Continuous crumbing machine for recycling rubber tires

An improved continuous crumbing machine for recycling rubber tires and other materials such as polyethylene containers, gypsum, hardboard, tin cans, glass jars and bottles. The device comprises a pair of rotating rolls having negative rake teeth of interlocking sprocket design formed on the outer periphery of each roll. The materials to be fragmented or crumbed are fed between pairs of rotating rollers having negative rake teeth. A plurality of stages of rotating rollers are placed in series to obtain the desired particle size.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
This invention is directed to an improved continuous crumbing machine for 
recycling rubber tires and other materials such as polyethylene 
containers, gypsum, hardboard, tin cans, glass jars and bottles. The 
device comprises a pair of rotating rolls having negative rake teeth of 
interlocking sprocket design formed on the outer periphery of each roll. 
The materials to be fragmented or crumbed are fed between pairs of 
rotating rollers having negative rake teeth. A plurality of stages of 
rotating rollers are placed in series to obtain the desired particle size. 
2. Description of the Related Art 
The following patents are directed to the crumbing and shredding of rubber 
tires: 
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Patent Number Inventor Date 
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3,843,061 Hammelmann 1974 
4,235,383 Clark 1980 
4,614,308 Barclay 1986 
4,757,949 Horton 1988. 
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Barclay & Horton are directed to continuous processes. Barclay employs a 
plurality of stator blades which intermesh with rotor blades mounted on a 
central, vertical shaft. The Barclay device is massive, the rotors being 
about 48 inches in diameter (See Col. 7, lines 16-30 of the Barclay 
patent). 
Horton has transversely disposed cutter wheels on adjacent parallel 
horizontal shafts. The shafts rotate at different speeds ranging from 
about 20-34 RPM for the first shaft, and about 26-42 RPM for the second 
shaft, the speed of the second shaft being about 6 RPM faster. 
Horton appears to be the closest reference, but Horton employs cutter 
wheels instead of negative rake teeth integrally formed into rotating 
rolls, as in the subject invention. Horton's differential RPM ratio is 
never as great as the subject invention, which may range from 4:1 to 25:1. 
Horton obtains particle sizes of one to two inches, and does not mention 
steel wire removal. In addition, Horton employs cutter wheels instead of 
negative rake teeth. 
Hammelmann's apparatus receives successive tires, stretches them and 
subjects the tires to a high speed water jet. Clark employs abrasive, 
counterrotating wheels to disintegrate a tire which is fed into the nip 
between the wheels in an upright position. 
SUMMARY OF THE INVENTION 
This invention comprises an improved continuous crumbing machine for 
recycling rubber tires, including steel-belted ones, and other materials, 
such as polyethylene containers, gypsum, hardboard, tin cans and glass 
containers. The apparatus is capable of taking a steel-belted tire from 
its original configuration down to its component parts. The wire in the 
steel belts is substantially completely separated from the rubber 
"crumbs", which are typically 40 mesh or smaller at the finish of the 
process. 
The apparatus of the instant invention substantially removes the steel wire 
from steel belted tires and produces a fine, granular crumb material in 
the range of about 40 mesh or less, which is entirely suitable for making 
various recycled products, including membranes on landfills, rubber 
conduits, bed liners, floats for nautical use, and various formed objects. 
The apparatus of the invention preferably comprises a plurality of pairs of 
heavy rollers (about 12-20" diameter ) which are disposed horizontally 
adjacent to each other, and which rotate downwardly and inwardly towards 
each other. The opposed roller surfaces have integral, negative rake teeth 
which intermesh along the length of the rollers so that an incoming object 
is gripped, compressed and torn apart by the rollers. 
The opposed rollers rotate at different speeds in the ratio of 4:1 to 25:1 
RPM to further increase the tearing and comminuting action as the incoming 
object is fed down into the nip of the opposing rollers. The rollers are 
driven by a drive system capable of developing 100,000 to 5,000,000 inch 
lbs. of torque at the nip between the rollers determined by the size of 
the rollers, and the material being comminuted. 
A second and third tier of similar opposed roller pairs are normally 
disposed below the first tier to receive the partially crumbed material 
and to comminute it further. The second and third tiers of roller pairs 
are capable of comminuting (crumbing) a steel belted rubber tire down to 
40 mesh or less in particle size, and to substantially completely separate 
the steel wire from the rubber crumb. 
A magnetic separator is used to remove all steel particles from the finely 
powdered crumb. The rubber crumb is then used to make various recycle 
products, such as rubber membranes for landfills, rubber conduits, bed 
liners, floats for nautical use and formed objects. In addition to 
crumbing steel-belted tires, the apparatus may be used to disintegrate and 
comminute polyethylene containers, gypsum, hardboard, tin cans, glass jars 
and bottles.

