ISO 20657:2017

INTERNATIONAL ISO
STANDARD 20657
First edition
2017-03
Glass in building — Heat soaked
tempered soda lime silicate safety glass
Verre dans la construction — Verre de sécurité de silicate
sodocalcique trempé et traité
Reference number
ISO 20657:2017(E)
©
ISO 2017

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ISO 20657:2017(E)

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© ISO 2017, Published in Switzerland
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ISO 20657:2017(E)

Contents Page
Foreword .v
Introduction .vi
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Glass products . 3
5 Manufacturing processes. 3
5.1 General . 3
5.2 Tempering process . 3
5.3 Heat soak process cycles . 4
5.3.1 Off-line process . 4
5.3.2 In-line process . 7
6 Fracture characteristics . 8
6.1 General . 8
6.2 Accidental human impact . 8
6.3 Fragmentation . 8
7 Dimensions and tolerances . 9
7.1 Nominal thickness and thickness tolerances . 9
7.2 Width and length (sizes) . 9
7.2.1 General. 9
7.2.2 Maximum and minimum sizes .10
7.2.3 Tolerances and squareness .10
7.2.4 Edge deformation produced by vertical tempering .11
7.3 Flatness .11
7.3.1 General.11
7.3.2 Measurement of overall bow .13
7.3.3 Measurement of wave or roller wave distortion .14
7.3.4 Measurement of edge lift (only for heat soaked tempered safety glass
which was horizontally tempered) .15
7.3.5 Measurement of perimeter deformation of glass produced by air cushion
tempering process .16
7.3.6 Measurement of local distortion (only for heat soaked tempered safety
glass which was vertically tempered) .16
7.3.7 Limitation on overall bow, roller waves and edge lift for heat soaked
tempered safety glass which was horizontally tempered .17
7.3.8 Limitation on overall bow, wave and perimeter deformation for heat
soaked tempered safety glass manufactured by air cushion process .18
7.3.9 Limitation on overall bow and local distortion for heat soaked tempered
safety glass which was vertically tempered .18
7.3.10 Other distortions .18
8 Edge work, holes, notches and cut-outs.19
8.1 General .19
8.2 Edge working of glass for tempering .19
8.3 Profiled edges.20
8.4 Round holes .20
8.4.1 General.20
8.4.2 Diameter of holes .20
8.4.3 Limitations on position of holes .20
8.4.4 Tolerances on hole diameters .21
8.4.5 Tolerances on position of holes .22
8.5 Holes/others .23
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ISO 20657:2017(E)

8.6 Notches and cut-outs .23
8.7 Shaped panes .23
9 Fragmentation test .23
9.1 General .23
9.2 Dimensions and number of test specimens .23
9.3 Test procedure .24
9.4 Assessment of fragmentation .24
9.5 Minimum values from the particle count .25
9.6 Selection of the longest particle .25
9.7 Maximum length of longest particle .25
9.8 Test Report .26
10 Other physical characteristics .26
10.1 Optical distortion .26
10.1.1 Heat soaked tempered safety glass produced by vertical tempering .26
10.1.2 Heat soaked tempered safety glass produced by horizontal tempering .26
10.2 Anisotropy (iridescence) .26
10.3 Thermal durability .26
10.4 Mechanical strength .27
10.5 Surface pre-stress .27
11 Marking .27
12 Packaging .28
Annex A (informative) Pendulum impact test methods .29
Annex B (informative) Alternative method for the measurement of roller wave distortion .30
Annex C (informative) Example of particle count .32
Annex D (informative) Method for the measurement of the surface pre-stress of heat
soaked tempered safety glass .34
Annex E (informative) In-line heat soak process control .36
Annex F (informative) Heat soak process system calibration test .38
Bibliography .48
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ISO 20657:2017(E)

