Posts tagged Maintenance

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.

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

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.

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.

 

 

 

High torque drive couplings usually involve a shrink fit.  The coupling is machined with a smaller diameter than the mating shaft.  The coupling is heated 300-400 degrees hotter, expands and can be slipped onto the drive shaft.  It cools, shrinks in diameter, and a tight mechanical fit is accomplished (with keyways or splines as well).

You may have to remove a shrink fit coupling when changing out drive motors or rotors.  Your manufacturer’s rep can get you some advice on the pulling force and strength needed for a successful removal.  Without adequate set up, you’ll bend or snap rods, and be left with hours of time to shed enough heat before you can work on the unit again for another attempt.

1. You’ll need a lifting device and rigging to hold up several hundred pounds of coupling as you slide it off the shaft.
2. 6 to 8 full diameter threaded rods seated full depth in your coupling’s end holes, and a few dozen nuts.  Use grade 8 rod (150 ksi tensile) to give you full strength and minimal elongation.
3. 2 inch thick backing plate
4. 12-20 tons of jacking force.  Hydraulic jack (s) and enough jack stroke to pull off the coupling.  This may require a stub shaft insert if you the jack stroke is less than the coupling length.
5. Torches and heating tips.  Rosebud heating tips of proper size (8 or 10) are important.  Using both propane and oxy acetylene torches is wise.  Acetylene burns hotter and there is limited space to apply torches to the coupling.  Make sure you have enough gases on hand in case you need more than one attempt to remove the coupling.
6. Fire retardant blankets
7. A clean and clear work area
8. Fire fighting gear, a clear work area, and heat resistant PPE for personnel
9. Your safety program may require a hot work permit

The key item is to heat the coupling quickly, so it expands before the shaft it’s mounted on heats up and expands as well.  The difference in temps for allows for expansion.  Also, excessive heat in the shaft can lead to damage of bearings, seals, and other components.

Always let things air cool.  Never cool with water or gases like a CO2 fire extinguishers.  If you have a fire emergency, do what you need to do to minimize loss of property or life.  However quenching with water or anything else would likely damage the coupling or shaft steel.

Now is a great time to pay a little attention to your double feed roll (DFR). 

Your feeding device is one of the most important productivity factors in your scrap metal shredding system. The feeder is tasked with adding feed stock to the shredder at a controlled rate, both pushing it in and holding it back. 

It cannot be effective without traction aides on the roller surface. Lateral bars and teeth welded to the rolls grab and move material and have sharp edges to assist. Edges are key. Rounded off lateral grab bars and teeth just don’t work as well.

Ideally, you have replacement feed rollers on the ground, ready to swap in place or have a slick one piece cast roller you can replace.  Many DFR units do not. You may not have the time for a large scale DFR renewal.

Enter the K2 Weld on Tooth.

You can renew in place replacing lateral bars and adding weld on teeth to the feed roll.  Adding them over a few maintenance shifts can give you the surfaces and edges you need to grab and hold tin, bales, and loose scrap, getting your feed rate closer to new. 

Fight less on the feed ramp, feed more in the shredder.  Give us a call for a set.

As we see markets and scrap flow drop, now is a great time to perform the maintenance you don’t normally get a chance to cover as thoroughly.

Feed Rolls

Time to get them cleaned up. Cut all the extra scrap accumulations away from the side to prevent bearing damage. Once they are cleaned it is a good time to check for cracks around the shaft.  Build up roller edges. Consider K2 Weld On Feeder Teeth to restore edges and ability to efficiency grab and grip feedstock.

Grate Supports

For those shredders with welded-in side liner grate supports, now is a good time to pull the grates and check for cracks in the welds to the side walls. Also, build up the supports to make sure your grates fit correctly. Too much of a gap and the grates will bounce during production and cause them to break or warp.

Shredder Box

Pressure wash it down inside and out. Then check for cracks in the housing. Replace any loose liner bolts which cannot be tightened.  Be sure to check your hinge pin bushings, pin, etc. Don’t forget to check your safety retainer pin holes and pins themselves to make sure they are not too worn. You want a snug fit.

Electrical

Schedule a vac and clean for your switchgear, infrared scans for possible problem spots.  Drain and clean you liquid rheostat tank if you got one.  Wash down air coolers.  Change air filter media.

In Feed Conveyor

Check your upper drive sprockets and replace any missing or worn segments. Look at the reverse side of your flights for wear from the rails it rides on. If you see some deep gouges on the back of the flights, it is a sign it is time to replace the rails.  Clear out scrap caught up in the chain and finally take the slack out of that sagging chain.

Wear Parts

Clean up and consolidate your parts inventory.  Find a way to work in parts with a bit a life left in them.  Adjust your order times, but don’t hold back too long.  As soon as it gets busy, everyone orders.  Be on the front end of that upswing.  Order earlier enough!

These are just a few of the things you can check. A little fresh paint will also do the shredder good.