Saturday, September 5, 2015

Direct Spun Yarns[1]
Art Resource

Marie-Therese Wisniowski

Preamble
This is the forty-third post in the "Art Resource" series, specifically aimed to construct an appropriate knowledge base in order to develop an artistic voice in ArtCloth.

Other posts in this series are:
Glossary of Terms
Units Used in Dyeing and Printing of Fabrics
Occupational, Health & Safety
A Brief History of Color
The Nature of Color
Psychology of Color
Color Schemes
The Naming of Colors
The Munsell Color Classification System
Methuen Color Index and Classification System
The CIE System
Pantone - A Modern Color Classification System
Optical Properties of Fiber Materials
General Properties of Fiber Polymers and Fibers - Part I
General Properties of Fiber Polymers and Fibers - Part II
General Properties of Fiber Polymers and Fibers - Part III
General Properties of Fiber Polymers and Fibers - Part IV
General Properties of Fiber Polymers and Fibers - Part V
Protein Fibers - Wool
Protein Fibers - Speciality Hair Fibers
Protein Fibers - Silk
Protein Fibers - Wool versus Silk
Timelines of Fabrics, Dyes and Other Stuff
Cellulosic Fibers (Natural) - Cotton
Cellulosic Fibers (Natural) - Linen
Other Natural Cellulosic Fibers
General Overview of Man-Made Fibers
Man-Made Cellulosic Fibers - Viscose
Man-Made Cellulosic Fibers - Esters
Man-Made Synthetic Fibers - Nylon
Man-Made Synthetic Fibers - Polyester
Man-Made Synthetic Fibers - Acrylic and Modacrylic
Man-Made Synthetic Fibers - Olefins
Man-Made Synthetic Fibers - Elastomers
Man-Made Synthetic Fibers - Mineral Fibers
Man Made Fibers - Other Textile Fibers
Fiber Blends
From Fiber to Yarn: Overview - Part I
From Fiber to Yarn: Overview - Part II
Melt-Spun Fibers
Characteristics of Filament Yarn
Yarn Classification
Textured Filament Yarns
Fabric Construction - Felt
Fabric Construction - Nonwoven Fabrics
A Fashion Data Base
Fiber Construction - Leather
Fabric Construction - Films
Glossary of Colors, Dyes, Inks, Pigments and Resins
Fabric Construction – Foams and Poromeric Material
Knitting
Hosiery
Glossary of Fabrics, Fibers, Finishes, Garments and Yarns
Weaving and the Loom
Similarities and Differences in Woven Fabrics
The Three Basic Weaves - Plain Weave (Part I)
The Three Basic Weaves - Plain Weave (Part II)
The Three Basic Weaves - Twill Weave
The Three Basic Weaves - Satin Weave
Figured Weaves - Leno Weave
Figured Weaves – Piqué Weave
Figured Fabrics
Glossary of Art, Artists, Art Motifs and Art Movements

The Glossary of Terms, Timelines of Fabrics, Dyes and Other Stuff, A Fashion Data Base, Glossary of Colors, Dyes, Inks, Pigments and Resins, Glossary of Fabrics, Fibers, Finishes, Garments and Yarns and Glossary of Art, Artists, Art Motifs and Art Movements have been updated in order to better inform your art practice.

If you find any post on this blog site useful, you can save it or copy and paste it into your own "Word" document etc. for your future reference. For example, Safari allows you to save a post (e.g. click on "File", click on "Print" and release, click on "PDF" and then click on "Save As" and release - and a PDF should appear where you have stored it). Safari also allows you to mail a post to a friend (click on "File", and then point cursor to "Mail Contents On This Page" and release). Either way, this or other posts on this site may be a useful Art Resource for you.

The Art Resource series will be the first post in each calendar month. Remember - these Art Resource posts span information that will be useful for a home hobbyist to that required by a final year University Fine-Art student and so undoubtedly, some parts of any Art Resource post may appear far too technical for your needs (skip over those mind boggling parts) and in other parts, it may be too simplistic with respect to your level of knowledge (ditto the skip). The trade-off between these two extremes will mean that Art Resource posts will hopefully be useful in parts to most, but unfortunately may not be satisfying to all!


Introduction
The long straight continuous nature of filament yarns has limited their use in utility garments and in garments for comfort and warmth. Early efforts to over come these limitations in the synthetic fibers consisted of collecting continuous filaments in large ropes called tows, as they came from the spinneret, then cutting them into staple lengths, baling them and spinning them into yarn on one of the mechanical spinning systems.

More recently methods have focussed on:
(i) Retaining the continuity of the filament tow strand while the fibers are “stapled” and made into yarn – the direct spun system.
(ii) Retaining the continuous nature of fibers while imparting spun-like characteristics – texturizing yarns.


Direct Spun Yarns
The direct spinning systems were developed as a way of by-passing some or all of the conventional systems without disrupting the continuity of the strand of filament tow. The tow-to-yarn process and tow-to-sliver process are two such examples.

Tow-to Yarn System
The Direct Spinner performs all the operations of stapling (making tow into staple) and spinning. It is a machine that processes 4,400 denier high-tenacity viscose rayon.

The tow is fed into the machine via levelling rolls, passes between two nip rolls, across a conveyor belt to a second pair of nip rolls, which travel at a faster rate of speed and creates a tension that causes the fibers to break at the weakest points. The strand is then drawn out to yarn size, twisted and wound on a bobbin.

