TECH DATA -
INTRODUCTION TO URETHANE DISPENSE SYSTEMS –
Typical urethanes for bulk adhesive dispense come in 5, 55 and 300 gallon
containers. The curative (Ashland’s is typically green), is a non-reactive material until
mixed with the resin or prepolymer side (Ashland's is typically brown, we will call it
resin ). If you spill it on the floor it will remain in its wet state, resins on the other hand
have isocyanate in them.
Isocyanates are reactive with many things, especially water. When I say water, I
mean H2O, like the molecule. Moisture in the air is something we cannot see but it will
cause this material to react on a minor scale. If this material is spilled on the floor, the
surface will start to get hard after a day. Not curing all the way through, just forming a
reacted skin on top. After several days the spill will react with moisture in the concrete
and set up all the way.
With this in mind, we must use this info in relation to the dispense equipment. Any part of the resin material which can be exposed to air (with moisture) will have some sort of reaction forming gels or skins. Before we go farther, let’s take a look where we are going. The pump side tolerances, in the market, are typically between .0004 & .0014 inches. There is less room than a typical hydraulic pump for any
abnormal materials. These pumps do not react well to urethane resin gels or cured
particles. It is important to have this understanding.
Back to the containers, pails, drums etc.. when the material is fed to the pumps, air
must replace the material in the pail/drum. Any air which enters the container can, via
moisture, form a skin or gel we do not want, this will eventually make it to and through
the pump. On all pails, drums or totes there is a desiccant drier tube used. Any air which
enters the container is void of moisture. No moisture, no reaction, no issues.
Let us now apply this info to the pumps and dispense gun. Because the pressures
can reach as high as 3000 psi, there are several high pressure seals in the system. There
is no such thing as a perfect seal. There will always be a minor line where the air and the
product meet at the seal on any system. This segment or line will be susceptible to
reaction from moisture. When this happens, the seal is shortly thereafter damaged. To
avoid this, at every point that moisture may effect a seal, there is a barrier fluid used
(dotp or mesamol) to isolate the seal from moisture as well as lubricate the seal. The
rear of the gun body has a fluid pocket for barrier fluid. One or both ends of the
metering pump has a barrier fluid pocket. Rotary shafts seal very well with this set up.
Sliding pins or shafts are greatly improved, but always drag out a microscopic film on
the pin which eventually becomes an issue. The guns usually have sliding pins. this will
be the weakest link in the chain.
Now to the meat of the systems. The resin and curative are gravity fed out of the
drums to the pumps. A production dispense system may have reservoirs which, when
the drum is empty, allows the use of the system for a reasonable span of time while the
drum is being changed. Without the reservoirs, the system could empty completely and
get air voids in the lines which will create off ratio spurts until the air is purged. This is a
terrible waste of time in production and may also scrap some parts. Running out of
material also can cause a minor cross feed condition at the dispense gun which will
cause issues. Bottom line is if you must use your machine while the pails/drum are
changed we recommend reservoirs.
The metering pumps are gerotor style ( S.E.E., EMC, Bandit ). They are
toleranced and labeled as either resin or curative. Bandit pumps run a wider tolerance.
They last longer with less scuffing internally. This is discussed in “Why Bandit” which
In general, when pumps are in good condition, what goes in comes out. The
pumps create the adhesive ratio with the gears which connect the pumps on the machine
base. Some brands use other systems such as timing pulleys and belts or chains and
sprockets. Bandit feels this adds extra side load to shafts and wears front bearings and
On the outlets of the pumps is a check valve. This is a very important check valve
which allows stopping and starting systems at a constant pressure in the dispense hoses.
If or when these check valves fail, they must be replaced. If not, every start of dispense
will be off ratio until the hoses swell to their proper dispense pressure size. This is a fact
on any dispense system.
There is a rupture disc fitting on the outlets of most brands. A simple aluminum
disc is sized by thickness such that if its rated pressure is exceeded, it ruptures. Typical
ratings are from 900 psi to 2950 psi. A system which would use a spring loaded relief
would only work 1 or 2 times till moisture cured the resin on the spring and seat
requiring it to need replacement.
After the adhesive is metered, it is sent to the gun via high pressure hoses. Teflon
lined stainless steel braided hoses are typically used although some companies use
others such as Syn-flex. Bandit likes Teflon for urethanes.
The adhesive then reaches the gun. It is typically an air cylinder operated pin
valve. Sliding pins move into and out of seals which open or close valve ports. A hand
trigger usually operates the gun and also sends a signal (air or electric) to the machine to
start and stop it.