Application challenges

Chemical industry

Basic chem­i­cals plants are gen­er­ally dom­i­nated by pumps; agitator ap­pli­ca­tions can only be found in certain processes, such as HDPE (high-den­sity poly­eth­yl­ene) man­u­fac­tur­ing. The poly­mer­iza­tion reactors used in this area are equipped with me­chan­i­cal seals, as are often the cen­trifuges in which the HDPE is sep­a­rated out down­stream of the reaction. The shafts of the reactors and crys­tal­liz­ers used in PTA (purified tereph­thalic acid) pro­duc­tion are also equipped with me­chan­i­cal seals.

Fine chem­i­cals plants gen­er­ally contain dis­con­tin­u­ous processes and many dif­fer­ent machines and equip­ment and offer a wide range of possible ap­pli­ca­tions for me­chan­i­cal seals. Suc­ces­sive pro­duc­tion steps, such as mixing, reacting and sep­a­rat­ing are typical here. The processed batches are often rel­a­tively small, while the processes are so­phis­ti­cated and the products often very valuable. Flexible, multi-pur­pose plants, usually equipped with ag­i­ta­tors, reactors, filters, dryers and other special equip­ment, are pre­dom­i­nantly used.

The par­tic­u­lar chal­lenge for sealing tech­nol­ogy arises from the dif­fer­ent man­u­fac­tur­ing processes and the crys­tal­liz­ing, paste-like, highly viscous or highly cor­ro­sive media under changing pressure and tem­per­a­ture con­di­tions.

EagleBurgmann agitator seals have become the es­tab­lished standard in the chemical industry. They are robust and durable, sig­nif­i­cantly con­tribut­ing to the plant avail­abil­ity.

Pharmaceutical and food industry

The phar­ma­ceu­ti­cal industry is a special area of the fine chem­i­cals industry. In addition it requires machines, seals and supply systems which are easy to clean.

The sealing system is designed ac­cord­ing to hygienic design rules. To achieve a hygienic design, con­sid­er­a­tion must be given to the design of the seal and in­stal­la­tion space and to im­por­tant criteria in the material se­lec­tion. Parts of the seal in contact with the product must be suitable for CIP (Cleaning in Place) and SIP (Ster­il­iza­tion in Place). Other features of seals in this category are a minimum of dead spaces, open gaps, springs pro­tected against the product and smooth, polished surfaces.

The ma­te­ri­als of the sealing system must always fulfil the statu­tory re­quire­ments for the ap­pli­ca­tion. Phys­i­o­log­i­cal harm­less­ness along with chemical and me­chan­i­cal re­sis­tance play a central role here. Nat­u­rally, the ma­te­ri­als used must also not affect food­stuffs or phar­ma­ceu­ti­cal products in terms of odor, color or flavor.

EagleBurgmann uses high quality standard ma­te­ri­als, such as silicon carbide (Q1) and food grade carbon graphite (B) as sliding ma­te­ri­als, EPDM (E1), PTFE (T, T2), FFKM (KL) and silicone rubber (S1, S2) for the sec­ondary seals and finally 1.4571 (316 Ti) (G), 1.4404 (316 L) (G), 1.4435 (316 L) (G) and 2.4610 (Hastel­loy®-C4) (M) as con­struc­tion ma­te­ri­als.

EagleBurgmann has defined hygienic cat­e­gories for me­chan­i­cal seals and supply systems in order to simplify the se­lec­tion of the right com­po­nents for man­u­fac­tur­ers and endusers. Hygienic re­quire­ments on the seal are linked to design features of the seal and supply system. The higher the class, the higher the re­quire­ments on ma­te­ri­als, surface quality and sec­ondary seals (with the cor­re­spond­ing con­se­quences in terms of cost).

Steel and glass-lined vessels

The two cat­e­gories of steel vessels and glass-lined vessels have a sig­nif­i­cant in­flu­ence on the version of the me­chan­i­cal seal. The EagleBurgmann me­chan­i­cal seal series Sec­coMix481 (dry-run­ning), AGSZ481 (gas-lu­bri­cated) and M481 (liq­uid-lu­bri­cated) are designed for use on steel vessels. With the Sec­coMix461, AGSZ461 and M461 series, the parts in contact with the product, such as the con­nect­ing flange, are glass-lined.

Vessels coated with enamel are cat­alyt­i­cally inert. This means that they do not affect the product due to re­ac­tions with the vessel material. They are also highly re­sis­tant to chem­i­cals and are easy to clean, which is why glass-lined devices are often used for ap­pli­ca­tions with strict hygiene re­quire­ments.

Large shaft diameter, heated shafts, large axial movements

The trend is moving toward in­creas­ingly large plants and thus to larger machines and shaft di­am­e­ters. In plants for man­u­fac­tur­ing PTA (purified tereph­thalic acid), the standard shaft di­am­e­ters for reactors and crys­tal­liz­ers are now 200 mm (7.87") or more. The largest shaft diameter to date for such a facility is now 480 mm (18.90").

The di­men­sions and weight of the cor­re­spond­ing me­chan­i­cal seals of up to 1,500 kg sets new chal­lenges for the seal and machine man­u­fac­tur­ers and for the assembly team on site at the plant.

The dif­fi­culty with such large seals is to be able to control the de­for­ma­tion of the sliding seal parts and thus the gap geometry over the entire sliding face. This is a pre­con­di­tion for low and stable leakage and a minimal sliding face tem­per­a­ture, which has a decisive effect on the service life of the seal. To de­ter­mine the optimum gap geometry, ex­ten­sive cal­cu­la­tions are carried out by our in-house experts which are then verified by means of test runs.

Heated shafts, as are often found in dryers or filter dryers, for example, are another chal­lenge for the seal as they sig­nif­i­cantly increase the tem­per­a­ture at the seal. The right se­lec­tion of design and sliding ma­te­ri­als, the elas­tomers and the bearings and bearing grease are par­tic­u­larly im­por­tant for guar­an­tee­ing the seal func­tion­al­ity.

Not least it is es­sen­tial to control large axial shaft de­flec­tions of the type that occur due to thermal ex­pan­sion in paddle dryers with bearings on both sides or due to active lifting move­ments in the case of nutsche filters.

EagleBurgmann has con­sid­er­able ex­pe­ri­ence in the sealing of tech­ni­cally chal­leng­ing pa­ra­me­ters and im­ple­ments in­no­v­a­tive and safe sealing so­lu­tions in close col­lab­o­ra­tion with man­u­fac­tur­ers and endusers.

ATEX conformity

Solvents and other ex­plo­sive sub­stances are used in many process steps with the result that a po­ten­tially ex­plo­sive at­mos­phere can arise. In these cases, the seals must meet the re­quire­ments of the ATEX di­rec­tive (2014/34/EU). The agitator seal is gen­er­ally treated as an equip­ment, rather than a machine com­po­nent, so a separate ATEX cer­tifi­cate of con­for­mity must be issued for it.

We have there­fore carried out EU type ex­am­i­na­tion on our standard series for ag­i­ta­tors and special ma­chin­ery and are able to issue a de­c­la­ra­tion of con­for­mity for them. In­di­vid­ual ac­cep­tance tests can also be carried out for en­gi­neered seals. In this case, the seal is tested for its tem­per­a­ture be­hav­iour on a test rig. EagleBurgmann is qual­i­fied by the TÜV to in­de­pen­dently carry out its own type ex­am­i­na­tions and in­di­vid­ual ac­cep­tance tests.