A composite cable of aramid and polyamide yarns is proposed as a reinforcement for aircraft tyres by The GoodyearTire & Rubber Co of Akron, Ohio, USA. Aircraft tyres must be capable of withstanding severe operating conditions, including heavy loads, high speeds and large degrees of cyclic deformation. At the same time, rising fuel costs and concerns about the environmental impact of air travel dictate that reducing the weight of the tyre is highly desirable. (European Patent 2 045 379, US Patent 2009/090447 and Chinese Patent 101403154). Traditionally, bias-type (or cross-ply) aircraft tyres have been made using polyamide (PA) 6 or 6.6 as reinforcements. PA has excellent ductility that translates to high fatigue resistance, which is important given the repeated cyclic deformation aircraft tyres must endure. One way to reduce weight in the tyres is to use a stronger reinforcement such as aramid fibres. The aramid fibres are considerably stronger than those of PA, they have a much poorer ductility. As a result, PA fibres are more durable when exposed to repeated tension and compression loading such as an aircraft tyre endures in use. Hybrid or composite reinforcement cords, made from two or more materials such as PA and aramid, have been used, but are difficult to design in order to meet the stringent performance requirements. Further, the complexity of aircraft bias tyres makes them difficult to model. As a result, such hybrids tend to end up being heavier. Goodyear's latest invention aims to overcome these shortcomings and, in one form, consists of a hybrid cord containing one or more (preferably only one) aramid yarn. Specific examples of suitable yarns are DuPont's Kevlar 29 and TeijinAramid's Twaron 1000. These yarns can be in the range 220-3300 dtex, but are ideally 1670 dtex. Each aramid is twisted in the z-direction. The degree of twist can be in the range 1. 18-6.30 twists a centimetre (3 to 16 twists an inch) but is preferably 4.21 twists a centimetre (10.7 twists an inch). The other half of the cord comprises one or more yarns of an aliphatic PA, preferably PA 6.6. Ideally only a single yarn of PA is needed and this should be in the range 220-2100 dtex, most preferably 1400 dtex. The PA yarn also has a z-twist and again in the range 1. 18-6.30 twists a centimetre (3 to 16 twists an inch), though this time it is preferred if the twist is 2.44 twists a centimetre (6.2 twists an inch). The two types of yarn are plied together to form a cable with an s-twist in the range 1. 18-6.30 twists a centimetre (3 to 16 twists an inch), ideally 3.82 twists a centimetre (9.7 twists an inch). this cord construction, both in greige and dipped forms, has a higher break strength than pure aramid (5% increase) or pure PA (45% increase). Moreover, it remains greater even after repeated cycling (120 000 cycles). Stress-strain measurements show the dipped cord performs as well as the PA construction and better than that of aramid. The hybrid cord also has a 24% lower elongation at break than the PA one and a similar energy to break. With respect to tenacity, the hybrid has a 25% increase compared with PA, while its toughness is on a par with the aramid construction. Finally, there is a 55% decrease in hybrid cord's shrinkage compared with its PA counterpart.
Hybrid cord for aircraft tyres
Advances in Textiles Technology ; Jul ; 4-5
2009
2 Seiten, 1 Bild
Article (Journal)
English
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