Long before oil was automatically dispensed onto parts in assembly workstations, it was automatically dispensed onto the axles and bearings of a moving train. In 1872, Canadian engineer Elijah McCoy developed a lubricating cup for the Michigan Central Railroad that automatically dripped oil when and where needed on the train’s axles and bearings. Because railroad purchasing agents loved this product and wouldn’t settle for imitations, they began demanding that only “the real McCoy” dispensing cup be used on their trains.
More than 140 years later, manufacturers of trains, planes, automobiles and consumer goods regularly dispense oil onto parts during assembly to ensure they stay lubricated. Grease also is dispensed onto parts, but for other reasons. Unlike oil, which is thin and runs off a part, grease is thick and stays in place. It often acts as a sealant to prevent water penetration.
“Manufacturers always want to dispense just enough lubricant,” explains Ken Walker, managing director for DOPAG (US) Ltd. “Too much oil or grease just results in a mess.”
Applying more lubricant than is needed also hits companies in the pocketbook. For example, many greases cost about $100 per pound, or as much as $25,000 for a 55-gallon drum.
Manufacturers also must meet their customers’ ongoing demand for improved dispensing accuracy—whether the assembly requires jetting a small shot of oil or placing a thin bead of grease. Suppliers offer a wide range of dispensing valves, pumps and delivery systems to help manufacturers meet all of these challenges.
Thicker Than Water
Many people tend to interchange the terms “oil” and “grease” because both lubricants minimize friction. Although the two are derived from petroleum or their synthetic equivalents, they are distinct in composition.
Oil is a liquid with a low, nonchanging viscosity (less than 10,000 centipoise). It is usually sprayed onto a part or into a cavity.
Grease is a semisolid lubricant consisting of oil, soap, thickeners and additives. It is thixotropic, which means it has a medium to high initial viscosity (20,000 to 50,000 centipoise or more) that drops upon the application of shear force. Grease is usually placed directly onto a part, but can be sprayed depending on the grease formulation and valve used.
Because it is a liquid, oil can drip and collect contamination when applied excessively. Similarly, grease may attract dust and negatively impact the performance of a part, such as a gear.
In addition, grease may drool or string during automated dispensing, resulting in material waste. This problem can be prevented by programming the robot to shorten dispensing time and drag the tail of the dispensed grease back onto the center of the bead.
The viscosity of grease changes depending on the temperature of the work environment. Walker says certain greases may be more viscous and difficult to dispense in the morning, when it’s cold, than in the afternoon, when it’s warmer.
Positive-displacement-type systems provide repeatable dispensing regardless of changes in viscosity. Some grease types will separate during storage and need to be agitated prior to use. It is crucial that manufacturers prevent air bubbles from forming in the material—especially if the application requires a high degree of shot consistency.
Choose Your Method
For most of the 20th Century, assemblers applied oil with a squeeze bottle and grease with a brush. With the onset of automation, however, most manufacturers turned to automated dispensing to keep up with increased production.
Valve dispensing was introduced in the 1980s and remains the most popular method. Manufacturers use a piston, positive-displacement or diaphragm pump to move lubricant to the valve.
Several types of valves dispense oil and grease, including air spray, air-oil spray, precision spray, jet, needle, metering, spool and auger. The jet valve is the newest type, having been developed in the last few years. It provides noncontact dispensing, whereby hundreds of microscopic lubricant drops are released every second without a dispensing tip.
Another fairly new type is the air-oil spray valve, which prevents oil from being forced into the air system if the lubrication lines get damaged. Air also combines with the oil after the fluid outlet check, preventing air from backing up into the source oil system.
When dispensing very thick grease, a heavy-duty valve is recommended. Its tip size should be four times greater than that of the grease’s filler particulate to prevent blockages and protect the valve’s seals.
Pneumatic time-pressure systems, such as those made by Nordson EFD, are an alternative to valves for low-volume applications. The grease is dispensed from a syringe attached to an air-powered dispenser. The assembler steps on a foot pedal to activate dispensing. A piston inside the syringe pushes grease out of the tip, providing consistent deposits.
Manual thumb-press syringe barrels and handguns are used by some assemblers, also in low-volume applications. These devices offer ergonomic and production benefits over a squeeze bottle or brush.
At the other end of the spectrum is a bulk-delivery system, which is essential for large automotive and white-goods manufacturers. In this system, a high-pressure pump (10,000 psi or more) moves lubricant from a central 55-gallon drum to valves (via hoses) at several workstations.
Electronic metering systems, another delivery option, offer accuracy and cost-effectiveness. One DOPAG customer, a Tier I manufacturer of shock absorbers, uses eight metering systems. Each system ensures exact dispensing of oil for the various types of shock absorbers being assembled.
Some suppliers specialize in dispensing valves, while others, like Fisnar Inc., also offer standard and custom dispensing workcells. These workcells are used by manufacturers in industries such as electronics, automotive, solar and agriculture.
