DEVICE AND METHOD FOR CONTINUOUS CURE CONTROL

Abstract: With the intention of continuously measuring, monitoring and controlling the degree of vulcanization in vulcanization equipment, an arrangement and a method are incorporated in the equipment. The arrangement is essentially comprised of a part (4A) which is mounted for movement in an upper press half (2) and which has a top part (4B). The press further includes a lower press half (3) in which a non-movable part (4F) is mounted. The non-movable part has a recess (4G) which faces towards the top (4B) and which has a shape corresponding to the shape of the top (4B). The non-movable part is fixed in the lower press half (3) and the top (4B) and the recess (4G) are configured to define a gap (13) therebetween when the press (1) is closed.

Description: DEVICE AND METHOD FOR CONTINUOUS CURE CONTROL. The invention relates to a method of continuously mea¬ suring, monitoring and controlling degrees of vulcani- zation and parameters which are related to the physi¬ cal properties of a vulcanized object in conjunction with vulcanizing processes in equipment intended therefor, and also to an arrangement incorporated in said equipment and operative in putting the method into effect. The invention is intended primarily to continuously measure, monitor and control the degree of vulcanization, or state of cure, of rubber objects which are shaped and vulcanized in a curing or vulca¬ nization press, said press preferably working in accordance with the injection and/or compression and/or transfer principle. The degree to which the object is vulcanized is controlled primarily by adapt¬ ing curing time. According to alternative embodiments of the invention, such physical parameters of rubber objects as tensile strength, tear strength, wear strength and compression, are also monitored. The inventive arrangement is preferably incorporated in a curing press of the aforesaid kind. The rubber compound used when moulding and vulcanizing objects in a rubber injection press, for instance, is produced in relatively large mixing machines in which rubber is mixed with sulphur compounds or some other vulcanization agent, optionally together with filler and/or other additives. For reasons of an economical and process/technical nature, such rubber compounds are not produced in small quantities in immediate connection with the moulding and vulcanizing of rubber objects, but are produced in large batches and given a web-like or band-like form. These bands are then stored for periods extending from some few days up to several months, before being moulded and vulcanized. The extent to which the vulcanization properties of such rubber bands are changed is difficult to anticipate, although the extent of this change will not be negligible as a result of the aging that occurs during this storage period. The property changes of the rubber compound are caused both by chemical reac- tions in the actual rubber compound and also by exter¬ nal influences, such as ambient temperature and the effect of certain gases in the ambient air. When moulding and vulcanizing rubber objects in a press of the aforesaid kind for instance, it is neces¬ sary to measure (determine), monitor and control accu¬ rately a number of conditions, such as temperature, pressure and time, in order to produce a final product that has optimal properties. Among other things, it is important that the curing time is not too short at constant temperatures, since the thickest parts of those objects to be produced will not then be vulca¬ nized throughout. Non-vulcanized parts can never be accepted. If the curing time is somewhat longer than the time required for all parts to be vulcanized throughout, no unfavourable effects are likely to occur. On the other hand, if the curing time is longer than a given maximum time, so-called overvulcanization occurs, therewith drastically impairing the properties of the objects. Thus, there is found an optimal curing time and a minimum time and a maximum time for each individual vulcanization process. If the curing time is shorter than the minimum time or exceeds the maxi¬ mum time, the objects will obtain unacceptable proper- ties. As will be evident from the following, it is not possible to predetermine with certainty either the optimal curing time, the minimum curing time or the maximum curing time for a given vulcanization process in a given curing press. Thus, it is particularly important in practice to con¬ trol the curing time, both from a technical aspect and from an economical aspect, as mentioned above, since correct control will afford time gains in production, among other things. Hitherto, this control has been based on rheological parameters which are measured on a rubber compound prior to introducing the mixture into the press. On the basis of these parameter val¬ ues, measured prior to vulcanization, manufacturers have then estimated a suitable curing time on the basis of earlier experiences obtained with empirical tests and from measurements obtained with the aid of different, well-known free-standing rheometers (cure- meters) of the Mooney