a Bleaching: A process where color bodies are destroyed and the fabric is whitened u Mercerizing: Caustic treatment of cellulosic fabrics improving luster, water absorbance, dye yield and fiber strength Carbonizing: Acid ofwool for removingvegetable matter Heat Setting: Heat treatment of fabrics containing thermoplastic synthetic fibers. Stabilizes fabric by reducing shrinkage and distortion CHAPTER PREPARATION PROCESSES e Various ty pes of equipment can be used for preparing fabric. The ultimate goal of any preparation process is to produce fabric that is clean and rid of all impurities that interfere with dyeing and finishing. The preparation steps can be carried out as either batch or continuous processes. The fabric may be transported as a rope or as an open sheet through the equipment. The choice is often predicated on the dye- house itself. The distinguishing feature of batch equipment is that all of the fabric is simultaneously submerged in the liquor. The fabric is agitated by moving it through the liquor. In continuous processes, the fabric passes non-stop through compartments and/or stages so that the fabric is incrementally subjected to the action of the chemicals. The equipment used for dyeing fabrics is also suitable for preparing fabric. In this section, the equipment used to perform fabric preparation will be described . YARN PREPARATION EQUIPMENT Stashing is the process where Size is applied to warp yarns for weaving. The purpose of size is to protect the yarn from the abrasive action of the loom. The process is carried out on a Slasher and the application procedure is called Sizing or Slashing. While technically this process is not considered as a step in preparing
Bleaching: A process where color bodies are destroyed and the fabric is whitened. Mercerizing: Caustic treatment of cellulosic fabrics improving luster, water absorbance, dye yield and fiber strength. Carbonizing: Acid treatment of wool for removing vegetable matter. Heat Setting: Heat treatment of fabrics containing thermoplastic synthetic fibers. Stabilizes fabric by reducing shrinkage and distortion. CHAPTER 1 PREPARATION PROCESSES Various types of equipment can be used for preparing fabric. The ultimate goal of any preparation process is to produce fabric that is clean and rid of all impurities that interfere with dyeing and finishing. The preparation steps can be carried out as either batch or continuous processes. The fabric may be transported as a rope or as an open sheet through the equipment. The choice is often predicated on the dyehouse itself. The distinguishing feature of batch equipment is that all of the fabric is simultaneously submerged in the liquor. The fabric is agitated by moving it through the liquor. In continuous processes, the fabric passes non-stop through compartments and/or stages so that the fabric is incrementally subjected to the action of the chemicals. The equipment used for dyeing fabrics is also suitable for preparing fabric. In this section, the equipment used to perform fabric preparation will be described. I. YARN PREPARATION EQUIPMENT Slashing is the process where Size is applied to warp yarns for weaving. The purpose of size is to protect the yarn from the abrasive action of the loom. The process is carried out on a Slasher and the application procedure is called Sizing or Slashing. While technically this process is not considered as a step in preparing 2
fabric, the materials used in this operation, to a large measure, account for the bulk of what must be removed. Because the desizing step is highly dependant on what size was used, it is deemed instructive to discuss the slashing process as well as discuss the nature of the sizing materials Figure 1 shows a schematic diagram of a slasher. In slashing, section beams are combined to create a loom beam and at the same time apply the appropriate size to the warp yarns. The section marked (1)is the let-off station where one or more section beams are combined and fed through the rest of the range. The warp yarns are let-off as a flat sheet and then pass through a size applicator(2)consisting of a trough containing the size formulation and squeeze rolls. The yarns pass over heated cans 3)to dry. Located at the exit end of the slasher is an arrangement of bust bars which separate each warp end from its neighbor. The individual warp ends pass through a reed which guides the yarn onto the take-up beam. Associated with the slasher is a cooking station, where the sizing material(starch or polyvinyl alcohol) is dissolved and stored. The solution is metered to the applicator as needed to replenish what has been taken up by the warp sheet. The chemical nature of the size will be discussed in a later section along with the conditions needed to effectively remove the size Figure 1. Schematic of a Slasher 三三三 3
fabric, the materials used in this operation, to a large measure, account for the bulk of what must be removed. Because the desizing step is highly dependant on what size was used, it is deemed instructive to discuss the slashing process as well as discuss the nature of the sizing materials. Figure 1 shows a schematic diagram of a slasher. In slashing, section beams are combined to create a loom beam and at the same time apply the appropriate size to the warp yarns. The section marked (1) is the let-off station where one or more section beams are combined and fed through the rest of the range. The warp yarns are let-off as a flat sheet and then pass through a size applicator (2) consisting of a trough containing the size formulation and squeeze rolls. The yarns pass over heated cans (3) to dry. Located at the exit end of the slasher is an arrangement of bust bars which separate each warp end from its neighbor. The individual warp ends pass through a reed which guides the yarn onto the take-up beam. Associated with the slasher is a cooking station, where the sizing material (starch or polyvinyl alcohol) is dissolved and stored. The solution is metered to the applicator as needed to replenish what has been taken up by the warp sheet. The chemical nature of the size will be discussed in a later section along with the conditions needed to effectively remove the size. Figure 1. Schematic of a Slasher
IL FABRIC PREPARATION EQUIPMENT A. Batch machines In batch processing, machines are used where the entire load of fabric is immersed in the total amount of liquid needed for that process. These machines are primarily used to dye fabric, however, in many cases they are also used to prepare fabric prior to the dyeing cycle. The section that follows describes some of the more popular machines 1. Becks a beck is the simplest type of wet processing batch equipment. It is a large vat thich holds the entire lot of fabric the fabric is fed into the machine in the form of a rope and is made into a continuous loop by sewing the two ends together. The length of the loop is equal to a piece length, usually 100 to 200 yards. The fabric is agitated by the action of a lifter wheel which gently moves the fabric through the liquor by lifting and dropping the rope in and out of the liquor. Lot size is determined by the number of loop strands that can be accommodated by the machine and is a function of the front width of the machine. Commercial machine are available ranging from one strand to 16 strands. A schematic of a beck is shown in figure 2 Figure 2. Schematic of an Atmospheric beck guide roller fabric
