GB2138740A

GB2138740A - Splicing Elongate Webs

Info

Publication number: GB2138740A
Application number: GB08408286A
Authority: GB
Inventors: Ramon Blanco Fernandez; Stephen Edward Palguta; Mundo Renato Santiago Del
Original assignee: BP Chemicals Hitco Inc
Current assignee: BP Chemicals Hitco Inc
Priority date: 1983-04-11
Filing date: 1984-03-30
Publication date: 1984-10-31
Also published as: FR2547603B1; JPS6253627B2; GB8408286D0; DE3413471A1; DE3413471C2; FR2547603A1; JPS59223362A; GB2138740B

Abstract

A flexible splicing arrangement is provided for joining the edge of an elongate web of tows of polyacrylonitrile material to the edge of an elongate web of glass or other high temperature resistant cloth so that the ends of the tows of polyacrylonitrile material are protected from the effects of high temperature during oxidation or other high temperature processing of the polyacrylonitrile tows. Following the application of a layer of silicone rubber adhesive to a portion of the web of cloth adjacent the edge thereof, the end of the web of polyacrylonitrile tows including the taped ends of the tows is placed over part but not all of the layer of adhesive. A cover of glass or other high temperature resistant cloth approximately equal in size to the layer of adhesive is prepared, following which a second layer of adhesive is applied to the underside thereof. The cover is placed over the web of polyacrylonitrile tows opposite the web of cloth so that the cover is generally coextensive with the first layer of adhesive. Heat and pressure are then applied to cure the layers of silicone rubber adhesive. <IMAGE>

Description

SPECIFICATION Splicing Elongate Webs The present invention relates to methods and apparatus for joining together elongate webs of flexible material, and more particularly to methods and apparatus for splicing a web of heatsensitive material to a second web in a manner to protect the end of the heat-sensitive web during subsequent processing in a high temperature environment.

It is known to carbonize polyacrylonitrile (PAN) or other carbonizable material by first oxidizing the material and thereafter heating the material in an inert atmosphere to a temperature sufficient to substantially carbonize the material. In the case of PAN, such material is often processed in the form of an elongated web of tows which are disposed in generally parallel, side-by-side fashion along the length of the web formed thereby. The web is fed under tension through relatively complex paths defined by rollers within one or more oxidizing ovens prior to being introduced into a carbonization furnace. Within the oxidizing oven the web makes multiple passes through different stages of the oven maintained at temperatures designed to achieve the desired oxidation of the PAN tows.

The nature of the PAN tows is such the the web cannot be allowed to remain at rest but must be kept continuously moving through the oxidizing oven when the oven is at oxidizing temperatures. To allow the web to remain at rest for any period of time would permit rapid deterioration and possible exotherming of the PAN tows. Moreover, even when the web is kept continuously moving through the oven, there cannot be any loose ends or knots in the tows. If loose ends of knots are present, they will usually exotherm in the hot oven resulting in interruption of the process and frequently the need to shut down the entire process and again introduce the web into the oxidation oven when cool.

For this reason the web of PAN tows is typically introduced into the oxidizing oven when the oven is cool. Introduction is accomplished by tying the individual tows to various iocations along the length of a threader bar having cables attached to the opposite ends thereof. The cables are used to pull the threader bar and attached tows into and through the oxidizing oven.

Because the oven is cool, the knots and loose ends of the tows where they are tied to the threader bar do not exotherm.

When the tows have been pulled completely through the oxidizing oven by the threader bar, the oven is turned on and is heated up to oxidizing temperatures as the web of tows continues to be fed therethrough. The oven normally requires approximately two hours to reach oxidizing temperatures, during which time the web is continuously pulled through the oven. When the oven reaches oxidizing temperatures, new portions of the web entering and pulled through the oven are oxidized in the desired manner. The preceding portions of the web which typically comprise about 200 to 400 pounds of PAN tows must be discarded as wastage. Because the PAN tows are relatively expensive, this represents a significant economic disadvantage in terms of the economics of the overall process.

