SLG Kunststoff GmbH: When cooling takes the place of heating
Founded by Walter Stockkamp and supported by his son Dieter Stockkamp, SLG Kunststoff GmbH began producing plastic parts in 1978. The consistent implementation of a proactive energy-saving policy and ongoing process optimization in production have made a significant contribution to the company’s success. The continuity of these efforts is evidenced by the ongoing modernization of cooling system technology and process technology in the area of mold temperature control.
SLG Kunststoff GmbH, with its two production sites in Heitersheim and Bernau, is an innovative and successful manufacturer of high-quality plastic products for a wide range of industrial sectors. The company develops products and system solutions in collaboration with its customers.
SLG offers a full range of services in the field of plastic injection molding, spanning everything from tool design and toolmaking, single- and multi-component injection molding (including in cleanroom environments), thermoplastic foam molding, gas-assisted molding, and various in-mold processes, all the way through to the assembly of complex subassemblies. In addition to efforts to maintain and further expand a hard-earned leading position in all disciplines of its service portfolio, the company’s management also keeps a constant eye on areas such as energy efficiency and process optimization in manufacturing. For years, the company has closely monitored the continuous rise in energy prices and responded with an ongoing campaign to improve energy efficiency. “For us as an energy-intensive company, it is clear that energy costs are becoming increasingly significant, and that competitiveness can only be maintained if we reduce energy consumption to a minimum. We have therefore been proactively addressing this issue for years and consistently rely on smart energy-saving concepts that have already been successfully implemented. To implement the new cooling system concepts and optimize tool temperature control processes at both SLG locations, we have therefore partnered with the systems specialist ONI, who has impressively convinced us with exemplary system solutions,” explains Dieter Stockkamp, outlining his reasons for choosing this partner for energy and process optimization. Cooling circuit splitting creates energy-saving potential.
SLG Kunststoff GmbH, with 48 injection molding machines in the clamping force range
SLG Kunststoff GmbH operates 48 injection molding machines at its two locations, with clamping forces ranging from 250 to 15,000 kilonewtons. From the outset, SLG Kunststoff GmbH was clear that the new cooling water systems must incorporate all economically viable options for highly energy-efficient operation. Thus, the decision was made in favor of the cooling energy supply system presented by ONI, which is divided into two closed circuits. This system technology supplies the mold and machine cooling circuits via separate piping with different temperatures. A flow temperature of 12 or 15 degrees Celsius is provided for the mold circuits, and a temperature of 30 degrees Celsius for the machine cooling circuits.
The system’s design as a dual-circuit cooling system and the selected temperatures in the circuits ensure that highly efficient energy-saving measures can be implemented in both areas of cooling energy generation. This enables the use of so-called “winter load reduction” in the mold cooling circuit and the utilization of waste heat for heating purposes in the machine cooling circuit. Reusing expensively paid-for energy multiple times?! This is certainly a wish shared by everyone who has to pay energy costs. Although impossible in most industrial sectors, this opportunity for multiple use of energy exists for plastics processors. Hydraulic injection molding machines convert part of their electrical drive power into heat during operation, which is transferred to the hydraulic oil.
To dissipate this waste heat via recooling systems, expensive electricity must once again be used as a power source. If, on the other hand, the thermal energy from the hydraulic oil cooling system is used for heating purposes, the waste heat generated by electricity is put to good use. This means that part of the machine’s electrical power is utilized twice over, and the additional energy required for the recooling that would otherwise be necessary is eliminated. The waste heat from the machine cooling circuit is available at a temperature of 35 degrees Celsius and is ideally suited for heating office, workshop, warehouse, or production areas via underfloor heating or specially designed air heaters.
At SLG, the machine waste heat is used to heat office spaces, the toolmaking department, and storage areas. This low-temperature technology also offers a particular advantage regarding heat distribution within the room. Heat emitted by conventional heating systems naturally travels along the shortest path to the ceiling of the room or hall, where it is typically not desired. Low-temperature heating mixes much more quickly with cooler room air, so that ultimately the heat reaches where it is truly needed. A prerequisite for the multiple use of energy in the machine cooling circuits is closed, glycol-free cooling circuits that are recooled via free coolers designed as self-draining systems. This ensures that the water quality in the cooling circuit can be maintained at a consistently high level and that frost protection is guaranteed even in the event of a power outage. Equipped with a so-called adiabatic system, the free coolers deliver a sufficient cooling water temperature even at high outdoor temperatures.
