ISO 21876:2020

INTERNATIONAL ISO
STANDARD 21876
First edition
2020-09
Machinery for forestry — Saw chain
shot protective windows — Test
method and performance criteria
Machines forestières — Ecran de protection contre la projection
d’éléments de scies à chaîne — Méthodes d'essai et critères de
performance
Reference number
ISO 21876:2020(E)
©
ISO 2020

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ISO 21876:2020(E)

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© ISO 2020
All rights reserved. Unless otherwise specified, or required in the context of its implementation, no part of this publication may
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ISO 21876:2020(E)

Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Test equipment. 2
5 Cutting attachment . 3
5.1 Guide bar . 3
5.2 Chain speed . 3
5.3 Saw chain . 4
6 Test samples and pre-conditioning . 4
6.1 Test samples . 4
6.2 Test temperature . 4
7 Pre-calibration of test arrangement . 5
8 Set up of window test sample in test rig . 5
9 Test procedure . 6
10 Total number of test runs . 7
11 Performance requirements . 8
12 Labelling . 8
13 Test report . 8
Annex A (normative) Saw chain stopping device .10
Bibliography .12
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ISO 21876:2020(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
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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
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www .iso .org/ iso/ foreword .html.
This document was prepared by Technical Committee ISO/TC 23, Tractors and machinery for agriculture
and forestry, Subcommittee SC 15, Machinery for forestry.
Any feedback or questions on this document should be directed to the user’s national standards body. A
complete listing of these bodies can be found at www .iso .org/ members .html.
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ISO 21876:2020(E)

Introduction
On the basis of a risk analysis, the types of saw chain breakage can be determined and a saw chain shot
protective window selected that provides protection against these risks.
Saw chain shots can be generated if the saw chain is broken on the upper or lower side of the guide bar
as well as when broken at the nose sprocket. ISO 11837 provides requirements for a saw chain guarding
system that provides protection against saw chain breakage on the cutting (lower) side of the bar.
When a saw chain is broken on the upper side or at the nose sprocket, the guarding system according to
ISO 11837 does not protect from saw chain shots generated in the direction of the guide bar seen from
position of the drive sprocket.
This document establishes a test method and performance criteria for windows intended to provide
protection against saw chain shot.
The test apparatus specified in this document is designed to simulate the situation in which the saw
chain is broken. The end of the saw chain passes the drive sprocket in the guide bar plane. At different
saw chain speeds and combinations of distance to the saw chain breakage, the break force, guide bar
geometry and saw chain preload will throw the saw chain in a curve, producing a whiplash that can
create a saw chain shot.
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INTERNATIONAL STANDARD ISO 21876:2020(E)
Machinery for forestry — Saw chain shot protective
windows — Test method and performance criteria
CAUTION — The test method specified in this document involves the use of processes which can
lead to a hazardous situation. The test creates saw chain shots. Under no circumstances shall
the test be performed without the protective enclosure for the test apparatus in place. The
protective enclosure is only to be removed when rotating parts are standing still.
1 Scope
This document specifies a test method and corresponding performance requirements for saw chain
shot protective windows on forestry machines equipped with a chain saw for cutting, harvesting or
processing as defined in ISO 6814. It also applies to machines that have been modified to perform
cutting, harvesting or processing (such as excavator) with a chain saw cutting attachment.
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 536, Paper and board — Determination of grammage
ISO 11837, Machinery for forestry — Saw chain shot guarding systems — Test method and performance
criteria
EN 13984, Flexible sheets for waterproofing — Plastic and rubber vapour control layers — Definitions and
characteristics
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:
— ISO Online browsing platform: available at https:// www .iso .org/ obp
— IEC Electropedia: available at http:// www .electropedia .org/
3.1
saw chain shot
object flying with high speed and consisting of one or more parts (drive links, side links, cutters) of a
broken saw chain
3.2
relevant saw chain shot
saw chain shot (3.1)
— consisting of an assembly of one or more pieces of saw chain joined by up to two rivets;
— consisting of no more than one assembly (excluding additional loose parts of saw chain generated
during the breakage event);
— that does not hit the test sample clearly sideways; and
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ISO 21876:2020(E)

— with shot angle (3.9) of 0° ± 12°.
3.3
maximum saw chain speed
C
highest saw chain speed under no load, recommended for a given combination of cutting attachment
(3.4) and machine
3.4
cutting attachment
combination of saw chain, guide bar and drive sprocket mounted on the harvester head or grip saw
3.5
saw chain shot protective window
window that provides protection to the operator of the forestry machine from saw chain shots (3.1)
generated from a broken saw chain
3.6
shot measurement panels
two planes used for detecting and measuring the saw chain shot (3.1) direction and shot speed
3.7
shot indication panel
plane used for indicating a saw chain shot (3.1) passed through the window test sample
3.8
shot through
saw chain shot (3.1) completely passing through the saw chain shot protective window (3.5) and the shot
indication panel (3.7)
3.9
shot angle
angle between the saw chain shot (3.1) direction and a perpendicular line to the window test sample
Note 1 to entry: See item G in Figure 3.
4 Test equipment
4.1 Test apparatus, as described in ISO 11837 or equivalent, shall be used for generating the saw
chain shots against the window test sample. The saw chain guarding system including saw casing shall
not be attached. A device for mounting the window test sample shall be attached to the test rig.
4.2 Drive unit, shall be capable of maintaining a constant saw chain speed of ±2 m/s during breakage,
taking into account the increased force involved in the breakage of the saw chain.
NOTE One way to accommodate this is using an electric motor (15 kW and 50 r/s) with a belt transmission
gearing up the speed four times and with a flywheel mass of 15 kg mounted on the drive shaft (360 mm in
diameter and 19 mm in thickness).
4.3 Saw chain speed control, shall be possible to run and adjust the saw chain speed with a maximum
tolerance of ±2 m/s.
4.4 Drive shaft speed measurement, used to verify the saw chain speed with a maximum uncertainty
of ±1,0 % of the reading.
4.5 Saw chain lubrication system, shall lubricate the saw chain.
4.6 Saw chain stopping device, as specified in Annex A or an equivalent means.
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ISO 21876:2020(E)

4.7 Protective window test sample fixture, shot indicat
...