AU2003200629B2 - Butt Welding Apparatus and Method of Butt Welding Therefor - Google Patents

Description

21. FEB. 2003 17:13 WRAY AND ASSOCIATES NO. 950 P. 4/25 P/00/011 28/5/91 Regulation 3.2

AUSTRALIA

Patents Act 1990

ORIGINAL

COMPLETE SPECIFICATION STANDARD PATENT Name of Applicant: Actual Inventors Address for service is: Canaust Management Services Pty Ltd Michael John Brophy lan Leonard Kreplins WRAY ASSOCIATES Level 4, The Quadrant 1 William Street Perth, WA 6000 Attorney code: WR Invention Title: "Butt Welding Apparatus and Method of Butt Welding Therefor Details of Patent Application No: 53654/99 filed on 12 August 1998 The following statement is a full description of this invention, including the best.

method of performing it known to me:- 21. FEB. 2003 17:13 WRAY AND ASSOCIATES NO. 950 P. 5/25 -2- "Butt Welding Apparatus And Method Of Butt Welding Therefor" Field of the Invention This invention relates to butt welding apparatus for welding objects in co-axial alignment and more particularly to apparatus for welding plastic objects, such as polyethylene piping, in co-axial alignment Background Art Plastic piping such as polyethylene piping that is employed in agricultural, mining and industrial applications has traditionally been joined by the use of joining devices that are commonly hard plastic threaded devices that comprise several parts.

These joining devices are separate to the sections of pipe that they join together.

These joins are therefore susceptible to leakage and, over time, often contribute to splitting and/or rupturing of the pipe at the point where the device is connected to the pipe. Also these joining devices often degrade and become brittle through prolonged exposure to the sun. This contributes to fracturing and rupturing of pipe joins.

One of the reasons for the continued use of these joining devices is that the alternative method of butt welding is typically unavailable in the field due to a lack of electrical supply and a lack of portability In the design of the butt welding devices.

A further problem with butt welding in the field is the need to have accurate cutting of the pipes, so that their end faces are located in a plane that is perpendicular to the longitudinal axis of the pipe.

Achieving an end face that is sufficiently perpendicular to the longitudinal axis of the pipe requires the use of additional equipment that may also be difficult to power in the field remote from conventional 240 volt power supplies.

21. FEB. 2003 17:13 WRAY AND ASSOCIATES NO. 950 P. 6/25 A further problem with operating butt welding devices for plastic piping In the field is accommodating the various diameters of piping that are encountered so that they are welded in coaxial alignment.

Prior art devices such as US 5,241,157 provide a series of collars for locating different diameter pipe in coaxial alignment. This requires an operator of a butt welding device to carry with them a range of collars for welding the various diameters of pipe that may be encountered.

This reduces the durability and portability of these butt welding devices as their collars may be broken or lost during their movement from site to site. The need for a series of collars in this manner also increases production costs of these butt welding devices.

The preceding discussion of the background to the invention is intended only to facilitate an understanding of the present invention. It should be appreciated that the discussion is not an acknowledgement or admission that any of the material referred to was part of the common general knowledge anywhere in the world as at the priority date of the application.

Disclosure of the Invention It is an object of the present invention to provide a portable butt welding device for plastic components, for example plastic pipes such as polyethylene pipes, that has a simplified control mechanism for the heating element that heats the end face of the components being butt welded.

According to a first aspect of the present invention there is provided butt welding apparatus comprising a heater plate for heating objects located by said apparatus for later butt welding of aid objects wherein said heater plate is in operative association with a power supply and is further adapted to attain thermal equilibrium at a temperature in a pme-defined range of temperatures independently of regulation of said direct current power supply.

21. FEB. 2003 17:4 WRAY AND ASSOCIATES NO.950 P. 7/25 -4- Preferably said equilibrium temperature is dependent on ambient temperature.

Preferably said heater plate is thermally associated with a heater sink whereby said element maintains said thermal equilibrium.

