Silicone Purged
Silicone Purged Bearings Fit For Cuisine Bearings play an essential role in food processing from bakeries to seafood canneries to bottling plants. Like any component in a high-speed, high-volume pr...
Silicone Purged
Bearings Fit For CuisineBearings play an essential role in food processing from bakeries to seafood canneries to bottling plants. Like any component in a high-speed, high-volume production line, their unexpected failure or unscheduled maintenance can be devastating. To reduce the risks and avoid painful consequences, engineers must observe housing and insert materials as well as the type of Stainless steel pipe bearing itself. What follows is a review of these important factors and practical advice for times when bearings are in contact with food. In the house Sometimes, for example, acids, cooking fats, and other chemicals used in food and beverage processing may come into contact with the bearings. This can be avoided by employing composite or thermoplastic-housed units. Another option is cast stainless steel (usually made of AISI 300), which withstands strong chlorine and hydrogen peroxide concentrations. Other materials such as high-strength, cast iron work best for red meat, pork, and poultry processing. Nickel-plated, cast-iron housings, on the other hand, are easier to clean and rid of debris and bacteria because of their smooth surface finish and solid-base mountings. The most common plating — CNC (copper, nickel, chrome) — durably resists corrosion and appears bright and shiny. Proper CNC sanitation prevents E. coli, salmonella, and staphylococcus aureus growth. Many of today's bearing housings also contain antimicrobial coatings to further thwart bacterial and fungal growth. In addition, polymer housing offers excellent corrosion resistance, a chip-free exterior (as opposed to plated housings), and economical prices compared to stainless steel. But unlike stainless steel, polymer materials do not provide equal load strength. Insert here Zinc-coated inserts also guard against corrosion, come in most sizes, and cost less than stainless steel and TDC. However, plane bearings are needed during severe operating conditions where rolling-element inserts are not allowed. They usually install into any mounted housing that accepts rolling-element bearings. In addition, polymer and seamless pipe combinations comply with requirements for a bushing-type design. Lube stop When relubrication is not possible, however, polymer-solid lubricants can be employed. During bearing operation, they release a small amount of oil to coat rolling elements and raceways, resist washout, and reach hard-to-maintain areas. On the downside, they handle speed and environmental limitations poorly. Daily specials Wet environments — due to water and equipment washdown In any of these environments, bearings must be shielded from corrosion. This is achieved through corrosion-resistant platings, coatings on metal surfaces, or materials that inherently offer corrosion resistance, such as stainless steel or polymers. Stainless steel offers the best corrosion resistance in the aforementioned environments and is therefore preferred in meat-processing plants for equipment and bearings. Plated bearings, on the other hand, best suit wet areas with limited chemical washdown. Their lubricants must be USDA-approved food grade (H1 or H2) only. Many high-end, food-grade greases lubricate as effectively as conventional petroleum greases and contain additional qualities such as low-temperature operation and washout resistance. Basic styles Unmounted bearings are made of stainless steel and other highly corrosion-resistant materials such as high nitrogen corrosion-resistant steel (HNCR). HNCR resists corrosion better than any stainless steel while maintaining a material hardness similar to average bearing steel. HNCR materials therefore eliminate the capacity reduction inherent in stainless-steel bearings. High-temperature bearings generally incorporate a graphite separator that lubricates bearings at temperatures above 600° F — something conventional lubricants such as grease and oil cannot do effectively. These mounted bearings increase life and lower maintenance costs in difficult baking, frying, and drying applications. Plane bearings consist of a bushing-type design where two surfaces mate to each other without a ball or roller. They are available in several housing styles and bearing-material combinations for lubricant-free operation (sometimes required for sanitation) and easy cleaning. Unlike conventional ball bearings, they can be completely disassembled, cleaned, and reinstalled for safe use in and above the product zone — where conventional rolling-element bearings are unapproved. However, this style limits both speed and load compared to conventional ball bearings. Plane bearings are made of stainless steel or polymers for various operating requirements and temperature ranges. Other options End closures added to housed units further protect the inserts, prolong bearing life, and act as safety measures against rotating parts. There are open-type units, which allow shafts to extend through and closed types for stub shafts. Most often, covers are made from either stainless steel or composites. Other options for a complete food-grade bearing assembly include stainless steel or nylon cages, Stainless steel setscrews, stainless steel or corrosion-resistant coated fingers, corrosion-resistant collars, and Stainless steel grease fittings. Survivability is key for the bearing, as well as the load. About the Author Stainlesssteelseamlesspipe.net is The TOP 1 Stainless steel pipe store,we sell Stainless steel,you can buy Stainless steel and seamless pipe from us. |
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Crack Down on Heat Exchanger Fouling
Crack Down on Heat Exchanger Fouling
Written by Mike Watson, Technical and Managing Director, T.T.I.L.
