MANAGING ROTATIONAL MOLDING MACHINE ENERGY COSTS
By Adam Covington, Sales Engineer, Ferry Industries, Inc.
As the management adage says, you cannot manage what you don’t measure. The use of great procedures and systems designed to help control, measure and manage a process will help combat the impact of energy and utility costs on the rotomolder’s bottom line.
The rotational molding industry faces stiff competition from competitive processes, lower wage economies, and we are continually fighting against trends for rising energy prices. The costs of utilities – natural gas, electricity, water and even compressed air as a type of “4th utility”– should be managed and monitored where possible to lower operating costs.
Steps that help the industry remain competitive will include good market knowledge, an effective energy management process, product technology, state of the art equipment & systems and sophisticated process management and control.
Ferry Industries’ RotoSpeed™ rotational molding machines use advanced controls, features and systems available for new rotational molding machines and many retrofit applications to help the rotomolder manage the machine’s functions, resulting in managed energy usage and in many cases, a measured effect of the energy being used. So we will explore those systems offered by Ferry Industries to help the rotomolder control, measure and manage the rotomolding process.
Machine Control & Reporting Software
Ferry Industries, Inc., offers all of their new RotoSpeed™ rotational molding machines with RotoCure™ 7.0. This software package allows rotomolders to control, manage, measure and report in several areas, such as:
• Process Management
• Process Trending
• Cure Recipe Storage & Retrieval
• Fault Monitoring & Maintenance
• Production Data Acquisition
RotoCure™ 7.0 allows a rotomolder to manage the machine parameters, view and log trends of temperatures verses time, create reports, allow viewing of trends and quickly identify any issues that could be causing poor performance or could lead to wasting energy. Without these tools, the rotomolder is operating without factual data and could be assuming production is running smoothly or even worse, not know why or where to look for issues with the machine configuration or faults that reduce the number of parts produced per day while allowing utility consumption to rise a simultaneously.
Infrared Thermometry™ (IRT)
Ferry Industries, Inc., exclusively offers Infrared Thermometry™ (IRT), a system of hardware and software added to RotoCure™ 7 and to the machine. This is an automatic non-contact process monitoring system that continually controls the machine, within set limits, to allow the machine to be adaptive to conditions in the factory based on temperature inputs taken directly from the mold surfaces. Both the heating and cooling phases of the cycle can be managed and controlled, resulting in less manual user adjustments of the process parameters and resulting in a more automated control package.
IRT monitors external mold temperature and computes the amount of thermal energy absorbed by the mold package; IRT controls the machine accordingly, causing more consistent processing. IRT provides the ability to add processing events during the oven phase and cooling phase at required temperature points. IRT provides process consistency in the oven and cooler and greatly reduces the impact of environmental changes, mold changes and operator errors or delays.
Benefits of IRT include:
• Assures process and part consistency cycle to cycle
• Decreases scrap due to ambient temperature changes
• Recovers quickly from operator induced faults
• No thermocouple wires to connect or repair
• Saves valuable machine time – no need to pre-heat the oven
• Assures optimum cure for optimum part properties
• Saves time by preventing cycle redundancy
• Help products maintain dimensional stability
• Integrates into Ferry RotoCure™ 7.0 System Manager
On a Ferry Industries RotoSpeed™ rotational molding machine, a gas meter can be installed on the machine’s main gas supply line. The gas meter reports the amount of gas coming through the meter. The pulse counter sends pulses to the machine control and this data can be logged and reported on the RotoCure™ screen and via exported reports.
So why use a gas meter? The gas meter is a tool, combined with RotoCure™, that measures the gas usage and we already know that if we measure it, we can manage it. The data can help determine gas consumption for part costing, maintenance indicator or productivity measurement. The digital gas meter quantifies gas usage and the data is stored for logging and reporting in the RotoCure™ 7 process control system on Ferry Industries RotoSpeed™ rotational molding machines.
