Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
Docket No. 1987
Description
IMPROVED POROUS IRRIGATION PIPE AND METHOD
Technical Field
This invention relates to the production of
porous irrigation pipes and, more particularly, to
an irrigation pipe fabricated by an improved method
utilizing a novel precursor material.
~ackground Art
As population steadily increases, water
becomes a more important and increasingly scarcer
and more expensive resource. Agriculture is one
of the most important uses of surface water. It is
necessary to develop more efficient systems for de-
livering water to plants. Surface watering tends
to be wasteful since water that is not absorbed
quickly enough runs off or evaporates, and the water
that is absorbed must wet the soil until it reaches
the roots, the water gathering system for most
plants.
Surface irrigation systems must be removed
and replaced each time the field is tilled or plowed
for replanting. Irrigation systems interfere with
mechanical harvesting and require substantial main-
tenance. Above ground watering should usually be
conducted during the day since many plants are sub-
ject to decay at night. Furthermore, above-ground
watering interferes with usage of recreational
areas such as parks, athletic fields and golf courses.
Surface watering is non-specific in that the crop and
weeds are both equally watered.
Because of the limitations in above-ground
irrigation, subsurface irrigation systems have been
developed in which water is directly fed at an optimum
subsurface depth to the roots of the cxop being
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cultivated. The pipe must be inert to the soil en~
vironment, must be capable of withstanding hydro-
static pressure in the presence of hard objects such
as rocks without collapse and preferably is ~lexible,
so tllat it does not suffer brittle failure and can
be bent to ~ollow crop-line contours.
There are numerous agricultural applications
for an ir~ig~tion pipe which leaks water slowly over
its entire surface and length. Such pipes can be
buried underground at levels appropriate for the
particular crop being grown, and will supply water
directly to the root system. With proper controls,
the water level in the soil can be maintained at
near-optimum levels. With some crops, this has been
shown to increase yields substantially.
A porous irrigation pipe has been produced
from reclaimed, tire rubber mixed with a binder such
as polyethylene. This mixture is extruded to form
the pipe, and the water present within the hot
extrudate vaporizes, producing the small pores
through which water seeps under pressures of a few
psi. While this pipe is useful for some appl~cations,
it has several drawbacks for many large-scale agri-
cultural uses. The most important proklem with the
present product is its highly variable porosityO
Some sections had no pores and other sections very
large pores. The rate at which water emerges from
this product varies by 50 to 75 percent or more
within a few feet along its length~ If it were used
with closely spaced plantings, such as densely
packed sugar cane plants, some areas would be over-
watered, while others would be essentially dry.
Another problem is that the overall porosity
of the pipe is poorly controlled from lot to lot.
This causes severe engineering problems when one
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tries to design a wa-ter system for a particular
location. What is normally done is to use many
pressure regulators throughout the system. This is
expensive and further limits the potential applica-
tions of the porous pipe material.
I-t has been discovered that the wide vari-
ation in porosity is due to failure to control the
moisture content of the raw materials. The dry
powder is somewhat hygroscopic and prior produc-
tion systems disclosed by Turner in U.S. Patent No.4,003,408; No. ~,110,420 andNo. 4,168,799 relied
on ~bsorption of water by the crumb material to
provide the blowing or pore forming agent. However,
the water content of each batch or portion of a
batch varies with humidity, temperature, etc. of
the environment. Since the amount of water present
in the extrudate is very important to the porosity
of the final pipe, variations in the water content
of the feed will produce unacceptable variations
of the product. Turner attempted to control excess
water by venting the extruder but this did not ef-
fectively control variations in porosity.
The raw material is a mixture of fine powders
and small amounts of oils. Such materials do not
feed well in single-screw extruders. Moreover, uneven
feeding of the powders will produce variations in the
density and thickness in the wall of the pipe. Since
~hese factors are important to the porosity of the
wall, uneven feeding in the extruder will result in
further inconsistent leak rates.
Statement of the Invention
Porous irrigation pipe has been developed in
accordance with this invention having extremely con-
sistent porosities along the length of the pipes.
Irrigation systems containing fewer pressure regulators
can be deployed. Crop yields will increase since a
hi~her percentage of plants will receive a uniform
amount of water. The porous pipe of the invention
will have particular application to underground drip
or continuous irrigation of densely packed crops
such as sugar cane.
The improved, porous irrigation pipe is made
possible by accurate control of the water content
f the raw material and by providing the raw material
in a form in which it feeds consistently and reliably
to the extruder. The high surface area crumb and
powder mixture had water contents varying from about
0.2 percent by weight up to several percent water by
weight and varied throughout the batch. The moisture
content of the material of the invention has a
moisture content not varying by more than +10 percent
throughout the batch and is at a value between 0.5
to 3 percent by weight, preferably from about 0.75
pexcent by weight to 1.5 percent by weight of water.
