Effective aluminium melting and dosing furnace maintenance is particularly important in this respect, not only in terms of achieving optimal equipment performance – for instance manufacturer-specified energy consumption ratings or metal yields – but also in relation to avoiding unnecessary downtime and issues that may impact the quality of melt produced for casting.
Puzzled by scrap rates creeping up? Wondering why your melting furnace’s energy consumption is not what it once was? Dosing accuracy not quite right? It could be that a maintenance issue is the culprit. To help, here’s a handy guide to some simple checks, measures and tools that can make a big difference to energy consumption, liquid metal quality and casting productivity.
Properly maintaining an aluminium melting or dosing furnace is essential to its performance and service longevity. However, while some maintenance requirements are inevitable. Others are avoidable.
Here are some tips to help:
Correct use = better performance: While not strictly a maintenance tip, it is important to remember that the best equipment with the best features will always underperform if they are not operated correctly. For example, a shaft laser scanner for melting furnaces is of no use if it is not set up correctly. Or automatic charging has no effect if there is no full car in the charging unit.
Incorrect usage can also result in the premature failure of parts and/or excessive energy consumption.
With this in mind, our next tip is…
Most furnace manufacturers will offer dedicated training packages to help ensure operating and maintenance teams know exactly what to expect from their furnace and what to do to guarantee specified performance levels are achieved.
Having personnel with in-depth process and equipment knowledge is particularly important for optimizing dosing furnace performance.
Furnace control solutions will quickly highlight the right data for operators to take action but having an informed and knowledgeable team in place that can act swiftly in response to control system messages can make a huge difference to on-going productivity and to avoidable downtime.
Digital solutions have a lot to offer in terms of supporting effective process and equipment maintenance management.
This could, for example, be in the form of equipment specific control software, for instance dosing furnace control software that facilitates real time monitoring of pressure sensor data and automated correction of dosing volumes. Remember though, it’s important to liaise closely with your supplier to make sure you are using the latest version in order to leverage full functionality from your equipment.
Did you know: Other digital solutions can help too – especially those that can deliver real time analysis of KPIs to quickly flag issues and alert teams to any action required. Learn how our Monitizer suite of products, could help you.
Every melting or dosing furnace comes with specific performance guarantees, from energy consumption values to dosing accuracy. However, these figures are based on the exact engineering employed by the manufacturer.
Modernizing existing equipment can be a highly effective way to prolong equipment life and improve its performance to ‘better than new’. In this sense, equipment modernization is the ultimate preventative maintenance measure, avoiding the need for costly replacement of key equipment.
In addition to these general tips, there are also some specific maintenance measures that are important to remember in relation to melting and dosing furnace optimisation. Here are a few which may help keep your melt shop on top form.
Regular cleaning of melting furnaces is essential for two important reasons. Firstly, failure to remove deposits can reduce furnace capacity and impact melt quality, which in turn can increase scrap rates. Secondly, repeated build up can damage the refractory lining. This can result in unwanted heat loss (and the unwanted bills associated with this) and inefficiencies in the process which once again can have a detrimental impact on melt quality.
Once the melting furnace refractory lining is worn out, its ability to withstand metal penetration and erosion is compromised – minor wear can become a major issue relatively quickly. Having to replace a furnace lining after a certain time, depending on operation, is inevitable. Having to replace it early is entirely avoidable with, among other measures, the right cleaning care. A quick check in the operating manual will give you all the detailed information you will need, for example on the recommended amount and use of additives/salt.
Access is everything
If you are looking for a new melting furnace, choose one specifically designed to make the furnace interior more accessible for cleaning. One with an internal geometry reachable with recommended cleaning tools, no hidden or difficult-to-reach corners, and which uses materials that resist adhesion as long as possible. Easy accessibility of the furnace interior also contributes to minimized metal loss during dross removal.
Did you know: StrikoMelter’s specially designed doors and the different, adjusted inclination angles of the melting table, optimize cleaning conditions. We’ve developed a range of videos, guidelines and specifications to help customers clean and keep their furnaces in top condition for maximum metal yield.
Focus on free melting
For shaft melting furnaces, daily ‘free melting’ on full power is also necessary to ensure dross removal and a clean, efficient melting process. Covering the shaft during this process with an optional hot gas baffle retains heat (also preventing energy wastage) and allows better separation of the metal from the dross.
Another interesting fact: As well as facilitating easier dross/metal separation, StrikoMelter’s hot gas baffle reduces energy consumption during the free-melting process by up to 15%.
Strengthen with steel
Retrofit solutions to help prolong furnace lining life and avoid early replacement are also a good option to explore. At StrikoWestofen, for example, we offer specially designed steel impact plates as a retrofit option to help customers avoid damage and mechanical wear to the furnace lining in the upper shaft area which is a zone suspectable to stress, particularly if charging heavy and sharp-edged materials.
Don’t forget: When it is time to reline your melting furnace, you should expect your supplier to modernize performance, e.g. gas consumption per ton of molten metal, based on the latest knowledge and materials used, and provide validation data from onsite testing.
Excess air is one of the most common contributors to increased energy use by melting furnaces, often caused by unbalanced air-to-gas ratios.
