RTM
Resin Transfer Moulding is a resin injection process for which Rotec uses polyester, vinylester or epoxy resins as required by the client, associated with fiberglass reinforcement in the form of veil, chopped strand mat and a wide range of roving or mat/roving association. Using these materials, high quality products can be manufactured, with high strength to weight ratios, with corrosion resistance adapted to the particular application, and with dimensional precision and guaranteed reproduction of all properties. Advantages The disadvantages of the process are especially in the case of high-pressure injection the high investment costs for the moulds, the injection equipment and the hydraulic presses. Further more the total control of the process from initial design through all stages of production requires a great deal of experience.
Five phases
The RTM process consists of five phases; placement of the reinforcement, mould closure, resin injection, resin cure, and finally demoulding or removal and final trimming. Prior to beginning the process one needs to manufacture the mould, generally in steel, generally in two sections, to a high level of precision, and equipped with the required resin inlet/outlet connections.
To begin the moulding process one places the layers of fiberglass reinforcement in predetermined size, shape and weight into the open mould. The mould is then closed and a clamping force is applied. The third stage of the process requires the injection of the matrix material (resin, hardeners or catalysts, pigments etc), using one of three possible procedures; vacuum injection, low pressure injection or high pressure injection. Once the injection phase is completed, curing is achieved either at ambient temperature, or, depending upon the nature of the resin used, by the application of heat. The final phase requires that the flange be removed from the mould and be trimmed to remove any excess resin.
To a large extent the process is automated and therefore has significant advantages over alternative labor intensive activities such as hand lay up or spray up methods. These advantages include:
The RTM process is still gaining importance in the manufacturing sector. On the one hand it is replacing compression moulding and spray up technologies due to the high surface qualities obtained, and on the other hand it is being employed with increasing frequency where mechanical properties are of utmost importance.
High Quality
Because of the high quality required by users of composite Flanges, Rotec decided to specialize in the high pressure resin injection, whereby, using this technique, an especially high fiber content can be attained, with volume percentages between 35 to 50% (approximately 60 to 75% fiber content by weight). The fiber content, along with precise fiber orientation and the properties of the resin system are the determining facts in the obtaining of high quality products.
Rotec has developed the RTM technology even further and have built up years of experience in the development of proprietary technology. The glass fiber material, either as chopped strand mat, woven roving or mat/roving combinations is cut precisely with an advanced CNC cutting device, and is then laid as a ready made preform into the open mould. When the mould is closed, the layers of reinforcing material are pressed together using an hydraulic press, yielding products with a high glass content as indicated above.
Resins
Polyester, vinylester or epoxy resins are injected into the closed mould. The core material may include such materials as polymer concrete. The precise dimensions and composition of the products are based upon initial tests and calculations carried out at the TNO Institute and the engineering company BPO, both located in Delft, using Finite Element Analysis. This initial data has been constantly refined and updated based upon product testing and long term behavior in the field.
In addition to Flanges, and in the same line of production, Rotec also produces Manholes, Manhole Covers, panels and custom made products using the RTM method.