ULTRASONIC MOLD CLEANING
The use of ultrasonic cleaner for routine injection mold maintenance has been
effectively employed for many years. As a non-contact method, mold detail is
not damaged during cleaning and critical tolerances can be maintained,
extending mold life. The high cleanliness level achieved with ultrasonic results in
better part release and longer runs. This improves productivity and reduces
scrap. The penetrating nature of ultrasonic cleaning removes residual polymer,
mold release and outgas residue extending the mold life. It can remove residue
from the cooling channels and vent lines improving polymer flow. In most cases,
molds can be cleaned without disassembly, which significantly reduces the manhours required for the cleaning process
How does it work?
Ultrasonic cleaning uses high-frequency
sound waves to remove mold residues and
fouling from tooling and plates that are
immersed in a heated (usually 160 to 180 F)
aqueous solution. An ultrasonic generator
converts standard line- frequency current
(60 or 50 Hz) into high- frequency electrical
energy (20,000 Hz or more). The generator is
connected to small transducers that are
mounted to the bottom or sides of a wash tank. These transducers vibrate at
ultrasonic frequencies (20 kHz and above) when the current passes through. This
causes the bottom or sides of the tank to vibrate like the diaphragm in a speaker,
which creates microscopic bubbles that form and collapse in the tank (a
phenomenon known as cavitation), which scrub and loosen vent residues and
grime. The energy released from these microscopic scrubbing bubbles produces
forces at 10,000 F at 7500 psi, which is powerful enough to loosen contaminants
without damaging critical edges or surface finishes
The cleaning ability of ultrasonic depends on several key factor
Cleaning solution: The type of detergent required is dependent upon the
process and type of resin you run, which leaves behind specific types of offgassing residue. Highly alkaline solutions such as sodium hydroxide do the best
job of removing stubborn contaminants, light rust, and heavy grease on most
tooling and plates, with no harm to most plating and coatings. On the downside
it can be caustic, posing a potential health risk, and may require neutralization
before disposal, depending upon local codes.
Mild alkaline solutions also are available that perform well on many residues
without the caustic issues. But in general, the friendlier the detergent, the less
effective it will be on stubborn contaminants.
Slightly acidic solutions, such as those containing low concentrations of citric
acid, excel at rust and oxide removal, but must be used with caution on some
tool steels because they can react with the iron in the steel, turning it gray. This
normally does not cause a technical problem but doesn’t sit well with
toolmakers.
tendency to fail slowly over time. Transducers may be placed at specific locations
in the tank to correlate with the size and configuration of plates being cleaned.
Tank design and construction: Buy a tank large enough to fully immerse your
largest mold plates. You will regret saving a few bucks to get a small tank that
will require you to flip the mold plates over for complete cleaning. Also make
sure the tank is constructed of at least 12-gauge stainless steel and be sure to
have the manufacturer weld a few support bars across the bottom to keep
plates and tooling baskets from resting directly on the bottom of the tank.
SYSTEM BENEFITS
- Reduced labor
- Longer mold life
- Reduced mold damage from cleaning
- Longer runs
- Reduced scrap
- Easy to maintain system
EQUIPMENT AND PROCESS
Ultrasonic cleaning is an immersion process that requires three components. The
first is the tank to hold the liquid, the second is the chemistry in the tank and the
third is the ultrasonic power supply and transducers. TRANSONIC offers systems
in a number of configurations depending on your needs. Sizes range from
tabletop tank and generator systems that are effective at cleaning inserts, core
pins and small molds, to fully integrated wash/rinse/dry systems for larger
molds. Most mold cleaning applications utilize powerful 25 kHz ultrasonic but
TRANSONIC offers 30 kHz for molds that are more delicate. While the chemistry
can vary based on the mold material and type of soil, most molds are cleaned in
a buffered alkaline solution with a pH above 12. It is important that the cleaning
agent contains a rust inhibitor to prevent flash rusting when the mold is removed
from the cleaning solution. The mold is then rinsed by hand with cold water or
immersed in a rinse tank. Drying is usually accomplished by blowing the mold off
with compressed air and spraying it with a rust preventative. The typical wash
time is less than 30 minutes and most molds do not need to be disassembled for
processing.
Ultrasonic cleaning can give the following advantages
- Short wash process leading to reduced time spent in cleaning
- No manual labor required. An operator is not required when the machine is
cleaning the mold.
- High levels of cleanliness give longer life in production.
- No abrasion of precise edges and surfaces gives longer mold life.
- No solvents needed because of aqueous process.
- Suitable for all molds, large and small.
- Machinery is simple and easy to use.
- Standard features include Options include
- Totally stainless-steel construction
- Thermal and noise insulation
- Surface skimming of liquid and a weir in wash tank
- Low level protectionThermostat controlled heating
- Drain valve
- Water inlet valve
- Work support grill*
- Cascade water refill*
- Rim lip ventilation channels on all stages*
- Protective guide rails*
- Submersible transducer boxes*
APPLICATION:
The use of ultrasonic cleaning equipment for routine injection
mold maintenance has been effectively employed for many years. It provides
a number of benefits not achievable using more traditional methods. As it is
a non- contact process, mold detail is not damaged during cleaning. Critical
tolerances can be preserved, thereby
extending mold life. The higher levels of cleanliness attained using ultrasonic
cleaning also results in better releases and longer runs while improving
productivity and minimizing scrap. The penetrating nature of ultrasonic cleaning
minimizes the requirement for mold dis-assembly and removes residual polymer
and releases from mechanically active mold components thus extending their
life. It can also remove buildups from internal cooling ports and channels,
thereby improving polymer flows. ULTRASONIC TECHNOLOGY: Ultrasonic
cleaning utilizes cavitation and implosion, the rapid formation and violent
collapse of minute bubbles or cavities in a cleaning liquid, to enhance cleaning.
This activity, when combined with an appropriate cleaning chemistry, creates a
unique penetrating action that is highly effective, even in blind holes and tiny
crevices. This combination of high energy and deep penetration without part
contact gets
Buying considerations
In the real world, mold plates will get slammed into the sides of the wash tank
and baskets full of tooling will be dropped in too fast. Exposed knobs will be
ripped off. The tank will run 24/7 because everyone will suddenly have
something that needs to be ultrasonically cleaned, as will be evident by the grass
clippings and paint residue floating on the surface of the wash tank. And, due to
the nature of ultrasonic operations—high heat and constant vibration, the
system’s parts can shake loose, wear through, and burn out. Heavy duty, bulletproof, robust, and solid are the words to keep in mind when shopping for an
ultrasonic cleaning system that will perform reliably in a busy mold-repair shop.
Unless absolutely necessary, stay away from bells and whistles such as automatic
loaders, conveyors, dryers, and fancy cabinetry.
However, do make sure of the following:
- • The transducers are warranted for the life of the system.
- The tank is warranted for 20 years or more against cavitation wear-through, which can
cut transducer life drastically.
- The wash tank has a pump filtering system and is easily accessible.
- The pump intake is screened to keep small dowels, O-rings etc. from damaging the
pump impeller.
- The tank drain valves are easily accessible.
- There are no protruding knobs, handles, switches, or buttons on the console.
- Tank heaters are easily accessible.
