AU2016200836A1 - Procedure For A Multi-Pass Weld - Google Patents
Procedure For A Multi-Pass Weld Download PDFInfo
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- AU2016200836A1 AU2016200836A1 AU2016200836A AU2016200836A AU2016200836A1 AU 2016200836 A1 AU2016200836 A1 AU 2016200836A1 AU 2016200836 A AU2016200836 A AU 2016200836A AU 2016200836 A AU2016200836 A AU 2016200836A AU 2016200836 A1 AU2016200836 A1 AU 2016200836A1
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- Australia
- Prior art keywords
- weld
- procedure
- roller
- pass
- repairing
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Abstract
Abstract The present invention provides a procedure for a multi-pass weld. The procedure comprises heating a parent metal to a predetermined temperature, before applying a first pass of the weld at a reduced level of energy that being 70-75% of fill material energy. The procedure then requires controlling the weld penetration of the first pass into the parent metal, before applying subsequent weld passes to provide the required weld build up. The procedure further comprises managing the weld deposition rate using variable off set square wave technology and relieving the stress caused by the weld once the required weld build up has been achieved. 'IS isM
Description
Procedure For A Multi-Pass Weld TECHNICAL FIELD
The present invention generally relates to a procedure for a multi-pass weld. In particular the present invention relates to a multi-pass method of welding for cladding.
BACKGROUND ART
Typically, welding is used to fix two or more objects together. However, welding can also be used to clad a machine part in order to extends its life. Cladding, or refined cladding, is a welding process whereby metal is added to a parent metal to repair the part, or to provide it with a sacrificial surface.
Cladding is the application of metal to a part's surface by means of applying a weld to the surface with one or more welders. During this process it is typical for a series of welds to be applied to the surface until sufficient metal has been deposited on the parent metal.
Metal parts exposed to abrasive environments will lose dimension and functionality due to wear. Eventually these parts wear to a point where they fail and/or can no longer fulfill their intended purpose. When the part is relatively inexpensive they can be economically replaced. However, when the part is an expensive piece of equipment it is desirable to repair/modify the part so it can return to active service. This can often be achieved by cladding.
Cladding may be used to repair a worn, or otherwise damaged surface of a part. It may also be used to apply a protective layer to a surface of new equipment before the equipment is commissioned.
As with any weld, flaws or imperfections can be incorporated into the weld due to a variety of factors. When cladding using multi-pass welding, the majority of these weld flaws or imperfections occur with the first pass, which is especially susceptible to cracking. It is critical that the first pass of weld coalesces sufficiently with the parent metal.
The first pass of a multi-pass weld is the most critical for weld soundness. If the first pass solidifies too quickly, it can trap gas and slag. This compromises the bond between the weld of the first pass and the parent metal. With time this can lead to failure of the weld, and the rapid wearing of the built up material. A cross section analysis of a cladding multi-pass weld demonstrates considerable variation in fracture toughness. In particular, the coarse grain heat affected zone can incorporate brittle zones that degrade the resistance of the weld to fracture initiation. A common flaw with cladding occurs when the weld metal fails to adequately fuse with the parent metal or with the preceding weld bead in multi-pass applications, resulting in incomplete fusion. Failure to achieve a sound bond between the weld and the parent metal may result in the creation of a mechanical notch within the heat-affected zone of the weld. The mechanical notch reduces the strength of the weld and can lead to cracking and failure of the weld.
Also, when gas becomes trapped along the surface or inside of the weld metal, porosity occurs. Like other weld flaws, porosity results in a weak weld that must be ground out and reworked.
Current techniques allow for cladding of equipment parts. However, these techniques create flaws within the heat-affected zone which compromise the strength of the weld and therefore reduce the service life of the repaired part. As a result, in parts used in high wear applications, cladding is generally only suitable for spot repairs of surfaces.
The preceding discussion of the background art is intended to facilitate an understanding of the present invention only. The discussion is not an acknowledgement or admission that any of the material referred to is or was part of the common general knowledge as at the priority date of the application.
