IEC 60068 2 75 Edition 2 0 2014 09 INTERNATIONAL STANDARD NORME INTERNATIONALE Environmental testing – Part 2 75 Tests – Test Eh Hammer tests Essais d’environnement – Partie 2 75 Essais – Test Eh Essa[.]
Severities
General
The severity is defined by the impact energy value chosen from 4.1.2, and the number of impacts according to 4.1.3.
Impact energy value
The impact energy value shall be one of the following, as prescribed by the relevant specification:
NOTE Figures in brackets appear in previous IEC 60068-2 standards, although no longer recommended, they may be used for historic consistency.
Number of impacts
Unless otherwise prescribed by the relevant specification, the number of impacts shall be three per location.
Test apparatus
Description
Three types of test apparatus are available to perform these tests:
The test apparatus types are categorized as Eha, Ehb, and Ehc, as outlined in Clauses 5, 6, and 7 The coordinated characteristics of the striking element are fundamentally consistent across all three tests, as detailed in Table 1 and illustrated in Figure 1.
Dimensions are in millimetres Tolerances are as per class m of ISO 2768-1, unless otherwise stated
Table 1 – Coordinated characteristics of the striking elements
The dimensions specified are D mm 18.5 (20), 35, 60, 80, 100, 125, and f mm 6.2 (10), 7, 10, 20, 20, 25, with r mm values of – – 6 – 10, 17 Adjustments should be made to match the equivalent mass, as detailed in Annex A The Rockwell hardness range is defined as 85 ≤ HRR ≤ 100, in accordance with ISO 2039-2 Additionally, for Fe 490-2, the Rockwell hardness is specified as HRE 80 to 85, following ISO 6508 standards.
The values in brackets for the equivalent mass and diameter of the striking element, applicable for energy values of 1 J or less, reflect the current test Ef Additionally, values from the previous test Eg are provided for these parameters While these older values are not recommended for coordination reasons, they continue to be utilized by certain industries for historical comparison.
Figure 1 – Example sketch of a striking element
The striking surface shall be visually examined before each impact in order to ensure that there is no damage that might affect the result of the test.
Mounting
As prescribed by the relevant specification, the specimen shall either a) be mounted by its normal means on a rigid plane support, or b) be placed against a rigid plane support
To ensure the specimen is securely supported during testing, it is essential to place it against a solid plane, such as a brick or concrete wall or floor, which should be covered with a tightly fixed sheet of polyamide.
To ensure optimal performance, it is crucial to maintain minimal air gaps between the sheet and its support The sheet must possess a Rockwell hardness ranging from 85 to 100, as specified by ISO 2039-2, and should have a thickness of about 8 mm Additionally, the surface area must be adequately sized to prevent any mechanical overstressing of the specimen due to insufficient support.
A mounting arrangement is considered adequately rigid if the displacement of the impact surface on the plane support remains within 0.1 mm when subjected to an impact with energy equivalent to that of the specimen.
NOTE 1 For specimens to be subjected to impact energies not exceeding 1 J, some examples of mounting and support are shown in Figures D.3, D.4 and D.5
NOTE 2 When the mass of the mounting is at least 20 times that of the specimen, the rigidity of the mounting is likely to be sufficient.
Preconditioning
The relevant specification may call for preconditioning; it shall then prescribe the conditions.
Initial measurements
The specimen shall be submitted to the visual, dimensional and functional checks prescribed by the relevant specification.
Testing
General
Secondary impacts, i.e rebounds, shall be avoided r R f l
Attitudes and impact locations
The relevant specification outlines the expected attitudes of the specimen and identifies specific locations where damage is most likely to occur during practical use, as well as the points of impact Unless stated otherwise, impacts should be applied perpendicularly to the tested surface.
Preparation of the specimen
The relevant specification shall state any requirements for the securing of bases, covers and similar items before the specimen is subjected to the impacts
NOTE Account may need to be taken of requirements for functional monitoring (see 4.5.4 b)).
Operating mode and functional monitoring
The relevant specification shall state: a) whether the specimen is required to operate during impact; b) whether any functional monitoring is required
In both cases, the relevant specification shall provide the criteria upon which the acceptance or rejection of the specimen is to be based
NOTE Attention is drawn to the fact that, in case of breakage of the specimen, internal parts may become hazardous.
Recovery
The relevant specification may call for recovery and shall then prescribe the conditions.
Final measurements
The specimen shall be submitted to the visual, dimensional and functional checks prescribed by the relevant specification
The relevant specification shall prescribe the criteria upon which the acceptance or rejection of the specimen is to be based.
