8.5. Vertical high-temperature high-pressure yarn dyeing plant

The recent realization (between ITMA '83 and ITMA 87) of fully automated and robotized yarn dyeing plants based on RBNV dyeing machines and matching ARSPV pressure dryers is the most updated result of years of technological research and development activities and continuous dedi­cation to all details of engineering, manufacturing, testing and servicing of yarn package dyeing machines.

Performance, reliability and technological life are based on a wide range of major technical features summarized in this pamphlet.

Technological features of RBNV apparatus include:

1. Air cushion pressurization.

2. Adjustable liquor ratio.

3. Flexible loading capacity.

4. Helicocentrifugal liquor circulation pump.

5. Automatic differential pressure control.

6. Flow rate regulation system.

7. Dynamic hydroextraction by compressed air.

8. Modular design.

9. Integrated dyehouse automation.

Standard design and manufacturing features include:

• Three-level safety systems for rapid lid locking system.

• Water protected motors (EC Standard IP54). .

• Electro pneumatic control board in aisi 316 stainless steel.

• Magnetothermal motor protections.

• Heat exchangers rated for 15.0 kg/cm² operating pres­sure.

• Heating gradient 5°C./minute (range 20-80°C steam pressure 6.0 kg/cm²).

• Cooling gradient 3°C./minute (range 130-108°C water temp. 15°C, pressure 2,5 kg/cm²).

• Pneumatic lid lifting and lowering, rapid lid locking system.

• Nominal loading capacities from 25 to 1000 kgs.

• Pressure rating of 5.0 kg/cm², upto 140°C temperature.

• Construction entirely in AISI 316 stainless steel, all parts included.

1. AIR CUSHION PRESSURIZATION.

RBNV dyeing machines operate with material fully immerged in dyeing liquor.

Liquor flow through the material is bi-directional for perfect dyeing quality; liquor flow direction is reversed automati­cally at preset time intervals from inside-to-outside to out­side-to-inside of textile material under process.

Pressurization is generated by a cushion of compres­sed air in the upper part of the autoclave (see Fig. 8.8.) and automatically controlled to keep a preset value.

Compared with conventional dyeing machines, the RBNV pressurization system determines a wide range of technological advantages:

— Expansion volume is realized directly into dyeing autoclave and no continuous external circulation in a side tank is necessary.

(In conventional apparatus, on the contrary, is neces­sary to have a second external circulation circuit in an expansion tank on the side apparatus).

— The entire liquor volume participates to the dyeing pro­cess and dyestuff exhaustion is perfectly homogene­ous.

(In conventional apparatus the liquor in the expansion tank does not participate to the dyeing process and the dyestuff exhaustion level is reduced).

— During cotton dyeing with indanthrene dyestuffs the dyeing liquor is not subject to a continuous oxidation due to external air, and sodium hydrosulphite can be added in stoechiometric quantities at the start-up of dyeing cycle; no intermediate checking of reduction level and additions during operation are needed. (In conventional apparatus the oxidation is continuous and uncontrolled).

• Substantial savings are realized in terms of cooling water, steam and electric power, since static pump, cooling and re-heating for continuous external circula­tion are eliminated.

• Dyeing liquor temperature remains perfectly steady at preset value, (since no continuous liquor cooling/ heating is performed as in conventional apparatus).

Fig. 8.8. Capability variations of circulation of liquor in apparatus

Fig. 8.9. Choice of the filling level staff working solution

Fig. 8.10. Helicocentrifugal liquor circulation pump

• The RBNV dyeing apparatus can be rapidly pressurized at low liquor temperature.

• Air cushion pressurization permits to inject dyestuffs and chemicals quickly and directly into main liquor circuit.

• Feeding can be performed by means of a single tank or a multi-tank color kitchen which can be installed near the RBNV apparatus or in a remote position, designed for centralization of products preparation.

• Dyestuffs are injected into the highest turbulence point of liquor circulation pump, in order to originate an in­tensive stirring effect.

By comparison in conventional dyeing machines dyestuffs are inserted in a lateral expansion tank, which has a slow speed peripheral liquor circulation with the main dyeing ap­paratus, thereby causing long feeding times and uneven dyestuff exhaustion.

2. ADJUSTABLE LIQUOR RATIO.

On RBNV apparatus liquor ratio is adjustable to optimize processing condition, by means of automatic liquor level controls.

Level controls are performed by a floating level indicator combined with three adjustable electro-magnetic switches (L3 empty level, L2 normal level, L1 high level) in connec­tion with automatic water filling valve (see Fig. 8.9.).

The RBNV apparatus can operate at:

• a) Low liquor ratio during dyeing phase.

In dyeing phase RBNV dyeing machines operate with liquor ratio from 1:4 to 1:8 in function of yarn package de­nsity. Level (L2) is activated. Low liquor ratio during dyeing saves process water, steam and auxiliary products added in fixed quantities in relation to liquor volume (detergents, salts, etc.) and determines economical operating costs.

• b) Higher liquor ratio during wash-off phase.

Adoption of higher liquor ratio during wash-off phase im­proves the solubility of unfixed dyestuffs, which can be easily eliminated from yarn under process. Level (L1) is ac­tivated. This characteristic allows for performing soaping and wash-off phases after cotton dyeing with fiber reactive or indanthrene dyes at a liquor ratio ranging from 1:8 to 1:13, with substantial reductions in both number of phases and times.

c) Fully-flooded during continuous rinsing phase.

The overflow valve is installed in the upper part of the au­toclave closing lid, so as to perform a complete autoclave washing simultaneously with continuous rinsing of material under process, after the dyeing cycle. No liquor level is activated and the RBNV apparatus is fully flooded.

Adoption of a specific liquor ratio among the above re­quires a very simple operation of actuating the relevant au­tomatic level probe.

3. FLEXIBLE LOADING CAPACITY.

Besides full load capacity, the RBNV apparatus can be loaded, when necessary, with reduced loads, keeping an almost constant liquor ratio.

This characteristic, of extreme importance for commission yarn dyers, offers unmatched operating flexibility as economical dyelot size is no more tied up with available machine capacity. Reduced load can be obtained (see Fig. 8.11.):

a) Normal total load.

b) Reduced load by fitting blind tubes on upper part of yarn package columns, or replacing yarn package spin­dles with shorter ones, or

c) Half load by loading one semi-carrier only, for machines designed to operate with two superimposed dyeing carriers.

In all such cases it is sufficient to adjust liquor level switches and liquor flow rate to dyeing conditions for re­duced load.

Reduced loads on conventional apparatus result in high in­creasing of liquor ratio and necessity of recipe and sample corrections.

Fig. 8.11. Facilities of reduced load

4. HELICOCENTRIFUGAL LIQUOR CIRCULATION PUMP.

The heart of RBNV dyeing apparatus is the liquor circula­tion pump, specifically engineered for dyeing use and de­signed for high liquor rates in the head pressure range from 4.0 to 15.0 meters water column, which are the actual operating conditions of more than 90% of yarn package dyehouses.

Higher head pressure values can be achieved when neces­sary by incresing shaft's rotating speed. Motor and pump's shaft rotate always in a single direction. Drive transmission from motor to pump is made by pulley and vee-belts in order to avoid vibrations.

Fig. 8.12. Equipment installed in production

Fig. 8.13. Equipment for yarn dyeing (Hisaka, Japan)

Fig. 8.14. Kinds of cartridges for yarn