It is seldom practical or for that matter possible to keep processes of this type running on an indefinite basis because of the need to keep personnel present at all times on an around-theclock basis. In addition, power failures and other interruptions usually result in the need to let the oxidizing oven cool off, following which the startup process described above must be repeated. Also the lengths of raw tow carried on the supply spools are limited, making periodic shutdown necessary. Accordingly, wastage of substantial quantities of PAN tows has become a routine and necessary part of carrying out such processes.

Because of the need to have a web of material under appropriate tension present within the oxidizing oven in preparation for the oxidation of fresh PAN tows, one technique commonly employed for shutting down the process is to continue running the web through the oven after the oven is turned off until the oven has cooled down sufficiently so that the web can be brought to rest. Upon subsequent startup, movement of the web through the oven is begun and the oven is heated up to oxidizing temperatures. The portions of the web which are run through the oven during the cooling off of the oven and the subsequent turning on thereof must be discarded as wastage.

In some cases the individual tows of the web are severed at the entrance to the oven after the oven has cooled down and the passage of the web therethrough stopped. When this occurs the process may be started by securing the web to be oxidized to the PAN tows residing within the oven. In such instances the individual tows of the web to be introduced into the oven are tied to the individual tows of the web residing within the oven, following which advancement of the web through the oven is begun. To prevent exotherming of the knots and loose ends where the tows are tied together, the oven is turned on in stages with each stage being turned on after the ties in the tows have cleared that stage.

Again, substantial amounts of the PAN tows are wasted before the oven can be brought up to operating temperature so as to begin oxidizing the web in the desired fashion.

Where the web comprises PAN fabric rather than individual tows of PAN material, lengths of the fabric have been joined together using various techniques such as that shown by way of example in U.S. Patent 4,077,822. In this patent webs of PAN tows are spliced together using a plurality of layers of silicone rubber adhesive. One such layer of adhesive is disposed between overlapping portions of the wbs with other layers of the adhesive being applied to the outsides of the overlapping web portions. Heat and pressure are applied to cure the layers of silicone rubber adhesive.

In our co-pending application No.

filed the same day as the present application.

corresponding to U.S. Application No. 483922 of 1 itch April 1983 entitled "Method of heat-treating a web of heat-sensitive material" and naming as inventors Khin Maung Lay, Stephen Edward Palguta, Ramon Blanco Fernandez and Santiago Cabalquinto, a process is described in which a web of PAN tows is introduced into an oxidizing oven by initially feeding a leader in the form of a web of silica cloth or other heat-resistant material through the oven and then heating the oven if the oven is not already hot. The trailing edge of the leader which remains outside of the oven is spliced to the leading edge of the web of carbonizable tows, and the leader is used to pull the web of tows into and through the hot oven.

Use of the heat-resistant leader greatly reduces wastage within the web of carbonizable tows.

This co-pending application describes a process of splicing the trailing edge of the leader to the leading edge of the web of PAN tows by taping, stitching and folding the two edges to form loops therein into which elongate rods are inserted. The two edges are then secured within a splice bar, the opposite halves of which define slots for receiving the two edges and the included rods. The splice bar may be removed to uncouple the leading edge of the web of carbonizable tows from the leader after the leading edge has passed through the oxidizing oven.

Although this technique for splicing the trailing edge of the leader to the leading edge of the web of PAN tows has been proven to be highly satisfactory, it would be desirable to provide an alternative method and apparatus for effecting the splicing of the webs which would have application in general to situations in which elongate webs are to be spliced together in a flexible manner as well as to the particular situation in which one of the webs is comprised of heat-sensitive material and therefore must be protected in high temperature environments against exotherming and other problems. The previously referred to U.S.Patent 4,077,822 does not provide guidance in this area as it addresses the different problem of splicing together different webs of carbonizable tows without consideration of the protection of one such web where the other web is of silica cloth or other heat-resistant material.

