BELT CALENDER AND METHOD FOR MANUFACTURING PREIMPREGNATED COMPOSITES

Abstract

A belt calender for manufacturing preimpregnated composites includes a first roller, which is rotatable around its longitudinal axis, a first belt running at least partly around the first roller; and a second belt running in between the first roller and the first belt. The first belt and the second belt guide a feed of material between them. The belt calender includes auxiliary rollers which are rotatable around their longitudinal axes, and are arranged substantially parallel to the first roller around at least a part of a circumference thereof. The first and second belt run in between two adjacent ones of the plurality of auxiliary rollers, thereby defining a meandering path for the feed of material. A method for manufacturing preimpregnated composites by using such a belt calender.

Claims

1. A belt calender for manufacturing preimpregnated composites, comprising: a first roller, which is rotatable around its longitudinal axis; a first belt running at least partly around the first roller; and a second belt running in between the first roller and the first belt, wherein the first belt and the second belt are configured for guiding a feed of material between them, wherein a plurality of auxiliary rollers, which are rotatable around their respective longitudinal axes, are arranged substantially parallel to the first roller around at least a part of a circumference thereof, and wherein the first and second belt and any material therebetween run in between two adjacent ones of the plurality of auxiliary rollers, thereby defining a meandering path for the feed of material.

2. The belt calender according to claim 1, wherein the meandering path is defined or definable around at least a part of the circumference of the first roller.

3. The belt calender according to claim 1, wherein the meandering path is definable around at least a part of the circumference of the first roller.

4. The belt calender according to claim 1, wherein the first belt, the second belt and any material therebetween runs, in a transport direction of the feed of material, alternatingly along the inside and the outside of two adjacent ones of the auxiliary rollers as seen from the first roller.

5. The belt calender according to claim 1, wherein the first belt, the second belt and any material therebetween runs, in a transport direction of the feed of material, along the first roller, and subsequently along the auxiliary rollers.

6. The belt calender according to claim 1, further comprising heating means for heating at least one of the plurality of auxiliary rollers.

7. The belt calender according to claim 1, wherein at least one of the plurality of auxiliary rollers urges the first belt and the second belt and any material therebetween against the first roller.

8. The belt calender according to claim 7, wherein another one of the plurality of auxiliary rollers adjacent to the one of the plurality of auxiliary rollers is arranged at a distance from the first roller.

9. The belt calender according to claim 1, wherein a radial position of at least one of the plurality of auxiliary rollers with respect to the first roller is adjustable.

10. The belt calender according to claim 1, further comprising pre-heating means for pre-heating the first and/or second belt and/or the feed of material, arranged upstream of the first roller as seen in a transport direction of the feed of material.

11. The belt calender according to claim 1, further comprising cooling means arranged downstream of the first roller as seen in a transport direction of the feed of material for cooling the feed of material.

12. The belt calender according to claim 11, wherein the cooling means comprise at least one plate cooler.

13. The belt calender according to claim 1, wherein the first belt and/or the second belt is an endless belt spanned across a system of return rollers defining a return path for said respective first or second belt, which return path runs free of the first roller.

14. The belt calender according to claim 13, wherein the system of return rollers comprises a moveable roller for adjusting the tension force in said respective first or second belt.

15. The belt calender according to claim 1, wherein a tension force of the first belt and/or the second belt produces a pressing force on any material between the first belt and the second belt, wherein the pressing force is between 1.8-3.0 kg/cm.sup.2.

16. The belt calender according to claim 1, wherein the first belt and/or the second belt is a glass fiber reinforced Teflon belt.

17. The belt calender according to claim 1, wherein the plurality of auxiliary rollers comprises 2-10 auxiliary rollers.

18. The belt calender according to claim 1, wherein the first roller has a diameter larger than at least one of the auxiliary rollers.

19. A method for manufacturing preimpregnated composites by using a belt calender according to claim 1, comprising the step of: a) feeding a feed of material between the first belt and the second belt.

20. The method according to claim 19, wherein the belt calender, comprises: a first roller, which is rotatable around its longitudinal axis; a first belt running at least partly around the first roller; and a second belt running in between the first roller and the first belt, wherein the first belt and the second belt are configured for guiding a feed of material between them, wherein a plurality of auxiliary rollers, which are rotatable around their respective longitudinal axes, are arranged substantially parallel to the first roller around at least a part of a circumference thereof, wherein the first and second belt and any material therebetween run in between two adjacent ones of the plurality of auxiliary rollers, thereby defining a meandering path for the feed of material; wherein a tension force of the first belt and/or the second belt produces a pressing force on any material between the first belt and the second belt, and wherein the pressing force is between 1.8-3.0 kg/cm.sup.2; the method further comprising: adjusting the tension force so that the pressing force is larger than 2 kg/cm.sup.2, preferably at least 2.5 kg/cm.sup.2, more preferably approximately 3 kg/cm.sup.2.