The improved pipe is preferably produced in
accordance with the invention by preprocessing the
raw material into a shaped pellet form. This material
feeds very consistently and reliably into a variety
of types of single screw extruders. This makes it
possible to produce the porous pipe in virtually
any location where standard extrusion equipment is
available. This reduces cost of shipping, production
and installation of the porous pipe. Additionally,
the moisture content of the pellets can be adjusted
to predetermined, specific values depending on the
desired porosity and leak rate. The pellets are
stored under water-excluding conditions such as in
vapor barrier containers. The pellets are much less
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hygroscopic than the high surface area powder materials
of the prior art.
Another difference in the production methods
is that the use of a non-vented extruder becomes
possible since water content is known and there is
no need to vent excess vapor pressure. Since the
parameters of water content and feed rate are con-
trolled and the temperature is controllable,
porosity can be controlled by preselection of water
content of the pellets. Alternately, since all
variables are controlled, porosity of a batch or run
can be controlled by changing the temperatures in the
extruder and die.
Another novel feature of the invention is
the provision of pelletizable formulations. The
powder materials previously utilized are not capable
of being pelletized. The pellet form of feed con-
taining controlled moisture content and pelletizing
additives makes possible continuous production in
high volume of porous irrigation pipe with very
consistent leak rates on a variety of extruders
anywhere in the world where the pipe is needed.
The porous pipe can be optimized for porosity,
size and strength for the intended application.
In addition to the savings in shipping and produc-
tion, the porous pipe of the invention produces
irrigation systems which in many cases will yield
substantial increases in crop yields due to more
accurate watering cycles.
These and many other features and attendant
advantages of the invention will become apparent as
the invention becomes better understood by reference
to the following detailed description when considered
in conjunction with the accompanying drawing~.
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Brief Description of the Drawings
Figure l is a schematic view of a train of
equipment for producing pellets in accordance with
the invention;
Figure 2 is an enlarged view in elevation
of a pellet;
- Figure 3 is a partially broken-away view in
elevation of a humidity-controlled storage container;
Figure 4 is a schematic view of a system for
extruding porous pipe in accordance with the
invention; and
Figure 5 is a view in section taken al~n~
line 5-5 of ~igure 4.
Detailed Description of the Invention
The pelletizable mixture of the invention
includes a major portion of elastomer in crumb form,
a minor amount, usually from l.0 to ~.0 phr of a slip
agent, preferably a mineral such as talc and 0.1 to
l.0 phr of a lubricant, such as a metal stearate.
The elastomer can be natural rubber which is
cis-1,4-polyisoprene or synthetic homopolymers of
butadiene or isoprene or their copolymers with minor
amounts of 0.1 to 20 percent by weight of vinyl mono-
mer~ such as styrene, isobutylene or acrylonitrite.
It is preferred that the elastomer be vulcanized. A
ready and inexpensive source of prevulcanized crumb
rubber is available as rubber reclaimed from auto-
mobile tires after removal of the metal tire cords
and metal reinforcement in the head. The rubber is
ground into crumb particles no larger than those
passing through a 10 mesh screen, preferably ~rom
20 mesh to 60 mesh.
The binder resin is a thermoplastic material
* parts per hundred of resin
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capable of softening at a temperature below 300F so
that pores will form during extrusion. The resin
must be stable ~o longterm exposure to soil environ-
ment and to fertilizers, herbicides or pesticides
seeping into the adjacent soil or to fertilizers,
growth regulators herbicides or pesticides dispensed
by dissolving in the irrigation water. The resin
must be inert to the other components of the pipe such
as the crumb rubber under extrusion conditions.
Polyvinyl acetate is excluded from use since it will
react with the crumb rubber. Styrene polymers in-
cluding impact polystyrene copolymers are useful
as are linear polyamides such as various Nylon , poly-
vinyl-chloride, polypheneylene oxide and polypheneyiene
sulfide polymers
The most preferred group of polymers are the
linear polymers of alkenes of 2 to 4 carbon atoms such
as polyethylene, polypropylene or polybutene. These
polymers are unreactive in soil and in the extrusion
barrel and have long segments of linearity providing
crystalline behavior. Polyethylenes have lower
melting temperatures, are tougher and hold shape
better. High density polyethylenes have densities
from about 0.94 to about 0.97 gm/cc, and porous pipe
prepared with all high density polyethylene binder
are somewhat stiff, brittle and difficult to extrude.
