AUTOMATED PROCESS CONTROL IN TEXTILE AND APPAREL INDUSTRY

Textile and garments process control technology is not as specific as vision technology; process control encompasses all textile manufacturing sectors. The process controllers relevant to textile manufacturing are basic information-electronic systems that, installed on the textile and garments machine, control certain fundamental parameters relating to the production process carried out on the machine itself. Essentially, they can be broken down into 4 categories according to the technology of the controller involved, which is itself dependent upon the type of process being controlled.

AUTOMATION IN PROCESS CONTROL SYSTEM
1.Cycle programmers: These process control system are present on many dyeing machines and they are based on the general principle of activating outputs according to inputs of the process. But their actual functioning is more specific. Those control system are pre-programmed to manage a sequential cycle of operations automatically. This facilitates programming, because the only thing that has to be done is determine the sequence of the steps in the cycle and the conditions required for the passage from one step to the next (the reaching of a certain temperature, the expiry of a set time, the arrival of a go-ahead signal, etc.). There exist two types of cycle programmer: one based on a microprocessor whose hardware and software remains the property of the supplier, and one based on a PC- or PLC-formatted architecture, which offers all the advantages of standard hardware and flexible software of automated process control.

2. PC-driven Programmable Logical Controllers (PLCs): these systems of process control are equipped to receive logical information (from switch or pushbutton contacts, limit switches, photocells, any kind of ON/OFF sensor) and to activate logical outputs (electric drives, relay contacts, etc). A controller checks continuously the status of inputs (openings/closures, presence/absence of electrical current), and according to the configuration of the inputs, activates its own outputs (activated/deactivated, ON/OFF, command presence/absence). The logical correlation between input status and the output status consequently imposed is determined when programming the system. Thus, the PLC can be regarded as a completely general purpose tool, capable of carrying out, when duly programmed by the user for proper process control, the most diverse functions. In practice, PLCs are used to resolve all those problems relating to automation and sequence management that used to be resolved using electrical systems and relay logics for process control. They feature on practically all the systems used for automated process control, in textile finishing, for operations such as washing, mercerization, dyeing, drying, calendaring, raising, pad-batching and steaming.

3. Numerical Controls of process control: these control system are electronic systems, specifically designed to control the positioning of a number of moving organs (e.g., robot axes). Using special languages, they programmed the sequences of the positions of the various axes, each of which is controlled through measurement of the position of the organ. This measurement is carried out by high precision transducers (encoders, resolvers, optical rulers), which transmit to the numerical control a number (hence the name of the system) which represents that position.

4. Special programmers: This automated process control system is developed specifically to carry out dedicated functions of textile process. These programmers are designed with and for the machine, in such a way that input and output signals and processing capacity are kept to the absolute minimum. In order to reduce costs, size and maintenance of production, they are often engineered in the form of single electronic cards. The four systems of process control described above are can be integrated with one another, and are often used together.

Benefit of automated process control
 -Better process quality
 -Reduction of errors
 -Greater production flexibility
 -Rationalization of the cycle according to scientific criteria
 -Rapid personnel training
 -Greater familiarity with production characteristics
 -Scope for integration with other company information systems
 -Repeatability of procedures
 -End quality no longer dependent upon the skill and experience of staff

Limitation of automated process control
 -Need for organizational changes
 -Difficulty personalizing the system to specific requirements
 -Difficulty interfacing with different IT products
 -Need for assistance and maintenance

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AUTOMATED COLOR ANALYSIS AND COLOR CONTROL OF DYEING INDUSTRY

AUTOMATED COLOR ANALYSIS AND CONTROL OF DYE HOUSE

It is worth remembering that in the past the assessment of color reproduction was exclusively entrusted to the ability and to the experience of the eye of highly skilled operators working on the color kitchen, whose judgment, however, could be influenced by a number of physical, physiological and psychological restrictions. The success and the development of electronics have deeply transformed the color control task thanks to the introduction of new measuring instruments, which have allowed definitely scientific and objective assessment.

