The present invention relates to a gripper for use in restrained water fittings including flange adaptors and couplings. In particular, the gripper of the invention can be used in a gripper assembly for large diameter water fittings for example on water supply pipes.

Background of the Invention

Devices which are used for joining water supply pipes are required to grip the pipes so that they are not displaced by force of water in the pipes.

However, known devices do not provide a sufficiently good grip on the pipes.

In light of the problems discussed above, various proposals have been made, but there remains a need for an improved gripper which address one or more of the problems presented by prior art arrangements. In this regard, the present invention seeks to provide an alternative gripper which preferably addresses one or more of the problems presented by prior art arrangements.

Summary of the Invention

In accordance with a first aspect of the present invention there is provided a gripper for gripping a pipe wherein the gripper comprises a body having a length being a distance between a first set of two parallel planes defined at a proximate end and a distant end of the body respectively with reference to a longitudinal axis of the pipe, and a width being a distance between a second set of two parallel planes defined at sides of the body, each plane of the second set being substantially perpendicular to the planes of the first set, the body defining a substantially planar surface from which project a plurality of triangular teeth defined by first and second surfaces which are inclined to each other at an angle of about 40 degrees to about 60 degrees.

Preferably, the first surface of the teeth extends substantially normal from the surface of the body and the second surface of the teeth is inclined to the first surface between the first surface and the distant end of the body. In other words, each tooth has a cross section substantially defined by a right angled triangle with the right angle proximate to the proximate end of the body. Advantageously, it has been found that this geometry provides the best possible grip on a pipe.

Preferably, the teeth defined by first and second surfaces which are inclined to each other at an angle of about 45 degrees. Advantageously, it has been found that a gripper having teeth having an angle of 45 degrees proved to be the most effective angle in achieving good gripping results. In addition, advantageously, when the angle at which the first and second surfaces of the teeth are inclined to each other is about 45 degrees the teeth have been found to effectively dig into the pipe surface and stop the pipe from pulling out when under end load.

Preferably, between the proximate end and distant end of the body, the teeth are arranged in two rows to four rows. Most preferably, the teeth are arranged in three rows. Advantageously, it has been found that arranging the teeth in this number of rows provides superior gripping onto the pipe.

Preferably, between the proximate end and distant end of the body, the teeth arranged in two columns of teeth and a channel is provided between each column of teeth.

Preferably, the channel has a width of about 2mm to about 8mm and this is located equidistant between the sides of the body. Most preferably, the width of the channel is about 5mm. This has been found to allow for better excess material distribution if a soft pipe material is used. Advantageously, it has been found that this channel size and location provides superior gripping performance and allows excess pipe material on soft pipe to run down the channel.

Preferably, each gripper has a width of about 45mm to about 75mm. Advantageously, it has been found that this width allows for an even load distribution on the pipe, leading to a better gripper performance. Preferably, between the proximate end and distant end of the body, the gripper comprises six teeth arranged in three rows and two columns of teeth having a channel between each column. Advantageously, it has been found that this number of teeth provides superior gripping to the pipe.

Advantageously, the position of the tooth closest to the distant end of the body and the tooth closest to the proximate end of the body has been shown to impact the grippers performance, the tooth position has been found to provide an effect on the amount of work each tooth provides, this was shown through testing where the depth of cut varied throughout the gripper teeth location.

Advantageously, it has been found that the spacing of the teeth (the gap between each tooth) remarkably improves the gripping on the pipe and improves the performance. Regarding the spacing of the teeth, remarkably, it has been found that reducing the teeth gap reduces the overall effective gripping area on the teeth. In view of this, once the optimum number of teeth is determined, preferably, the gripper comprises the maximum spacing available between teeth taking account of other physical constraints on the gripper. Preferably, each tooth is equidistant from adjacent teeth.

Preferably, the depth of teeth, being the extent to which each tooth projects from the surface of the body, is about 2.5mm to about 7.50mm. Most preferably, the depth of the teeth is about 5mm. Advantageously, it has been found that teeth having this depth provide superior gripping results without damaging the pipe surface. The teeth dug into the pipe most effectively and restrained the pipe from pulling out. In addition, the depth of cut into the pipe by the teeth has been found to be within the allowable limits.