21. The method according to claim 19, wherein the first roller and the auxiliary rollers are driven to rotate at different circumferential speeds.

22. The method according to claims 19, wherein the material comprises a material comprising uni-directional oriented fibers.

Description

[0052] The invention will be further explained with reference to the attached figures, wherein:

[0053] FIG. 1 shows a schematic representation of a side view of an embodiment of a belt calender according to the invention; and

[0054] FIG. 2 shows an enlarged view of a part of FIG. 1.

[0055] FIG. 3 shows a schematic representation of a side view of another embodiment of a belt calender according to the invention.

[0056] In all figures, the same elements are referred to using the same reference numerals.

[0057] FIG. 1 shows a belt calender 1 for manufacturing preimpregnated composites. The belt calender 1 comprises a first roller 2 which is rotatable around its longitudinal axis 3. In this embodiment the first roller 2 is a drum. The belt calender 1 includes a first belt 4 which runs at least partly around the first roller 2, and a second belt 5 running in between the first roller 2 and the first belt 4. The first belt 4 and the second belt 5 are configured for guiding a feed of material 6 between them. The feed of material 6 initially comprises a material to be impregnated and a matrix material. The matrix material may be supplied on one side or on both sides of the material to be impregnated. As the feed of material 6 moves along the belt calender 1, the matrix material penetrates into the material to be impregnated, eventually resulting in a prepreg. The matrix material is usually a thermoplastic material, which may require softening by pre-heating in order to sufficiently penetrate into the material to be impregnated. For that reason the belt calender of this embodiment is provided with pre-heating means 19. In the embodiment shown the pre-heating means are constituted by two plate heaters 19 disposed on both sides of the first belt 4, however a single plate heater 19, especially below the first belt 4, may also be sufficient. Alternatively, other pre-heating means 19 may be employed. As the first roller 2 rotates in a rotation direction r.sub.2, the two belts 4, 5 move with it in a feeding direction f.sub.4 and f.sub.5. In this specific embodiment, the feed of material 6 is transported by the first belt 4 from an infeed position 7 upstream of the first roller 2 in the feeding direction f.sub.4 towards the first roller 2, where it is met by the second belt 2 at a starting location 8 for clamping the feed of material 6 between the two belts 4,5. The feed of material 6 is from that starting location 8 clamped between the two belts 4, 5 which guide the feed of material 6, so that the feed of material follows the path of two belts 4, 5 around the first roller 2. The two belts 4, 5 separate at a separation location 9, thereby feeding out a finished feed of material 10, i.e. a prepreg. For the sake of clarity, the belts 4, 5 and the feed of material 6 have been drawn at distance from each other, whilst in reality they are in contact.

[0058] According to the invention, the belt calender of FIG. 1 comprises a plurality of auxiliary rollers, in this case five auxiliary rollers 11, 12, 13, 14, 15. It is noted that the belt calender could also comprise another number of auxiliary rollers 11, 12, 13, 14, 15, such as any number of auxiliary rollers 11, 12, 13, 14, 15 ranging from for example two to six. The auxiliary rollers 11, 12, 13, 14, 15 are arranged substantially parallel to the first roller 2 around a part of its circumference. This is shown in FIGS. 1 and 2 by longitudinal axes 11′, 12′, 13′, 14′, 15′ of the auxiliary rollers 11, 12, 13, 14, 15, which are arranged substantially parallel to the longitudinal axis 3 of the first roller 2.