Foreword
ISO (the International Organization for Standardization) is a worldwide federation of national standards
bodies (ISO member bodies). The work of preparing International Standards is normally carried out
through ISO technical committees. Each member body interested in a subject for which a technical
committee has been established has the right to be represented on that committee. International
organizations, governmental and non-governmental, in liaison with ISO, also take part in the work.
ISO collaborates closely with the International Electrotechnical Commission (IEC) on all matters of
electrotechnical standardization.
The procedures used to develop this document and those intended for its further maintenance are
described in the ISO/IEC Directives, Part 1. In particular the different approval criteria needed for the
different types of ISO documents should be noted. This document was drafted in accordance with the
editorial rules of the ISO/IEC Directives, Part 2 (see www .iso .org/ directives).
Attention is drawn to the possibility that some of the elements of this document may be the subject of
patent rights. ISO shall not be held responsible for identifying any or all such patent rights. Details of
any patent rights identified during the development of the document will be in the Introduction and/or
on the ISO list of patent declarations received (see www .iso .org/ patents).
Any trade name used in this document is information given for the convenience of users and does not
constitute an endorsement.
For an explanation on the voluntary nature of standards, the meaning of ISO specific terms and
expressions related to conformity assessment, as well as information about ISO’s adherence to the
World Trade Organization (WTO) principles in the Technical Barriers to Trade (TBT) see the following
URL: w w w . i s o .org/ iso/ foreword .html.
This document was prepared by Technical Committee ISO/TC 160, Glass in building, Subcommittee SC 1,
Product considerations.
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ISO 20657:2017(E)

Introduction
Heat soaked tempered soda lime silicate safety glass has a safer breakage behaviour when compared
with annealed glass. This behaviour is a direct result of the high surface pre-stress.
It also has a known level of residual risk of spontaneous breakage arising from the possible presence of
critical nickel sulfide (NiS) inclusions in the thermally toughened soda lime silicate glass.
Heat soaked tempered soda lime silicate safety glass has a known behaviour under accident human
impact together with known mechanical and thermal stress resistance.
Other requirements, not specified in this document, can apply to heat soaked tempered soda lime
silicate safety glass which is incorporated into assemblies, e.g. laminated glass or insulating glass
units, or undergo an additional treatment, e.g. coating. The additional requirements are specified in the
appropriate glass product standard. Heat soaked tempered soda lime silicate safety glass, in this case,
does not lose its mechanical or thermal characteristics.
NOTE 1 ISO/TC 160/SC 2 is producing standards for the determination of the design strength of
glass and is preparing a design method.
NOTE 2 In Europe, instead of “heat soaked tempered”, the term “heat soaked thermally
toughened” is used.
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INTERNATIONAL STANDARD ISO 20657:2017(E)
Glass in building — Heat soaked tempered soda lime
silicate safety glass
1 Scope
This document specifies product definitions, product characteristics, i.e. tolerances, flatness, edgework,
etc., fracture characteristics, including fragmentation, and the physical and mechanical characteristics
of flat heat soaked tempered soda lime silicate safety glass for use in buildings.
This document does not cover curved (bent) glass according ISO 11485.
2 Normative references
The following documents are referred to in the text in such a way that some or all of their content
constitutes requirements of this document. For dated references, only the edition cited applies. For
undated references, the latest edition of the referenced document (including any amendments) applies.
ISO 1288-3, Glass in building — Determination of the bending strength of glass — Part 3: Test with
specimen supported at two points (four point bending)
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
ISO and IEC maintain terminological databases for use in standardization at the following addresses:
— IEC Electropedia: available at http:// www .electropedia .org/
— ISO Online browsing platform: available at http:// www .iso .org/ obp
3.1
heat soaked tempered soda lime silicate safety glass
heat soaked tempered safety glass
glass within which a permanent surface compressive stress, additionally to the basic mechanical
strength, has been induced by a controlled heating and cooling process in order to give it greatly
increased resistance to mechanical and thermal stress and prescribed fragmentation characteristics
and which has a known level of residual risk (3.2) of spontaneous breakage due to the presence of critical
nickel sulphide (NiS) inclusions
3.2
level of residual risk
risk of spontaneous breakage of heat soaked thermally toughened soda lime silicate safety glass, on a
statistical basis, due to the presence of critical nickel sulphide inclusions
Note 1 to entry: It is considered that the level of residual risk is no more than one breakage per 400 tonnes of heat
[6][7][8]
soaked thermally toughened soda lime silicate safety glass .
3.3
flat heat soaked tempered safety glass
heat soaked tempered (thermally toughened) glass which has not been deliberately given a specific
profile during manufacture
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ISO 20657:2017(E)

