Mechanical cleaning refers to the removal of loosely bound fibers by mechanical means, such as brushing or sueding or grinding. Mechanical cleaning process is viable alternatives to traditional solvent-based cleaning operations. They reduce waste production and eliminate potential safety problems with the handling and usage of toxic, ozone-depleting, and often-flammable solvents. Mechanical cleaning operations are such as sanding, grinding, polishing, brushing / sueding, cropping and shearing. Mechanical cleaning avoids the use of toxic or dangerous chemicals by substituting mechanical work for chemical work. The mechanical cleaning of a textile involves the use of tools such as scalpels, dental picks, brushes, sponges, ultrasonic tools, and low suction vacuum cleaners.
The pre-cleaning of grey fabrics may be carried out in a separate unit just before cropping and shearing operations. The efficiency of pre-cleaning is the foundation of good cropping and shearing. The pre-cleaning operation is achieved with:
- Thorough grinding of the cloth surface by emery covered rollers.
- Scraping with suitable designed and located scraping blades.
- Efficient brushing on both sides of the cloth.
With the progress of grinding and scraping action, the cloth surface gets covered with thread ends, dust, fluff, dirt etc., thus the pre-cleaning unit should have a good dust exhausting system. Mechanical cleaning processes offer a wide range of cleaning and surface preparation options to solvent cleaning.
The purpose of brushing / sueding is to remove the short and loose fibers from the surface of the cloth. It also removes husk particles clinging to the cloth. Brushing is mainly done to fabrics of staple fiber content, as filament yams usually do not have loose fiber ends. Cylinders covered with fine bristles rotate over the fabric, pick up loose fibers, and pull them away by either gravity or vacuum. The raised fiber ends are cut off during shearing operation. Brushing before cropping minimizes pilling.
Brushing is also used as a mechanical finishing process in which a fabric is abraded on one or both sides to raise or create a fibrous surface. This fibrous surface improves the fabric appearance, gives the fabric a softer, fuller hand, and can mask fabric construction and subdue coloration. These improved aesthetics can increase the value of a fabric in the marketplace.
In the textile industry, the process of brushing / sueding is also known as ‘sanding’ or ‘emerizing’. Normally, this process is done only as per buyer’s requirement.
Cropping and shearing:
After inspection and mending, small projected yarns may remain on the surface of the fabric, which obstruct adsorption of dyes on the fabric surface
during dyeing and printing processes. They may also be entangled with machine parts causing damage of the materials. These projected yarns are removed by a process called shearing and cropping, during which the projected fibers or yarns are cut from the fabric surface.
In shearing operation, dry or occasionally slightly dampened fabric is drawn between a shearing table and the shearing device, which consists of a shearing cylinder and a ledger blade. The action is similar to that of a lawn mower. The shearing machine may have two or four cutting heads.
Shearing is an operation consists of cutting the loose strands of fibers from either surface of a fabric with a sharp edged razor or scissors. By manipulating the shearing it is also possible to cut designs into pile fabrics. Good cropping is perhaps, the simplest way of reducing the tendency of blended fabrics to ‘pill’. In the case of cotton fabrics, in particular, care should be taken to see that the shearing blades do not scratch the surface of the fabric, which otherwise can cause dyeing defects during subsequent dyeing.
The term ‘cutting point’ denotes the contact line between the spiral shearing cylinder and the ledger blade, over which the fabric has to pass during cropping and shearing operation. Each cutter is provided with adjustable ledger blade. Before leaving the machine, the cloth is brushed by a spiral revolving brush. The machines are of totally enclosed construction with exhaust channels. Although there have been no major changes in the latest cropping and shearing machines, a modem fully automatic shearing range has the following features:
- Fabric feeding device (electronically controlled) ensuring the entry of crease free fabric.
- A soft bed under the cutters so that the blades which cut the fibers close to the surface do not damage the fibers in the yam.
- Seam joint sensors (electronic) which lift the shearing rolls away from the fabric surface when a seam passes.
- Magnetic metal detectors sense the iron particles embedded with the cloth and activate the limiting switch, so that the machine stops, the concerned particles are removed and the machine restarted.
- Hydraulic speed gear system has been replaced by suitable DC drives. Modem shearing machine can operate up to a speed of 100m/min. The units have been made more modular, in order to facilitate quick installation.
Shearing machines fitted with serrated blades have been found satisfactory for the cutting of polyester materials. Polyester staple fiber fabrics are cropped and singed mainly to control the pilling tendency. For polyester/wool blended fiber fabrics a good cropping is essential if the fabric is not to be milled. If it is desired to finish simulating wool, loose polyester should first be removed by brushing, cropping and singeing and then the fabric is soap-milled to produce a wool cover, which can be cropped to give the required appearance and handle.
- Chemical Technology in the Pre-Treatment Processes of Textiles by S.R. Karmakar
- Handbook of Value Addition Processes for Fabrics By B. Purushothama
- Handbook of Textile and Industrial Dyeing, Volume 1: Principles, Processes and Types of Dyes Edited by M. Clark
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Founder & Editor of Textile Learner. He is a Textile Consultant, Blogger & Entrepreneur. He is working as a textile consultant in several local and international companies. He is also a contributor of Wikipedia.