SUMMARY OF INVENTION
It is an object of this invention to provide a procedure for a multi-pass weld which reduces the likelihood of flaws within the weld.
The present invention provides a procedure for a multi-pass weld, the procedure comprising: heating a parent metal to a predetermined temperature; applying a first pass of the weld at a reduced level of energy that being 70-75% of fill material energy; controlling weld penetration of the first pass into the parent metal; applying subsequent weld passes to provide the required weld build up; managing the weld deposition rate using variable off set square wave technology; relieving the stress caused by the weld once the required weld build up has been achieved.
By applying the first pass of the weld at a reduced level of energy the operator is controlling the heat added to the parent material in the first pass.
Preferably the procedure comprises undergoing a heat treatment cycle during the welding process to diffuse hydrogen from the weld. A temperature heat treatment carried out upon completion of welding by increasing the heat by at least 100Ό and maintaining this temperature for a period of time assists in the diffusion of hydrogen in the weld or heat affected zone, reducing the risk of hydrogen induced cracking.
Preferably the procedure comprises controlling the temperature of the parent throughout the procedure. This assists in managing Hydrogen within the heat affected zone and the weld, minimizing the risk of hydrogen induced flaws.
Preferably the procedure comprises controlling weld penetration of the first pass into the parent metal up to 15mm penetration.
Preferably the procedure comprises controlling weld penetration of the first pass into the parent metal to 15mm penetration
By controlling the depth of penetration of the first pass the metallurgical diffusion between the interface of the parent metal and weld is managed.
Preferably the procedure comprises depositing weld at a rate up to 30 kg/hr. Preferably the procedure uses at least one tandem welder to deposit the weld.
Preferably the wires are fed from the at least one tandem head welder in an offset and staggered relation, each wire being fed into a single pool.
Preferably the procedure comprises running AC power on a lead arc of the tandem weld head. This reduces or can eliminate the arc blow in the weld pool.
Preferably the procedure comprises running AC power on a trailing arc of the tandem weld head. This reduces or can eliminate the arc blow in the weld pool.
Preferably the procedure comprises managing the dimensions of the weld bead using variable off set square wave technology.
Preferably the procedure comprises controlling the welding parameters to manage the residual hoop stress, largely formed as a result of weld shrinkage. This can be achieved by heat treatment designed to reduce the residual stresses. As the temperature of the metal is raised, the yield strength decreases, allowing the residual stresses to be redistributed. Cooling from the stress relief temperature may be controlled in order to minimise the formation of thermal gradients.
Preferably the procedure comprises heating the weld and parent metal to a predetermined temperature and retaining the weld and parent metal at that temperature for a period of time.
The current procedure eliminates the formation of a mechanical notch at the interface of the heat affected zone with the parent metal by controlling the temperature of the materials, the depth of penetration of the first pass, the speed of wire feed, the amperage and voltage. This provides a weld which is free of any flaws which would compromise the required integrity of the weld.
The present invention provides a roller used for the crushing of ore wherein the roller has undergone the welding procedure as herein before described.
The present invention provides a method of repairing a surface of a roller used for crushing ore, the method comprises: removing any bodies extending from the surface; filling any cavity until the surface is of a relatively uniform diameter; cladding the surface until the smallest diameter of the hardfaced roller is at the required diameter; removing a portion of the hardfaced roller to provide a roller at the required diameter
Preferably the cladding process is in accordance with a procedure for a multi-pass weld as hereinbefore described.
The present invention provides a method of repairing a surface of a roller used for crushing ore, the method comprises: removing any bodies extending from the surface; removing a portion of the roller until the surface is of a relatively uniform diameter; cladding the surface until the smallest diameter of the hardfaced roller is at the required diameter; removing a portion of the hardfaced roller to provide a roller at the required diameter
The method may further comprise drilling a plurality of holes in the repaired roller and installing hard bodies therein.
