Machinery & Equipment: Chiller check-up
Picture the fall-out from a chiller failure: machine A is producing bad parts, wasting time and resin; you are scrambling to find and install a replacement; profit margin on that contract is evaporati...
July 1, 2002 by Canadian Plastics
Picture the fall-out from a chiller failure: machine A is producing bad parts, wasting time and resin; you are scrambling to find and install a replacement; profit margin on that contract is evaporating faster than water on a hot barrel. Now, go take a walk around your chiller to make sure this scene doesn’t occur.
“Too often, chillers are not regarded as production machinery, yet loss of cooling capacity will result in lost or stopped production,” explains Henry Lezon of Freeze Co. Systems Ltd.
Taking a few minutes to periodically check your chilling system can avoid both subtle declines in performance and catastrophic failures. Patrick Klingberg, product manager for Sterling Inc., contends that fluid quality is the number one reason that a temperature control unit or chiller fails to perform to its best ability. When using water, fluid quality is determined by measuring the pH level and suspended solids (usually measured in parts-per-million). The pH level determines how corrosive the water is to the different materials with which it comes into contact, explains Klingberg. He recommends a pH level of 8.5 for water. That is slightly above neutral and will retard aggressive behavior towards metals.
Suspended solids, especially in the form of calcium carbonate, can plate out of solution on hot surfaces and create an insulation barrier preventing heat transfer. This can cause longer cycle times and a variety of other problems, such as hot spots, says Klingberg.
Heat transfer fluid, a fluid that is typically petroleum-based and can operate at elevated temperatures, also needs to be monitored. Klingberg explains that as the fluid breaks down, organic acids are formed, as well carbon deposits called coke. As the fluid ages it may also become more viscous, therefore reducing the flow rate. Another result of aging is the reduction of its heat transfer capabilities, resulting again in hot spots and longer cycle times.
To check heat transfer fluid quality, use sight and smell, suggests John Fuhr, president of Paratherm Inc., a supplier of heat transfer fluids. If the fluid smells burnt or pungent, it should probably be replaced. To perform a visual check, put some fluid in water in a clear glass or beaker. Tip the glass back and forth and observe how the fluid reacts on the walls. “If it forms a thick film, like a milkshake, it’s carrying a lot of crap,” says Fuhr. “Trust your instincts. If it smells bad or looks bad, chances are it is.”
VISUAL INSPECTION IMPORTANT
“A general walk-around of your chilling equipment on a regular basis to look for oil or water leaks, or listen for unusual sounds, can help head off major chiller failures before they happen,” says Roger Lambert, president of Temperature Corp., a manufacturer of chillers and temperature control units. “Our chillers have no side panels, making it easy to check for leaks and noise.”
More detailed periodic inspections are also recommended. Sterling’s Klingberg suggests personnel should check the channels for any buildup of rust every time a mold is changed. The rust can flake off and plug the channel.
Also check the heaters for any type of buildup, whether from scale or coke. Clean the heaters of any debris that is on the hot section of the elements. This will extend the life of the heater, provide better temperature control, and reduce energy consumption. You may have to use a light acid solution to remove coking if the heater has not been cleaned for a long period of time (years), says Klingberg.
Also, inspect the cooling devices (i.e. solenoid valves, shell-and-tube or brazed-plate heat exchangers) for any blockages. Placing a filter/strainer up stream of the device will help prevent any blockage from forming, but filters are only good when they are clean.
The Sterlco hot oil systems have a Y-strainer as standard with 1/16th inch perforations to help to remove large debris. All of the Sterlco chillers with brazed-plate evaporators also have a Y-strainer to help remove large debris. For central systems, Sterlco offers a wide variety of full-flow or side-stream devices, and can even be setup for self-cleaning.
Lambert notes that keeping both filters and condensers clean reduces the discharge temperature of the refrigeration compressor, resulting in longer compressor life and trouble-free chiller operation.
Periodic checks should also include the contacts on all electro-mechanical contactors, especially those used for heating elements. As the contactor ages, the contact surfaces wear due to arcing and can weld shut over time. If a large amount of carbon dust is found around the contactor, it should be checked thoroughly, and replaced if needed.
