Making-up cut and sew knitwear
Knitted fabrics are inherently soft and stretchy - properties that make them comfortable to wear, yet difficult to make-up. To help manufacturers overcome these problems, most equipment suppliers have developed machinery specifically for cut and sew knitwear. Here Niki Tait reviews of some of this technology.
The looped yarn constructions of knitted fabrics make them inherently soft, flexible and elastic - which is why they are so comfortable to wear and so useful for casual, sports and under garments.
However, this elasticity and instability also causes problems in production. Woven apparel is usually constructed using lockstitch seams, but because these are the least elastic of all seam types their use in knitwear is restricted to areas where elasticity needs to be constrained - such as the neck opening of a polo shirt. So to make up knitted garments, the more elastic chainstitch, coverstitch, and overlock stitches are the norm.
Cutting also has its own differences, since cut and sew knitwear is normally made from circular knit fabric produced in tubular form.
Unlike knit to shape, or fully fashioned knitwear, where individual garment pieces are indeed knitted to shape and then sewn or linked together, cut and sew knitwear is produced from a roll of knitted fabric. This roll has to be laid up and cut in a similar manner to woven fabric.
Nearly all cutting room equipment suppliers cater for cut and sew knitwear. Assyst Bullmer, for example, provides several models ideal for spreading open knit fabrics. Spreading tubular fabric, though, is the speciality of the Bullmer Economic 12 which gives tension free spreading and can be equipped with a variety of stretchers and fabric inspection lighting. A special feature is a cross laying device to spread the crease line down the longitudinal centre of the lay, automating a task that is traditionally carried out by hand, or avoided altogether with a corresponding waste of fabric. Transport to the cutting area by air flotation or conveyor table is normal to avoid unnecessary handling or stretching of the lay.
Automatic cutters such as the Bullmer Procut XL which cuts lays up to 7.5cm deep and 3 metres wide are ideal for knitted fabrics. The Bullmer range has a large presser foot to enable the cutter to leave and then re-enter a tubular lay when cutting pieces lying on the folded edge.
For bulk cutting large orders Bierrebi claims its LTE automated die cutter gives fabric savings of 5-10 per cent, labour saving over 75 per cent and space saving over 75 per cent. Suitable for products such as T-shirts, briefs, vests, sportswear, leisurewear, pyjamas and underwear, the entire cutting process is concentrated in a single, integrated system. Available in various forms, the 4 Strand LTE, for example, enables four layers of fabric to be drawn off and cut simultaneously from four different pieces of fabric.
Stripes are knitted into circular fabrics as a spiral - so after opening this fabric they are slightly angled or 'inclined'. When stentering, the stripes can be left at the angle they are knitted, pulled horizontal to straighten them, or pulled into a reduced inclination. If the stripes are manipulated into position the fabric has a tendency to relax back into its original structure after washing - the result being twisting at the side seam. Quality manufacturers tend to work without manipulating the stripes, a method used commonly by manufacturers for the US market, and increasingly by those serving Europe.
To spread and match knitted fabrics with inclined stripes Veith Systems has developed a special Pin Table, where the needle bars can be turned in an inclined position of up to 12 degrees. Similar to the standard Veith Pin Table this unit can be equipped with various accessories to suit individual manufacturers' demands.
Most striped knitted fabrics can be treated similar to woven fabrics in the cutting room: marker making, spreading and matching the fabric on a pin table and then cutting. It is easier to compensate for fabric inconsistencies when cutting manually, since CNC-cutting demands patterns that are geometrically constant. A cutter with selvage alignment is a great advantage.
Jaquard knitted fabrics are probably the most difficult to match. From experience Veith has found that cutting is best carried out manually, because of the need for in-process correction.
The Pegasus MHG-130 3-needle, cylinder-bed, interlock stitch machine automates and de-skills the circular hemming operation on the bottom of tubular goods such as T-shirts and polos. By attaching optional parts the unit can also sew flat fabric, such as open sleeves. Hem width can be set any where between 15-40mm, minimum circumference equates to 360mm
Due to its linked loop construction, chainstitch tends to unravel at the end of sewing in much the same way as knitted stitches. Pegasus's new pneumatic underbed thread trimmer has been designed to prevent this. A special stitch locking feature trims the end of the looper thread after it has passed through the left-side needle thread loop, effectively knotting the stitch and securing the seaming.
The Juki MF7605A-U06-B64UT13/SC380 universal style 3-needle, 5-thread, flatbed top and bottom coverstitch machine has been developed for flat hemming operations on T-shirts, underwear, sports and leisure wear. With quick change main and differential feeds, pneumatic top and bottom "klipp-it" thread trimmers and pneumatic presser foot lift, the machine comes standard as a hemmer and coverseamer. By adding optional parts, however, it converts to collarette operations.
For attaching elastic or lace, up to 40mm wide, to ladies' panties, briefs and lingerie Juki recommends its MF7407A-E12-D56MD1TC4/SC380 3-needle, 4-thread, flatbed coverstitch machine. The right hand knife gives a quality finish while the metering device can be programmed for up to 50 seams. For bottom coverstitching the top cover thread can be removed
The BAS-750KL is Brother's automatic pocket setter for single-row sewing of pockets to the front body. A needle plate adjustment makes it possible to give knitted products a soft-looking finish.
The Brother MA4-V91A/V92A high speed adjustable top and bottom feed safety stitch sewing machine contains an improved feed mechanism while the presser foot shape gives smooth and gentle feeding reducing any potential damage to the fabric. Its closed type needle bar mechanism and the 'perfect' seal on the feed bar prevent oil leaking. The needle bar and top looper have been given a special coating to improve durability.
Rimoldi's Mizar 93T-66-3LD-04, combines advanced technology with flexibility. This mini cylinder bed machine (160mm diameter) is fitted with top feed and an automatic stitch condensing facility at the start and end of the seam and has been designed to hem knitted garments as well as topstitch elastics. A removable raised work surface also allows open garments to be sewn. The Sirio 62F-16-2MD-01 is a flatbed head developed for binding operations with a decorative seam recommended for children wear, ladies' underwear and knitted pyjamas.
For fully automatic circular hemming of stretched waists on standard type T-shirts, athletic shirts, nightwear and sportswear, Schips AG has developed the HS C9J-F7 two needle cover stitch bottom hemmer. Difficult and curly materials can be sewn on the company's automat HS C9F-F3 which makes the operation almost totally tension free. This machine contains features such as variable needle distances, automatic seam end detection, consistent hemming width and exact oversewing at the seam end via an edge guiding system. The optional left hand knife and waste disposal are useful for garments with side seams.
The Schips HS C9K 2 needle coverstitch machine, on the other hand, has been developed for flat hemming sleeves, breast pockets, front and back parts of T-shirts, polo shirts and vests. High productivity can be achieved through continuous tape feeding and permanent loading of the automat to enable the machine to sew at maximum speed. With its modular format the system can be adapted to different manufacturing requirements. Options include edge guiding instead of edge trimming, laser light lines for loading striped materials, and an upgrade to a combi-automat for hemming and closing sleeves.
In terms of thread, Gütermann launched its Piuma No 140 only last year. This textured microfibre sewing thread in 100 per cent polyester has a soft feel skin and is ideal for underwear, lingerie and swimwear. It can be used for both needle and looper thread with an optimum speed of 5,500rpm on chainstitch, overlock and coverseam type machines.
Niki Tait, C.Text FTI, FCFI heads Apparel Solutions, which provides independent assistance to the apparel industry in the areas of manufacturing methods, industrial engineering, information technology and quick response.
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