Improving Shredder Efficiencies

“I just took over an aging shredder. How do I determine if I need a new rotor and how much life is left in it?”

Good question! First, compare the original condition to the current condition. Try to find the rotor arrangement drawing, which came with the shredder when it was new or when the replacement rotor was purchased. This drawing should show disk thickness and key dimensions.

✔️ Check that the tie rods are still holding the rotor tightly together
Measure the outside-outside end disk distance across the rotor. If it’s growing an inch or more, the spread can mean loose or broken tie rods or loose or missing end disk nuts. A loose rotor will have limited life.

✔️ Look at rotor disk thickness and edge wear
Monitor the disks diameter indirectly, by tracking the distance between hammer pin hole and edge of the disk.

✔️ Monitor disk thickness and “wash out” around the hammer swinging area about the pin hole.

✔️ Check bearing bolts for tightness and bearing housings for damage
Clean up debris and keep bearing areas clear.

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Infrared Camera Side Mount on Scrap Metal Shredder Feed Chute — a K2 Castings project.

To ensure the best possible throughput, your shredder operator needs the best possible view of the material entering the shredder. It’s why you’ll often see shredder control cabs mounted to a tower; the set up allows the operator to peer into the infeed and get the last possible glimpse of the feedstock before it enters the shredder.

The view from this point of entry allows your operator to adjust the feed to keep the shredder operating right in the sweet spot. Too slow of a feed and you’re giving up productivity, too fast and you risk jams and incomplete shredding.

It’s tempting to place your operator’s chair as close to the mouth of the shredder as possible, and while this position gives the operator the most direct view, one can achieve just as much, if not more, with cameras.

When properly located, a camera can give your operator a near direct view down the throat of your shredder. Additionally, close-up views of the output can give him the information he needs to produce the highest quality shred, as well as knowing when the hammers need replacement.

Not only that, but FLIR cameras, properly utilized, can give your operator a view through the steam produced in a shredder with water injection, while also giving him an intuitive sense for the temperature of the machinery, without the need to be staring at dials.

Additional reading on the K2 blog: Infrared Camera Positions for Shredder Infeed.

Sub-standard scrap poses significant risk to your shredder, people, the surrounding environment — and your entire business. One explosion due to a compressed tank could mean months of closure — or business bankruptcy and closure.

In this blog post, I’ll cover the materials that can wreak havoc with your inbound stream, as well as causing minor to major issues — from a clogged system or broken parts to increased costs and environmental hazards.

Heavy or dense raw material

“Heavies” are raw materials that are simply too heavy in size and density/mass and therefore can’t be easily shredded. Heavies inevitably damage internal components of your shredder, including castings such as hammers and pins, and material handling systems.

Damage from heavies can cause prolonged periods of downtime and safety risks to operations personnel when replacing damaged components.

Damaged wear part (upper left) due to “heavies.”

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Excessive moisture in your shredding process is an ongoing challenge. Lessening the amount of moisture can have a significant improvement on your bottom line, especially during weather-related inclement months.

Excessive moisture can cause the following issues:

Excessive oxidation
Poor scrap quality of FE (ferrous) and NF (non-ferrous) is mostly associated with excessive oxidation of the finished product, and represents yield loss for the end consumer.

Most domestic FE and NF scrap is consumed within the period when it’s transferred from the processer to the end consumer – generally within 30 days or less.

When this material is shipped internationally via export container or bulk vessel, however, the travel time from processor to end consumer is increased by an average of one (1) to two (2) months – causing a lot more oxidation to take place and yield loss for the consumer.

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When do you know it’s time to change your scrap metal shredder hammers?  What does it mean to “change” hammers?

Changing hammers refers to both replacing hammers with new, as well as “flipping” or “turning” hammers to another side to expose a fresh leading edge, or rotating hammers to a new position on the rotor.

Change — swap new for used casting

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Shredder Rotor Replacement

Your wear parts have been doing a great job for many tons of production.  After several years, it’s time to replace your shredder rotor.  What are your options and what exactly do you need to plan the job?  How do you start finding a replacement?  Here’s some information and explanation to get you started.

