High Voltage Subsystems
Manufacturer of Insulating Gloves
Switches to Vertrel® for High-Voltage Applications
Because of superior materials compatibility and dielectric properties, Vertrel® XF was selected by a manufacturer of insulating sleeves and gloves for the quality assurance function in high voltage product testing.
When technicians and linemen work around high voltages, it is crucial that they be completely insulated from the dangerous circuits upon which they are working. Importantly, the insulation must be prefect because even an invisible flaw in an insulating sleeve may be sufficient to serve as a path for a catastrophic accident.
One company which makes insulating sleeves and gloves needed to change their solvent in their sleeve testing equipment. The test involves submerging the sleeves in an insulating bath of solvent, running an electrical current through the materials and measuring any leakage, which would indicate a flaw in the sleeve. Until recently, CFC-113 was used for this critical task. Importantly, the plastic components must remain unaffected by the solvent.
Vertrel® XF showed superior performance when compared to CFC-113 and other solvent alternatives. During tests, the fluid held AC voltages in excess of 40,000 volts during testing of a sleeve at an immersion depth of 5.08 cm (2 in) with no flashover through the fluid. Based on these tests, DuPont recommends a minimum immersion depth of 7.62 cm (3 in) in commercial testing.
Other observations made during the testing included: no hang-up of water globules on the rubber, eliminating the need to time-delay the test or pre-coat the sleeves with vegetable oil. Also, there was no observed effect on the rubber sleeves after repeated exposures to the solvent.
Tesing showed most elastomers are compatible with Vertrel® XF. Table 1, below, summarizes test results on short-term exposures of unstressed elastomers. Compatibility was defined as a weight change of less than one percent after immersion for 15 minutes at room temperature.
It has been observed that some elastomers will swell upon exposure to the solvent and will, in most cases, shrink back to within a few percent of original size after air drying. Swell, shrinkage, and extractables are strongly affected by the compounding agents, plasticizers, and curing used in the manufacture of plastics and elastomers. Therefore, thorough testing prior to wide-scale deployment is particularly important in this application.
Additional long-term compatibility data simulating exposure of the most common components and materials is available from DuPont upon request.
Table 1 – Elastomer Compatibility Test Results on Insulating Sleeves
Compatible: Buna N, NBR, Nitrile Buna S, SBR, GRS, Butyl Rubber, IIR, Chlorosulfonated PE, EPM, EPDM, Nordel®, Polysulfide, Natural Rubber, Isoprene, Neoprene, Polyurethane
Incompatible: Viton® B, Silicone
Notes: Material composition varies depending upon compounding agents, plasticizers, processing, etc. Specific materials should be tested for compatibility with solvent.
Test Procedure: Immersion,15 Minutes at Room Temperature, weigh and measure.
About the Solvent
Vertrel® XF is a proprietary hydrofluorocarbon fluid with zero ozone depletion and low global warming potential. Nonconductive, it is ideally suited for use in high voltage applications, particularly those in which the materials of construction may be vulnerable to stronger solvents. Vertrel® XF can replace chlorofluorocarbon (CFC-113 or Freon® TF) and the perfluorocarbon fluids (PFC-5052) currently used in this application.
Vertrel® XF is a clear, colorless liquid which dries very quickly with very little aroma. Unique physical properties include a higher boiling point and lower surface tension when compared to CFC-113. This, combined with high dielectric strength, nonflammability, chemical and thermal stability, low toxicity, and ease of recovery by distillation and filtration make Vertrel® XF ideal for this application.
Vertrel® for Defluxing
PCB Makers Choose Vertrel®
XMS Over Co-Solvent Defluxing
A California-based manufacturer of high-power radio frequency (RF) power amplifier systems for application-specific and scientific, medical, and wireless applications chose Vertrel® XMS for defluxing applications because it is compatible with the components, it avoided problems with water cleaning, and lowered their total cost-per-part-cleaned.
American Microwave Technology, Inc. (AMT) is a Brea, California based manufacturer of high-power radio frequency (RF) power amplifier systems for application-specific and scientific, medical, andwireless applications. Its customers are original equipment manufacturers worldwide. Due to the critical nature of the components and the high-tech applications, extreme cleanliness of all the electronic subassemblies is essential.