Information to be given in the relevant specification
When a test from this section of IEC 60068 is referenced in a relevant specification, it is essential to provide specific details, especially for the items marked with an asterisk (*), as this information is always mandatory.
The article outlines essential testing parameters, including the impact energy specified in subclause 4.1.2, the number of impacts per location if different from three as noted in 4.1.3, and the types of test apparatus required under 4.2.1 It emphasizes the method of mounting in section 4.4.2, preconditioning procedures in 4.3, and initial measurements detailed in 4.4 The document also addresses the attitude and impact locations in 4.5.2, securing bases and covers in 4.5.3, and the operating mode along with functional monitoring in 4.5.4 Acceptance and rejection criteria are specified in sections 4.5.4 and 4.7, while conditions for recovery are outlined in 4.6, culminating with final measurements in 4.7.
Test apparatus
General
The test apparatus features a pendulum that rotates at its upper end, maintaining a vertical plane The pivot axis is positioned 1,000 mm above the measuring point.
The pendulum is composed of a nominally rigid arm and of a striking element complying with the requirements of Table 1
For testing large or challenging specimens, a portable pendulum can be utilized It must adhere to specific guidelines, with its pivot either fixed directly on the specimen or on a movable structure Prior to testing, it is crucial to ensure that the pendulum's axis is horizontal, its fixation is adequately rigid, and the impact point aligns with the vertical plane through the axis.
In all cases, when the pendulum is released, it shall be allowed to fall only under the influence of gravitational force.
Test apparatus for severities not exceeding 1 J
The striking element comprises a steel body with a polyamide insert having a hemispherical face Its combined mass is 200 g (150 g) ± 1 g so that the equivalent mass complies with
Table 1 Annex D gives an example of a test apparatus.
Test apparatus for severities of 2 J and above
The mass ratio of the arm to the total mass of the striking element must not exceed 0.2, and it is essential for the center of gravity of the striking element to be positioned as near as possible to the arm's axis.
In certain applications, a cord may substitute the pendulum arm, and a spherical steel ball may replace the striking element However, this practice is not advisable, as the ball does not meet the geometric specifications outlined in IEC 60068 for the striking element.
Height of fall
To produce impacts of the required severity, the striking element shall be released from a height depending on the equivalent mass of the pendulum, according to Table 2
NOTE 1 Figures in brackets appear in previous IEC 60068-2 standards; although no longer recommended, they may be used for historic consistency
NOTE 2 In this part of IEC 60068, the energy, J, is calculated taking the standard acceleration due to the earth's gravity (g n ), rounded up to the nearest whole number, that is 10 m/s 2
Testing
To prevent secondary impacts or rebounds, it is essential to hold the hammer after the initial strike by gripping the striking element while keeping the arm clear to avoid distortion.
Figure 2 – Derivation of measuring point
Test apparatus
The spring hammer consists of three principal parts: the body, the striking element and the release system
The body comprises the housing, the guide for the striking element, the release mechanism and all rigidly fixed parts
The striking element comprises the hammer head, the hammer shaft and the cocking knob
The mass of this assembly is 250 g (200 g) for severities not exceeding 1 J, and 500 g for 2 J
The force to release the striking element shall not exceed 10 N
The design of the hammer mechanism ensures that the hammer spring releases all its stored energy approximately 1 mm before the hammer head impacts the target During the final millimeter of its travel, the hammer acts solely as a freely moving mass with kinetic energy, devoid of any stored energy Additionally, once the hammer head passes the impact plane, it can continue to move freely for an extra distance of 8 mm to 12 mm An example of a test apparatus is provided in Annex E.
In order to comply with Table 1, the shape of the release head for 2 J shall be cylindrical for a length of 23 mm with a diameter of 35 mm (see Figure 3)
Measuring point Axis of striking element
Figure 3 – Shape of release head for 2 J
Influence of earth's gravity
When the spring hammer is positioned at an angle other than horizontal, the energy delivered is affected by a factor of ∆E This variation is positive for downward blows and negative for upward blows.
The formula for calculating energy transfer in a spring hammer is given by ∆E = 10 × m × d × sin α, where \( m \) represents the mass of the striking element in kilograms, \( d \) denotes the travel distance of the striking element within the spring hammer in meters, and \( α \) indicates the angle between the axis of the striking element and the horizontal plane.
This variation shall be taken into account when establishing the actual energy delivered.