The ideal goal for any foundry is to ensure their gas burns completely without any excess of air – this level is known as a "stoichiometric air-to-gas ratios". As well as reducing gas costs (up to 2% compared to a burner with too much air surplus), maintaining a stoichiometric air-to-fuel ratio will help reduce metal oxidation and optimize the furnace’s overall productivity.
A periodic review of burner calibration and alignment as part of standard maintenance measures is therefore one of the easiest ways to ensure your melting process is working as efficiently and effectively as possible.
Burner alignment and positioning is also very important to avoid flame impingement. Shorter flames and lower flame speeds prevent direct contact with the charge material, thereby reducing dross formation and metal loss.
Automating key processes is another option for reducing unnecessary maintenance and improving efficiency, especially with melting furnaces. For example, charging at the correct time, with the right volume and material mix, can not only dramatically reduce energy consumption, it can also help optimise furnace ‘health’ by minimizing maintenance and maximizing service life.
Adopting an automatic charging system and shaft laser scanner can therefore have a big impact.
With melting furnaces considerable amounts of heat escape through poorly sealed doors, or when doors are poorly positioned. Maintaining the rope seal on furnace doors may seem a very small detail but even this can generate an energy saving of 1%. Together with the self-sealing cleaning door, the rope seal achieves perfect tightness. Having a tight seal in place saves energy by reducing heat loss during melting and holding, while also preventing air ingress which could result in oxidation and corundum formation.
Pump-based dosing furnaces that employ a pump inlet valve, pump pots and separate transfer system to feed liquid metal into the pump, require more cleaning due to the additional chambers involved. The process is also more prone to contaminant build up due to melt exposure to the atmosphere.
By contrast, single chamber dosing furnaces that employ a riser tuber system have less mechanical parts (reducing machine wear) and areas to clean. In fact, analysis shows a riser tube requires 94% less cleaning compared to a pump system. Additionally, melt quality is enhanced due to melt being taken from below the bath surface, mitigating any risk of oxidation contamination.
While reducing the total amount of cleaning and maintenance required this does not, however, mean that single chamber dosing furnaces can’t be optimized with the right care.
Just as with melting furnaces, regular and timely cleaning of dosing furnaces is vitally important for product lifespan and melt quality. Optimal cleaning frequency will depend on factors including metal quality, specific alloys used and dosing frequency however, here are 3 cleaning habits that could help ensure your process is as productive as possible.
Shift it, with clean tools: Once per shift, it is advisable to scrape the side walls of material deposits and remove aluminium oxide from the surface of the metal bath in order to optimise melt quality and ensure efficient furnace operation. Always ensure that tools used are dry and free of oil and grease for optimal results. It’s also advisable not to use cleaning salts for this process. Check your furnace’s operating manual for more information on cleaning methods and frequency.
Don’t let your riser rim be grim: While dosing furnaces employing a riser tube mechanism reduce the risk of melt contamination by taking metal from below the bath surface, it is important to keep the riser tube run-out rim clean and free of possible aluminium deposits. As well as impacting the quality of the melt, this can also avoid deviations in dosing accuracy.
Did you know: Westomat dosing furnaces feature a Rim Cleaning Jet option which employs short, compressed air jets to continuously remove aluminium deposits, helping to reduce maintenance requirements and improve uptime
Love your launder: The transfer launder is another area where cleaning and maintenance are crucial to avoid issues relating to dosing accuracy, process consistency and to the quality of cast parts. Shorter transfer launders help minimize this risk and are therefore preferable but keeping them clean is always essential. It is also worth considering using self-cleaning launders treated with special coatings to optimize metal flow by preventing adherence and metal threading to the launder surface.
As previously mentioned, when equipment replacements are required as part of ongoing maintenance plans, using OEM parts can make a big difference. In addition to lasting longer, which has clear financial implications, they also ensure equipment performs as it should for maximum productivity. While this is true of any piece of foundry equipment, it is particularly important in dosing furnaces. Here are two examples to explain why:
Riser tube: incompatibility = inaccuracy
While a riser tube may seem an easily interchangeable part, even small variations in tube tightness, composition and dimensions can have a significant impact on dosing furnace performance – most noticeably through lost pressure which in turn can skew dosing accuracy.
Non-OEM replacement riser tubes may also lead to incorrect positioning in the melt, either in initial deployment or over time as changes in tube diameter may occur during furnace operation. The end result is the same - dosing inaccuracy caused by part incompatibility, with even the slightest deviation in dimensions potentially causing big problems.
Furnace lining and components: fit for purpose
OEM replacement linings and refractory parts for dosing furnaces guarantee exact fit. Why is this so crucial? Because a poorly fitted replacement lining can increase total energy consumption by as much as 30%. It can also lead to pressure tightness problems, resulting in dosing inaccuracies, and to a poor fit of parts – all of which can negatively impact dosing furnace service life, productivity, and melt quality.
The specific design of OEM parts is also important, as slight deviations in shape can make a big difference. For example, the shape of our grey cast iron funnel for Westomat is optimized for maximum flow rates, rapid filling and simpler cleaning.
While one product may look the same as another, the processes and materials used can vary significantly meaning that, for example, mechanical abrasion resistance levels are dramatically different. This may result in premature part failure and the need for further replacements ahead of budgeted maintenance schedules.