Indian Journal of Fibre & Textile Research
`Vol. 19, September 1994, pp. 189-194
`
`The development of 3D shaped knitted fabrics for technical purposes on a
`flat knitting machine
`
`H Hong, A A Filho, R Fangueiro & M D de Araujo
`Depanment of Textile Engineering, Minho University, 4800 Guimaraes, Ponugal
`
`The use of a new electronic flat knitting machine (Shima Seiki SES 122FF) for producing three(cid:173)
`dimensional shaped fabrics for technical purposes is described. The three methods which can be ap(cid:173)
`plied to knit to shape, i.e. using different structural combinations, using different loop lengths, and
`altering the number of knitting needles and knitted courses, are discussed. Further, the different knit(cid:173)
`ted elements ( tubular forms, spherical forms, box forms and car seat covers) developed on the SES
`122FF machine are described in detail.
`
`Keywords: Flat knitting machine, Knitted fabrics, Loop structure, Technical textiles,
`Three-dimensional shaped knitted fabrics
`
`1 Introduction
`Technical textiles have been applied in different
`fields such as protection clothing, transportation
`related textiles ( cars, planes and space crafts),
`geotextiles, building construction related text~les,
`packaging materials, military
`related
`textiles,
`medical textiles, sports related textiles, etc.
`For many years, technical textiles were consi(cid:173)
`dered as very high-modulus fabrics, exhibiting ex(cid:173)
`tremely high structural stability and made of high(cid:173)
`tenacity, low-elongation yams. With the further
`development of new end uses, it has been realized
`that each technical product requires a different
`technical textile, with a different set of character(cid:173)
`istics and some of these characteristics might be
`found in "loop based" structures.
`Flat knitting machines are traditionally used for
`producing pullovers and other outerwear gar(cid:173)
`ments. One of the main advantages is the facility
`of these machines to knit fabric pieces to a parti(cid:173)
`cular shape or form. The combination of the indi(cid:173)
`vidual needle selection technique and the use of
`the presser foot or holding down sinkers on the
`new generation of computer-controlled flat knitt(cid:173)
`ing machines increase this ability a great deal. By
`using the new flat knitting machines,it is possible
`not only to knit the new loop structures which are
`not possible on the conventional flat knitting ma(cid:173)
`chines, but also knit fully fashioned garments.
`This is very important to reduce the waste of ex(cid:173)
`pensive materials during cutting as well as in eli(cid:173)
`minating the additional making up operation. If
`
`the ability of knitting to shape of the flat knitting
`machines is used to produce 3D knitted technical
`textiles, it is not difficult to foresee their new end
`uses in the future.
`This work describes the use of the new flat
`knitting machines to knit 3D structures by using
`different
`techniques
`in
`the Shima Seiki SES
`122FF flat knitting machine. It is thought that
`these knitted shapes can be interesting as techni(cid:173)
`cal textiles and may also stimulate the imagination
`towards new applications.
`
`2 Short Description of the Shima Seiki SES
`122FF Flat Knitting Machine
`The SES 122FF machine is one of the new
`generation of computer-controlled flat knitting
`machines. The main features of this machine are
`as follows:
`-the double cam system r
`knitting and trans(cid:173)
`fer facilities at each cam system in which 31
`different stitch lengths can be set;
`-the combination of holding down sinkers and
`presser foot is the machine facility which en(cid:173)
`ables the knitting of fancy stitch effects and
`knit to shape;
`-the belt drive system gives smooth and high(cid:173)
`speed carriage travel which enables the yam
`to be picked-up or not, as required;
`-the set-up device and finely tuned take-down
`system for added take-down requirements;
`aRd
`-the machine controller which is programmed
`for knitting and shaping from a micro compu-
`
`Skechers EX1039-p.1
`Skechers v Nike
`
`