According to a second aspect of the present invention there is provided a method of butt welding in a butt welding apparatus having a heater plate for heating objects prior to abutting said objects so as to formn a butt weld, said method comprising the steps of: 1) heating said heater plate with a power supply; and 2) thermally associating said heater plate with a heat sink whereby said heater plate attains a thermal equilibrium independent of regulation of said power supply.

Preferably said apparatus further comprises thermal insulation between said heater plate and said heat sink whereby limiting the amount of heat dissipated through said heat sink- Brief Description of the Drawings Embodiments of the invention -shall now be described by way of example only and with reference to the accompanying drawings in which: Figure 1 is a perspective representation of a butt welding apparatus; Figure 2 is the butt welding apparatus of Figure 1 with two sections of pipe located in clamping arrangements; Figure 3 is a perspective representation in greater detail of a heater element and associated handle of Figure 1; and Figure 4 is an expoded isometric representation of the heater plate in Figure 3.

21. FEB. 2003 17:14 WRAY AND ASSOCIATES NO. 950 P. 8/25 Best Mode(s) for Carrying Out the Invention Throughout the specification, unless the context requires otherwise, the word "comprise" or variations such as "comprises" or "comprising", will be understood to imply the inclusion of a stated integer or group of integers but not the exclusion of any other integer or group of integers.

Butt welding of plastic parts is the operation of bringing the end faces of plastic components to a near liquid state and compressing these end faces together so that their semi-liquid polymers inter-mix whereby the components are welded at their end faces upon returning to ambient temperature.

Butt welding in this manner requires two plastic items to be heated to a predetermined temperature and for them to be brought into contact under some pressure.

In operation embodiments of the inventibn locate objects, typically plastic objects, in co-axial alignment so that they may be butt welded. The plastic objects are usually polyethylene pipes used in rural irrigation and mining applications. These pipes are typically of the type specified in Australian Standard AS2698.2-1985. A clamping arrangement is used to achieve this that is universal in the sense that it operates with a variety of pipe diameters without the need to utilise different fittings for these different diameters.

Further embodiments bring plastic objects that are to be welded into abutment with a heating plate. The heating element is preferably planar so that an end face of a plastic object that is in abutment with the element melts, at least partially, whereby the end face assumes the planar profile of the heating element. This assists the butt welding apparatus to be a portable apparatus as the need for components to have their end faces cut with precision is reduced.

A further embodiment utilises a self regulating heating element that attains thermal equilibrium independent of power supply regulation. Equilibrium is maintained, in part, through use of the chassis of the butt welder apparatus as a heat sink so that the element does not overheat. This enables the heating 21. FEB. 2003 17:14 WRAY AND ASSOCIATES NO. 950 P. 9/25 element to operate off of a constant voltage Supply Such as a 1 2V lead acid battery independently of voltage and current regulation circuitry. This increases the portability of the butt welding apparatus.

Refening now to Figure 1 which is a perspective representation of butt welding apparatus 100. It comprises a chassis 115 that supports a first clamping arrangement 105 on the left hand side of the chassis and a second clamping arrangement 110 on the right hand side of the chassis. In the present embodiment each clamping arrangement comprises a slide having a first surface 145 and a second surf-ace 146 that are angularly disposed relative to each other.

The first and second surfaces 145 and 146 respectively are elongate planar surfaces mhat may be forrmed from sections of C-channel, or angle though fabricated plate may also be used.

The clamping arrangements may alternately be comprised of at least first and second support members disposed at an angle to each other. These support members are preferably planar elements. Such an alternate arrangement may be a cradle arrangement having an elongate central member located in a horizontal plane with a plurality of support elements angularly disposed to the horizontai plane. The plurality of support members comprise first and second sets disposed at an angle relative to each other.

In operation a pipe is located in abutment with support members and is prevented from moving relative to the support members due to their relative angular displacements.

The clamping arrangements are preferably supported by a planar support surface on the chassis 115 that locates eifthr the first 145 or second 146 surface of each of the clamping arrangements. This support surface of the chassis enables the clamping arrangements to be lOmted relative to each other so that the first surfaces 145 of each clamping arrangement ios, 110 are aligned in a co-linear manner and so that the second surfaces 146 of each clamping arrangement 105, 110 are aligned in a co-linear manner.

