Maag’s gear pump for EPDM films for building industry

maag gear pump for epdmFOR technical requirements in particular, plastics are being used more and more and undergoing constant development in order to satisfy ever-growing demands. In the construction sector, because EPDM sealing films especially need to deliver excellent protection against leakage over the lifetime of a building, new mixtures represent a constant challenge to suppliers. In order to develop EPDM films further, Swiss equipment supplier Maag has launched a gear pump as a laboratory solution. This will enable the end product, film, to be optimised to a laboratory scale and “tuned” for new large-series applications.

Although penthouses with sloping walls have their charms, the Mediterranean flat-roofed construction has become more and more commonplace in Central Europe too since the 1970s. Although flat roofs were quite striking to begin with, since they couldn’t cope with the weather conditions prevalent in the region, they have been improved massively since then and, thanks to a plastic, are now given an almost “endless life”. This material is EPDM (ethylene propylene diene monomer), a terpolymer elastomer that is rubber-like and belongs to the family of co-polymers (as defined by DIN7864). EPDM is manufactured from the by-products of ethylene and propylene.

Sealing webs have been extruded from EPDM for the construction sector since the 1960s. These sealing webs are primarily used to seal flat roofs, back-ventilated facades and ponds. The advantages of EPDM are clear. Sealing webs made from EPDM can stretch by up to 500% and are permanently elastic, even in extreme temperature fluctuations between -40°C to +120°C. A lifespan of decades makes these films the ideal sealing solution.

In light of the undisputable advantages in terms of durability offered by the saturated polymer framework, the realm of possible practical applications is extremely diverse. The Deutsche Industrienorm organisation talks about the M Group – the opposite of which is the R Group, to which monomers with unsaturated hydrocarbon chains such as natural rubber (NR) or styrene-butadiene rubber (SBR) belong – with limited possibilities.

Classic applications for EPDM films include:

• Roof and construction seals
• Seals, such as O-rings, sliding ring seals and flat seals
• Hoses for hot water and steam applications
• Absorbent mats for improved thermal insulation
• Pond liners.

Conventional EPDM rubbers have an ethylene content of between 45% and 75% weight. Polymers with a low ethylene content (45-55% weight) are amorphous and have the best flexibility in cold conditions. As the ethylene content increases, so does the crystallinity. Pure, linear polyethylene, therefore, is highly crystalline. An EPDM with a moderate ethylene content (55–65% weight) is partially crystalline.

Terpolymers with an ethylene weight of over 65% have larger crystalline areas and therefore behave like thermoplastic elastomers. These have a strong resistance to tearing, even in their un-crosslinked state. The diene content of commercial products is between 2-12% weight, corresponding to a proportion of 3 and 16 double bonds per 1,000 C atoms. A higher diene content causes faster crosslinking, greater solidity and less residual deformation. The resistance to ageing, weathering and ozone, on the other hand, dwindles as the diene content rises. Therefore, depending on the requirements in hand, the right mixture needs to be produced in order to deliver the properties needed, such as higher rigidity or resistance.

Maag Pump Systems has been familiar with the use of EPDM for many years, with its largest gear pumps in the Polymer-polyrex series used in the manufacturing of these rubber-like applications, it decided to use its expertise to develop EPDM films further. Hence, solutions for batch operation, small plants and laboratory solutions are available as innovation drivers in order to facilitate the testing of new methods and procedures on a small scale. This experience can later be transferred in a targeted manner to mass production. Industrial pumps made from stainless steel with a special, wide inlet geometry are particularly ideal for these types of laboratory solution.

For removal from the reactor, the company is promoting its recently developed heated version of the therminox-V pump size 28/28 (TX-V 28/28). This gear pump features a special inlet geometry. The design facilitates the removal of highly viscous fluids, such as pre-polymers (up to 4 million mPa/s) under vacuum. The pump is directly flange-mounted on the suction side flange on the reactor in order to keep the NPSH as small as possible. The pump housing is the only thing that reveals that the pump is suitable for the toughest, corrosive applications.

When developing this test system for EPDM manufacturing, not only did process temperatures of 150°C need to be taken into account for this special design but so too did a viscosity of up to 1.7 million mPa/s at an NPSH of 5.5 mbar, an inlet pressure of 5.2 bar and an outlet pressure of 10.2 bar. For this reason, Maag used shafts made from 1.4112 stainless steel and bronze-aluminium bearings for this customer-specific application. The shafts and bearings can withstand the process parameters of pressure and temperature. Emergency running properties were also needed.

To ensure durability, a gland packing is used as the seal, which is also simple to maintain. In order for the process to be run with the exclusion of an atmosphere, and in order to prevent reaction of the EPDM medium with air, the seal was made up of a locking, spring-loaded and adjustable packing. Another advantage of the use of an adjustable seal is the prevention of “bearing pick-up” at high pressure, caused by inadequate lubrication.

This pump series has been developed especially for highly viscous media and prepolymers with a low inlet pressure for use in laboratories and small plants. (PRA)