type, for instance, and with the aid of calculating programs, possibly computer soft¬ ware. Control methods based on this principle are used, for instance, in a number of computer software systems. An example of such systems is found in the advanced control program Curetrac ® retailed by the French company REP. Thus, known vulcanization process¬ es are not effected while directly and continuously measuring, monitoring and controlling the degree of vulcanization or state of cure, which when practicing known techniques is solely determined indirectly on the basis of other parameters. However, with regard to the aforesaid properties of the rubber compound, a vulcanization process effected on the basis of the rheological measurement values of the rubber compound determined prior to commencing vulcanization results in a control process which can lead to quality deficiencies and a high percentage of faults in the manufactured products, and which is insufficiently accurate and also both complicated and expensive. Neither is it possible when applying indi¬ rect control methods to achieve the quality level in the production process stated in the intentions of the quality standard ISO 9000. With the intention of circumventing the aforesaid drawbacks, Applicant proposes a completely novel arrangement and a completely novel method by means of which the degree of vulcanization of an object is measured, monitored and controlled continuously actu¬ ally within the vulcanization equipment used. The inventive method and arrangement are based on the understanding that the degree of vulcanization is in direct relationship with the modulus of elasticity of the material being vulcanized. The invention does not influence the vulcanization process or those objects being vulcanized, and functions under the same condi¬ tions as those rubber objects in the process of being vulcanized, irrespective of temperature, pressure and rheological surroundings, and is also highly reliable, simple to practice and relatively inexpensive. Distinct from prior art methods and arrangements, the invention enables vulcanization processes to be con- trolled by continuously and directly measuring and monitoring the degree of vulcanization in a precise manner. The inventive arrangement and inventive method can also be readily adapted to different rubber ob¬ jects to be vulcanized. The products produced with the aid of the invention will thereby have a higher and more uniform quality than products produced in accor¬ dance with earlier known methods. The inventive ar¬ rangement and method also fulfil the intentions in the aforesaid quality standard ISO 9000, among other things with regard to statistic process controls which, with the aid of the invention, can be carried out with a starting point from a measurable parameter which is in direct and steady relationship with the properties of the products manufactured. Other characteristics of the invention and advantages afforded thereby will be evident from the following description of an exemplifying, non-limiting embodi¬ ment of the invention. Although the exemplifying embodiment is illustrated with reference to an injec¬ tion-type curing press, it will be understood that the invention can also be applied to curing presses of other kinds, possibly with the inclusion of minor modi ications embraced by the concept of the inven¬ tion. The exemplifying embodiment is described with reference to the accompanying schematic drawings, wherein mutually identical components in respective Figures of the drawing have been identified with like reference signs. Figure 1 illustrates schematically and in perspective an open compression moulding press 1 which comprises an upper press half 2, a lower press half 3, an inven- tive measuring, monitoring and controlling arrangement 4, a rubber test piece or specimen 5, a drive motor 6, an eccentric 7, an arm 16 (not shown in Figure 1), a drive belt 8, one or more wire strain gauges 9, one or more mould cavities 10 for rubber objects 15 (not shown) to be vulcanized, and a test piece channel 11 into which a rubber test piece or specimen 5 is in¬ jected, said channel 11 being identical to cavity supply channels 12 from a process aspect. Figure 2 is a schematic, sectioned view of part of the press halves 2 and 3 illustrated in Figure 1, and shows the press halves when closed. Figure 2 also shows in greater detail the inventive measuring, monitoring and controlling arrangement 4, which is mainly comprised of a movable part 4A which is mounted for movement in the upper press half 2 and which has a top 4B. The top 4B preferably has the general shape of a truncated cone and is able to rotate in a first bushing 4C and in a second bushing 4D. The upper end of the device 4 is fitted with an attachment arrange¬ ment 4E. Fixedly mounted in the lower press half 3 is a part 4F which has a recess 4G, preferably in the general shape of a truncated cone, which faces towards the upper press half 2. The part 4F is secured in the lower press half 3 by means of a further attachment device 4H and defines a gap 13 with the opposing surface of the top 4B when