In its simplest form a package-dyeing machine is a vessel capable of containing packages of textile material through which heated dye liquor is passed by means of a circulation pump. Later developments accelerated by the need to dye polyester at temperatures above the boil lead to enclosing and strengthening such vessels so that they could operate upto 140° c at pressures around 70 psi (4.95 kgs per/ sq. cm.)
Accessories were added to allow samples to the extracted without depressurizing the whole system and to inject dyes and chemicals from out with the main circulation circuit. Later still, simple controls of time and temperature were replaced with fully automatic programmes based on sophisticated microprocessors that reduced operator involvement in the dyeing process to a minimum and elevated LOA (Limits Of Accuracy) sophistication previously unattainable levels.
We expect a main circulating pump to deliver 30 litres of liquor per kg of thread at 1.26 kgs per sq.cm. pressure which usually means the bath is pumped through the thread load upto four to five times per minute.
Exceptionally, cheese-bleaching machines need only deliver half of the discharge tobe effective.
Many of us, when faced with an unlevel cheese dye lot, blame our troubles on poor liquor flow which, because the dyeing process, by necessarily, is unobservable and because there is no instrument to read out the flow. Is hard to prove one way or another.
But a small one, however, can interpret the evidence available to him e,g,, here are a few tips on how to ascertain whether or not abnormal liquor flow is the source of Unlevelness.
1. Check the in-out and out-in pressure gauges and compare the readings with your past
experience. Your Dalal and Staffi machines with their modest pumps should register a pressure differential of around 0.5 kg per sq.cm. If the differential is significantly lower than this value, liquor may be freewheeling or channeling through a badly seated carrier, a sprung cap or a loosely loaded column of cheeses.
2. Likewise pressure differential higher than 0.5 kgs per sq.cm could indicate that something is causing unduly high back pressure e.g. very dense cheeses.
3. Unlevelness on a number of cheeses which represent one spindle or multiples of one spindle might indicate poor sealing of the number(s) of spindles involved.
4. Unlevelness on a number of cheeses that represent one complete layer as horizontal cross section of a carrier load of cheeses may mean that the machine has (leveled out) for sampling or during a power failure exposing the top most layer of cheeses to oxidation or differential dye uptake.
5. Loss of air pad pressure in one way low liquor dyeing can cause reduced liquor flow.
Open expansion tank:
This tank is sized so that the top row of cheeses is exposed when liquor is leveled bag to the expansion tank from the kier by gravity.
The tank feeds the suction side of the secondary pump, which normally discharges into the main pump housing via the non-return valve.
The expansion tank is an invaluable aid to level dyeing as it allows controlled additions of chemicals and redip dyes, when pressurized.
Extraction rate from the expansion tank is usually 5 to 25 litres per minute with the pump running at a pressure of around 3.6 kgs. per sq. cm.
It is important that the right balance between expanding main kier liquor and expansion tank injection rate is struck otherwise liquor flow may be affected. This balance is obtained by drilling out the orifice plate on the cooled liquor return from the main kier to the expansion tank.
The efficiency of the back cooler or condenser is also important since if the temperature in the expansion tank is allowed to rise about 80 to 85°C, the adversely secondary pump may cavitate thus affecting the flow characteristics of the dyeing system. If the liquor is over cooled, energy is wasted in reheating it in the main kier and of course cooling water volumes are unnecessarily high.
April 18, 2008