[0059] More particularly, the auxiliary rollers 11, 12, 13, 14, 15 are arranged in a part of the circumference of the first roller 2 in an area where also the first and second belt 4, 5 run. The first and second belt 4, 5 run together,—possibly with the feed of material 6 disposed in between—in between two adjacent auxiliary rollers 11, 12, 13, 14, 15, see e.g. pairs of auxiliary rollers 11, 12; 12, 13; 13, 14; 14, 15. The path along which the two belts 4, 5 and any material in between therefore run is meandering, meaning that it makes a series of at least one relatively sharp bend 16. Consequently, the meandering path moves towards and away from the first roller repeatedly. A relatively sharp bend 16 herein may mean that the bend has a smaller radius than the first roller 2. For that reason, at least one of the auxiliary rollers 11, 12, 13, 14, 15 may have a radius which is smaller than the radius of the first roller 2. As can be seen best in FIG. 2, when following the first belt 4 and the second belt 5 in the their respective feed directions f.sub.4, f.sub.5 defining a transport direction t.sub.6 for the feed material in the same direction, the first belt 4 and the second belt 5 run alternatingly along the inside of an auxiliary roller 11, 13, 15 and on the outside of an auxiliary roller 12, 14. The meandering path thereby runs in a series of relatively sharp bends 16 around the auxiliary rollers 11, 12, 13, 14, 15. A meandering path like this creates changing compressive and shearing forces exerted onto the feed of material 6 transported between the belts 4, 5, thereby effectively massaging the matrix material into the material to be impregnated. The relatively sharp bends 16 in the meandering paths are in this specific embodiment separated by straight sections 17. Some of the straight sections 17 may be lengthened or shortened, introduced or removed by moving at least one of the auxiliary rollers 11, 12, 13, 14, 15 radially towards or away from the first roller. This concept is illustrated in FIG. 2, where auxiliary roller 12 is also drawn in a dotted line as auxiliary roller 12-1 moved radially further away from the first roller 2. Therefore, the straight sections 17′ of the meandering path are longer than original straight sections 17 between auxiliary roller 12 and its adjacent auxiliary rollers 11, 13. By altering the positions of the auxiliary rollers 11, 12, 13, 14, 15, some or all of the straight sections 17, which run substantially in a radial direction with respect to the first roller 2, may be removed completely. When no straight sections 17 are present, they may be introduced by moving at least one of the auxiliary rollers 12, 14 along which the belts 4, 5 run on the outside of, away from the first roller 2. As is shown by forces F.sub.11, F.sub.13, F.sub.15 (FIG. 2) auxiliary roller 11, 13, 15 of the plurality of auxiliary rollers of the belt calender 1 of this embodiment urge the first belt 4 and the second belt 5 and any material therebetween against the first roller 2. Depending on the desired performance of the belt calender, one, some or all of the auxiliary rollers 11, 13, 15 may be disposed at a larger distance from the first roller 2, so that they do not urge the belts 4, 5 against the first roller 2. The urging force of the rollers 11, 13, 15 introduced above, enhances the massaging effect described above, thereby ultimately leading to a more thorough impregnation. Although multiple auxiliary rollers 11, 13, 15 are shown to urge the first 4 and second belt 5 and the feed of material 6 against the first roller 2, a single auxiliary rollers could also be used to urge the belts 4, 6 and material 6. In particular, any of the auxiliary rollers 11, 13, 15 along which the belts 4, 5 run on the inside of, in any combination, may be used to urge the belts 4, 5 and material 6 against the first roller 2. In contrast, the auxiliary rollers 12, 14 along which the belts 4, 5 run on the outside of, which are adjacent said auxiliary rollers 11, 13, 15, are arranged at a distance from the first roller 2.

[0060] In the shown embodiment, the belt calender 1 also includes heating means 18 (see FIG. 2) for heating at least one of the plurality of auxiliary rollers 11, 12, 13, 14, 15. While only auxiliary roller 12 is in this case shown to be heated using the heating means 18, the invention also concerns multiple heated auxiliary rollers 11, 12, 13, 14, 15 using the same or separate heating means 18.

[0061] The belt calender 1 of this embodiment also includes cooling means 20 arranged downstream of the first roller 2 as seen in the transport direction t.sub.6 of the feed of material 6 for cooling the feed of material 6. As an example, the cooling means 20 may comprise two plate coolers 20 arranged on opposite sides of the belts 4, 5, but one plate cooler 20 may also be sufficient. Using the cooling means 20, the material between the two belts 4, 5 can be cooled quickly and/or evenly.