Find your rotor arrangement drawing.  The drawing shows the entire rotor and describes its major dimensions, weight, shaft size and general assembly.  With this drawing, a rotor builder understands the style and quantities needed to build a rotor.

Example Rotor Assembly Drawing (courtesy of PG&H Engineering)

They can estimate materials and general time needed, enabling them to provide you a quote.  You need to describe what it is you are buying. A picture is worth a thousand words.  Here is a rotor template drawing from PG&H if you need to make your own.

Describe your hammer and hammer pin size.  A drawing with some basic dimensions is ideal. If you don’t have one, go to our quote page and download the hammer template you need (such as bell hammer) and use it to describe your hammer.  The rotor builder needs to confirm your hammer swing radius, thickness, and pin hole size.  Provide them hammer pin diameter and length.  We have a template for hammer pins as well.

Get with your operating crew and determine the specific needs at the shredder.  Yes, you need a new rotor, but what else?  Here are the common replacement items for a rotor change out.

Bearing housings

These hold the bearings and attach the rotor shaft to the shredder.  They get worn and damaged as well.  If in good shape they can be renewed.
You should have a spare set on hand and can plan to use them.  If they have yet to be renewed, get them cleaned up and sent out to a shop that can build them up and machine them to restore a secure fit.

Oil seals

Seals keep the lubricant inside the bearings housings.  They are long lasting, but always replace with new during a bearing change.

Rotor bearings

Photo courtesy of Schaeffler / FAG Roller Bearings

Generally spherical tapered roller bearings are used.  You should have a spare set on hand.  If you need a fresh set, order early as lead times can vary by many weeks.  Be sure your spare set is well stored and free of minor rust and dirt.  Larger machines have oil cooled bearings, smaller mills may use greased bearings (not needing an oil re-circ system).

Coupling device

A means to connect the drive shaft to the rotor.  You may be able to remove the old one and reuse it, use a spare, or plan on having a new one made by your rotor shop.

Drive Shaft

You will have the rotor out, so it’s the right time to service your drive shaft.  Plan for it.

Bearing Base Plates and Shim Kit

The saddle is the mounting area on the shredder base where the bearing housing sits to anchor the rotor to the shredder itself.  These surfaces are subject to wear themselves.  The bearing housings should wear first, but in reality, both wear.  The saddles will have to be cleaned and ground flat.  The bottoms of the bearing housings will be milled flat in the shop.  A steel base plate is used when you need to make of the difference in height from the wear of these two surfaces.  A shim kit is useful for rotor alignment.  It is a set of pre-cut metal shims to help you adjust rotor height when aligning the rotor drive train.

Thermocouples and Instrument Wiring

Oil cooled bearing generally have a temperature monitoring probe on the bearing oil. Often the probes and wiring will be damaged after years of shredder service.  If they need to be replaced, plan for it now.

Bearing oil piping, hoses, fittings

Similarly, your bearing oil delivery system takes abuse over the years.  You may need to replace piping or use fresh hose.   You might want to get the bearing oil pump & reservoir cleaned and serviced during the rotor change as well.

Bearing bolts

The studs or bolts that hold down the bearings to the saddle base should generally be replaced.  Bolts are made to have a certain amount of stretch.  Once they have stretched and done their job, they don’t stretch and hold quite the same the next go around.  Its a finer point and often, the bolts or studs are often reused.  It’s best if you change them.  Often the threads and nuts get damaged, so a fresh fastening system is good.  After spending so much to  replace the  rotor, you’re are going to cut corners elsewhere in the installation?  Just saying.

You have your shopping list.  Go find yourself a rotor and replacement supplies.   Call you your Original Equipment Manufacturer or one of the replacement builders out there, such as PG&H Engineering.   Contact us if you need some advice.

