WO2008084267A1

WO2008084267A1 - Method for controlled fine pulverization of elastomers by ultra high pressure jet extraction

Info

Publication number: WO2008084267A1
Application number: PCT/HU2008/000002
Authority: WO
Inventors: György MOLDOVAN; Laszlo Baliko
Original assignee: Moldovan Gyoergy; Laszlo Baliko
Priority date: 2007-01-10
Filing date: 2008-01-09
Publication date: 2008-07-17
Also published as: HU0700019D0; HUP0700019A2

Abstract

Method for controllable grain size production of elastomer-powder of high surface activity by extraction and simultaneous grinding with ultra high pressure liquid jet. The main feature of the method is that specific technological parameters of the extracting process such as extraction limit value of liquid jet pressure, as well as characteristic parameters of correlated position and motion between the liquid jet and the workpiece being extracted are to be determined from the tearing energy of the elastomer being extracted.

Description

Method for controlled fine pulverization of elastomers by ultra high pressure jet extraction

Subject of present invention is a method for production of controllable grain-size production of fine elastomer-powder by ultra high pressure liquid jet extraction, by which valuable raw materials can be produced from recyclable waste materials. Background of invention In addition to considerable quantity of used rubber tyres world-wide, the quantity of different elastomer wastes without thermoplastic properties is also continually increasing. Production wastes and rejects of such products further increase the quantity of these post-consumer waste materials.

Besides that all kind of elastomeric wastes - regardless their actual physical shape - burdens our environment in the same way therefore we consider their treatment equally important, for the time being social sensitivity can be perceived rather towards the waste tyres. This can be directly measured through the fact that distinguished attention is devoted to recycling questions of end-of-life tyres almost everywhere in the world, while recycling of other wastes and in-production rejects of similar materials is not a key issue even in developed economies. Though e.g. in the European Community several directives related to handling of end-of-life tyres are in force for many years and their positive effect has already brought concrete results, handling control (e.g. unambiguous banning of deposition) of other elastomeric wastes cannot be considered as controlled in full scope. As a result of these facts there are several recognized recycling methods of waste tyres applied partly in practical utilization, partly as experimental methods. Main directions of everyday implementations are incineration, construction and - even if it can be realized with compromises, as it will be discussed later - direct in-material utilizations (to be appeared in the form of new products). Energy-related utilization of tyres in cement plants and power plants offers double advantage, as in parallel to significant decreasing of waste tyre quantities it helps saving primer energy carriers. Besides advantageous usage of considerable energy content of tyres, the increasingly equal issue is the emission of liberated as well as developing solid and gaseous materials, being harmful both to human health and the environment. Safe and efficient separation and neutralization of emitted materials accompany with further substantial investment and operation costs.

Obvious solutions of non-thermal utilization are different civil engineering applications in whole, shredded or semi-coarse ground form, mainly for dam and road-bed constructions. The purpose of even finer grinding is primarily the yielding of rubber material for higher-valued applications. From this point of view the main direction of in-material recycling is the utilization of rubber (as well as separated metal and other carcass materials).

The most wide-ranging process in this respect is the mechanical grinding of tyres at normal ambient temperature or in deep-frozen state. In general these processes reach the necessary grain fineness via gradual shredding and grinding of the tyres. An unquestionable advantage of the processing at ambient temperature is the production of rubber crumb in commercial quantities, however its drawback is the very limited utilization ability of the product.

One reason is that different components of tyre (various rubber materials, steel and non-metallic cord materials) are processed together and the perfect separation of components cannot be solved. This statement is especially valid for separation of different rubber materials of the tyre, but even non-magnetic metal particles remaining in or taken into product just by the grinding equipment mean considerable problem.

Besides separation problems other disadvantageous phenomenon is the frictional heat-generation of fine-grinding technology of rubber-powder that oxidizes (cokes) the surface of rubber particles, so they will considerably lose their chemical activity. Although there are such known processes for handling of oxidation problem where fine grinding is performed out of air and in cooling medium (e.g. under water), but the special technology raises the price of product to such degree that practical utilization possibilities are drastically limited. Cryogenic (deep-frozen state) grinding performed below glass transition point of rubber, like descriptions of Lovette US 4,025,990 or Bernd DE 10357968 among others, eliminates surface oxidation, but chemical activity of product is also limited because of degrading polymer chains and the characteristic morphology of "glass-breaking" shell-like shaped surface of particles due to technology.

Ail these properties extremely limit the higher-grade direct polymer- technology applicability, so-called "upcycling" of mechanically-ground product. There are recognized devulcanization processes with the aim of increasing chemical activity, but these, in addition to further increasing the product price, cannot handle the problem of non-separated impurities remaining in the product.

The so-called buffing technology intends to prevent the problem of metal contamination, yet the original purpose of this technology is preparation of tread-part of the usable tyre structure before re-treading. Rubber material of rather acceptable purity can be obtained by mechanical buffing technology, but disadvantages of the process are the frictional heat generation and the considerable remaining rubber material on tread surface. Namely, the extraction of rubber particles should be stopped in a safe distance from the metal-cord surface, in order to prevent the metallic pollution of product. Due to this fact the cleaning of outer surface of tyre from rubber material is not perfect, while acceptable professional extraction of internal rubber material of tyre is not possible with this process for the time being.

Most part of above-mentioned handicaps may be eliminated in advance by the extraction process of ultra high pressure liquid jet. Bases of this process are known for decades and several important developments and patents have been introduced in this subject. Despite of this knowledge the extraction by ultra high pressure liquid jet may not be considered a general and widely applied practical process yet.

