Mechanical, or rather electronic seals

3To optimise their performance, mechanical seals use electronic control that regulates their behaviour on the basis of working conditions. This not only improves performance and boat reliability, but also reduces maintenance costs.

The world of mechanical seals

Microtem has always been distinguished for its technological evolution, and recently has introduced an electronic control for its mechanical sealing systems for marine use. The aim of this technological innovation is to optimise the performance of systems that for years have been the core business of Microtem. The company, founded on the basis of long experience of industrial plant and shipbuilding, has always concentrated its attention on the problems of mechanical seals, developing specific competence in the development of technological solutions for this market niche. Mechanical sealing is, as is known, a problem that exists in all plant with rotating shafts immersed in different fluids. In the marine sector, in particular, a deteriorating seal affects the efficiency of propulsion and so the performance and reliability of the vessel. Inheriting wide experience built up in the naval sector, through revision of mechanical seals for yachts, oceangoing and cruise ships, Microtem personnel have studied in depth the problems that make mechanical seals and important working element in the propulsion systems of vessels. Reliability, efficiency and ease of maintenance are among the objectives that Microtem pursues constantly in designing its solutions, which have evolved over the years thanks not only to the experience of the designers but also to the availability of specific equipment in the company’s La Spezia headquarters for experimentation, production and testing.

Mechanical excellence

To attain a high level of reliability and performance, the Microtem range of mechanical seals for marine use draws on design experience that is aware of the problems connected with vibration, misalignment and stress common to all machines with rotating shafts. In vessels with an inboard motor and an outboard propeller the problems of unwanted flows of fluid between contiguous spaces occur where the drive shaft passes through the hull, and it is here that efficient mechanical seals are needed. Since the seal is assured by the close proximity between surfaces in contact and moving over each other, it is important that the system guarantees efficiency even with the inevitable heating produced by the moving surfaces in contact. To achieve the twin result of perfect adherence and friction reduction, the technology perfected by Microtem uses a high level of smoothing of the surfaces, with a careful process of lapping that makes it possible to reduce roughness to about 0.1 µm. To do this, the lapping machines in Microtem use a patented technology that exploits the vaporising of synthetic diamond, ensuring not only a high level of surface finish but also the possibility of working on specific materials such as graphite, ceramics, steel and carbides. Among the structural peculiarities of the MTM400, the meeting point of creative and innovative design solutions, is a double series of springs that make it possible to compress both the opposing faces of the sealing system. With the compression of the two surfaces obtained with this structure, it is possible to compensate better the inevitable geometric imperfections between the shaft and the hull, such as angular and radial misalignment caused by vibration, resonance, turbulence and other stresses present in the propulsion systems of a vessel. In addition to optimising the compensation of geometric non-linearity with a precise structural solution and a careful choice of materials, the MTM400 has features that simplify installation and maintenance. The quality of the seal depends on a careful choice of materials and sophisticated quality controls carried out using special measuring machines, while its long life is guaranteed by the use of a pump ring that can dissipate the heat generated on the rotating surfaces. Microtem not only makes a high efficiency mechanical seal, but also perfects equipment that makes it possible to simplify maintenance and so reduce running costs.

Electronics in the seal

In line with the performance targets of its mechanical seals and their reliability and maintenance, Microtem has recently equipped its MTM400 sealing system with electronic control that guarantees continuous monitoring of the levels of efficiency and gives indications on the state of wear, suggesting maintenance programs to optimise the use of the propulsion system. And so the MTM470 was born, the first mechanical sealing system for propeller shafts with electronic control. The MTM470 combines the innovative mechanical characteristics of the consolidated MTM400 system and electronic device that makes it possible to use software to manage its operating conditions in real time. The seven sensors in the MTM470 system acquire a series of data on the operating conditions of the seal, such as radial and axial vibrations, temperature and pressure of the cooling liquid, temperature of the moving surfaces, speed in rpm and the level of wear on the moving surfaces. Using standard communication protocols such as CAN BUS, CAN OPEN and TCP/IP, the data acquired in this way are transmitted in real time to a control panel which records them and, when required by the operator, shows a structured display which uses different colours to highlight the actual condition of the seal. Green means the operating conditions are within the limits set by Microtem, yellow means an alert while red indicates a state of alarm in the system requiring immediate intervention to avoid breakage of the seal. The data are not only displayed but are processed by a latest generation chip which, using an algorithm perfected by Microtem, diagnoses the current conditions of the seal and suggests the maximum number of operating hours it can still guarantee. This indication is particularly important for managing preventive maintenance, which is fundamental for top range vessels and for those used in activities where the economic effects of downtime are particularly important. Thanks to the information collected by the control panel, the operator can intervene on the state of monitoring of the seal, setting the display of the “lifetime” which is constantly updated so as to display current working conditions and the risk of faults in the future. This service is provided by the control panel since it can manage not only the sensors connected to the mechanical seal but also those connected to the propulsion system, for example monitoring temperature and vibrations. The control panel can also acquire commands and evaluate if it is possible to carry them out, thus itself taking action to avoid damage caused by faults. In the case of seal breakage, for example, the system could intervene by stopping the engine and making it possible to isolate the hull. “With MTM470”, says Mattia Chiodetti, co-owner and marketing manager of Microtem, “we have added to a robust and well-tested mechanical device electronic control that can add new functions to the seal, but we didn’t stop there. We wanted remote management of the control panel, entirely made in Italy, making it able to transmit data for controlling an entire fleet, that is monitoring conditions on several boats. According to the type of vessel propulsion, it is also possible to carry out timely and comparative analyses for effective cost management by careful programming of preventive maintenance.” This electronic element gives the traditional mechanical seal a characteristic that makes it a true system, rather than a simple working component. The system can also manage not only sensors but also web cams and other accessories that can provide a wide range of information that can be transmitted using various communication protocols via GSM, satellite, Bluetooth or Wi-Fi. Conceived and produced to supply a tool for monitoring mechanical seals on board, the MTM470 is today an instrument that can manage an entire fleet. Medium and long-term analysis of the data produced by the MTM470 system in fact make it possible to identify the most frequent faults and the best configurations, recording also ordinary and extraordinary maintenance operations.  “The characteristics of the MTM470”, says Chiodetti, “make the system particularly suitable for mega yachts, professional and military craft, where downtime due to faults causes considerable economic damage that is difficult to quantify.”

 

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