Is maintaining troublesome plant wasting valuable resources?

Whether you’re responsible for maintenance, reliability, continuous improvement or process engineering, or whether you’re an operations or quality manager, we are constantly challenged to:

• Improve product quality
• Improve process reliability
• Improve condition monitoring
• Increase efficiency
• Reduce downtime
• Reduce manufacturing costs
• Reduce unscheduled maintenance

This can be especially challenging, in the food, pharmaceutical and chemical processing industries where many production processes depend heavily on large mixing and blending equipment. Applications are varied, from powder blenders for the manufacture of pharmaceuticals and protein shakes to steam mixers for cooking ready meals. There are a huge range of rotary blade, plough and paddle mixers and blenders available to blend, dry, cook and homogenise.

The size of the plant and processing duties alter the magnitude of issues experienced but there are several typical issues that they have in common. 

Unlike high speed rotary pumps, which are typically well balanced with minimal shaft run-out, many mixing and blending process equipment types inherently suffer from run-out and eccentric shaft movement. 

Furthermore, the length of the shaft means that span between the supporting bearings can often be significant – leading to shaft deflection.  

Also, due to thermal cycling and subsequent thermal expansion and contraction during operation, the seal and bearing arrangement must be able to allow and compensate for this. The process media needn’t be heated for this to occur. The shearing motion of the mixing and blending process can create sufficient heat as to cause thermal expansion of the shaft.

These characteristics can be further exacerbated with the addition of powders, solids, liquids and slurries that create additional torsional loads on the shaft along with shock loads.

To add further complexity, many seals used are a shaft contact seal. That is to say that the seal running surface is in contact with, and runs against the shaft, which causes friction. 

The friction generated has several potentially detrimental effects, including:

1.     The seal can wear down the shaft leading to shaft damage requiring expensive repair or replacement

2.     The seal contact face experiences wear leading to seal failure and replacement

3.     Worn sealing materials can migrate into the process media

4.     The frictional heat generated can damage the process media

There are ways and means to work with the highlighted issues such as applying a wear sleeve to the shaft, using low friction seals or adding a cooling and lubricating media to the seal area. 

However, these are not always practical solutions as they can add layers of cost and complexity. Furthermore, the use of cooling media is not always practical in a hygienic production environment, or during a drying process or dry blending applications.

Especially in the case of large mixers and blenders, the maintenance and replacement of seals can be challenging. The weight and bulk of the shaft, along with the inherent need to de-couple the drive and remove the bearings, is time consuming and often requires heavy lifting equipment. Additionally, reassembling the shaft, bearings and drive after work on the seals is complete takes valuable time and resources.

How can we address these issues?

Select a seal that can handle shaft runout – because shaft runout is not going to go away! Many seals can be compacted and deformed by eccentric shaft motion which ultimately creates a leak path. The MECO seal range allows up to 6mm shaft runout as standard, and so works with this inherent issue rather than fighting it and damaging the seal.

Take away the dynamic contact with the shaft to prevent friction and the build-up of heat in the sealing area and wearing of the shaft. This can be simply achieved by opting for a dynamic face seal whereby one sealing face (the stator) remains static and a dynamic sealing face (the rotor) is fixed to and rotates with the shaft. This can significantly reduce the overall cost of ownership of a rotary mixer especially when considering the direct labour and material costs and downtime associated with replacing a worn shaft or the cost of scrapping a batch of product due to heat damage. All MECO seals adopt this design feature.

Simplify the seal repair and replacement process by choosing a split seal design that requires no major machine disassembly, saving time and resources and getting your plant back online quicker, much quicker! MECO split designs allow you to get up and running in the fraction of the time without compromising seal performance.

Click the link to find out more about the MECO range and other solutions available from FTL Technology.