Low density polyethylenes have densities from about
0.90 to 0.93 gm/cc, and porous pipe prepared with all
low density polyethylene binder are very flexible and
can readily be bent to follow a desired path and are
readily extruded. These pipes are very useful for
above-ground irrigation. However, wall stiffness may
not be adequate for subsurface systerns. The pipe
develops kinks in the bends and does not hold its
shape. The optimum binder which provides a porous
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pipe which holds its shape without brittleness yet has
adequate flexibility is composed of 50 percent to 80
percent by weight of high density polyethylene, prefer-
ably 60 percent to 70 percent to 20 percent to 50 per-
cent by weight of low density polyethylene, preferably30 percent to 40 percent. The polyethylene can be used
in any co~mercial form such as powder, flake or pellets.
Reclaimed polyethylene materials can also be used. The
form and color of such materials h~ve little effect
upon the product.
The slip agent aids in extruding the rubber bin-
der mixture. Finely divided minerals other than talc
can be utilized such as clays, silicas, carbonates, or
~icas. The metal stearate lubricant can be selected
from calcium, magnesium or zinc stearates.
Referring now to Figures 1-3, the crumb rubber,
additives and binder are thoroughly dry blended in
blender 10 such as a ribbon blender or other suitable
mixing device to form material which is fed to the
hopper 12 of the extruder 14. The mixture is pelle-
tized by being extruded into a die-face pelletizing
system. An extruder feeding directly into an under-
water or water-ring pelletizer 16 is illustrated. A
turn-screw extruder is preferred though a single-screw
extruder equipped with a good crammer can be utilized.
Strand pelletizers do not work well with the rubber-
binder composition of the invention. The extruder is
maintained at a temperature of from 320F to 400F
and the die at a temperature from 250F to 325F by
means of separate heating systems such as a set of
heating jackets 18, 20 receiving separate flows of
heated exchange fluids. The extruded strand material
should have a bulk density after drying of at least
0.25 gm/cc and has a diameter from 3 to 20 mm, pre-
ferably 4 to 10 mm. The strand is broken into
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lengths of 3 to 20 mm by means of a mechanica] knife
22 immersed in the water bath 24. The water in the
bath is cool, usually from 20F to 80F and as the
extruded strand 26 enters the water 28, it congeals
and sets so that a thin blast of air from nozzle 30
breaks the strand 26 into pellets 32 which fall into
the ccllector portion 34 of the water bath 24. The
nozzle 30 is connected to an air supply 36 which is
pulsed by a controller 38.
The dispersion of pellets in water is fed
from water bath 24 into a separator such as a cyclone
separator 4~. The water is recycled to the bath 24
through line 42 while the pellets 32 are delivered
by conveyor belt 44 to a dehumidifying drier 46 to
dry the pellets to a preselected moisture content
between 0.5 to 2.5% by weight depending on -the
porosity desired. The conveyor belt 44 carries the
dried pellets 32 into a closed hopper 48 having a
humidity controlled atmosphere which feeds the
pellets into a storage container such as a poly-
ethylene bag 50. The bag is closed with a secure
closure such as a band 52 of metal and can be placed
in an outer protective container such as a box or a
barrel 54. The dried pellets contain a uni.form
moisture content which can be accurately controlled
and the moisture content is stable for extended
periods. The pellets have a much smaller suface
area than the prior powder materials and are
humidity stable without storage for short periods
of time.
Referring now to Figure 4, the pellets 32
are fed to hopper 60 of a pipe extruder 62. The
hopper has a lid 61 to isolate the feed from the
environment. The extruder preferably contains a
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single low pressure screw 64 and has a length to
diameter ratio of at least 24/1, preferably at
least 35/1. The compression ratio of the feeding
section to the metering section can be from 1.5/1
to 2.2/1. The diameter of the barrel 66 is suitable
to produce pipes having outside diameters from 2 to
10 inches, usually from 3 to 6 inches. Mixing pins
are to be avoided since the crumb rubber can foul
these elements.
The process is operated at a temperature high
enough to meltthe bin~er resin but below the melting
temperature of the elastomer. Good temperature control
of the barrel and expecially of the die 68 is required
usually to within +5F. A more uniform porous pipe
is prepared by providing an increasing temperature
profile over the length of extruder 62. Separate
heating jackets 70, 72, 74 can surround the feeding,
transition and metering sections, respectively, of the
extruder barrel 66. Each jacket receives a separate
flow of heat exchange fluid. The feeding section can
be heated to 340F - 360F (Tl), the transition section
from 360F - 370F (T2), and the metering section from
365 F to 375 F (T3).
The die 68 is also provided with a separate
temperature control. A suitable die is shown in
Figure 5 of U.S. Patent No. 4,168,799. The die
contains an outlet orifice 72 in front of which is
mounted a mandrel 84 for forming the bore 86 of the
porous pipe 88. The mandrel may be removable to
vary the wall thickness of the pipe. The thickness
is selected depending on desired flow rate, leak
rate and wall strength to avoid collapse. Wall thick-
ness is usually from 0.1 to 2.0 inches. In U.S.