Looking for its reasons we can state that although the described solutions introduce different processes (first of all aiming the handling of tyres), they treat the production of rubber powder during extraction as a fact, like description of Rutherford US 5,115,983 from whole tyre and also Rutherford's US 5,794,861 from p re-shredded materials, or FR 2,798,090 of Lambert et al..

The practical experience with these processes is that the particle-size of extracted products is inhomogeneous, and at the same time they cannot be considered as fine-grain products, due to their real size-appearance. The mentioned processes do not provide instruction that in fact how the elastomers

- in most cases tyres - can be extracted in such way that the created product would be the desirable, possibly homogenous and fine-grained powder material.

With other words several known solutions contain important recognitions, the enormous power demand, which is necessary for the process, and the limited industrial applicability of created products has ruled out the economic utilization of processes applying theory of ultra high pressure liquid jet.

Prime cost of ultra high pressure liquid in the necessary flow quantity for extraction technology is rather expensive, according to present state of high- pressure technology. For extraction of the product in commercial quantity there is a need of several hundred liters per minute volume of ultra high pressure liquid. In everyday industrial practice it can be produced with high pressure pumps and/or pressure boosters, that equipment require very extensive - even several hundred kilowatts or several megawatts - built-in driving capacity for the generation of necessary liquid flow quantity. It can be perceived from above that from the point of economic application it is very important to achieve the possibly most economic utilization of energy, transmitted by liquid jet and produced with significant cost, namely the optimization of pressure conditions as well as the producible material quantity and product quality. From technological considerations we regard these points as bases of practical utilization of ultra high pressure extraction.

There are several solutions and equipment for the extraction of elastic polymers (mainly post-consumer tyres) by ultra high pressure water jet. Most part of these would start from whole tyres, like process of Rutherford described in US5,115,983 or Labroue et al. FR2793436, as mentioned before, as well as Shinal US5,683,038 and Hino JP2005046758 and Berry GB2,339,708 and Jaccachoury FR2,773,727 and Begler et al. DE 198 18 566, as well as Balikό et al. WO01/53053. A returning question during evaluation of the mentioned and other known processes is the means of extracting process, namely the examination of those features which would properly create just that product quality as mentioned in these descriptions. A statement can be read in several descriptions that use of abrasive material may increase the yield of liquid jet extraction for rubber material, which is advantageous. Nevertheless it is a disadvantage of these processes that separation of any kind of abrasive material from rubber powder is practically impossible, in addition it increases the process cost. At the same time the surface of created product-grains will be typically plane-type, due to cutting effect of abrasive material, which is disadvantageous from the point of view of further utilization because of the small specific surface.

It is common character of the quoted process descriptions that they explain the characteristic working movements in general. According to these descriptions the workpiece - normally tyre - typically moved with certain forward/feeding, while the extracting water jet stands above the workpiece or it is moved along a spatial - in most cases circular or oscillating and planetary motion. The known solutions would not provide education that how the quality of produced material may be influenced, or rather how the processing parameters can be adapted to the material of workpiece to be processed.

Summarizing we can state that the known solutions are not suitable for economic production of quality grain-products from elastomers. Aim of the invention

The aim of the invention is the realization of - production of the most achievable quantity and possibly most homogeneous fine-fraction grain, and

- reaching optimum yield between energy used for extraction and the produced material quantity and

- accomplishing these targets in frame of limited, possibly one technological step.

Recognition of invention basis 00002

Examining from product point of view, the desirable product structure is mainly below 500 micrometer, containing the most volume of achievable fine fractions. The valuable process for commercial application is which is able to produce this product structure in one technological step, besides optimized energy consumption.

Based upon these we have reached the recognition that fine product of big specific surface, being advantageous for premium utilization, can be mainly reached by tearing-type extraction, where the tearing energy should be transmitted to the material being extracted just by the liquid jet itself without abrasive material, while the parameters of extraction shall be adjusted according to a properly-selected material-character in order to secure the desirable product structure.

The effect of tearing phenomenon can be increased by a quick relative motion between workpiece being extracted and the liquid jet, as well as by the angle of impacting jet, and by the adjustment of active distance of the extraction.

The effect of tearing phenomenon can be also increased by application of a material-fatiguing pulsing-pressure liquid (similar to hammer-drill-like effect).

In the course of review of following solutions we shall use the expressions of "liquid jet" and "workpiece" for the sake of language simplification, but we expand the interpretation of solutions also for several liquid jets and/or several workpieces. We apply this linguistic simplification also at other related places of introduction of the method. Also for linguistic simplification we use the term of "jet" with understanding of "liquid jet". Summary of the invention and further advantageous features Accordingly, the invention is a method for extraction and a simultaneous grinding of elastomers by controlled ultra high pressure jets, where jet is aimed at the surface of the workpiece being extracted and at the same time the workpiece and the jet are in a correlative motion. It is also characteristic to the method that technological parameters of extraction process - first of all the extraction limit value of jet pressure and characteristic parameters of the correlative motion between the jet and workpiece being extracted - are to be specified from the tearing energy of the elastomer to be extracted. In a preferred embodiment of the method the correlative motion between controlled jet and the workpiece being extracted is a planar vibrating motion in such a way that the plane of vibration is perpendicular to the forward movement of the workpiece and simultaneously it has an inclination of 0 to 15 degrees to a perpendicular drawn on the surface of the workpiece (in case of a spatial surface, e.g. a toroid/torus surface the perpendicular is drawn on the actual tangent of the surface).

It is a further that the vibrating movement is realized by the movement of the nozzle of jet, while in other cases it may be more suitable to realize the vibrating motion by movement of the workpiece being extracted.

