reducing aluminum melting costs via process, equipment control.
Related methods to improve cost efficiency.
Aluminum Foundry faces many factors that have a significant impact on their profitability.
From the rise in energy, materials and labor costs to the threat of additional government regulation, the focus of the aluminum foundry is divided into issues related to metal casting and practical issues related to metal casting
The world reality of manufacturing today.
For many operations, the increase in these operating costs occurs when the production volume drops and the customer asks to reduce the selling price of the castings.
Therefore, the foundry hopes that each department will have the opportunity to reduce costs.
In this paper, the cost center of aluminum casting chamber is studied, and a specific and practical cost improvement method is proposed.
While some changes require nominal capital investment, most of the changes can be achieved through existing melting devices to develop a real economy for aluminum foundry.
The energy required to bring the metal to the pouring temperature is the sum of three quantities--
The energy required to increase the metal from room temperature to melting point (
Usually 55% of the total);
The melting heat of an alloy or the energy required to convert it from a solid to a liquid metal (
(30% of the total);
The energy of overheating the metal to the pouring temperature (
(15% of the total).
If the melting operation is carried out in a separate furnace and the alloy is transferred to the bracket on the casting production line, additional energy must then be added to compensate for the temperature loss associated with the transfer.
The problem with aluminum casters is that a fraction of the energy input from any furnace will heat the molten alloy.
By melting the surface, the furnace shell and the wall of refractory materials, and the energy lost to the flue gas and radiation through the operation constitute most of the inefficiency that leads to the increase in melting costs.
To make these losses more complicated, any direct savings from process improvements must be multiplied by the efficiency factor of the furnace being used.
Therefore, if the furnace operates at 25% efficiency, the benefits of process improvement must be multiplied by four times to assess the impact on fuel consumption.
Figure 1 shows the effect of these losses on the available energy that can be transferred to the aluminum melt.
These losses are the driving force behind the use of the boom and the improved \"clam shell\" furnace design for the stacking melting device.
Combustion optimization if the aluminum furnace is heated through a combustion process, then the process should be optimized for the burner design and the current ambient atmospheric conditions.
This will improve the efficiency of the melting operation, reduce fuel consumption and reduce the impact on the environment.
Most burner systems receive oxygen supply from Blower systems that provide constant volume air.
Unfortunately, due to ambient temperature and humidity, the amount of oxygen in each cubic foot of air changes dramatically with the season.
While seasonal adjustments are not always required, the combustion reaction will change significantly if the combustion conditions are allowed to drift outside the optimal range.
Cubic feet of air contains fewer Oxygen Supplies for Medicine molecules in hot and humid summer than in dry winter and can lead to more reductions (less efficient)combustion.
In extreme cases, unburned fuels can be discharged into the flue gas in the form of carbon monoxide and hydrocarbons.
Under these conditions, in addition to the impact on energy costs, it also affects the hydrogen pickup in the melt.
On the contrary, operating under the condition of excessive oxidation promotes combustion inefficiency by reducing the flame temperature, because excessive nitrogen and unburned oxygen produce a extinction effect.
This can also lead to increased loss of melting and the formation of diamond deposits on the wall of the furnace.
Melting loss the normal loss associated with melting aluminum alloy is directly related to the mass and surface area of the charge and the general cleanliness of the material.
If any period of time prior to melting is exposed to medium temperatures, a thin molten material will have a disproportional loss of melting.
In addition, the presence of moisture or organic films will result in the direct conversion of valuable metals into alumina and carbide.
The aluminum alloy is easily oxidized at all temperatures, but by heating the metal above the minimum temperature required for the process, the loss is exaggerated.
For example, if the base temperature is 1225F (663C)
Assume that the temperature is increased to 1400F on behalf of normal oxidation loss (760C)
The loss will be increased by 20%, and faster log growth will occur over this temperature.
Losses at 16 degrees Fahrenheit on the same basis (815C)
Loss of more than 200% at 122SF.
The continuous overheating of more than 16 degrees Fahrenheit will eventually reach the temperature at which the aluminum alloy burns in the air, which is similar to magnesium alloy.
Another important consideration about the surface deposition formed during the charging or turbulent transfer of molten alloys is that these thin film deposits usually deposit a large amount of high-quality aluminum alloy in the mixture.
The relatively clean skims taken out of the pouring bucket or the holding furnace well may contain up to 90% of the available alloys, while from the wet-
The well furnace that receives the typical mixture returned by the ingot and process will contain up to 70%.