Preferably, the tooth sharpness of each tooth, being the closest distance between the first and second surfaces of each tooth is about 0.1mm to about 1mm. Most preferably, the tooth sharpness of each tooth, being the closest distance between the first and second surfaces of each tooth is about 0.5mm. Advantageously, it has been found that the sharpness of each tooth has a significant effect on the performance of the gripper, with sharper teeth engaging more with the pipe surface, providing a superior gripping force.

Preferably, the gripper is manufactured of stainless steel. Advantageously, this material has been found to provide superior performance.

In accordance with a second aspect of the present invention there is provided a gripper assembly comprising a gripper according to the invention together with a retention insert, star washer and a bolt.

Preferably, the bolt has a diameter of about 10 to about 20mm, more preferably about 16mm and threads having a pitch of about 1mm to about 3mm, more preferably about 2mm. Most preferably, the bolt is an M16 bolt.

Advantageously, the gripper of the invention accommodates a large diameter wide tolerance pipe. The teeth gripping geometry have proved to be effective when under tensile load. The pull out force achieved has been found to be sufficient for the gripper to be used. This is due to the shape of the teeth as well as the spacing of the teeth. Studies have been performed and they have shown the critical effects of changing the spacing between each tooth. The angle of the tooth allows the teeth to dig effectively into the pipe providing superior gripping onto the pipe.

Brief Description of the Drawings

The invention will now be further described with reference to the accompanying drawings in which:

Figure 1 shows a gripper assembly including an embodiment of a gripper according to the invention;

Figure 2 shows an embodiment of a gripper according to the invention under end load; Figure 3 shows an arrangement for testing grippers according to the invention. As shown in Figure 3, once a tensile machine is turned on the pipe is pulled from both directions. Once the grippers start to fail there is movement of the pipe, as the pipe is moving the gripping force is lost, this test was carried out multiple times for multiple configurations of gripper;

Figure 4 shows a an embodiment of a gripper according to the invention having three teeth;

Figure 5 shows an embodiment of a gripper according to the invention having two teeth;

Figure 6 shows an embodiment of a gripper according to the invention having six teeth;

Figures 7 to 13 show embodiments grippers according to the invention having various geometries;

Figures 14 to 16 show embodiments of grippers according to the invention having various depths of teeth. Figure 14 shows a gripper having three teeth having a depth of 5mm; Figure 15 shows a gripper having two teeth having a depth of 2.5mm; and Figure 16 shows a gripper having three teeth having a depth of 2.5mm.

Figures 17 and 18 show embodiments of grippers according to the invention having teeth of various widths. Figure 17 shows a gripper having teeth of 35% reduced width; and Figure 18 shows a gripper having teeth of multi offset reduced width;

Figures 19 and 20 show embodiments of grippers according to the invention having teeth at various angles. Figure 19 shows a gripper having teeth of 45 degree tooth angle; and Figure 20 shows a gripper having teeth of 60 degree angle; Figure 21 shows an embodiment of a gripper according to the invention having blunt teeth;

Figure 22 shows an embodiment of a gripper according to the invention having a single channel between rows of teeth;

Figure 23 shows isometric, side and bottom views of an embodiment of a gripper according to the invention.

Detailed Description of the Invention

It will be appreciated that aspects, embodiments and preferred features of the invention have been described herein in a way that allows the specification to be written in a clear and concise way. However, unless circumstances clearly dictate otherwise, aspects, embodiments and preferred features can be variously combined or separated in accordance with the invention. Thus, preferably, the invention provides a device having features of a combination of two or more, three or more, or four or more of the aspects described herein. In a preferred embodiment, a device in accordance with the invention comprises all aspects of the invention.

Within the context of this specification, the word "about" means plus or minus 20%, more preferably plus or minus 10%, even more preferably plus or minus 5%, most preferably plus or minus 2%.

Within the context of this specification, the word "substantially" means preferably at least 90%, more preferably 95%, even more preferably 98%, most preferably 99%.

Within the context of this specification, the word "comprises" means "includes, among other things" and should not be construed to mean "consists of only".

The invention provides a gripper (1) for use in restrained water fittings including flange adaptors and couplings. In particular, the gripper (1) of the invention can be used in a gripper assembly (2) for large diameter water fittings for example on water supply pipes (20).

