The textile industry – that is, the commercial manufacture of yarn and cloth – is one of the oldest in manufacturing, and it is arguably the oldest mechanised industry of all.
The Spinning Jenny, after all, is many people’s idea of the first example of factory machinery. But it was only the start of the story. From the moment the original Industrial Revolution powered up production with mechanical might in the mid-eighteenth century, there has been no shortage of inventions designed to expedite and upscale every stage of the cloth-making story.
The range of processes alone is encyclopaedic: from the very beginnings of the narrative – where saw-toothed cotton gins are used to extract fibre from the rest of the plant – through the various automated procedures that step by step clean and tidy the fibre (first as lap, then as slivers) into usable strands, thence through the great and complex processes of machine spinning and weaving; this before even mentioning the dyeing, printing and other production stages further down the line.
Variable speed drives figure throughout these operations – wherever there are energy savings and efficiency gains to be made from the improvements they bring to different types of process control. Of these, there are a few which are especially important to, and typical of, the textile production industry, almost regardless of scale of enterprise.
Spinning machines are perhaps the most obvious beneficiary of smooth-performing motors. While at the sliver stage (between uncombed lap and prepared yarn) textile fibres are fragile and yet bulky. Machines called speed frames (or fly or roving frames) draw the slivers out into suitably fine threads, supply the threads with a slight but strengthening degree of twist, and wind the product onto bobbins.
Ring frame spinning machines (by no means the only kind of yarn-producing machine, but a common one) use draughting rollers to take these threads up and attenuate them further: sets of rollers, individually adjustable, rotate at different speeds in order, between them, to lengthen the fibres and pull them into parallel position. The threads (being transformed in this way into yarn) are subsequently fed through rotating rings, which both twist the yarn and wind it around similarly, though more slowly, rotating spindles.
Throughout the spinning process, synchronised control of multiple components’ running speeds equates more or less exactly to product consistency and quality. At almost every point, for example, too little tension in the strands is a recipe for snarls and tangles; too much obviously causes snapping. Either means stops and downtime.
It is a problem that spinning machines have traditionally attempted to handle by entirely mechanical means – speed control systems dependent on different-sized pulleys, belts, valves, compressed air and the like. Viable up to a point, such systems have become unpopular in the industry due to their relatively poor efficiency and – above all, according to those who have worked with them – to the frequency with which they break down, stalling whole factories and sending engineers off on quests for increasingly elusive spare parts.
Variable speed drives strongly recommend themselves as an alternative approach to speed regulation for this type of machinery. An optimal level of starting torque accompanied by smooth motor acceleration produces a quality of thread tension measurably superior to that achievable by other means – and with proportionally fewer snags and breakages.
Not only that, but – as always with drives – a more sensitive handling of the product implies less stress on the motors (which otherwise run continuously at full power), and therefore lower energy consumption, less heat in the system and an appreciably lower component part burn-out rate.
Although the principle of efficiency through precise motion control holds true for a long list of textile production machines, the degree of precision required naturally varies according to particular function. For instance, drives are used to supply consistent rotational speed to circular knitting machines; in these cases a 10:1 speed range is sufficient. For printing and dyeing machinery, however, where low-speed accuracy is essential to the quality of the product, drives with a speed range more in the order of 20:1 are necessary.
Of course, the industrial machinery involved in textile production is not restricted to processes that directly handle the materials.
Air humidification is a vital environmental consideration in the cloth manufacturing plant. Natural fibres dry out rapidly on the factory floor: material that is delicate to begin with is liable to lose elasticity and become even more vulnerable to tearing if the surrounding ambience is too dehydrating. Synthetic materials are prone to misbehave in dry atmospheres for a different reason: they are natural generators of static electricity. Either way, properly regulated air humidity contributes directly towards product quality, productivity and worker safety.
Air filtration systems are no less important. The fine dust particles generated by the industrial treatment of cotton and other fibres, together with the chemical presences associated with fabric dyeing, can pose a serious risk to workers’ respiratory health if not comprehensively and continuously extracted by means of fan-driven air filter machines.
Effective as the conventional method of running motors for humidification and filtration systems is, it is also highly inefficient. Adopting variable speed drives to enable ongoing speed control for these applications represents certainly the single most significant energy-saving measure available to the textile plant: the power drawn can be cut by anything from 20 to 40 or even a good 50%.
Textile manufacturing plants are generally electricity-intensive operations. And it has been suggested that the motor systems used for material handling processes, pumps, fans and compressed air devices account for over 80% of electricity use within the industry. Variable speed drives have a clear role to play here – a fact most pressingly true, perhaps, for those important centres of industry (such as India and Bangladesh) where recent surges in demand for output threaten further stress on already limited energy reserves.