Shearography: An economically successful investment
These days, two major trends within the European retreading sector are making the use of shearography systems increasingly necessary. First, casings are becoming harder to source due to weakness in the new tyre market and the growth in new tyre manufacturers’ involvement in retreading; they strive to retain ‘their’ casings within their own systems. Second, the focus on quality amongst medium-sized retreaders is becoming ever more important – both customers and the business’s competitive environment demand this. In an interview with Tyres & Accessories, market leader Steinbichler challenges those retreaders who continue to believe they can’t afford investments of 100,000 euros or higher: “For each of our customers, an investment in shearography has been crowned with economic success.”
Shearography using expensive silver coated film has been employed in the retreading of aircraft tyres for decades. Since filmless shearography systems were introduced in the early 1990s the technology has become more prevalent in the wider retreading sector, most notably in the retreading of truck tyres. While most larger, quality-conscious retreaders in Steinbichler’s home market of Germany utilise shearography and other Western European markets have very little catching up to do, in Eastern Europe shearography still is not very widespread.
So what exactly is behind the shearography process? “Shearography is a comparative test process. It recognises the smallest of deformations. Tyres with air pockets, so-called separations, are subject to decreasing ambient pressure, and therefore these air pockets expand and deform the tyre tread. Shearography can identify very small air pockets by safe and non-destructive means,” explains Rainer Huber, product manager at Steinbichler Optotechnik responsible for products related to non-destructive tyre testing. Today, shearography systems are not just used to inspect truck tyres upon their entry into a retreading shop, rather they are also employed in the new tyre sector. Shearography products are also utilised in other industries, primarily in aerospace, in order to identify air pockets and separations in composite materials. Steinbichler Optotechnik has also built up a number of development partnerships with vehicle manufacturers such as BMW and Audi and for mobile shearography units also with the aircraft manufacturer Airbus.
Shearography, used in association with a vacuum chamber to inspect tyres, recognises defects that are characterised by pockets of trapped air plus separations such as belt edge separation, loose cord in the casing and particularly the ply turn-up, advanced subsurface corrosion with separations, broken cords in the sidewall accompanied by air diffusion, and detachment of the airtight butyl inner liner. “Manufacturing-related air pockets that may lead to tyre failure can also occur during the partial vulcanisation of retreaded tyres and during new tyre production; these can be identified through shearography,” the product manager stresses.
Signs of damage such as these would even be missed by an experienced professional casing examiner who was completely focused on the task at hand. Visual examination can only occasionally identify internal damage to a tyre through external signs. Examiners would also be on the lookout for ‘problem tyres’ that are the subject of frequent complaints. “Through intense work an examiner can declare a tyre to be relatively safe. However an external examination can never identify every detail in the way that shearography would show it. The examiner would also take much longer to make an appraisal and couldn’t fully concentrate on the task at hand for eight hours a day,” Rainer Huber emphasises. “Therefore, experienced casing examiners are particularly enthusiastic about shearography” when working with a unit such as the “Intact” system from Steinbichler Optotechnik. Error indicators are in most cases unambiguous and casing examiners working on checking incoming items can “take a chance with problem tyres that were previously avoided.” This particularly helps with casing quality in this time of declining casing availability and enables companies to manage their capacity better and “significantly” reduce the level of product returns, shares the Steinbichler product manager.
Limitations of non-destructive testing
Shearography can’t do everything, however. Problems such as irregular material dispersion, weakened or kinked casing cord and air pockets under one millimetre in diameter cannot be identified using shearography. In addition, cuts and air pockets in contact with the air outside the tyre cannot be identified due to air pressure equalisation.
In addition to the system’s technical aspects, the economic advantages it delivers is of particular interest to retreaders. Minimising errors during the control of incoming items leads to cost savings when purchasing casings. Furthermore, shearography gives verifiable proof as to why a particular casing can’t be purchased – which helps retreaders avoid trouble with their suppliers. Retreaders who operate their casing entry control without employing shearography risk extra avoidable costs should they pass a defective casing and go to the expense and effort of retreading it, only to have it fail later during the retreading process. And should a retread fail when in use on a customer’s vehicle and be returned, shearography offers the significant advantage of allowing the retreader to provide evidence that the casing was in pristine condition at the time of retreading.