Diagram of direct spinning: Perlock high tow-to-yarn system.
Courtesy reference[1].

Direct spun yarns have a higher degree of strength and uniformity than conventionally spun yarns. They can be distinguished from conventionally spun yarns by “backing” the twist out of a single yarn. The fibers will have a staple length in excess of six inches (15 cm), whereas conventionally spun yarns have fibers, which are usually less than two inches (ca. 5 cm) in length.

There is no control over the average staple length and there is not sufficient time after stretching and before winding for the fiber to relax, so the yarns have a high potential for shrinkage – 14% in wet finishing operations. This shrinkage makes it possible to produce fabrics such as Rayon-Acetate Taffeta etc.

Direct spun yarns and fabrics.
Courtesy reference[1].

High shrinkage yarns in the filling are alternated with low shrinkage yarns and are puckered by contraction of the high shrinkage, direct spun yarns.

Dense, compact rain wear fabrics can be made by using the direct spun yarns in the filling direction. When these shrink, they bring the warp yarns closer together.

Novelty yarns are produced by combining a high-shrinkage ply with a low-shrinkage ply to produce a bouclé effect.

The strength of direct spun yarns is best utilized in upholstery fabrics. The disadvantages are expense, lack of crimp and the impossibility of producing blends.

Tow-to-Top System
The tow-to-top process reduces the tow to staple and forms it into slivers on either the Pacific Converter or the Perlock heavy tow machine.

The Pacific Converter is a diagonally cut stapling machine that changes the tow into a staple of equal or variable lengths, and forms it into a crimped sliver ready for further drawing, blending, and spinning operations.

The tow enters the machine through a series of levelling rolls, which spread the fibers out in a sheet about 14 inches (i.e. 35 cm) wide.

Courtesy reference[1].
The Pacific Converter.

The Pacific Converter acts like a lawn mower. A helical cutting blade cuts the fiber band in diagonal strips, while it is carried along on a conveyor belt, thus preventing disruption of the parallelism of the fibers. The cut fibers are flexed to break open any sections that might have fused together and are drawn lengthwise to make them into a thinner sheet. They are moved by serpentine action between fluted rolls, which cause further separation. The thin sheet is then rolled into a continuous sliver and a slight crimp is imparted to the fibers by the crimping unit. The sliver is collected and coiled in a can ready to be taken to a conventional drawing or roving machine.

The spinning of the yarn is done on a conventional spinning machine. Natural fibers are not processed on the Pacific Converter except when wool top is to be added for a blend. A blending attachment is used with the converter.

Diagram of a Pacific Converter.
Courtesy reference[1].

The Perlock machine operates on the principle that, when tow is stretched, the fibers will break at their weakest points (random breakage) without disrupting the continuity of the strand. A sheet of tow nine inches (22.5 cm) wide (i.e. 180,000 denier or more) enters the machine through levelling rolls and then passes between two sets of nip rolls that apply the breaking tension. Breaker bars between the set of rolls control the length of staple. As the tow travels through the breaking zone, tension is applied suddenly and the fibers break in the breaker bar area. This process is then repeated as more tow enters the breaking zone. The fiber strand moves on through another set of rolls into a crimpling box and emerges as crimp sliver. The rest of the yarn making process is completed on conventional spinning machinery.

Hi-Bulk Yarns
Bulk is desirable for warmth, texture, and cover. Bulking characteristics result when the curl or crimp of fibers prevents orderly arrangement and creates airspaces within the yarn.

Thermoplastic fibers can be used to make hi-bulk yarns by processing them on either the Perlock machine or the Pacific Converter if a heat attachment is added. A Perlock heavy tow machine is called a Turbo-Stapler.

The Turbo-Stapler.
Courtesy reference[1].

Thermoplastic fibers, in a flat sheet, are heat stretched as they are passed between heater plates and are then changed to staple in the breaking zone. This gives the fibers high shrinkage properties. Acrylics will shrink 20% or more when they are subsequently relaxed by another heat treatment. The fibers are crimped and a portion of the heat stretched sliver is sent in louvered cans to a Fiber-Setter. Steam enters the can through the slot openings and relaxes the fiber from the strains of heat stretching. This shrinks it so that it loses its high-shrinkage properties. It then re-joins the portion that was not heat-relaxed.

The Pacific Converter processes hi-bulk in two different ways. If a heat-stretching attachment is added, part of the tow is passed through the heat-stretching attachment while the remainder is passed above it. The two parts of the tow are combined before entering the cutting zone, where it is cut into staple. The yarn at this stage is similar to other yarn, since the bulk has not been developed. Subjecting the staple tow to high temperature, usually in the dyeing process, causes the heat-stretched fibers to shrink; and as they are shortened, they force the rest of the fibers to buckle and so create the bulk. The yarn usually consists of 40% non-relaxed and 60% heat-relaxed fibers, but are other ratios might also be used.

In the second method of producing hi-bulk yarns on a Pacific Converter, the tow is purchased as high-shrinkage types and blended before it enters the converter. The spun yarn is heat-treated to create the bulk.

Much hi-bulk yarn has gone into the knit apparel trade, especially sweaters. These are labelled as “Hi-Bulk Orlon” etc. Hi-bulk yarns are also used in woven apparel.

High-bulk yarn. Left: before steaming. Right: after steaming.
Courtesy reference[1].


Reference:
[1] N. Hollen and J. Saddler, Textiles, 3rd Edition, MacMillan Company, London (1968).

No comments: