GB2342136A

GB2342136A - A sheath for a fire protection sleeve

Info

Publication number: GB2342136A
Application number: GB9821270A
Authority: GB
Inventors: Sylvan Andrew Whalley
Original assignee: PREFORM TECHNOLOGIES Ltd
Current assignee: PREFORM TECHNOLOGIES Ltd
Priority date: 1998-10-01
Filing date: 1998-10-01
Publication date: 2000-04-05
Also published as: GB9821270D0

Abstract

A sheath 11 for a fire protection sleeve intumescent strip 17 which expands when subject to heat, wherein the intumescent strip 17 is housed in an expandable sheath 11 of a knitted fabric. The sheath is mainly knitted of a yarn made of an inorganic material (21, figure 3), e.g. glass fibre, and has portions knitted from a thermally degradable yarn (32, figure 3) so that on exposure to heat the thermally degradable yarn disintegrates allowing the fabric of the sleeve to ladder and expand with the intumescent material. The sheath 11 may have a single jersey tubular construction, or may be formed as two layers 12,13 joined together. Preferably, the thermally degradable fibres (32, figure 3) are knitted at regularly spaced intervals 16 along the length of the sheath 11.

Description

2342136 A Sheath for a Fire Protection Sleeve

Field

This invention relates to fire protection sleeves which include an intumescent strip and which are used around pipes or ducting to inhibit the spread of fire.

Backqround Fire sleeves are used around pipes etc. where they pass through walls, floors, ceilings etc. and include an intumescent material sometimes in strip form, which in the event of fire swells to form a fireproof seal between the wall and pipe/ducting. Some sleeves include a fLre protection collar made from metal foil which surrounds the intumescent material, see for example EP-A-0236539. At very high temperatures in excess of 1000 degrees centigrade the metal foil burns away and the intumescent material may expand by a factor twenty times its original volume.

on expansion the intumescent material may loose its cohesiveness and crumble.

The presenr invention seeks to provide a fire protection s-leeve having a more cohesive intumescent layer.

2 Statements of Invention

According to the present invention there is provided a sheath for a fire protection sleeve in which an intumescent strip is wrapped around an elongate object, the strip expanding when subject to heat, wherein the intumescent strip is housed in an expandable sheath of a knitted fabric, the sheath being knitted largely of a yarn containing inorganic material, and having at least a portion of one course knitted from a thermally degradable yarn so that on exposure to heat the thermally degradable yarn disintegrates allowing the fabric of the sleeve to expand in the coursewise and walewise direction of knitting.

The preferred thermally degradable yarn is one end of 167 decitex Grillon, available from EMS of Switzerland, or alteratively comprises a polyester yarn.

Preferably, the yarn is a class fibre yarn, or comprises mixed silica fibres and glass fibres. The preferred glass fibre yarn is 4 X Vetrotex 680 decitex flat T6 E glass.

Preferably the sheath is formed from two single jersey layers joined along their selvedges and the thermally degradable yarn is kn-itted in one layer only so that in 3 use, after the strip has been wrapped around the pipe or ducting, the thermally degradable material lies adjacent the pipe or ducting.

Alternatively, the sheath is formed of a tubular knitted fabric single jersey construction, knitted on a circular knitting machine, and having at least one course formed from thermally degradable yarn.

The sheath is formed from fabric having the thermally degradable yarn knitted in selected wales in a plurality of spaced apart courses so that after the yarn disintegrates the knitted fabric ladders along said respective wales. The sheath may be provided with non-laddering portions at each end thereof by knitting a plurality of courses in an air textured glass fibre yarn, preferably 3 X 1660 decitex air textured glass yarn.

The invention also relates to a fire protection sleeve incorporating a sheath as described above.

Also according to the invention there is provided a method of manufacture of a sheath for a fire protection sleeve in which an intumescent strip is placed in said sheath, wherein the sheath is of knitted fabric, the fabric having been knitted from an inorganic fibre yarn and having selected courses knitted at least in part from a thermally degradable yarn.

4 Preferably the fabric is knitted in two layers on a flatbed knitting machine being two independently operable needle beds with the two layers being joined at their selvedges, wherein at least a portion of at least one course of one layer of the sheath is knitted from a thermally degradable material. The knitting macine may be equiped with a presser foot or other device to assist in take down of the knitted fabric.

The thermally degradable material is knitted on one needle bed only, and is preferably knitted on spaced apart needles, preferably on alternate needles in the needle bed for its respective course of knitting. Pref erably the thermally degradable yarn is knitted in spaced apart courses of knitting, preferably every 10-15 courses.

Alt-ernatively, the sheath is knitted on a small diameter single jersey circular knitting machine Description of Drawings

The invention will be described by way of example and with reference to the accompanying drawings in which:

Fig-1 is a plan view of a sheath according to the present invention, Fig. 2 is a cross-sectional view of a sheath with the intumescent material therein, Fig. 3 is a knitting diagram for theknitted structure shown in Fig. 1, and Fig. 4 is an knitting diagram of one end of a needle bed showing the linking of the two layers using double jersey wales.