Oven Exhaust Fan VFD
All newly manufactured RotoSpeed™ machines are manufactured to use variable frequency drives to control the speed of the oven exhaust fan rather than the use of a modulated mechanical damper. With oven exhaust fan speed managed by a variable frequency drive (VFD), when controlled by Ferry’s RotoCure™ machine control system and burner components, will result in an 8-12% energy savings. Unmanaged exhaust fan speeds or modulated exhaust fan dampers attached to fans still running at 100% speed regardless of burner demand is the old way of processing; it is time to allow the machine controls to manage the process.
A VFD controlled exhaust fan reduces the amount of heat that is extracted from the oven and sent up the exhaust stack resulting in less energy being lost in the rotomolding process. This type of VFD system can be retro-fitted to existing machines to replace the mechanical damper assembly and to allow the machine control to manage the exhaust fan speed relative to burner demand.
Oven Circulation Fan VFD
Like the oven exhaust fan variable frequency drive (VFD), the oven circulation fan VFD allows the fan speed to be managed and controlled by Ferry’s RotoCure™ software, allowing flexibility to adjust air scrub rates during processing as well as allowing the fan motor horsepower (HP) to be lower than in year’s past. With a lower horsepower fan running and the ability to control processing speeds, the electrical energy usage of the largest HP electric motor on the machine can be reduced. The results are maximum airflow with minimum power consumption at high temperature levels.
Many of Ferry’s RotoSpeed™ rotational molding machines use the Maxon OVENPAK® LE style burners that offer clean combustion with lower CO2 and lower NOx compared to previous burner systems. These burner systems also offer a 50:1 turndown ratio for exceptional process control. The overall efficiency of the burner combustion is increased while using low gas supply pressures.
The burner on a rotational molding machine is extremely important to the rotomolding machine and the process. A properly sized burner for the machine, large enough for quick oven temperature recovery that is gas efficient will assist in managing the cost of the energy input to the process. Monitoring the gas usage with the burner with a gas meter helps ensure the burner is tuned properly and can catch drift or maintenance problems based on logged history of gas consumption; they go hand-in-hand for sustainable process control.
Oven Heat Exchanger
Oven heat exchangers are offered for both new and existing Ferry RotoSpeed™ rotational machines. The system of mechanical components can reduce gas consumption by 18-22% and the return on investment can be calculated against the cost of gas and frequency of use of the machine, but in rotational molding, these are large numbers to consider towards the bottom line.
• The heat exchanger uses oven exhaust stack heat to preheat inbound combustion air to the burner rather than the burner heating ambient inbound air
• Improved oven cycle times are also possible due to faster oven heat recovery
• System can be installed on new machines and retrofitted to existing machines
• Look for incentives from federal and local government agencies for rebates and tax credits to lower the ROI on this long term money saving investment
RotoLog™ provides the ultimate level of real-time analysis and logged data of a rotomolded part’s internal air temperature. By monitoring and logging the data, key decisions can be made about process parameter changes that can result in high quality and qualified parts as well as optimizing cycle times and utilizing only the energies needed by the machine to make the parts required and nothing more.
Advantages of RotoLog™:
- Optimize cycle times – develop optimum cure & cooling times and temperature set points
- Develop correct molding cycles for new molds the first time
- Optimize cycle times for multi-cavity spiders
- Reduce scrap quantities
- Save energy through cycle optimization
- Improve quality of rotationally molded plastic products
- Provide quality control data for customers
- Evaluate and qualify new materials and molds
- Capable to run continuously, 24 hours per day, with proper upkeep and ice pack exchanges
Again, when the process and the parts are measured, the process and parts can be managed. RotoLog™ can save the rotomolder time, energy costs and raw materials which all effect long term profitability.
RotoCycle™ Production Simulation Software
RotoCycle™ is a computer software program, developed by Dr. Paul Nugent, which enables a rotomolder to simulate rotomolding machine production, station utilizations and assist in showing bottlenecks in the cycle. By simulating scenarios that improve oven and cooler utilizations, a rotomolder improves their capability to reduce energy consumption. Energy can be saved by using this tool in preparation of machine production to provide metrics to measure the actual machine production against, thus reducing energies spent testing production scenarios on the machine. Other benefits include:
- Mold mix on the arms of multiple styles of machines; turrets, independent arm, and in-line shuttle
- Calculate production cycles
- Select proper machine types for product mix
- Save/Name simulations
- Analysis of cycle simulation
- Graph utilization of stations
- Projection of completed cycles for each arm in a given time frame
- Select saved simulations for review
By using actual time study data from a rotomolders process, the software can estimate production capabilities to provide metrics that managers can use as a guide for physical production. The data serves as targets for production, though efficiencies and planned maintenance need to be factored in to the raw output calculations that are offered by the software.
