BS EN 60068-2-75:2014 Environmental testing Part 2-75: Tests – Test Eh: Hammer tests

BS EN 60068-2-75:2014 Environmental testing Part 2-75: Tests – Test Eh: Hammer tests.
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.
In order to ensure that the specimen is rigidly supported, it may be necessary when performing the test to place the specimen against a plane solid support, for example a wall or a floor made of brick or concrete, covered by a sheet of polyamide which is tightly fixed to the support.
Care shall be taken to ensure that there is no appreciable air gap between the sheet and the support. The sheet shall have a Rockwell hardness of 85 <HRR <100 according to ISO 2039-2. a thickness of approximately 8 mm and a surface area such that no parts of the specimen are mechanically over-stressed due to the supporting area being insufficient.
The mounting arrangement is deemed to be sufficiently rigid if the displacement of the impact surface of the plane support does not exceed 0,1 mm when struck by an impact applied directly to it with the same level of energy as for the specimen.
NOTE I For specimens to be subjected to impact energies not exceedIng 1 J, some examples of mounting and support are shown in Figures D3, D.4 and 0.5.
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.
4.3 Preconditioning
The relevant specification may call for preconditioning; it shall then prescribe the conditions.
4.4 Initial measurements
The specimen shall be submitted to the visual, dimensional and functional checks prescribed by the relevant specification.
4.5 TestIng
4.5.1 General
Secondary impacts, i.e. rebounds, shall be avoided.
a) Impact energy *
b) Number of impacts, if other than three per location
c) Type(s) of test apparatus to be used
d) Method of mounting *
e) Preconditioning
f) Initial measurements*
g) Attitude and impact locations *
h) Securing of bases, covers and similar components
i) Operating mode and functional monitoring*
j) Acceptance and rejection criteria *
k) Conditions for recovery
5 Test Eha: Pendulum hammer
5.1 Test apparatus
5.1.1 General
The test apparatus consists basically of a pendulum rotating at its upper end in such a way as to be kept in a vertical plane. The axis of the pivot is at 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 heavy, voluminous or difficult-to-handle specimens, a portable pendulum may be used. It shall comply with the above description but its pivot may be fixed directly on the specimen or on a movable structure. In this case, it shall be ensured that, before the tests, the axis of the pendulum is horizontal, that its fixing is sufficiently rigid and that the impact point is in the vertical plane passing through the axis.
In all cases, when the pendulum is released, it shall be allowed to fall only under the influence of gravitational force.
5.1.2 Test apparatus for seventies not exceeding I 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 0 gives an example of a test apparatus.
5.1.3 Test apparatus for seventies of 2 J and above
The ratio of the mass of the arm to the combined mass of the striking element shall not be greater than 0,2 and the centre of gravity of the striking element shall be as close as is practicable to the axis of the arm.
For some particular applications, the pendulum arm is replaced by a cord and the striking element by a spherical steel ball. This is not recommended as the ball does not conform to the geometry of the striking element specified in this part of IEC 60068.
5.2 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.
6 Test Ehb: Spring hammer
6.1 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 seventies not exceeding 1 J, and 500 g for 2 J
(see Table 1 for tolerances).
The force to release the striking element shall not exceed 10 N.
The configuration of the hammer shaft, the hammer head and the means for the adjustment of the hammer spring is such that the hammer spring has released all its stored energy approximately 1 mm before the tip of the hammer head reaches the plane of impact. For the last millimetre of its travel, prior to impact, the striking element is thus, apart from friction, a freely moving mass having only kinetic energy and no stored energy. Moreover, after the tip of the hammer head has passed the plane of impact, the striking element is free to travel, without interference, over a further distance of between 8 mm and 12 mm. Annex E gives an example of a test apparatus.
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).
6.2 Influence of earth’s gravity
When the spring hammer is used in a position differing from the horizontal, the energy actually delivered is modified by E. This variation is positive when the blows are applied downward, and negative when applied upward:
iE = 10 x m x d x Sin a where
m is the mass of the striking element, in kilogrammes;
d is the travel of the striking element inside the spring hammer, in metres:
a is the angle of the axis of the striking element with the horizontal.
This variation shall be taken into account when establishing the actual energy delivered.
6.3 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.
7 Test Ehc: Vertical hammer
7.1 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 characteristics of the striking element shall comply with Table 1. The fall of the striking element shall be along a guideway, for example three or four rails, with negligible braking. This guideway shall not rest on the specimen and the striking element shall be free of the guideway on striking the specimen. In order to reduce the friction, the length I of the striking element shall not be smaller than its diameter D, and a small gap (for example 1 mm) shall be provided between the striking element and the guideway.
7.2 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.BS EN 60068-2-75 pdf download.BS EN 60068-2-75:2014 Environmental testing Part 2-75: Tests – Test Eh: Hammer tests