`

`190
`
`INDIAN J. FIBRE TEXT. RES., SEJ7J'EMBER 1994
`
`ter with floppy disc drive, and has a screen
`resolution of 1024 x 1024 pixels.
`The major advantage of this machine is that it
`has overcome former restrictions in knitting de(cid:173)
`sign and shaping, thus enabling the development
`of 3D knitted structures for technical purposes.
`
`3 Techniques for Knitting to Shape
`On flat knitting machines,· it is possible to use
`the following techniques for knitting to shape:
`
`-using different structural combinations;
`-using different loop lengths; and
`-altering the number of operating needles
`-from course to course.
`
`3.1 Using Different Structural Combinations
`It is not diffieult to reach the objective of knitt(cid:173)
`ing a 3D shape by using different loop structural
`combinations when knitting a technical course,
`because the different loop structures have differ(cid:173)
`ent geometrical shapes under conditions in which
`the yarn counts and the loop lengths arc the
`same. The new flat knitting machine can knit
`most weft-knitted structures, and so the combin(cid:173)
`ations of different structures for knitting to shape
`arc easily realised. However, it is necessary to
`bear in mind that this technique is not suitable in
`cases in which a technical product requires homo(cid:173)
`geneous properties in all parts, as the parts knit(cid:173)
`ted with different structures present different pro(cid:173)
`perties.
`
`3.2 l 1sing Different Loop Lengths
`Fabrics knitted with the same knitted structure
`but using different loop lengths have different
`geometrical dimensions. If one fabric is knitted
`with different loop lengths in different courses,
`shaping can take place. One simple example is
`circular jersey fabric knitting in separate needle
`beds. It is not difficult to change the circum(cid:173)
`ference by changing the loop length from course
`to course. On the new flat knitting machines, the
`stitch c~ms can he automatically adjusted during
`knitting and so changing of loop length is very
`easy. It offers the facility of knitting to shape by
`changing loop lengths.
`
`3.3 Altering the Number of Operating Needles rrom Course
`to Course
`This technique is widely used in flat knitting for
`the production of fully fashioned panels. Two op(cid:173)
`erations can be performed: increasing and dec(cid:173)
`reasing the number of operating needles. On the
`new flat knitting machines, these two operations
`
`are very easily realised due to electronic single
`needle selection.
`It is necessary to note that during the increasing
`(widening) or decreasing (narrowing) operations
`(Fig. 1 }, some needles are rendered inactive for a
`long time while retaining their loops. The tension
`applied to the fabric by the take-down rollers is,
`in, this case, transferred solely to these needles,
`distorting the loops and subsequently breaking the
`yarn. For this reason, the use of the presser foot
`is necessary.
`The presser foot (Fig. 2) is a metal wire which
`is securely fixed to the carriage by the presser
`foot mechanism, and moves across the machine
`with the carriage. During knitting,' the presser foot
`precedes the needles which are rising. The wire
`
`B 9 10
`8 9 10
`8 9 10
`
`Take Down Tension
`Tl>T2>Tl>T4
`Fig.I - Fashioning operation:
`decreasing and increasing the
`number of knitting needles in one
`needle bed
`
`Fig.2 - PF - Presser Foot
`FB - Front needle bed
`BB - Back needle bed
`
`Skechers EX1039-p.2
`Skechers v Nike
`
`

