John Crane - Polymers
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Polymerisation is the first basic step in plastics production. Depending on the monomers, it can be carried out in bulk, in a solution, or in an emulsion.  If monomer solutions are introduced into the reactor, they are first filtered to separate impurities. Filtration is also used after polymerization to recover monomer residues from polymer solutions/suspensions and to return them to the polymerization reactor. Thermoplastics are an important class of plastic raw materials, like polyamide (PA), polymethyl methaycrylate, polycarbonate, or polyether ether ketone (PEEK). After polymerisation, these materials are either directly granulated for further processing elsewhere, or they are directly melted and processed by extrusion or injection moulding.  Our screen changers and melt filter systems are used in this stage.

Fibre production

There is an increasing demand for nonwovens for the production of technical textiles, including filter media, textiles for the clothing industry, hygiene articles, etc.  Synthetic fibres form a large share of the raw materials. In addition to the well-known polyesters, nylon and viscose, which is based on natural resources, are used. Polyurethane fibres are essential parts of elastic textiles. High performance fibres from chemically and thermally resistant polymers, as well as bi- or multi-component fibres, enable new technical applications. In addition to the production of nonwovens, synthetic fibres are used for stabilizing materials, in tyres for example.

To obtain required technical features at minimum material consumption, e.g. for achieving lower flow resistance with low specific weight, the trend is towards finer fibres. Development of micro-fibre or nano-fibre media is made possible by means of sophisticated spinning and melt blown processes. The fine nozzles, which are essential for the production of ultra-fine fibres are prevented from being blocked by particles or gels by melt filter systems and filters for spinning solutions.

Film production

There are three processes for film production depending on the polymer used. These are extrusion from the melt, stretching (mono- and biaxial) of a deformable solid, or casting of a polymer solution.  Casting is used with polymers that do not melt or which only melt under disintegration, like polyimides.  Casting processes are also of interest for the production of ultra-thin films from thermoplastic polymers, like polyester or polycarbonates. Filtration is an essential step within film production to pre-treat melts or polymer solutions. Depth filters retain undissolved polymers or gels from solutions, which would be detectable as specks within the cast film. These specks would significantly reduce the tear resistance of the films.  The production of ultra-thin films for challenging applications, e.g. in medical technology, is made possible by the high level of purity of the filtered melts and solutions. 

Membrane production

Most technical membranes for gas and liquid filtration with filter grades in the sub-micron and the molecular range are made from polymers. Producing flat sheet membranes is quite similar to foil production, while hollow fibre membranes are made by spinning through a ring spinneret by means of a central air or water jet. The chemical composition of the casting and spinning solution respectively, as well as the process parameters, influence the pore size distribution of the membrane. Colloids or solid particles in the solution must be avoided in order to exclude membrane defects (like outsized pores) or embeddings that affect mechanical stability.  Leading membrane producers use Seebach filters for pre-treating polyethersulphon solutions prior to the production of ultrafiltration membranes.

Cable sheathing

Power cables are insulated by sheathing with plastics like polyethylene or polypropylene. The higher the voltage and the more extreme the conditions surroundings of the cable, the higher the demands on stability and freedom of defects in the sheathing. This is particularly true for submarine cables that connect offshore wind power turbines with each other or with the land. Again our melt filter systems ensure the highest purities of the melts prior to sheathing.

Production of polymer products

Polymer melts are used for the production of polymer products by injection moulding, and for the production of foils or fibres. The melts can be classified on the basis of their viscosities and flow behaviour depending on the temperature, their chemical structure, and the level of polymerisation. Melt filter systems ensure that polymer melts entering processing machines are free of particles and gels. This prevents defects in the finished products. Seebach is the market leader in the design of customized and product-specific melt filter systems and their optimum adaption to existing production plants. We produce filter candles, filter discs, and complete melt filter systems. Problems with gels are solved by specially adapted depth filter systems.

John Crane has first-class references in the field of high-performance polymers. Our Seebach product design and construction experts produce optimum filter systems without dead zones and lengthy dwell times.

The John Crane Seebach product line includes:

Filter Candles / Cartridges are cylindrical filter elements with flat or pleated media. Filter candles and filter cartridges are used in almost all applications in the industrial solid-liquid separation, particular the polymers industry.

Leaf Discs are used in catalyst recovery and deployed mainly in the plastic melt technology. A filter disc is welded and available in three hub designs: hard hub, semi-hard hub and soft hub.

Filter Discs are flat, with sealed edges, single or multilayer packages of filter media. These are used essentially as “screens” in a line, e.g. in the melt filtration in so-called screen changers.

Melt Filters are especially large area filters designed for the processing of plastic melts. They are used for high pressures and high temperatures to clean plastic melts of gels, degenerated material and debris.