Summer is here and the risk of a fire in your scrap feed stock and fluff piles go up substantially.  Summer brings an uptick in yard flow and several holiday weekends.  Many of us have received that call in the middle of the night that you have a fire emergency at the yard.  We all need to remain vigilant and not let our guard down. Here are some simple rules to minimize the chances of that call.

Preventive measures to take:

1. Keep your scrap piles at least twenty feet away from both fixed and mobile processing equipment. Infeed conveyors, loaders, cranes, need clear space from scrap storage piles. Space means access and time in the event of a fire.
2. Don’t accumulate large feed stock piles. Production schedules that keep intake to a minimum are best.  If you are down for extended maintenance, add fire breaks and gaps to segregate large piles.  Once you shred it, the problem is gone.
3. Regular housekeeping is needed at the shredder. Excessive material buildup becomes a problem when contaminants hit the piles.  Consider this scenario.  Scrap builds up between your shredder and the motor room over several weeks.  An auto slips by inspectors with a full fuel tank and it ruptures as it slides down the feed chute.  Flammable liquid runs out of the mill and into that pile of build-up right where your important machinery is located.  Your bearings, hydraulic lines, drive shafts, control wiring, or your mill motor won’t be the same if that pile ignites.  Clear what does not belong on a weekly rotation.
4. Make sure your fire control systems are in place, hoses and nozzles are in good condition, all fire extinguishers checked monthly, and missing items replaced promptly.
5. Review with your inspectors hazardous materials which can start a fire such as batteries, gas tanks, propane bottles, and other ignition sources. While 99% of infeed scrap is remediated and prepared for shredder, some things get through the inspection process.  Sometimes dressing up the piles of infeed materials received earlier that day can trigger a problem load lurking in the day’s intake.
6. Make sure all shreds have been run off the conveyor belts and wet down the conveyors belts and area around the shredder. Be sure to look closely at all of the fluff piles for signs of hot spots.  Make it a priority to have the fluff piles at minimum levels especially before an extended holiday shutdown.
7. Lastly, have a supervisor walk around the processing area prior to shutdown. An early morning inspection can help set expectations for the end of day shut down walk when your team is wrapping up for a holiday weekend.

Have a safe production summer!!

Ben Guerrero has penned a story for Recycling Product News ‘The Risks of Not Staying on Top of Shredder Maintenance.’  Survival in times of low markets dictate many cut backs in shredding facilities worldwide.  When you are low on people, finding man hours to tackle even the most basic maintenance is a challenge.  Ben outlines some of the do’s and don’ts in this article.

While it may be ‘preaching to the choir’ for operators, this simple advice should be acknowledged by senior management.  Shredders and non ferrous separating systems won’t keep running without minimum maintenance.  Idled plants won’t start up or hold much resale value if they are ‘put away cold and wet.’   Deferring too much maintenance could lead to larger issues.

Some scenarios to consider, all actual incidents:

• Failure to clean the motor air cooling system filtration leads to dirt build up in the windings.  Warmer operating days lead to high motor temps, then overheating and a motor fire.
• The cleaning crew continues to defer cleaning the spillage that slowly builds up between the shredder and motor building.  Your inspectors miss an auto with  fuel in the tank.  Fuel runs out as the auto slides down the infeed chute, it trickles down next to that scrap pile, and there is ignition.  A fire right next to your mill machinery now needs attention.
• Extending runs times between grate changes saves part costs.  Eventually grate holes are 30% larger than new, the distance between hammer tips and anvils is large, and cream puffs of balled up sheet drop from your stacker instead of dense shred.  Your fluff loads have more metal than you remember.  You check the last 3 months of production records and realize your non ferrous recovery has dropped noticeably.  Ferrous production is up but shipping density is down, zorba volume is down, and so is revenue.  Was it feed stock, weather, or maintenance? Compare the savings in wear parts to the revenue decline.

