GB2479401A

GB2479401A - A welding rod drive system for hand held hot gas high speed welding

Info

Publication number: GB2479401A
Application number: GB1005908A
Authority: GB
Inventors: David William Beddoes; Robert James Ward
Original assignee: Individual
Current assignee: Individual
Priority date: 2010-04-09
Filing date: 2010-04-09
Publication date: 2011-10-12
Also published as: GB201005908D0

Abstract

A mechanized drive system G for use in a hand-held hot gas high speed welding comprises a sharp toothed pinion gear which drives a plastic welding rod D and in turn controls the welding speed. The rotational speed of the pinion and thus the welding speed may be varied by the operator and the system may be releasably attached to a hot gas gun A or stick welder. Adjustable pressure H may be exerted on the pinion gear such that shallow cuts are made into the plastic welding rod — this awards flexibility to the plastic welding rod to enable welding in tight corners, a reduction of the tendency for the rod to weld itself inside the nozzle and better regulation of the pressure exerted onto the nozzle by an operator. When used the system allows one handed operation of the gun.

Description

Hot Gas Welding System

Background to invention

A plastic material that can be heated and melted is known as a thermoplastic. Plastic welding is a fabrication process for thermoplastic materials that was invented in the mid 20th centuiy.

Typical uses are for the construction of chemical storage tanks, water treatment equipment and fabrication of membranes.

Current plastic welding equipment Electric socket This is mostly used to weld pipes. Electric power heats a wire inside a socket. The plastic melts and expands. The pressure of the expansion joins the parts together.

Ultrasonic welding Ultrasonic uses an acoustic tool to transfer vibration energy through the plastic parts top the weld area. Friction melts the plastic. Welding occurs under pressure when the vibrations stop.

High-frequency welding Similar to ultrasonic welding except that the welds are continuous instead of stamped. Often used to join very thin polymer films.

Hot plate welding This process as the name suggests uses a heated plate inserted between two parts of the same shape, for example a pipeline joint. The parts melt under heat, the plate is removed and the parts are held together under the necessary pressure.

Spin welding Spin welding uses frictional heat from rapidly rotating parts held against a stationary substrate. Friction melts the plastic with a weld formed as parts cool.

Injection welding Injection welding uses a heated tip to heat the weld area and injection pressure to form welds.

A hot (interchangeable) tip melts the surface of the plastic and creates a weld zone into which molten plastic is injected. The molten plastic is produced from plastic rods or pellets that pass through a screw or auger mechanism and are then heated before being injected under pressure.

Extrusion welding Extrusion welding uses a gas that is heated and exits at a nozzle to heat the weld area. The extrusion welder has a screw or auger mechanism that moves plastic rod or pellets through a barrel, inside the barrel the plastic mixes, compresses, and melts. The auger pushes the melted plastic out of the welder creating the weld bead. These units are generally large and heavy. They are very useful for providing large weld beads for heavy construction. Patent W0208141685 (Al) 2008-11-27 shows an extrusion welding device.

Hot gas weldiflg Hot gas welding uses a stream of heated gas to heat and melt both a plastic welding rod and the plastic items to be joined (substrate). A fusion weld is produced between the welding rod and the substrate.

Many hand held hot gas welding guns use a gas supply with a heating chamber incorporating temperature control to produce the hot gas and a nozzle where the heated gas exits the gun so that it heats both the plastic welding rod and the plastic substrate. However the gas supply to these guns can be from a remote source.

Three types of interchangeable nozzle are used: (1) Tacking nozzle to tack items together before welding.

(2) Round nozzle for hand welding. In the process of hand welding the welding rod is fed into the joint by hand. The round nozzle is continuously moved in a pendulum motion along the joint and up the welding rod, heating both as the weld progresses. It is very difficult to maintain a constant pressure with one hand onto the welding rod whilst performing the pendulum motion of the gun with the other hand. To prevent overheating, the weld nozzle must always be held at a constant distance from both welding rod and substrate with the substrate ideally receiving double the heat input of that given to the rod. A great deal of operator skill is required.

