Foundry Ladle Maintenance and Trouble Shooting
In many foundries the ladle is still the most common method for transporting and pouring molten metal. Compared to many other pieces of foundry equipment, the typical ladle is still a fairly basic item with a design that hasn’t changed greatly for decades. A workhorse of the foundry, it is expected to work when required, day in and day out, without fuss or drama. As such it is often taken for granted, overlooked until something goes wrong, and only getting attention when either production and/or safety is compromised.
The purpose of this article is to therefore give some guidelines on how a foundry can get the best use out of their ladles, and avoid unexpected breakdowns.
Much of what follows is common sense, and will already form part of a good foundry practice but it doesn’t hurt to be reminded. (Hopefully avoiding grandma and egg sucking along the way).
The Right Ladle for the Right Job
General ladle maintenance and trouble shooting is simpler if the basics are right to start with and the ladle is designed for the actual purpose it is used for. It is appreciated that over the years many foundries build up a stock of ladles, usually of different types and often in various states of repair. Typically only a few of the ladles may get regular use with the rest being held in storage on the off chance that one day they might be needed.
Therefore , if you are looking at changing or adding to your casting process it may seem unnecessary to get a new ladle especially if your spare ladles look like they could be used but this can be false economy as it is better, and safer if the right ladle is used for the right job.
The ladle should be sized for the intended working capacity plus safe freeboard for a given refractory lining thickness. You should never fill a ladle to the brim either by accident or to squeeze a bit more capacity out of the ladle. This is especially true with ductile treatment ladles that have extended freeboards to contain the treatment reaction and, if over filled, can hold much more than their rated capacity. Ladles are designed with safety margins but this margin may vary from manufacturer to manufacturer and should not be used to allow a ladle to be persistently overfilled.
Over filling can upset the balance and handling of the ladle, and can also lead to accelerated wear on parts such as the gearbox and trunnions. Ladles should therefore be filled in a way that the contents can be measured and quantities known.
Conversely it is not good practice to use an over sized ladle. If you have a 2t capacity ladle going spare but find that you only need 1t capacity then it’s not advisable to use the 2t ladle only half full. The ladle is going to be bottom heavy, difficult to rotate and wear rates will be increased.
Match the Ladle to the Refractory Lining
If you are looking to purchase new ladles, then discuss your refractory lining requirements with your ladle supplier as well as your refractory supplier. It is not my place to tell you what type of refractory or which refractory supplier you should use but it is my job to make sure that the ladle offered is designed to work most effectively with the refractory lining you wish to use.
One of the basics is to make sure that the ladle shell is sized to give the working capacity for the refractory lining used. In the past many ladles used to have firebrick linings which are typically half the thickness of today’s castable concrete refractories. If the ladle shell isn’t sized for a castable concrete refractory but is still sized on a firebrick lining you could find that the working capacity of the ladle is significantly reduced and that the freeboard is compromised.
There are also a number of details that can be added to a ladle design, usually with very little additional cost, that can make the wrecking out and relining of ladles much quicker and easier for your maintenance crew. Detachable bottom sections or push out base plates can greatly reduce the time it takes to remove a heavy-duty castable concrete lining, avoiding the need for prolonged use of power hammers, freeing up personnel and quickly recouping the additional cost of the ladle.
It also helps if you have the time to let the ladle cool down before wrecking out the lining. It is not uncommon to see ladles with patched or distorted shells where the hammer has either punctured through a shell or has created a bulge that then acts as a lining anchor making the refractory removal harder. In extreme cases the ladle shell can become so deformed that new lining cannot be safely fitted.
One other point to be aware of with regard to ladle linings is if you send the ladle off to your refractory company to have a new lining fully dried in an oven then the ladle gearbox and sidearm assemblies should be first removed. Soaking a complete ladle at temperatures of 120°C (248°F) and above for an extended period during the drying cycle will damage the bearings in the gearbox rendering the gearbox inoperable.
Initial checks with a new ladle.
Before a new ladle is brought into service, check that all the lubrication points are properly greased and that the gearbox has the correct amount of oil in it. The ladle handbook will show all the grease points and give information on the correct type of lubrication to use. Check that everything is working mechanically, especially the safety catches. Suspend the ladle and fully rotate it. This will also help to distribute the lubrication around the moving parts.
Follow your refractory company’s instructions for installing a new lining.