It is also an advantageous feature that in case of e.g. an oversized motionless workpiece the forward motion can be also made by the extracting jet. It is also a preferred embodiment of our method that in parallel to the jet extraction a fine grinding is also accomplished in such a way that the characters of extracting-grinding process are adjusted to previously planned and calculated values, regardless the appearance shape of the workpiece (ring, belt, tyre etc.). It is also a advantageous feature of the process that the jet-affected part of the workpiece is firmly supported in order to eliminate the compensation effect that originates from the flexible structure of the workpiece. It is an important feature of the invention that the motions of jets are directly aimed at the extraction area of the workpiece.

It is practical in most case to use extreme-purity water for extracting- grinding jet.

In the course of implementation of our process the utilized liquid, namely the water in given case is partly or completely re-circulated and the returned liquid is to be cooled to the temperature acceptable for continuous operation of the high-pressure pump (in case of water it is 17-28 degrees centigrade).

A further important character of the method is that for adjustment of extracting-grinding parameters the pressure of liquid is understood at the place of extraction (the bottom of the jet). Together with the former features it is also important to perform the extraction with an optimum diameter range of extracting jet between 0.05 mm (0.002") and 0.5 mm (0.02").

A further important character of the method according to the invention is that the extracting jets are vibrated in a linear way over the aimed area at a constant frequency between 250/min and 1250/min.

In a preferred embodiment the extracting jets are vibrated at amplitude that characteristically corresponds to the distance between the in-lined nozzles at its minimum, and the forward movement of workpiece is set at a value conveniently adjusted to vibration frequency.

It is further characteristic of our method to increase the material fatiguing effect with exploiting the hammer-drill effect that helps the extraction, thus at generation of high-pressure liquid we apply high-pressure plunger pump without pressure-equalizer. It is very advantageous that together with extraction and grinding we also implement mastication by liquid jet.

In a most preferred embodiment the extracting energy of the liquid jet is set at a value which is adjusted to tearing energy of elastomer.

A practical utilization of our invention is to adapt the method for direct re- processing of factory rejects in such a way, that for the further optimization of extracting parameters the tearing energy is directly specified with a tearing test of the own manufactured material.

It is also preferred in the mentioned case that volume and pressure of the liquid-flow, and such way the capacity of high-pressure pump is set at the value, which is calculated from the tearing energy; furthermore adjustment of the pump capacity is made with consideration of nozzle diameters and the number/quantity of nozzles, namely tuning with the nozzles.

According to a preferred embodiment of our invention the jet is inclined with an α degree to a perpendicular drawn to the workpiece. It is advantageous in every case of application of the method, if the actual distance between extraction head and workpiece is continuously optimized by a control system. The quality of product can be further improved applying a low-powered soft post-crumbling, but not causing degradation of polymer structure; whereby an additional fining of the in-material pre-split grains is to be carried out.

Brief description of drawings The invention will be interpreted in details on basis of drawings, where

Figure 1 introduces the working area of extraction;

Figure 2 a-c shows a practically-known nozzle-line arrangement in three views;

Figure 3 we introduce the main movements of extraction on a sketchy top-view of working area; Figure 4 shows the geometric relationship of forces affecting the attack-point of the workpiece in case of inclined extracting jet;

Figure 5 shows the control system for optimization of distance between extraction head and the workpiece;

Figure 6 shows a typical appearance of conventional mechanically-ground rubber grains, taken by a scanning electron microscope (SEM);

Figure 7 shows a typical appearance of rubber grains produced by the present method, taken by a scanning electron microscope (SEM).

In addition to above we included verbal explanations on 1/a, 3/a and 5/a for the sake of direct interpretation. For specifying the produced grain characteristics we have to take a closer look on the extracting phenomena with a consideration whether extracting-grinding takes place optimally under the determined movement parameters.

Characters of the extracting movement Phenomenon of well-known jet-cutting occurs in such a way, that flow speed of the jet considerably exceeds the lateral traveling (or forward) speed of jet. If we significantly increase the traveling speed of jet, a substantially different event will happen instead of a penetrative cutting phenomenon, which may be characterized in the following way. In the moment of attacking the workpiece, the jet will exercise certain pressure to the material surface at the bottom area of jet. Within the critical distance measured from the discharge rim/edge of the nozzle, this surface can be well considered approximately the same as the area of nozzle aperture. It is important to state that here and in followings we examine the extracting phenomenon within the effective zone of the jet. Namely in that distance, where free-flow characters of jet are the same as the characters of the jet when leaving discharge rim of nozzle. We interpret the effective zone as critical distance, which critical distance can be defined from the flow characters of jet with liquid-flow technology related knowledge.

Assumed according to Figure 1 , and at the same time prescribed as a basic condition that 101 workpiece is fixed and it has a 103 firm support on the opposite side of action-direction of 102 jet, thus it may not dodge/evade in any direction from the influence line of the jet, the 104 extraction area affected/attacked by 102 jet will be compressed according to material elasticity character of the workpiece. Compression will continue until the strain resulting from pressure would exceed strength of material. Reaching the stress limit the 105 material element will be torn off.

Material extraction will take place where workpiece is opened at least one direction, because extraction of the material piece, which is surrounded by other material parts will be blocked by surrounding "supporting" material elements. Beside this basic condition the extraction is also promoted by the fact that material faults in elastomers are typically in the range of 10^"2 mm, thus these faults can be the local starting points of extraction with a conveniently selected diameter of extracting jet of a similar range.

Starting of extraction in case of belt-type workpiece is obviously the starting edge of material, in case of a circular material (e.g. tyres) is either rim of ring. After separation of material element the extraction may be continued in the created cavity, therefore in order to continue the extraction it is expedient/practical to forward the jet in the direction of cavity.