Circuit board assemblies containing RMA flux must be cleaned as part of their manufacturing process. Any flux residue that is left on the circuit board assemblies can eventually result in failures. The chip capacitors are especially vulnerable. Due to the high power involved in the application of these units, heat can build up in areas where flux residue remains. In the case of a chip capacitor, the flux can cause the capacitor to crack.
AMT had been using a co-solvent process in a Detrex AVD 212 vapor degreaser. They were using Solvating Agent #24 with PFC 5060 from 3M Corp. as the rinsing agent. The relative amounts were 30%/70% respectively on a weight basis.
Although the cleaning performance of this system was satisfactory (and an improvement over the previously used 1,1,1-trichloroethane system), there were concerns about the excessive consumption of the rinsing agent. The odor of the solvating agent was a secondary issue. Additionally, there was concern that the solvating agent was getting trapped under components and not easily rinsed out. The circuit boards had to be oriented very carefully to ensure that pockets that could trap solvent were eliminated. Fluid entrapment also was a concerned under the Teflon® sleeving used on custom-designed subassemblies. Lastly, another concern with the co-solvent system was that wire assemblies that are attached to some of the boards were not being cleaned effectively.
Alternative Chemistry Solution
In an effort to eliminate some of the concerns with the co-solvent system, AMT began to investigate alternative chemistries. They chose to evalutate DuPont’s Vertrel® cleaning agents because these products offered many advantages over the co-solvent system. Tests were conducted at the DuPont Applications Laboratory in Wilmington, DE. Both Vertrel® SMT and Vertrel® XMS were tested on circuit board assemblies.
The test was more stringent than typical production because the flux had been allowed to age on the boards for approximately nine days. Both products performed significantly better than the existing co-solvent process, with Vertrel® XMS showing a slight advantage.
The boards were inspected under high magnification for the presence of flux residue. There was no residue and no fluid entrapment under the Teflon® sleeving used on customdesigned subassemblies, which had been a recurring problem in the existing system.
The swtich to Vertrel® solvents was fast and easy because the vapor degreaser did not need to be modified to switch from the co-solvent process to the solvent process; just a few thermostats needed to be adjusted.
Cleaning Oxygen Lines and Systems
with Vertrel® Solvents
Vertrel® MCA has been approved by several manufacturers as the ideal cleaner for the maintenance of oxygen systems.
Oxygen system cleaning is a critical cleaning application with more demanding parameters than usual. Oxygen systems are critical subsystems in many industrial, analytical, laboratory, military, medical, space and aviation products. Such systems are highly sensitive to contamination. For example, particles left as a residue in an oxygen line may hinder the operation of valves, sensors and controls or otherwise cause excessive friction in moving parts. Friction causes heat and premature component wear; this may be a potential source of system failure.
Oxygen systems need to be cleaned at the point of use, such as within an aircraft system. However, systems used to manufacture and transport oxygen also need to be rigorously cleaned.
Oyxgen systems come in all shapes and sizes. Here is an example of a six-inch gate valve used in an oxygen processing facility. This product was cleaned with Vertrel® using an immersion and wiping process. Cleanliness then was verified under a UV light, as specified in the customer’s procedures.
Previously, the most widely accepted oxygen system cleaning solvent was CFC-113. The continuing escalation in prices for CFC-113 – plus the well-known environmental drawbacks – have made it an undesireable choice. This has forced most companies to search for alternatives.
Several companies also have introduced slow-drying hydrocarbon solvents for this task. However, low-vapor pressure solvents are inadequate to the task for two reasons: they are combustible, and they are slow-drying. It is impossible to guarantee that slow-drying solvents will not be trapped within the complex shapes of an oxygen system. These combustible residues may contribute to an explosive situation once pure oxygen is reintroduced into the system (combustible materials ignite more rapidly in an oxygen rich atmosphere). Even particles which are not normally combustible behave differently in an oxygen atmosphere and may develop a high potential for explosion. For example, some metals will burn in an oxygen atmosphere if an ignition source is available.
