ADJUSTING STENTER MACHINE SET UP FOR A KNIT FABRIC
This Paper is the result of hard work of Mr. John Hardiker
| A | General | ||||||
| 1 | Before adjusting the machine set up to change the fabric performance; check if the machine is set up as per the machine specifications and there is nothing obvious on the machine which could be having a negative affect. | ||||||
| 2 | N.B The width cannot be made narrower than the specifications (customer cutting efficiency could be drastically reduced, resulting in a claim). Generally the width is fixed (could be made wider is the gsm and shrinkages are within tolerance). | ||||||
| 3 | When adjusting a machine to achieve the fabric width, gsm and skewness, consideration has to be given to length/width shrinkage and spirality. | ||||||
| 4 | If the fabric length and width shrinkages are known before processing, the expected shrinkages after processing can be calculated. This information can be used to adjust the gsm and width (if not specified) to their optimum; eliminate batches being rejected for shrinkage after processing. | ||||||
| B | Formula for calculating shrinkages | ||||||
| 1 | before processing | ||||||
| Width cm | width % shrinkage | target width after | affect on width shrinkage | customer allowed max % | calculated shrinkage | ||
| 148 | 6 | 151.02 | 2.00 | 8 | 8.00 | ||
| 2 | before processing | ||||||
| length % shrinkage | customer allowed max % | min required % reduction in length | |||||
| 11 | 8 | 3 | |||||
| C | Check & adjustment for length shrinkage | |||||||||||||
| 1 | Measure and mark 100 cm before the fabric enters the machines, measure the marked fabric exiting the machine. For every 1cm reduced, equals a reduction of 1% in shrinkage. OR use a measure specifically designed for checking fabric shrinkage after processing. | |||||||||||||
| 2 | Subtract the reduction in % length shrinkage from the fabric shrinkage (before processing) to give the calculated fabric shrinkage after processing E.g. 12% before processing; length reduced by 5%; calculated fabric shrinkage = 7%. Customer specifies a maximum of 8% length shrinkage. | |||||||||||||
| 3 | If the fabric length shrinkage is not known before processing; this measure will only indicate the amount of length shrinkage during processing, NOT the actual shrinkage of the fabric. | |||||||||||||
| 4 | To add ‘safety to the length shrinkage (fabric length increased on “rolling”) the calculate shrinkage after processing could be set at 1% to 2% below the customer targets. E.g. Customer specifies 8% shrinkage, calculated shrinkage = 7%. | |||||||||||||
| 5 | Stenter – To reduce or increases the length shrinkage by 1%, increase or reduce the overfeed by 5%. Re-check the % length shrinkage. | |||||||||||||
| D | Check & adjustment for width & width shrinkage | |||||||||||||
| 1 | After processing measure the width of the fabric (could be overall width, useable width), compare to the target width. | |||||||||||||
| 2 | If the width is narrow/wide, increase/decrease the width of the chain by same number of cm. E.g. if fabric 175cm and target is 178cm, increase the chain width by 3cm. | |||||||||||||
| 3 | For calculating the width shrinkage (if shrinkage known before processing) Measure the width (cm) before and after processing, calculate the shrinkage. | |||||||||||||
| example – calculate shrinkage | ||||||||||||||
| width before 170cm with 5% width shrinkage | ||||||||||||||
| width after 175 cm | ||||||||||||||
| 175 – 170 = 5cm | ||||||||||||||
| 5/175 x 100 = 2.86% | ||||||||||||||
| Total calculated shrinkage = 7.86% (5 + 2.86) | ||||||||||||||
| E | Check & adjustment of grams per square meter (g.s.m) | |||||||||||||
| 1 | Before checking the gsm, the width should be within specification | |||||||||||||
| 2 | Take a sample and cut the sample with a gsm disc cutter. Weigh the cut sample; compare to the target, minimum and maximum allowed gsm. N.B The target gsm could be conditioned or UN-conditioned. | |||||||||||||
| 3 | If the gsm is too high; the gsm could be reduced by reducing the overfeed. N.B Reducing the overfeed, increases the length shrinkage. Calculate the affect on length shrinkage before adjusting. | |||||||||||||
| 4 | If the gsm is too low, the gsm could be increased by increasing the overfeed (refer example below) by 10%, slowing down the compactor by 20%. | |||||||||||||
| 4.1 | Stenter – To reduce or increase the gsm, increase or reduce the overfeed by 8%. Re-check the gsm. | |||||||||||||
| 5 | Re-check the gsm after adjusting the overfeed. | |||||||||||||
| F | Check & adjustment of fabric skewness | |||||||||||||
| 1 | The skew is measured by the deviation of the course line across the width against the width. | |||||||||||||
| 2 | Measure height of course traversed and the width of the fabric | |||||||||||||
| 3 | % skewness = height/(fabric width) x 100% | |||||||||||||
| course | height | |||||||||||||
| width | ||||||||||||||
| 4 | Compare the result against the maximum allowed skewness. | |||||||||||||
| 5 | For every 1% above the maximum allowed skewness, increase the angle of the courses straightner by the same %. Re-check % skewness. | |||||||||||||
| G | Courses and wales | |||||||||||||
| 1 | Courses and wales can also be used to check if a fabric is within tolerance | |||||||||||||
| H | Adjust of the machine does NOT achieve the width, gsm and shrinkages | |||||||||||||
| Usually means the knitting or the dyehouse has affected the fabric in a negative way | ||||||||||||||
| 1 | Stop processing the fabric; INFORM the finishing manager. | |||||||||||||