Beside the phenomenon described above we also should recognize that jet should stay in extraction zone for the only necessarily short period of time, until extraction of material element will happen, otherwise a considerable portion of jet power would be used for penetration in material instead of extraction. U2008/000002

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According to the mentioned state of the art knowledge it is repeatedly recommended to move the jet in extraction zone - utilizing rotor-nozzles in most case - a circular or a similar spatial oscillating-planetary motion. In the course of development of our method we found however that efficient extracting- grinding motion of jet should happen in the plane that perpendicular or slightly inclined to the perpendicular to surface and, at the same time it should be perpendicular to forward/feeding movement of the workpiece, namely it may not get off from that plane. This movement can be realized by vibration of the liquid jet. There is another argument for planar movement of extracting jet that operation and maintenance costs of the mostly recommended rotor-nozzles, which realize the spatial movement and working in the range of ultra high pressure using extensive liquid flow quantity, are considerably exceeding the similar costs of generation and sustentation of vibrated liquid jet. Besides that it also decreases the efficiency of extraction energy of circular movement that the jets moving on "running out" part of circular orbit will once again move along the surface previously worked off at "running in" semi-circumference.

The extracting effect will occur even more conveniently if not one jet, but several in-line jets carry out the process, like nozzle-line arrangement schematically represented on Figure 2, which nozzle-arrangement is otherwise well known from other fields of application (e.g. high-pressure surface cleaning).

It is expedient to apply such number of nozzles that, together with one amplitude movement of vibration would overlap the workpiece in its whole width.

It can be acknowledged that moving of jets in a certain zone should be continued until the desired extraction depth is reached. According to Figure 3, the 301 workpiece (or in other solution a row of jets above the workpiece) should be forwarded with a properly adjusted constant 302 feed, below the 304 nozzle-line moving in 303 transversal plane.

The above system of movements of workpiece and liquid jet is obviously valid also in other arrangements; the determining is the system of movement between jet and the workpiece, interpreted in the way described above. Accordingly, the vibrating motion may be performed by workpiece and feeding motion by the simultaneously vibrating jet, but effective extraction will occur also on the workpiece performing a simultaneous transversal vibrating and longitudinal forward/feeding movement under stationary jet. Determination of extraction parameters The necessary power need for extracting-grinding of elastomers may be conveniently determined from strength characteristics of a given elastomer. The extraction can be considered successful in that case if the transmitted influence exceeds the material strength. It is however a basic problem in case of elastomers that tensile strength of material itself is not suitable to properly describe the complex strength characteristics of material and furthermore, the reproducibility of tensile strength of elastomers is not sufficient because of the inherent cracks, present inclusions and other material faults.

Practical experiences prove that structural change occurred by physical influence starts at the weak points of the material. In case of elastomers the process continues in the way that crack-growth or tear that develops from a shocking influence will start at one of discontinuities being present in material- structure and then it will propagate in the material in such way that the main tearing surface is patterned with micro-ruptures. Therefore strength investigation of elastomers in connection with fracture process is a very complex task.

Examination of fracture process of elastomers in technical practice is conveniently made from the respect of energy-balance, according to a specific energy defined by Rivlin and Thomas with introduction of the concept of an energy that is characteristic to the fracture process developing at a material fault, which is/namely the so-called tearing energy. Convention of tearing strength is also used to this, which is characteristic to a given elastomer. This material characteristic besides its relatively simple and reproducible determination by proper test, defines the complex properties of material pretty well. Basis of approach is the recognition that tearing resistance of elastomers basically would not be determined by tensile strength, but by the energy occurred from the physical influence and being cumulated until maximum elongation; which is/namely the tearing energy. This energy is characteristic not only for the tensile strength of the material, but it also incorporates the modulus, maximum elongation as well as the viscous resistance of material that occurs against strain before tear.

The tearing energy according to Rivlin and Thomas definition, simplified with consideration of practical viewpoints applied in our method, can be expressed in the following form:

T = - h (1 ) where F is tearing force, h is width of tearing that corresponds in our case to 2R diameter of the jet. The F tearing force in our case is transmitted by the jet, to which the following relation can be written in effective zone of the jet, in case of quasi- stationary flow:

F = p A v_kr ² (2) where p is the density of the liquid A = R² π the cross-sectional area of the jet

V_kr is the critical average speed of the jet, which is necessary for the fracture to be created in the workpiece; with other words the minimum average speed of the jet, which is necessary for extraction of a material with given parameter. Expressing from this F = p R²πv_kr ² (3)

It can written from above relations that

from which expressing vv

(5)

Having known the jet velocity, the necessary jet pressure for tearing - namely the limit value of extraction pressure - can be determined from relationship of jet force and the effective area:

Pkr = (6)

A

where py_r is the limit value of extraction pressure of jet A is effective area of jet

On this basis and applying the known substitutions, determination of critical tearing pressure is the following:

_ pAv_kl ² _ ₂ Pu ~ _A - f»* ₍₇₎

For the effective realization of extracting-grinding it is obviously necessary to reach or exceed this calculated liquid pressure.

The in-material penetration depth of jet, which can be characterized with above parameters, can be determined with the kinetic work of jet. Also assuming quasi-stationary flow for the inspected environment, the kinetic work of jet:

In the course of its penetration into workpiece until s_& depth, the jet performs work of W = F S_b . Expressing S_b penetration depth from the relationships:

1 2

— mv_h W 1 m

F P^Avκ, from which ²P^ (9) Work-performing mass of jet corresponds to mass-flow at a unit of time, that is m = ^: P

A v_kr t

„ P^AvJ using that ^{b ~} IpA namely (10) The t is time interval, till the jet performs extraction of an element from the workpiece. This time can be determined from the transversal vibration of jet as follows.

