with other construction materials in the future, the industry will have to consider a different approach and try to bring in a new kind of production flexibility in the subsequent value chain. One way to move forward in this situation could be to bring innovation to the processes used to produce the reinforcements from carbon fibre. Because traditional weaving technologies cannot be employed for converting a high-count tow into a thin woven fabric of low areal weight, new weaving techniques are required. Similarly, filament winding technologies could be improved, because when laid during winding, a tow is a flat, narrow (and unspread) tape of carbon fibres. Alternatively, suitable new technologies could be created to replace the filament winding process, at least partially if not completely.
Because one of the main reasons for producing low-count tows is the need to meet demand for low-areal-weight fabrics, the new kind of flexibility required by the fibre producer could involve considering the emerging yarn-to-fabric conversion technologies that use high-count tows to produce low-areal-weight fabrics. Today, a handful of companies like Oxeon, Teknomax, Maruhachi and Hexcel are exploring the commercial feasibility of spreading high-count tows (12K, 24K and 48K) into thin wide tapes and then either weaving or stitching them to produce low-arealweight fabrics (starting at 80g/m²).
Instead of controlling the areal weight of the fabric through the use of a specific tow count, these technologies reach the desired areal weight by controlling the width of a single count of tow and converting tows into tapes of different widths. This novel approach introduces enormous flexibility when it comes to increasing the worth of the value chain.
Using fibrous tapes in weaving
The fabrics produced using spread tows are known as “tape woven fabrics”. Compared to traditional woven fabrics, the flat-tape woven fabrics show improved mechanical performance [2, 3] because the crimp angle is greatly reduced. Tape woven fabrics can be made very thin, and hence have low areal weight, yet exhibit very good surface smoothness.
The weaving looms employed today are of conventional working design. They require 200 to 400 bobbins of nearly the same fibre length for the warp setup. In order to produce the correct fabric length with less fibre waste, bobbins with greatly differing tow lengths are not used. (Unlike for clothing fabrics, fibres used for reinforcement fabrics cannot be knotted together to reach greater lengths or to mend a problem.) Also, even if fibre fuzziness is relatively rare in carbon-fibre production, rewinding bobbins to obtain equal tow lengths for use as warp does cause fuzziness, and such bobbins are disqualified for weaving purposes. Many woven fabric and UD-tape producers have experienced being stuck with leftover substandard bobbins of 3K and 6K count tows on this account. With the new tape-weaving technologies, this problem does not arise. For example, using a single 24K tow bobbin 2,500 metres long, a 20-mm-wide tape can be produced and then woven into a thin low-areal-weight fabric of 160 gsm. In other words, 25m2 of high-performance tape woven reinforcement can be obtained from one bobbin, which is impossible to achieve with traditional weaving practices.
Opportunities in producing fibrous tapes
Some of the problems discussed above could possibly be overcome if fibre producers themselves were to supply different standard widths of thin spread tapes directly. This would be easy and would require virtually no investment, as the fibrous tows from the spread-tow process could be wound into rolls (as opposed to bobbins) at a suitable point in the process, in their pre-spread condition, with a film to separate fibrous layers. This, however, would eliminate neither the problem of leftover materials on rolls nor that of material waste occurring with rolls that have different lengths wound on them. In this case, when the first roll is used up, the remaining rolls would be rendered useless in a process like weaving. Of course, larger rolls of fibrous tapes supplied by the fibre producer could be rewound later into suitable smaller rolls of equal lengths without creating fuzziness.
As innovative technologies emerge, it is important that major end users of lowcount tows (e.g. aircraft builders) start considering the use of relatively higher count tows. It would not only make more carbon fibre available to the rest of the market, but also lower their own costs. Furthermore, using 12K or 24K high-count tows instead of 1K, 3K or 6K low-count tows could save a lot of money. These savings could also be a motivating factor for investing in the recertification of new materials.
The high-growth industrial segments that are expected to consume the most carbon fibre over the next ten years include wind energy, pressure vessels, rollers, civil engineering and off-shore. These applications will require mainly high-count tows (>12K), and this will promote high-count production. Demand for low-areal-weight fabrics will still remain for many existing applications. The solution to this problem could be found in novel fibre-to-fabric conversion processes. There will certainly be cases where the developing tow-spreading and tape-weaving technologies have a favourable impact on the carbon-fibre industry and its value chain, and it would be interesting to know about the innovations involved.