`

`HONG et al: 3D SHAPED KNITfED FABRICS
`
`191
`
`slides just underneath the crossing or intersecting
`opposing needles on both needle beds and
`presses against the stitch laying between the. two
`needle beds. As a result of this the take-down
`tension given to the fabric by the take-down roll(cid:173)
`ers becoines unnecessary.
`tension allows
`The absence of
`take-down
`stitches to be held on idle needles which are tem(cid:173)
`porarily inactive, while neighbouring needles con(cid:173)
`tinue to knit normally. This is just one of the re(cid:173)
`quirements of knitting to shape.
`When this method is used to knit three-dimen(cid:173)
`sional structures, the main technique consists in
`transferring the three-dimensional form to two-di(cid:173)
`mensional patterns, because the fashioning opera(cid:173)
`tion (increasing or decreasing the number of knitt(cid:173)
`ing needles) is only determined according to two(cid:173)
`dimensional patterns. The
`three-dimensional
`shaped knitted fabrics presented in this work are
`all knitted by using this technique.
`
`4 Three-Dimensional Shaped Knitted Faltrics
`Developed on the Shima Seiki SES 122FF
`Machine
`4.1 Tubular Forms
`The tubular forms are kll\,tted on both needle
`beds. When the number of operating needles in
`one bed is changed, a "knee" form is developed.
`The different tubular forms· knitted on the SES
`122FF flat knitting machine are shown in Figs
`3-6. These types of structures can be used as tube
`connections for reinforcing purposes to enhance
`flexibility and strength, while preventing fatigue
`and cracking.
`
`The tubular form in Fig. 3 is one version at
`right angle with the rectangular cross-section. The
`knitting operation for this, which is very similar to
`knitting a hose, is shown in Fig. 3(2). The ab and
`cd lines represent the operation of decreasing the
`number of operating needles, while ba' and de'
`represent the operation of increasing the number
`of operating needles. During these operations, the
`needles which are temporarily inactive hold the
`stitch on them so that the decreasing and increas(cid:173)
`ing lines become one connecting line after knitt(cid:173)
`ing. When the decreasing and increasing lines are
`at a 45° angle with the wales, a right angle is
`formed.
`Fig. 4 shows another right angle tubular ·form
`but in this case with a circular cross-section. The
`radius R of the "knee" can be chosen according
`to the application requirements. For knitting this
`form, first of all it is necessary to determine the
`decreasing and
`increasing knitting curvature
`[Fig. 4 (2)], i.e. establishing the relation between
`the number of operating needles and the number
`of consecutive knitted course~ produced w:th
`those needles ( C). This relation can be deter(cid:173)
`mined by the following equation:
`
`C= _N_[ 1_-_c_o_s (_n_nl._'N_)]
`4aM
`
`... (1)
`
`where C is the number of knitted courses; N, the
`total number of active needles in one needle bed
`( depends on the required diameter of tube); n, the
`number of operating needles during an increasing
`(widening) or decreasing (narrowing) operation;
`
`d
`
`h.------+------~h
`
`a'
`
`b
`
`I d
`
`I
`
`[_.)--------·-······
`g
`.-·e
`
`a +a•
`
`I
`
`FB
`
`g
`
`C
`
`C
`
`BB
`
`g
`
`(]) 3D Theoretical Form
`
`(2) 2D Pattern
`Fig.J - Tubular form with rectangular cross-section
`( t -T1'ke-down direction )
`FB = front needle bed
`BB = back needle bed
`
`(3) Knitted Fabric
`
`Skechers EX1039-p.3
`Skechers v Nike
`
`

`

`192
`
`INDIAN J. FIBRE TEXT. RES., SEPTEMBER 1994
`
`m
`
`m
`
`.:::::===~m
`
`4
`repetts
`
`, r ! D
`
`I I
`
`FB
`
`BB
`
`1rD
`
`(1) 3D Theoretical Form
`
`(2) 2D Pattern
`Fig.4 -Tubular form with circular cross-section
`
`(3) Knitted Fabric
`
`r-----+-----:19,------'hi'---~'g
`
`h
`
`II
`
`T
`
`d
`
`b
`1•
`i
`i
`i
`i
`i
`i
`i
`i
`I
`i
`FB
`BB
`c....._.....,.,...__--:----.!..!:!.----,-..!!E!..._.J
`I
`C
`
`(2) 2D Pattern
`(1) 3D Theoretical Form
`(3) Knitted Fabric
`.
`.
`F1g.5 - Tubular form : one mam tube connected to two smaller tubes
`
`M, the number of increasing/decreasing repeats;
`and a, the loop shape factor (Poisson ratio).
`The tubular forms shown in Figs 5 and 6 have
`the required shape to connect one larger tube to
`two smaller ones in a "Y" shape. The angle a bet(cid:173)
`ween the two smaller tubes can be changed ac(cid:173)
`cording to the requirements. During knitting, the
`two smaller tubes are separately knitted with two
`cam systems.
`
`4.2 Spherical Forms
`It is not difficult to knit a spherical form in the
`SES 122FF flat knitting machine. To knit a sphe(cid:173)
`rical form with a radius R, it is necessary to start
`by transferring the three-dimensional concept to a
`
`two-dimensional pattern, as shown in Fig. 7, and
`then establishing the relation between the number
`of operating needles and the number of knitted
`courses as follows:
`N Ji - sin2(irn/ N)
`C= - - - - - - -
`2aM
`
`... (2)
`
`For knitting this type of article, a double knitted
`structure is normally used. In this case, it is possi(cid:173)
`ble to introduce a weft inlay thread to enhance
`the dimensional stability of the fabric.
`
`4.3 Box Forms
`The box form (Fig. 8) is another example of
`
`Skechers EX1039-p.4
`Skechers v Nike
`
`