Vertrel® MCA has been tested and approved for oxygen system cleaning. It was found to have the optimal combination of handling, cleaning, safety, environmental and economic characteristics. The material is nonflammable, noncorrosive, and environmentally benign. This makes it ideally suited for oxygen service cleaning applications.
Typical System Components
Cleanliness requirements differ depending on (a) the type of surface coming in contact with the oxygen (fixed surfaces such as the insides of pipes, or moving surfaces such as valve gates) and (b) whether the oxygen is in the form of a liquid or a gas. Oxygen systems also demands the use of a solvent that is compatible with the wide variety of materials and elastomers used in such systems.
- Instrument valves
- Flow valve assemblies
- Pumps, compressors, and diaphragms
- Heat exchangers
- Cylinders and containment vessels
- Tubing, hoses and pipes
- Flow meters
- Safety relief valves
- Stainless steel
- Low carbon steel
- Threaded pipe
- Particulate matter
- Handling soils
- Hydrocarbon oils
- Water contaminants
Today, Vertrel® MCA is listed by the Compressed Gas Association in the official Directory of Cleaning Agents for Oxygen Service. Vertrel® MCA also meets the mechanical impact testing requirements for cleaning liquid oxygen systems, in accordance with NHB 8060.1C, Method 13A. (NASA Handbook 8060 for Mechanical Impact-Liquid and Gaseous Oxygen, Test 13).
Components may be cleaned by a variety of methods. The required degree of cleanliness defines the number of cleaning steps. Whichever method is selected, oxygen service components require a sequence of methods that allow for cleaning, rinsing and drying. The sequence applies to not only new and refurbished parts, but also to field maintenance cleaning. Vertrel® MCA can be used in any of the following cleaning methods to individually or sequentially define a suitable cleaning process:
1. Vapor Degreasing
This method uses the vapors of heated solvent to remove contaminants from intricate, irregular or hard-to-access locations. Spraying with vapor condensation is also used to further remove contaminants from surfaces. In a typical two-sump degreaser, components are rinsed in pure solvent condensate. Extra cleaning power is provided by ultrasonic energy to remove fine particulate. As the parts equilibrate to the temperature of the solvent vapor, condensation ceases. The parts are clean, dry, and safe to handle. This method typically combines all steps necessary for cleaning, rinsing and drying.
Easy access, flat surfaces may be cleaned with a solvent-moistened, lint-free cloth. Aerosol sprays are a convenient way to handle the solvent and apply it to the wipe. This method is used when surfaces are large and flat, and/or when other methods are impractical.
Flushing forces solvent through a closed system with a sufficient flow and pressure to remove residual contamination. This method is typically used as a final rinse, after a preliminary cleaning process and before drying. Some systems require a vacuum to be “pulled” on the system to ensure the total evaporation of any residual solvent.
In this method, components are submerged in solvent for a specified time to dissolve and lift surface contaminants. Solvent agitation and ultrasonic energy are often used to dislodge particles and break up difficult-to-remove soils. Spraying in glove box environments is also used. This method is often used for a first pass, preliminary cleaning process.
Major Bearing Manufacturer Chooses Vertrel®
Bearing Manufacturer Chooses
A large manufacturer of precision bearings selects a Vertrel product for degreasing because of its overall cost-effectiveness.
The cleaning of ball bearings immediately before and after assembly are critical steps in their manufacture. The reliable performance of the bearings depends on surfaces that are clean and free from particulate. One of the largest producers of ball bearings uses several vapor degreasers to accomplish this cleaning task. Today, those degreasers are equipped with Vertrel® MCA Plusfor this precision degreasing task.
The cleaning process removed both particulate and Houghton MB cutting oil that is used during machining and as a preservative. A variety of concerns with the existing process prompted the evaluation of alternatives.
This manufacturer previously used a co-solvent process consisting of Solvating Agent #19 with PFC 5060 as the rinsing agent. Although the cleaning performance of this system was satisfactory, there were concerns about excessive system change-outs and the long cleaning cycle time (1 hour). The solvating agent in the vapor degreaser had to be changed out every three days in order to maintain the cleaning effectiveness. Additionally, there were concerns about the odor of the solvating agent, the high global warming potential of the PFC 5060, and the need to handle two components.
