Improvements in or relating to collets for tube couplings

Abstract: The disclosure relates to a cylindrical collet (12) for a tube coupling body (10), the collet having at least one arm (26) of arcuate cross section which is free to flex radially under the action of an encircling tapered cam surface (19) in the tube coupling body. The arm has a projecting tooth (27,28) on its radially inner side having an inner edge (29) to engage and grip a tube (11) extending through the collet. The inner edge (29) of the tooth extends linearly transversely of the arm to engage the tube tangentially and, with pressure from said cam surface, to bite into the surface of the tube.

Description: This invention relates to collets for tube couplings which receive and automatically grip and hold a tube inserted in the coupling. More particularly the invention relates to collets for tube couplings of the kind having a body formed with a throughway open at one end and having a encircling cam surface tapering towards said open end with a cylindrical collet located in the open end of the throughway and projecting into the throughway to receive a tube, the collet being formed with flexible arcuate section arms having projecting teeth on their inner surfaces to engage the tube and engageable on their outer surfaces with the tapered cam surface so that outward movement of the collet causes the arms to be pressed inwardly to grip and hold the tube in the bore. Hence, a pull on the tube, causes the collet arms to be pressed into tighter engagement with the tube. The tube may be released from such a coupling by pressing or holding the collet axially inwardly of the coupling body whilst the tube is withdrawn. Examples of said tube couplings are described and illustrated in my U.K. Patent No. 1520742, U.K. Patent No. 1573757 and U.K. Patent No. 2132296. My U.K. Patent No. 1573757 discloses a particular form of collet in which the inner surface of the radially flexible arm of the collet is formed with an inwardly projecting tooth to engage and grip the tube inserted through the collet. The projecting tooth enhances the grip of the arm with the tube and it is an object of the present invention to further enhance the grip which the arm can apply to the tube. This invention provides a cylindrical collet for a tube coupling, the collet having at least one arm of arcuate cross section which is free to flex radially under the action of an encircling tapered cam surface in the tube coupling, the arm having a projecting tooth on its radially inner side having an inner edge to engage and grip a tube extending through the collet, wherein the inner edge of the tooth extends linearly transversely of the arm to engage the tube tangentially and, with pressure from said cam surface, to bite into the surface of the tube. More specifically, the or each flexible arm may be formed by spaced slots extending through the wall of the cylindrical collet from one end of the collet. In one specific arrangement in which a single flexible arm is provided, the slots defining the arm may be spaced apart by 90° around the axis of the collet and the remaining part-cylindrical portion of the collet supports the tube against the action of the resilient arm. In another specific arrangement, the collet may be formed with four equi-spaced resilient arms, at least two of which arms disposed diametrically opposite each other have said linerarly edged teeth. In a modified form of the latter arrangement, all four arms may be provided with said linearly edged teeth. In any of the above arrangements, the collet may be formed from a flexible plastics material and the or each flexible arm of the collet having a tooth may have a metal insert moulded into the arm to project from the inner side thereof and provide the linear edged tooth. In a particular preferred construction according to the invention, the metal insert may comprise an arcuate base portion moulded into the arm with an inner peripheral portion projecting from the inner surface of the arm and angled to provide an inwardly facing linear edge projecting through the tooth to engage and grip the tube extending through the collet. In any of the above arrangements, the end of the collet in which said resilient arm or arms are formed is also formed with an enlarged encircling head around its outer periphery to engage the tapered cam surface in the throughway. Also, in any of the above arrangements, the end of the collet remote from said flexible arm may have an out-turned encircling flange to enable the collet to be gripped. The invention also provides a tube coupling comprising a coupling body having a throughway open at one end and a collet in accordance with any of the above arrangements, the coupling body having a cam surface encircling the throughway and tapering towards said open end to engage the flexible arm or arms of the collet. The following is a description of some specific embodiments of the invention, reference being made to the accompanying drawings in which: Figure 1 is a longitudinal section through a tube coupling including a collet for locking a tube in the coupling; Figure 2 is an end view of the collet employed in the tube coupling of Figure 1; Figure 3 is a section along the line 3-3 on Figure 2; Figure 4 is a view looking in the direction of the arrow A on Figure 3; Figure 5 is a similar view to Figure 2 showing a further form of collet; Figure 6 is a section along the line 6-6 on Figure 5; Figure 7 is a view looking in the direction of the arrow B on Figure 6; Figure 8 is an end view of yet a further form of collet in accordance with the invention; Figure 9 is a section along the line 9-9 of Figure 8; Figure 10 is a view looking in the direction of the arrow C on Figure 9; and Figures 11 to 13 show further modifications. Referring firstly to Figure 1 of the drawings, there is shown a tube coupling comprising a coupling body 10 for affecting a coupling to a tube 11 using a collet 12. A throughway 13 extends into the coupling body from an open end 14 and has a shoulder 15 forming an end stop for the tube 11 when inserted in the coupling. An enlarged diameter portion 16 of the throughway contains an O-ring 17 which abuts the shoulder 18 in the coupling body and which, in use, seals against the external surface of the tube 11 and against the internal wall surface of the throughway in the coupling. The enlarged diameter portion 16 of the throughway extends towards the open end 14 and is formed with a tapered portion 19 providing an encircling cam surface tapering towards a narrow diameter section 20 adjacent the open end 14 of the body. The collet 12 which is moulded in a plastics material extends into the coupling body from said open end 14 and comprises a cylindrical portion 21 having, on the outer side of the tube coupling body, an out-turn flange 22 to enable the collet to be gripped for manipulating the collet. The other end 23 of the collet extending into the throughway is formed with an encircling head 24 and slot 25 extend from the end 23 of the collet towards the flanged end of the collet at four equi-spaced locations around the collet to divide the collet into four arcuate cross section flexible arms 26. Arcuate plates 27 are moulded into the head portions of the arms and inner edge portions 28 of the plates form teeth which project from the inner surfaces of the head portions and are angled to provide inwardly facing edges 29 to engage and bite into the surface of the tube 11 inserted in the collet. The angle of the inner edge portions can be varied as indicated at 30 according to the grip required. The edge portions could be angled up to 90° to the plates 27 but typically would be angled at about 40° to the plate portions. A small extraction movement of the collet 12 engages the outer sides of the head portions 24 with the tapered cam surface 19 in the throughway to press the head portions inwardly and cause the edges 29 of the arcuate plates to bite into the surface of the tube to grip and hold the tube in the tube coupling body. Reference is now made to Figures 2-4 of the drawings which show an improvement to the collet in accordance with the invention in which the projecting inner edge portion or tooth 28 on the arcuate plate 27 extends linearly to provide a straight edge 29 to bite tangentially into the tube as best seen in Figure 4. Figures 5-7 show a modified version in which only two of the resilient arms 26 disposed diametrically across the collet are formed with inwardly projecting teeth, the other arms being of plain form to engage the surface of the tube without biting into it. Figures 8-10 show yet a further arrangement in which only one pair of slots 25 is formed 90° apart around the collet to provide one resilient arm 26 with its inwardly projecting tooth 28 and the remaining three-quarter cylindrical part of the collet is of plain internal form to engage the tube. It will be understood that the collet can be formed with any practical number of flexible arms according to the size of the collet and the arrangements illustrated above are by way of example only. In those instances where a plurality of flexible arms are provided each with an inwardly projecting tooth to engage the tube, the engagement of one arm only with the tube should be sufficient to retain the tube so that should the teeth of the other arm or arms fail for any reason, such as overheating or chemical attack, the remaining arm will provide sufficient grip to retain the tube. Figure 11 of the drawings shows a modification to the edge portion 28 of a plate 27 in which the inner edge 29 is formed with serrations 31. Figure 12 shows a version with spaced apart serrations and Figure 13 shows a single serration.