the press 1 is closed. Figure 2 also shows the aforesaid arm 16. As will be evident from Figures 1 and 2, the measur¬ ing, monitoring and controlling arrangement 4 is incorporated in the press halves 2 and 3, i.e. in the same equipment as that used to vulcanize the rubber objects with which it is desired to measure, monitor and control the degree of vulcanization thereof. At least one of the press halves 2 and 3 is movable in relation to the other. The top 4B and the recess 4G are so configured that the width of the gap 13, which is of generally uniform width, will essentially be the same as the largest thickness of the rubber objects 15. The mutually facing surfaces of the top 4B and the recess 4G are constructed such that the rubber test piece 5 will be subjected to friction forces in contact with said mutually opposing surfaces during the process of oscillation described herebelow. To this end, the aforesaid surfaces are not totally smooth, but slight- ly roughened. These surfaces are therefore preferably provided with ridges and grooves of small height and depths in relation to the desired width of the gap 13 and extending generally parallel with the longitudinal axis of the arrangement 4. The aforesaid surfaces of the top 4B and the recess 4G are configured to effect the measuring, monitoring and controlling of the degree of vulcanization of the objects produced in the manner described below. These surfaces may be given another configuration when determining certain parame- ters, such as tensile strength, tear strength, wear resistance and compression set with regard to vulca¬ nized objects between the press halves 2 and 3. The intention of the inventive arrangement and method is to ensure that the degree of vulcanization that is measured, monitored and controlled will essentially be the same as the degree of vulcanization of the rubber objects 15. In practice, a measuring, monitoring and controlling arrangement 4 is used for each set of press halves 2 and 3 in the equipment. In this regard, the arrangement 4 is placed in a position which is representative with respect to the degree of vulcani- zation from a measuring/technical aspect. The arrange¬ ment 4 is best positioned in the vicinity of one of the cavities 10 located in the proximity of the outer edges of the press halves 2 and 3, since the tempera¬ ture in this region of the press may be somewhat lower than in the centre regions of the press halves 2 and 3, resulting in somewhat slower vulcanization than in said centre regions. When moulding and vulcanizing rubber objects 15 in the press 1, the press is closed and a rubber compound 14 is injected through the channels 12 and in between the upper press half 2 and the lower press half 3, so as to fill the cavities 10 with said rubber compound. At the same time, rubber compound 14 is injected through the test piece channel 11 and into the gap 13 to form a rubber test piece 5 therein. The movable part 4A of the arrangement 4 is driven by the drive motor 6, via the attachment device 4E, the drive belt 8, the eccentric 7 and the arm 16. The drive motor 6 constantly rotates in one and the same direction. The arm 16 is imparted a rocking motion with the aid of the eccentric 7, this rocking motion occurring in a plane which is essentially perpendicu- lar to the plane of the drawing in Figure 2. The arm 16 thus moves backwards and forwards together with the movable part 4A, which is therewith imparted an oscil¬ latory movement. It is important that the amplitude, i.e. the oscillation angle, and/or the oscillation frequency, is not so great as to generate frictional heat in the rubber test piece 5. The oscillation angle and/or the oscillation frequency is/are also chosen with regard to optimum measuring accuracy. In many instances, it is convenient to use an oscillation angle of between one-tenth of a degree and five de¬ grees in each direction, and an oscillation frequency of between 0.5 and 5 Hz. As the top 4B oscillates, there is generated a torque 17 which is dependent on the modulus of elasticity of the rubber test piece 5 and which is measured with the aid of the wire strain gauge or strain gauges 9. This modulus of elasticity is variable and will depend partly on the properties of the test piece 5 immediately it has been injected into the gap 13, and partly on those property changes that occur continuously in the rubber during the process of vulcanization and which, in addition to the chemical composition of the rubber compound 14, are mainly dependent on pressure, temperature, curing time and the width of the gap 13. As before mentioned, the width of the gap 13 is gener¬ ally the same as the largest thickness of the rubber objects 15. In order to enable the invention to be applied with rubber objects 15 of different thick¬ nesses, the measuring, monitoring and controlling arrangement 4 is preferably constructed so that the top 4B will have a given specific configuration and the movable part 4A is fixedly mounted in the upper press half 2, while the configuration of the recess 4G is adapted to the width of the gap 13 and the non- movable part 4F is removably