Calibration
The spring hammer shall be calibrated Annex B gives a standardized preferred procedure (see
Clause B.2 in particular for 2 J) Other methods of calibration may also be used, provided that evidence is available that they give equivalent accuracy
Test apparatus
The hammer consists basically of a striking element which falls freely from rest through a vertical height, selected from Table 2, on to the specimen surface held in a horizontal plane
The striking element must adhere to the specifications outlined in Table 1, ensuring it falls along a guideway, such as three or four rails, with minimal braking This guideway should not make contact with the specimen, allowing the striking element to be free from the guideway upon impact To minimize friction, the length \( l \) of the striking element should be at least equal to its diameter \( D \), and a small gap of approximately 1 mm should be maintained between the striking element and the guideway.
Height of fall
The height of fall shall be as given in Table 2, the equivalent mass stated therein being equal to the actual mass of the striking element
The annex figures illustrate the shape and characteristics of striking elements corresponding to the six energy values outlined in Table 1 These figures calculate the lengths of striking elements for vertical or pendulum hammers with negligible arm mass If the arm mass is significant, the lengths must be adjusted to ensure the equivalent mass complies with the specifications in Table 1 (refer to section 3.2).
Figure A.1 illustrates the key component relevant to energy values of 1 J or lower, indicating that the impact face must be constructed from polyamide with the hardness detailed in Table 1.
Figures A.2, A.3 and A.4 show the striking elements applicable to energy values of 2 J, 5 J and
10 J, respectively In these cases the impact face should be made of steel with properties, including hardness, as specified in Table 1
Figures A.5 and A.6 illustrate the key elements related to energy values of 20 J and 50 J For these scenarios, the impact face must be constructed from steel with specific hardness properties outlined in Table 1 Additionally, to meet the other requirements listed in Table 1, it is essential to hollow out the end opposite the striking face.
Every edge shall be smoothed
The tolerances are as per class m of ISO 2768-1, unless otherwise stated
Figure A.1 – Example of a striking element for ≤ 1 J
Figure A.2 – Example of a striking element for 2 J
Figure A.3 – Example of a striking element for 5 J
Figure A.4 – Example of a striking element for 10 J
Figure A.5 – Example of a striking element for 20 J
Figure A.6 – Example of a striking element for 50 J
Procedure for the calibration of spring hammers
Principle of calibration
The calibration procedure involves comparing the energy generated by a spring hammer, which is challenging to measure directly, with the energy of a pendulum, determined by its mass and height of fall.
Construction of the calibration device
The assembled calibration device is shown in Figure B.1 Apart from the frame, the main parts are a bearing "a", a drag pointer "b", a pendulum "c", a release base "d" and a release device
The calibration device features a key component, the pendulum "c," illustrated in Figure B.2 Attached to the lower end of this pendulum is a steel spring, detailed in Figure B.3 This spring, made of spring steel, does not require any special treatment and is securely fixed to the pendulum "c."
Figure B.4 shows some parts on a larger scale
This spring is specifically intended for calibrating spring hammers with energy values of 1 J or less, as outlined in Table 1 For spring hammers with characteristics designed for 2 J, a different spring design for the pendulum of the calibrating device is required.
To achieve optimal friction characteristics for the pointer, a thick woven cloth is inserted between the metal surfaces of the bearing, with the piano wires bent to apply a slight force against the cloth.
Because the release device is removed during the calibration of the calibration device, the release device is fixed to the release base by means of screws.
Method of calibration of the calibration device
The calibration of the device is performed using a calibration striking element "g" sourced from a spring hammer, as illustrated in Figure B.5 Prior to the calibration process, the release device must be detached from the calibrating device.
The calibration striking element is suspended by four linen threads from suspension points located 2,000 mm above the contact point with the pendulum in its rest position When allowed to swing, the striking element must not exceed a dynamic contact point, labeled "k," that is more than 1 mm below the rest position contact point Subsequently, the suspension points are elevated by the difference between these two contact points.
When adjusting the suspension system, it is crucial that the axis of the calibration striking element “g” is perpendicular to the impact surface of the pendulum “c,” ensuring that the calibration striking element remains horizontal at the moment of impact.
When the calibration striking element is in its rest position, the calibration device is placed so that point “k” is positioned exactly at the head of the calibration striking element
To obtain reliable results, the calibration device is rigidly fixed to a massive support, for example to a structural part of a building
The height of fall is determined at the center of gravity of the calibration striking element, and this measurement can be enhanced using a liquid level device made up of two interconnected glass tubes "j" via a flexible hose One of the glass tubes is stationary and features a scale "l" for accurate readings.