Methods and apparatus in accordance with the invention provide for a flexible splice of opposite elongate webs. Where one of the webs is comprised of heat-sensitive material, such web is joined to a second web in a manner which protects the heat-sensitive web in high temperature environments. Where the heatsensitive web is comprised of tows of carbonizable material, the flexible splice covers the exposed ends of the tows at the edge of the web in a manner which greatly minimizes the possibility of exotherming of the tows.

Joinder of a heat-sensitive web to a heat resistive web in accordance with the invention is accomplished by applying a coating of adhesive to a portion of the surface of the heat-resistive web to form a first adhesive layer. The end of the heat-sensitive web is then placed over part but not all of the first adhesive layer. A cover of heat resistive material is then provided and the underside thereof is coated with adhesive to provide a second adhesive layer. The cover is then placed over the end of the heat-sensitive web so that the second adhesive layer on the underside thereof bonds to the side of the heat-sensitive web opposite the heat-resistive web as well as to the portion of the first adhesive layer extending beyond the end of the heat-sensitive web. Heat and pressure are then preferably applied to cure the layers of adhesive.

The heat-resistive cover is preferably about equal in size to the first adhesive coating or layer and is applied so as to be generally coextensive with the first adhesive layer. Also, the web of heatsensitive material preferably covers approximately 60% of the first adhesive layer, leaving approximately 40% of the first adhesive layer exposed to the second adhesive layer at the underside of the cover. The ends of the tows defining the edge of the heat-sensitive web are preferably covered with tape prior to bonding of the heat-sensitive web to the first adhesive layer.

The web of heat-sensitive material may be comprised of tows of carbonizable material such as polyacrylonitrile material. The heat-resistive web and the cover may be comprised of silica cloth or other heat-resistive material. The layers of adhesive are preferably comprised of silicone rubber adhesive.

The invention is exemplified by the following more particular description of preferred embodiments, as illustrated in the accompanying drawings, in which: Fig. 1 is a plan view of apparatus used in a process for oxidizing a web of carbonizable tows; Fig. 2 is a perspective view of portions of the fill yarn inserter and adjacent tension stand of the apparatus of Fig. 1; Fig. 3 is a block diagram of successive steps in a method of introducing a web of carbonizable tows into the oxidizing ovens in the apparatus shown in Fig. 1; Fig. 4 is a block diagram of successive steps in a method of providing a flexible splice in accordance with the invention and which may be used in the method of Fig. 3; Fig. 5 is a perspective view of opposite webs and a cover useful in the method of Fig. 4; and Fig. 6 is an end view of the edges of the opposite webs and the cover of Fig. 5 together with the intervening layers of adhesive of the completed flexible splice.

A better understanding of the present invention may be had by first considering a process and apparatus for oxidizing a web of PAN or other carbonizable tows. Because such method and apparatus are described in detail in the previously referred to co-pending application they will only be briefly described herein.

Fig. 1 depicts apparatus used in a continuous process for oxidizing a web of carbonizable tows.

Such apparatus includes a rack 10 mounting a plurality of creels 12 which have tows of carbonizable material wound thereon. In the present example the tows consist of PAN material with each tow being comprised of from 3000 to 12,000 filaments depending in part upon how closely the tows are spaced together in the web formed thereby. As seen in Fig. 1 individual tows 14 are unwound from the various creels 12 and are drawn into a fill yarn inserted 16 via an assembly of combs 18. The combs 18 act as guides as the tows 14 are unwound from the creels 12 and pulled into a relatively flat, generally horizontal web 20 at the input to the fill yarn inserter 16. The web 20 has a width which can be as much as 53" and is comprised of as many as 600 of the tows 14.

The fill yarn inserter 1 6 is operative to interweave a fill yarn with the various tows 14 in order to hold the various tows 14 of the web 20 together for purposes of further processing. An example of the fill yarn inserter 1 6 is provided by the apparatus shown in U.S. Patent 4,1 73,990.

The fill yarn inserted by the fill yarn inserter 1 6 is typically removed following oxidation and further processing of the web 20 so that the tows 14 can be wound individually or in groups rather than only as part of the entire web 20.

