magical! Knitted axial fabrics are actually used on F-22 fighters?

Why are the magical knitted axial fabrics so excellent? How is it designed and produced? What are the characteristics and application areas? Xiaobian is coming for everyone.

The development of knitted axial fabrics is mainly developed to adapt to the application of high-strength, high-modulus high-performance fibers in textile composites. Axial knitting technology is an advanced weaving method in which one or more sets of parallel straight yarns are bound together by a woven yarn. Since the axial yarn to be lined is in a straight state at the time of weaving, the high-strength fiber high-strength and high-modulus characteristics can be fully utilized.

Therefore, high-performance glass fiber, carbon fiber, aramid fiber, basalt fiber, high-strength polyester and high-performance polyethylene are widely used in knitted axial fabrics, and glass fiber is used most. In addition, some metal fiber materials can also be applied, such as warp knitting nets woven with nickel wire for satellite antennas, cores made of pure alloy lead fiber, cored chemical fibers for anti-nuclear radiation soft lead screens and protective clothing.

Knitted axial fabrics can be divided into uniaxial, biaxial and multiaxial fabrics according to the direction of yarn lining; they can be divided into warp knitted axial fabrics and weft knitted axial fabrics according to different production and processing equipment.

Warp knitted biaxial fabric

Weft-knit biaxial fabric

Due to the low production cost, high production efficiency, structural integrity, design flexibility, good tear resistance and strong interlaminar shear force, the warp-knitted axial fabric has attracted more and more attention. It has great potential in the field of industrial use, especially as a skeleton of resin composite materials, which is increasingly used. The warp-knitted axial fabric is compounded with a resin as a skeleton material to form a fiber-reinforced composite material, which can be used for aircraft, spacecraft, automobiles, ships, armored vehicles, wind power generation and the like.

Multi-axial warp-Knitted (MWK) technology is a new type of multi-head weft knitting technology developed on the basis of uniaxial and biaxial technology. The longitudinal, transverse or oblique orientation of the reinforcing yarn at an angle according to the requirements of use can fully exploit the performance of each component of the fabric structure. Multi-axial technology is a new type of weaving technology developed rapidly in foreign countries in the late 1970s. It was widely researched and promoted in the 1990s. It is characterized by high demand, high production efficiency and low production cost.

Multiaxial warp knit fabric and its lamination

Germany has long been a technical monopoly in the manufacture of multi-axial warp knitting machines. For example, Karl Mayer's Malimo Multiaxial multi-axial warp knitting machine has a top speed of 1400 r/min and a corresponding output of 240 m/h. Production of a variety of process fabrics for wind turbine blades, vehicle and boat components, high pressure vessels and sports equipment. In addition, it includes the latest MAXTRONIC® models and the COP MAX 5 for the production of carbon fiber multiaxial warp knits.

China has successfully developed "RCD-1 multi-axial warp knitting machine", "GE2M-2 multi-axial warp knitting machine" and "GE2M-G high-speed multi-axial warp knitting machine", but only meets more fiberglass The production of axial fabrics cannot be used to produce carbon fiber multiaxial fabrics.

Foreign countries often use a single-sided flat-needle structure to bind the weft-knitted biaxial fabric of warp and weft, called COFAB knitted fabric. The raw materials used are mostly glass fiber and aramid, and its molding properties and warp knitting biaxial The fabric is close. Tianjin University of Technology has developed a weft-knitted multi-layer biaxial lining knitting machine, which uses ribbed structure to bundle up to 5 layers of lining and weft-inserting yarns. The bundled yarns can be made of flexible yarns such as aramid and polyester.

Weft knitting flat needle bundled with biaxial fabric

Weft-knitted ribbed bundled multi-layer biaxial fabric

The weft-knitted multi-layer biaxial fabric has the advantage of being cheaper than the warp-knit biaxial fabric, and the lining and weft-laid layers can be up to 5 layers. The fabric has excellent compression molding properties, which is woven fabric. Or warp knitted biaxial fabrics can't do it.

Hemispherical curved surface forming fabric of weft-knitted biaxial multi-layer woven fabric

At present, the disadvantage of warp-knitted multiaxial fabrics used at home and abroad is that when the layup yarns are stitched together by stitching yarns, the needles may damage the layup of the layup. The weft-knitted multi-axial yarn lining knitting machine developed by Tianjin Polytechnic University has a fabric width of more than 2m. There is no phenomenon that the needle piercing the lining in the fabric, and the cloth surface is clear; the yarn tube is directly used on the machine, and no matching is required. The warping machine; the weft-knitted form is used to simplify the machine structure.

Possible damage of stitched warp-knitted multiaxial fabric during knitting

Weft-knitted ribbed bundled multi-axial woven fabric

The weft-knit biaxial fabric produced by the flat knitting machine has low production efficiency due to the reciprocating weaving form of the bundled yarn. The circular knitting machine has the characteristics of multi-path, strong knitting continuity and high production efficiency. Therefore, a cylindrical biaxial looting machine for weaving high-strength and high-mode lining on a circular weft knitting machine is developed, which adopts weft-knit circular knitting machine. The weft-level needle tissue is used as a binding system to produce a circular weft-knit biaxial lining fabric, which will solve the disadvantage of low production efficiency of the weft-knit biaxial lining fabric with the V-shaped flat knitting machine as the binding system. Since the product is a continuous cylindrical cloth, it can be used for the development of round tube composite parts reinforcements such as oil hoses.

Source: Textile Guide

Editing and finishing: knitting industry

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