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USDA 3-A Dairy Standards - Bearings

USDA 3-A Dairy Standards - Bearings

USDA 3-A Dairy Standards - Bearings

Hi, I've not used this forum at all in the past, only knew of its existence. I've been making a conscious effort to have a scan through the forums lately in the search for engineering info.

Something I've not yet found anyone that has been able to help on over the past year is the USDA 3-A Dairy Standards. I work for a company that designs and builds automated food handling machinery - typically in the dairy industry. Most of our work is in the UK, but recently we sold a machine to the USA and we are currently working on a large concept proposal for a number of machines.

We have a number of rotating parts on these machines, and these need to run on bearings. Some are running at rpms of up to 250.

The 3-A dairy standards say...

"Rotating shafts, other than those covered by 3-A Sanitary Standards for Shear Mixers, Mixers, and Agitators, Number 73-, shall not have lubricated bearings, including sealed bearings, in the product contact area except as described below. Such lubricated bearings shall be mounted to provide a minimum of 1 inch (25mm) exterior open space on the shaft between the mechanical seal for the bearing and the nearest part of the
sanitary seal or the opening to the product contact area. The 1 inch (25mm) minimum space shall be open to the atmosphere and be easily accessible for inspection and cleaning."

Alternative designs are to be considered on a case by case basis, but these generally will use FDA approved plastic bearing materials or provide a complete enclosure to contain any lubricant in the event of a bearing failure.

In addition to this, all aluminium components are to be kept outside the product area (cannot be above product), so ally bodied drives and slides are a problem area.

Can anyone shed any light on designing to these standards? In some cases, it is perfectly achievable to mount bearings 1" outside the product contact area, but in others it is not feasible to design something to take the rotary motion that far away from the product.

I guess an engineer in America may be completely conversant in these standards and the solutions will be commonplace in the factories across the US. Is that the case? Or does dairy factory automation avoid rotating parts somehow?!

Just putting the question out there for discussion really! I have spoken to a number of UK suppliers on this subject, but none have any experience in this area. IGUS can supply plastic bearings, but their service life is fractional in comparison to their S/St sealed equivalents.

Thanks for any advise that may cometh...



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