14 January 2016, 08:05
For 30 years every Fassi crane has been developed according to a precise procedure in which fatigue tests are a fundamental step to ensure there is no compromise on quality and reliability – something that has always been a core value of Fassi Gru.
Fassi has been carrying out fatigue tests on its products since 1986, an experience that is in many ways unique worldwide in the lifting industry. Over the years an impressive body of data has been acquired, making it possible to identify the optimum parameters for running tests. Therefore whenever a new model goes into production, it is the culmination of a particularly challenging process that has seen designers and testers working for several months on a detailed programme.
Each new crane under development is put through approximately 200,000 lift cycles, on average. However, in some specific cases, depending on the crane’s intended use, the number of cycles can be reformulated. For example, grab cranes to be used in duty-cycle applications, such as waste handling, are put through more test cycles. In fact, the methodical application of the testing procedure gives particularly thorough results for any components that are common to several crane; castings, for example, can be subjected to several hundred thousand cycles, even up to a million.
These tests result in design decisions being made and, but most importantly, innovations being introduced: from welding methods to the use of new steels and alloys. In addition to the fatigue test conducted in the vertical plane of the crane, to check the stresses imposed by the lifting action, another 200,000 cycles are carried out in the horizontal plane to verify all the torsional stresses induced by the rotation torque.
At the end of the test the crane is disassembled and each individual component is assessed in its entirety. In addition to the research and development team, this involves other areas as well, such as the quality control staff in the technological laboratory and the production engineers in charge of the machinery that is required to produce each component. Obviously, the fatigue tests at Fassi also cover accessories such as hydraulic extensions and rotating stabilisers, and all kinds of hydraulic or electric components.
It is important to remember that fatigue strength is influenced by a large number of factors, many of which are difficult to quantify, so a broad range of tests is required. The three factors that have a primary influence on fatigue strength are: the effects of stress concentration; the number of load cycles; and their statistical recurrence. Other factors are the static resistance of the base metal, the mean stress, residual stress, sheet thickness, stress concentrations, environmental conditions, temperature, load frequency and even the metallic coatings such as zinc plating.
Clearly you cannot “pretend” to be an expert in fatigue testing – you cannot bluff or busk it – the know-how must be acquired with perseverance and determination. With its thirty-year experience, Fassi is able to simulate working conditions that are very similar to reality.
When carrying out tests, all calculations are carried out according to parameters laid out in the recognised industry standards. From 1980 this was the DIN15018 standard and since 2004 it is the new European standard EN12999. This classification applies to the entire product range: from the small M10 in the Micro range to the imposing F2150RAL.
How are the tests carried out? The prototype is mounted on a test bench equipped with the control tools. A special formula is applied to calculate the dynamic effects to be imposed by the load handling process and then the structure is “fatigued” by acting directly onto the lifting jacks. While combining various configurations of position and outreach, this allows the pressure on the main cylinder to be kept constant (simulating constant lifting power), thus maintaining the load moment at the value of the maximum strain.
The integrity of the structure is monitored at set stages with non-destructive visual checks. Using such methods as penetrant liquids, magnaflux, ultrasounds and strain gauges, it is possible to record both the positive results and any faults found. The progress analysis then determines the corrective action required.
This iterative testing process results in a crane ready to bear the Fassi name, with no compromise on either quality or reliability.
Source: PREWE Presse weltweit, Fassi Ladekrane GmbH