Fig.5 shows a sheath in which a portion has expanded after the thermally dergradable yarn has ruptured.

Detailed Description of the Invention

In order that the invention may be more fully understood reference is made to a flat V-bed knitting machine. The flat bed machine is well known and has a pair of independently operable needle beds.

The knitting machine used in the present invention is a Dubied NHF Handflat having 5 gauge needles. The machine can operate with a plurality of different yarns each of which is associated with a respective yarn carrier and cam box on the machine. The cam box traverses the needle beds supplying yarn to needles as desired in each direction of travel.

With reference to Fig.1 there is shown a sheath 11 knitted substantially from glass fibre yarn in a two-layer 12,13 single jersey construction with the two layers 12,13 joined together at the selvedges 14,15. As shown, the walewise direction of knitting extends vertically and the coursewise direction extends horizontally. In one layer 13 only, a 6 thermally degradable yarn is knitted in spaced apart wales in a plurality of spaced courses 16. Because the knitted loops in these courses 16 are larger the courses of the thermally degradable yarn are clearly visible on the exposed face of said one layer 13.

At least one end of the sheath is open to allow a strip of intumescent material 17 to be inserted into the sheath. The open mouth 18 (only one of which is shown) of the sheath is formed from knitting air textured glass yarn in both layers to prevent laddering at the ends of the sheath.

With reference to Fig-3 there is shown a knitting diagram for a sheath according to the invention. The knitting of the fabric, which is of a generally single jersey tube construction takes place on a flat bed knitting machine having a front needle bed for knitting a front layer of fabric and a rear needle bed for knitting a rear layer of fabric. The needle beds are shown schematically in Fig. 3 and each dot represents a needle. The lower row F represents the front needle bed and the upper row R represents the rear needle bed. The arrow represents the direction of travel of the machine yarn carrier.

Although only ten needles are shown in each needle bed it should be appreciated that any number or needles can be selected depending upon the size of the sheath. If the desired glass fibre yarn 21 is knitted in setup courses A, 7 and is fed to all needles on both beds R and F for one traverse of the carrier leftwards. On the return the yarn 21 is knitted on all needles on the rear bed R only. The set-up will close the end of the sheath 11.

The tubular sheath is then knitted in the yarn 21 with the yarn being knitted in a series of repeat units B in which the yarn is fed to all needles on the front bed during the leftwards traverse and all needles on the rear needle bed on the rightwards traverse. Any number of repeat units B may be knitted as is desired, the preferred number being ten repeats.

After knitting ten repeat units B, a thermally degradable yarn 32, on another yarn carrier, is knitted on selected spaced apart needles, preferably alternate needles, on the front bed F during a leftwards traverse C. When the cam box returns rightwards the yarn carrier remains at the left hand side of the bed and there is a blank traverse and yarn is not fed to any needles, as is shown at traverse D.

The further ten repeat units B are knitted with yarn 21 followed by the a blank traverse E which returns the cam box for the yarn carrier for the degradable yarn 32 to the left side, followed by a rightwards traverse F of that carrier knitting the yarn 32 on alternate needles on the front bed F. The traverses B,C,D, B,E, & F form a larger repeat unit Z which may be knitted for as many times as is 8 desired, preferably 9 or 10 times.

After knitting the desired number of repeats Z the sheath is finished by knitting a further five repeat units B in yarn 21, --ollowed by a further ten repeat units B in an air zextured glass fibre yarn 33 on another yarn carrier.

These last courses form the mouth 18 of the sheath 11 and help prevent complete laddering of that area of the sheath.

If it is desired that the sheath is open at both ends, knitting may commence with the yarn 33 being knitted for a desired number of repeat units B, preferably ten repeat units B, before commencing knitting the repeat units Z.

The two layers 12 and 13 of fabric formed on the two needle beds R and F can be linked at their selvedges by the yarn being f ed f rom the rear bed carrier to the f ront bed at the end of one traverse and by feeding yarn from the front bed carrier to the rear needle bed at the end of the other 20 traverse.

Alternatively the sides of the two layers 12 and 13 of the sheath may be joined by two or three wales of double jersey knitting as shown in Fig.4, or alternatively by using 25 stitch transfer techniques.

The sheaths 11 may be knitted as a plurality of sheaths formed sirt,.'. 1ltaneous-y across a large needle bed with the 9 single jersey tubular sheaths being separated wales of double jersey construction.

When a fire protection sleeve incorporating intumescent material within the sheath is subject to heat which triggers expansion of the intumescent material, the thermally degradable yarn 32 disintegrates allowing the sheath to ladder along the wales which incorporate loops of the yarn 32, which in turn allows the sheath to expand in the coursewise direction without contracting in the walewise direction. The natural slack in knitted material may also allow for some walewise elongation of the sheath. The expanded sheath is shown in Fig. 5.