What’s the best balance? The answer is different for each plant.  Safety and environmental compliance are non-negotiable operating absolutes.  Operating maintenance is not too far behind.  Ideally it’s all the same mindset at your facility, and peak performance and efficiency continue to be the goal of all team members.  Yes, there must be rational tradeoffs between budget, readiness, and acceptable downtime.  Plan in advance to be ready for seasonal or market upticks in volume.  Be sure your facility stands ready to execute for a return to higher production when opportunity arrives.

Find Ben’s article Recycling Product News – Ben Guerrero.

Early 2015 is a tough time to be in the shredding business. Scrap prices continue their deep dive while the input side of the business tries to adjust to the change in value.  It may be the sign of a fundamental reset in the value of scrap.  Obsolete scrap volumes may lag for some time until the economics of disposal and transport become clear.  If you are running a shredder on a limited schedule, can you safely defer routine maintenance?

What do we mean by routine?  They are the habitual tasks that are part of best practices.  They are the small things you know are important, but are tempted to defer because of limited run time or available maintenance hours.  And they are normal maintenance expenditures you might be tempted to put off until better markets return.  Skipping what you know works isn’t ‘adapting’ to new realities but a mentality that will cause more costly problems down the road.

Everyone just needs to take stock of their current production requirements and adjust upon facts, not guesses. The plain truth of the matter is the shredder has to be opened and looked at after every production shift.  Inspecting the box is a matter of routine, not tons.  Who has not had a problem in the first part of a production shift? There may be a piece of scrap jammed in such a way it will pop off end caps or bind the rotor during start up.  Inspecting after each production shift helps you plan for regular maintenance and reduces the chances of surprises.

Everything needs to be checked, despite reduced manning and run hours.

• bolts have to be tightened
• liners have to be replaced when wore down
• feed rolls have to be cleaned of scrap and maintained
• hammers need to be flipped, moved, or replaced
• check the distance between hammers and grates & anvils
• Non-ferrous recovery systems need regular checks to be sure they are fully functioning

Grates have to be checked for proper distance from the hammers to be sure you are getting the best density and non ferrous recoveries from your processing.  The anvil to hammer distance keeps cutting and sizing working to ensure efficient throughput in the mill. Many things are checked on each shift that influence how well the shredder performs and keeps production costs in line with expectations.

Planning ahead on vital spares and replacement parts cannot be deferred too far into the future.  If you shred, often you will need it sooner than you think.  Rotors, motors, bearings can fail at the least opportune moment.  Ordering ahead of time and using your labor hours in a pre-determined way helps keep overtime and costs level.

In the business of shredding scrap, not everything works out as expected.  Despite economizing on maintenance and repair, you know where you can defer and where you can’t.  Go with the things you know work best. It will save you headaches and money in the long run.

Keep your shredder drive motor breathing clean air.  Change out the air filters!  Whether running an electric motor or reciprocating engines in the heat of the North American summer, you need max air flow.   If you have a closed water cooled system, make sure the heat exchanger externals are clean.

Even if you have an outdoor air cooled motor, you likely have a filter within the motor enclosure.  Check it monthly if not more.  Motors outside of buildings are often subject to more dust and dirt than those housed in buildings.

If your motor is housed in a building, keep it positive pressured to cut down on dirt and dust.  Many motor rooms have a negative pressure, noticeable when you first open the door.  Dirty intake filters and obstructed vents are the first place to look.  If that doesn’t do it you need to study the situation and find out why your exhausting more air than your drawing in.  Keep in mind the answer if often add more air in, but there is a practical balance for each installation.

Your shredder’s motor protection relay is monitoring stator air temps and trying to keep the motor temp below the point the motor’s insulation suffers most.  To cool the motor, that means it’s turning without load, limiting your ability to shred.  A clean motor and clean filters will make for more effective cooling.

The photo below is from a dirty air cooled motor.  The build up in the stator is combustible fine shredder fluff and dirt.  It’s plugging up the stator section, preventing air flow through the motor.

The motor was in the shop due to a motor fire.  You can guess the cause.?

Filter media can be expensive and a chore to change weekly or monthly.  But it is preferable to downtime and damage.

Dirt Clogged Motor Stator