The method may comprise removing the portion of the roller by turning.
The method may comprise removing the portion of the roller to a diameter below any cavity within the roller. For example, in those cases where the roller has a plurality of hard bodies located in cavities within the roller, material may be removed from the roller until the surface of the roller is located below the bottom of the cavities.
The method may comprise removing the portion of the roller to a predetermined diameter and filling any remaining localised worn/damaged zones with a weld.
Preferably the cladding process is in accordance with a procedure for a multi-pass weld as hereinbefore described.
BRIEF DESCRIPTION OF THE DRAWINGS
Further features of the present invention are more fully described in the following description of a non-limiting embodiment thereof. This description is included solely for the purposes of exemplifying the present invention. It should not be understood as a restriction on the broad summary, disclosure or description of the invention as set out above. The description will be made with reference to the accompanying drawings in which:
Figure 1 is a cross sectional schematic view of a cladding procedure comprising multi-pass welds;
Figure 2 is a cross sectional view of a cladding weld showing the depth of penetration within the parent metal, as well as the penetration of subsequent welds into the previous welds;
Figure 3 is a cross sectional view of a cladding weld illustrating the various regions within the weld; and
Figure 4 is the results of a Vickers test applied to the weld of figure 3.
In the drawings like structures are referred to by like numerals throughout the several views. The drawings shown are not necessarily to scale, with emphasis instead generally being placed upon illustrating the principles of the present invention.
DESCRIPTION OF EMBODIMENTS
While cladding can be used to repair most metal parts, it has particular application for those parts subject to wear. One such application is in relation to the equipment used in the processing of ore, particularly grinding rollers used in the comminution process.
Grinding rollers are subject to significant forces during operation. These forces, along with the abrasive nature of the ore being processed, can quickly wear the surface of the roller. While the surface of the roller incorporates technology to minimise wear, the rollers do ultimately wear and require repair or replacement. Owing to the replacement cost, it is highly desirable to repair the rollers and place them back in service.
In the past cladding of the roller surface has been difficult and tends to provide a built up weld which is inferior to the parent metal, leading to failure. This inferiority is usually the result of the first pass of the welding procedure, also known as the buffering layer, 11. The present invention overcomes or at least minimizes the impact of any flaw within a multi pass weld. In particular the welding procedure provides a first layer with a heat affected zone which has at least the same strength of the parent metal. Hence, if the cladding formed using the welding procedure of the present invention were to fail it would generally not be a result of the first pass. The hardness/strength of the weld is visually represented in figure 4. Figure 4 is a representation of the hardness of the heat-affected zone (HAZ) 13, the weld material 15 as shown to the left of the heat-affected zone, and the parent material 17as shown to the right of the heat-affected zone.
Figure 4 represents the results of the application of a Vickers procedure carried on a weld 23 as shown in figure 3. The Vickers procedure was carried out at numerous locations 21a, 21b, 21c on the weld 23 formed from the welding procedure of an embodiment of the invention. The test locations are represented by the black dots on figure 3 as highlighted by the oval shape. The Vickers test makes it possible to carry out a survey across the weld 23, including individual runs and the heat affected zones.
As represented in figure 4, the hardness within the heat affected zone 13 is relatively uniform, showing no mechanical notches within that zone (as would be represented by a significant spike on the graph). This illustrates that the characteristics of the heat affected zone are relatively uniform and therefore relatively flaw free.
The procedure for a multi-pass weld according to an embodiment of the invention is discussed below with reference to repairing a surface of a roller (not shown).
When repairing a roller any hard bodies incorporated in the roller need to be removed and the surface of the roller needs to be prepared before the procedure for applying a multi-pass weld can commence. In some instances preparing the roller may simply require the turning of the roller until the surface is relatively clean and uniform. In other instances it may require the localized repair of significant worn areas of the roller.