mounted in a lower press half 3 and is configured so as to enable it to be readily exchanged between different lower press halves 3. The temperature during vulcanization is generally the same as the temperature in/outside the cavities 10 when the rubber compound 14 is injected into the press 1. Since the curing time has a duration of only some few minutes at the most, the vulcanization temperature can only change to a limited extent. The pressure during the vulcanization process is generally the same for the rubber test piece 5 and the rubber objects 15. The inventive measuring, monitoring and controlling arrangement 4 operates in accordance with the follow¬ ing steps 1 to 9 inclusive: 1. It is determined whether the degree of vulcaniza¬ tion of the rubber test piece 5 shall be measured, monitored and controlled with each vulcanization sequence in the press 1 or only after a given number of predetermined vulcanization sequences. 2. The wire strain gauge or gauges 9 and associated read-off instrument(s) are set to zero to prevent the measuring, monitoring and controlling process being influenced by ambient conditions which have no signif¬ icance to the vulcanization process, for instance idling friction in the arrangement 4. 3. The preheated press 1 is closed. 4. The drive motor 6 is started-up, therewith oscil¬ lating the top 4B against the piece 5. 5. The rubber compound 14 is injected into the cavi- ties 10 and into the gap 13. 6. The torque 17 generated as the top 4B moves against the piece 5 is measured continuously with the aid of the strain gauge for gauges 9 either in abso- lute values or in percentages of a maximum value. 7. The measured value of the torque 17, which is in direct relationship with the modulus of elasticity and therewith the instantaneous state of vulcanization of the rubber objects 15, is then used directly to control the vulcanization process in progress, partic¬ ularly the curing time, this control either being effected manually or with the aid of computerized means. 8. When the value of the torque 17 indicates that the rubber objects 15 have reached the desired degree of vulcanization, the press 1 is opened and the rubber objects 15 and the rubber test piece 5 removed from the press 1, wherewith the test piece 5 is either scrapped or used again in a later evaluating process. 9. Return to step 2 a desired number of times. When the rubber objects 15 are removed from the press 1, in accordance with item 8 above, they are still warm and will cool in dependence on their respective thicknesses and on the ambient temperature. The vulca¬ nization process thus continues after having removed the rubber objects 15 from the press. It has been found in practice that the objects 15 can normally be removed from the press 1 when they have been vulca- nized to 90% of the desired degree of vulcanization, whereafter the residual thermal energy of the objects 15 completes the vulcanization of said objects. This procedure results in higher productivity and a reduc¬ tion in energy costs. In those instances when there is no prior knowledge as to when the objects 15 are vulcanized to 100%, the following procedures are preferably followed under item 8 above: A) In the first vulcanization process effected in a given set or array of press halves 2, 3 with associat¬ ed cavities 10 and with a given rubber compound 14, vulcanization is carried-out in the press 1 until the value of the torque 17 is no longer considered to increase, i.e. it has reached its maximum value, which indicates that 100 percent vulcanization has been achieved, whereafter the rubber objects 15 and the test piece 5 are removed from the press 1. B) During a given number, preferably ten, subsequent vulcanization processes, the rubber object 15 and the test piece 5 are removed from the press 1 when the torque 17 has reached a predetermined percentage of the maximum value recited under A) above, preferably about 90%, which indicates that the same predetermined proportion of 100 percent vulcanization has been achieved, since the torque 17 is in direct relation- ship with the degree of vulcanization reached. C) A new step A) is carried out when step B) has been carried out a predetermined number of times. Step C) is carried out since the maximum torque value recited under A) can fluctuate as a result, primarily, of the prevailing properties of the rubber compound 14. It will be understood that the inventive measuring, monitoring and control arrangement 4 can be modified and changed without departing from the scope of the present invention. For instance, the top 4B and the recess 4G may have shapes other than the shape of a truncated cone and may also have surface structures different to those described above. The movable part 4A may also be driven in a manner different to that described. The torque 17 may also be indicated with the aid of means other than the aforesaid wire strain gauge 9. When modified appropriately within the scope of the inventive concept, the invention may also be applied to measure, monitor and control the curing or solidifying process of objects other than rubber objects.

