GB2091830A

GB2091830A - Plastics tube fitting

Info

Publication number: GB2091830A
Application number: GB8102145A
Authority: GB
Original assignee: VFP CORP
Current assignee: VFP CORP
Priority date: 1981-01-23
Filing date: 1981-01-23
Publication date: 1982-08-04

Abstract

A fitting 18 for securing the end of a plastics tube 12 in a connector 8 comprises a rigid tubular member 20 having arms 36 with detents 38 for holding the fitting in place in the connector. To anchor the tube 12 in the fitting 18, the member 20 has two sets of inwardly projecting barbs 26 and 28. The barbs 26 are of greater axial extent but radially shorter than the barbs 28 and are accordingly stiffer than the barbs 28. The barbs 26 bite into relatively hard plastics tubing and hold it in place, but relatively soft tubing tends to flow around the barbs 26 so that it is not properly gripped. The relatively soft tubing deflects the softer barbs 28 axially inwards as the tube is pushed into the fitting and then if an attempt is made to pull the tubing out of the fitting, the barbs 28 bend back and bite into the tubing and so anchor it in place. The fitting is thus capable of gripping plastics tubing of a wide range of hardness. <IMAGE>

Description

SPECIFICATION Plastics tube fitting This invention relates to fittings which are adapted to receive the end of a length of plastics tubing and to hold the tubing firmly in place in the fitting despite forces which might be encountered in use tending to separate the tubing from the fitting. The fitting may for example, be adapted to be inserted into and locked in place in a female tube connector. The connector is adapted to form a seal with the end of the plastics tubing.

One of the problems which has arisen in the past with such fittings is that any given fitting operated successfully with plastics tubing only within a limited range of Tubing with a hardness outside the limited range was too easily pulled out of the fitting.

Accordingly the main object of this invention is to provide a fitting which will receive and firmly retain plastics tubing throughout a relatively broad range of hardness of the tubing.

To this end, according to this invention, a fitting for receiving and locking within it a length of plastics tubing comprises: a) an elongated relatively rigid hollow tubular member constituting a beam section; b) a plurality of compression barbs and a plurality of locking barbs projecting from the internal face of said member and disposed around its internal circumference; c) said compression barbs being located at sub stantiallythe midpoint of the length of said beam section and being thicker in an axial direction than said locking barbs to such an extent that said compression barbs are capable of transmitting a large compression force on the wall of said tubing from said tubular member to hold the tubing in place in the fitting; and, d) said locking barbs being thinner in an axial direction than said compression barbs to such an extent that said locking barbs are capable of flexing under longitudinal movement of tubing into said member and of digging into the surface of said tubing upon reverse movement of the tubing to retain said tubing in place.

Preferably, the locking barbs extend radially inwards further than the compression barbs.

An example of a fitting in accordance with the invention is illustrated in the accompanying drawings in which: Figure 1 is a longitudingal sectional view of the fitting in a connector taken along the line 1-1 of Figure 2 with the end of a length of plastics tubing received and locked within it; Figure 2 is an end view of the connector, fitting and tubing as seen from the right hand end of Figure 1; Figure 3 is a cross-section of the fitting by itself taken along the line 3-3 of Figure 1; Figure 4 is a fragmentary section to a larger scale taken along the line 4-4 of Figure 3, showing the position of one of the locking barbs of the fitting as the tubing is being inserted into the fitting; Figure 5 is a view, similar to Figure 4, but showing the position of the locking barb when an attempt is made to pull the tubing from the fitting; and, Figure 6 is a fragmentary section to a larger scale taken along the line 6-6 of Figure 3, illustrating the action of one of the compression barbs of the fitting.

A tubular connector 8 is externally screw theaded at 10 so that it may be screwed into the wall of a body to which it is desired to make a fluid-tight connection with plastic tubing 12. The connector 8 comprises a female member having a central bore 14, into which the tubing 12 is inserted. The internal surface of the bore 14 is provided with an a annular bead 16 which is adapted to form a fluid tight seal with the outer surface of the tubing 12.

In order to lock the tubing 12 firmly in place within the connector 8, there is provided a fitting 18 comprising a moulded tubular body formed with a relatively massive "beam" section 20 between its end 22 and a point 24. As shown in Figure 3, the beam section 20 of the fitting 18 is provided with a plurality of compression barbs 26 of comparatively short radial length and a plurality of locking barbs 28 of comparatively longer radial length between the compression barbs 26.

The construction and the action of the compression barbs 26 may be seen more clearly in Figure 6.

Each barb 26 is wedge shaped with a leading surface 30 at a low angle with the internal surface of the beam section 20 of less than twenty degrees, preferably about fourteen degrees. This low angle causes the surface 30 to act as a camming surface along which the leading edge of the tubing 12 is pressed as the tubing is inserted into the fitting 18.

Particularly if the tubing is quite hard, the tubing will exert a large component of its pushing force outwardly against the beam section 20 causing it to deflect outwardly by a small amount. As a result, the beam section exerts a strong compression force through the compression barbs 26 upon the outside surface of the tubing 12. The harder the tubing, the greater will be this compression force. This force is, of course, greatest upon the tubing 12 at the apex 32 of the wedge shaped barb 26. In order to maximize the force, the apex 32 is located substantially at the midpoint of the length of the beam section 20.