SOLUTIONS FOR RUST
If you do find rust, Sterling offers a DeScaler unit that circulates SterlClean, a non-toxic, environmentally-friendly solution, through the channels dissolving the rust and calcium carbonate buildup. You can even use this on the machine hydraulics to clean the heat exchanger, but beware, says Klingberg, if the heat exchanger is old it could actually eat through the rust that is holding it together. The solution can be used even in large central chiller or cooling tower systems, but this may require an extremely large amount of water since the system needs to be flushed after cleaning.
Paratherm has also introduced a cleaning liquid formulated to break up the sludge and carbon lumps that can develop in hot oil systems. Paratherm SC is said to restore peak performance in less than a day. It is compatible with any mineral oil-based thermal fluid as well as many synthetic fluids.
For the processor who needs to minimize or eliminate rust in their process water, or who wants to avoid corrosion-related maintenance, Conair is now offering a new Corrosion Resistance option package for TW Series Thermolator temperature control units.
The corrosion resistance package includes a special Teflon coating on the heater tanks and pump volute. Smaller pumps have stainless-steel impellers, while the larger units have impellers made of bronze. Square flanges on the heater and mixing tank are stainless steel, and all external piping, such as the cooling valve and mold purge, are brass.
For central systems, a fully-automatic system that maintains water quality is available from AEC/Application Engineering. The Tower Water Management system is designed to control scale, corrosion and microbiological fouling in both open and closed recirculating cooling water systems. The controller constantly monitors water flow and meters an accurate blend of scale and corrosion control agents into the tower system as needed. Biological fouling is eliminated by introducing microbiocide at pre-determined intervals. Suspended solids are automatically removed by means of a centrifugal separator coupled to a solenoid valve. In addition, AEC conducts a free quarterly water analysis.
Another consideration with water tower systems is filtration, reports Lezon of Freeze Co. “Filtration is critical because airborne particles are picked up readily by these systems. The choice of an appropriate filter medium and filter design along with automatic backflush systems can prevent costly downtime.”
DRASTIC MEASURES: REBUILDING
Should you find a problem with your system, both repair and remanufacturing are affordable options. Mokon offers repair and service through its Canadian distributor/representative, En-plas. En-plas stocks parts for immediate turn-around and offers technical support. And while your Mokon system is being repaired, a loaner system could be available for use.
Another solution available from Mokon is remanufacturing, which is performed at Mokon’s headquarters in Buffalo, New York. This comprehensive rebuild will restore your current equipment to original performance and productivity at a fraction of the cost of a new buy. Regardless of the condition of your old unit, this upgrade will include the replacement (or addition) of a low pressure switch, as well as replacement of pressure gauges, pressure regulator, motor, pump, heaters, plumbing
and the upgrading of your old control device. This service even includes painting, testing and calibration and a “New Model” warranty for your extended protection.
NEW TO THE COOLING SCENE
– A temperature controller with the rare ability to operate in either positive flow mode or in negative flow mode (for instances where there is a leaking or cracked mold) is now available in North America from Wittmann. The Tempro Basic 195 microprocessor-controlled mold temperature controller is already used in a large number of European molding facilities. The ability to convert to negative flow at the flip of a switch can help prevent downtime, as it is not necessary to unhook the mold temperature controller and bring in and re-plumb a separate leak-stopping unit to allow a leaky mold to continue operating.
– Thermal Care has redesigned the TX Series central chillers for even better performance with a smaller footprint. The TX takes up 25% less floor space than previous models. Standard features include:
two totally independent refrigeration circuits with manifolds and service valves on evaporators and condensers to allow for routine maintenance without costly downtime;
stainless steel brazed plate evaporators that require less refrigerant for better temperature response time;
screw compressors, which have fewer moving parts and lower torque to better tolerate liquid slugging than chillers with reciprocating compressors.
TX chillers are available from 80 to 212 tons in air-cooled, water-cooled or remote condenser models.
– The MicroMax air-cooled mold chillers from IMS combine small size with powerful cooling capabilities. They are suitable for use with smaller molding machines and are equipped with an electronic control panel. These 4000 BTU units have a 1.3 hp pump and a three-gallon fluid reservoir. Stainless steel and copper plumbing contribute to corrosion resistance.