“A typical high-volume automated workcell might require one robot to dispense oil on component A for corrosion resistance, and another robot to dispense grease on component B to extend the life of the end product,” explains Mark Sorenson, sales manager for Fisnar Inc. “The lubricants are fed from bulk packaging to their respective valves by means of suitable transfer systems, integrated within the workcell.”
The F-9960 workcell is a Fisnar standard model. It features a large work area (24 inches square) and three-axis cantilever design that handles high-pressure valves for grease and spray valves for oil applications. Intuitive operator interface controls enable easy programming of dispense points and paths in a 3D array. Some of the software features include tip change alignment, CAD file interpolation, step and repeat functions.
Also available from the company is the SV1000SS spray valve. Made of stainless steel, this valve handles light oil lubricants. It has an adjustable spray angle and a nonclogging nozzle.
Techcon Systems’ TS9200D Jet Tech valve dispenses up to 300 drops per second (as small as 10 nanoliters) and handles material viscosities up to 400,000 centipoise. Can La, product manager for Techcon, says the valve features a replaceable diaphragm that shortens cycle times (due to its very small size) and reduces the energy needed to eject a drop of fluid.
Aerospace manufacturers use the TS941 spool valve to dispense high-viscosity grease on mechanical parts. This high-pressure valve creates fast on-off dispensing, and it can handle very high material input pressure. All side ports can be rotated in 120-degree increments to conveniently locate valve connections.
Medical device manufacturers microspray their products with oil using the TS5540 valve. Its compact design and easy-mount threaded hole allow for easy integration into automated applications. The valve sprays oil through disposable dispensing tips in uniform patterns from 0.18 to 0.6 inch in diameter.
Automotive OEMs and Tier 1s use Nordson EFD’s PICO dispensing systems to jet small amounts of electrical and thermal grease onto parts for windshield wiper motors, trunk locks, door locks and electrical connectors.
The PICO xMOD noncontact jet valve features pieozoelectric actuation technology that dispenses lubricants at up to 500 cycles per second, notes Claude Bergeron, product line manager—dispense valve devices for Nordson EFD. It deposits amounts as small as 2 nanoliters with high accuracy and excellent process control. The valve’s major components are interchangeable and assemble or disassemble quickly.
To enhance the performance of its syringe barrels when dispensing thick grease, Nordson offers the Optimum Clear Flex piston made of pliable rubber. The piston fits snugly into the syringe but flexes under pressure to reduce piston bounce, which occurs when air bypasses the piston in the syringe during dispensing. The piston also creates a tight seal that maintains barrel wall wiping throughout the dispensing cycle, reducing costly material waste.
A Tier1 manufacturer in India dispenses grease with six of Graco Inc.’s automatic metering valves (AMV). Each stroke of the AMV applies 0.2 cc of grease. The AMV is ideal for robotic dispensing, and it has a high feed pressure rating. Stainless steel wetted components are standard, but an integrally mounted solenoid valve is optional.
The Indian manufacturer uses the AMV in conjunction with Graco’s Fire-Ball 300 series pump, which has a maximum working pressure of 2,700 psi. Positioned directly in the lubricant reservoir, the pump features an air motor with few moving parts for less downtime and low maintenance. Large air ports provide efficient use of compressed air supply for continuous pump operation.
DOPAG’s Series 415 chamber metering valves feature a chamber whose size is adjusted to the metering volume. These pneumatic valves dispense lubricant in metered shot sizes from 0.05 to 100 cc without drooling or stringing. The valves are material-pressure driven, therefore the metering speed depends on the material viscosity and pressure. The valve body is made of aluminum or stainless steel.
Series 419 needle metering valves consist of two separated parts, making it impossible for any leaking material to flow into the actuating air cylinder. Walker says that this series has recently been upgraded to provide operators with electronic data feedback to confirm lubricant dispensing. Metering volume is adjustable and reproducible from 0.001 to 3 cc. The valve seat and needle are made of tungsten carbide to withstand abrasive media.
Other DOPAG valves that work with the company’s custom single-component metering systems include standard dispensing, membrane dispensing and cartridge chamber metering. The systems’ flow regulator reduces lubricant flow at the end of the electronic metering cycle to stay within allowable tolerances and prevent overdosing.
An electronic volume counter carefully measures lubricant as it’s dispensed.
Pneumatic drum pumps generate high operating pressure to feed high-viscosity lubricants directly from original containers. The pumps also feature an automatic cut-out function that activates when the container is empty to prevent air introduction into feed lines.
Graco’s Trabon MSP divider valve enables manufacturers to simultaneously deliver lubricants to multiple workstations. This manifold proportioning device features an inlet, an end section and a minimum of three valve sections. Each valve section contains a piston, built-in outlet check valves and passageways that meter the flow of lubricant.
“A pump with an output hose connects to this valve, which has up to 16 ports,” explains Lee Brown, strategic sales manager—industrial lubrication equipment for Graco. “The divider valve enables a company to automatically dispense lubricant from as many or as few ports as their production demands. It also precisely measures the amount of lubricant dispensed.”