As shown in Figure 23, an embodiment of the invention comprises a stainless steel gripper (1) for gripping a pipe wherein the gripper (1) comprises a body (3) having a length (4) being a distance between a first set of two parallel planes defined at a proximate end (5) and a distant end (6) respectively with reference to the pipe, and a width (7) being a distance between a second set of two parallel planes defined at sides (8)(9) of the body, each plane of the second set being substantially perpendicular to the planes of the first set, the body (3) defining a surface (10) from which project a plurality of triangular teeth (11) defined by first and second surfaces (12)(13) which are inclined to each other at an angle of about 45 degrees.

The first surface (12) of the teeth (11) extends substantially normal from the surface

(10) of the body (3) and the second surface (13) of the teeth (11) is inclined to the first surface (12) between the first surface (12) and the distant end (6) of the body (3). In other words, each tooth (11) has a cross section substantially defined by a right angled triangle with the right angle proximate to the proximate end (5) of the body (3).

The gripper (1) comprises six teeth (11) arranged in two columns of teeth (11) arranged in three rows and a channel (23) is provided between each column of teeth

(11). The channel (23) has a width of about 5mm and this is equidistant between the sides (8)(9) of the body (3). Each gripper (1) has a width of about 45mm to about 75mm.

The depth of teeth (11), being the extent to which each tooth (11) projects from the surface (10) of the body (3), is about 5mm. The tooth sharpness of each tooth, being the closest distance between the first and second surfaces ( 12)( 13) of each tooth (11) is about 0.1mm to about 1mm. The gripper (1) is part of a gripper assembly (2) shown in Figure 1. A retention clip (14), also referred to as a retention insert, and star washer (15) combination is used to lock the gripper (1) in place in the assembly (2). In this regard, the body (3) defines a chamber (16) having first (upper) and second (lower) flanges (17)(18) and the retention clip (14) and star washer (15) are inserted between the first and second flanges (17)(18), the retention clip (14) being adjacent the second flange (18) and the star washer (15) being adjacent the first flange (17).

Apertures defined in the first flange (17), star washer (15), retention clip (14) and second flange (18) are aligned and an M16 bolt (19) shown in Figure 1 is threaded through the apertures and torqued on the product which provides a normal force on the gripper (1) to the pipe (20) as shown in Figure 2, allowing the gripper teeth (11) to dig inside the pipe (20). When the product is pressurized an end load is subjected to the pipe (20) as shown in Figure 2. The gripper teeth (11) provide frictional and mechanical support to prevent the pipe (20) from sliding.

Examples

Comparative tests were carried out and these are described below.

Introduction to the test method

A large diameter water fitting is being developed which will be used on water supply lines. Due to the working pressure of the product the product which is under development includes a total of 30 grippers. In order to provide a model of the large product for testing purposes, a smaller sized model was manufactured which included only 3 grippers equally spaced around a pipe.

The grippers could be bolted down using various torque values and pulled along the longitudinal axis of the pipe. The pull out force which the grippers needed to achieve in the small product was calculated by taking the end load which the product will be exposed to and diving it by the number of required grippers, this value then represented the amount of load each gripper was required to resist in order to pass the test. On the small scale model the value needed was 160kN which equated to around 53 kN per gripper.

A tensile machine was used to pull a pipe from test grippers from both directions. The test set up is shown in Figure 3. Once the grippers started to fail there was movement of the pipe, as the pipe is moved the gripping force is lost. The test was carried out multiple times for multiple designs of gripper.

Various configurations of gripper teeth angle, teeth gap and teeth spacing were tested. Comparative tests were completed on different gripper specimens whilst focusing on a specific properties of the gripper to verify how through modifying the gripper superior gripping results could be achieved. The following parameters were investigated in depth and the effect of changing those parameters was documented.

Example 1

Parameter 1) Number of teeth

The shape of the gripper evolved throughout the project, different gripper geometries were tested and the overall shape of the gripper evolved throughout the project. The number of teeth (shown in Figures 7 to 13) was investigated as a key potential factor which led to the contribution of the gripping force. Also the number of teeth was investigated to see how changing the number of teeth affected the performance of the gripper when in contact with a pipe. The spacing between each tooth was also investigated.

Example 2

Parameter 2) Teeth Geometry

Figures 7 to 13 show grippers having various geometries.