After insertion of the fill yarn, the web 20 is fed into a tension stand 22 comprised of a plurality of spaced-apart rollers 24. Within the tension stand 22 the web 20 follows an alternating path around the various rollers 24 before exiting the tension stand 22 and being fed into a first oxidizing oven 26. The tension stand 22 is conventional in design and insures proper tension on the web 20 as the web enters the oxidizing oven 26.

The oxidizing oven 26 together with a second oxidizing oven 28 comprises an oxidizing oven assembly 30. Within the first oxidizing oven 26 the web 20 follows a relatively tortuous path as it winds around various different rollers 32 mounted at the opposite ends of the oven 26. From the first oven 26 the web 20 is drawn into the second oxidizing oven 28 where it again follows a relatively tortuous path as it winds around a plurality of rollers 34 at the opposite ends of the oven 28. While not shown in Fig. 1 the oxidizing ovens 26 and 28 are typically divided internally into a plurality of different stages, each of which may be maintained at a temperature somewhat different from the temperatures in the other stages.The rollers 32 and 34 within the ovens 26 and 28 cooperate with the tension stand 22 and a tension stand 35 outside of the exit end of the oven 28 in maintaining a desired tension in the web 20 as the web is drawn through the ovens 26 and 28. At least part of the tension occurs as the result of shrinkage of the PAN material comprising the web 20 as such material is oxidized. At the exit of the second oxidation oven 28 the web 20 is directed through the tension stand 35 and onto a rotating takeup roll 36 where it is stored in preparation for carbonization and further processing. The tension stand 35 is similar in construction to the tension stand 22.

Fig. 2 illustrates in greater detail a portion of the arrangement of Fig. 1 including in particular the fill yarn inserter 16 and the tension stand 22.

As seen in Fig. 2 the individual tows 14 which are drawn through the combs 1 8 from the creels 1 2 are drawn between a pair of opposite rollers 38 and 40 where the web 20 is formed. As described in previously referred to U.S. Patent No.

4,173,990, alternate ones of the tows 14 travelling between the rollers 38 and 40 are separated from the remaining ones of the tows 14 by heddles 42 and 44 forming a part of the fill yarn inserter 1 6. A rapier assembly 46 inserts a fill yarn 48 between the separated tows 1 4 just prior to the separated tows 14 again being converged into a single plane to refrom the web 20 complete with the fill yarn 48. As seen in Fig.

2 the fill yarn 48 alternates back and forth across the width of the web 20 in zig-zag fashion.

Fig. 3 sets forth successive steps in a method for introducing the web 20 into the oxidation ovens 26 and 28 which is described in greater detail in the above-mentioned co-pending application. Initially, a leader in the form of an elongate web of heat-resistant material is run through the oxidizing ovens 26 and 28, following which the trailing edge of the leader is spliced to a leading edge of the web of tows to be oxidized.

The leader is then used to pull the web of tows through the ovens 26 and 28 where the tows of the webs are oxidized in desired fashion. When the leading edge of the web of tows has cleared the tension stand 35 adjacent the exit end of the second oven 28, such end may be separated from the trailing edge of the leader. The use of a heatresistant leader enables the ovens 26 and 28 to be heated to oxidizing temperatures before the web of carbonizable tows is started into and through the ovens, thereby reducing or eiiminating wastage of the carbonizable tows.

As shown by a first step 52 in Fig. 3 the heatresistant leader comprising an elongate web of heat-resistant material such as silica or aramid cloth is fed into the oxidizing ovens 26 and 28 until the leader has passed completely or substantially completely through the ovens with the trailing edge thereof remaining outside of and adjacent the entrance 50 to the oven 26. In a second step 53 the oxidizing ovens 26 and 28 are heated up to oxidizing temperatures if they are not already so heated. In a third step 54 the leading edge of the web 20 formed by the tows 14 and provided by the fill yarn inserter 1 6 is spliced to the trailing edge of the leader. In a fourth step 56 feeding of the leader through the ovens 26 and 28 is continued so that the web 20 is fed into and then through the oxidizing ovens 26 and 28.When the leading edge of the web 20 of carbonizable tows 14 has passed all the way through both ovens 26 and 28 and the tension stand 35, then in a fifth step 58 such leading edge may be separated from the trailing edge of the leader.