`

`HONG et al: 3D SHAPED KNITI"ED FABRICS
`
`193
`
`---+----'t'l"-----+----,•d
`
`b
`
`d
`
`h ~-~· e ~-~. f
`
`BB
`
`e
`
`FB
`
`BB
`
`e
`
`(1) 3D Theoretical Form
`(3) Knitted Fabric
`(2) 2D Pattern
`Fig.6 - Tubular form : one main tube connected with two smaller tubes
`
`T
`
`(1) 3D Theoretical Form
`
`FB + BB
`(2) 2D Pattern
`Fig. 7 - Spherical form
`
`(3) Knitted Fabric
`
`fabric on
`three-dimensional knitted
`the SES
`122FF machine. As shown in Fig. 8(2), the in(cid:173)
`creasing and decreasing lines are linear at 45°
`with the direction of knitting (wales direction).
`This type of form is also knitted with a double
`knitted slructure introducing a weft inlay thread.
`
`4.4 Car Seat Covers
`Knitted fabrics have been widely used in the
`automotive industry. At present, the most used
`knitted fabrics are circular weft knitted and warp
`knitted fabrics. In the last few years, however, the
`flat knitted fabrics have also been used for this
`purpose. The advantages of using the flat knitting
`machine to produce car seat covers are as fol(cid:173)
`lows:
`• knitting directly the 3D shapes can overcome
`fabric waste and diminish the labour cost in-
`
`herent to the use of two-dimensional fabrics
`which have to fit the variable geometry of a
`three-dimensional seat bum. Automation, des(cid:173)
`pite several attempts, has not been as success(cid:173)
`fully applied to this sector as it has to others,
`using two-dimensional fabrics.
`the capability of electronic flat machines can
`be used to produce fabrics in greater structural
`and pattern variety than in any other type of
`knitting machine.
`
`•
`
`There are different types of seat covers. In or(cid:173)
`der to knit a complete cover, the knitting process
`might be extremely complex. The conventional
`electronic flat knitting machines have difficulties
`in producing this type of fabric. For this reason, a
`simple form of car seat cover (head rest) deve(cid:173)
`loped on the SES 122FF is presented (Fig. 9).
`
`Skechers EX1039-p.5
`Skechers v Nike
`
`

`

`194
`
`INDIAN J. FIBRE TEXT. RES .. SEPTEMBER 1994
`
`e..----'-------------'m~~g
`h;
`
`;1
`
`g
`b
`
`FB -t BB
`
`j
`
`b
`
`(2) 20 Pattern
`Fi~. 8 - Box form
`
`(]) Kniltcd Fabric
`
`(I) JD Theoretical Form
`
`:·-- ... ,,,:;' .. ,,.,···
`..
`
`e
`a
`
`T
`
`a
`
`h
`
`g
`
`e
`
`d
`
`C
`
`b
`
`!I
`
`(I) JD Theoretical Form
`
`(2) 20 Pallcrn
`Fig. 9 - Car scat cover (head rest)
`
`(]) Knitted Fabric
`
`FB t BB
`
`5 Conclusions
`The three-dimensional shaped knitted fabrics
`presented in this paper arc only examples which
`have been developed on the SES 12 2FF flat
`knitting machine. By exploiting the capacity of
`this machine, it is possible to knit more types of
`three-dimensional knitted fabrics. The properties
`of fabrics knitted on the flat knitting machine arc
`different from those of other types of textiles.
`Woven and multiaxial fabrics are stiffer than con(cid:173)
`ventional weft knitted fabrics and so more suit(cid:173)
`able when high tenacity/low strain is required. If
`weft inlay threads are introduced, the stiffness of
`these fabrics can be increased at least in one di(cid:173)
`rection.
`
`If it is required to produce technical textiles (or
`parts) on flat knitting machines, the end-products
`should be able to exploit at least one specific ad(cid:173)
`vantage of the machine. For the production of
`large pieces of fabrics for technical textiles, weav(cid:173)
`ing machine, warp knitting machines or even the
`circular knitting machines may be more suitable.
`The flat knitting machine is more suitable for
`small shaped pieces and it is in this area that it
`will find its uses in the future.
`
`References
`I Thomas Stoll, Knining Imemationa/, 98 ( I 169; ( I 991) 96.
`2 Raz ·S, Flat knitting: The new generation (Meisenbach
`Bamberg, Germany'), 1991, 440.
`
`Skechers EX1039-p.6
`Skechers v Nike
`
`