(3) High speed nozzle. In hot gas speed welding the welding rod is fed manually into a joint via a tube in the front of the speed welding nozzle. The speed welding nozzle introduces hot gas to welding rod and substrate joint. The toe of the speed welding nozzle is used by the operator to apply pressure to ensure a high quality weld. This is a difficult process needing a skilled operator as one hand manually feeds the welding rod whilst the other hand has to maintain adequate pressure on the speed nozzle whilst also moving the gun and nozzle along the joint. The weld quality depends greatly on the skill of the operator.

Regardless of which type of plastic welding equipment is used, the important parameters for welding of plastics are always the same: (1) Temperature: each thermoplastic melts within a temperature range to its melting point. It is of utmost importance to stay between the minimum and maximum weld temperatures. Any drift outside of this zone will result in a poor quality weld.

(2) Pressure: the application of force lets the plastic molecules mix together. For the best quality of weld there needs to be physical mixing of the plastics. Pressure needs to be continuous and maintained at the same level. Pressure that is too high or too low will result in a poor quality of weld.

(3) Welding speed: welded plastics need a certain time to heat up and cool down. Heating the plastic too fast results in the plastic not melting properly.

(4) Gun position: the right position for the gun is important. The wrong position will decrease the quality of the weld. The substrate must be preheated by directing the heated gas or applying the heated tip to the correct zone in front of the weld. If the distance is too far or too close the weld is too cold or too hot.

These four welding parameters are of course interdependent. In particular, with hand held welding equipment the management and the subsequent quality of weld produced depends on a high level of operator skill.

In order to provide a quality weld the welding operations rely mostly on the skills of the operator. The operator is responsible for the delivered quality of the product.

To make matters worse, in a real life' situation we find that perfect working conditions are not always available. There are shop welds' and field welds'. If the operator can work in a shop with all necessary equipment and tools, good ventilation, sufficient illumination, and a workbench with the best available position for parts to be joined then everything would be ideal to concentrate on the four parameters.

More often than not the parts to be welded are difficult to reach and may be tucked away in dark tight spaces. Work areas can be contaminated needing the operator to wear constrictive special protection that inhibits both movement and the field of view.

Sometimes a ladder and/or safety harness may be required to weld joints at the inside top corners of tanks. Working in some positions will put the operator in an unstable posture where they find it extremely difficult to maintain suitable pressure and also provide movement to a heavy gun. Health and safety legislation now requires an operative on a ladder to maintain a minimum of three contact points at all times. This means that any operation needing two hands can no longer be carried out and if a hand held gun is heavy the operator will have great difficulty in producing quality welds with single handed usage. To keep the heavy hand held gun in the right position, apply the necessary constant pressure and move the gun along can be very challenging when supported by a safety harness or standing on a ladder. It is like sitting on a child's swing. When the operator tries to apply the correct pressure they themselves are simply pushed backwards.

Welding inside small boxes is very uncomfortable for operators with heavy hand held guns.

Overhead welding can be extremely dangerous with hand held guns that melt the plastic rod or pellets to form a molten weld bead. Operator mistakes with any of the four parameters can result in the operator being showered with molten plastic.

In general, the most common band held equipment in use is injection welding guns, extrusion welding guns and most common of all, and the cheapest to produce, the hot gas welding gun.

The hand held injection welding gun uses a heated tip to heat the weld area. It is sometimes not possible to access fully into tight corners to heat the substrate sufficiently with a fixed heated tip. The hand held injection gun also needs to have a robust mechanism for platicizing and heating the plastic to form a molten bead, the weight of this mechanism can make the gun very heavy. When used overhead by an operator there is a great deal of skill required to balance the weight of a heavy gun whilst also providing sufficient pressure onto the heated tip to ensure a quality weld. The operator has to maintain continuous constant pressure on the gun whilst also moving the heavy gun along the weld at the optimum speed. In overhead work any mistakes made may subject the operator to falling molten plastic as it is pushed out of the gun under pressure.

Similarly, when working on a bench although there is no threat from falling molten plastic, the operator must apply the correct pressure to the weld whilst allowing for the weight of the gun now acting downwards. Too great a pressure influenced by the weight of a heavy gun will result in poor weld quality. A great deal of operator skill is needed.

The hand held extrusion gun uses hot gas to heat the weld area but again needs a robust mechanism to supply molten plastic from rod or pellet as a weld bead. This again results in the problem of a large heavy gun that is difficult to use in tight corners. With overhead work, we have the same problems as the injection gun of falling molten plastic and the operator skill needed to maintain weld pressure when supporting and moving a heavy gun.