In accordance with the method set forth in Fig.

3, the heat-resistant leader can be fed into the ovens 26 and 28 when the ovens have already been heated to the oxidizing temperatures. The leader can remain at rest within the heated ovens 26 and 28 without being adversely affected. In a more typical situation where the apparatus shown in Fig. 1 is to be shut down for a period of time, the heat-resistant leader is fed into the ovens 26 and 28 as the process is being shut down and the ovens cooled. Upon subsequent startup of the process, the ovens 26 and 28 are brought up to oxidizing temperatures while the heat-resistant leader remains at rest therein. In the meantime the trailing edge of the leader may be spliced to the leading edge of the web 20 so that upon reaching the oxidizing temperatures the leader and then the web 20 can be advanced through the ovens 26 and 28.

The above-mentioned co-pending application describes a method and apparatus for splicing the web 20 of carbonizable tows to the heat-resistant leader 78 in which the opposing edges of the webs are covered with opposite lengths of tape, with the portions of the tows of the web 20 which extend beyond the opposing length of tape then being trimmed off. Each of the edges so formed is then stitched along the length thereof and then folded over on itself so as to form a loop into which an elongate rod is inserted. The opposing edges and the included rods are then disposed between the opposite halves of an elongate splicing bar, with the opposite halves then being drawn toward each other by tightening screws along the length of the bar so as to secure the opposite webs within the splice bar.When the splice bar has been fed all of the way through the oxidizing ovens 26 and 28, the web 20 can be separated from the temperature-resistant leader by loosening the screws along the length of the splice bar so as to separate the opposite halves of the bar and release the edges of the webs previously secured therein.

The present invention provides an alternative method and apparatus for providing a flexible splice of the web 20 to the temperature-resistant leader, which method and apparatus are also applicable to other environments in which the opposing ends of two different elongated webs are to be joined together. The successive steps in such method are set forth in Fig. 4 in conjunction with the perspective view of Fig. 5 and the end view of Fig. 6.

Referring to Fig. 4, in a first step 64 a cover 66 of glass cloth, aramid cloth or other heat-resistant flexible material is prepared. As seen in Fig. 5 the cover 66 has a width W equal to the width of an elongate web 68 which forms the temperature resistant leader. The web 68 is also comprised of glass or aramid coth or other temperature resistant material. The width W of both the cover 66 and the web 68 is approximately 1/2" greater than the width of the web 20 of carbonizable tows. The cover 66 has a length L which may be any appropriate value but which is 1 0" in the present example.

In a second step 70 shown in Fig. 4 an adhesive coating or layer 72 is applied to the end of the web 68 adjacent an edge 74 thereof. The adhesive coating 72 is approximately equal in size to the cover 66.

In a third step 76 shown in Fig. 4 and end 78 of the web 20 of carbonizable tows is placed onto a portion of the adhesive coating 72 so that the web 68 and the included adhesive layer extend beyond each of the opposite edges of the web 20 by approximately 1/4". Prior to this, opposite lengths of tape are applied to opposite sides of the end 78 of the web 20 with the portions of the tows extending beyond the tape being trimmed away so as to form an edge 80 of the web 20. An upper length of tape 82 is shown in Fig. 5 with the opposing lower length of tape being hidden from view. The end 78 of the web 20 is placed on the adhesive layer 72 so that the end 78 covers part but not all of the adhesive layer 72. In the present example the end 78 of the web 20 covers approximately 60% of the area of the adhesive layer 72 such that the edge 80 is approximately 6" from the edge 74 of the web 68.This leaves a 4" wide strip of the adhesive layer 72 exposed.