Alternative Chemistry Evaluation
Several solvents were evaluated as alternatives to the existing process. The solvents evaluated were Vertrel® MCA Plus, Vertrel® MCA, Vertrel® SMT, and HCFC-225. All were evaluated in actual cleaning tests in vapor degreasers equipped with ultrasonics. Cycle times were varied to determine the optimal times. After cleaning, the parts were inspected under a microscope for the absence of particles and staining.
As a result of this testing, Vertrel® MCA PlusPlus emerged as the superior solvent from a cleaning effectiveness standpoint. Additionally, the Vertrel® cleaning agents were preferred due to their more favorable toxicity profile
The New Process
The conversion to Vertrel® MCA Plus in three vapor degreasers went smoothly. The machines required only minor adjustments to the controls to convert to the new chemistry. Some of the key advantages of the new process are:
- Higher Soil-Loading Capability – This allowed the bearing manufacturer to significantly extend the time required between system change-outs. The target change-out time was extended by 100%.
- Shorter Cycle Times – The use of a single solvent eliminated the need to work with two separate components and the extra time required to remove solvating agent from the parts.
- Safety – The low emissions of solvent from vapor degreasers ensures that concentrations near the equipment are well below the allowable exposure limit.
- Low GWP – The global warming potential of Vertrel® MCA Plus is only 652 (100 yr ITH).
Aircraft Maker uses Vertrel®
to Clean Aircraft Landing Gear
Because of superior cleaning results, toxicity ratings and materials compatibility, Vertrel® MCA was selected by a major aircraft manufacturer as a replacement for trichloroethylene for the degreasing of landing gear components.
Aircraft wheel and brake assemblies undergo high mechanical and thermal stresses. During an aircraft landing, extraordinary quantities of kinetic energy is transformed first into heat from the braking system while carrying the mechanical stress of the aircraft and its cargo. The brake heat pack assembly subsequently transfers this thermal load to surrounding elements, including the wheel, tire and brake components.
Further stress occurs while in flight. The hot wheel assemblies quickly are subjected to extremely cold temperatures at high altitudes. Due to the potential for generating ice crystals, entrapment of moisture in the wheel assemblies is a primary concern.
Cleaning and subsequent lubrication of these parts is critical to safe operation. Vertrel® MCA has been used successfully in the cleaning of the wheel assemblies as part of a continual preventive maintenance program to maintain highly reliable operation.
Items to be cleaned included:
- Wheel bearings
- Bearing seals
- Heat shields Retaining pins and rings
- Bushings Valves
Cleaning with Vapor Degreaser
The cleaning process for landing gear assemblies and their component parts uses a standard two sump vapor degreaser. The process consists of an immersion in the boil sump, followed by a spray, followed by a rinse sump immersion, then drying. This process removes contaminants from the intricate parts and from hard-to-access locations.
The initial immersion in the boil sump removes the majority of the soil. Spraying with pure solvent vapor distillate further removes contaminants from component surfaces. Components then are rinsed using ultrasonic energy to remove any fine particulates.
After removal from the rinse sump, the parts are held in the vapor zone. There, the parts equilibrate to the temperature of the solvent vapor, condensation ceases, and the parts are clean, dry and safe to handle.
Typical materials and surfaces cleaned included aluminum, steel, titanium and various gaskets for the hydraulic systems.
Typical contamination removed included grease, hydrocarbon oils, Krytox® dry lubricants, water with a wide variety of contaminants, and various particulates including tarmac from the runways.
Typical cycle times are less than eight minutes per batch of parts.
Major Advantages of Vertrel® MCA
- Low residues
- Excellent solvent penetration
- Fast and thorough drying
- Easily recycled
- Chemically stable
- Environmentally preferred
- Low (good) toxicity
Disadvantages of Other Cleaning Systems
- Moisture entrapment
- Low grease-cutting capability
- Long soak times for cleaning
- Low penetration for complex parts
- Long drying time
- Large potential for rust
- High energy consumption
- Hazardous composition
- Extensive venting required
- Banned in some regions due to
- high photochemical reactivity
- High disposal costs