Friday, January 15, 2010

Pad Dyeing Machines

Padding Mangles


The pad dyeing machines overcome the deficiency of winch and jigger dyeing machines of smaller batch size and discontinuity in dyeing. Padding mangle offer continuous process of the fabric in concerned liquor , such as pretreatment, dyeing or finishing.
Application of dyestuffs is conducted in the pad dyeing machines with single or multiple dipping in solution .During padding, the fabric passes into a solution of chemicals, under a submerged roller and out of the bath. It is then squeezed to remove excess solution .The objective of this process is to mechanically impregnate the fabric with the solution or dispersion of chemicals Pad impregnation is common for the dyeing of fabric and for the application of finishing chemicals.

A Practical Introduction to the Continuous Dyeing of Woven Fabrics

Machine Description

Main parts of a padding mangle

The main frame

The frames are usually fabricated construction , to withstand vibrations and heavy workloads.

Tension elements

While the cloth passes on to the padding machine no slackness should occur in fabric either in weft or warp directions and the weft threads of cloth should remain parallel to the nip at the squeezing point.

The padding mangle bowls

The nip rollers (often called bowls) are the key to successful pad dyeing. In general, two-bowl nips are preferred for lightweight or standard fabrics running at moderate speeds, whereas three-bowl arrangements are intended for heavier or more densely woven qualities that may be more difficult to wet out and thus require a double-dip and double-nip treatment.

Cloth Guiding arrangement

Are provided so that machine should have a universal feeding and delivery system at a uniform tension .

Pressure generation and application

It is either pneumatic or hydraulic.

The dye trough

The pad trough is usually a deep U-shaped vessel with a single roller attached to the base of a displacement block that leaves a narrow passage to accommodate the moving fabric.
A cost study of thermosol and continuous solvent dyeing

Dyeing Method

The padding operation itself consists of two essential steps: thorough impregnation by immersion of the absorbent fabric in a dye solution containing a wetting agent, followed by squeezing of the wet fabric between rollers to expel air and replace it with dye liquor, as well as expressing surplus liquor back down the sloping fabric surface to the pad trough.

The cloth to be padded is taken up by either from the folded form or from the batched condition and fed to the padding machine over a set of guide rollers. The fabric is straighten in warp as well as weft directions .It is necessary to attach and end piece on both the sides of batch.

The fabric to be padded should be padded should be pretreated , free from loose fly ,waste ,oily matter , flat , crease free and with opened-out selvedges.

To obtain consistency of shade it is most important that the fabric running speed and the length of immersion of fabric in the dye liquor remain constant throughout the padding run. The three main types of automatic level control are:

1. Float switches: these are reliable and are unaffected by foam but they are relatively bulky

2. Conductivity probes: these are small and neat but foaming of the pad liquor adversely affects their performance

3. Differential pressure detectors: those with a hollow tube projecting downwards from the liquor surface are difficult to clean and the preferred type is that with a closed diaphragm set in the base of the vessel.

4. The control of pad liquor temperature is highly desirable to achieve consistent results.

Further Readings
 Jet or pad/wet steam dyeing of tublualr knitted cotton fabrics with reactives: Which costs less? : a summary report (Hatra research report)
Pad-batch Dyeing of Plant Fibres (Rural Technology Guide)

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  1. need calculation regarding padding operation

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