Even more importantly, shearography offers the significant advantage of allowing the retreader to avoid unpleasant and sometimes expensive complaints. “In particular, shearography leads to lower production waste, increased quality retreads and more satisfied customers,” comments Huber. “Furthermore, on-road reliability and safety increases.” Summarising, the product manager adds: “Shearography is indispensible for quality-conscious retreading. It benefits the retreader’s reputation and helps avoid annoying and costly customer returns. Moreover, it offers the potential to achieve savings when purchasing casings and during production.”
Alternative and complementary processes
In past years, numerous systems that serve as useful additions to the production process have come onto the market; however to-date no true alternatives to shearography have emerged, and for this reason shearography is extensively used in the highly developed Western European markets. Prior to the technology’s adoption, a possible procedure was to test the tyre or casing using ultrasound. “This didn’t prove suitable for widespread utilisation and has largely been replaced by shearography. X-ray technology can provide confirmation of defective metal cords, but due to the high cost connected to operating such a unit this is rarely found in retreading. Pressure tests with pressure close to the tyre’s working pressure uncovers sidewall flaws and through this removes the danger of accidents during tyre mounting. At the moment it is indispensible as a complementary test method to shearography,” Huber shares with Tyres & Accessories.
Steinbichler Optotechnik also firmly believes that a further useful complement to shearography systems, one that can be safely employed by semi-skilled workers without specific prior training, is tyre testing using high voltage. “Nail holes can currently only be effectively found using high voltage. Such systems are therefore particularly useful as returns due to undetected nail holes during entry control occur frequently.” The company now offers a multi-function test machine that combines shearography, nail hole detection and visual inspection in a single unit: the “Intact V20”.
The cost a retreader faces when investing in a modern shearography system can amount 70,000 to 100,000 euros or more. A simple Steinbichler Optotechnik unit for bead-to-bead inspections can be purchased for under 100,000 euros, Rainer Huber notes. “This can be significantly higher for increased testing capacity,” the product manager adds. “However the extra investment costs buys the retreader disproportionately higher inspection capacity.” The cycle time, for example, of the “Intact 30” or “Intact 80” are comparable to new tyre manufacture and “through their ability to be completely automated provide the basis for the technology’s further growth in this market segment.” An entry-level solution for tread and shoulder testing is the recently introduced “Steinbichler Intact V20t”, which can be acquired for less than 70,000 euros; this machine can be upgraded to handle bead-to-bead testing at a later date.
“In future it will be even more important to avoid accidents and returns,” opines Huber. “Without shearography it will be hard to live up to the expectations of all but the most price-oriented customers. It will become even harder to acquire acceptable casings. The potential ‘Intact’ offers to avoid the unnecessary costs of purchasing and working on defective casings is particularly large for the OTR tyre retreading sector as OTR tyre retreading is very labour intensive and the casings more expensive.” The product manager is certain that the cost of shearography pays off: “Investing in shearography has been an economic success for all of our customers.”
Steinbichler Optotechnik GmbH
Steinbichler Optotechnik GmbH has its headquarters in Bavaria, in southern Germany, and is led by Dr. Marcus Steinbichler, the son of Dr. Hans Steinbichler. The company founder, who passed away in 2005, was quick to recognise the opportunities non-destructive material testing offers and established Steinbichler Optotechnik GmbH in 1987. In those early days the development of new products benefitted a great deal from emerging computer technologies. Today the retreading sector represents around half of Steinbichler’s shearography system business and generates about a third of the firm’s turnover; last year this amounted to some 27 million euros, a year-on-year increase of 32 per cent. “Alongside these products we offer outstanding solutions for digital optical measuring technology, surface scanning and medical technology. Our stated goal is to, as we have done in the past, grow significantly in all business areas. To this end we are widely positioned and can achieve continued success despite market fluctuations,” stated Rainer Huber in closing.
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