Table 1 - results table from channel vs no channe

The grippers were initially tested at 60Nm of torque on the radial bolt, figure 6 showed very weak performance therefore moving forward the channel was incorporated into all designs, it can be seen that by increasing the torque figure 5 performed better, however the margin of change was small. The depth of cut was larger which suggests that greater torque helps the gripper to dig more into the pipe. By increasing the number of channels better results were not achieved, a reason for this was due to losing a lot of tooth surface area across the gripper leading to poor gripping.

The effect of adding a channel to the gripper was investigated, when the gripper comes into contact with a softer pipe such as polyethylene pipe the teeth dig in easier, when the product is under end load and the pipe wants to pull out the channel in the middle acts as a runner for any excess polyethylene. Both of the grippers were tested and the results can be seen in table 1. Following continuous studies on the gripper, the shape of the gripper was considered to be a factor which was causing the gripper to have a low pull out force, the shape of the gripper was made to match the surface of the pipe. Different teeth shapes were also tested from table three high pull out force can be seen for each design as well as an increased depth of cut.

Example 3

Parameter 3) Effect of tooth depth

Figures 14 to 16 show grippers having different tooth depths.

Figure 14 - three teeth 5mm deep Figure 15 - two teeth 2.5mm deep

Figure 16 - three teeth 2.5mm deep

Table 2: Results from tooth depth analysis

From the results presented in table two it is clear that the tooth depth has significant effects on the pull out force. Bigger tooth depth means a larger engagement with the pipe which can also be reflected on the depth of cut. Torque was also investigated and by increasing the force on the radial bolt the grippers gripped onto the pipe for longer. Example 4

Parameter 4) Gripper Tooth Width

Figure 17 - 35% reduced width Figure 18 - Multi offset reduced width

Table 4 - Gripper width analysis

Analysing the impact of reducing the gripper width can be seen in table 4. The main reasons for this analysis was to see if the overall cost of the product can be brought down without having affecting the grippers performance, by reducing the width considerably the results were poor, there was much less gripping force on the pipe and the gripper would fail early on. Through reducing the width slightly good results were seen which suggests that maintaining a high surface area across the whole gripper was beneficial to the gripper's performance.

Example 5

Parameter 5) Gripper Teeth Angle

Figure 19 - 45 degree tooth angle Figure 20 - 60 degree angle

Table 5 - different tooth angle analysis

Teeth angle proved to be one of the critical parameters for this gripper, when the tooth angle was set at 60 degrees the results were very poor and the overall performance was poor. However when the angle became smaller to 45 degrees the tooth engagement with the pipe was much better and the results were closer to the goal. The depth of cut was also considerably smaller for the 60 degree tooth angle, this was because the gripper was sliding off the pipe rather than gripping the pipe.

Example 6

Parameter 6) Teeth Sharpness

Figure 21 - blunt teeth

After every test the results were analysed by the engineering team, one of the reasons why the blunt teeth design was tested was due to the potential of the gripper slicing through the pipe due to teeth sharpness rather than gripping the pipe, however the table below shows how by blunting the teeth the performance of the gripper was worse.

Table 6 - blunt teeth analysis

Example 7

Parameter 7) Torque applied to the radial bolt

From the start to finish of the gripper experiments different torque values were used, these can all be seen in the result tables throughout the document. By applying a lower torque value the engagement between the gripper and the pipe was poor which had an effect on the overall performance. The depth of cut was also an important factor to consider because the depth of cut can only be within 10% of the pipe thickness. Polyethylene pipe is widely produced in many different SDR ratings therefore it was important that the design will work with all pipe sizes and thickness relevant to the product application. In the end the value of torque used was 160Nm, this has given the best results across many different gripper variants. Example 8

Finalised gripper design and tensile testing results

Figure 22 - Single channel gripper (final)

Table 7 - Single channel gripper (final) analysis

After a thorough analysis and many different geometries being used the gripper which provided the best results was the single channel gripper, the angle of the face was created to match the outer diameter of the pipe which meant that the gripper was fully engaged with the pipe, the spacing on the teeth and the tooth depth was determined through carrying the tooth depth analysis, similarly to the angle of the teeth proved to be a critical factor in performance of the gripper. The final design was used on the large diameter water fitting and through the development of the gripper the overall amount of grippers was reduced.

The tests carried out demonstrated that the gripper according to the invention was remarkably more effective that grippers outside the scope of the invention.

The above described embodiments have been given by way of example only, and the skilled reader will naturally appreciate that many variations could be made thereto without departing from the scope of the invention.