Air with airoxide-
The aluminum mixture is very sensitive to the continuous oxidation rate faster than normal aluminum volume, and if it is allowed to enter the firing furnace cylinder area of the melting device, in the process known as \"thermal reduction, white ash that may be converted into alumina--
Heat release reaction of aluminum combustion to oxide.
Some melting room operators believe that when white ash is observed after being removed from the furnace cylinder of the furnace, white ash is a beneficial indicator of low melting loss, but in fact, this may be bad practice depending on the time and the way ash is formed.
Surface energy transfer aluminum surfaces are effective in terms of radiation energy and are an additional area of improvement to control energy costs.
At a base alloy temperature of 1225F, the molten aluminum surface will radiate 9200 Btu/sq ftlhr, and the loss rapidly rises to 20,000 Btu/at a temperature of 16 degrees F/
Conversely, when present on the molten aluminum surface of the melting furnace, a layer of scum and oxide may be an insulator that is not needed.
Figure 2 describes the loss of heating efficiency associated with an increasingly thick scum layer and confirms the benefits of frequent removal of this material, one of the best ways to maintain primary melting rates, Meltus
Many cases below
The normal melting rate has been solved by a simple method of removing the slag from the furnace bed to expose the clean melting surface to the atmosphere of the furnace bed chamber.
Improved measurement although one of the easiest ways to improve the operation of the measuring melting chamber is to view the total heat consumption reported on the utility bill at the end of the month, referred to
There are also terminology methods.
The simplest thing is to observe the furnace in operation (
If there is no direct reading instrument).
Depending on the ignition train and burner combination used on melters, most units will switch between on/off mode or high modefire/ low-fire mode.
High-time ratiofire and low-
Fire or timeon versus time-
Off will be a direct measure of energy consumption.
Another method, while not as effective as measuring the ignition time, measures and records the flue gas temperature.
An increase or decrease in temperature from an optimized level (
For example, 2100F to 2500F)
This means that more energy is piling up, representing a 10% efficiency loss of available melting energy.
Therefore, an early indication of the need to improve charging practices and even maintenance of the furnace or burner can be provided.
The first step in reducing the process cost and reducing the melting cost is to optimize the melting process of the foundry by ensuring that all equipment operates with optimal performance.
Optimization of burner combustion-
The requirements for burner adjustment and calibration have been discussed and it is noted that regular maintenance is required in this area.
Many business units have found that fuel costs can be greatly reduced and performance improved in this way.
With today\'s burner system and ignition system, a certain degree of expertise and equipment is required for fine-tuning
Adjust the combustion process for a full range of operations.
However, visual indicators can indicate the need for corrective action.
For the furnace with an open loading well, the method of preheating the loading by hanging the loading material on the open well is a good way to produce.
With 60% of the total melting and overheating energy required to raise the material to the melting point, any free energy recovered on the oil well is a positive benefit.
Preheating to 600-
It will save more than 30% of total energy demand.
Many operations do achieve some form of preheating by extending the ingot to the charging ledge, but half
Permanent rack for supporting and exposing more ingot surface area, while preheating is beneficial (Fig. 3).
For those operations that return with bottom drop or dump Hopper charging, the container can even be suspended on the charging well for preheating benefits.
If the main melting device is designed with a dry furnace charging system, the charging method of the material should allow as many charging surfaces as possible to be exposed to the flue gas.
It should be avoided to place solid bales on the furnace cylinder, and if the sow is charged, the space above the sow should be full of returns.
In addition to the benefits of energy saving, if the charging material contains moisture or organic matter, direct benefits will be obtained to reduce the loss of melting.
Cover the well--
The radiation heat loss on the surface of molten aluminum confirms the need to cover any inactive furnace well surface with a lid or a refractory blanket to minimize the loss.
The uncovered surface will emit energy at an estimated cost of more than $0.
If the furnace efficiency is 30% and the energy cost is $6, it is 30/hour/square foot.
When many jobs cover their support wells, they ignore the damp-
Charge their main furnace.
The size of these devices is usually for the convenience of charging and cleaning the furnace, and there are a lot of areas that are not needed for most of the production day.
If these surfaces cannot be converted to preheated areas, efforts should be made to install a removable cover for the surface when no contact is required (Fig. 3).
High operating temperatures are another area where costs can be reduced.
While the efficiency of the furnace will directly affect the amount of savings, the additional 100F temperature is likely to increase the energy required to overheat by 10%, and then keep the metal at high temperatures.
Reduce furnace setting temperature during non-period
Operating time will result in direct savings in melting loss and energy consumption.
