T H E PROBLEM OF M E A S U R I N G T H E H A R D N E S S OF

AND C E R T A I N O T H E R N O N M E T A L L I C M A T E R I A L S

(UDC 620.178.182.2)

A. S. B e n d i n a n d B. E. G a l i n k i n

Translated from Izmer i t e l ' naya Tekhnika, No. 9, p. 86, September, 1966

HARDBOARD

The conditions specified by GOST 9627-61 are not suitable for evaluating the hardness of sma l l - s i ze compo- nents and specimens made of hardboard. In evaluating the hardness of small hardboard components, even with the min imum load (490 N) and bal l d iameter (5 mm) specified by the standard, these components are damaged con- siderably and the hardness characterist ics are not obtained. Moreover, the smaIlest thickness of the tested compo- nents specified by the standard must not be less than 10 mm.

In carrying out our exper imenta l work we had to find a method and instruments which would permit us to

evalua te the hardness of smal l and thin hardboard components2 As a result of our experiments we adopted Brinell 's method (GOST 9012-59) with the smallest possible parameters for attaining an indentation of the tested component. These parameters consist of P = 153 N, D = 2.5 mm, and the exposure t ime on the load amounts to 60 sec, i .e . , these are the min imum parameters used for evaluat ing the hardness of nonferrous alloys.

The instrument used by us consisted of hardness gauge type TP which, in addition to its basic purpose of test- ing Vickers hardness (GOST 2999-59), can also be used for testing Brinell hardness at small loads and small d i am- eter bails.

Owing to the bad i l luminat ion of the tested specimen 's surface, the bal l indentat ion was not sufficiently clear. Therefore, the opaque l ight of gauge TP was replaced by a more powerful i l luminator type OI-7, which was mounted on the microscope 's revolving head. The light was shone onto the surface at a large angle, thus making the dark imprint of the bal l c lear ly visible on the i l luminated surface of the tested component. Moreover, the la terai direc- tion of the luminous flux does not t i re the exper imenter ' s eyes. The d iameter of the indentation can be convenient- ly measured with the microscope incorporated in the TP gauge.

This method was used by the authors of this ar t ic le for testing not only hardboard but also various plastics

(with a low elast ic deformation). The Brinell hardness values thus obtained with the TP gauge were in good agree- ment with the published data. In part icular , this method was used for checking the hardness of theplas t ic ~overing

of renovated bearing beds, whose thickness is below 2 mm.

On the basis of the above exper imental results we can recommend the appl icat ion of this method under pro- duction conditions for evaluating the hardness of small plastic components. It is even more convenient for evalua- ting the hardness of nonmeta l l ic mater ia ls to use hardness gauge T P 2 , in which the image of the indentation, the scale, and the reading graduations of the microscope are simultaneously projected onto a frosted screen.

In order to obtain on the frosted screen of gauge TP-2 a clear image of the tested hardboard or plastic speci- mens ' surfaces, the la t ter were ground, coated by means of a brush with dry aluminum paint, and polished with a f lannel rag. The remaining ext remely thin layer of paint provided a clear image of the specimen's surface on the frosted screen. A comparison of the hardness number obtained on the same specimens with and without paint did not revea l any essential differences in hardness. Any discrepancies obtained in certain cases were within 2% of the

measured hardness value.

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