Method for controlling mixtures especially for fabric processing
A method for supplying liquid mixtures on a mix-on-demand basis for consumptive use, and for maintaining the composition of such mixture on a highly accurate and stable basis. For wet-on-wet processing of fabrics, the processing solution is supplied at start-up on a mix-on-demand basis to precise specifications and is maintained at such precise specifications throughout fabric processing, which involves continuous additions of water by the incoming fabric and removal of solution by the exiting fabric. Recirculation of the solution at a high rate, together with rapid and repetitive measurements of the composition of the recirculating solution enables the solution to be precisely monitored and maintained. Periodic small additions of chemical are injected as necessary to maintain highly stable, accurately controlled process conditions. Extraordinary economies, both direct and indirect, can be realized with the new system.
1. A method of processing a continuously moving web of wet fabric by the addition of a processing chemical thereto, which comprises,
(a) providing a processing pan having a limited volumetric capacity for containing a small quantity of processing solution, including said processing chemical as a minor component and water as a major component in predetermined proportions,
(b) the volumetric capacity of said processing pan being such that only a small portion of the moving fabric web is exposed to the processing solution at any time,
(c) providing separate valve-controlled sources of a concentrated solution of said processing chemical in water and of said water,
(d) continuously passing said wet fabric into and through said processing solution in a manner causing fabric to pick up and remove a first quantity of processing solution from said processing pan while the fabric causes the continuous introduction into said processing pan of a quantity of water which is dilutive of the processing solution,
(e) continuously withdrawing processing solution from said processing pan and recirculating said withdrawn solution back to said processing pan,
(f) said step of continuously withdrawing and recirculating said processing solution including a pumping stage, a mixing stage, and a measuring stage,
(g) said pumping and mixing stages taking place in advance of said measuring stage,
(h) the volumetric rate per minute of recirculation of said processing solution being greater than the volumetric capacity of said processing pan,
(i) rapidly and repetitively measuring the content of said processing chemical in the continuously flowing, recirculating stream of said processing solution,
(j) said step of rapidly and repetitively measuring the content of said processing chemical being performed by an in-line optical sensor positioned in optical exposure to the continuously flowing, recirculating processing solution, and
(k) adding supplemental amounts of said concentrated solution of said processing chemical to said continuously flowing, recirculating solution as required in order to continuously maintain said predetermined proportions of said processing chemical and water in said processing solution,
(l) the steps of adding supplemental amounts of said processing chemical including introducing said processing chemical into the continuously flowing, recirculating solution at a location in advance of said pumping and mixing stages.
2. The method of claim 1 , wherein
(a) the level of processing solution in said pan is continuously sensed,
(b) in response to the level of said processing solution becoming lower than a predetermined level, initiating a cycle of replenishing said processing solution by introducing additional quantities of both water and processing chemical in said predetermined proportions into the continuously flowing, recirculating processing solution until the level of processing solution is increased to a level above said predetermined level, and
(c) within each replenishing cycle introducing said water and said processing chemical in multiple injections with a short time interval between such injections.
3. The method of claim 1 , wherein
(a) said processing solution is withdrawn and recirculated at a volumetric rate per minute which is a multiple of at least three times the volumetric capacity of said processing pan.
4. The method of claim 3 , wherein
(a) the measuring of the content of said processing chemical in the flowing stream of said recirculating processing solution takes place multiple times for each period of time in which the volumetric capacity of said processing pan is recirculated.
5. The method of claim 1 , wherein
(a) said processing chemical is introduced at a predetermined flow point in the recirculation of said processing solution, and
(b) said measuring step is performed at a flow point in said recirculation located downstream of said predetermined flow point.