The use of a heavy gun be it injection or extrusion is extremely difficult when the operator is subjected to the field weld' conditions as mentioned above. In particular, the situation where the welding has to be carried out by the operator holding the gun with one hand whilst The hand held hot gas gun is light and small in comparison as it has no plasticizer for rod or pellets. Indeed some hand held guns do not even incorporate a compressor for the gas supply as this is done by a remote unit. Some guns are very lightweight as they just heat the gas supplied. The minimal weight of the gun makes the field weld' much easier, particularly when judging pressure to be applied to the gun.

The use of a welding rod that is heated and applied to the weld area as opposed to being pushed out of the gun as a molten bead makes overhead work much safer.

However, the hand held hot gas gun requires the operator to hold the gun with one hand and feed the solid plastic welding rod with the other hand. This is therefore a skilled two handed operation for a shop weld' and the process would not be possible as a field weld' when

Statement of invention

To overcome this problem with current welding equipment this invention proposes a mechanised system of lightweight, self driving, hand held, hot gas high speed nozzle welding that requires lower levels of operator skill to produce consistent high quality shop and field welds even in poorly accessible corners.

Advantages Continuous mechanised feed of the welding rod into the speed welding nozzle means the operator only has to use one hand for hot gas high speed nozzle welding.

The mechanised rate of feed of the solid plastic welding rod controls the speed of movement of the hand held hot gas gun and thereby the welding speed which is one of the four welding parameters.

The operator will now have two hands to manage other parameters of pressure and gun position, this being particularly useful at awkward tight corners and changes in direction.

One handed operation will now allow lightweight hot gas high speed nozzle welding to be carried out off a ladder or safety harness.

Shallow cuts made by the mechanised drive system award greater flexibility to the solid plastic welding rod and allow it to be bent into smaller radii to enable more upright gun positioning for better access into tight corners.

The shallow cuts configure the solid plastic rod to more readily lie in the centre of the nozzle guide tube at the nozzle toe and not twist or move laterally out of position for the weld.

The shallow cuts into the smooth surface of the plastic welding rod produce turbulence of the hot gas within the nozzle and weld area. The turbulence facilitates better heat exchange between hot gas and plastic rod and substrate thereby using less energy and is a green feature of this invention.

The flexibility of the plastic welding rod produced by the shallow cuts allows welding of more intricate and corrugated profiles where radii rapidly and continuously change from convex to concave profiles.

The flexibility of the welding rod decreases the back pressure exerted on the gun by the previously stiff solid rod as it moved through the high speed nozzle. This gives the operator more delicate control over the pressure they exert onto the nozzle toe itself in order to enable a better quality of weld.

L ___

The flexibility of the welding rod also produces less contact pressure between the solid welding rod and the common wall structure between the rod guide tube and the nozzle hollow tube that transfers the hot gas to the substrate. This greatly reduces the tendency for the welding rod to prematurely absorb heat and weld itself within the guide tube before exiting onto the weld area. Binding and blockage of nozzle guide tubes is a major cause of delays in high speed welding.

Of the four hand held welding parameters that require operator skill, two are now satisfied by a mechamsed hot gas speed welding system. Temperature and gun speed are very closely interdependent as temperature is preset to material and previously too fast a gun speed by the operator meant a cold weld and a poor quality product. With a mechanised system, the temperature and gun speed can both be set to match the manufacturers optimum settings. The operator now only needs half the previous skill level to manage the two remaining parameters of pressure and gun position. A further advantage is that the operator also now has two hands available to manage a lightweight gun.

Less positioning aids need fixing and less tack welding needs to be carried out as one hand is now available to steady the parts whilst welding proceeds with a lightweight gun. This of course saves operator time and money.

Operators can continuously use a light weight gun for overhead welding without tiring so quickly as before and without the danger of being burned by molten plastic beads that are extruded from the other types of injection and extrusion guns.

A hot gas gun or stick welder that requires less operator skill will increase production for shop welds and is ideal for field welds in difficult locations.

The mechanised gun can be used on construction sites to join waterproof membranes and rigid geo-textile membranes. It can also be used in the construction industry to custom produce the stiff waterproof collars that surround stanchion bases when they penetrate waterproof membranes.

