Saturday, August 6, 2016

Weaving and the Loom[1]
Art Resource

Marie-Therese Wisniowski

Preamble
This is the fifty-fifth 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
Direct Spun Yarns
Textured Filament Yarns
Fabric Construction - Felt
Fabric Construction - Nonwoven fabrics
A Fashion Data Base
Fabric 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
Crêpe Fabrics
Crêpe Effect Fabrics
Pile Fabrics - General

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.

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Introduction
Weaving is the process of interlacing two or more sets of yarn at right angles to each other - one set running in the lengthwise direction called the warp and the other inserted crosswise and is called the filling (or weft). An interlacing is defined as the point at which a yarn changes position from the surface of the fabric to the underside of a fabric or vice versa, by passing over or under one or more yarns. The number of interlacings is important in fabric properties such as firmness, flexibility, resilience, slippage and ravelling. There are fewer interlacings in a fabric when a yarn from one direction floats over two or more yarns from the other direction. A fabric can be identified as a woven fabric if yarns can be ravelled from adjacent sides (see below).

Yarn arrangement in weaving. Warp and filling (weft) arrangements.

Today’s post deals with weaving and loom developments in fabric construction.


Loom Developments
Weaving is done on a machine called a loom. The primitive loom consisted of a frame that held the warp yarns in position as the filling yarn was woven under and over the warp by the use of fingers. A wooden bar was the first device used to separate the warp.

Weaving on a weighted loom.
Photograph courtesy of G. Weinlinger.

The harness of heddles, which was developed later, is still a major part of the modern loom. A heddle is a wire with a hole in the center through which a warp yarn is threaded. A harness is a frame to hold a number of heddles. The simplest plain weave can be made on a loom with only two harnesses.

Simplified diagram of a two-harness loom.

By the use of additional harnesses more intricate patterns can be woven. Notice in the above diagram that, as one harness is raised, the yarns form a shed through which filling yarn can be inserted. A beam at one end of the loom holds the warp yarn and the woven cloth is wound on a beam at the other end of the loom. A shuttle carries the filling yarn through the shed and a reed or batten beats the filling yarn back into the coth to make the weave firm.

Before the warp creel-beam is placed on the loom, the yarns are unwound from it and run through a starch bath to seal the fiber ends and strengthen the yarns so that they will withstand the stresses of weaving. This treatment is called slashing (see diagram below).

Slashing warp yarns to prepare them for weaving.

All weaves that are known today could be made by the primitive weaver. The loom has changed in many ways, but the basic principles and operations are still the same. Weaving consist of three basic steps:
(i) Shedding: the raising of one or more harnesses to separate the warp yarns and form a shed.
(ii) Picking: passing the shuttle through the shed to insert the filling.
(iii) Beating up: the reed pushes the filling yarn back into place in the cloth.

Loom developments over the years have centered on: (i) devices to separate the warp for more intricate weaving patterns; (ii) speedier methods of inserting the filling; (iii) the use of computers and electronic monitoring systems.

The number of harnesses that a loom can operate efficiently is limited. When the repeat of the woven pattern requires more than six harnesses, an attachment is added to the loom to control the raising and lowering of warp yarns. For small-figure patterns requiring not more than 25 interlacing patterns, a dobby-head attachment is used.

Terry towel Rapier loom with electronic Dobby.

The weave pattern is controlled either: (i) by a chain of wooden bars with steel pegs; (ii) by punched paper patterns; (iii) by plastic tapes; (iv) by computer-controlled patterns. Large-figured weaves are made on a Jacquard loom, which was invented in France in 1805. It was one of the first automated looms, since each warp was controlled individually by punch cards (which nowadays are computer controlled).

Each different pattern is loaded into the computer running the loom by means of a diskette. The control of the jacquard is then performed by the computer.

Other attachments used on a loom are the swivel attachment for dotted swiss, the box loom for weaving yarns of different size, color etc., the doup attachment for leno weave, and the lappet attachment for extra-yarn woven figures.