Patent 4,168,799, the die is chilled to a temperature
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of from 40 F to 80F in order to avoid forming an
impermeable skin on the surface of the pipe, and
the barrel is vented to remove excess pressure.
However, in accordance with the present invention,
the barrel need not be vented and the die is heated
to a preselected temperature from 240 F to 300F to
control porosity of the porous pipe. An annular
jacket 90 receives a flow of preheated heat ex-
change fluid (T4).
As the screw 64 is rotated by motor 92, the
feed moves forwardly and the binder resin melts. The
water vaporizes and the expanding bubbles of steam
form a network of pores 96 extending from the bore
86 to the surface 98 of the porous pipe. The pipe
88 can be extruded through the die 68 into the
ambient and enters a chilling bath 100 containing
water at a temperature of about 25F to 50F before
being pulled onto rewind stand 102. The chiller
bath usually has a length of at least 40 feet.
The invention will now be illustrated by
the following specific examples of practice.
The dry materials were mixed in a ribbon
blender and fed into the hopper of a twin-screw ex-
truder heated to 360F - 390F with a 5 mm die hea~ed
25 to 300F. The water bath was maintained at 35F -
400F and the 5 mm strand was chopped into approximately
ground pellets about 8 - 9 mm in diameter by an air
knife. After drying the pellets had a density of
0.275 gm/ml.
Example 1
The following mixture was pelletized and
dried to 0.75 percent moisture content:
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Crumhed Tire Rubber (4~ Mesh) 100 lb.
Low Density Polyethylene 35 lb.
Finely Powdered Talc3 lb.
zinc Stearate .25 lb.
These pellets were extruded in an unvented single
screw extruder into porous pipe with an I~ of 0.55
inch and a wall thickness of 0.2 inch. The extruder
temperatures were:
Extruder (all zones)350F.
Gate 340F
Spider 335 F.
~ie 335F
This porous pipe had the following porosities at
10 psi:
0.27+.02 GPM/100 Linear Feet
0.11+.003 GPM/100 Square Feet
Example 2
This same pelletized raw material of Example
1 was extruded under the same conditions, except that
the die temperature was 290F. This pipe had the
following porosities at 10 psi.
0.19+0.17 GPM/100 Linear Feet
0.076+0.007 GPM/100 Square Feet
Example 3
Example 1 was repeated except that 35 lb.
of high density polyethylene was substituted for
the low density polyethylene binder. The pellets
were more difficult to extrude and the pipe was more
brittle and less flexible.
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Example 4
Crumbed Tire Rubber (40 Mesh) 100 lb.
High Density Polyethylene25 lb.
Low Density Polyethylene10 lb.
Slip Agent-Talc 3 lb.
Lubricant-Calcium Stearate0.25 lb.
The formulation was processed into pellets and dried
to contain 1.0 percent moisture. The pellets were
extruded in a 2.5 inch diameter, 24/1 L/D, Prodex single-
screw extruder. The extruder was equipped with a PVC
type screw, which had a compression ratio of 1.9/1,
and a circular pipe die with a land-length of
16/1. Temperatures in the extruder were maintained
at 340F - 360F. The gate, spider and die tempera-
tures were adjusted to yield an extrudate having the
temperatures shown below. Porous pipes having a wall
thickness of 0.165 inch were produced having the
following properties:
APPROXIMATE LEAK RATE
Extrudate GPM/100 linear feet
Temperature 0.5"1.0"
(F.) GPM/100 sq ft ID PipeID Pipe
250-260 0.10+0.02 0.25+0.040.50+0.08
275-285 0.20+0.03 0.50+0.081.00+0.16
300-320 0.40+0.06 1.00+0.162.00+0.32
340-360 0.80+0.12 2.00+0.324.00+0.64
The pellet material fed smoothly and the
porous pipe had good compression strength, yet was
flexible. The pipe had uniform porosity along its
length. The consistency of leak rate is measured
by determining the amount of flow of one foot in-
crements over 50 feet of pipe to determine the
consistency factor, Cv, --the standard deviation/5 flow rate.
For most prior commercial porous pipes, the
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Cv achievab.le is from 0.25 to 0.5. For most appli-
cations, a Cv of 0.2 is preferred and for densely
packed plants such as sugar cane, a Cv of 0.1 is
necessary to reduce no-growth in overwet or dry
areas of irrigation.
A one-half inch I.D. porous pipe produced in
accordance with the invention having a flow rate of
1 gpm/100 linear feet at 10 psi pressure has a Cv of
0.1 to 0.15 and a porous pipe having a flow rate of
0.25 gpm/100 linear feet has a measured Cv of 0.05
to 0.1.
It i5 to be realized that only preferred embo-
diments of the invention have been described and that
numerous substitutions, modifications and alterations
are permissible without departing from the spirit and
scope of the invention as defined in the following
claims.