Heat exchangers are the unsung heroes of many industrial processes and as such they tend to be taken for granted - nobody likes paying for what is often seen to be unnecessary maintenance. Heat exchangers provide duty for so long, that when they start to drop in efficiency, it's usually a gradual process that goes largely unnoticed - until their performance has deteriorated sufficiently to be a problem. Then it really is a problem - and one requiring urgent attention.
What aggravates the situation is the heat exchanger that has never been cleaned properly, coupled with the commercial need to keep it on-line. When the decision is made to carry out cleaning, often nobody knows what the performance of the exchanger is meant to be, either because the drawings have been lost, or no record of any improvement was made after the original cleaning.
When the exchanger finally is opened up to ascertain the extent of the fouling, it's not surprising to find it is so severe that cleaning takes a lot longer than planned. Any benefit that might have been gained by a quick traditional clean is offset by the extended cleaning duration and costs - and, of course, lost production.
If that sounds like a nightmare scenario, bear in mind that this is the sort of situation specialist cleaning companies encounter every week. Cleaning is often carried out without any firm knowledge of how much of an improvement the cleaning will give and how long its effects will last. Having to make 'finger in the wind' predictions clearly is not a satisfactory way to plan maintenance.
One of the most popular and widely-employed heat exchanger configurations in industry, is the straight or hairpin shell-and-tube exchanger. With hundreds or thousands of small-bore tubes bundled together, the extent of quite modest scaling can involve major work to return the exchanger to anything near its commissioned performance. If the outside of the bundle is heavily scaled as well, the cleaning challenge rises by an order of magnitude.
There is potential to bring about a significant improvement in heat exchanger accessibility and 'cleanability', by working more closely with the people who design heat exchangers and fabricate industrial plants.
Better design would lead to improved cleaning - where improved means faster, cleaner and safer, possibly in-situ or even on-line and with better waste containment. It would then be easier and quicker to clean exchangers back to bare metal to return them to duty and their design performance faster.
Plants are generally specified and ordered on the basis of throughput, not accessibility and ease-of-cleaning. Suppliers are happy to comply with this and therefore tend to design heat exchangers with 30-40% excess capacity to ensure that they can continue to provide duty, even when quite extensively fouled. Heat exchangers the world over are currently designed and installed with a view to using one of three systems for cleaning: chemical, pressure jetting and/or mechanical and this approach has remained unchanged for over 50 years.
When it comes to maintenance, refineries - like most of industry - tend to compete on the same basis - a 21-day shutdown is decreed because it's been done that way for maybe the last 20 years. The same cleaning methods are generally used slavishly, with high-pressure water as the cleaning medium.
Most companies look at their heat exchangers in isolation and simply try to extend their run-time, instead of having them designed or re-designed so they can be cleaned more regularly, but faster and better. BP's Coryton refinery, for instance, managed to reduce cleaning time on one shell-and-tube heat exchanger from three days to three hours by applying a different approach to cleaning it.
If a plant is optimised for cleaning, almost full production can be maintained throughout the cleaning process. Relatively minor mechanical changes, such as adding isolating valves to heat exchangers, means that each exchanger, or bank of exchangers, can be taken down and cleaned while the others remain on-line. A redesign of the exchanger so that a header can be removed, means it can then be cleaned with a different system to the standard high-pressure water jetting, in a few hours instead of several days.
At Dow Corning's silicone plant in Barry, south Wales, a tubular boiler and fire tube in the Energy Recovery Unit (ERU) required the removal of a 5mm layer of deposit in as short a time as possible to minimise lost production. Another obstacle was that the unit, which carries waste gases, takes 48 hours to cool and prepare - even with the introduction of a chilled nitrogen purge - before personnel can enter to clean it manually.
The solution involved developing a bespoke remote de-scaler, which was inserted through a small 50cm man-way. Once inside, the de-scaler expanded to fit the hot fire tube, while reaching the full length of the carbon steel tube. With cooling time and man entry eliminated, the shutdown was reduced from five days to three and there was a noticeable improvement in performance of the ERU when it came back on line.
Improved cleaning cycles also mean the rate of future fouling build-up is reduced, which in turn reduces the risk of tubes corroding as a result of the exchanger being open to the atmosphere longer for cleaning.
Heat exchange surfaces therefore remain smoother and provide better heat transfer. If and when the exchanger does foul up, it's easier to clean next time around, using whichever system is preferred. This would represent a change of practice to what has been the norm since the 1980s, for instance, when what was then Mobil in the UK was one of the first refineries to decide that it would extend run-times by abandoning the annual clean and only clean every two years.
Today, typical service intervals have become stretched to three and even four years in some cases, but the apparent operational savings are actually a false economy. Shareholders are indeed happy, because they are getting longer run times, while competing refineries have little choice but to play the same game or lose millions during more frequent shutdowns. Four years down the line, however, the plant will have to come down for major cleaning and maintenance and it will experience a far higher capital replacement cost than ever before.
About the Author