Metallurgical Engineering

 

Glass Fiber

 

Introduction

 

Glass fiber was invented by Russell Games Slayter in thermal building insulation. There are many different compositions available but usually glass fibers are silica based (~50-60%) and a host of oxide(iron,aluminium,etc.) is also present in the fiber. It is cheap compared to other fibers and can be achieved in a variety of forms.

 

Production

 

Glass fiber is made by requiring raw materials melting in a hopper and transferring into molten glass. Raw materials are added into the hopper through batch mixing. After that some addition of other oxides are done and then the mixture is melted in the furnace.

 

After achieving molten glass, it is passed through the electrically heated platinum bushings or crucibles to achieve fibers of required diameters. Usually there are 200 holes in the crucibles. Outcome after molten glass is passed through crucibles is wounded on a drum. The schematic of this production is shown in Fig.(1).

 

 

Fig. (1) : Schematic Diagram of Glass Fiber Fabrication

 

 Glass Fiber Forms

 

Commercial forms of Glass Fibers are as shown in Fig. (2) : Continuous strand is a group of individual fibers; roving is a group of parallel strands; chopped fibers consists of strand or roving chopped to lengths between 5 and 50 mm. Glass fibers are also available in the form of woven fabrics or nonwoven mats.

 

Fig. (2) : Glass fiber is available in a variety of forms: (a) chopped strand, (b) continuous yarn, (c) roving, (d) fabric

 

 Structure

 

Glass fibers have basically inorganic polyhedron crystalline structure as shown in Fig.(3a). Some glass fibers are made of amorphous structure by adding some metal oxides. These metal oxides join polyhedron structure ionically rather than directly. High composition of metal oxides can affect the glassy structure formation.

 

Fig. (3) : Amorphous structure of glass: (a) a two-dimensional representation of silica glass network and (b) a modified network that results when Na₂O is added to (a).

 

Properties

 There are three types of glass fibers but all of them have almost the same mechanical properties with some variation. So we will discuss the properties of E-Glass. It has good strength but has low density and low Young’s modulus. Due to this some advanced fibers(i.e boron,carbon,etc) have been replaced especially in the aerospace industry.Still it is used as reinforcement of polyester,epoxy and resins.

 Table -1 : Mechanical Properties of E-Glass

Density(g/cm3)	Tensile Strength(MPa)	Young’s Modulus (GPa)	Coefficient of Thermal Expansion(K-1)
2.55	1750	70	4.7x10-6

 

Moisture decreases glass fiber strength. Glass fibers are also susceptible to static fatigue; that is, when subjected to a constant load for an extended time period, glass fibers can undergo subcritical crack growth. This leads to failure over time at loads that might be safe when considering instantaneous loading.

 

Applications

 

Glass fiber reinforced resins are used widely in the building and construction industry. Commonly, these are called Glass-Reinforced Plastics(GRP). They are used in the form of a cladding for other structural materials or as an integral part of a structural.

 Boat hulls were primarily made of GRP. Use of GRP in the chemical industry is fairly routine. The rail and road transportation industry and the aerospace industry are other big users of GRP.

  

 

Prepared by,

Shail Shah,

Metallurgical and Materials Engineering,

FOTE,

The M.S University, Baroda