21. FEB. 2003 17:14 WRAY AND ASSOCIATES NO. 950 F. 10/25 -7- The chassis 115 may alternately have a pair of support surfaces that are disposed relative to each other at an angle that corresponds to the angle at which the first and second surfaces 145 and 146 of the clamping arrangements are disposed relative to each other. This angle is preferably Where the clamping arrangements comprise a section of C-channel or a section of angle or fabricated plate, a longitudinal apex 150 is formed intermediate the first and second surfaces 1 '45 and 146 respectively of the clamping arrangements 105, 110. When the dlamping arrangements are located on the chassis 115 in co-linear alignment the longitudinal apex 150 of each clamping arrangement is coaxial.

The clamping arrangements 105 and 110 are moveable relative to the chassis 115 so as. to effect a butt welId between a pair of pipes or to b ring the end fa ces of pipes being welded into proximity With a heating element. Preferably the clamping arrangements are moveable along an axis parallel with a plane containing the elongate surfaces 145 and 146 of the clamping arrangements 105, 110. This movement of the clamping arrangements 105, 100 is such that the co-linear alignment of the first surfaces 145 and the second surfaces 146 is maintained. In other words where a damping arrangement has a longitudinal apex 150, movement of the dlamping arrangements relative to the chassis is in a direction that is parallel with the longitudinal apex 150 of each clamping arrangement.

The clamping arrangements operate to locate sections of pipe in abutment with the first surface 145 and the second surface 146. When two sections of pipe with similar or identical diameters are located, one on each of the clamping arrangements 105 and 110, the co-linear alignment of the clamping arrangement cause the sections of pipe to be located coaxially relative to each other.

The arrangement allows pipes of similar though not identical diameters to be joined. For example, imperial and metric equivalent diameter pipes may be joined, Where such a join is implemented the walls of the pipe need to overlap to an extent that enables a mechanically strong join to be Tonmed. Under Australian 21. FEB. 2003 17:15 WRAY AND ASSOCIATES NO.950 P. 11/25 Standard AS2698.2-1 985 variations in outside diameter and inside diameter by 0.9mm and 0.3mm respecively can be anticipated.

When the clamping arrangements are moved relative to the chassis so as to bring the sections of pipe into abutment with each other to form a buff weld, the movement of the clamping arrangement should be such as to bring the sections of pipe into abutment with coaxial alignment.

The clamping arrangements further comprise clamp member 160 and clamp member support 155. The clamp member support 155 operates so that the clamp member 160 is moveable relative to the first surface 145 and the second surface 146 of the clamping arrangement. In operation the clamp member 160 is moved relative to the clamp support 155 so as to contact a section of pipe that has been located in the clamping arrangement in abutment with the first surface 145 and the second surface 146. This contact between the clamp member 160 and the pipe operates to retain the object In abutment with the first surface 145 and the second surface 146 of the clamping arrangement. Preferably the dlamp member 160 is a threaded member that is received by a threaded aperture in the clamp member support 166.

Preferably the clamp member 160 contacts an object located in~ abutment with the surfaces 145 and 146 of the clamping arrangement at an angle relative to a longitudinal axis of the first and second surfaces 145 and 146. In this way the clamp member 160 has a line of action that both retains the object in abutment with the first and second surfaces 145 and 146 respectively of the clamping arrangement and also has a line of action that reacts against longitudinal forces imparted to the object. Preferably the clamp member ISO subtends an angle relative to the first and second surfaces 145 and 146 that dissects the angle at which fth surfaces 145 and 146 are disposed relative to each other.

Preferably each clamping arrangement has a handle 135 to effect manual movement of the clamping arrangement relative to the chassis. Other mechanical, electrical or hydraulic means of moving the clamping arrangements 21. FEB. 2003 11:15 WRAY AND ASSOCIATES NO. 950 P. 12/25 may be used, however in a portable device it is preferable that manual operation be provided so as to retain simplicity of design in the butt welding apparatus.

The butt welding apparatus further comprises a heater plate 125 and handle 140 for moving the heater plate between an operative position that is intermediate the clamping arrangements and a non-operative position, where the heater plate is remote from the clamping arrangements 105 and 110.

The chassis 115 may contain heater plate location means, that is preferably a location slot 120 that receives the heater plate 125 when in the operative position. This location slot 120 limit lateral movement of the heater plate 125 when located in the operative position due to contact between the heater plate and an end face of a pipe located within the damping arrangement This contact typically occurs when the object is being heated before it is welded.

The heater plate should attan operating temperature before this contact occurs.

The slot also limits contact between the heater plate 125 and the chassis so as to minimise heat loss from the heater plate 125 thmough the chassis 115. It also allows pipe ends to abut a central area on the heater plate which ensures that the end face of the pipe adjacent the chassis attains operating temperature.

Referring now to Figure 2 which is a perspective representation of the butt welding apparatus with the first dlamping arrangement 105 retaining a first section of pipe 200 and the second clamping arrangement 110 retaining a second section of pipe 205. The first section of pipe 200 has a first end face 210 and similarly the second section of pipe 205 has a second end face 215. In operation the sections of pipe preferably have similar diameters for example within the tolerances defined under Australian Standard A82698.2-1 985 so that they can be buff welded together in co-axial alignment so as to form a continuous section of pipe.

In operation the end faces of the pipes 200 and 215 should pmoject beyond the first and second surfaces 145 and 146 so that the pipes Can abut without the clamping arrangements coming into contact with each other.

21. FEB. 2003 17:15 WRAY AND ASSOCIATES NO. 950 P. 13/25 In operation the first pipe 200 is located into the first clamping arrangement so that its external wall abuts the first elongate surface 145 and the second elongate surface 146. Effectively the pipe is retained against the apex 150 formed between the first and second sections 145 and 146 respectively of the clamping arrangement. Hence the outer surface of the piping section abuts the first and second surfaces 145 and 146 in a tangential manner. This allows different diameter piping to be accommodated by the clamping arrangements 105 and 110 whilst locating these various diameter piping sections in coaxial alignment.

This occurs because the first surfaces 145 of the first and second clamping arrangements 105 and 110 are in co-linear alignment and because the second surfaces 146 of the first and second clamping arrangements 105 and 110 are in co-linear alignment. Hence two sections of pipe, each one located in one of the two clamping arrangements 105 and 110, have their outer walls in co-linear alignment due to the co-linear alignment of the first and second surfaces 145 and 146 of the clamping arrangements. As their outer surfaces are in co-linear alignment the sections of pipe are in coaxial alignment where these sections of pipe are of similar diameters. This alignment of outer surfaces of piping sections allows the clamping arrangements to accommodate a variety of pipe diameters, without needing to change collars or other types of fittings.

Each of the clamping arrangements 105 and 110 has a clamp member 160 and clamp member support 115. The clamp members 160 are elongate members that are located at an angle relative to a plane that is perpendicular to the longitudinal axis of the first and second surfaces 145 and 146 in their respective damping arrangements, In particular the clamp members 160 on both clamping arrangements are located on a portion of the clamping arrangement so as to contact the pipe sections adjacent a point where the pipes abut during a butt welding procedure or where the pipes contact the heater plate during a heating procedure. Preferably the clamp member 160 contacts the pipe a sufficient distance away from the end face that prevents deforming of the outer wall and end face of the pipe 21. FEB. 2003 17:16 WRAY AND ASSOCIATES NO. 950 P, 14/25 -11- The provision of elongate clamp members 160 provides a single point of contact between the clamp member 160 and a section of pipe clamped into the clamping arrangement. This single point of contact is advantageous for butt welding of plastic pipes, such as polyethylene pipes. This is because these plastic pipes typically have a' natural radius of curvature from being wound onto a drum after manufacture. This natural radius of curvature does not tend to spring out of the pipes and so needs to be accounted for by the clamping arrangements. A single point of contact between the clamp member 160 and the pipe allows the pipe to curve around this single point of contact.

In operation the butt welding apparatus operates according to the following steps. Plastic objects such as polyethylene pipes that are to be butt welded are located in the clamping arrangements. The heater plate 125 is then moved into an operative position by means of heater plate handle 140 so that the heater plate is located within location slot 120.

The heater plate may already be at an operative temperature which is preferably above 200'C and below 220°C for polyethylene pipe though temperatures above 220'C can produce adequate welds. To achieve this operating temperature the heater plate is connected to a 12 Volt DC power supply and allowed to stand until a heater element located internally to the heater plate 125 causes the heater plate 125 to attain this operating temperature.

When the heater plate 125 is at this operating temperature the clamping arrangements are moved along the chassis so that the sections of pipe retained in the clamping arrangement contact the heater plate. The end faces of the pipes in contact with the heater plate are left to stand so as to saturate at the operational temperature of the heater plate 125. This saturation typically occurs over a narrow length of pipe as typically the pipes being butt welded are poor thermal conductors. Saturation of the pipe at the operational temperature of the heater plate is typically identified by the formation of a bead of semi liquid plastic material at the end face of the pipe that is in contact with the heater plate 125.

21. FEB. 2003 17:16 WRAY AND ASSOCIATES NO.950 P. 15/25 -12- Advantageously the heater plate is a planar element. This enables the heat of the plate 125 to square off the ends of the plastic pipe that contact it In other words the semi-liquid state of the end face of the pipe enables the end i~ce to assume a profile corresponding with the profile of the heater plate.

This use of a contact heating plate in a portable device is particularly advantageous as it reduces the need for precision cutting of end faces of plastic pipes and other objects that are to be butt welded.

Once the end faces of the objects that are to be butt welded have saturated at welding temperature, and thereby formed a bead of semi-liquid material, the heater plate 125 may be removed to a non-operative position that is remote from the clamping arrangements. Preferably the clamping arrangements are moved so that the end faces no longer abut the heater plate 125 before the heater plate is moved to the non-operative position.

Once the heater plate has been removed, the clamping arrangements are moved together so that the beads of plastic material, on the end faces of the objects being butt welded 7 contact one another. The clamping arrangements are retained in this position until the semi liquid material has returned to ambient or near ambient temperatures, whereby a join is formed between the two sections of pipe.

Referring now to Figure 3 which is a schematic representation of the heater plate 125 and the handle 140 to which it is attached.

The heater plate is preferably made of two sections of 6mm thick aluminium or aluminium alloy plate making the heater plate 12mm thick overall, Other metals may also be used, however it is preferable that they have thermal conductivity properties. Other metals may require different thickness plate for strength considerations. Lugs 300 attach fth heater plate 125 to the handle 140 by use of fastening means 315. It is preferable that the lugs 300 are insulated from the handle 140. The handle 140 may be made of metal so that fth handle can operate as a heat sink for the heater plate 125. This use of a heat sink assists 21. FEB. 2003 17:16 WRAY AND ASSOCIATES NO. 950 P. 16/25 -13with regulating the operating temperature of the heater plate 125, in particular it assists with limiting the upper temperature attained by the heating plate.

Fibrous washers may be located intermediate the heater plate 125 and the handle 140. These fibrous washers act as thermal insulators so as to reduce the amount of heat that is conducted between the heater plate and the handle 140.

The use of two lugs 300 to locate the heater plate 125 onto the handle assists with reducing the amount of heat that is transferred from the heater plate 125 to the handle 140. This helps the heater plate 125 attain its minimum operating temperature of 200'C.

In operation this thermal arrangement between the heater plate and the handle 140 allows the heater plate to attain an equilibrium temperature independently of voltage and current regulation circuitry.

The external surface of the heater plate that contacts the end faces of objects that are to be butt welded, is preferably coated with a non-stick coating such as polytetra fluoroethylene woven glass fabric coated with PTFE. Such material is available from as Chemstik 100 available from Chemfab in the United Kingdom.

The heater plate is preferably made in two halves that are located in a back to back arrangement. It is believed that 6mm aluminium plate provides sufficient strength in these halves to withstand warping and other defects occurring at operational temperatures. The plate 125 preferably provides an operational area having a 75mm diameter.