“To cool our injection molding tools, we need cooling water with a constant supply temperature of 12 or 15 degrees Celsius. In the past, we generated this cooling water year-round using chillers. Due to steadily rising electricity prices, we are forced to implement every economically viable cost-saving measure in this area to keep our energy costs from spiraling out of control. The ONI winter relief system was exactly the solution we needed. The results achieved are impressive,” says Dieter Stockkamp, describing the situation regarding the chilled water supply.
Chillers are energy guzzlers and result in high electricity consumption and a correspondingly high electricity bill. Against this backdrop, chillers should therefore only be used when absolutely necessary. At SLG, the ONI concept provides for a cooling energy supply via chillers only during the warm summer months and a transitional period. Chillers are not used for approximately 65 percent of production hours. This saves a great deal of energy and thus operating costs for electricity. During cooler seasons, a so-called winter relief system takes over the cooling energy supply for the tool circuit. This technology utilizes a portion of the existing air coolers, which are fully available for hydraulic cooling during the summer months. As soon as the outside temperature drops below the temperature of the return water from the tool cooling circuit, recooling begins via the glycol-free, idle air cooler.
The idle function, which operates without auxiliary power, ensures frost protection for the free coolers in all operating conditions, even without the use of glycol. This not only results in significantly higher system efficiency but also relieves the operator of safety regulations and anticipated safety requirements. If the outside temperature drops slightly below 12 or 15 degrees Celsius, the free cooler takes over the full cooling capacity of the chillers while consuming only two to three percent of the chillers’ energy usage. At this point, the chillers are simply shut down. With this winter load reduction, the freely available ambient air is used as a cooling medium during the transitional and winter seasons, thereby replacing the electrical energy required by the chiller. Even the most powerful system needs to be optimally organized if it is to operate with a minimum of energy. For this reason, a dynamic management system developed by ONI handles the organization of the energy supply at SLG. At the center is a PLC module with the energy-optimizing ONI system software. All information regarding the system status of the entire plant converges here, is evaluated, and from here, the essential system components receive all necessary commands. For example, the control system immediately detects when the chiller can be taken off load and automatically activates the free cooler. This ensures that winter load relief remains active for as long as possible, because every hour the chiller remains shut down is worth real money to the operator. The organization of heat recovery works in a similar way. If heating is required in a specific area of the facility, the necessary capacity is provided from the machine cooling circuit. The resulting reduction in cooling capacity then leads to a decrease in free cooling capacity, which saves additional electricity.
Rhytemper® ensures process optimization
In injection molding, quality, process stability, and unit costs are largely determined by mold temperature control. In contrast, process managers at SLG quickly recognized the advantages of the dynamic Rhytemper® mold temperature control system. The quality of SLG’s plastic parts and unit costs are critical factors when it comes to customer loyalty and competitiveness. For some products, it had become apparent that achieving the required product quality with conventional temperature control technology was difficult, and the necessary short cycle times could not be realized. This problem had to be addressed, and the company turned to the dynamic Rhytemper® system. To obtain an objective comparison between conventional temperature control technology and dynamic systems, comparable conditions had to be created.
Thus, operating and manufacturing processes were optimized in advance, and all possibilities of conventional temperature control technology were exhausted. Only after this optimization was implemented and results regarding quality, process stability, and cycle time were available was production continued using the Rhytemper® technology. The results in this area were very convincing.
This led to a massive reduction in cycle times and energy consumption, as well as a noticeable decrease in the scrap rate. An additional benefit was that the load on the tool cooling circuit decreased significantly.
“If you consider the time from the initial consultation to the turnkey handover of the entire system, add in the smooth project execution and the impressive energy savings, the overall result is excellent—a testament to the outstanding collaboration with the ONI experts. Together, we have implemented a project that, through the use of state-of-the-art energy-saving technology, ensures that our energy costs remain at an absolute minimum and thus helps us secure our competitiveness to a certain extent,” concludes Dieter Stockkamp.