Claims: CLAIMS 1. An arrangement incorporated in vulcanization equipment for continuously measuring, monitoring and controlling the degree of vulcanization of objects shaped and vulcanized in said equipment and parameters which relate to the physical properties of said ob¬ jects, c h a r a c t e r i z e d in that the ar¬ rangement is incorporated in a compression moulding press (1) which includes an upper press half (2), a lower press half (3), and cavities (10) which are contained in the lower press half (3) and in which rubber objects (15) are vulcanized; in that at least one of said press halves is movable in relation to the other press half; in that the arrangement includes a part (4A) which is movably mounted in said upper press half (2) and which includes a top (4B) which is mount¬ ed for rotation in a first bushing (4C) and a second bushing (4D), said top (4B) being provided with an attachment device (4E) at its upper end; in that the arrangement further includes a non-movable part (4F) which is mounted in said lower press half (3) and which includes a recess (4G) which faces towards the top (4B) and the shape of which corresponds to the shape of said top (4B), wherein the non-movable part is secured to the lower press half (3) with the aid of a second attachment device (4H), and in that the top (4B) and the recess (4G) are configured so as to define a gap (13) between the mutually opposing sur- faces of said top and said recess when the press (1) is closed. 2. An arrangement according to Claim 1, c h a r ¬ a c t e r i z e d in that the arrangement is con- struσted so that the gap (13) will have a desired width within a predetermined range, preferably by giving the top (4B) a specific configuration and by preferably fixedly mounting the movable part (4A) in the upper press half (2) while adapting the shape of the recess (4G) to the desired width of the gap (13) and the non-movable part (4F) is preferably detachably mounted in a lower press half (3) and is constructed so as to enable said non-movable part to be exchanged readily between different lower press halves (3). 3. An arrangement according to any one of the pre¬ ceding Claims, c h a r a c t e r i z e d in that the gap (13) has a width which is generally equal to the largest thickness of the occurrent rubber objects (15). 4. An arrangement according to any one of the pre¬ ceding Claims, c h a r a c t e r i z e d in that the top (4B) and the recess (4G) have the shape of a truncated cone. 5. An arrangement according to any one of the pre¬ ceding Claims, c h a r a c t e r i z e d in that the movable part (4A) is imparted an oscillatory movement, preferably of variable amplitude and frequency, such as to generate a torque (17). 6. An arrangement according to Claim 5, c h a r - a c t e r i z e d in that the mutually facing surfac¬ es of the top (4B) and the recess (4G) are constructed so that a rubber test piece (5) will be subjected to sufficient friction against said surfaces during said oscillatory movement, preferably by providing said surfaces with ridges and grooves of small height and small depth respectively in relation to the width of the gap (13) , these ridges and grooves extending generally parallel with the longitudinal axis of the measuring, monitoring and control arrangement (4) . 7. An arrangement according to Claim 5 or 6, c h a r a c t e r i z e d in that the top (4B) and the recess (4G) are constructed in a manner which enables the torque (17) to provide, either directly or indirectly, information relating to the degree of vulcanization and/or the tensile strength and/or the tear strength and/or the wear resistance and/or the tendency towards compression set of the rubber test piece (5) . 8. An arrangement according to Claim 5, 6 or 7, c h a r a c t e r i z e d in that the oscillatory movement is generated with the aid of drive means incorporated in the movable part (4A) of said arrange¬ ment. 9. An arrangement according to Claim 5, 6 or 7, c h a r a c t e r i z e d by an external drive means which acts on the movable part (4A) to produce said oscillatory movement. 10. An arrangement according to Claim 9, c h a r ¬ a c t e r i z e d in that said oscillatory movement is effected by means of an arm (16) which is connected to the first attachment device (4E) and also to an eccentric device (7) , which in turn is connected to a motor (6) via a drive belt (8). 11. An arrangement according to Claim 10, c h a r ¬ a c t e r i z e d in that the arm (16) is of variable length, which length can be adjusted manually and/or with the aid of a control or servo system in a manner to change the amplitude of said oscillatory movement. 12. An arrangement according to any one of Claims 5- 11. c h a r a c t e r i z e d by torque measuring means . 13. An arrangement according to Claim 12, c h a r ¬ a c t e r i z e d in that the torque measuring means is comprised of one or more wire strain gauges (9) and associated indicator or read-off means. 