All the systems currently available on the market have basically the same fundamental structure and differ only in their performance and in the algorithms adopted for color analysis. These systems generally feature:

1. A spectrophotometer, which measures the different spectral components of the sample analyzed. Today the measurement is carried out by means of a xenon flash, a prism separating the chromatic components and a CCD sensor (of the type used for modern solid state television cameras that have only a single row of light-sensitive elements or pixels), which reads the intensity of all the components simultaneously;

AUTOMATION IN TEXTILE FINISHING

AUTOMATED OPERATION OF TEXTILE FINISHING:
Automation in textile finishing industry is not a new concept, but it is being modern day by day. The textile factory is characterized by a considerable fragmentation of the production cycle into a number of segments specialized in the production processing of different fibres/yarns; even the single steps of automated production are often considerably fragmented, which entails the need for them to be perfectly organized for guarantee good final results of automated production. The Initial steps for production of the textile cycle are less fragmented but fragmentation unquestionably increases during the finalized finishing stage, for this reason the large amount of processes required by the market. Modern automation technologies for textile finishing based on electrical and electronics, computer programmability and smart systems show great potential for textile applications and currently aim to the achievement of important objectives such as flexibility and quality, according to three reliable paths:
1) The automated standardization of components
2) The automated compatibility of systems
3) The popularity of personal computers in case of textile finishing.

The automated standardization of components takes place thanks to the concentration of automation technologies in some basic types of automated processes which must be done by the mechanical forces by machine. The machine is defined and summarized by a system made of inputs and outputs for automated textile production system. Inputs of textile production are sensors which transform the physical variables of the system into electrical values which can be read and processed by an electrical and electronic unit. Outputs of automated production are the actuators controlling the machine and consequently the process (motors, solenoid valves, thermo resistors).

Any system may usually refer to this operating scheme and can be controlled by making inputs operating in relation to the state of the output and following a preset sequence of times. The computer, by means of the appropriate automated operating software, supplies the logical links between inputs and outputs and controls the right operating sequence for Automation in textile finishing industry.

Through its gradual introduction, automation has affected:
1. Machines: the immediate objective was the reduction and simplification of the operator’s tasks;
2. Processes: the subsequent evolution stage has ensured the links between the various production steps with the automatic control of the textile mill, leaving the operator with only control and supervision tasks. The full insolvency of the different production areas (inventory control systems, preparation of dyes and auxiliaries, dyeing equipment, material storage, etc) and /or services such as planning, laboratory, design pattern development, technological planning of cycles and production still needs to be addressed. The most advanced integration solutions available today are mainly production cells.

The main difference between automated systems essentially lies in the quantity of variables controlled. Here are the finishing segments most affected by technological development:
1. Color analysis
2. Process control
3. Production control systems
4. Color kitchen
5. Automated inventory control systems
6. Transport and robotized systems
7. Machine control systems

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NEW INVENTION IN TEXTILE DYEING AND FINISHING

Ultra and new modern technologies are always regarded as likely for dyeing and finishing of textile. Usually the process of textile dyeing and finishing are very slower and the process takes almost 8 to 12 hours for dyeing cotton knitted fabric with winch or jet  dyeing machine and almost 5 to 8 hours for finishing that fabric in finishing machine. It takes too much time, costly, labor depended. If we use new technology in textile dyeing and finishing, we will get a very good result.

 

On 16 January, the Hong Kong Productivity Council (HKPC) organized a seminar on dyeing/finishing and functional treatments of textiles. The seminar decision provides new perspectives on industrial upgrade by promoting new technologies in textile dyeing and finishing which both is energy saving and waste reducing. As part of the Cleaner Production Partnership Programme, the seminar aims at helping enterprises achieve green production and cost reduction at the same time.

Electrochemical Process Technology in textile dyeing and finishing:

A modern invention in textile dyeing and finishing is the development of Electrochemical process technology. Electrochemistry means the use of electrical energy in initiating chemical reactions, replacing traditional aid agents in direct chemical reactions. Taking sulphur dyes as example, in traditional technology, sulphides (such as sodium sulphide, Na2S) are used as reducing agents.

What ever the reduction process of dyeing is fast and direct, but it is wasted large amount of chemical energy and Green production has become necessary for enterprises under the update and conversion policy. The Hong Kong Productivity Council (HKPC) promotes new technologies in textile dyeing and finishing, injecting new thoughts to the industry.

New invention in Textile Dyeing and Finishing wastewater with high chemical oxygen demand (COD) value is produced, operation inefficiency become long-term. When electrochemical reduction is adopted, no reducing agents are needed and the

COD value of wastewater can be largely reduced, hence cost of wastewater treatment will be lowering. So using of direct electrochemical reduction is undoubtedly more efficient than the traditional technology, and the underlying chemical principle is also simple. However, as the stability and oxidizing/reducing power of different chemical substances are not the same, dyes can not be directly and effectively reduced by electrodes. Hence the scope of utilizing direct electrochemical reduction is quite narrow.