Let the frequency of transversal vibration of jet be f_r with an amplitude L. Period of one-way run along the amplitude 1 L²Z- (11)

N = - ^L

Utilizing the jet diameter IR discrete position of extraction can be determined along the L amplitude. Time-period of one extracting position from this

t =± ' N (12) from which the penetration depth at one extracting position can be determined:

² (13)

Size of material element extracted in the size of depth of above determination will be characteristic to the average extracted grain size. The status of "average" should be emphasized due to the fact that because of inhomogeneous cross-linked structure of elastomers and their incorporated material faults smaller and bigger size of grains may also be extracted during the process. In determination of movement parameters the relative forward speed between the workpiece and jet has a special importance because dwelling period of jet in a given extraction zone can be controlled also by the forward/feeding speed. That is extracting depth, namely product yield of extracting process can be controlled also by this way.

It can be recognized that average dwelling time of a given effect-point of the vibrating jet in the extraction zone will last until the workpiece traveling with V_et forward speed will move along a mean path corresponding to the diameter of extraction jet. In a relationship

(14)

Repetition of the jet, which periodically attacks the workpiece in the extraction zone, can be expressed with the ratio of the longitudinal and transversal movement-period. Namely the number of extraction takings:

*> (15)

Having known the number of extraction takings the extraction depth can be determined:

^S _f = z_fh (16)

Summing up it can be stated that with the help of above relationships the optimum production target parameters of a given elastomer, such as the necessary local pressure for extraction, the desired average extraction grain size and the extraction depth to be reached by one forward movement can be determined from a reproducibly measurable character of tearing energy with the help of parameters taken up from practical considerations, like diameter, forward speed, vibration frequency and amplitude of extraction jet. Diameter of extraction jet For determination of jet diameter the main points to be considered are the followings. From the point of view of capacity optimization of pump, which demands extremely big driving power for generation of working pressure, it is expedient to increase the mass flow (namely the nozzle diameter) in parallel with decreasing the flow speed (namely the pressure of pump). This may result considerable saving of costs in both investment and operation.

At the same time it is an important factor to be taken into consideration that jet diameter is a characteristic determinant of product fineness to be extracted .

The convenient approach is selection of the finest possible jet diameter that is still productive enough in practical sense. Taking all these into consideration, on basis of practical viewpoints and our experimental results we determined the diameter of extraction jet between 0.05 mm (0.002") and 0.5 mm (0.02").

Effects of jet motion characteristics to the extraction

Vibrating movement of jets is very convenient also from the point of view that even those particles of liquid that do not perform extraction would contribute fatigue stressing of material due to their cyclic presence, thus promoting the extraction effect of the next (following) jets. (It should be remarked that the referred pulsing flow-supply of plunger-type high-pressure pumps causes further fatigue stress effect.)

The lowest limit of jet vibration frequency is determined by the fact that in case of decreasing frequency the dwelling time of extracting jet is longer, thus the deeper penetration causes more coarse extracted grains. According to our experiences, fine fraction of an acceptable quantity can be obtained at the vibration frequency above 250/min.

The extracted grain size will be finer by increasing jet vibration frequency, but frequency increasing over a certain value will considerably boost the construction and maintenance technical costs. According to our experiences the production and maintenance costs of jet vibration over 1250/min are not rational/proportional to the value of created product.

The convenient vibration amplitude of jet is equal to or slightly (with maximum a nozzle-diameter) more than the distance between in-line nozzles. It can be secured in this way that no omitted workpiece area would remain between the aligning extractions and each jet mainly affects the area to be newly extracted. 02

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Lower limit of amplitude-influencing nozzle distance would result from material strength characteristics and sizes of applicable high pressure nozzles, and it comes in the range of 7-8 mm (0.3"). Theoretical upper limit of amplitude can be determined from the desired and extractable grain size. It can be seen from the relationships above that keeping the frequency unchanged and simultaneously increasing the amplitude, the dwelling time of jet would decrease, namely the grain size will acquire refinement. It can be conceivable however, that there are technological limits of such implementation.

For determining of forward speed of workpiece it should be taken into consideration that increasing of forward speed will again decrease the dwelling time, thus number of extraction takings, ultimately the thickness of extraction. It is expedient therefore to determine the dwell-time from the desirable extraction thickness and from that the optimum forward speed can be calculated for the given material. The pump pressure necessary for extraction and its fine tuning

We should like to emphasize that at determining the extraction parameters of jet (flow area, velocity, pressure), they all are applied to the location of extraction, as it can also be interpreted from discussed relationships. Having known the necessary local critical pressure, the necessary pump pressure can be determined summing this critical pressure, the flow pressure losses between pump discharge flange and the bottom of jet and the heat loss resulting from impact work of the jet; these energy losses can be calculated from fluid mechanics.

As it was mentioned before, the most applicable pumps for jet extraction are the plunger pumps. One of the most important characteristic of these pumps is that they are designed for a given pressure and flow value and resulting from their construction they can be controlled in an extremely limited range. Therefore one should control them not at pump side, but rather at discharge point, with the fine tuning of the nozzle-line. In practice it can be realized in the way of forming one or more nozzle- spaces on nozzle-line (conveniently at the end of the nozzle-line), where one or more nozzles will not take place in extraction. The role of these nozzles is definitely the fine tuning of the flow characteristics (pressure, flow volume). The value of calculated flow pressure necessary for extraction will thus become controllable with the nozzles having different discharge apertures (so-called tuning nozzles) and with the number of tuning nozzles, so the power consumption of pump-driving engine can be decreased to the optimum level. Resulting from above, if pump pressure corresponds to pressure value necessary for extraction (corrected with flow losses), namely regulation of driving power input is not necessary, the discharge diameter of tuning nozzle (or nozzles) is zero. Effect of tearing phenomenon can be further increased if the necessary flow pressure is produced by plunger pump in such a way that pressure compensator or pressure storage vessel is not used. In that case the pulsing pressure of jet will reinforce the tearing phenomenon also with continuous material-fatiguing effect of impact drill character. Effects of penetration angle of extraction jet

Examining the circumstances of extraction and determining the parameters of extracting-grinding we assumed that the jet arrives at perpendicular to the surface of workpiece. (In case of body of rotation e.g. extraction of tyre tread it corresponds to radial arriving of jet.) Let us investigate the extraction process also in such case, when the jet inclines to incidence normal (perpendicular to surface) with an α angle (Figure 4).