The ability of the lightweight gun to produce a quality weld in the field on plastic pipes and ductwork installations will be a major asset, particularly for companies involved in repair and maintenance work that is carried out at the customers' premises.

The mechanised system can be an add on feature to an existing hot gas welder or can be made as part of a complete hot gas gun, however in either case the gun will be able to be used in manual or mechanised mode as chosen by the operator.

Introduction to drawings

An example of the invention will now be described by referring to the accompanying drawings: Figure 1 shows a hot gas high speed welding nozzle in use.

Figure 2 shows the mechamsed system fitted to a hot gas gun.

Figure 3 shows a hot gas gun with the mechanised system incorporated within the gun itself.

Figure 4 shows the detail of the mechanised drive system.

Figure 5 shows an alternative arrangement for the drive system.

Figure 6 shows an enlarged diagram of a high speed nozzle and illustrations of bending the plastic welding rod.

Detailed description

In figure 1 the hot gas gun or hot gas stick welder (A) supplies hot gas via the pipe (B) to the high speed welding nozzle (C).

The plastic welding rod (1)) is hand fed into the guide tube in the speed welding nozzle (C).

The speed welding nozzle introduces the hot gas to both the welding rod (D) and the substrate to be joined together.

The direction of travel of the gun is shown by the arrow (F).

The toe (T) of the speed welding nozzle is used to apply the pressure required for welding.

The finished weld (E) is shown behind the toe(T) of the speed welding nozzle (C).

The operators hand holding the gun (A) must force the gun downwards to apply the necessary pressure to the toe (T) as welding progresses.

With the other hand the operator must feed the welding rod (D) into the guide tube on the speed welding nozzle. The rod (D) must be fed at constant speed whilst the operator must also maintain force on the toe (T) and simultaneously travel the gun along the weld in direction shown by (F) at a constant speed.

The operator needs a great deal of skill to produce a high quality product.

In figure 2 the mechanised drive system (G) has been fitted to the hot gas gun (A).

In this example straps around the body of the gun hold the system (G) in place on top of the gun. The brackets forming part of the body of the mechanism (G) could be held to the gun body by any suitable fixings.

Hot gas is supplied through pipe (B) to the high speed nozzle (C).

The plastic welding rod (D) now passes through the drive mechanism (G) and then into the guide tube on the high speed nozzle.

In this example the electric motor (J) drives a sharp toothed pinion gear that drives the welding rod (D) through the guide tube at a continuous rate. The continuous feeding of the solid plastic welding rod into the high speed nozzle now pushes the hand held gun forwards in direction (F) to determine the gun welding speed.

The welding speed can be adjusted for different materials by the operator varying the rate of rotation of the electric motor (J).

The operator is able to set the pressure adjustment knob (H) to ensure that sufficient pressure is exerted between the welding rod and the sharp toothed pinion gear to provide a positive and continuous drive to the welding rod and hence control the welding speed of the gun.

The operator can now concentrate on the pressure applied to the toe (1) and gun position as the feed of the welding rod (D) and the weld speed are catered for by the mechanical drive system (0).

The finished weld (E) is shown behind the toe (T).

The mechanisecj drive system does not always have to be used when fitted to the gun. The mechamsed system can be switched independent of the hot gas gun. The hot gas gun can be used in manual mode requiring both hands to operate it at any time as described in figure 2 above should the operator need to do this at any time. The operator can then revert to mechanised use whenever needed by re-routing the welding rod back into the mechanised drive system (0).

Figure 3 shows the mechanised system incorporated into the body of a hot gas gun. The welding rod (D) enters the rear of the gun body and passes throught he mechanised drive system.

The welding rod exits the front of the gun and then passes down to the guide tube on the high speed nozzle (C). The adjustment knob (H) ensures that the sharp toothed pinion gear provides positive drive to the welding rod (D) and hence continuous gun welding speed (F).

The trigger (L) can be used as a two stage trigger to first start hot gas supply and then a further pull to start the mechanised drive action of the sharp toothed pinion gear, alternatively the drive can be independently switched to allow the gun to be used in manual mode when needed by the operator.

Figure 4 shows the internal drive arrangement of the mechanised drive system (G).

The outer casing (R) is held to the body of the hot gas gun using straps or other fixings to the brackets (S). This example shows the sharp toothed pinion gear (P) that is turned by an electric motor fitted to the outer casing (R).

