The government’s net zero targets, and the war in Ukraine have resulted in some of the highest energy costs on record, writes Andrew Tagg, technical manager at John Winter & Co Ltd. This has put huge financial pressures on the cast metals industry. To mitigate the significant rising cost, foundry’s need to put energy efficiency at the centre of their manufacturing strategy.
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 utilisation and melt capacity.
- Minimising lost energy.
- Utilisation of waste energy.
NET PROCESS YIELD
Net process yield has a significant affect 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 tonnes of good castings per year, with a total melt of 67,000 tonnes, the net process yield is 47.8 per cent. The foundry has efficient melting capabilities at an average of 585kWh/tonne. The number of total units is 39,195,000. By increasing net process yield by ten per cent, the foundry will produce the same 32,000 tonnes of castings with a total melt of 55,363.3 tonnes at 585kWh/t equalling 32,387,531 units, a saving of 6,807,469 units. If we use £0.20 as an average unit cost, then this equates to a saving of £1,361,493.00 p/a with increased capacity of 6,726 tonnes.
Net process yield is affected by four major factors – melt yield, spill and pigging, box yield, scrap, and rejects. The box yield is a major factor and by utilising the latest gating techniques, such as John Winter MT/MTV high density exothermic sleeves that have a 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 on 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 maximised. 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 and foundry returns, and the use of a protective cover flux, can all play a vital role in improving melt yield. Every tonne of slag/dross removed is one tonne 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 and 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 UTILISATION AND MELT CAPACITY
Foundries are energy intensive industries, maximising plant efficiency to increase output per hour plays a significant role in energy efficiency. The foundry needs to produce the castings sold in the shortest possible time, or for a given time increase the overall output. With regards to melting, it is essential to maximise the melting capacity of the furnaces to reduce metal holding and decrease kWh/tonne 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 and pouring ladles and pouring furnaces to reduce build up on fill spouts and inductors.
MINIMISING LOST ENERGY
Minimising lost energy takes place across the full spectrum of the foundry process, from melting through to finishing. In melting, in addition to what we have discussed above, reducing lost energy can be achieved by using simple actions, such as:
- Ensure furnace lids and covers fit snuggly and are closed.
- Utilising lower density insulating refractories (where applicable) to reduce energy loss and to remove requirement to preheat ladles.
- Use of enclosed focused extraction plant to reduce the overall volume of air being extracted. In simple terms, every cubic metre 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 on the extraction plant motors thus 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 and 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 centralised 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.
- Insulating buildings.
- Solar panel introduction – foundries have large roof areas, solar panels can be employed to off-set electrical energy costs. John Winter recently employed solar energy, and it is paying benefits.
UTILISATION 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 utilising 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.
- Utilising 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 utilisation 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 for future plans, to alleviate financial stress.
Note: Figures quoted are from results at a UK foundry.
For images, refer to the full printed version of the February/March 2025 issue of Foundry Trade Journal.
Contact: John Winter & Co Ltd, Washer Lane, Halifax, West Yorkshire HX2 7DP UK. Tel: +44 (0) 1422 364213, email: [email protected] web: www.johnwinter.co.uk