Practice / Causes and solutions of raw spots, alkali spots, calcium spots, yellow spots, and alkaline spots

Boiling blemishes mainly include spots, such as raw spots, alkali spots, calcium spots, yellow spots, and alkaline spots. So, the question is, how do these stains occur? How to solve it?

  1. raw spots

Defect morphology:Part of the fabric is dark yellow. Sometimes cottonseed hulls remain and the capillary effect value is very low.

Cause : ① Insufficient dosage of chemical additives during boiling.

 

② The boiling temperature is too low.

 

③ Insufficient boiling time.

 

④ The voltage is raised too quickly, causing the temperature to rise too quickly.

 

⑤ The liquid-liquid ratio is too small or liquid leaks midway, and some fabrics are not immersed in the liquid.

 

⑥ The fabrics are stacked too tightly when loading into the pot, the iron pipe in the heater is blocked, or the flow rate and flow rate of the liquid pump are insufficient, resulting in poor boiling circulation.

 

The above reasons will cause uneven boiling and produce spots.

 

Solution

① Formulate and strictly implement the boiling process, paying special attention to controlling the pressure and heating rate and boiling temperature.

 

② Control the reasonable liquor ratio to prevent liquid leakage during the boiling process and prevent some fabrics from being immersed in the boiling liquid.

 

③ When pouring fabrics into the pot, stack them with appropriate tightness, and control the flow and speed of the liquid pump appropriately to ensure smooth and even circulation of the boiling liquid.

 

Repair method: When spots appear, you can repeat the boiling process to repair them. During boiling, the dosage of caustic soda and surfactant can be slightly lower, and the boiling time can be slightly shorter.

  1. alkali spots

Defect morphology: Parts of the fabric have dark brown stains from residual liquid.

Cause: Alkali spots are mainly caused by lye drying on fabrics.

  • When the boilingbath ratio is too small or liquid leaks during the process, part of the fabric is not immersed in the boiling liquid, causing the residual boiling liquid to dry up on the fabric, causing alkali spots and even local alkali shrinkage.
  • After boiling, if the liquid is discharged too quickly, the washing water is fed slowly or too late, or the water volume is insufficient. And part of the fabric is not immersed in water, causing the residual liquid to dry up on the fabric, which can also easily cause alkali spots and even local alkali shrinkage.
  • After being removed from the pot, the fabric still contains some residual liquid. If the pickling is not timely or the pickling is not sufficient, the residual liquid will be adsorbed on the fabric, which can easily cause alkali spots.

Solution

  • Control the reasonable liquor ratio to prevent liquid leakage during theboiling process and make the fabric completely immersed in the scouring liquid.
  • Ensure the effect of pickling and water washing after boiling, and prevent uneven and dirty washing, as well as local residual alkali solution.

Repair method: Alkali spots can be removed by repeated washing with hot dilute acid or hot water. Severe cases need to be re-done. If local alkali shrinkage has been caused, repairs cannot be performed.

  1. calcium spots

Defect morphology:The color of the spots is similar to the color of the fabric after boiling, so it is generally difficult to detect in appearance. Calcium spots can make the fabric feel rough and even become water-repellent.

Cause :If the hardness of the scouring water or post-scouring washing water is too high, calcium soap, magnesium soap or inorganic calcium salts will easily adsorb on the fabric, forming calcium spots.

Solution:

Use soft water for scouring and washing.

 

Repair method: If calcium spots are found, wash them repeatedly with hot dilute acid to dissolve the calcium salts.

  1. yellow spots

Defect morphology:Parts of the fabric are dark brown

Cause :If the water used for souring, pickling, and washing after boiling contains a large amount of sediment or iron, it will easily cause yellow spots (especially when pickling and washing are carried out by spraying).

Solution:

Pay attention to water quality and the quality of water delivery pipes.

 

Repair method: If the yellow spots are caused by sediment, you can wash them repeatedly. If the macula is caused by iron, it can be treated with 2-3g/L oxalic acid solution under medium temperature conditions. At this time, the iron ions will turn into soluble iron oxalate complex and be removed.

  1. alkaline spots

Defect morphology:The fabric feels rough and hard, making the fabric water-repellent

Cause :If the amount of alkaline in the scouring solution is too much, and the water washing and pickling are not timely or sufficient, the alkaline, silica, calcium silicate, and magnesium silicate are easily adsorbed on the fabric, causing alkaline spots.

Solution:

Control the dosage of caustic soda, increase the washing temperature and strengthen the washing.

 

Repair method: Wash repeatedly with hot dilute acid or hot water. In severe cases, re-training is required.

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