The direction of rotation of the sharp toothed pinion gear (P) is shown by the arrow.

The welding rod (D) is sandwiched between the sharp toothed pinion gear (P) and the adjustable pressure roller (M). The sharp toothed pinion gear is used to convert rotational motion into linear motion.

The electrically powered sharp toothed pinion gear rotates. The pinion teeth form shallow cuts (Q) into the plastic welding rod (D) and drive it linearly forwards to provide the continuous feed of the rod (D).

The depth of the shallow cuts (Q) can be adjusted by means of the knob (H) which varies the force applied to the pressure roller (M). The speed of the linear drive to the rod (D) and hence the welding speed of the gun can be adjusted by varying the rotational speed of the sharp toothed pinion gear (P).

As well as adjusting knob (H) for depth of cuts and therefore positive driving force, the knob can also be adjusted for different thicknesses of welding rod and/or different cross sectional shapes of welding rod (D).

If needed sets of guide rollers (N) can be used before and/or after the rod passes between the sharp toothed pinion gear (P) and the pressure roller (M), these may be necessary for some cross sectional shapes of welding rod.

Figure 5 shows an alternative drive arrangement for use in the mechanised drive system.

An electric motor switched either by the gun or independently powers the sharp toothed pinion gear (P). The rotational speed of the electric motor can be varied by the operator.

The rotation of the sharp toothed pinion gear (P) forms shallow cuts (Q) into the welding rod (I)) and the rod is driven linearly forwards.

The sharp toothed pinion gear (P) is surrounded by a block (Z) made from PTFE or similar material. The welding rod (D) is sandwiched between the sharp toothed pinion gear (P) and the block (Z), the pressure exerted between the two can be adjusted by knob (H).

The block (Z) is free to slide within the body of the mechanism as it is loosely held by slider brackets (U).

The block (Z) has a guide hole across its width through which the welding rod (D) passes, this guide hole can be shaped to suite a particular cross sectional shape of welding rod, for example a triangular hole for triangular welding rods used as corner welded fillets in box fabrication.

The simple arrangement described has few moving parts, however the block with its individual guide hole shape needs to be changed when a different cross sectional shaped rod is used. When a large quantity of triangular rod is to be welded during fabrication then this block (Z) is simple and easy to use and again the linear positive drive provided to the plastic welding rod will control the gun welding speed for the operator.

Figure 6 illustrates some of the advantages given by the shallow cuts (Q) made in the welding rod (D) by the sharp toothed pinion gear (P).

The high speed welding nozzle (C) is shown with hot gas input and welding rod (D) entering the guide hole on the nozzle. As the welding rod (D) has to negotiate the sharp corner around the toe (T) there is a lot of pressure exerted by the rod onto the common wall area (V).

This common wall area (V) is heated by the hot gas coming down the tube (B) from the gun and a combination of the pressure exerted due to bending of the rod and the heat at (V) means that any momentary pause in manual rod feed can result in the rod welding itself in the guide tube to the common wall (V). This occurrence is a common source of delays in high speed nozzle welding.

The cuts (Q) made into the underside of the welding rod (D) reduce the pressure produced when the welding rod negotiates the sharp bend and the instances of premature weld at the common wall (V) are reduced partly due to the reduction in pressure and also partly due to the continuous rate of welding rod feed that can only be provided by a mechanised system as described.

The three lower sketches in figure 6 show first the normal bending radius of a solid plastic welding rod (D).

The sketch (X) shows a concave bend can be made with a much smaller radius when the rod has shallow cuts (Q) made by a sharp toothed pinion gear.

Sketch (Y) illustrates how a convex radius bend can be made much smaller due to cuts (Q).

The flexibility awarded to the welding rod (D) by the cuts (Q) made by the sharp toothed pinion gear enables use of the welding gun in tighter corners.