The extracting F force vector can be divided into two components; an F_m force component perpendicular to surface of workpiece and an F_t force component, which is parallel with the surface of workpiece. Function of these two force components is basically different. The F_m component will perform the extraction, but in respect of effective extraction the Ft component has also an important role.

The characteristic elastic property of elastomers is principally due to chain molecules of great elasticity, yet elasticity is also affected by the characteristics of cross-links. The chain molecules in standstill state of elastomer are inordinate, having a clew/ball-like shape. Upon influence of an outside pulling force the chain molecules will unwind, become tightened. This 02

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phenomenon will occur even at the influence of a relatively small mechanical tension. In a terminological way it can be expressed that elastomers have low modulus of elasticity; namely creating a unit elastic elongation a specific pulling force (tension) of rather small value is enough. Tearing the tightened and ordinate macromolecules is more effective than the inordinate clew-type polymer chains. Inclination of extracting jet will create just this phenomenon. The F_f tangential force component will unwind the chain molecules of elastomer and pre-stress them, efficiently promoting the effect of F_m extracting force. The α inclination angle will be determined from a technically widely used characteristic, the modulus of elasticity with due consideration that even a low-rate tension is enough for the effective extraction. In technical practice a specific pulling force affecting in the range of a 100%- 200% modulus-value provides sufficient result. On this basis the limit value of α extracting inclination can be determined as follows.

A where E is the modulus of the given material

F_f is tangential component necessary for elastic elongation A = R² π is area of jet Determination of F_t:

F, = F sma or in scalar form F_f = F sina

With substitution

F sina F

E = = — sinα

A A where FfA is equal to the formerly determined Pkr pressure value. Expressing sinα from this

E sm a =

from which the minimum necessary α extracting inclination can be determined. Applying extracting inclination we have to take into consideration that increasing of inclination will decrease the value of extracting force component ( Fm = F cos α ), namely it causes loss of extraction power, which is however not considerable at small inclination angles. Nevertheless increase of F_t component over 100%-200% modulus-range is unnecessary in most cases of practical application.

Other advantage of application of inclination is that fine tuning of extracting penetration depth can also be realized. Although this may accompany with certain power loss according to above, but in technical practice the importance of fine control of extraction depth may compensate the rate of power loss. Further optimization of extracting parameters

According to previous discussion, one of the most important rules of high-pressure jet extraction of elastic workpieces is that the workpiece, especially its part affected by jet should be properly fixed and supported opposite to action vector of the jet, otherwise considerable part of jet energy would be lost due to mechanical compensator effect of workpiece. Lack of proper supporting would cause ineffective extraction, the created product arises in uncontrollable sizes or the extraction would not occur at all. A further basic point of optimization of extraction energy is the minimization of distance between discharging edge of nozzle and the surface to be extracted (namely upkeeping the critical distance as discussed before). The minimized nozzle-workpiece distance can be preserved most safely by a continuous control of distance between nozzle and the workpiece. It has a special importance in case of varying thickness of layer to be extracted or if the distance to surface is changing; e.g. different wearing degree/rate of used conveyor belts or eccentricity or ellipticity of treads of used tyres.

Figure 5 shows a possible control system for optimal adjustment and control for distance between nozzle and workpiece. According to introduced process control system, the 501 marker control unit produces the 502 transmission signal, which is transmitted by the 503 combined distance-monitoring transmitter-receiver to the surface of 504 constantly forwarding 505 workpiece. The 506 monitor signal returns from the surface and goes through the 507 signal amplifier and 508 signal conditioning and digitizing unit, arriving at 509 extraction head position base-signal generator and real-time position analyzer that produces base-signal for positioning of extraction head and analyzes the head position in real time. With the help of 510 marker signal produced by 509 position analyzer, the 511 extraction head position controller by means of 512 extraction head positioning mechanism will complete the optimized 514 positioning of 513 extraction head to actual surface character of 505 workpiece. With assistance of discussed control system the actual extraction- distance position of workpiece (that is perpendicular to surface of workpiece) can be measured continuously, compared to the pre-set head-position base signal. Distance between nozzle-plane (plane of discharging edges of nozzles) and workpiece can be composed from real-time measurement with consideration of necessary technological distance. Extraction head can also be adjusted by real-time control to the momentary surface position of workpiece.

