Energy efficiency comes down to one simple measure: the total energy used by the business per unit of sales. The main factors affecting energy efficiency are:
- Net process yield.
- Plant utilization and melt capacity.
- Minimizing lost energy.
- Utilization of waste energy.
Net process yield has a significant effect on energy efficiency by the simple fact that a business only gets paid for what they sell, not what is melted. By increasing the net process yield, a business is able to sell more for a standard unit of melt.
Example: A foundry is selling 32,000 tons of good castings per year, with a total melt of 67,000 tons, the net process yield is 47.8%. The foundry has efficient melting capabilities at an average of 585 kwh/ton. The total number of units consumed is 39,195,000 Kwh. By increasing net process yield by 10% the foundry will produce the same 32,000 tons of castings with a total melt of 55,363.3 tons at 585 kWh/t, equaling 32,387,531 units – a saving of 6,807,469 units. If we use 0.20 pounds as an average unit cost, then this equates to a saving of 1,361,493.00 pounds p/a, with an increased capacity of 6,726 tons.
Net process yield is affected by four major factors: melt yield, spill & pigging, box yield, scrap, and rejects. The box yield is a major factor and by utilizing the latest gating techniques – such as John Winter MT/MTV High Density Exothermic Sleeves, having much higher efficiency than conventional sleeves – significant improvements can be made.
Additionally, these sleeves exhibit high crush strength and small contact areas so their placement can be focused to parts of the mould where conventional sleeves cannot be used, giving possibility of increasing numbers of cavities per mould, further improving yield. Another option, generally more suited to jobbing foundries, is the use of direct pour techniques. This method has a significant impact on increasing box yield, John Winter supplies TXP exothermic pouring units coupled with a range of filters, giving the foundry another option to increase yield.
Increasing melt yield, or inversely reducing melting losses, must be maximized. In simple terms, if you charge a lot of non-metallic materials into the furnace your melt yield will reduce as a result of increased slag production. More related to non-ferrous applications, the more oxidation loss, the less metal is produced. Therefore, the use of clean scrap & foundry returns, and the use of a protective cover flux, can all play a vital role in improving melting yield. Every ton of slag/dross removed is one ton less metal produced for the same amount of energy. John Winter supplies a range of cover fluxes and metal treatments designed to improve metal cleanliness and melt yield.
Spill and pigging are a function of pouring issues, metal changes and plant up time. There should be constant focus on improving the following:
- Pouring techniques.
- Ladle lids & insulation.
- Reducing the number of metal changes.
- Reducing plant stoppages, which can result in increased pigging. This is especially important when using un-heated auto-pour units.
Reducing scrap and rejects is particularly important as high scrap has a disastrous effect on net process yield, besides the other negative costs associated.
Plant Utilization and Melt Capacity: Foundries are energy intensive industries, maximizing plant efficiency to increase output per hour plays a significant role on energy efficiency. The foundry needs to produce the castings we sell in the shortest possible time, or for a given time increase the overall output. With regards to melting, it’s essential to maximize the melting capacity of the furnaces to reduce metal holding and decrease kWh/ton of metal produced.
Another factor to consider is cleanliness of the melt which effects slag build-up on linings, reducing actual furnace capacity and increase melt cycle times associated with difficulty slagging off. Slag build reduces lining life and in the case of heated auto-pour furnaces, adversely effects the life of the inductor, and causes blocked fill spouts resulting in downtime. John Winter’s SlagCure K, a Fluorine free cleaning flux, can and is used in melting furnaces, treatment & pouring ladles and pouring furnaces to reduce build up on fill spouts and inductors.
This takes place across the full spectrum of the foundry process, from melting through to finishing. In melting, in addition to what we have discussed in previous paragraphs, reducing lost energy can be achieved by using simple actions, such as:
- Keeping furnace lids and covers in place.
- Utilizing lower density insulating refractories (where applicable) to reduce energy loss and to remove the requirement to preheat ladles.
- Use of enclosed focused extraction plants to reduce the overall volume of air being extracted. In simple terms, every cubic meter of air extracted from a facility must enter. This is more important in colder climates.
- Use of air make-up systems to bring air from the outside into enclosed extraction systems, reducing energy requirement to heat the facility.
- Ensuring extraction plant is operating efficiently and is cleaned. A blocked extractor will increase demand for the extraction plant motors increasing electrical consumption, whilst not extracting dust.
- Reducing and controlling shot blasting times, improving sand peel and adherence to castings by better sand control and use of coatings such as John Winter Cleancast mould & core coatings.
- Use of power factor control across the whole facility to keep the COSø as close to 1.0.
- Zoning of compressed air supplies to enable isolation when not in use.
- Use less centralized compressed air systems and focus on reducing leaks. Compressed air is one of the highest energy intensive sources used by foundries.
- Where possible, switch to electrical actuators and motors.
- Investing in new machinery or upgrading existing plant. Modern technologies are usually more energy efficient.
- Switching off plant compressors and lights.
- Using low energy lighting systems.
- Insulate buildings.
- Solar panel introduction, foundries have large roof areas, solar panels can be employed to offset electrical energy costs. John Winter recently employed solar energy, and it is paying benefits.
Utilization of Waste Energy: As discussed earlier, the foundry process is energy intensive and, in most cases, energy is lost to the environment as heat. Looking at ways of utilizing waste heat can be very advantageous such as:
- Using heat pumps to generate hot water from extraction air, this can be used for office heating or supplied to other facilities as a source of heat.
- Utilizing hot extraction air from pouring lines for core and paint drying facilities,
- Using hot water from cooling systems to cool dies (permanent moulds).
In summary, with increasing energy costs, it is becoming more important that energy utilization and recovery are part of future planning for energy intensive industries, such as foundries. Management should make energy efficiency a top priority in day-to-day operations, and future plans, to alleviate financial stress.
Andrew Tagg
Technical Manager