Claims

Claims 1 A mechanised drive system for use in hand held hot gas high speed welding, the plastic welding rod being driven by a sharp toothed pinion gear which in turn controls the welding speed.
2 A drive system according to claim 1, in which the rotational speed of the pinion and therefore the welding speed can be varied by the operator to suite different materials to be welded and/or different weld temperatures.
3 A drive system according to claim 2 incorporated into a hot gas gun or that can be releasably attached to a hot gas gun or hot gas stick welder as an upgrade to mechamse existing equipment.
4 A drive system according to previous claims that is fitted to hot gas welders that generate their own hot gas and/or are remotely supplied with hot gas.
A drive system according to previous claims in which the adjustable pressure exerted onto a sharp toothed pinion gear enables shallow cuts into the plastic welding rod to provide a positive and continuous drive for welding speed.
6 A drive system according to previous claims in which cuts are made into the plastic welding rod by the sharp toothed pinion gear to award greater flexibility to the rod to enable welding in tight corners needing small radii and also reduce the tendency for the rod to bind and prematurely weld itself inside the speed nozzle.
7 A drive system according to previous claims in which the cuts made by the sharp toothed pinion gear allow better heat exchange between the hot gas and the smooth plastic welding rod.
8 A drive system according to previous claims that can be used with any size or cross sectional shape of welding rod.
9 A drive system according to previous claims that uses an adjustable pressure roller to exert pressure onto the plastic welding rod to allow the sharp toothed pinion gear to cut at various depths into the rod to ensure a positive drive.
A drive system according to previous claims that uses a guide roller or set of guide rollers before and/or after the sharp toothed pinion gear.
11 A drive system according to previous claims that uses a movable guide block made of PTFE or similar material to enclose the sharp toothed pinion gear, suitably orientate the welding rod and by adjustment of the block relative to the pinion gear the plastic rod is cut into by the pinion gear at various depths to ensure a positive drive.
12 A system substantially as herein described above and illustrated in the accompanying text and drawings.
13 A method substantially as herein described above and illustrated in the accompanying text and drawings.Claims 1. A mechanized drive device for use in hot gas welding comprising a thermoplastic welding rod being positively fed as a result of the series of cuts made into the rod by the pressure exerted from an electrically driven rotating sharp toothed pinion gear in direct engagement with the rod which converts rotational motion into a positive linear drive of the welding rod.2. A device as in claim 1 in which the welding rod is pressed against the sharp toothed pinion gear by a spring or adjustable mechanism so that the sharp toothed pinion gear digs into the welding rod and makes a series of regular cuts into the surface and/or body of the welding rod to ensure a positive and continuous feed in both directions.3. A device as in previous claims in which the direct engagement between sharp toothed pinion gear and welding rod feeds the welding rod into a guide tube and out of the high-speed welding nozzle to control the travel speed of a hot gas gun.: 4. A device as claimed in any of the foregoing claims in which the addition of a * modulator allows the rotational speed of the electric motor driving the sharp toothed * pinion gear to be adjusted, allowing the welding traverse speed to be varied by the operator to suite different materials and welding rods and/or different welding *:*. temperatures.5. A device as claimed in any of the foregoing claims also comprising a movable guide block made of PTFE or similar material that wholly or partly encloses a sharp toothed pinion gear, the movable guide block being used to orientate the welding rod and by * adjustment of the movable guide block relative to the sharp toothed pinion gear the depth * . of cut into the welding rod by the sharp toothed pinion gear can be regulated.6. A device as claimed in any of the foregoing claims also comprising a guide roller or set of guide rollers before and/or after the sharp toothed pinion gear.7. A drive device according to previous claims in which the cuts made into the welding rod by the sharp toothed pinion gear give greater flexibility to the welding rod to enable welding in tight radii and also reduce the tendency for the welding rod to bind and prematurely weld itself inside the speed nozzle.8. A drive device according to previous claims in which the cuts made by the sharp toothed pinion gear allow better heat exchange between the hot gas and the welding rod.9. A drive device according to previous claims that can be used with any size or cross sectional shape of welding rod.10. A drive device according to previous claims that uses an adjustable pressure roller to exert pressure onto the welding rod to allow the sharp toothed pinion gear to cut at various depths into the welding rod to ensure a positive drive.11. A device as claimed in any of the foregoing claims that additionally can be releasably attached to a hot gas gun or a hot gas stick welder.12. A device as claimed in any of the foregoing claims that additionally can be releasably attached to hot gas guns that generate their own gas andlor are remotely supplied with hot gas.13. A device as claimed in any of the foregoing claims that is used with band held hot gas welding guns.
14. A welding device substantially as herein described above and illustrated in the accompanying text and drawings. *.... * I ** I * ** * SI *s.. * I ***.II...., I *