DETAILED DESCRIPTION OF THE INVENTION 
As shown in FIG. 1, crumb rollers 10 each have an integral drive axle 11, 
and a shorter, integral support axle 12. The cylindrical body 13 of each 
crumb roller 10 is shown in an intermediate stage of manufacture, in which 
a plurality of transverse, integral grooves 14 have been machined on the 
peripheral surface 15 of the crumb roller 10 to define ridges 16. 
Intermeshing, integral teeth 17 are machined into the ridges 16, as shown 
in FIG. 2. Crumb rollers 10 are disposed horizontally parallel to each 
other so that the integral teeth 17 of one roller 10 are disposed in the 
grooves 14 of the opposing roller 10. The rollers 10 are disposed more 
closely together than is shown in FIG. 2 for optimum crumbing action. The 
preferred clearance between outer tips 17a of teeth 17 and bottom 14a of 
groove 14 is about 0.001 to 0.250 inch, with the clearance being 
adjustable for different materials. 
FIG. 3 shows only some of the grooves 14 and the ridges 16 which carry the 
teeth 17. The grooves 14, ridges 16 and teeth 17 extend along the complete 
length of each roller 10. The drive axle 11 are disposed at opposite ends 
of the assembled pair of crumb rollers 10 to simplify space requirements 
for the respective independent drives. 
Rollers 10 are typically about 12-20 inches in diameter in a typical 
three-stage crumbing machine for crumbing steel belted tires. The diameter 
of the rollers 10 is determined by the particular material to be 
disintegrated. Rollers 10 rotate downwardly and inwardly towards each 
other. The opposing rollers 10 are independently driven to rotate at 
different speeds, preferably in the range of speed ratios from 5:1 to 
25:1. The rotational speed differential greatly enhances the crumbing 
action, and makes possible the complete separation of the steel belting 
wire material from the rubber of the steel-belted tires. 
Each crumb roller 10 can be manufactured from a single, solid steel core, 
and the grooves 14 and teeth 17 may be machined integrally on the outer, 
peripheral surface 15 of the core body 13. It is important that the 
finished crumb roller 10 have a Rockwell hardness in the range of 50-70 in 
order to have significant useful life and wear in the crumbing operation 
to make the apparatus economically feasible for recycling typical waste 
materials, such as steel belted tires, polyethylene containers, gypsum, 
hardboard, tin cans, glass jars and bottles. 
The crumb rollers 10 are preferably made from high alloy steels and tool 
steels, such as AISI A2 and M2. More specifically, AISI Steels #4140, 4150 
and 4340 have been used. AISI # 4340 is presently preferred for tire 
crumbing apparatus. The crumb rollers are heat treated to obtain a 
Rockwell hardness of 50-70. 
For certain comminuting applications, the crumbing rollers 10 can be made 
of a ceramic material. The important requirement is that the crumbing 
rollers 10 be harder than the material being comminuted. 
A typical crumb roller 10 used for crumbing steel-belted tires has grooves 
14 which are about 0.455 inches wide and about 1/12 inches deep. The teeth 
17 are about 0.375 inches wide. The outer diameter of these crumb rollers 
10 are about 9.6 inches, and their length is about 33-40 inches, not 
including the axles 11 and 12. 
As shown in FIG. 4, the crumb rollers 10 are typically arranged in 
horizontally disposed stages 18, 19 and 20, each stage comprising a pair 
of horizontally disposed, closely intermeshing crumb rollers 10. Material 
to be crumbed, such as steel-belted tires, or tire fragments 21, is fed 
into stage 18 to produce a first stage crumb 22, which drops by gravity 
into the nip between crumb rollers 10 of second stage 19. Second stage 19 
produces a second stage, finer crumb 23 which falls by gravity into the 
nip between the crumb rollers 10 of the third stage 20. Third stage 20 
produces a final stage powdered crumb 24, substantially completely 
separate from steel wire 24a. Steel wire 24a can then be removed from the 
powdered crumb product 24 by means of a magnetic separator (not shown). 
As can best be seen in FIG. 5, an important feature of this invention is 
the negative rake teeth 17. It has been discovered that a rake of about 30 
degrees measured between the radius of the roller and the transverse side 
surfaces of each of the teeth 17. The negative rake teeth 17, in 
combination with the differential rotational rates of the pairs of 
crumbing rollers 10, insures optimum crumbing action for tires, or tire 
fragments 21, first stage crumb 22, and second stage crumb 23, to produce 
a finely powdered crumb 24, from which all the steel wire 24a can be 
removed, as by magnetic separation. 
In a typical first stage 18, the crumb rollers 10 have about 40-72 teeth, 
equally spaced around the circumference of a 10-12 inch diameter roller 
10. About 60 teeth around the periphery of the first stage roller 10 is 
preferable. Side clearances between the teeth 17 of the opposing first 
stage rollers 10 is about 0.050 inch, and the diametrical clearance 
between teeth 17 and the opposing groove 14 of the opposing roller 10 is 
about 0.060 inch. The width of the teeth 17 in the first stage 18 is 
preferably about 0.355 inch for a roller 10 about 30 inches long. 
