Contemporary Rotating Unions for Modern Printing Machines
25/06/2009 - They operate in the background, but without them the functionality of modern printing machines would not be possible:Rotating unions.
Whether sheet-fed offset printing, web offset or gravure printing, rotating unions are the link between rotating rollers and the pipelines and hoses of the heating or cooling circuit for maintaining the temperature of ink application rollers, printing ink unit or dampening system.
Generally speaking, temperature setting and keeping of constant temperatures in the above mentioned assemblies are a material precondition for continuous and reproducible quality at highest machine speed. This is also the key to reduction of waste paper produced during start-up or production - a cost factor which must not be disregarded.
Why is the "rotating union" that important for this task?
As it guides the medium into and/or out of the rotating part, its technology and degree of development significantly affect the efficiency of the entire machine:
o Primarily by way of optimized flow channels and reduced turbulence which also means a continuous temperature profile, i.e. increased quality with reduced waste paper.
o Secondarily by considering the required energy, as modern rotating unions feature only minor pressure losses and reduced coefficients of friction so that the pump and motor rating can be lower.
In addition to the savings of costs, the reduced energy consumption also entails a reduction of CO2, an important topic today. Furthermore, the third aspect should not be ignored in this consideration: The service life of a rotating union.
Especially in this respect, chaff (low-cost product) is separated from wheat (branded product) quickly.
It is undisputed that each rotating unit which is based on the principle of the "balanced mechanical seal" is a wear part, as the mechanical seals are subject to wear although they are lubricated by the flow medium.
One cost driver can be derived therefrom easily: How often does the service department have to replace the rotating unions? Can this be affected in the scope of the regular maintenance intervals of the machine or does it imply nonscheduled (expensive) machine downtimes?
The quality philosophy of manufacturers of branded products such as DEUBLIN includes that the user has to deal with maintenance as rarely as possible, i.e. that the service life is increased.
This, however, requires consequent materials research in order to be able to use highly wear-resistant material combinations for mechanical seals. Furthermore, a high surface quality and concentricity of the mechanical seals are to be achieved in the production process as they also immediately affect the service life.
Low-cost rotating unions often lack these features. Neither the material combination nor the surface quality or the concentricity are designed to allow the operator long intervals without maintenance. In a total-cost-of-ownership analysis which also includes machine downtimes and (frequent) maintenance operations, the cost driver "low-cost rotating union" would stand out quickly.
But this experience can be avoided, if the machine manufacturer or the design engineer focuses on quality from the outset when developing the printing machines and if the user itself, e.g. as foreman, further pursues this focus during operation.
In the long run, cutting-edge technology pays off!
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