Some common problems and solutions in sanding finishing
Wrinkle marks
Improperly processed sanding products can lead to regular or irregular wrinkles on the fabric’s surface. These marks can harm the product’s appearance and sanding effect. The main causes of wrinkle marks and the measures taken are:
(1) The fabric stays folded or wrinkled for a long time. Its weight presses the surface, causing uneven warp and weft wrinkles. Change the fabric storage method to large, stacked rolls. This can help prevent wrinkle marks.
(2)During pre-sanding, if the fabric gets too hot, it can cause permanent wrinkles. This mainly affects chemical fiber and blended fabrics. This wrinkle mark is difficult to remove and often requires one-time shaping. For cotton or lightly wrinkled fabrics, a spray wet and dry device can be configured before the sanding machine to solve the problem.
(3) Wrinkle stripes can happen during fabric pre-treatment and dyeing. They may result from issues with the process, equipment, or operation. Improper seam ends can also be a cause. Thus, to overcome the wrinkle defect of sanded products, each process should be strictly controlled.
During sanding, the fabric’s weft wrinkles usually go away. But, warp wrinkles stay, leaving behind uneven fluff marks on the surface.
White core
The white core on the surface of sanded fabric is mainly due to the presence of cotton knots on the grey fabric. These cotton knots can be covered after dyeing, but once sanded, the cotton knots are removed and white spots are left. In severe cases, small holes may even be caused, affecting product quality. For the gray fabric, cut or move the cotton knots to the back. You can also sand before dyeing and dye after sanding to fix the white core defect.
Stripe
Causes
(1)The sanding roller’s surface isn’t flat, or the sandpaper isn’t applied correctly. This causes uneven abrasive particles and stripes.
(2) The sanding roller was first used to sand narrow fabrics and then to sand wide fabrics. Due to the uneven wear of the sanding roller surface, it is very easy to cause the grinding edge to be uneven and produce stripes on both sides.
Solution
(1)The corundum sheet must press flat against the guide roller. The guide needs to be straight. The surface should stay flat and clean, free of dirt.
(2) The corundum sheet should be wrapped around the roller in an oblique or striped manner, and both ends should be rolled firmly.
(3) Check the equipment regularly to ensure that the guide roller is flat and the sanding sheet is in good bonding with the guide roller.
Color difference
After the fabric is sanded, the color will change. It will usually get lighter. This causes a color difference between the sanded and unsanded fabrics. This is mainly due to the different reflection of light on the surface of the sanded fabric. Therefore, when dyeing, the color difference after sanding should be fully considered, and a slight margin should be allowed for the dyeing depth. In addition, the dyeing rate is the key, and the requirements for dyeing are higher than those for general dyed fabrics.
Experiments show that different dyes affect fabric color changes after sanding. This happens because each dye has unique molecular structures, dyeing properties, and affinities. Light-colored fabrics dyed with vat and reactive dyes show less color change before and after sanding. This makes them good for the dyeing-first-and-sanding process. In contrast, medium and dark-colored fabrics have a larger color difference before and after sanding. These are better suited for the sanding-first-and-dyeing process, which achieves fuller and more uniform dyeing.
Folds
Causes
Semi-finished product wrinkles, mercerizing clips, crescent folds; folds caused by long stacking time; live folds caused by non-parallel guide rollers and folds caused by edge absorbers, and live folds caused by uneven drying cylinders.
Solutions
You can repair the crescent and clip-off folds of semi-finished products, along with the folds of the drying cylinder edge absorbers, on the tentering machine.
Poor sanding effect
Causes
The semi-finished product is hard. The fabric doesn’t penetrate well. Tension is low, and the speed is high. The sandpaper has been used for a long time. The DC motor runs at an unstable speed, and the fabric is damp.
Solutions
Notify the pre-treatment to repair or apply softener, tighten the chain shaft tension, reduce speed, increase pressure, replace new sandpaper and fully dry the fabric.
Grinding willow
Causes
The sandpaper seams overlap, the sandpaper rotates in the same direction, the thread ends are wrapped around the grinding roller, and the sandpaper joints are printed or damaged.
Solutions
Re-tighten the sandpaper. Change its rotation direction. Adjust it left and right to clean the thread ends on the grinding roller.
Left, middle and right hair difference
Causes
The left and right cloth pressing rollers are uneven. The sandpaper has been used for a long time. Also, the wear on the sand grains is different between the edge and the middle.
Solutions
Adjust the balance roller so the left and right sides match. Also, replace the sandpaper to fix the middle difference when switching from narrow to wide.
Poor strength
Causes
The fabric yarn is thin, the sandpaper mesh is low, the strength is high, the pressure is high, and the speed is slow.
Solution
Replace high-grit sandpaper, relax tension, reduce pressure, and increase speed.
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