Pumping at the heart of Composites

By Edward Barrington, Slack & Parr Ltd.

The precision gear pump has been used to meter different polymers in the man-made fibre production process for over 70 years and is sometimes referred to as the ‘heart’ of the machine.  It usually operates constantly 24/7 with minimal maintenance, high expectations of output consistency and often in arduous installations.

The constituent components of Composite materials are no different, from Carbon Fibre to Aramid Fibre, the base yarn needs geared booster pumps to boost / pressurise and control the flow of the polymer through the machine. From there, high precision gear spinning pumps are used to very accurately meter the polymer and extrude the polymer through spinnerets to actually form the shape of the yarn.

The performance of the gear metering pump is hugely influenced by the design resulting from the process conditions supplied at the point of order or quotation.  The selection of material, application of surface treatments and even decisions, which result in microns of component dimensional difference, can greatly influence the performance and life expectancy.

Carbon Fibre is produced from Acrylic fibre, and this acrylic fibre is processed with solvents of either N-Dimethylformamide (DMF) or Sodium Thiocyanate. The latter requires the pump materials to be far superior to that of a pump for the DMF process.

Aramid fibres use the Sulphuric Acid as the processing solvent, this again requires the use of some very specialised pump materials for both corrosion resistance and wear resistance.

To convert the Acrylic Fibre to Carbon Fibre it is then processed, through a series of furnace’s to create the thermos-chemical reaction that converts the fibre to greater than 90% Carbon.

It is these fibres that are combined with resins that are weaved, knitted, braided or stitched in to the composites structures that are becoming ever more commonplace in our daily lives.

Slack & Parr are proud to work with the majority of the market leaders for the production of Acrylic / Carbon Fibre and Aramid Fibres.

Image 1: Typical 2 outlet, solid Stellite Aramid spinning pump

Selection of Gear Pumps for Manmade Fiber Polymer Extrusion

By Richard Hallsworth, Slack & Parr Ltd

The gear pump used to meter polymer in the man-made fiber spinning process is sometimes referred to as the ‘heart’ of the machine.  It usually operates constantly 24/7 with minimal maintenance, high expectations of output consistency and often in arduous installations.

Consequently, when there is a problem with the overall process of fiber manufacture, attention soon centers on the performance and or the condition of the polymer metering pump.

Although damage is often found within the metering pump such as either broken parts or damaged critical surfaces, in the vast majority of cases this damage is caused as a result of problems elsewhere upstream in the process rather than a defined and clear gear pump problem.

The performance of the gear metering pump is hugely influenced by the design resulting from the process conditions supplied at the point of order or quotation.  The selection of material, application of surface treatments and even decisions, which result in microns of component dimensional difference, can greatly influence the performance and life expectancy.

It is, therefore, surprising that in too many instances end-users are reluctant or fail to understand the implication of supplying vague, inaccurate or incomplete process conditions to the gear pump manufacturer.

At the very minimum, to provide a product that will work satisfactorily, the gear pump supplier must be informed of the following:

  • Polymer / dope type
  • Viscosity of polymer /dope
  • Operating temperature
  • Minimum Inlet pressure
  • Maximum Outlet pressure
  • Required thru-put

For more standard applications, this information is in most cases adequate, but more data will allow the gear pump manufacturer to optimize the product, such as:

  • Polymer / dope additives
  • Abrasive / acidic / aggressive properties of polymer dope, additives or solvents
  • Required operational duty cycles
  • Possible process fluctuations
  • Cleaning and maintenance

These are all additional factors that combine to implicate the overall performance and lifetime of the gear pump.  All these parameters and possibly others can be made available for consideration at the design stage and will result in the optimization of the final gear pump product.

Gear metering pumps supplied for more standard PET or PA6 applications are manufactured from fully hardened high quality tools steels from a narrow band of ISO steel grades; the basic component geometries being formed prior to specialist heat treatment.  The heat treatment specification may vary depending upon the part with considerations of toughness and outright harness required.  All final dimensions are achieved in the hardened state during grinding operations.

More difficult applications often require pumps at least partially manufactured from more exotic alloy materials with sometimes several different materials combined in a pump assembly.  To resist heavy wear, abrasion and possible chemical corrosion, surface treatments may need to be applied to heavy duty and critical parts.  Component dimensional tolerances to microns will still be required to be maintained, hence, surface treatments need to be carefully selected and evaluated.

Typical efficiency curve for correctly specified gear metering pump

In recent years, new developments have allowed advanced plasma coatings to become technically and commercially viable while material selection can now go beyond metallic alloys to ceramic and even engineered plastics.

With the gear metering pump being such a critical component of most man-made fiber processes, it is important that the end-user and manufacturer fully understand the expectations and limitations of the product. While a manufacturer may have years of experience in the design and supply of gear pumps and will able to make suggestions relating to performance and economics, the end-user will know the idiosyncrasies of the product in daily operation and will often have valid  suggestions to improve efficiency and commercial performance.  The best results will always be achieved when both parties work as partners and share information.

Slack & Parr gear pumps have been involved in the manufacture of manmade fibers for many years and their first gear pump was supplied in 1947.

A dedicated Sales and Engineering department is employed and proposals can be provided for all applications directly from technical data sheets.  If customers already have competitor products or need enhancements within existing space envelopes then solutions can also be provided.

In developing products for special and difficult applications it is often necessary to sign confidential I.P. agreements.  These can be used to protect the I.P. of both parties and are often necessary when projects start at the development stage with a long -term target of production equipment.

Over 1,500 different designs comprising standard range products and made to order customer request products have been supplied.  Gear pump capacities range from 0.017cc/rev to 600cc/rev and applications range from metering of de-mineralized water to booster / transfer of aramid dope.

All products are supported via the U.K. factory and repair centers in the U.S. and China.

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