Energy Management in Plastics Processing - Part 5
A series of energy efficiency
worksheets by Dr. Robin Kent for the Carbon Trust to help the plastics
industry reduce costs through efficient use of energy.
UK Government Environment and Energy Helpline 0800 585 794
The cost of energy has traditionally been between 4 and 5% of the cost of a moulding, but this is increasing rapidly with rising energy prices. Energy efficiency is not a secondary issue - it can easily be the difference between profit and loss for a company.
Energy efficiency can be the difference between profit and loss for a company.
Despite proven energy efficient performance and many other benefits, all-electric injection moulding machines have been slow to penetrate the UK market. Early all-electric machines were more expensive than hydraulic ones, but this differential is decreasing rapidly. The important cost is the 'whole life' cost (initial cost + operating costs) and all-electric moulding machines offer real and significant savings in total costs compared with conventional machines.
All-electric injection moulding machines have the potential to reduce the energy costs for a moulding by between 30 and 60%, depending on the moulding and the machine. Similar savings are possible across a broad range of materials and material grades, and can be achieved even if the cycle time is kept at that required for conventional machines. However, in many cases, shorter cycle times are also possible by using parallel operations (e.g. opening and ejection at the same time) to further reduce energy consumption and increase productivity.
All-electric machines also eliminate the need for cooling the hydraulic system, together with the associated equipment requirements and energy use.
All-electric machines can show energy efficiency during all phases of the injection cycle.
All-electric machines can significantly reduce the energy consumption and production cost for many mouldings.
Removing the hydraulic system is one of the major benefits with all-electric machines. It brings many benefits, including:
- There is no hydraulic oil to be stocked, provided, filtered, changed or disposed of
- There is no hydraulic oil to contaminate the product, the operations area or the general environment
- There is no start-up time delay while waiting for the temperature of the hydraulic oil to stabilise
- There are no production effects due to temperature changes in the oil.
All-electric machines allow machine movements to be integrated directly with the control system. This greatly improves machine set-up, adjustment and process control.
Improved control means that process movement and shot weights are often ten times more accurate than conventional machines, i.e. shots weights can be controlled to within 0.001 grams (1mg). This increased precision improves product quality and reproducibility. It also allows easy monitoring of process parameters and can be used to improve mould protection.
The direct drive from motor to machine movement reduces the system inertia (there are no valves to open or close) and makes the process quicker, more direct and more controllable. This can lead to significant cycle time reductions (up to 30%) without any loss of product quality.
All-electric machines generally require much less maintenance; hydraulic systems account for a high proportion of the maintenance needs of conventional machines. Removing the hydraulic system means:
- There are no consumables such as oil and filters to carry
- There is no need for cleaning and servicing, or fixing oil leaks
- The smaller number of parts means fewer to service and replace
- Servicing is less complex, faster and cheaper.
Overall, all-electric machines have a much lower risk of failure and are generally easier and cheaper to maintain and repair than conventional machines.
Hydraulic control of cores on existing moulds that is currently powered by the machine hydraulic system is possible using an accessory hydraulic power pack.
All-electric machines bring significant energy and cost benefits. Energy savings of 30% are typical, but can rise to 60% if cycle time reductions are considered.
All-electric machines use less water; depending on the product, water consumption can be reduced by up to 65%.
Improved cycle times and increased precision gives improved productivity, while the reduced need for production capacity can lead to significant cost reductions overall.
All-electric machines offer a chance for the UK moulding industry to save energy and carbon, while also reducing costs. Overseas competitors are already doing it.
The "Energy Management" series is designed to give plastics processors an insight into how to manage a valuable resource.
Download the complete series as an Adobe Acrobat file.
Last edited: 11/03/10
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