During the course on new technologies of non-destructive testing of case depth and hardness of gears, organized jointly by ASSIOT and ASSOFLUID last November at the CISAM-ERNST headquarters, the HTD and ESATEST® technologies were introduced; these provide measurements without destroying the sample while drastically cutting down on test times.
by Silvia Crespi
On November 21st at the CISAM-ERNST headquarters in Induno Olona (near Varese), ASSIOT and ASSOFLUID organized jointly a new appointment of the Training Factory. The course was focused on new technologies allowing non-destructive testing of the hardness and depth of heat treatment of gears. Open to laboratory managers operating in the material science and quality control fields, the course illustrated HTD technologies for the measurement of the thickness of heat treatment and ESATEST®, aimed at hardness control, both developed by Ernst. The works were opened by Danilo Parlatano, Global Sales Director, CISAM-ERNST, who introduced the course and announced the topics being examined. Presentations were followed, in the afternoon, by practical tests on samples provided by client companies.
An innovative system to measure the depth of heat treatment
Measurement of case depth matters in many applications, from the automotive to the aerospace industry, from machine tools to the military sector. Traditional technologies, however, present limitations linked especially
to the long time it takes to carry out tests. The HTD technology offered by CISAM-ERNST allows fast (less than a minute) and accurate measurement of surface hardened hardened layers with no need for cutting, mounting, polishing and sequential tests. The functioning principle is based on the processing of the hardness curve obtained by means of the continuous acquisition of values collected during the progressive application of the load without any influence due to collapsing or bending of the item being tested. HTD produces a single imprint applying progressively the workload and measuring at regular intervals the depth reached by the imprint. This sampling corresponds to taking a very high number of imprints at a single point. The result is a load-hardness curve which summarizes all the measurements carried out during the test.
An algorithm developed by ERNST processes the information obtained by the hardness curve and derives the value of the depth of the heat treatment and the schematic curve of the hardened superficial layer.
The absolute hardness value is converted into a Vickers hardness value using standard conversion tables.
The two machines, HTD 1500 and HTD 4000, are capable of measuring thickness up to 1.3 mm and 2.7 mm respectively. They are equipped with a stand having a great capacity and can carry out tests of large-sized parts, up to 315 mm high and 315 mm deep. The hard metal indenter has a working life of 2,500/3,000 tests depending on the type of material and the maximum established workload.
Parlatano summarizes: “Unlike traditional methods, this technology allows operators to take action immediately and to improve the quality of their production. The results cause uncertainty to diminish and improve communication between supplier and client, reducing waste and optimizing productivity. Eliminating the metallographic preparation of the sample, the time for the test and the reduction of waste allow costs to be considerably reduced. In a scenario where the importance of quality in all industries is growing, where process control and norms are being strengthened, HTD represents an added value in the measurement and in the analysis of the commercial and production segments of heat treatment. HTD provides operators with the possibility of evaluating the consistency of the heat treatment, reducing at the same time the costs and time taken to carry out the measurement”.
Hand-held and portable instruments to determine hardness
The ESATEST® technology is aimed at the measurement of hardness in points which cannot be reached with traditional instruments without destroying the item. The MTR X tester (available in hand-held and portable versions) operates according to the principle of hardness determination by means of the ESATEST® measurement of the electrical resistance patented by Ernst: the diamond indenter also works as a probe to determine the size of the imprint by means of the electrical resistance of the indenter itself. CISAM-ERNST’s Marco Alfieri explains: “This technology makes it easy to carry out the measurement operation without having to section, and therefore destroy, the item. This, for instance, holds valid for the teeth of gears, just like the troughs, crests, holes, involutes and so on. The agility of this tool, along with the endowment of accessories, makes it possible to carry out measurement in points which are difficult to reach, a “mission impossible” for traditional hardness testers”.
The instrument uses a hard indenter, with a semi-conducting surface to measure the electrical resistance. The relationship between greater penetration and lower measured resistance (load/resistance curve) allows the hardness to be determined. The curve is compared to a gauging curve previously determined with constant hardness. If the resistance measured is the same, the penetration is the same. If this result is obtained with different forces, the proportion of these forces is equal to the proportion between the hardness of the item being measured and the gauging item. The final result is a measurement of hardness. It is a simple mathematical proportion”. Because of its properties, ESATEST® is particularly suitable for items with very complex geometries, such as gears. The durometer is available in hand-held and wireless portable versions, both being very easy to use. The second version, e-handy, is based on the same principle illustrated previously, and allows to obtain, with a single test, the hardness values, detected on a wide range of loads, and on any metal (ferritic, martensitic, austenitic steels, aluminium, copper, brass and so on), which is particularly useful to control parts with surface treatments, for an immediate evaluation of heat treatment. The diamond indenter here also performs the function of sensor to determine the imprint. Many possibilities are offered by the Android application: creation and storage of a large number of measuring files, result conversion to different scales, calculation and visualization of statistics, graphs and histograms, creation and web printing of reports.