November 3, 2009
Maximize the payback of synthetic screen media with proactive vs. reactive maintenance.
by Marc Lovallo and Alan Tindall
Proactive maintenance is described as preventive, planned, and predictive — while reactive maintenance is simply a run-it-until-it-breaks approach. Indeed, the latter leads producers into a costly crisis mode. Regarding synthetic screen media, proactive maintenance delivers numerous benefits — maximum cost efficiency and uptime, longer wear life, consistent specification accuracy, and the security of a reliable and sound screening system.
Proactive maintenance appears to be a no-brainer, yet in reality, according to a recent survey, nearly 50 percent of plant operators consider their maintenance practices to be merely satisfactory or poor. The remaining 50 percent rank themselves in the good to excellent category — and this top half is arguably the clear winner where profitability is concerned.
With that said, let’s take a look at some media maintenance matters that are guaranteed to maximize the payback of your synthetic screen systems.
Due to its long wear life, it’s common to find a set-it-and-forget-it attitude surrounding synthetic media — and that should be avoided. It’s very important to inspect your synthetic screen decks periodically for loose panels or unusual wear patterns which may be caused by a change in feed rate or by high-pressure spray water, for example. Consider that if a screen panel is not replaced before it is worn entirely through, it could result in out-of-spec material, damage to the fastening system, or even to the steel supporting deck.
Monitor quality control samples
Regular sampling can tell producers a lot about the wear life and condition of the synthetic screen panels. A sudden or gradual change in specifications indicates a need to inspect the screen deck for wear. Operations that do not conduct frequent sampling may not realize that the deck has worn to a point that material is out of spec.
Fixing the feed box
Consider lining your feed box (and discharge lips as well) with the same high-quality synthetic material that is used on the screen deck itself. This will help prevent a premature failure of the feed box. Prone to much wear, steel feed boxes are most often patched and plated in an attempt to extend their useful life — a tactic that affects the feed distribution of the material onto the screen deck itself, creating more impact and causing excessive wear at the feed end of the deck.
Check side wear liners
Synthetic side wear liners are bolted or clamped onto the side of the screen box to protect the walls of the deck and to hold the synthetic screen panels down along the outside edge. As side wear liners typically last longer than the actual screen surface, they are often overlooked during inspections. Side wear liners should be checked for wear and for any loosening of the bolts or clamping hardware. If all liners are not securely tightened, screen panels can move, resulting in damage to the side wear liners, the screen panels themselves, or even to the modular screen system support structure. Loose side wear liners can also allow screen panels to disengage, causing material to go out of spec.
Proper support and tensioning
Support side-tensioned synthetic screen mats with high-quality bucker bar rubber. Do not use the same bucker bar rubber that is used with wire cloth. It is also important to tension the screen properly upon installation and to re-tension the mats on a regular basis. As steel wears more quickly than the synthetic material, do not use standard steel products to clamp down the screen in the center. Instead, use components that are compatible with the screen surface, either rubber or polyurethane.
Protect the screen surface during repairs
Take the proper precautions when welding on or near the screen deck by protecting the synthetic screen surface from damages caused by hot steel or sparks. Before beginning, spray the entire deck down with water and cover it with a fireproof blanket or plywood sheets. Keep a hose near the work site in case additional water is needed.
Follow recommended replacement & installation methods
First, make sure that you complete any necessary repairs (such as replacing worn cross members) to the screen box itself before you install a new screen deck. Also, make sure the screen machine is thoroughly cleaned before installation. When installing new screen panels, lubricate the outer edges with soapy water. This will allow them to go in more smoothly. Do not use WD40 or any oil or petroleum-based products for lubrication as it will cause a deterioration of the synthetic material.
When replacing worn screen panels, clean any dirt, sand, or grime buildup from the steel support work and fastening system to allow the new panel to properly lock itself in place.
Post and follow a deck layout sheet
If your media supplier has provided you with a diagram of the deck layout, post it as a reference tool for the maintenance crew. This is especially important if the deck layout contains a number of different panel types and opening sizes. This will ensure that the correct layout is maintained as panels are replaced — and will ensure that the deck design remains accurate for the given application.
Maintain maintenance records
Keep records on what, where, and when screen panels are replaced. Note the location of the panel and the date of replacement. This will allow you to document the wear life of each panel and will aid greatly in the forecasting and future purchasing of replacement panels — and the overall budgeting for yearly screen costs.
Proper care and storage
During an extended plant shutdown, protect your equipment investment from weather, ice, or sun damage by covering your screen decks with a tarp or with plywood. If you are stockpiling replacement panels, stack and store them inside the maintenance building in a cool, dry area. Never stack or store them outside and under the heat of the sun.
Choose a detail-oriented media manufacturer
Working with the right screen media manufacturer or dealer is imperative. You should choose a vendor who will take the time to analyze every detail of your application in order to specify the right screen media solution. Choose a hands-on vendor who will conduct a complete evaluation of your screening circuit at various points before, during, and after your production season.
Proactive vs. reactive
While the reactive run-it-until-it-breaks strategy may be appropriate when operating a light bulb, it is obviously not recommended for major processing equipment. The goal of all good maintenance programs is to maintain the reliability of your valuable equipment by repairing or replacing worn components before they actually fail. This keeps your screening operation running and helps prevent emergency breakdowns.
While the use of synthetic screen media definitely reduces maintenance labor requirements, it does not eliminate it. Be proactive with media maintenance. Doing it the right way will maximize the payback. Cutting corners will cost you more in the long run.
Marc Lovallo is the vice president of sales for Polydeck Screen Corp.; and Alan Tindall is the Polydeck regional sales manager for the West Coast. Polydeck Screen Corp. is a Spartanburg, S.C.-based manufacturer of modular synthetic screen media systems.