3.4
enamelled heat soaked tempered safety glass
heat soaked tempered (thermally toughened) glass which has a ceramic frit fired into the surface
during the tempering (toughening) process
Note 1 to entry: After tempering, the ceramic frit becomes an integral part of the glass.
Note 2 to entry: The application of the ceramic frit may be by a continuous application or discontinuous, e.g.
screen printing.
3.5
horizontal tempering process
process in which the glass is supported on horizontal rollers
3.6
air cushion process
process in which the glass is supported by an air cushion with or without additional rollers
Note 1 to entry: In this process, the glass will be between horizontal and 45° of horizontal.
3.7
vertical tempering process
process in which the glass is suspended by tongs
3.8
edge deformation
deformation of the edge caused by the tong marks
3.9
edge lift
edge dip
distortion produced in heat soaked tempered safety glass (3.1) which was horizontally tempered, at the
leading and trailing edge of the plate, as a result of the glass during the tempering (toughening) process
not being supported by a roller
Note 1 to entry: This is a distortion produced by a deviation from surface flatness.
3.10
perimeter deformation
distortion around the edge of heat soaked tempered safety glass (3.1) manufactured by air cushion
process (3.6)
3.11
local distortion
local deformation underneath the tong marks of heat soaked tempered safety glass (3.1) which was
vertically tempered
3.12
overall bow
deformation of the whole pane of heat soaked tempered safety glass (3.1) caused by the heating and
cooling process
3.13
roller wave distortion
periodic distortion produced in heat soaked tempered safety glass (3.1) which was horizontally tempered
as a result of the glass during tempering process being in contact with the rollers
Note 1 to entry: This is a surface distortion produced by a reduction in surface flatness.
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ISO 20657:2017(E)

3.14
wave distortion
distortion produced in heat soaked tempered safety glass (3.1) manufactured by air cushion process (3.6)
as a result of the tempering process
3.15
heat soak process
heat treatment after the tempering process during which majority of NiS inclusions is removed resulting
in a known level of critical NiS inclusions in the heat soaked tempered soda lime silicate safety glass
3.16
in-line heat soak process
heat soak process (3.15) which follows immediately after the quenching process whereby the glass
temperature is directly reduced from quenching to the heat soak temperature in an in-line heat soak oven
3.17
off-line heat soak process
heat soak process (3.15) carried out after the quenching process whereby the glass is cooled down to
room temperature and heated up again to the heat soak temperature in an off-line heat soak oven
4 Glass products
Heat soaked tempered safety glass is made from a monolithic glass generally corresponding to one of
the following standards:
— basic soda lime silicate glass products according to ISO 16293-1;
— float glass according to ISO 16293-2;
— patterned glass according to ISO 16293-5;
— coated glass according to ISO 11479-1.
NOTE For drawn sheet glass, an ISO standard is not available. Therefore, see EN 572–4 or national standards.
Other nominal thicknesses of glass than those covered in the above standards are possible.
5 Manufacturing processes
5.1 General
Heat soaked tempered safety glass is manufactured as follows.
Basic soda lime silicate glass products (see Clause 4) are cut to size, shaped and edgeworked (see
Clause 8).
The prepared glass panes are then tempered (see 5.2).
The tempered panes are then subjected to an off-line or in-line heat soak process cycle (see 5.3.1 and 5.3.2)
After manufacture the heat soaked tempered safety glass shall comply with the fragmentation test (see
Clause 9) and mechanical strength requirement (see 10.4).
5.2 Tempering process
The cut, shaped and edgeworked glasses are tempered. The heat soaked tempered glass shall comply
with the flatness criteria for horizontal or vertical tempering or the air cushion process (see 7.3).
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ISO 20657:2017(E)