The introduction of process control was made on planar workpiece, but the solution can be obviously applied also to spatial curved surface (e.g. toroidal surface of tyre). In case of a complex surface contour it is practical to apply several/multiple monitoring heads, and the actual positioning control signal can be composed from the signal-package integrated to the given technology. Grain-size structure of extracted product

The observable fact that there are always smaller and bigger - even above 500 micrometer - grains present in the final product can be attributed to the phenomenon that in the beginning of extraction process the jet that runs to the edge of workpiece will extract a material element, which is not fully supported by surrounding body elements of workpiece. Material elements at internal part of workpiece are better embedded from mechanical point of view, so from there more homogenous fine product can be obtained. The extraction from less-supported edges of higher degree of freedom will repeat at every cycle of extraction taking, and this can also be observed at the grains extracted from the run-out edges. The more running-in run-out edges are in the surface of workpiece, the ratio of coarse particles is bigger, but according to our practical experience the rate of fine fraction extracted by the introduced method exceeds 75% even in case of a well-patterned tyre tread. The introduced method of jet extraction as mastication process Mastication is a well-known process in the rubber industry. This is a kind of devulcanization process created by intensive mechanical work, namely reversing the thermoset elastic state into moldable, plastic state mainly through rupture of double bonds. The material resulting from mastication process has improved chemical bonding properties. Conventional means of masticaton are roll mills, high shear mixers or extruders transmitting intense mechanical forces. Economic disadvantage of these mechanical processes is that material to be devulcanized (e.g. conventionally ground rubber product) must go through again a technological process of considerable equipment demand and energy consumption. In the course of extracting-grinding process the forces resulting from discussed movement parameters of jet and workpiece can be corresponded to the forces occurring during mastication. It is a considerable difference however that for the jet-type mastication there is no need for additional energy input, as the energy transmitted by the jet is enough. It is an additional advantage of our extracting-grinding method that by the result of process a material structure of such surface properties can be obtained, which is equal or in certain cases even better than properties of conventionally masticated material. Special properties of jet-extracted rubber product

In addition to fine grain size that represents considerable added-value utilization in chemical industry - so-called upcycling - , another desirable property of the product is such a surface morphology that promotes its highest possible grade of chemical bonding activity, thus assuring the chemically stable integration into newly-produced polymer matrices. A product with such properties represent remarkable added value, because through its utilization the ratio of usually expensive chemical-bond improving surface modifying and compatibility promoting materials can be considerably decreased in polymer compounds. Thus production cost of final product, which may contain jet- extracted product in higher ratio than other known crumbs, can be remarkably decreased.

Properties of material produced with ultra high pressure jet - comparing with the properties of products of different mechanical and/or cryogenic shredding-grinding process - represent application advantage in various fields of further utilization because due to introduced technology the material of product and polymer structure of surface do not degrade.

The scanning electron microscopic (SEM) photos of Figure 6 and Figure 7 show well that contrary to morphology of product obtained from conventional grinding the shape of grains produced by the introduced jet-extraction method is amorphous. Their typical characteristic is the numerous convex-concave micro- surfaces, and their structure is micro-porous due to tearing- featured extraction- grinding. Effective surface of rubber powder grains is between 0.2-2 m²/g, but it may reach even 3-4 m²/g in certain cases. Therefore the introduced method results a pure rubber product with amorphous, big specific surface that contains active centers. It can be further processed without chemical or other activation or devulcanization of surface.

The product is an "intelligent" additive just by itself in various polymer systems.

Application fields of high chemical activity rubber powder obtained by our method are wide, from which we emphasize the followings on basis of practical experiences up to now. Production of rubber powder-based polymer systems

A unique property of the introduced jet-extracted product is that it is directly suitable for revulcanization without devulcanization, namely manufacturing of new product, even solely from itself. The powder nevertheless shows very good compatibility with different types of polymers. It has been proven in the course of laboratory and factory application tests and trial productions that in those mother batches that utilized jet-extracted powder considerably less quantity of compatibilizer, curing agent or plasticizer were necessary compared to utilization of mechanical or cryogenic products. According to wide-range laboratory and industrial application tests the proper formulation of fine rubber powder below 500 micrometers can be successfully applicable not only for rubber-base systems, but also as reactive additive for PVC/CPE and HDPE or LDPE thermoplastic elastomer systems. It is a further advantage of the produced mixtures that they can be processed on standard equipment with commonly applied technologies of the rubber and plastics industries (calandering, injection molding, continuous extrusion).

The powders of high-fineness (below 200 micrometer) can be further beneficially used as elastic fillers of thick coating systems with good chemical and corrosion-proof properties, as well as fillers of elastic paints. Rubber bitumen systems

Advantages of road pavements made from rubber bitumen compared to asphalts made from conventional bitumen are longer life-span, smaller deformation, better surface grip, less traffic noise ("quiet asphalt"), easier de- icing and better slip-prevention ability. Rubber bitumen is made from bitumen, rubber crumb and certain additives. Production of rubber bitumen utilizing rubber crumbs made by mechanical or cryogenic grinding requires special transportation and processing systems. Contrary to conventional rubber bitumen systems the rubber bitumen produced with jet-extracted rubber powder is chemically and physically stable, therefore its processing can be performed by conventional bitumen-transporting and processing systems. Increasing of fine product yield of the process

Introducing the extraction process it was already discussed that in case of elastomers a tearing process is initiated. In that course the crack-growth or tear due to discontinuities being present in material-structure will propagate in the body of polymer. The characteristic of propagating tear among others is that the main tearing surface is patterned with micro-ruptures.

These micro-ruptures can be observed also on the surface of product made by jet-extracting. If the product is subjected to such low-power soft post- crumbling that would not cause degradation of surface polymer structure (namely it maintains the properties of the original material), then further separation of pre-ruptured grains, namely fining of grain sizes can be promoted. This post-crumbling is especially successful in case of internal butyl rubber (isobutylene-isoprene rubber) of modern tyres and other polymers with similar physical properties and rheology, but it improves the fine-grain ratio even in case of different polymers. Advantages related to the invention

We emphasize that the ultra high pressure jet process that we discuss is substantially aiming at grinding of such polymers - first of all elastomers - of which otherwise could be finely ground only with complicated processes, or if their product would be out of interest for considerable value-added utilization due to surface degradation of their original polymer structure. Besides "common" rubber products (e.g. tyres) these are the expressly soft technical elastomers, like EPDM or silicon rubber materials.