Referring now to Figure 4a which is an exploded representation of two back to back halves that form the heater plate 125. Each heater half comprises a recess 405 that locates a resistive heating element 400. When these halves are placed in the back to back arrangement the recesses form a cavity internal to the heater plate 125.

The resistive heating element is located internally to the cavity. Preferably the recess in each half provides equal thickness of metal from the operational 21. FEB. 2003 17:16 WRAY AND ASSOCIATES NO. 950 P, 17/25 -14surface of the plate 125 to the external surface of the heater element. This ensures that each operational surface of the plate reaches the same operating temperature.

It is preferable that this heater element is a resistive heating element that, for arrangements using 6mm aluminium plate, draws approximately 11.5 amps at 12 Volt DC so as to generate approximately 140 Watts of power.

As stated above the heater plate is thermally conductivity with the handle 140.

This enables the handle 140 to operate as a heat sink for the heater plate. This enables the heater plate to attain an equilibrium temperature in the operational range of 200°C to 220'C independently of voltage and current supply regulation devices. The chassis. may also operate as a heat sink through thermal contact with the handle.

With this arrangement, the operational temperature of the heater plate may vary slightly depending on ambient temperature. Where ambient temperature is relatively low, such as below 15'C, then it may be beneficial to provide some form of insulating cover for the heater plate so that it can attain operational temperature, The cover may also be beneficial in windy conditions. The cover is preferably made of a thermally insulating material capable of sustaining contact with metal plates at temperatures at or above 200°C for extended periods. For moderate ambient temperature conditions, between say 15C and 30'C the heater plate typically attains an equilibrium temperature between the range of approximately 200 0 C and 220C,. This enables a standard 12 Volt lead acid car battery to supply power to the heating element for a continuous periods. The heater plate attains equilibrium temperature typically within the range of 200°C to 220'C. This obviates the need to have regulation devices for the power supply.

Referring now to Figure 4b which is a view of heater element 400 in section. The heater element preferably comprises a resistive heating element 450 that is circular in shape and has a diameter of 21, FEB, 2003 17:17 WRAY AND ASSOCIATES NO. 950 P. 18/25 The resistive heating element 450 is located in contact with mica plates 455, one on each side. In operation the mica plate abut the walls of the heater plate halves so that any air gap between the walls of the plate halves and the mica plates are minimal so as to transfer the maximum amount of heat from the resistive heating element to the heater plate 125.

The specification refers generally to plastic pipes, however other plastic objects may be butt welded by the apparatus described herein. The invention is understood not to be limited to plastic pipes.

Claims (1)

1. 21. FEB.2003 17:17 WRAY AND ASSOCIATES NO.950 P. 19/25 -16- Claims The claims defining the invention are as follows: 1. A butt welding apparatus comprising a heater plate for heating objects located by said apparatus for later butt welding of said objects wherein said heater plate is in operative association with a power supply and is further adapted to attain thermal equilibrium at a temperature in a pre-defined range of temperatures independently of regulation of said power supply. 2. A butt welding apparatus as claimed in claim 1 wherein said equilibrium temperature is dependent on ambient temperature. 3. A butt welding apparatus as claimed in claim 2 wherein said heater plate is thermally associated with a heater sink whereby said element maintains said thermal equilibrium. 4. A butt welding apparatus substantially as herein described. A butt welding apparatus substantially as herein described with reference to the accompanying drawings. A method of butt welding in a butt welding apparatus having a heater plate for heating objects prior to abutting said objects so as to form a butt weld, said method comprising the steps of. 1) heating said heater plate with a power supply, and 2) thermnally associating said heater plate with a heat sink whereby said heater plate attains a thermal equilibrium independent of regulation of said power supply. 7. A method as claimed in claim 6 wherein said apparatus further comprises thermal insulation between said heater plate and said heat sink hereby limiting the amount of heat dissipated through said heat sink. 21. FEB. 2003 17:17 WRAY AND ASSOCIATES NO. 950 P. 20/25 -17- 8. A method of butt welding substantially as herein described.