Chainless Mercerizing Range
The chainless mercerising machines are so-called, because the is no fabric stretching by clip-chains in this type of machines. The underlying principle in these machines is to apply tension to the fabric before and during the mercerising process and not to allow the cloth to shrink, till it reaches their stage when shrinking does not take place, with a view to achieve satisfactory mercerising results with reasonable production speeds.
The features of chainless cloth mercerising machines can be briefly mentioned as follows:
1. Fabric entrance: This consists of the entrance scaffolding, automatic cloth guiders, tension bars and a fabric pre-tensioning system. These parts take care of their ceaseless cloth passage to the mercerising section with sufficient the tensioning, so that the possible shrinkage during the action of mercerising lie can be almost eliminated. The pre-tensioning system consists of three curved rubber covered expanding rollers, in which necessary tension can be developed by their proportional displacement of the middle curved roller. At the end of the pretensioning section, the fabric is introduced the into the mercerising impregnating compartment.
2. Lye impregnation: The lye impregnation section consists of cylindrical metal rollers, partially immersed in the mercerising alkali lye, having a specific gravity of 56° TW. Rubber covered cylindrical metal rollers rest above and between the metal rollers. These roller it is cease their good impregnation and restrict the weft wise shrinkage and stop they also provide the means of fabric traction, through the machine. There is an arrangement to spray the lie over the fabric in the impregnation compartment.
3. Adjustable squeezing devices: At the end of each section of the chainless mercerising machine, provision is made for an effective adjustable squeezing device. In the case of longer impregnating compartments, it becomes necessary to arrange for an additional squeezing device within the impregnation section. This is necessary in order to complete the lye impregnation at that pre-determined speed and to cope up with the production target. The driven rollers of the squeezing devices are connected to the D. C. multimotor coordinated driving system. One of the drives is arranged as the pilot drive and all the preceding and succeeding drives are co-ordinated in such a manner that the tension in the Warp and the Weft directions is maintained which is very essential for achieving a good degree of mercerisation.
4. Adequate number of top and bottom rollers: With a view to obtain a perfect mercerising effect, it is necessary that the cloth should be in contact with the lye for the predetermined lye acting time. It can be understood that the more the number of rollers, the longer the dwelling time. The idea is that the lye acting time of 50 seconds can be arranged by designing the impregnation compartment to suit the ideal level, by adjusting the number of rollers in the impregnation compartment as correctly as possible.
In some chainless mercerising machines, there may be an additional set of metal and rubber covered rollers, which help in covering up the lye acting time. For higher dwell times , the machine speed to be reduced. Similarly for Shorter lye acting time, the speed is to be increased.
5. Stabilization of the mercerising effect: As has been explained earlier, there will be uncontrollable shrinkage in the fabric, if the mercerising lye contents are very quickly reduced from the mercerising cloth. In order not to allow this shrinkage to take place, the initial treatment of the cloth should be with a weak lye solution. The stabilizing action is obtained in the stabilizing section. In some cases, the stabilization is brought about by passing the mercerised fabric over a set of an expanding system consisting of three or more rows of metallic segmented curved revolving rollers. This expanding system is also called Mycock stretching contrivance. This stretching device exercises a widthwise stretching effect, thus giving a much better width control over the lye impregnated fabric. The entire arrangement including the weak lye spray-over the fabric, while on the Mycock rollers, is termed "the stabilizing section". The strength of the week lye splayed is generally about half the strength of the mercerising lye strength.
The weak lye can be stored separately and is sprayed on the fabric in the section in the form of the a good spray, by means of their circulation pump and is spraying system. This possible shrinkage from this stage of the fabric to the fully washed stage is not appreciably and can be controlled without much difficulty.
6. Recuperation of the mercerising lye: The mercerising lye picked up by the cloth during the process and which is still on the fabric after the stabilization is required to be recovered, ie., recuperated, to a great extent in the recuperation section. This section comprises a tank, with top and bottom rollers. The fabric passes over the top and bottom rollers, during which passage it is treated with hot water, maintained at the temperature of 90° Celsius are slightly above. Heating of the water and maintaining the temperature are carried out by means of a closed the steam coil.
7. Neutralizing the lye on the cloth: After coming out of the recuperation, the mercerised and hot water washed fabric is passed through a squeezing device into the neutralizing section. This section is provided with an arrangement to wash the fabric with a weak acid solution. Neutralizing with an acid solution is necessary only when there is no further alkali boiling process or any other wet process which requires the use of alkali containing solutions. Whenever mercerising is carried out before bleaching, neutralizing is not required . This section is provided with a device to introduce a predetermined acid dose automatically. Whenever as in addition is not to be carried out, the neutralizing compartment can be used as a normal washing compartment.
8. Washing Zone: The purpose of the washing zone, which may consists of one, two or more washing compartments, is to wash the mercerising fabric free from alkalinity. As explained the above, whenever a further boiling process is called for, the presence of small traces of residual alkali may not be objectionable. However, if there is any overnight stoppage of the washing process, a thorough wash is recommended to avoid any staining part other takes of defects in the mercerised cloth.
9. Tension regulation system: The chainless mercerising machines are characterized by their continuous fabric can, with free selvedges. this means that there is no direct stretch exerted on the fabric width. The fabric run, therefore, needs a constant consistent control and a Thorough regulation of the fabric tension, that is, fabric width.
Inadequate tension in the lye impregnating section would mean a corresponding loss in the cloth width, which is a very adverse factor, as for us the user is concerned. the tension in the cloth to be maintained is, usually, in the ascending order in mercerising, ie., cloth entry, cloth impregnation, lye action, and stabilization section. On the other hand, once the mercerising action is completed, the cloth pension should be in the descending order, that these recuperating, neutralizing and the washing zones.
10. Versatility of the chainless mercerising machines by way of the choice of fabric webs: the chainless mercerising machines give the processor the choice of the number of fabric webs to be processed, which will be based on the narrowness of the cloth width as also on the fabric weight per square meter. Such novel variations are possibly only in the chainless system. because the cloth salvages are not to be gripped in the chain clips and are free. It is also necessary to remember that the fabric is not allowed to run on its own, but is constantly held between rollers till the mercerising process is completed and only washing the lye a way remains to be carried out.
Most Important aspects of the chainless system:
The following points are very important and should be borne in mind in respect of the chainless mercerising machines:
Good lye pickup but not in excess of the mercerising needs, that it, say, 1 kg of mercerising lye/ 1 kg of fabric.
Good length of continuous lye impregnation gives a better degree of mercerisation.
Excellent squeezing effect at the pneumatic squeezing devices, regulating the lye pick up to the optimum level.
Wet fabrics (including gray material) can be processed, thus eliminating drying one process altogether ( by pre-squeezing).
Closed circuit washing of the treated cloth gives good results with less quantity of wash water.
When all the safe guards and precautions are properly observed, the chainless mercerising machine offers an improved over all mercerising efficiency.
In order to achieve top quality mercerising results, the following optimum conditions are now being observed:
Strength of mercerising lye - 28° to 30°Be.
Time of impregnation - 40 to 50 seconds
The lye temperature - 15° to 25°C
Note: The polyester/cotton blends also give very good results under the above conditions. However, it is possible to obtain very satisfactory results with a slightly higher lye strengths and lower lye acting time, say, above 25 to 30 seconds
Courtesy: Handbook of Textile Processing machinery R.S.Bhagwat.