This operation is crucial for fabrics made of synthetic fibres (PE, PA, elastomers), for triacetate, and partly for PAC fibres (setting), since it grants excellent dimensional stabilization and crease proof properties, maintained till the fabric is exposed (by air blowing) to temperatures exceeding the heat setting one (after being treated with water at a temperature above the second order glass transition temperature, i.e. 80-85°C for acrylics).
Heat setting is carried out on gray fabrics (scarcely applied), on scoured fabrics (frequently applied) and on dyed fabrics (scarcely applied).
The process grants excellent dimensional stability and good crease-proof properties.
As far as operating conditions are concerned, the fabric must be treated in accurately controlled moisture and temperature conditions.
Fibre | Min T. °C | Max. T. °C | Time (in seconds) |
Polyester (PE) | 170 | 210 | 15-50 |
Polyamide (PA) 6.6 | 170 | 210 | 15-40 |
Polyamide (PA) 6 | 160 | 180 | 15-40 |
Triacetate | 160 | 180 | 15-40 |
Acrylic (PAC) | 160 | 180-200 | 15-40 |
Elastomers | 170 | 180-200 | 15-40 |
Machines used: stenters.
Fluctuating temperatures inside the stenter cause a consistent variation of crystallinity in the fibre structure, which leads to different affinity for dyes.
The moisture in the fibre produces soft hand, but variable moisture percentages in the different fabric sections create the above mentioned defect (variable crystallinity).
Too low temperatures do not allow a good setting while too high temperatures and too long setting times cause yellowing (PA and elastic fibres), stiff hand (acrylics), and loss of elasticity (elastic fibres).
The presence of combustion gas (NOx) produces a yellowing of the elastomers.
The heat setting process carried out before scouring could fix the stains on the fabric or make the scouring process more difficult due to the modification of the lubricating products (cracking with emission of polluting gas).
Heat setting after dyeing could lead to the sublimation of disperse dyes (if not accurately selected).