[0062] In this embodiment the two belts 4, 5 are endless belts 4, 5, which are spanned across a system of return rollers 21, 22, 23, 24, 25, 26, 27. The return rollers 21, 22, 23, 24, 25 associated with the first belt 4 define a return path for the first belt 4, which runs free of the first roller 2. Accordingly, the first belt 4 forms a continuous loop around the first roller 2, following the meandering path and the return path. As a result, the first belt 4 may be driven continuously as long as desired. Similarly, the return rollers 25, 26, 27 associated with the second belt 5 define a return path for the second belt 5, which runs free of the first roller 2. Accordingly, the second belt 5 forms a continuous loop around the first roller 2, following the meandering path and the return path. As a result, the second belt 5 may be driven continuously as long as desired. It is noted that the return rollers 21, 22, 23, 24, 25, 26, 27 are distinct from the auxiliary rollers 11, 12, 13, 14, 15, as the return rollers 21, 22, 23, 24, 25, 26, 27 do not contribute to the meandering path and/or do not contribute to impregnating the material to be impregnated. In stead, the return rollers 21, 22, 23, 24, 25, 26, 27 merely guide the belts 4, 5 in a closed loop through the return path, thereby passing the pre-heating means 19 and the cooling means 20 if desired. The return rollers 21, 22, 23, 24, 25 for the first belt 4 include one moveable roller 23 for adjusting the tension force in the first belt 4. Similarly, the return rollers 25, 26, 27 for the second belt 5 include one moveable roller 26 for adjusting the tension force in the second belt 5. The moveable return rollers 23, 26 can be moved in order to lengthen or shorten the return path of their respective belts 4, 5. Lengthening the return path increases tension in the respective belt 4, 5, whereas shortening the return path decreases tension in the respective belt 4, 5. Practically, the moving return rollers 26, 23 are held in position by cylinders 28, 29, respectively, which are configured for continuously providing an adjustable force F.sub.28, F.sub.29 respectively. By means of the adjustable forces F.sub.28, F.sub.29 associated with the moveable return rollers 26, 23 the position of the rollers 26, 23 may be held so that a constant but adjustable tension exists in each belt 4, 5. The tension force in the belts 4, 5 produces a pressing force on any material therebetween. The embodiment of FIG. 1 also includes a waltz roller 15 urging the first belt 4, the second belt 5 and any material therebetween against the first roller 2 with a waltz force F.sub.w. Although in this case the waltz roller 15 is one of the plurality of auxiliary rollers 11, 12, 13, 14, 15, a separate waltz roller may also be provided. It is advantageous of the waltz roller 15 is either the last of the auxiliary rollers 11, 12, 13, 14, 15 or arranged downstream of the auxiliary rollers 11, 12, 13, 14, 15. Alternatively the waltz roller may be the first of the auxiliary rollers. As explained above, tension in the first 4 and/or second belt 5 produces a pressing force on any material between the belts 4, 5. Therefore, the pressing force aids in the penetration of the matrix material into the material to be impregnated. In the embodiment shown, which also corresponds to an embodiment of the method according to the invention, the pressing force exceeds the waltz force F.sub.w. Due to the meandering path, the pressing force changes in magnitude and direction, so that increasing the pressing force increases the massaging effect of the meandering path, thereby causing a more thorough penetration. The first belt 4 and the second belt 5 are in this case glass fiber reinforced Teflon belts 4, 5.

[0063] FIG. 3 shows another belt calender 100 for manufacturing preimpregnated composites. This belt calender 100 is somewhat similar to the belt calender 1 according to FIG. 1, but differs in the arrangement of the auxiliary rollers 111-114 and comprises additional return rollers. Elements in FIG. 3 which are similar to elements of the belt calender 1 in FIG. 1 (i.e. the elements designated by reference numbers 2-9, 19-29) are designated in FIG. 3, increased by 100 (e.g. first roller 2 becomes first roller 102), and will only be described in as far as they might be relevant for distinguishing the difference between the belt calenders 1 and 100.

[0064] The belt calender of FIG. 3 comprises a plurality of auxiliary rollers such as, in this case, four auxiliary rollers 111, 112, 113, 114, arranged substantially parallel to and spaced apart from the first roller 102, of which the longitudinal axes 111′, 112′, 113′, 114′ are arranged substantially parallel to the longitudinal axis 103 of the first roller 102. The auxiliary rollers 111, 112, 113, 114 are arranged in an area where also the first and second belt 104, 105 run.

[0065] In the direction of transport f.sub.104, f.sub.105, the first and second belt 104, 105 run together—with the feed of material 106 disposed in between—along the first roller 102, running free from the auxiliary rollers 111, 112, 113, 114, and subsequently along a meandering path between the auxiliary rollers 111, 112, 113, 114, in a direction opposite to the direction r.sub.102, running free from the first roller 102. The meandering path creates an effect similar to the meandering path created by the auxiliary rollers 11, 12, 13, 14, 15 of the belt calender 1 according to FIG. 1.

[0066] In an embodiment, one, more or all of the auxiliary rollers 111, 112, 113, 114 may be moveable to a position in which the one, more or all of the auxiliary rollers 111, 112, 113, 114 are arranged around the first roller 102, and possible urge the first belt 104 and second belt 105 and any possible material 106 in between against the first roller 102.

[0067] In addition to the return rollers 121, 122, 123, 124, 125, 126, 127, the belt calender 100 also comprises return rollers 115, 116, in order to guide the first belt 104 and second belt 105 towards the separation location 109, accommodating for the reversed order of passage of the auxiliary rollers 111, 112, 113, 114 as compared to the belt calender 1 of FIG. 1. These additional return rollers 115, 116 are also distinct from the auxiliary rollers 111, 112, 113, 114. The return rollers 115, 116 do not contribute to the meandering path. The contribution of the return rollers 115, 116 to the impregnation of the material is at least minor with respect to the contribution by the auxiliary rollers 111, 112, 113, 114 (e.g. may originate from rest heat present in the material) but may even be negligible.

[0068] Although the invention has been explained with reference to particular examples or embodiments, it is not limited thereto. In stead, the invention also concerns the subject matter covered by the claims which now follow.