Claims: A cylindrical collet for a tube coupling body, the collet having at least one arm of arcuate cross section which is free to flex radially under the action of an encircling tapered cam surface in the tube coupling body, the arm having a projecting tooth on its radially inner side having an inner edge to engage and grip a tube extending through the collet; wherein the inner edge of the tooth extends linearly transversely of the arm to engage the tube tangentially and, with pressure from said cam surface, to bite into the surface of the tube. A collet as claimed in Claim 1, wherein the or each flexible arm is formed by spaced slots extending through the wall of the cylindrical collet from one end of the collet. A collet as claimed in Claim 2, and in the case where a single flexible arm is provided, wherein the slots defining the arm are spaced apart by 90° around the axis of the collet and the remaining part-cylindrical portion of the collet supports the tube against the action of the resilient arm. A collet as claimed in Claim 2, wherein the collet is formed with four equi-spaced resilient arms at least two of which arms disposed diametrically opposite each other have said linearly edged teeth. A collet as claimed in Claim 2, wherein all four arms are provided with said linearly edged teeth. A collet as claimed in any of the preceding claims, wherein the collet is formed from a flexible plastics material and the or each flexible arm of the collet having a tooth has a metal insert moulded into the arm to project from the inner side thereof and provide the linear edged tooth. A collet as claimed in Claim 6, wherein the metal insert comprises an arcuate base portion moulded into the arm with an inner peripheral portion projecting from the inner surface of the arm and angled to provide an inwardly facing linear edge to engage and grip the tube extending through the collet. A collet as claimed in Claim 6 or Claim 7, wherein the inner edge of the metal insert is formed with one or more serrations. A collet as claimed in any of the preceding claims, wherein the end of the collet in which said resilient arm or arms are formed is also formed with an enlarged encircling head around its outer periphery to engage the tapered cam surface in the throughway. A collet as claimed in any of the preceding claims, wherein the end of the collet remote from said flexible arm has an out-turned encircling flange to enable the collet to be gripped and moved axially with respect to the tube coupling body to lock/release a tube in the body. A tube coupling comprising a coupling body having a throughway open at one end and a collet as claimed in any of the preceding claims, the coupling body having a cam surface encircling the throughway and tapering towards said open end to engage the flexible arm or arms of the collet.

Inventors: GUEST JOHN DEREK, GUEST, JOHN DEREK
Applicants: GUEST JOHN D, GUEST, JOHN DEREK
Application year: 1993
Main classification: F16L37
IPC codes: F16L37, F16L21