Chapter 8: Washing & Classifying | P&Q University Handbook

Safety

Every wash plant should have clear safety guidelines that include best practices for the entire plant. Safety, after all, requires a proactive role to prevent workplace accidents.

Make sure you and your operators are trained in proper safety and maintenance procedures of your site – including washing equipment. The top priority with any maintenance task is safety. Review the conditions surrounding the tasks and determine which tools are required to complete them.

Which employees are needed and how many in all? Are they properly trained on procedures? What communication is needed with other employees and contractors that may be on your site? Conditions such as time of day, weather and area around equipment can all affect a maintenance task and, in turn, everyone’s safety.

Keeping equipment and operators safe

As part of routine maintenance, check safety guards and warning decals.

Guards can sometimes be seen as inconvenient and are removed from a machine to allow for easier access to components. These guards may not be put back on because operators lose the bolts and don’t bother to replace them.

Guards are intended to keep operators safe. If they need to be removed for maintenance, they should be put back before startup.

Warning decals are also put in place to keep operators safe, so be sure to keep them clean and intact. Should an equipment warning decal become damaged, contact the manufacturer immediately for a replacement.

Always be sure to check the integrity of all safety items before use. Tips to keeping a safe site are:

1. Walk it daily
2. Ensure training on proper lockout/tagout procedures
3. Check guarding around equipment
4. Keep the site clean

Some equipment – especially vibratory – requires retorquing of bolts. A review of the manufacturer’s manual for this data is recommended. If missed, it can cause damage to equipment and possibly a loss of warranty.

A torque-multiplier may be needed if torque specs are higher than available tooling. Check if lubricated or dry threads are used prior to this procedure.

While lubrication schedules vary, check the quantity and type of grease or oil that’s required. Also, be aware of the recommended frequency for lubrication.

Is lubricant replacement needed after a fixed time following startup? Is that timeframe based on environmental conditions? 

Also, keep your grease fittings clean. This step should be obvious but is not always followed. Grease fittings should be cleaned before engaging the gun to lubricate your equipment.

Additionally, keep dirt and other foreign material cleaned out from around oil-filling points, and be sure to inspect old lubricants for contamination. In some cases, a lubrication analysis should be made for tracing contaminants associated with some failures, which can lead to potentially unsafe washing equipment.

Don’t allow yourself to turn a blind eye to a hazard or an unsafe situation. Don’t allow yourself to say: “it’s not my job” or “someone else will fix it.” 

When doing inspections or maintenance, every worker involved should lock out. Never remove a lock until positive identification verifies all personnel are out of the area.

Every incident, accident or event should be investigated. Through investigations, recommendations can be made to improve safety and prevent the event, incident or accident from happening again. It is vital these recommendations be implemented. Otherwise, sites are destined to repeat mistakes of the past.

Keeping washing equipment safe

Scrubbers/trommels

In addition to proper lubrication, mounting alignment is critical to prevent damage to tires and drives. Check liners and screen media condition for wear. Inspecting internal lifters and advancing/retarding paddles are just as important for production, because if their height is below a certain critical point, material will not rotate and interact effectively.

Allowing paddles to wear away and not replacing them may save a few dollars upfront, but this may result in unclean material. By taking these steps to maintain your scrubber or trommel, you are complying with safety regulations and ensuring a safe machine to operate.

Log washers, blade mills, aggregate conditioners, coarse material washers and fine material washers

Order equipment with optional guards to prevent accidents, and add guards if there are dangerous access points.

The rear bearing assembly designs vary by manufacturer. Some are complex and feature a “submerged” bearing, while others are a simple outboard pillow block with a rubber boot seal assembly. Each claim different advantages, but they all require lubrication.

Paddles and flights need periodic inspection for wear and possible replacement. With metallic paddles or shoes, it’s important to be aware that worn ends become razor sharp and can cause serious injury if not handled properly. It’s important to check wear on these items and fasteners, as the latter secure the wear parts to the shaft.

Occasionally check the shaft for runout, as a bent shaft can cause premature failure of support bearings and even the shaft. Personnel should carry out shaft straightening, but only after consulting the manufacturer’s manual.

To assure proper lubrication of bearings, many manufacturers offer optional automatic lubrication systems, which are often inexpensive. These can assure more regular, periodic lubrication and minimize operator personnel exposure to a plant-operating environment.

Slurry pumps

These are the heart of a wet process. However, serious injury can result from a bad installation where solids settle out and an explosion can occur. So, be sure to consult the manufacturer when reinstalling or modifying an installation. The correct selection of construction materials is critical to long-term, cost-effective service life and safe operation.

There are three key areas in any pump: wet end, gland and bearings. It is important, particularly with open vane-style impellers, to check the clearance between the impeller and the suction side liner. Too wide a gap leads to bypass inefficiency and, in slurry pumps, accelerated wear.

Impeller wear should be monitored, as reduction in performance is most likely due to this factor. Do not apply heat to any area of the pump’s impeller if trying to loosen it during maintenance, as serious injury or death can occur.

Hydrocyclones

While hydrocyclones have no moving parts, there are two failure modes – delamination and wear – that affect performance and can affect the safety of your machine.

Liners that become loose due to wear or adhesion cause disruption of flow inside the unit. This ultimately causes poor performance with misplaced particles.

Checking the internal lining of a cyclone should be done at least seasonally. This is particularly important when dealing with siphon (vacuum)-assisted cyclones/separators. The apex (spigot) is the fastest-wearing component.

These are sized based on mass-flow. That way, as they wear, the underflow becomes more dilute and more fines will bypass into that stream, affecting the removal of deleterious fines.

Also, check the apex if your product is getting dirtier. Worn vortex finders can allow coarse fractions to short circuit to the overflow and fill the ponds or contaminate the next stage of production. The worst case is wear can cause the pipe to detach from the plate, causing significant damage to equipment and possibly injuring nearby personnel.

Dewatering screens

Safer working conditions result from the use of dewatering screens, as they discharge a drier sand and result in less carryback and spillage to clean up around conveyors.

While they typically have a lengthy service life, there are still some areas to watch to keep them running safely and effectively. For example, notice if cracks occur in the side plate. Trace the crack to its end with dye penetrant and drill a 1/8-in. to 3/16-in. hole. This often takes care of the problem, and the side plate will last the life of the screen.

Cracks in cross members should be referred to the manufacturer immediately, as should any bolt breakage. Often, the problem with cracking in dewatering screens is the support structure rather than machine integrity.

Lubrication is a general maintenance task but take extra care because some vibrator motor manufacturers use special grease that, if not used, may void the warranty. Motor wiring that is draped across a vibrating motor to the side of the screen and vibrates against adjacent surfaces is a very dangerous condition. Visually check this and replace the wiring as needed. Also, always check the direction of motor rotation upon restarting after electrical work to keep equipment running properly.

Final thought

It’s important to make your washing site as safe, clean and productive as possible. By keeping your site clean and training operators on safety procedures, you are taking the steps to keep your site and operators safe while they perform their job.

Keeping your washing equipment well-maintained will keep your equipment running longer, and promoting cleanliness and safety everywhere in your plant helps to send employees home safe.

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