|The Production of Bullet Resistant Glass - Part 1|
|Firstly, it would be great if everyone in the glass industry refrained from calling this product “bullet proof” I seriously doubt if anything is ultimately bullet proof, bullet resistant is indeed the correct terminology and within the industry this is abbreviated to BRG. The production of BRG requires top class manufacturing technology especially within the sphere of bending moulds/tools.|
|This first part of our technical article will review the various ballistic standards which designate the various types and categories of BRG products. The second part will discuss the production challenges associated with BRG.
BALLISTIC TEST STANDARDS
Whilst BRG is the correct terminology there are a number of various international ballistic test standards which form the actual “language” of the business. Most countries have their own test standards however; there are three standards which dominate BRG production and International sales, these are:
BS EN 1063 is a British/Euro standard, NIJ is the most prominent USA standard and STANAG is now the NATO standard. The first two standards have been around for quite a while whilst STANAG is relatively newer and primarily sets the standards for NATO military vehicles. Civilian vehicle armourers generally specify their BRG requirements against the BS EN 1063 and NIJ standards although STANAG is gaining popularity within this sphere of armouring.
All ballistic test standards incorporate “threat levels” which designate a specific calibre; an example of this would be BS EN 1063 level 6 which translates into a threat level of 7.62 x 51 NATO ball ammunition. The individual test standards also dictate their own testing procedures which will include the required test piece size, number of test pieces, test temperatures, shot test pattern, shot distance etc.
The most commonly requested threat levels are – by calibre:
It should be noted, that the international specifications are not standardised and therefore you have the situation where NIJ level 3 = 7.62 x 51 NATO BALL this equates to level 6 for BS EN 1063. It is imperative that the manufacturers and the clients “talk the same language”.
- 7.62 x 51 NATO BALL
- 7.62 X 51 NATO ARMOUR PIERCING
- 7.62 X 54 RUSSIAN (API)
- 7.62 X 39 RUSSIAN (BALL AND API)
- 5.56 X 45 NATO (SS-109)
- 44 MAGNUM
- 12 GAGE SHOT GUN (BRENNEKE SLUG)
BRG PRODUCT TYPES
BRG has two primary types: “no spall” and “low spall” however, it should be noted that the low spall types of BRG have generally been surpassed by the no spall products. Spall being glass particles that are ejected off the back face of BRG during ballistic attack; spall can obviously be dangerous to eyes etc.
Low spall products are generally manufactured from “all glass” laminates and represent the low end of the market. Most products are now “no spall” (sometimes called asymmetrical formulations) and are a combination laminate, which consists of glass and polycarbonate, the polycarbonate is generally on the back face and eliminates the glass spall effect.
However, the primary function of the polycarbonate is to act as a shock absorber, the shock absorbing characteristics of polycarbonate is so effective it allows the laminator to manufacture thinner and therefore lighter BRG sections per ballistic threat level. This of course provides a massive weight saving advantage for the vehicle armourers.
In general terms the all glass, low spall types of BRG are approximately 75% thicker than their glass/poly counterparts which represents a massive weight differential. Low spall BRG is generally confined to architectural applications/static applications where weight is of less concern.
It should be noted that laminators usually apply a polycarbonate which has one face “hard coated”, this hardened face is on the rear and exposed face of the BRG – non attack face and forms a reasonable barrier against abrasions and scratches.
There is a third type of BRG which is not very common place and is termed as a “symmetrical formulation” which is: glass/polycarb/glass, this is sometimes used for architectural applications and is a lighter type of low spall glass. The requirement to protect exposed polycarbonate from abrasions and scratches probably led to the design and manufacture of the “symmetrical formulations”, a glass surface can take far more abuse than a polycarbonate face. BRG products with “asymmetrical formulation” are typically applied in banks and older military vehicles.
There are probably two main areas of concern and complexity facing any new or existing manufacturer of BRG firstly, to develop light weight laminations that will meet the required ballistic threat levels and secondly the ability to consistently manufacture optically correct curved sections of automotive BRG.
The production of curved automotive BRG requires perfectly tailored tooling and manufacturing processes that will ensure both good quality and ultimately, the good reputation of the manufacturer. Any doubt or lack of knowledge in these areas can create very long and very expensive development programmes which leads to a loss of confidence for both the manufacturer and ultimately their clients.
Safety Glass Experts, offers a comprehensive package of technology and experience within this very specialised industry which, enables us to provide the very best of advise and “hands on experience” to new and existing producers of bullet resistant glass products.
The upcoming second part will discuss the production challenges associated with BRG
For more information visit www.sge.fi or contact:
Safety Glass Experts International Oy Ltd
Talviseisaus 2 D 8
FI-20400 Turku Finland
Phone: +358 400 979 300
Fax: +358 2 6518 2539
All graphics, photographs, and text appearing in this article belong to Safety Glass Experts International Oy Ltd. Redistribution or commercial use is prohibited without express written permission.
Photos: Safety Glass Experts International
Last review: May, 2011
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