The trailing surface 34 of the barb 26 forms a much sharper angle with the internal face of the beam section 20 and is preferably disposed at about ninety degrees with respect to the leading surface 30. As a result, when a force is exerted upon the tubing 12 tending to pull it out of the fitting 18, only a small component of the force will be exerted through the trailing surface 34 outwardly against the beam section 20. This small component will be insufficient to overcome the strong compression force exerted by the beam section 20 against the barb 26. Therefore, the compression force will keep the tubing 12 locked firmly in place.

However, if the tubing 12 is sufficiently soft, it may tend to flow around the compression barbs 26 and thus be released from the locking action of the compression barbs. This difficulty is overcome by means of locking barbs 28. Each locking barb is not only radially longer than the compression barbs 26 but is also axially thinner. As shown most clearly in Figures 4 ancd 5, each locking barb 28 is preferably formed with an apex angle of less than twenty degrees, preferably about twelve degrees. The section 20 is formed with each barb 28 inclined towards the left hand end of the section 20 as seen in the drawings, that is axially inwardly of the section 20, the inclination being preferably of the order of sixty degrees or less, preferably about forty degrees.As a result of its radial length and axial thinness, each locking barb is sufficiently flexible to flex under the pressure exerted by tubing 12 which is soft enough to flow around the compression barbs 26. As shown in Figure 4, when the tubing 12 is inserted into the fitting 18 within the beam section 20, in the direction of the arrow in Figure 4, the locking barbs 28 will flex with their apices pointing in the direction of such travel. When, however, a force is exerted on the tubing 12 tending to pull it out of the fitting 18, as shown in Figure 5, the apex of each locking barb 28 will dig into the surface of the tubing 12 and will tend to straighten the barb 28. Thus the greater the pull on the tubing 12, the greater will be the extent to which the locking barbs 28 dig into the tubing 12.

Thus the softer tubing will be locked firmly in place as well as the harder tubing, as described above. The fact that each barb 28 is radially longer than the barbs 26 ensures that despite any constricting deformation of the tubing 12 by the barbs 26, the end of each barb 28 will project into the path of the tubing 12 sufficiently to be engaged and flexed by the tubing 12.

A pair of resilient latching arms 36 extend from the end of the beam section 20 remote from the end 22.

Each arm 36 carries a latching detent 38 which is adapted to snap into a detent groove 40 formed in the right hand end of the connector 8. As the fitting 18, carrying the tubing 12, is inserted into the connector 8, the detents 38 will engage in the grooves 40 and lock the assembly consisting of the fitting 18 and the tubing 12 into the connector 8.

Each arm 36 extends beyond its detent 38 and terminates in a release button 41. Thus the fitting 18 may be released by manually depressing the release buttons 41.

Claims

1. A fitting for receiving and locking within it a length of plastics tubing, the fitting comprising : a) an elongated relatively rigid hollow tubular member constituting a beam section; b) a plurality of compression barbs and a plurality of locking barbs projecting from the internal face of said member and disposed around its internal circumference; c) said compression barbs being located at substantially the midpoint of the length of said beam section and being thicker in an axial direction than said locking barbs to such an extent that said compression barbs are capable of transmitting a large compression force on the wall of said tubing from said tubular member to hold the tubing in place in the fitting; and d) said locking barbs being thinner in an axial direction than said compression barbs to such an extent that said locking barbs are capable of flexing under longitudinal movement of tubing into said member and of digging into the surface of said tubing upon reverse movement of the tubing to retain said tubing in place.

2. Afitting according Claim 1, in which the locking barbs extend radially inwards further than the compression barbs.

3. Afitting according Claim 1 or Claim 2, in which each of said compression barbs has a camming leading surface, which faces towards the direction in which said tubing is inserted into said fitting, disposed at an angle of less than 20 degrees with respect to the axis of said member and a trailing surface disposed at a substantially greater angle to said axis than said leading surface.

4. Afitting according to any one of Claims 1 to 3, in which each of said locking barbs has an apex angle of less than 20 degrees.

5. A fitting according to Claim 4, in which the axis of each of said locking barbs is inclined in the direction of insertion of said tubing at an angle of 60 degrees or less with respect to the axis of said fitting.

6. Afitting according to any one of the preceding Claims, in which said tubular member is provided with a pair of latching arms extending from one end of said beam section, each of said latching arms carrying a latch detent adapted to be received into a detent in a connector or other body into which said fitting is intended to be connected.

7. Afitting according to Claim 6 in which the outer end of each latching arm is provided with a latch releasing button.

8. A fitting according to Claim 1, substantially as described with reference to the accompanying drawings.

9. A connector for connecting plastics tubing, the connector comprising a tubular body having a bead adapted to seal against the external surface of the tubing and a fitting in accordance with any one of the preceding Claims held within the body for locking the tubing in the body.