14. An arrangement according to any one of Claims 5- 13, c h a r a c t e r i z e d in that the amplitude of said oscillatory movement is between one-tenth of a degree and five degrees in each direction; and in that the frequency of the oscillatory movement is between 0.5 and 5 Hz. 15. A method for continuously measuring, monitoring and controlling the degree of vulcanization of objects vulcanized and shaped in vulcanization equipment, and parameters which are related to the physical proper¬ ties of said objects, c h a r a c t e r i z e d by using an arrangement according to any one of Claims 5- 14 in the vulcanization equipment for continuously measuring, monitoring and controlling the degree of vulcanization of said objects and by carrying out the following steps 1 to 9 inclusive: 1. Determining whether the degree of vulcanization of the rubber test piece 5 shall be measured, monitored and controlled with each vulcanization sequence in the press 1 or only after a given number of predetermined vulcanization sequences; 2. Setting the wire strain gauge or gauges 9 and associated read-off instrument(s) to zero to prevent the measuring, monitoring and controlling process being influenced by ambient conditions which have no significance to the vulcanization process, for in- stance idling friction in the arrangement 4; 3. Closing preheated press 1 is closed; 4. Starting-up drive motor 6 and therewith oscillate the top 4B against the piece 5; 5. Injecting the rubber compound 14 into the cavities 10 and into the gap 13; 6. Continuously measuring the torque 17 that is generated as the top 4B moves against the piece 5 with the aid of the wire strain gauge for gauges 9, either in absolute values or in percentages of a maximum value; 7. Using the measured value of the torque 17, which is in direct relationship with the modulus of elastic¬ ity and therewith the instantaneous state of vulcani- zation of the rubber objects 15 directly to control the vulcanization process in progress, particularly the curing time, this control either being effected manually or with the aid of computerized means; 8. Opening the press when the value of the torque 17 indicates that the rubber objects 15 have been vulca¬ nized to the desired degree of vulcanization, and removing the rubber objects 15 and the rubber test piece 5 from said press, wherewith the test piece 5 is either scrapped or used again in a later evaluating process; and 9. Returning to step 2 a desired number of times. 16. A method according to Claim 15, c h a r a c ¬ t e r i z e d by carrying out step 8 in the following manner: A) In the first vulcanization process effected in a given set or array of press halves 2, 3 with associat¬ ed cavities 10 and with a given rubber compound 14, vulcanization is carried-out in the press 1 until the value of the torque 17 is no longer considered to increase, i.e. it has reached its maximum value, which indicates that 100 percent vulcanization has been achieved, whereafter the rubber objects 15 and the test piece 5 are removed from the press 1. B) During a given number, preferably ten, subsequent vulcanization processes, the rubber object 15 and the test piece 5 are removed from the press 1 when the torque 17 has reached a predetermined percentage of the maximum value recited under A) above, preferably about 90%, which indicates that the same predetermined proportion of 100 percent vulcanization has been achieved, since the torque 17 is in direct relation¬ ship with the degree of vulcanization reached. C) A new step A) is carried out when step B) has been carried out a predetermined number of times. 17. A method according to Claim 15 or 16, c h a r - a c t e r i z e d by measuring the torque (17) in step 6 with the aid of a strain gauge (9). 18. A method according to Claim 15, 16 or 17, c h a r a c t e r i z e d in that the amplitude of the oscillatory movement in step 5 is between one- tenth of a degree and five degrees in each direction and the frequency of said oscillatory movement is between 0.5 and 5 Hz. 19. A method according to Claim 15, 16 , 17 or 18, c h a r a c t e r i z e d by utilizing the torque (17) to provide information relating to the tensile strength and/or the tear strength and/or the wear resistance and/or the compression set of the rubber test piece (5) in addition to or instead of informa¬ tion relating to the degree of vulcanization of said rubber test piece, and choosing the amplitude and frequency of the oscillatory movement in accordance with that or those parameters of which information is required.

Inventors: HANSEN ERIK CORNELIUS, HANSEN, ERIK, CORNELIUS
Applicants: HANSEN ERIK CORNELIUS, QMD QUALITY MEASURING DEVICE A, QMD QUALITY MEASURING DEVICE AKTIEBOLAG
Application year: 1993
Main classification: G01N11
IPC codes: B29C35, B29C43, G01N3, G01N11, G01N33