The heat soaked tempered safety glass shall have a level of fragmentation that will ensure that after the
glass has been through the heat soak process, and subsequently tested to the fragmentation test (see
Clause 9), it shall comply with 9.5.
5.3 Heat soak process cycles
5.3.1 Off-line process
5.3.1.1 General
The heat soak process cycle consists of a heating phase, a holding phase and a cooling phase (see
Figure 1).
Key
T glass temperature at any point, °C
t time, h
1 first glass to reach 250 °C
2 last glass to reach 250 °C
a
heating phase
b
holding phase
c
cooling phase
d
ambient temperature
Figure 1 — Heat soak process cycle
5.3.1.2 Heating phase
The heating phase commences with all the glasses at ambient temperature and concludes when the
surface temperature of the last glass reaches 250 °C. The maximum heating rate is 3 °C per min. The
time to reach this temperature is defined in the calibration process. This time will be dependent on
the size of the oven, the amount of glass to be treated, the separation between glasses and the heating
system capacity.
The glass separation and rate of heating should be controlled to minimize the risk of glass breakage as
a result of thermal stress.
To facilitate economic heating, the air temperature within the oven may exceed 290 °C. However, the
glass surface temperature shall not be allowed to exceed 290 °C. The period of glass surface temperature
in excess of 270 °C shall be minimized.
NOTE Care should be taken to ensure the maximum temperature of the glass does not exceed 270 °C as there
is a possibility of the nickel sulphide inclusion reconverting.
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ISO 20657:2017(E)

5.3.1.3 Holding phase
The holding phase commences when the surface temperature of all the glasses has reached a
temperature of 250 °C. The minimum duration of the holding phase is 2 h.
Precise oven control is necessary in order to ensure that the glass surface temperature shall be
maintained in the range of 260 °C ± 10 °C during the holding phase.
5.3.1.4 Cooling phase
The cooling phase commences when the last glass to reach 250 °C has completed its holding phase, i.e.
been held for two hours at 260 °C ± 10 °C. During this phase, the glass temperature shall be brought
down to ambient temperature.
The cooling phase can be concluded when the air temperature in the oven reaches 70 °C.
The rate of cooling should be controlled to minimize the risk of glass breakage as a result of thermal stress.
5.3.1.5 Heat soak process system
5.3.1.5.1 General
The heat soak process system consists of the following:
— oven (see 5.3.1.5.2);
— glass support (see 5.3.1.5.2);
— separation system (see 5.3.1.5.4).
The oven shall be calibrated (see 5.3.1.5.5 and Annex F) and this determines the method of operation of
the heat soak process system during manufacture of heat soaked tempered safety glass.
5.3.1.5.2 Oven
The oven shall be heated by convection and shall allow an unhindered air circulation around each glass
pane. In the event of glass breakage, the airflow shall not be hindered. The airflow in the oven shall be
led parallel to the glass surfaces.
The openings for the air ingress/egress should be designed to ensure that fragments of broken glass do
not cause blockages.
5.3.1.5.3 Glass support
Glasses may be supported vertically or horizontally. The glasses shall not be fixed or clamped; they
have to be supported to allow free movement.
NOTE Vertically means true vertical or up to 15° either side of true vertical.
The distance between glasses affects the airflow, heat exchange and the heating time. Glass to glass
contact shall not be allowed.
5.3.1.5.4 Glass separation
The glasses shall be separated in a manner that does not hinder the airflow. The separators shall also
not hinder the airflow, e.g. see Figure 2.
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ISO 20657:2017(E)

Dimensions in millimetres
Figure 2 — Example of a vertical glass separator
The minimum separation of the glasses shall be determined during the calibration of the oven, see
5.3.1.5.5 and Annex F.
NOTE 1 Generally, a minimum separation of 20 mm is recommended (see Figure 3).
NOTE 2 If glasses of very different sizes are put on the same stilla
...