The calibration striking element may be held in its upper position by means of a thin thread "m" which, when ruptured, causes the release of the calibration striking element
To scale the calibration device, a circle is drawn on the scale plate with its center aligned with the pendulum's bearing The radius of the circle extends to the drag pointer, and the zero point, labeled 0 J in Figure B.6, is marked at the position indicated by the drag pointer when it contacts the pendulum at rest.
The calibration is made with an impact energy of 1 J, which is achieved with a height of fall of 408 mm ± 1 mm, with a calibration striking element of 250 g
To determine the 1 J point on the scale plate, the suspended calibration striking element is allowed to swing and strike point "k" on the pendulum's spring After the impact, the calibration striking element remains stationary This process is repeated a minimum of 10 times, and the 1 J point is calculated as the average of the drag pointer's readings.
To determine the other points on the scale, a straight line is drawn from the center of the circle to the 0 J point The orthogonal projection of the 1 J point onto this line is marked as P The distance between the 0 J and P points is then divided into 10 equal segments Perpendicular lines are drawn through each division point to intersect the circle, which correspond to impact energy values ranging from 0.1 J to 0.9 J.
The same principle can be used for extending the scale beyond the 1 J point The division of the scale plate "f" is shown in Figure B.6.
Use of the calibration device
To calibrate the spring hammer, place it in the release base and operate it three times using the release device, ensuring that it is not released manually.
To calibrate the spring hammer, the striking element is positioned differently for each operation The actual impact energy of the specimen is determined by calculating the average of three readings obtained from the calibration device.
Key a bearing b drag pointer c pendulum d release base e release device f scale plate k point where blows are applied, i.e impact point
Figure B.3 – Steel spring of pendulum "c"
Figure B.4 – Details of calibration device
Key c pendulum of Figure B.1 g calibration striking element h linen threads j glass tubes k impact point l scale
NOTE For clarity only, the pendulum "c" of the calibration device is shown in this figure
Figure B.5 – Arrangement for the calibration of the calibration device
Figure B.6 – Division of scale plate "f"
When is an impact test appropriate?
An impact test is essential for equipment intended for use in areas with unrestricted access, where the likelihood of impacts is high Conversely, for equipment designed for restricted access areas, an impact test may still be relevant, but it typically involves a lower severity level.
It is particularly applicable when the equipment is of a brittle nature.
Choice of test apparatus
IEC 60068 outlines three test methods designed to yield comparable results Achieving repeatable and reproducible outcomes relies significantly on the specifics of the test apparatus, more so than in typical IEC 60068 standards.
The selection of test apparatus is influenced by the orientation of the surface and the required energy level Not all testing methods are universally applicable; for instance, a pendulum hammer is suitable only for vertical surfaces without overhangs, while a vertical hammer is typically restricted to accessible horizontal surfaces When the specimen cannot be moved or adjusted, options become limited The spring hammer offers versatility, as it can be utilized in various positions, provided there is adequate space and the impact energy does not exceed 2 J However, for higher energy levels, using a spring hammer may pose handling difficulties and safety risks for the operator.
Choice of energy level
The energy of impacts is determined by the mass and speed of the striking object, which can be influenced by its fall Theoretical energy levels are provided in Table C.1, aligning with the values specified in IEC 60068.
Table C.1 – Energy levels in joules
Mass of striking object kg
The values of Table C.1 correspond to blows perpendicular to the specimen surface
In situations involving vandalism or car accidents, significantly higher energy levels can occur, necessitating the implementation of additional protective measures like barriers or walls.
Information for testing
The temperature of the specimen may influence the results of the tests and the relevant specification should take this into account, when applicable
Impact tests can be conducted in conjunction with other assessments; however, it is important to note that certain standardized tests must be carried out on new specimens, thereby excluding any prior hammer tests.
The main performance criteria should be derived from how the operational and survival characteristics of the specimen are influenced by mechanical impacts
The other important aspect is safety, which can be the prime consideration in certain circumstances
Example of pendulum hammer test apparatus
The pendulum hammer test apparatus depicted in Figure D.1 is designed for energies up to 1 J The striking element adheres to the specifications outlined in section 5.2.2 and is illustrated in Figure D.2 The apparatus features a steel tube arm with a nominal external diameter of 9 mm and a nominal wall thickness of 0.5 mm.
Specimens should be affixed to an 8 mm thick, 175 mm square plywood sheet, in accordance with ISO 1098, and secured at the top and bottom edges to a rigid bracket of the mounting fixture, as illustrated in Figure D.3 The mounting fixture, weighing 10 kg ± 1 kg, is attached to a rigid frame using pivots, with the frame anchored to a solid wall.
