From the Rolls-Royce experimental archive: a quarter of a million communications from Rolls-Royce, 1906 to 1960's. Documents from the Sir Henry Royce Memorial Foundation (SHRMF).
The requirements, construction, and use of a R.A.B.R.M. rubber hardness gauge.
| Identifier | ExFiles\Box 93\1\ scan0166 | |
| Date | 27th June 1935 guessed | |
| 2 The Requirements of a Rubber Hardness Gauge. The ideal hardness gauge should be inexpensive, portable, simple and rapid in operation, consistent in its readings, independent of the personal factor, adapted to the testing of rubber in a variety of forms and compositions, and its indications should be in standard scientific units rather than in terms of an arbitrary scale. The hardness is expressed by the number of hundredths of a millimetre which an indenting ball, either 1/8 or 1/4 in. diam., is depressed into the sample, when loaded with a 1 kg. weight. In the R.A.B.R.M. gauge simplicity and rapidity of operation are attained by reducing the measurement to a single operation, as against two required in the usual dead-load types of hardness tester. This is done by eliminating the need for setting the instrument to zero before each measurement. The gauge is applicable to the testing of small flat specimens, sheets of any size, and rollers of any diameter from 1 1/8 in. upwards. Consistency of readings is attained by using a dead weight to provide the indenting force, thus eliminating all possibility of variation with lapse of time, or between one instrument and another, such as may occur in spring-loaded instruments. Fig. 3. Measurement of thickness of Tensile Test Ring. Measurements of Thickness of Tensile Test Rings (Fig. 3). In making tensile tests with ring test-pieces, as on the well-known Schopper machine, the thickness of each ring (i.e. the dimension parallel to the axis) must be measured. This is normally done by a hand calliper gauge, with which several readings must be taken round the circumference of the ring and these readings averaged. This is a tedious operation, and the necessity for averaging introduces the possibility of errors. The new R.A.B.R.M. gauge is provided with a fitting which enables an average thickness to be measured directly in one operation, thus saving a considerable amount of time and eliminating errors. Permanent Set. It is often required to measure the permanent set of broken ring tensile test-pieces or rings which have been stretched under some standard conditions. The accurate measurement by ordinary means of the length of a broken ring, or a ring that has been stretched and cut open, is troublesome owing to the difficulty of holding the ring out straight without stretching it. In the new gauge a simple device has been incorporated for measuring directly the percentage permanent set of such specimens without the danger of errors due to stretching. 3 CONSTRUCTION OF THE INSTRUMENT SECTIONAL DIAGRAM ILLUSTRATING PRINCIPLE OF R.A.B.R.M. HARDNESS TESTER Diagram Labels: 1 KG., LOADING PLATFORM, GAUGE STEM, GAUGE CASE, REFERENCE MEMBER, RUBBER SPECIMEN, INDENTATION. Fig. 4. The new instrument measures hardness as the depth in hundredths mm. of the indentation by a 1/8 in. or 1/4 in. diameter ball under a load of 1 kg. A dial micrometer gauge, graduated in .01 mm., is provided with a stem projecting at both top and bottom. The lower end carries the indenting ball, and the upper end terminates in a knob on which rests a removable platform to carry the 1 kg. weight (see Fig. 4). The gauge slides vertically on a pillar fixed to the U-shaped base of the instrument. On the bottom of the gauge is a flat circular foot having a central opening for the passage of the gauge stem. The foot rests on the sample under test, and provides a reference surface from which the depth of the indentation is measured. To enable the gauge to be used for testing rubber-covered rollers, the under side of the base is provided with two pairs of parallel grooves, and two rods are supplied which can be fitted into these grooves so that the instrument will rest on a cylindrical surface with the rods parallel to the axis of the latter. (See Fig. 2). The inner grooves are used when testing small rollers (diameter 1 1/8 in. upwards) and the outer grooves for larger ones (diameter 5 3/4 in. upwards). The measurement of the average thickness of a ring test-piece is effected by using a disc carrying three toes which rest on the ring at equidistant points. A seating in the centre of the disc engages and depresses the gauge stem; this seating is adjustable to enable the zero of the instrument to be correctly set. A supporting disc, fitting over a boss on top of the gauge case, carries and centres the ring. When the 3-toed disc is then placed on the ring, the gauge indicates directly its average thickness at the three points of contact with the toes (see Fig. 5). The present instrument is similar to that described by Daynes, Johnson and Scott (I.R.I. Trans., 1930, 6, 63) but with two important improvements: (i) elimination of the need to use a standard ring to set the zero for thickness measurements, (ii) the provision of a special gauge with two sets of graduation figures for hardness and thickness respectively (as these run in opposite directions) and with an auxiliary dial indicating whole millimetres, in addition to the main .01 mm. scale. The gauge now supplied, therefore, differs slightly from that illustrated. PRICE A 12011. GAUGE, designed by Daynes, Johnson and Scott, of the Research Association of British Rubber Manufacturers:—to measure hardness, thickness of ring test-pieces, and permanent set. Complete apparatus including stand, gauge reading in mm. and .01 mm., 1/8 in. and 1/4 in. balls, loading platform, 1 kg. weight, 3-toed disc and supporting disc for thickness measurements, rods for hardness tests on rollers, and glass plate. All in leatherette-covered wood case, 7 x 5 1/2 x 4 1/2 in., with instructions for use . . . £ s. d.{John DeLooze - Company Secretary} . . 7 15 0 0 | ||