A leno heald consists of two heald frames (lifting frames), one doup frame, and the doup frame drives. Leno weaving can be done using the upper shed, lower shed or upper/lower shed techniques as desired.

In the simplest loom, a “flying” shuttle is “batted” across through the shed of warp yarns by a picker-stick at the sides of the loom. The speed with which it can be sent back and forth is limited – usually less than 200 picks per minute (p.p.m.) (Note: pick is another name for filling yarns). Manufacturers have long sought a way to replace the shuttle and increase the speed of weaving. The different types of shuttle-less looms give higher weaving speeds and reduction in noise level in factories – a factor of significant importance to workers.

6"x75" automatic shuttleless loom for cotton.

The rapier type loom weaves (primarily) spun yarns at 200 to 250 picks per minute (ppm). It has two metal arms about the size of a small pen knife called carriers or “dummy shuttles”; one on the right side and the other on the left side of the loom. A measuring mechanism on the right side of the loom measures and cuts the correct length of the filling yarn to be drawn into the sheds by the carriers. The two carriers enter the warp shed at the same time and meet in the center. The left-side carrier takes the yarn from the right-side carrier and pulls it across the left side of the loom. After each insertion, the filling threads are cut near the edge and protruding ends tucked back into the cloth to reinforce the edge.

The carrier arms of a rapier-type shuttleless loom.

The water-jet loom was developed in Europe. The looms are compact and take up less space than the conventional loom. They can operate at speeds of 440 p.p.m. Hydrophobic (water hating) yarns such as nylon filament are more suitable than hydrophilic (water loving) yarns such as cotton, which require a special drying device. Water-soluble sizings such as starch usually used on cotton yarns would be washed away. The filling yarns comes from a stationary package at the side of the loom, goes to a measuring drum, which controls the length of each pick, then continues through a guide to a water nozzle where a jet of water carries the filling through the shed. After the yarn is beaten back, it is cut off at both sides of the cloth. If thermoplastic fibers are used in the yarns, they are cut by electrically heated wires. Water is then removed by a slanted warp line or by a special suction device. Very little tension can be applied to the filling and for this reason, weaving of stretched fabrics is not yet possible. Also, box looms for weaving colored yarns are not practical.

A water-jet loom.

The air-jet loom or pneumatic method was developed in Sweden by a textile engineer, who thought of the idea whilst sailing. He noticed the short regular puffs that came from the exhaust of a diesel motor. His first loom used a bicycle pump to furnish the compressed air. The first loom was sold in 1955 and by 1960 100 were is use. The filling is premeasured and guided through a nozzle where a blast of air sends it across. The loom can opertate at 320 p.p.m.

Air-jet loom.

Computers and electronic devices now play an important part in weaving and also in other areas of textile manufacture. Computers have been used to develop design tables for setting up weaves of “maximum weavability” for properties such as tightness and compactness in wind-repellent fabrics, ticking etc. of any fiber content. The computer plays a part in textile designing. It can be programmed to prepare a paper from which punch cards can be made to control the operation of the loom. More recently with digital-to-analogue and analogue-to-digital devices, the computer program itself controls the entire weaving operation. Whilst computer assisted design (CAD) programs are all the rage, nevertheless, designers still have carriage of the concept of the design leaving the technical implementation of the design in the hands of computer programs. The computer is also used to control temperature and pressure in dyeing and bleaching.

The TC1 with displayed cloth in progress. The PC controls the pick plan – the foot pedal advances the software and the loom by 1 pick each time. There is no bench – weaving is done standing. It is still a handloom – with a bit of technology added.

Electronic devices also play an important role in the quality control process. Photo-feelers, for example, can sense the amount of yarn on the bobbin and signal for bobbin transfer. Cloth straighteners are photo-electronic devices attached to the tenter frame to keep crosswise yarns at right angles to the lengthwise yarns as the fabric is dried and so eliminate the “off-grain” fabrics that create such a problem to the home sewer as well as to the garment manufacturer.

Weft detectors & Sensors/Dornier photo electronic feeler.


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

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