The system of indirect electrochemical reduction is the same, but in operation another strong oxidizing/reducing agent acts as medium, which makes the technology more applicable to different kinds of dyes. Taking indigo as example, traditional technology takes sodium dithionite (Na2S2O4) as a reducing agent, and the product should be re-oxidized in the air afterwards to fix the colour. Just like traditional reduction of

sulphides, large amount of chemical energy is wasted and wastewater with high COD value is produced.

Enterprises attempt to reduce the amount of sodium dithionite used in order to lower production cost, but such attempt produces other difficulties as well. For example, the oxidation of sodium dithionite can reduce by injecting nitrogen but is very costly. Addition of aldehydes or directly powering with electricity may devloped the reducing power of sodium dithionite, but the wastewater problem remains.

If electrochemical reduction is involved indirectly, sodium dithionite can replace as the reducing agent by the medium. The medium may supply both oxidizing and reducing substances and can regenerate so that both waste and pollution can be removed. Past experiments show that reduction by electrolysis can save about 90 percent of production cost when compared with reduction by sodium dithionite.

For reducing dyes, electrochemical process technology can be utilized in other aspects. Taking bleaching as example, the core principle of electrochemical mercerizing and bleaching is that bleaching chemicals can be produced by electrical energy and can be regenerated; hence the process is easily controlled, waste-reducing and energy-saving.

The process can be monitored so that bleaching occurs evenly. Also, the cost and danger of transportation is greatly reduced, particularly regarding hydrogen peroxide which is explosive.

Another emerging project is the technology of ozone electrolysis. Ozone is strongly oxidizing and can be used in decolorizing and other waterless dye treatments (e.g. ozone jets to prevent wearing out of jeans). As ozone can self decompose, it will not cause pollution problems once carefully treated. New perspectives on industrial upgrade by promoting new technologies which are both energy saving and waste reducing.

In conventional technology of dyeing with water, textiles should involved multiple processes with the help of aid agents, chemical salts, surfactants and reduction clearing agents. In contrast, for the supercritical waterless dyeing technology, only supercritical liquid is needed for dyeing and migration, after which the pressure and temperature can be lowered and the whole process is finished, without producing any wastewater. Also, as carbon dioxide automatically detaches from textiles and remaining dyes, the latter can be reused. More importantly, as operation procedures are reduced, the dyeing cycle is also shortened from several hours to 15 to 60 minutes; energy is also saved due to the lower operational temperature.

Regarding the cost, although the equipment required for the process is quite expensive, the supercritical substance (carbon dioxide) is cheap and the technology enjoys an overall advantage in cost. On the other hand, although the technology is not mature enough regarding application in natural fibres, the quality of the end-product made of synthetic fibres is high. Overall, the effects of interactions between different textiles with supercritical substances are yet to be fully discovered.

Plasma Treatment Technology in textle dyeing and finishing:

When a substance in its gaseous phase absorbs enough energy, the outermost electrons in the atoms will escape the nucleus’ control and become free electrons, while the atoms become positively charged. This chemical status of a substance is called plasma. As it is volatile, it can discharge electricity under certain physical conditions and react with other substances (including textiles), leading to various chemical fusions and fissions. These effects can alter the surface structure of textiles; hence plasma is suitable for surface treatment.

Since only the surface structure of materials is altered by plasma, the substrate characteristics of textiles will not be affected. Also, as small amount of plasma is enough to produce profound effect and one set of equipment can accommodate to different kinds of gaseous chemicals, the equipment is relatively cost effective and user friendly. The kinds of plasma undergoing testing are varied, including silanes (SinH2n+2) (waterproof), freons (increasing surface tension and oil- and dirt-proof effects) and phosphoruscontaining organic monomers (fireproof), etc.

Plasma treatment technology can also improve existing dyeing technology, including the newly developed technology of metallised fabrics. On the other hand, HKPC attempts to integrate plasma treatment technology and supercritical fluid dyeing technology, and replace supercritical fluid with plasma in the dyeing process. The lowpressure plasma dyeing technology is still being developed.

The textile dyeing and finishing industry is considered energy-wasting and highly-polluting, which will be forced to withdraw under the upgrade and transformation policy. However, with technological development on a full swing, traditional industries are able to overcome technical difficulties and revive after the financial crisis.

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