Hank Yarn Dyeing Machine

Overview

A hank yarn dyeing machine colours yarn that has been wound into hanks, also called skeins: loose loops of yarn rather than yarn wound tightly onto a cone or beam. Dyeing in hank form lets the dye liquor reach every part of the yarn freely, so the result is a soft, lofty, even shade. This matters for hand-knitting yarns, carpet and rug yarns, woollen and acrylic yarns, and any yarn where bulk and handle are as important as the colour. The trade-off is lower productivity than package dyeing, which is why hank dyeing is reserved for yarns that genuinely benefit from it.

The yarn hangs on a set of removable Carrier Stick poles loaded into a Hank Carrier Frame. The whole carrier drops into a stainless Dyeing Vessel filled with dye liquor. A Circulation Pump drives the liquor through a Shower Header and Nozzles so it is forced through the hanks rather than just washing over them. A Heat Exchanger heats and later cools the bath, a Dosing and Addition Tank meters dyes and chemicals in on schedule, and a Control and HMI System runs the whole recipe.

How it works

A typical batch begins with loading. Hanks are hung over the carrier sticks, the sticks are seated in the carrier end plates, and the loaded carrier is lifted by the Lid and Hoist and lowered into the vessel. The lid is closed and, on a high-temperature machine, clamped down with the Lid Clamp set so the vessel can hold pressure.

The vessel then fills with water through the Fill Valve valves to the set liquor ratio, usually between 1:8 and 1:15. The Circulation Pump starts and pushes liquor through the Heat Exchanger and up to the Shower Header and Nozzles, where an array of Spray Nozzle nozzles forces it down through the yarn. Forcing liquor through the hanks, rather than relying on slow diffusion, is what gives even dye penetration in a reasonable time.

Dyes and auxiliary chemicals are pre-mixed in the Dosing and Addition Tank and metered into the circulating liquor by the dosing pump at the points the recipe calls for. The heat exchanger raises the bath temperature on a controlled ramp, typically 1 to 3 °C per minute, holds it at the dyeing temperature, then later cools it with water through the Cooling Water Valve. Throughout, the Flow Reversal Valve Set valve set periodically reverses the direction of liquor through the hanks, every one to five minutes, so neither the top nor the bottom of a hank is favoured and the shade comes out level end to end. Some designs also gently lift or rotate the carrier on its Carrier Drive Shaft for the same reason.

When dyeing is complete the bath is dropped to the drain through the Drain Valve, the yarn is rinsed in fresh water on the same circulation path, and the carrier is hoisted out for unloading and drying.

Real subsystems

The Dyeing Vessel is the heart of the machine: a 316L stainless tank with a dished bottom draining to a central Liquor Sump that feeds the pump. It carries Temperature Probe probes, a level sensor, and on HT machines a Pressure Sensor for vessel pressure. An insulated jacket cuts heat loss during the long hot holds.

The Circulation Pump is a centrifugal pump driven by a Servo Motor on a variable-frequency drive, so flow can be tuned to the batch. A Flow Meter on the discharge confirms the liquor is actually moving through the hank bed, and the Flow Reversal Valve Set differential pressure sensors watch for the bed clogging with lint.

The Liquor Filter Unit keeps loose fibre out of the loop with a removable Filter Basket, and the Heat Exchanger does both heating and cooling through one tube bundle by switching between the Steam Control Valve and the cooling water valve. The Control and HMI System ties it together: a PLC runs the stored recipe and drives the valves, pump, and dosing through I/O modules and a bank of relays, while the operator works from a touchscreen HMI.

Materials

Everything wetted by hot dye liquor is stainless steel, normally 316L, because dye baths are hot, salty, and often acidic or alkaline. The vessel shell, sump, pump casing and impeller, exchanger shell, header, nozzles, and carrier are all stainless. Seals and gaskets use heat- and chemical-resistant elastomers such as EPDM or PTFE, sized through the O-Ring Set and Lid Gasket items. The base frame is welded carbon steel, painted or clad, since it never touches liquor. Insulation is mineral wool under a stainless cladding jacket.

Atmospheric versus HT variants

Atmospheric machines run with the bath open to air and top out at 98 °C, just below boiling. They suit cotton, wool, and acrylic yarns dyed with direct, acid, or reactive dyes, where temperatures near boiling are enough. The lid mainly contains splash and heat.

High-temperature (HT) machines are pressure vessels. The lid is sealed and clamped, and the bath can be taken to 140 °C at around 4 bar, well above boiling. That heat is needed to open up polyester and some acrylic fibres so disperse dyes can enter. HT machines carry the full pressure-rated lid clamp set, a vessel pressure sensor, relief protection, and a Safety Interlock that blocks the lid from opening while the vessel is still hot or pressurised.

Use and maintenance

A dye house chooses hank dyeing when handle and loft matter and when colour evenness across a long length of yarn is critical. Cycles are long, often two to four hours including heat-up, dyeing, cooling, and rinsing, so machines tend to run batch after batch through the day. Routine maintenance centres on the wetted parts: clearing the Filter Basket of lint, checking the pump Mechanical Seal for liquor weep, descaling the heat exchanger tubes, and replacing the Lid Gasket when sealing gets marginal. On HT machines the clamp set and the pressure relief path are inspected on a schedule because they are what keep a pressurised hot bath safe.