The ovens of rotational molding machines commonly have fabricated and insulated floor sections. An alternative to this type of floor is to exchange this insulated fabricated floor for a layer of fire brick, like building a patio, covered by appropriately shaped and sized sheet metal cover sheets.
The layer of fire brick provides an improved barrier to heat loss from the oven cavity to the concrete floor as well as allows for some heat reflectivity and recovery once the oven doors close for each cycle. Ferry Industries has worked with some customers to implement this solution and the reports indicate some benefits to oven performance. Fire brick materials and densities must be properly specified to ensure appropriate performance.
The sheet metal covers ensure plastic powder does not fall into and melt onto the fire brick to reduce the chances of the melted plastic from ruining the bricks and provides a layer of protection should something fall onto the bricks.
Oven Door Seals
Maintaining and replacement of the oven door seals is important to reduce the heat losses created by the gaps between the oven doors and main oven structure. These gaps, if not properly sealed, will allow substantial heat to escape as well as allow shop air to enter the oven chamber resulting in a less efficient oven. This type of air leak likely won’t be a large cost over a couple days or even a week, but if you add up the extra gas used to heat the oven due to the leaks over a year or two, this could become a sizable number. Also ensure the oven doors are properly adjusted to fit tight to the new seals you just installed.
Oven Burner Maintenance
At a minimum, all rotomolding machines should have their oven burners evaluated, tuned and tested for proper function and performance on an annual basis by trained personnel; more frequently depending on production schedule, fuel being used and temperatures set points. There are maintenance services and companies specializing in burner maintenance as well as some of the burner manufacturers who can assist a rotomolding company complete preventative services that will catch potential problems early before the costs for repair and down time escalate.
All too often this type of maintenance practice is over-looked or regarded as too expensive and too time consuming; what is expensive is when a failure occurs at the worst possible time, repair parts have to be shipped for expensive next day am delivery and emergency service work has to occur and be scheduled, not to mention the cost per hour of lost production. It’s better to plan the maintenance around production, implement the service and by checking the burner condition and performance on a frequent basis, minor problems never become major shut downs.
There have been many articles in our industry trade magazines as well as presentations at trade shows and conferences on this very topic; this topic is being constantly discussed because it is so important. If the maintenance is managed and monitored, gas consumption and oven performance is measured, the return on investment and production output can be tracked as a visible impact of this maintenance.
Fan Horsepower and Flow Rate
At Ferry Industries, the fans we use on our RotoSpeed™ machines for the oven and cooling stations are being evaluated to find lower horsepower fans that use improved air flow and mechanical design technology to sustain the same, or in some cases, higher flow rates. The impact is a fan that draws less power while delivering the same or more flow rate compared to its larger horsepower relative. These types of initiatives and changes help reduce electrical energy consumption over long term use of the machine while not sacrificing performance and production cycle time.
If water is used as a medium for cooling the molds in a rotomolder’s process, evaluating ways to lower water consumption should be considered, since for some rotomolders this is yet another utility and cost of production. If heavy water spray is used in the cooling chamber, this water will gather and pool in the cooler pans. Rather than allowing this water to just drain or evaporate, implementing a water filtering and recirculation system can help recover and reuse this standing water for the cooling process reducing water consumption and utility cost.
Alternatively, high pressure mist systems or air/water atomization systems can be used to improve the surface area and coverage of the applied water resulting in less or no standing water in the catch trays. The fine water droplets are fully consumed by the evaporation process on the hot molds. Water meters could be used to measure and monitor water usage if the consumption needs to be monitored for costing and process control monitoring.