The sheath 11 may also be formed on a small diameter circular knitting machine having 5 to 7 gauge needles with a high/low butt needle selection, and at least two yarn feeders. The inorganic yarn is preferably 1 end Vetrotex ET 140 D glass and the thermally degradable yarn is 1 end 167 decitex polyester yarn.

The glass yarn is knitted on all needles in alternate courses, separated by courses of polyester yarn knitted on alternate needles, or other combination e.g 1 in 3, or 2 in 3 etc.. This produces a continuous tube which is simply cut to length.

When subject to heat the polyester yarn melts allowing the 1 L 0 tube to ladder as before.

in yet another method the sheath could be produced in double jersey fabric on a circular rib machine having needles in both a dial and cylinder and having at least two yarn feeders. The yarn is preferably 1 end of Vetrotex ET 140 D which is knitted in alternate courses on all needles of both the dial and cylinder, alternated by knitting the thermally degradable yarn on all needles, or spaced needles, in either the dial or cylinder.

A similar construction can be obtained on a V bed flat knitting machine by knitting alternate courses in glass fibre yarn on all needles on both needle beds, alternated with thermally degradable yarn on all needles in either the front or rear needle bed.

Fabrics manufactured by the latter two methods would require seamming of the two selveedges to form a tube, or could just be wrapped around the intumescent material prior to being inserted in any metal collar.

Claims

1. A sheath for a fire protection sleeve in which an intumescent strip is wrapped around an elongate object, the strip expanding when subject to heat, wherein the intumescent strip is housed in an expandable sheath of a knitted fabric, the sheath being knitted largely of a yarn made of an inorganic material, and having at least a portion of one course knitted from a thermally degradable yarn so that on exposure to heat the thermally degradable yarn disintegrates along the fabric of the sleeve to expand in the coursewise and walewise direction of knitting.

2. A sheath as claimed in Claim 1 wherein the sheath is formed as two layers of single jersey material which are joined together at the selvedges of the two layers.

3. A sheath as claimed in Claim 2 wherein the thermally degradable fibre is knitted in only one of the two layers.

4. A sheath as claimed in any one of Claims 1 to 3, wherein the thermally degradable fibre is knitted for at least a portion of a plurality of spaced courses of fabric forming the sheath.

5. A sheath as cla;lmed in Claim 4 wherein the 12 thermally degradable fibres are knitted at regularly spaced intervals of between 10 to 20 courses.

6. A sheath as claimed in any one of Claims 3, 4 and 5 when dependant upon Claim 2 wherein the degradable fibre is knitted for the full length of a respective course between the two selvedges of the sheath.

7. A sheath as claimed in Claim 1, wherein the sheath has 10 a single jersey tubular construction.

8. A sheath as claimed in any one of Claims 1 to 7, wherein for each course or portion of a course formed from the thermally degradable yarn, the yarn is knitted in 15 spaced apart wales.

9. A sheath as claimed in Claim 8, in which the sheath has a plurality of spaced courses of thermally degradable yarn is knitted in aligned wales in the respective courses. 20

10. A sheath as claimed in C iaim 8 or Claim 9, wherein the thermally degradable yarn is knitted in wales at intervals of between 1 and 3 wales.

11. A sheath as claimed in any one of the preceding Claims, when dependant upon Claim 2, wherein the two layers of single jersey material may comprise different numbers of courses and or wales so that the sheath takes ui) a curved 13 shape.

12. A sheath as claimed in any one of Claims 1 to 11, wherein the inorganic material is at least one of glass, 5 silica, or asbestos.

13. A fire protection sleeve incorporating a sheath as claimed in any one of Claims 1 to 12.

14. A method of manufacture of a sheath for a f ire protection sleeve in which an intumescent strip is placed in a sheath of fabric, wherein said fabric is a knitted fabric, the fabric having been knitted from an inorganic fibre yarn in a substantially single jersey construction and having selected courses knitted at least in part from a thermally degradable yarn

15. A method as claimed in Claim 14, wherein the fabric is knitted in two layers on a flat-bed knitting machine having two independently operable needle beds with the two layers being joined at their selvedges, and at least a portion of at least one course of one layer of the sheath is knitted from a thermally degradable material.

16. A method as claimed in Claim 15, wherein the thermally degradable yarn is knitted on one needle bed only.

14

17. A method as claimed in Claim 14 wherein the sheath is knitted in circular construction on a circular knitting machine.

18. A method as claimed in Claim 16 or Claim 17 wherein the thermally degradable yarn is knitted only on selected needles.

19. A method as claimed in any one of Claims 14 to 18 wherein the thermally degradable yarn is knitted at spaced courses.