Another advantage of the method that it can be adapted well for processing of workpieces with such shape or structure that cannot be processed by conventional shredding-grinding methods. Such are for example vulcanized rubber parts reinforced with strong metal frame, where metal structure would not allow mechanical grinding.

Above advantages are further amplified with such specialty of discussed method that it does not require pre-shredding or pre-cutting of the workpieces to be processed (e.g. tyre, conveyor belt, insulation materials of electric cables or elastic materials of different shape). Further advantage of the discussed method that even in case of workpieces with solid metal frame pure product can be obtained in one technological step according to expected economic requirements, and the product is a directly utilizable material for further applications.

The extracting-grinding is further promoted by the warming of liquid transportation between high-pressure pump and nozzles, which, in case of applied pressure level for water working medium may reach even 40-50 degrees centigrade, plus the local heat generation of workpiece-attacking jet. These heat effects jointly contribute to increasing of viscous elasticity of the workpiece, thus promoting the efficiency of the method.

Claims

1 ) A method for extraction and grinding of elastomers with ultra high pressure liquid jets; where one or more liquid jet being aimed to the surface of one or more workpieces to be extracted; and workpiece or workpieces to be extracted and the liquid jet or jets are to be moved in correlation to each other; and the method characterized by that technological parameters of the extraction process - first of all the pressure limit value of extraction jet as well as characteristic parameters of correlated movement of liquid jet or jets and workpiece or workpieces being extracted - are to be determined from the tearing energy of elastomer being extracted.

2) A method as claimed in claim 1 , characterized by that correlated movement of aimed liquid jet or jets and workpiece or workpieces being extracted is a characteristically planar vibratory motion and a simultaneous forward motion between the workpiece and liquid jet; where plane of vibration is perpendicular to forward motion of workpiece and to the surface of workpiece, or it is inclined by 0-15 degrees to the perpendicular of the workpiece.

3) A method as claimed in claim 2, characterized by that vibratory motion is to be realized by moving of nozzle or nozzles discharging the liquid jet.

4) A method as claimed in claim 2, characterized by that vibratory motion is to be realized by moving of workpiece or workpieces being extracted.

5) A method as claimed in claim 2, characterized by that forward motion is performed by workpiece or workpieces. 6) A method as claimed in claim 2, characterized by that forward motion is performed by liquid jet or jets. 7) A method as claimed in anyone of the previous claims, characterized by that liquid jet or jets perform extraction; and the liquid jet or jets simultaneously perform fine grinding in such way that characteristics of the extracting-grinding process are to be set to previously calculated and planned values independently of the shape of workpiece (ring, belt, tyre etc.) 00002

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8) A method as claimed in anyone of the previous claims, characterized by that flow and pressure of liquid as well as capacity of high pressure pump are to be set at the value being determined from tearing energy of elastomer to be extracted. 9) A method as claimed in anyone of the previous claims, characterized by that at setting the parameters of extracting-grinding, the determined pressure value of tearing energy of elastomer being extracted is to be defined to the place of extraction, namely to bottom area of extraction jet.

1O)A method as claimed in anyone of the previous claims, characterized by that method being applied for processing of own production rejects in such a way that for further optimization of extraction parameters the tearing energy is to be determined by previous measuring of the own manufactured material of the production reject.

1 1 )A method as claimed in anyone of the previous claims, characterized by that optimum capacity of high pressure pump is to be adjusted with tuning nozzles in such way that in addition to extraction nozzles further nozzles of different discharging diameter in different number being applied.

12)A method as claimed in anyone of the previous claims, characterized by that jet-affected part of fixed workpiece is to be firmly supported, thus eliminating the flexible compensation effect of workpiece or workpieces. 13)A method as claimed in anyone of the previous claims, characterized by that action vectors of liquid jet or jets are aimed right at extraction area of workpiece or workpieces. 14)A method as claimed in anyone of the previous claims, characterized by that process liquid performing extracting-grinding is of high purity water, produced practically by reverse osmosis, as well as of ion-treated and filtered.

15)A method as claimed in claim 14, characterized by that the water applied for extracting-grinding process being recirculated, and the recirculated water is cooled down to 17-28 degrees centigrade before feeding back to high pressure pump. 16)A method as claimed in anyone of the previous claims, characterized by that the extracting-grinding being performed by liquid jet of optimum diameter between 0.05 mm (0.002") and 0.5 mm (0.02").

17)A method as claimed in anyone of the previous claims, characterized by that extracting-grinding liquid jets are vibrated over the area to be extracted along a straight line, characteristically with a constant frequency between 250/min and 1250/min.

18)A method as claimed in claim 17, characterized by that extracting- grinding liquid jets are vibrated with an amplitude equal to or exceeding distance between nozzles in a row of nozzles.

19)A method as claimed in anyone of the previous claims, characterized by that forward speed between one or more workpiece and one or more liquid jets is to be set on a value adjusted to frequency of vibration.

2O)A method as claimed in anyone of the previous claims, characterized by that for the increasing extraction-promoting material fatigue, a hammer- drill effect is applied, thus the necessary liquid pressure being generated by plunger pump without pressure equalizer.

21 )A method as claimed in anyone of the previous claims, characterized by that besides extraction and grinding the mastication with liquid jet is also performed.

22)A method as claimed in claim 2, characterized by that value of α degree of inclination of liquid jet to the perpendicular of workpiece is to be determined from modulus of the material being extracted.

23)A method as claimed in anyone of the previous claims, characterized by that distance of extraction head and workpiece is continuously optimized by a process control system.

24)A method as claimed in anyone of the previous claims, characterized by that a low-power soft post-crumbling is applied that would not cause degradation of polymer structure, thus carrying out an additional fining of the in-material pre-split extraction grains.