II. FABRIC PREPARATION EQUIPMENT A. Batch Machines In batch processing, machines are used where the entire load of fabric is immersed in the total amount of liquid needed for that process. These machines are primarily used to dye fabric, however, in many cases they are also used to prepare fabric prior to the dyeing cycle. The section that follows describes some of the more popular machines. 1. Becks A beck is the simplest type of wet processing batch equipment. It is a large vat which holds the entire lot of fabric. The fabric is fed into the machine in the form of a rope and is made into a continuous loop by sewing the two ends together. The length of the loop is equal to a piece length, usually 100 to 200 yards. The fabric is agitated by the action of a lifter wheel which gently moves the fabric through the liquor by lifting and dropping the rope in and out of the liquor. Lot size is determined by the number of loop strands that can be accommodated by the machine and is a function of the front width of the machine. Commercial machine are available ranging from one strand to 16 strands. A schematic of a beck is shown in figure 2. Figure 2. Schematic of an Atmospheric Beck
2. Jet machines Jet machines are similar to becks in that a continuous loop of fabric circulates through the machine. They differ however in that a stream of liquor is forced through a venturi tube. This provides the force to propel the fabric through the machine. Temperatures in Jet machines that operate at atmospheric pressure cannot exceed the boiling point of water; however, higher temperatures can be obtained in those that are operated under pressure. An advantage of the jet machines is that lower liquor ratios can be used. In a beck, the liquid is stationary and the fabric moves through it. In a jet however, both the liquid and the fabric move in relation to each other. This increases the rate of interchange between the liquid and fabric and speeds up the process. The distinguishing features of jet machines are the venturi tubes which create the force to circulate fabric, and circulating pumps which cycle the bath through the venturi tubes. Figures 3 shows schematic diagrams of pressure and atmospheric jets Figure 3. Schematics of Jet Machines Atmospheric Jet Pressure jet Throttle valve Leading part Choth storace Add aye pump Schematic view of jet dyeing machine. (Courtesy of Gaston Cu
2. Jet Machines Jet machines are similar to becks in that a continuous loop of fabric circulates through the machine. They differ however in that a stream of liquor is forced through a venturi tube. This provides the force to propel the fabric through the machine. Temperatures in Jet machines that operate at atmospheric pressure cannot exceed the boiling point of water; however, higher temperatures can be obtained in those that are operated under pressure. An advantage of the jet machines is that lower liquor ratios can be used. In a beck, the liquid is stationary and the fabric moves through it. In a jet however, both the liquid and the fabric move in relation to each other. This increases the rate of interchange between the liquid and fabric and speeds up the process. The distinguishing features of jet machines are the venturi tubes which create the force to circulate fabric, and circulating pumps which cycle the bath through the venturi tubes. Figures 3 shows schematic diagrams of pressure and atmospheric jets. Figure 3. Schematics of Jet Machines Atmospheric Jet Pressure Jet 5
3. Jig A Jig or Jigger is a batch machine which handles fabric in open width. It is a simple machine consisting of let-off and take-up rolls, a trough containing the processing liquor and guide rolls which allow the fabric to pass from the let-off to the take-up roll. After all the fabric transfers, the driving mechanism is reversed and the fabric makes a second pass through the liquor by returning to the original let-off roll The cycle can be repeated as many times as it takes to achieve the desired effect Figure 4 shows a schematic of a jig Figure 4. Schematic of a Jig let-off roll takeup roll solution B. Continuous Preparation. Ranges Continuous ranges are used whenever large volumes of a relative few sty les of fabrics are being processed. The fabric moves continuously(at relative high rates of speed) through stages and compartments which provide the chemicals, time temperature and rinsing needed for cleaning the fabric. Many fabrics go through a three section range where each section is dedicated to desize. to scour and to bleach Some fabrics however, may only require one or two steps to complete the preparation process. For example knit goods are not sized so desizing is not necessary Synthetic yarns may not need to be bleached. Some fabrics may go through one section where desizing, scouring and bleaching is accomplished in one step. The pros and cons of each of these set-ups become fabric specific and the appropriate procedure is determined by trial and error
3. Jig A Jig or Jigger is a batch machine which handles fabric in open width. It is a simple machine consisting of let-off and take-up rolls, a trough containing the processing liquor and guide rolls which allow the fabric to pass from the let-off to the take-up roll. After all the fabric transfers, the driving mechanism is reversed and the fabric makes a second pass through the liquor by returning to the original let-off roll. The cycle can be repeated as many times as it takes to achieve the desired effect. Figure 4 shows a schematic of a jig. Figure 4. Schematic of a Jig B. Continuous Preparation. Ranges Continuous ranges are used whenever large volumes of a relative few styles of fabrics are being processed. The fabric moves continuously (at relative high rates of speed) through stages and compartments which provide the chemicals, time, temperature and rinsing needed for cleaning the fabric. Many fabrics go through a three section range where each section is dedicated to desize, to scour and to bleach. Some fabrics however, may only require one or two steps to complete the preparation process. For example knit goods are not sized so desizing is not necessary. Synthetic yarns may not need to be bleached. Some fabrics may go through one section where desizing, scouring and bleaching is accomplished in one step. The pros and cons of each of these set-ups become fabric specific and the appropriate procedure is determined by trial and error. 6