What is water hardness?

Hardness is the main monitoring index of dyeing and finishing water, which mainly indicates the content of calcium, magnesium and other salt impurities in water. The more salt impurities, the higher the hardness. Natural water is generally divided into temporary hardness and permanent hardness, and the sum of the two is called total hardness. The impurities that can form temporary hardness are mostly acid carbonates of calcium and magnesium, and the impurities that can form permanent hardness are mostly sulfates, nitrates and chlorides of calcium and magnesium. The former can be reheated to decompose insoluble carbonates, thereby reducing the hardness of the water; the latter must be chemically treated to remove impurities. Generally, surface water is less hard, while ground water is more hard.

At present, the method of expressing the hardness of water has not been unified. It is usually expressed by the mass of calcium carbonate contained in one kilogram of water, abbreviated as mg/kg or PPM, while other alkali metal salts in water are expressed as calcium carbonate content. According to the different amounts of calcium and magnesium salt impurities in the water, the water quality is usually divided into the following categories according to the hardness

It should be pointed out that due to the large water consumption in the printing and dyeing plant, it is difficult to use all soft water, and water of different quality can be used according to the different requirements of production and processing. For example, when preparing dye liquor and soaping liquid, soft water below 20PPM should generally be used; when preparing scouring liquor and bleaching liquor, soft water below 50PPM should be used; and for washing water, if the total hardness is below 150PPM, it can be used as appropriate according to the actual situation . If the water quality used in dyeing and finishing is too hard, various problems will occur. The common ones are that the whiteness, hand feel, and desizing effect after pre-treatment are reduced. In severe cases, the phenomenon of "white powder" will appear, which may cause uneven dyeing , The color is dull, the color fastness is reduced, etc. When the yarn is dyed, there will be a series of problems such as poor inner and outer layers, uneven dyeing, white core, and cylinder scale after a long time of use. In response to this situation, the quickest and easiest way is to add a chelating dispersant (some are also called water softeners), which can be directly added to the working solution without separate treatment. The specific dosage can be added according to the product instructions.