Maintenance and Troubleshooting your Existing Ladles
Due to their purpose, ladles are designed with a high safety factor. However this does mean that a ladle can often still carry on working, apparently OK, despite suffering from either prolonged neglect, damage or a combination of both. This can unfortunately mean that when the ladle does finally fail then this can be catastrophic with potentially dangerous consequences. The best and most simple way to avoid this is to carry out daily safety checks, before the ladle is to be used so that any potential problems can be spotted at an early stage and action can be taken without safety or production compromised.
Daily ladle checks
The ladle handbook will give a list of safety checks, some of which will be specific to the ladle, that should be carried out but the basics are as follows:
Carry out visual checks before the ladle is brought into service and when the ladle is cold.
Does anything look damaged, especially suspension parts such as the sidearms, lifting bail and hook?
If so, then don’t use the ladle and get it fixed.
Are the safety catches functioning correctly?
With the ladle on the ground try to rock the ladle sidearm; does the movement seem excessive? This is down to “feel” and it is difficult to give accurate guidelines as to what is acceptable as this is likely to be different for each type of ladle. However if you know your ladle you should be able to tell if the amount of backlash indicates that something is worn.
When the ladle is picked up by the overhead crane do the sidearms/lifting bail assembly visibly move as the slack is taken up in the sidearm bearings? (If so then the sidearm bearings definitely need changing).
Does the handwheel shaft move around in its housing? If so then the bearings are worn and it will be difficult to control the ladle pouring action.
With the ladle suspended, rotate the ladle in both directions. It is normal for the effort required to change as the ladle centre of gravity changes but the rotation should feel smooth with no jumping of the gears.
Is there excessive backlash in the gears?
The gearbox should be able to hold the ladle at any degree of rotation. If it doesn’t then the gearbox needs to be stripped down and examined.
Check for any signs of damage.
Keep the ladle clean and remove any metal splash build up.
Like all maintenance tasks this is best done as planned maintenance rather than in response to a breakdown.
The ladle handbook will have instructions on stripping down the ladle and examining the gearbox etc. This should be done periodically and be dependent on the usage that the ladle gets rather than simply following local regulations. If the ladle is used on a 3 shift basis 6 days a week then it will need more regular full inspections than if the ladle is only used once or twice a week.
General Ladle Handling
One of best ways of maximising the ladle life is to make sure that the ladle is correctly handled at all times, not just when the ladle is in operation but also during maintenance periods.
For example, if a ladle is to be handled by a fork lift truck (FLT), even for general handling rather than production purposes, the ladle design should reflect this and the ladle should have fork pockets incorporated into the design. Ideally these pockets should be on the ladle body. If a ladle is picked up under the ladle bail by a FLT and transported, the rocking motion transmitted back to the gearbox can, over time, cause accelerated wear and/or damage to the ladle gearbox, including shearing of the sidearm arm where it connects to the lifting bail. If foundry needs to transport a ladle in this way then fitting an additional sidearm safety catch to the ungeared sidearm can counter this rocking.
Rotating the Ladle Bail when the Ladle is sat on the ground.
There is often a need to rotate the ladle bail clear of the top of the ladle when the ladle is placed on the ground, typically during maintenance or if the ladle is to be pre-heated.
This creates two issues that the foundry needs to be aware of.
Firstly the ladle gearbox is effectively working in reverse to how it is designed to operate and the loading imposed on the gearbox and ladle drive trunnion will be greater than when the gearbox is used to rotate the ladle shell. This can lead to increased wear on the gearbox and especially the drive trunnion. If unchecked, and in extreme cases, this can lead to the failure of the gearbox and/or drive trunnion resulting in the uncontrolled descent of the lifting bail.
Ideally the ladle lifting bail will be supported at all times but this may not be practicable therefore the ladle design can be adapted to minimise this issue. Additional safety catches can be added so that the lifting bail is locked at the rotated angle and, if necessary, counter weights can be added to the sidearms to minimise the reverse loading on the gearbox.
A second issue is that a great deal of care has to be taken if an overhead crane is used to assist in returning the lifting bail to the vertical. It is very easy for the crane to “get ahead” of the gearbox so that the crane is effectively pulling the lifting bail against the gearbox. This can also cause damage to the gearbox.
Ladles are the basic workhorse of the foundry providing the critical link between the furnace and the moulding line. A small amount of regular TLC will ensure that your ladles give safe, reliable and efficient service every time you use them.
Acetarc Engineering Co. Ltd