A Strategy for Managing Resources in the Production of Preforms
The PET bottle, one of the most important mass products in the beverage industry, is made from a preform, which is produced in-house by converters or by fi llers when there is a very high demand. Injection moulding machines are used to produce such preforms - or more precisely injection moulding systems that consist of several components and therefore require special know-how. Even if the PET market is growing inexorably, the margins are not enormous; they are only achieved through large quantities or with niche products for special requirements. There is not much room for manoeuvre when it comes to purchasing PET raw materials. In the case of converters, this is compounded by the fact that their preforms are often sold as bulk material by weight, which means that the price structure does not allow much scope for pricing with known raw material prices. It is therefore not advantageous for the converter to achieve material savings by keeping the preform weight of the individual preforms as close as possible to the lowest tolerance limit - or by keeping the weight dispersion as close as possible to the tolerance limit. It looks more favourable for the direct end customer: every weight percent saved on the preform immediately brings a cost advantage.
Within the beverage industry, the preform industry, as already mentioned, generates its margins more from the mass, so that the PET raw material throughputs at a production site of approx. 100 to 400 tons per day are the usual order of magnitude. But where are profi t optimizations possible under these conditions?
IN PREFORM PRODUCTION, THERE IS ALMOST ALWAYS SIGNIFICANT POTENTIAL FOR COST OPTIMIZATION, WHICH CAN HAVE A DIRECT IMPACT ON MARGINS.First there are the fi xed costs, in which cost-intensive capital goods, typical of the preform industry, play a significant role in addition to salaries. For variable costs, production-related energy consumption and raw material (PET-material and additives) are by far the largest items in the cost structure. However, it has already been mentioned that converters often sell preforms by weight, so that the cost of the resource raw material seems less attractive at first. However, this assessment will be examined in more detail later. Energy consumption in preform production, on the other hand, always carries a worthwhile potential for cost savings, which is often underestimated and to which more attention should be paid.
EXAMPLEAn average preform system which, for example, uses 900kg/h of PET material has an approximate annual energy requirement of 3,200 MWh. If the price for industrial electricity is around 10 cents per kWh as in Germany, energy costs of around € 320,000 per system must be calculated. The processes of energy absorption of the PET material and the subsequent cooling of the finished preforms are subject to physical laws: On average, an energy consumption of between 420 and 500Wh/kg (average 460Wh/kg) is calculated specifically for 1 kg PET during production with a modern injection molding system. Depending on external influences, between 210 and 240Wh/kg (average 225Wh/kg) of this energy is physically bound by the PET and cannot therefore be influenced. However, the remaining energy quantity of 235Wh/kg - a good half of it - can be influenced, of which experience shows that an average potential saving of approx. 10% is possible. For this example, that would be €16,000 per year, which could flow directly into the margins, not taking into account any tax benefits. In order to realize this potential, in many cases hardly any investment is required - and if it is, it will be amortized within a reasonable period of time.
WHERE DOES THE ENERGETIC COST OPTIMIZATION START AT THE PREFORM SYSTEM?Decisions about the equipment of the components and also their positioning within the system are already decisive for energy consumption when purchasing cost-intensive production systems. Good negotiation skills and independent purchasing of individual components can apparently save a lot of money quickly: Injection molding machine manufacturers convince their customers with fast cycle times, efficient injection molds and low maintenance costs with low energy consumption. Dryer manufacturers praise efficient drying with likewise low energy consumption, and manufacturers of injection molds and cooling equipment argue similarly. But how do these components work in the finished system? Of course, a functioning production system can be put together from the offers of individual components, the preforms can lie within their specifications - but when it comes to checking the energy efficiency of the individual components for their specifications, it becomes more difficult than assumed. A rough overview of the overall power consumption is usually easy to obtain, but individual components of a PET system often cannot be evaluated because of a lack of relevant information. The energy consumption of individual components of a PET system depends not only on external influences, but also on their interaction during the production process. This has a considerable influence on energy consumption. As already mentioned, a savings potential of approximately 10% on variable energy consumption is possible. But if the individual components cannot be assessed, how can the overall process be optimized? A training course on energy management in preform production helps to realize significant savings. Comment of Western Container Corp. (WCC) Sugarland TX, USA, Roger Kerr, Paul Lovell: “It was eye-opening to see how much opportunity there is with injection presses!”
AN IMPORTANT AND OFTEN UNDERESTIMATED COMPONENT - THE DRYER UNITAt the beginning of the production process there is the dryer, whose task is not only the drying of the PET raw material - the second and equally important challenge is to supply the material with sufficient energy for the plasticizing process. The dryer’s ability to absorb large quantities of material gives it suffi cient time to condition the material economically. Whether the plasticizing process. This requires a clear agreement on the condition of the PET material if it is to be transferred from the drying process to the injection molding process:
- Regardless of the incoming PET material condition (temperature and humidity within the dryer specifi cation), the material must be delivered to the injection molding machine in a constant condition.
- The PET material temperature stands for an energy content that must be defined.
- The residual moisture must also be determined
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