The mounting design allows for precise specimen placement, ensuring the point of impact aligns with the vertical plane of the pendulum pivot It enables horizontal movement and rotation of the specimen around an axis perpendicular to the plywood surface, while also allowing the plywood to rotate about a vertical axis.
Specimens should be mounted on plywood as per standard service procedures If direct mounting is not feasible, an appropriate adapter must be specified according to the relevant guidelines Examples of adapters include those for flush-type switches (see Figure D.4) and lamp holders (see Figure D.5).
Figure D.2 – Striking element of the pendulum hammer for energies ≤ 1 J
Figure D.4 – Adapter for flush-type switches
Figure D.5 – Adapter for lamp holders
Example of spring hammer test apparatus
Figure E.1 illustrates a spring hammer test apparatus that adheres to Clause 5 for energies up to 1 J The body assembly has a mass of 1,250 g ± 10 g The hammer head is securely attached to the hammer shaft, ensuring that the distance from its tip to the impact plane (the plane of the cone truncation) aligns closely with the spring compression values specified in Table E.1 at the moment of release.
Table E.1 – Kinetic energy of striking element
Kinetic energy ( E ) just before impact Approximate spring compression with spring constant of 2,75 × 10 3 N/m
NOTE The approximate value of the kinetic energy in joules, just before the impact, can be calculated from the following formula:
F is the force exerted by the hammer spring, when fully compressed, in newtons;
C is the compression of the hammer spring, in millimetres
The energy stated above is achieved in the horizontal position
The cone weighs around 60 g, and its cone spring generates a force of about 5 N at the moment the release jaws are ready to release the striking element The release mechanism springs are finely tuned to apply just enough pressure to maintain the release jaws in the engaged position.
To operate the apparatus, pull the cocking knob back until the release jaws engage with the hammer shaft groove Position the release cone perpendicularly against the specimen's surface and gradually increase the pressure, allowing the cone to move back until it contacts the release bars This action triggers the release mechanism, enabling the hammer to strike the specimen.
Figure E.1 – Spring hammer test apparatus
ISO 1098, Veneer plywood for general use – General requirements
4 Dispositions communes à toutes les méthodes d’essai aux marteaux 40
4.5.2 Positions du spécimen et points d'impact 43
4.5.4 Mode opératoire et contrôle fonctionnel 43
4.8 Renseignements que la spécification particulière doit donner 43
5.1.2 Appareillage d'essai pour les sévérités ne dépassant pas 1 J 44
5.1.3 Appareillage d'essai pour les sévérités de 2 J et plus 44
6.2 Influence de la gravité terrestre 46
Annexe A (normative) Formes des pièces de frappe 48
Annexe B (normative) Procédure pour étalonner les marteaux à ressort 51
B.3 Méthode d'étalonnage du dispositif d'étalonnage 51
C.1 Quand un essai de choc est-il conseillé? 58
Annexe D (informative) Exemple d'appareil d’essai de marteau pendulaire 60
Annexe E (informative) Exemple d'appareil d’essai de marteau à ressort 63
Figure 1 – Exemple de pièce de frappe 42
Figure 2 – Détermination du point de mesure 45
Figure 3 – Forme de la tête de déclenchement pour 2 J 46
Figure A.1 – Exemple de pièce de frappe pour ≤ 1 J 48
Figure A.2 – Exemple de pièce de frappe pour une valeur 2 J 48
Figure A.3 – Exemple de pièce de frappe pour une valeur 5 J 49
Figure A.4 – Exemple de pièce de frappe pour une valeur 10 J 49
Figure A.5 – Exemple de pièce de frappe pour une valeur 20 J 50
Figure A.6 – Exemple de pièce de frappe pour une valeur 50 J 50
Figure B.3 – Ressort en acier du pendule "c" 54
Figure B.4 – Détails du dispositif d'étalonnage 55
Figure B.5 – Dispositif prévu pour l'étalonnage du dispositif d'étalonnage 56
Figure D.2 – Pièce de frappe du marteau pendulaire pour énergies ≤ 1 J 61
Figure D.4 – Adaptateur pour interrupteurs pour pose encastrée 62
Figure E.1 – Appareil d'essai de marteau à ressort 64
Tableau 1 – Caractéristiques coordonnées des pièces de frappe 41
Tableau C.1 – Niveaux d'énergie en joules 58
Tableau E.1 – Énergie cinétique de la pièce de frappe 63
Partie 2-75: Essais – Test Eh: Essais au marteau
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