The Firth Hardometer

This machine will test the hardness of medium and hard steels down to 1 m/m thick, and soft steels and non-ferrous metals down to 2 m/m thick when using a standard 120 Kg. load cylinder and a 1 in. microscope objective, or down to 1/2 m/m. thick and 1 m/m thick respectively when using a 30 Kg. load cylinder and a Jin. microscope objective. The maximum space between the anvil and the head is 8in., unless specially specified otherwise.

On repetition work, readings can be taken at the rate of over 100 per hour on the machine. The scale of impression diameters and Brinell Hardness Numbers corresponds exactly to that of the 3000 Kg. 10 m/m. ball Brinell Machine.

The machine is provided with a sliding head which is readily adjusted to take materials of different articles being tested. The load is applied through a specially calibrated spring and trip mechanism, and in such a manner that only the exact load can be applied. The whole of the mechanism is entirely enclosed and protected. The machine may be supplied alternatively -(1) with 120 Kg. load cylinder and lin. microscope objective for testing medium and hard steels down to 1 m/m. thick, and soft metals down to 2 m/m. thick, which covers all ordinary testing purposes ; or (2) with 30 Kg. load cylinder and Jin. microscope objective for testing medium and hard steels down to below ) m/m. thick or soft metals down to 1 m/m. thick. No. 1 method is the most suitable for workshop use, and is preferable where only the thicker range of materials require to be tested ; No. 2 method being a special-purpose alternative or for scientific research work. With the addition of a special diamond indenter the machine in either form will test the hardest of hardened steels.

With every machine is supplied a specially designed microscope of high magnification, permitting the rapid and reliable measurement of impressions; a standard Hardness Check Test Piece, the necessary ball retaining caps, Hardness numeral tables, two dozen spare balls, a waterproof cover, and a book of instructions. The diamond and tables appertaining thereto are supplied as an extra. The machine may be supplied with whichever load cylinder and objective is preferred.

It is recognised that in testing the hardness of steel the use of the hardened steel Brinnell ball is limited. Materials exceeding 600 on the Brinell scale tend to deform the ball, and there is very little discrimination in the hardness values above this range. Moreover, owing to unavoidable variations in the quality of the balls used for test, the results obtained on hard samples are frequently inconsistent as well as misleading as to relative values. To avoid such unsatisfactory conditions the tool used for making the " indentation " should substantially exceed the hardness of the sample to be tested.

It is now recognised that the best method of testing hardened steel of over 600 Brinell is to use a diamond, and with the " Hardo-meter" diamond " indenters " can be used by merely changing the ball for such an indenter. This change can be readily effected, and a suit-aide adapter is supplied with each diamond.

Diamond points-that is, diamonds of specially selected quality, cut and polished and set in a special holder-are supplied as an extra. These points, besides being very accurately made, are robustly mounted and are quite suitable for workshop use. By including one of these in the equipment the machine is then available for testing specimens up to the hardest High Speed or other tool steel, and will be found of exceptional value for the use of the Inspection Departments of motor car and other Works, where it is the practice to work to a standard of hardness for the hardened parts. It is advisable that the hardness numbers obtained when using the diamond indenter should be referred to as " Diamond Hardness Numbers " to distinguish them from the Brinell numbers obtained by the usual method with a steel ball.

Instructions To Users

Preparing the Article to be Tested : In many cases and for various reasons the majority of metals bear a skin of either harder or softer material than the internal bulk. For this reason, as well as to provide a flat surface, a small flat, sufficiently deep to remove the unrepresentative skin, should be filed or ground cn the article to be tested, then finally polished with No. O emery cloth wrapped on a suitable stick, to remove scratches and to ensure a reasonably good surface for measuring purposes.

Making The Impression

The article should be supported in a solid manner and the ball or diamond brought into contact with the prepared surface by means of the hand wheel, after which it will make approximately one complete turn when a click will be heard, and the hand wheel motion arrested. The exact load will then have been applied. The hand wheel should then be turned in the opposite direction, which will withdraw the indenter.

The adjustable anvil permits of irregular - shaped articles being readily tested, and a facing is prepared on one side of the anvil for the fixing (by the user) of a suitable spring or other clamp for the purpose of holding light and unbalanced articles such as table blades, etc.

To change the ball or diamond, the 2 m/m. or 4 m/m. balls bed on a small pad piece, and are held in position by a knurled cap. This cap should not be screwed up too tightly. The diamond is held by a similar cap, but the diamond setting in this case takes the place of the loose pad piece. When using a 1 m/m. ball, a pad piece of similar shape to the diamond setting is provided, and the ball should be held in position by the application of a little grease.