Maintaining your classifying tank, fine material screw washer

So you’ve done the research, planning and finally purchased a classifying tank or fine material screw washer.

Now what?

It’s time to start thinking about the best maintenance practices to ensure maximum availability of your equipment and reduce total production costs. Putting in place standard processes can lead to years of continuous, efficient operation.

Regardless of your site or equipment, all maintenance programs should have similar objectives. These include:

• Being “proactive” instead of “reactive”
• Ensuring the equipment can be operated safely and efficiently
• Ensuring a targeted reliability of equipment at a rated capacity
• Maximizing the life of equipment
• Ensuring training is provided to effectively perform and support maintenance activities

Sand classifying tank maintenance

All sands cause wear on processing equipment to varying degrees. In sand classifying tanks, valves and valve seats are among the most commonly replaced items.

While some manufacturers’ original components are hard cast iron alloys intended for abrasion resistance, these parts are often replaced by polyurethane components that offer extended wear life in most instances. Valve rods, torque motor paddles and paddle rods should be periodically inspected for wear and replaced when needed.

Sand discharging from the valves exits the sand classifying tank via down pipes often equipped with elbows to a sectionalized collecting flume. The elbows handling coarse sand experience wear and require more frequent replacement than valves discharging finer sand.

While many sand classifying tanks have used steel pipes and hard iron elbows, these metal components have been replaced with thick-walled PVC pipes and polyurethane elbows that are easier to handle, quicker to replace and provide equal or extended performance.

Liners in the sloping double- or triple-cell collecting flume should be visually inspected and replaced as needed, too. The flumes are used to direct the classified sands to dewatering equipment. Types of liners include abrasion-resistant steel, rubber and polyurethane. Liners should cover not only the bottom of the flume, but also the sides to protect the fabricated steel flume.

The opening and closing of the sand classifying tank valves is made via hydraulic cylinders connected to a valve rod. A self-contained hydraulic power unit is supplied to operate the cylinders via hydraulic hose or tubing. Periodic replacement of hydraulic fluid and filters, as specified by a manufacturer’s manual, should be followed.

For sand classifying tanks that are not operational during a seasonal shutdown period, even if not changing the fluid, the hydraulic reservoir should be checked for water that may have accumulated from condensation. The water should be drained from the reservoir, and the proper hydraulic fluid level maintained as recommended by the manufacturer.

Additionally, all electric systems, wiring and hydraulic lines should be checked periodically to make sure they are functioning properly and do not cause an improper grounding or leakage that can be a hazard to maintenance personnel. The control enclosure on top of the sand classifying tank that houses the hydraulic cylinders, torque motors, solenoid valves and associated electrical wiring and hydraulic lines should be cleared of any accumulated sand to ensure no interference that can cause component failure.

If a sand classifying tank is equipped with a rising current recirculating pump system, the impeller should be checked for wear and replaced when worn. V-belts driving the pump and bearing lubricant should be inspected and maintained as specified by the manufacturer’s manual.

While sand classifying tanks may seem complex from an initial overview, they can be easily maintained with periodic inspections and repairs, providing high operational availability. A manufacturer’s installation, operation and maintenance manual typically recommended spare parts that operators should keep in their own stock. Keeping some spares in inventory will minimize downtime when a sand tank’s component requires replacement.

Fine material screw washer maintenance

While the fine material screw washer may be among the simplest machines to maintain in an aggregate plant, appropriate safety precautions must always be taken. This includes using a lockout/tagout of the motor starters before performing maintenance on any moving components.

Proper lubrication of the bearings that support each end of the screw shaft should provide long bearing life. In some cases, the lubrication requirements of seals on submerged rear bearings are less than the requirements of the bearing itself. A non-lubricated seal almost always leads to more frequent rear bearing failures and downtime with a loss of production.

If the discharge end of the screw shaft is supported by a standard pillow block bearing, it is often recommended that a lube line be run down the support to near ground level so maintenance personnel can regularly supply grease if a service platform is not at the level of this bearing.

Typically, the screw shaft is turned by an electric motor with a V-belt drive into a shaft-mounted reducer. Periodic inspection of V-belts for both wear and tensioning is also recommended to reduce downtime and unexpected failures.

Changing the reducer gear oil in accordance with the manufacturer’s recommendations usually provides for a long gearbox life. If the reducer on the machine has been in service for several years, periodic evaluation for contaminants in the gear oil is recommended to avoid an untimely failure.

The need to replace wear shoes can easily be determined by visual inspection. Replacement shoes are typically available in the manufacturer’s standard iron, urethane or rubber types. The best abrasion-resistant material for wear shoes may be dependent on the chemical composition and particle shape of the sand being dewatered. For instance, very abrasive sands, such as crushed granite sand or sandstone, can abrade or gouge synthetic wear shoes, reducing wear life.

Performing your own checkup or getting the assistance of the manufacturer’s local dealer can often result in less downtime, providing the highest availability for the operation of a fine material screw washer. And just like sand classifying tanks, a manufacturer’s manual typically includes a list of recommended spare parts that operators should keep handy.

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Information for this article courtesy of McLanahan Corp.