Once the surface is ready for cladding, the roller is heated. The heating is maintained throughout the weld procedure at a range of 200eC-300eC depending on the grade of material.
When the roller is at a predetermined temperature a first pass of the weld is made. The energy input associated with the first pass is somewhat lower than subsequent passes, and is designed to penetrate no more that 15mm within the parent metal
Once sufficient material has been deposited on the roller by successive passes, the roller is turned to the required diameter. Due to the effects of the welding process the roller undergoes a further heat treatment process at 550SC-650QC, dependent on the grade of material, to relieve stress within the roller. The heating and cooling rate during this process is not to exceed 50 QC per hour.
The residual stresses locked into a weld, or created within the roller, may cause deformation outside acceptable dimensions to occur when the item is machined or when it enters service. These stresses increase the risk of brittle fracture.
Cladding involves the deposition of molten metal on to essentially a cold parent metal. As the weld cools the weld metal contracts but is restrained by the cold metal on the other side, the residual stress therefore increases as the temperature falls.
To reduce residual stress, the roller is heated to a sufficiently high temperature (550QC-650eC dependent on the grade of material). As the temperature is increased the yield point changes, allowing residual stress to decrease until an acceptable level is reached. The roller is held at this temperature for a period of time until a stable condition is reached and then cooled back to room temperature. The residual stress remaining in the weld is then equal to the yield point of the material at the heated temperature.
By lowering the temperature of the first pass relative to convention, controlling the welding parameters, facilitated by the use of the variable off set square wave technology, and using a heat treatment process, the resulting heat affected zone in the parent material has improved inherent strength characteristics. The present weld procedure enables equipment parts, which are exposed to significant force and wear, such as rollers, to undergo cladding in a manner which significantly extends the life of the roller.
Modifications and variations such as would be apparent to the skilled addressee are considered to fall within the scope of the present invention. The present invention is not to be limited in scope by any of the specific embodiments described herein. These embodiments are intended for the purpose of exemplification only. Functionally equivalent products, formulations and methods are clearly within the scope of the invention as described herein.
Reference to positional descriptions, such as lower and upper, are to be taken in context of the embodiments depicted in the figures, and are not to be taken as limiting the invention to the literal interpretation of the term but rather as would be understood by the skilled addressee.
Throughout this 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.
Claims (23)
1. A procedure for a multi-pass weld, the procedure comprising: heating a parent metal to a predetermined temperature; applying a first pass of the weld at a reduced level of energy that being 70- 75% of fill material energy; controlling weld penetration of the first pass into the parent metal; applying subsequent weld passes to provide the required weld build up; managing the weld deposition rate using variable off set square wave technology; relieving the stress caused by the weld once the required weld build up has been achieved,
2. The procedure for a multi-pass weld according to claim 1 wherein the procedure comprises undergoing a heat treatment cycle during the welding process to diffuse hydrogen from the weld.
3. The procedure for a multi-pass weld according to claim 1 or 2 wherein the procedure comprises controlling the temperature of the parent throughout the procedure.
4. The procedure for a multi-pass weld according to any one of the preceding claims wherein the procedure comprises controlling weld penetration of the first pass into the parent metal up to 15mm penetration.
5. The procedure for a multi-pass weld according to any one of claims 1 to 3 wherein the procedure comprises controlling weld penetration of the first pass into the parent metal to 15mm penetration
6. The procedure for a multi-pass weld according to any one of the preceding claims wherein the procedure comprises depositing weld at a rate up to 30 kg/hr.
7. The procedure for a multi-pass weld according to any one of the preceding claims wherein the procedure uses at least one tandem welder to deposit the weld.
8. The procedure for a multi-pass weld according to claim 7 wherein wires are fed from the at least one tandem head welder in an offset and staggered relation, each wire being fed into a single weld pool.
9. The procedure for a multi-pass weld according to any one of the preceding claims wherein the procedure comprises running AC power on a lead arc of the tandem weld head.