In a next step 84 illustrated in Fig. 4 a second adhesive coating or layer 86 is applied to the underside of the cover 66. Both the layer 86 and the first adhesive layer 72 may be comprised of silicone rubber adhesive, GE RTV No. 31 being one commercial example. The coatings or layers 72 and 86 are each approximately 1/8" thick in the present example but can have any appropriate thickness as circumstances dictate.

In a next step 88 shown in Fig. 4 the cover 66 is placed onto the end 78 of the web 20 and the exposed portions of the adhesive layer 72 such that the cover 66 and the adhesive coating 86 are both generally coextensive with the first adhesive coating 72. This causes the adhesive coating 86 at the underside of the cover 66 to bond to the end 78 of the web 22 and to the exposed portions of the adhesive coating 72. The cover 66, having a width W which is 1/2" greater than the width of the web 20, extends beyond each of the opposite edges of the web by 1/4".

In a next step shown in Fig. 4 heat and pressure are applied to the webs 20 and 68 and the cover 66 and the included adhesive layers 72 and 86 to cure the adhesive. It has been found that with the use of a stannous octoate accelerator, silicone rubber adhesive substantially completely cures in 5-1 5 minutes with the application of 7-1 5 psi of pressure at a temperature of 200-3000F. The heating under pressure may be accomplished within an air press using opposite Teflon release sheets placed over opposite hot plates within the press.

The completed splice is shown in Fig. 6. It will be seen that the end 78 of the web 20 is sandwiched between and protected by the heatresistant web 68 and the heat-resistant cover 66.

The ends of the individual tows comprising the web 20 at the edge 80 are completely surrounded and enclosed by the cover 66, the web 68 and the intervening adhesive layers 72 and 86, thereby reducing or eliminating the possibility of exothermic reactions in the high temperature environments found in oxidation and similar processes. At the same time the splice has been found to be very strong in addition to being highly flexible. At the end of oxidation or other processing the web 20 can be separated from the web 68 by cutting across the width of the web 68 adjacent the splice or alternatively by cutting through the splice itself comprised of the web 68, the cover 66, the adhesive layers 72 and 86 and possibly a portion of the end 78 of the web 20.

While the invention has been particularly shown and described with reference to preferred embodiments thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the invention.

Claims

1. A splice between the overlapping adjacent ends of first and second elongate webs; the splice being provided by a first layer of adhesive adhering one face of one end of the first web to an end of the second web and a length of material adhered over the other face of the one end of the first web.

2. A splice according to claim 1 wherein the length of material extends beyond the one end of the first web to overlap the second web and is adhered to the latter.

3. A splice according to claim 1 or 2 wherein the first web is heat-sensitive and the second web and the length of material are heat-resistive.

4. A splice according to any of claims 1 to 3 wherein the first web is comprised of a plurality of tows of carbonizable material.

5. A splice according to any preceding claim wherein the second web and the length of material are of silica cloth.

6. A splice according to any preceding claim wherein the adhesive comprises silicone rubber adhesive.

7. A method of splicing the ends of first and second elongate webs of flexible material comprising the steps of overlapping one face of one end of the first web and an end of the second web with adhesive therebetween, and applying a flexible cover over the other face of the one end of the first web with adhesive therebetween.

8. A method according to claim 7 wherein the cover extends beyond the one end of the first web to overlap the second web with adhesive therebetween.

9. A method according to claim 7 or 8 including applying heat and pressure to the first and second webs and the cover to cure the adhesive therebetween.

10. A method according to any of claims 7 to 9 including taping the one end of the first web prior to adhering it to the end o, the second web.

11. A splice between the ends of elongate webs, the splice being substantially as hereinbefore described with reference to Figure 6 of the accompanying drawings.

12. A method of splicing elongate webs, the method being substantially as hereinbefore described with reference to Figure 4 of the accompanying drawings.

13. A method of splicing elongate webs, the method being substantially as hereinbefore described with reference to Figures 4 and 5 of the accompanying drawings.