Tank/material retaining container
A machine needs a container to feed
the material from. A machine can be fed directly from drums, lined
from tank, or carry its own holding tanks.
The holding tanks for the component
materials need to have some pressure release mechanism as you
dispense to counter-balance the pressure. Desiccant filter or
nitrogen gas feeding is needed for isocyanate side for pressure
Heating capacity of the tank may be an
option if you prefer to control the material temperature higher. If
your material has phase separation issues, you may want to look at
agitators in tanks to constantly agitate the material.
For high-performance class materials,
heated tank is essential to retain the production parameters.
However, for room-temperature-curable materials for lower
performance end, drum feed is sometimes sufficient.
Depending on the type of process, you
need to choose appropriate lines (tubes/pipes) to carry the
component materials to the mixing head.
For elevated temperature process, line
may have to be heated. Some materials freezes very quickly when the
temperature is lower, which may cause the whole system to clog up.
Recirculation valve/line may help
keeping the steady temperature of material. It circulates the
component material back to the heated retaining tank, so when your
machine is not dispensing the material, the material within the line
does not freeze.
If you use corrosive material such as
solvents, you may choose PTFE coated feeding lines. Some
manufacturers also use rigid stainless steel tubing.
Piston mixing system (see below)
typically needs to retain higher pressure than gear pump system.
Gear pump/high pressure systems use the line as pressure buffer for
steady flow of the material.
In general, there are pneumatic and
electric driven systems.
Electric motors have better power and
can handle high viscosity materials better than pneumatic, but it is
usually more expensive. Also, if you use some flammable material,
it is more difficult to make it explosion proof.
Pneumatic driven systems, since they
do not require electric motor, they could contribute to the
explosion proof design of your equipment. However, when you use a
high viscosity material, the out-put rate may vary depending on the
viscosity. It may also be somewhat noisier to operate than electric.
You can choose to have individual
motor to each pump and agitator, or have one motor to drive all by
connecting them with shafts and gears.
If you need to handle high viscosity
material to be metered with a good precision, you may want to choose
electric. The unit cost of pneumatic is generally lower than
Metering pump is very important part,
but they have various qualities/prices. It is important that you
choose the pumps that are best-fit to your application.
Cheap/low-quality pumps slip and do not keep a good/constant
ratio. Commonly, gear pump systems and piston pump systems are
Gear pump system works at small output
as well as a large out put. It is relatively low pressure system
and dispenses the material continuously without pulse.
Piston metering system often relies on
the back-pressure of the material in the line for constant ratio.
There are continuous pulses as it dispenses, through-put control may
become difficult. It is generally noisier than gear pump.
In general, gear pump system is often
preferred for a common continuous casting operation. However,
piston systems create much higher pressure comparing to a gear pump
of same price range. This is why piston systems are widely used in
high-pressure spray machines. If your material requires high
pressure dispensing, such as a heavily filled material and a highly
viscous prepolymer, you may consider piston system. Some, low cost
machines use piston system, and it may suffice to cast low-end
room-temperature curable materials if it does not need a high
precision of constant mix ratio and output rate.
The choices are between static mixing,
dynamic mixing, dynamic-static mixing, and impingement mixing.
Static mixing will be easiest in terms
of maintenance as you would dispose of the disposable plastic mixing
tube each time. Static mixing heads are lower cost comparing to
others. However, if the component materials are harder to mix,
static mixing system may not blend the components sufficiently.
A dynamic mixing system mixes the
components dynamically by mixing rods in the mixing chamber, so it
mixes very well. It is higher price and for higher outputs. The
maintenance will be more difficult as dynamic mixing rods are
usually not disposable.
Dynamic-static mixing system is
something fairly new. It looks like a static mixing head, but the
spiral fixture within the disposable mixing tube rotates and
dynamically mixes the material. This mixes the component well and
maintenance is easier than the dynamic system.
Impingement mixing is generally used
for spray coating and RIM process. This usually requires high
pressure (piston) pumps. The component materials are dispensed from
nozzles with a high pressure and collide within a small mixing
chamber or right outside of the nozzle, the mixed material is
injected into a high pressure mold or sprayed directly on to a
substrate. Impingement mixing has more restrictions to mixing
ratios, output, and other processing parameters. Impingement
systems are often used in spray, foam, and RIM systems and not used
in liquid cast elastomer systems.
In most of polyurethane liquid
casting, static mixing works sufficiently. There are a variety of
tube sizes/lengths; you have some choice to higher output to lower
output with higher mixing turbulence with some choices of lengths,
which can be interpreted as mixing time. However, there is a limit
to static mixing. If you are mixing a third component such as
powder fillers, static mixing may not have capacity to mix. If A/B
components have a large difference in their viscosities, mixing may
become an issue. When the output requirement exceeds the capability
of static mixing systems, you may also need to look at other mixing
The required output rate is one of the
first questions the machine manufactures ask. You need to determine
the range of output material you need per minute for your
operation. Smaller machines are a few hundred grams to 1 – 2 pounds per minute. The larger
one would be as much as hundreds of pounds per minute. In general,
larger the output, more expensive the machine is. Also, if you need
a very small precision output, it may take a special machine.
They have some options for on-off
switches. You can probably choose from trigger, foot-switch, manual
on-off, or shot-timer. If you need the portability, you may ask to
put it on wheels. Some manufactures also provide design of
automated production lines and fabrication lines.
Fixed Ratio vs. Variable Ratio
The most of piston pump systems are
fixed ratio. Except for a few unique models, once you have a
machine, you cannot change or adjust the mixing ratio unless
switching the pumps. Piston pump systems are often lower cost, and
it creates higher pressure than gear pump systems. Insulation foam
machines and polyurea spray coating machines are often this type.
Advantage for gear/variable-ratio
system is that you can use different materials in the same machine.
Polyurethane and other resin systems are not all 1:1 or 1:2
systems. If you want to use a variety of materials with the same
machine, variable ratio system gives better flexibility.
Also, all resin materials come with a
small specification range that is accepted in the industry.
However, some application requires tight hardness control. Even the
material is within the specification range, you may need to
calibrate your machine to obtain exact ratio. This calibration
requires a variable mixing machine. By adjusting the actual mixing
ratio slightly, you can get more precise chemical balance of the
List of Manufacturers
The lists below consists of various
manufacturers/suppliers selling dispensing equipment and given as a
starting point for our customers. The list is not in a
particular order. The recommendations are based on our experience,
our knowledge on these suppliers may be limited, and the information
may not be current. Please contact each supplier for your
requirements. We will be happy to provide material and
processing information directly to your machine supplier.
For smaller output room-temperature
cure non-foam systems
Sealant Equipment and
Advance Process Technology
Trico Poly System
For large output room-temperature
cure non-foam and foam systems
Advance Process Technology
Sealant Equipment and
For elevated-temperature cure
Advance Process Technology
Trico Poly System
For spray-on coating/foam systems
Northstar Polymers, LLC
3444 Dight Avenue South
Minneapolis, MN 55406
All of the statements, recommendations, suggestions, and data
concerning the subject material are based on our laboratory results,
and although we believe the same to be reliable, we expressly do not
represent, warrant, or guarantee the accuracy, completeness, or
reliability of same, or the material or the results to be obtained
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