10. The procedure for a multi-pass weld according to any one of claims 1 to 8 wherein the procedure comprises running AC power on a trailing arc of the tandem weld head.
11. The procedure for a multi-pass weld according to any one of the preceding claims comprising managing the dimensions of the weld bead using variable off set square wave technology.
12. The procedure for a multi-pass weld according to claim any one of the preceding claims comprising controlling the welding parameters to manage the residual hoop stress.
13. The procedure for a multi-pass weld according to claim 12 wherein managing the residual hoop stress is by heat treatment.
14. The procedure for a multi-pass weld according to any one of the preceding claims comprising heating the weld and parent metal to a predetermined temperature and retaining the weld and parent metal at that temperature for a period of time.
15, A roller used for the crushing of ore wherein a surface of the roller has undergone the procedure for a multi-pass weld according to any one of the preceding claims,
16. A method of repairing a surface of a roller used for crushing ore, the method comprises: removing any bodies extending from the surface; filling any cavity until the surface is of a relatively uniform diameter; cladding the surface until the smallest diameter of the hard-faced roller is at the required diameter; removing a portion of the hard-faced roller to provide a roller at the required diameter
17, The method of repairing a surface of a roller according to claim 16 wherein the cladding process is in accordance with a procedure for a multi-pass weld according to any one of claims 1 to 15.
18. A method of repairing a surface of a roller used for crushing ore, the method comprises: removing any bodies extending from the surface; removing a portion of the roller until the surface is of a relatively uniform diameter; cladding the surface until the smallest diameter of the hard-faced roller is at the required diameter; removing a portion of the hard-faced roller to provide a roller at the required diameter
19. The method of repairing a surface of a roller according to claim 18 comprising removing the portion of the roller by turning.
20. The method of repairing a surface of a roller according to claim 18 comprising removing the portion of the roller to a diameter below any cavity within the roller.
21. The method of repairing a surface of a roller according to claim 18 comprising removing the portion of the roller to a predetermined diameter and filling any remaining iocaiised worn/damaged zones with a weld.
22. The method of repairing a surface of a roller according to any one of claims 18 to 21 comprising drilling a plurality of holes in the repaired roller and installing hard bodies therein.
23. The method of repairing a surface of a roller according to any one of claims 16 to 22 wherein the cladding process is in accordance with a procedure for a multi-pass weld according to any one of claims 1 to 15.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| AU2016200836A AU2016200836A1 (en) | 2015-02-09 | 2016-02-09 | Procedure For A Multi-Pass Weld |
Applications Claiming Priority (3)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| AU2015900405 | 2015-02-09 | ||
| AU2015900405A AU2015900405A0 (en) | 2015-02-09 | Procedure For A Multi-Pass Weld | |
| AU2016200836A AU2016200836A1 (en) | 2015-02-09 | 2016-02-09 | Procedure For A Multi-Pass Weld |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| AU2016200836A1 true AU2016200836A1 (en) | 2016-08-25 |
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Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| AU2016200836A Abandoned AU2016200836A1 (en) | 2015-02-09 | 2016-02-09 | Procedure For A Multi-Pass Weld |
Country Status (1)
| Country | Link |
|---|---|
| AU (1) | AU2016200836A1 (en) |
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN108229789A (en) * | 2017-12-04 | 2018-06-29 | 江苏利柏特股份有限公司 | A kind of chemical equipment modular manufacturing engineering welding manages system |
-
2016
- 2016-02-09 AU AU2016200836A patent/AU2016200836A1/en not_active Abandoned
Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN108229789A (en) * | 2017-12-04 | 2018-06-29 | 江苏利柏特股份有限公司 | A kind of chemical equipment modular manufacturing engineering welding manages system |
| CN108229789B (en) * | 2017-12-04 | 2021-07-27 | 江苏利柏特股份有限公司 | Welding management system for modular manufacturing engineering of chemical equipment |
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Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| MK1 | Application lapsed section 142(2)(a) - no request for examination in relevant period |