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Various ducts and sluice-gates are installed on large marine engines and are used for introducing seawater if required for cooling the engine. Composite parts elements have been developed by the DJP Company to replace their traditional metallic counterparts while bringing many advantages. Within the Vaneo program, DJP has bound thus a partnership with its customer the SEMT-Pielstick firm (now Man Diesel), the SERAM (a laboratory of the ENSAM school), and SPL Mecatronic (Cluster of enterprises specialized in mechanics of the Seine Amont area) to build up this new solution.
(Published on October - November 2007 – JEC Magazine #36)
(1) JEAN-PIERRE MATTEÏ - GÉRANT, DIRECTEUR TECHNIQUE D J P
(2) PHILIPPE PINAULT - RESPONSABLE BUREAU ETUDESMOTEURS MAN DIESEL
(3) HÉLÈNE RAMBERT - DÉLÉGUÉE GÉNÉRALE AU SPL MECATRONIC SEINE AMONT PR. ABBAS TCHARKHTCHI RESPONSABLE DU LABORATOIRE LIME (ENSAM)
Sea water Cooling ducts and sluicegate installed on large marine engines are usually made in a foundry from cast iron or steel. The technical developments of such engines have resulted in special localizations driving harsher promptings on equipments with potential risks of worse failures. Studies have been performed with the aim of making the devices lighter and reducing their exposure to the sort of severe vibrations with which they normally have to contend. At first, the devices were made of titanium but the results were not sufficiently conclusive to be adopted permanently. DJP, one of the specialists in producing hollow “in-one-shot” devices from composite materials designed and created monolithically with no need for assembly or adhesives, has entered into a joint venture with SEMT-Pielstick, SERAM (ENSAM), and SPL Mecatronic, to research applications for such composite products. The plans and specifications produced by the SEMT-Pielstick partner required special skills in the following areas: maintaining the pressure (until 6 bars); ensuring that the material could withstand vibrations; guaranteeing no fatigue fail from during the lifetime of the product (10 years), ensuring watertightness; that materials permanently exposed to seawater did not corrode and guaranteeing the geometry and especially the interchangeability between existing products and new products.
The development has been focused on the making of the two following products, both part of the engine water cooling circuit: a Y-shaped duct with an inner diameter of 140 mm and an outer size of 450 x 450 x 300 mm3.(figure 1).
The Y-duct is a bronze insert specially desi-gned to ensure the function of sectioning off a partition wall, ensuring that the coupling is watertight but without destroying the liner into which it is counter-sunk. It is created by means of two flanges created in one piece with the body of the duct. Water tightness is ensured by contact with the polyethylene flange of the liner which is reinforced by the composite. These flanges have waterproof threaded joints that are screwed into the materials. One of the arms of the elbow joint has a rigorously precise external geometry that is ensured by the design adopted by DJP. This feature is necessitated by the function of coupling to an external duct, connected by means of a special “marine” joint.
A linking box assuring a two ways sluicegate function (figure 2). The outer dimensions of this gate are of 340 x 350 x 370 mm3.
The valve body is a dual-conduit distributor that incorporates the same features as the Y-duct. To ensure that it functions correctly, it has internal devices that are incorporated into the liner, that enable a deflecting valve made of a composite to be inserted which, depending on its position, can diver the liquid into one or other of the directions chosen. This valve is operated from outside which means its must have special provision to ensure the movement while guaranteeing that it is watertight through the liner and the composite. In this arrangement, the liner ensures the water tightness and the composite the mechanical resistance. The difficulty has been to ensure that the valve was completely watertight when at rest on one or other of the surfaces. Mechanical resistance and distortions of the valve body were calculated through finite elements method using COSMOS software (figure 3).
The results of the calculations were used to define the Y-duct whose mechanical properties were similar. These two devices, which are polymorphous hollow bodies, are entirely made of composite materials, flanges included, in « one shot » without any assembling or gluing. They make up a block to take seawater (figure 4). The two products present an interface that is strictly identical to the materials used in conjunction with each other, such as the threaded joint on the surface of the liner flange and stainless steel fixing inserts countersunk into the composite and crossing the liner. The Mecatronic cluster made the assembled parts as inserts in
ducts and sluice-gates of the « Vaneo » program. The design of the sluice-gate mould has been carried out by the Mecatronic cluster while DJP kept the design of the Y-duct one. Finite analysis computations have been made by the cluster under the DJP specifications. Specification requirements led to a separation of functions architecture. The « watertightness » function is ensured by an inner thermoplastic liner, separately made, with the help of SERAM, monolithically without any weld. The “mechanical” function is ensured by a composite materials casing surrounding the liner in which stainless steel inserts are embedded to allow the fastening of the two products on the engine cooling circuit. One of the development difficulties has been to combine thermoplastics with thermoset materials.
Each of the two products is designed and produced using the following components:
A plastic (special polyethylene) liner, manufactured by rotational moulding, that is completely waterproof to the outside and through its design avoiding any contact between the fibres of which the structure is composed, and the liquid carried in the devices.
Consequently, stress is not put on the galvanised couplings linking the various components that are needed for the operation of the devices. The rigidity of this core enables it to be used as an inner lining during the manufacturing operation. The adjustment has been made by SERAM together with DJP. Rotational moulding tools have been designed and made by DJP according to SERAM advices.
This reinforcement is placed as a preform on the liner serving as the core. It is relatively thick for economic reasons:
Thus, the definition of the two products presented design difficulties which were removed as soon as the decision was made to separate the various functions required. The manufacturing difficulties were particularly numerous, the main ones being:
These functions were ensured in these two products (sluice-gate and Y-shaped bypass) in a hollow body requiring neither assembly nor adhesive, and by means of RTM (Resin Transfer Moulding). Furthermore, these composites consist of thermoplastic materials combined with thermoset materials which together are able to meet the demands of the various functions to be covered.
The added value of composites
The qualities of composite materials in terms of vibration filtration and of ability to withstand fatigue as well as of the natural frequencies of items made of them, added to the considerable weight gain (in the order of 7 to 8 for the programme under consideration), made possible to guarantee a long lifespan for the on loaded equipments adopted with great probability of success.
Materials used at sea are exposed to a particularly aggressive environment. Due to their resistance to such an environment, these composites make it possible to considerably reduce the costs of maintenance of such materials and procure an overall cost of use for such materials that is of great interest, despite the cost of the raw materials and the cost of shaping them.
All advantages of composites expressed in response of the program specifications have been used: time life (corrosion, vibrations, and mechanical resistance), watertightness, and superstructures lightening. The lightening has been made essential due to the really specific position of these products of which the cantilever assembly exhibited important risks facing vibrations.
The program development length has been of one year and a half. Several parts are already used in marine engines and the experimentation at sea is continuing. Seven Y-ducts and three sluice-gates have been necessary to validate the “VANEO” program. Four Y-ducts and one sluice-gate are under test at sea.
Introduction into general service of these devices and their derivatives on marine engines should have to allow return on investments in very few years from the time that all the duct and/or valve body shapes can be produced using the techniques perfected through the VANEO program. The partners are ready to invest in derivative applications and thus to pay off the investments they have made.
Furthermore, this programme allowed showing that large marine engines can be significantly lightened while benefiting from greater longevity in a difficult environment. This leads to predict that the end-user will have a real financial interest in choosing such techniques.
The achieved set « duct / sluice-gate » opens great prospects in terms of corrosion resistance, time life, mechanical stresses withstanding and lightening of engines and superstructures.
Every commercial marine construction is in position to incorporate numerous devices of this type, especially small and medium-sized fleets.
Here are few examples and update of these two techniques which can be seen in many application sectors now.