Also, the reason for keeping the temperature high should be re-
Check according to current requirements.
Is it considered that a high temperature is needed to balance the transfer loss between the furnace and the mold?
If so, it is beneficial to use ceramic pouring tanks with less radiators.
Alternatively, the transfer between the main furnace and the remote holding furnace should be carried out with a preheated transfer package with an insulating cover.
This is much cheaper than carrying 20,000 of metal in a primary melting device at high temperatures.
Many operators mistakenly believe that a higher set temperature will promote faster melting.
The reality is that the melting speed is controlled by the capacity of the burner and the capacity of the furnace cylinder to accept the supply of energy.
The accumulated scum layer will inhibit heat transfer and turn into alumina at high temperature with the mixing layer of metal and oxide, further increasing the loss of melting.
Precautions for furnace-
Another area that is often overlooked is the time when the furnace remains open for charging or maintenance cleaning. The time required to perform these operations should be studied in order to pass through equipment changes and personnel education.
Modern furnace design is very concerned about the energy lost in the non-open flue
Firing cycle of furnace operation (Fig. 4).
The designer of the newer furnace has worked to match the flue opening to the firing rate and seal the flue during the burner shutdown.
This will eliminate the chimney effect of the Open flue, which is greatly enhanced by air leakage around the poorly sealed door.
Improved maintenance of door seals and possible installation of automatic flue covers can generate a quick return on investment.
The choice of process equipment although most operations are reluctant to consider capital investment during periods of slow economy
Profitability is declining or low, which is actually the time when this investment is most needed. In-
Recycling of House slag--
Aluminum drops are common to skims
Any aluminum melting operation of the product, according to the charging material, melting and process method, the different operation of the product will be very different.
The power generation rate will be 1-using clean charging materials-
2% of the charge weight, but if light material containing water or organic matter is included in the charge, the yield may be as high as 10-
15% of the charging weight.
Traditionally, these common
The product can be disposed of through recycling channels, and the melt store can be compensated for a fraction of the value included.
Recent progress has allowed the recovery of metals from scum in power-generating furnaces.
The equipment model can be used to handle 20-
The weight of the manual or fully automatic separation material is 300.
In practice, the hot slag is transferred directly from the furnace to the process equipment, a small amount of flux is added to the process equipment and mixed with the scum to achieve gravity separation of metals and non-metalsmetallics.
Once separated, the aluminum value is transferred back to the melting device in the form of a molten or preheated ingot to retain potential energy.
For the foundry that processes the scum material on average, they ship up to 70% metal materials.
After treatment with scum recovery technology, up to 80% of these metal materials are recycled in order to immediately transfer back to the resulting melting unit.
If the average metal content of drosses is 70% before processing, the production operation will lose the new alloy equivalent to $45 per hundred weight at $0. 65/lb (
Minus any payments received from the collection/scum processor).
After 80% recovery of metal materials, the value of the material leaving the melting workshop has been reduced to less than $9 per pound (
Still valuable for recyclers).
Transfer by heating laundromat-
For those operations that are able to accept the limited flexibility associated with alloy changes and process temperature, using a heating transmitter to directly transfer the molten alloy from the primary melting device to the bracket on the casting line may be a great boon for their operation.
The economic savings are due to: * the operating temperature of the main fusion pick-up machine drops to the same level as the bracket (
With savings in fuel and loss of melting);
* Debris and oxide in the molten material generated by the turbulent transfer of the eliminated molten alloy;
* The pouring temperature range in the bracket directly benefits when short filling and mold welding;
* Elimination of shift labor and Crucible maintenance;
* Improved safety by eliminating spoon transfer of molten alloy.
Recent improvements in the refractory and heating elements of these systems reduce power consumption to 0.
56 KW/ft/hr, which is a big offset to the cost of other advantages of the equipment.
Other device options--
Many other device options can reduce direct costs, but they may only work for certain operations.
For example, if the furnace size is large enough, the use of the circulating pump is recorded, benefiting by increasing the melting rate and reducing the energy consumption of the processed material per pound, reduce melting loss by eliminating hot spots in the furnace and stabilizing chemical reactions.
With the rapid and sharp increase in energy unit costs, the economy of oxygen concentration is re-increasing
Many operations have been checked, as have the option to use the residual heat value currently discharged into the atmosphere through an aluminum furnace stack.
The heat-back burner can also provide an advantage for some operations, but it does greatly increase the initial capital investment of the melting equipment.
This article is adapted from the upcoming speech of the 6th International AFS fusion aluminum processing conference.