For the typical second stage 19, the crumb rollers 10 also have 40-72 teeth 
17 around the periphery of a 10-12 inch diameter roller 10, and about 60 
teeth 17 around the second stage roller 10 is again preferred. Side 
clearance between the opposing teeth 17 of the opposing rollers 10 in the 
second stage 19 is reduced to about 0.040 inch, and the clearance between 
the teeth 17 and the opposing groove 14 is reduced to about 0.050 inch. 
The teeth 17 have a width of 0.355 inch, as in the first stage 18. 
The crumb rollers 10 in the typical third stage 20 have about 60 to 90 
teeth around the circumference of the third stage rollers 10, which are 
about 10-12 inches in diameter. At present, when the third stage rollers 
10 are 12 inches in diameter, 72 teeth 17 around the periphery of the 
roller 10 is preferred. Teeth width for the third stage crumb rollers 10 
is preferably about 0.310 inch, which is less than in the first two stages 
18 and 19. The side clearances between the opposing teeth 17 of the third 
stage rollers 10 is also reduced, being about 0.025 inch. The clearance 
between the teeth 17 and the grooves 14 of the opposing roller 10 in the 
third stage 20 is in the range of 0.015 to 0.045 inch, and is preferably 
about 0.035 inch, which is less than the same clearance in the preceding 
stages 18 and 19. 
The left and right crumb rollers 10 in each stage 18,19 and 20 are each 
provided with an independent drive motor (not shown) to drive the rollers 
10 in all the stages 18, 19 and 20 of the crumbing machine through their 
respective drive axles 11. Reduction gears can be provided so that the 
rate of rotation of each roller 10 can be adjusted as required. 
The drive motor for the left (slow speed) side of stages 18, 19 and 20 may 
be an A. C. electric motor capable of driving the left set of drive axles 
11 and their respective rollers 10 in stages 18, 19 and 20 to develop a 
torque of 100,000 to 5,000,000 inch pounds under load. The drive motor for 
the right (high speed) side drive axles 11 may be a D. C. electric motor, 
and is connected to drive the right set of drive axles 11 of the right 1-5 
set of rollers 10 to develop a torque of 100,000 to 5,000,000 inch pounds, 
also. 
Controls (not shown) for the drive motors enable the operator of the 
apparatus to adjust the rotational speeds of the left set of rollers 10 in 
the stages 18, 19 and 20 separately from the rotational speeds of the 
right set of rollers 10 in stages 18, 19 and 20 to obtain a rotational 
differential between the right and left sets of rollers 10 ranging from 
4:1 to 25:1. 
Hydraulic drive motors (not shown) can also be used for either the left or 
the right side crumb rollers 10 in each stage 18, 19 and 20. In fact, any 
combination of hydraulic, diesel, AC, and D.C. drives may be used, so long 
as the RPM and torque requirements are met. The RPM of the crumb rollers 
10 on the low speed side may range from about 1/2 to about 25 RPM. The 
high speed side crumb rollers 10 may typically range from 10 to 250 RPM. 
It is the speed differential between the left and right side rollers 10 in 
the respective stages 18, 19 and 20 in combination with the negative rake 
teeth which gives the excellent crumbing action. 
When there is considerable heat buildup in the crumb rollers 10 in a 
particular tire crumbing application, the last stage 20 crumb rollers 10 
may be provided with cooling means. The crumb rollers 10 may be cored out, 
for example, and cooled with chilled water to bring the temperature of the 
crumb 23 entering the final stage 20 down to about 30 degrees F. The 
cooling produces a better final crumbing action, and improves crumbing 
efficiency. 
The above description applies primarily to effective crumbing of 
steel-belted tires. It is also contemplated that other materials may be 
comminuted or crumbed using the overall system of the invention. Tests are 
presently being conducted to determine the optimum conditions for crumbing 
or comminuting other materials such as "EPDM", "SBR", "VITON" (chemically 
resistant synthetic rubber) and silicone rubber chunks. It is presently 
believed that the crumbing rolls 10 will be operated within the general 
parameters set forth above. 
Other teeth configurations may be more effective for crumbing the 
last-named materials. For some applications, the negative rake teeth 17 
described above may be spaced at intervals around the outer periphery of 
the crumbing rolls 10 with an elongated ridge (not shown) filling in the 
intervals between the teeth 17. It is also possible that other teeth 
shapes may be more effective for crumbing certain materials. Teeth which 
are hook-shaped in profile are being considered for the crumbing of 
silicone rubber chunks. 
This invention makes possible the efficient recycling of high volume, 
extremely durable materials, such as steel-belted rubber tires, which are 
practically non-degradable in landfills. The resulting crumb products are 
in high demand for reprocessing into similar, or different products. These 
second generation products can also be crumbed and recycled again and 
again, using the system of the present invention, thereby greatly reducing 
the loading up of overtaxed landfills, and providing a recycling economic 
bonus as well.