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PWL#063 - Thruster Welding, High Strength Bolts, cleaning filler metals, Clad Steel, ceramic coating November 03, 2008 |
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| We hope you will find this Letter interesting and useful. Let us know what you think of it. PWL#063 - Thruster Welding, Welding High Tensile Strength Bolts, Cleaning Spooled Filler Metal Wires, How to weld Clad Steel, Ceramic Thermal Barrier Coatings, Welding Ductile Cast Iron, Explosion Welding and more... DON'T USE REPLY to send us your messages! Use Contact Us instead. This publication brings to the readers practical answers to welding problems in an informal setting designed to be helpful and informative. You are urged to pass-along this publication to your friends, if you like it, and if you want to help them. If you received this from a friend and if you like what you read, please subscribe free of charge and you will also receive a bonus book on Practical HARDNESS TESTING Made Simple. Note: References to articles or other documents are given here in one of two forms. If the links are "live" (usually underlined or otherwise highlighted) they are operated with a click of the mouse. If they are URL's (Uniform Resource Locator), which is the analogue of an address, they begin with "http://..." or "www.". These are not live and must be copied and pasted entirely into the browser (after having selected them with the mouse or otherwise). If they are long they may be displayed in two or more lines. In that case one has to care that the URL be copied completely in a single line without any space, and Enter.
1 - Introduction 2 - Article - Thruster Welding 3 - How to do it well: Welding High Tensile Bolts 4 - Cleaning Filler Metals 5 - Online Press: recent Welding related Articles 6 - Terms and Definitions Reminder 7 - Article - How to weld Clad Steel 8 - Site Updating: Welding Ductile Iron, Explosion Welding 9 - Short Items 10 - Explorations: beyond the Welder 11 - Contributions: Ceramic Coatings 12 - Testimonials 13 - Correspondence: a few Comments 14 - Bulletin Board 1 - Introduction This present Issue No. 63 of Practical Welding Letter, as you know it for more than five years, is going to be the last of the present series. Starting with the next issue, it will be split into two different newsletters that will be built with somewhat modified objectives. Our faithful readers will continue to receive at no cost an abridged edition of PWL that will include the complete Table of Contents, but only a few articles of general interest. The second newsletter spin off will be more focused on actual readers' interests and needs, as far as we can get indications as to what our audience prefers. I believe the new program will provide to a smaller interested audience more valuable information and will permit our deeper involvement in actual readers' problems with pertinent practical advice. This Issue begins with the description of experiments designed to research and test known physical principles to ascertain if Thruster Welding is a feasible process likely to provide advantages to the welding community. Then a reader asks if welding high strength bolts is a good idea and how to to it. What do you think? Further down the page new methods of cleaning spooled filler metal wire are reported. How to weld clad steel is the subject of an article referring to one of the two pages recently added to our website, which deals with Explosion Welding. The other new page provides information on how to weld Ductile Cast Iron. Another article reports on recent research dealing with advanced thermal barrier coatings designed to protect space vehicles in the re-entry stage to the atmosphere. Other sections are still present as usual in this issue where you may find additional information. We welcome your feedback. Click on Contact Us. 2 - Article - Thruster Welding A trace left in the records by the query of a reader, interested in the subject spurred us to investigate the matter. A quick search through the main sources of information for the welding industry (AWS, AMS, TWI) did not bring any news. A general search was not any more lucky either, with the exception of a short note consisting in the abstract of the research work reported hereafter. "The main aim of this work was to construct and study an electromagnetic device to weld and cut materials. This device, known as magnetoplasmadynamic thruster (MPDT) ionizes gas, forming a plasma jet at high temperatures. Firstly, tests were performed analyzing the influence of physical variables (electric current intensity, relative position of electrodes, gas flow rates and angle of the extremity of the cathode) on the plasma jet. Based on the results of these tests, the parameters best adapted for welding and cutting were chosen. So, autogenous welding of stainless steel sheets was performed, as well as cutting of sheets with different thicknesses and different materials. The results have shown that this electromagnetic device can be used for welding and cutting." It seems that the above research did not yet leave the development laboratory but we can rest assured that, if significant advantages can be demonstrated relative to current welding and cutting equipment, it will not take much time until MPDT will find its way to the average shop. The above abstract and the reference to the full text can be found at MPDT. If some reader knows more on the subject and can contribute additional information to let us understand better this technology, I will be glad to publish it in our next issue. A nice exposition of the physical principles underlying their application for a different purpose (space propulsion) can be found at Another article on MPDT propulsion can be found at 3 - How to do it well: Welding High Tensile Bolts Question: I am trying to find out if you loose tensile strength of threaded rod/bolts if you weld them end to end (to gain extra length)? The rod is high tensile steel. Answer: Don't weld high strength bolts. As you suspect you will loose strength. Welding heats the material and destroys the mechanical properties obtained through heat treatment. There is no suitable welding method that will preserve strength. If welding is performed however, depending on the type of steel, the mechanical properties could be partly restored only by repeating completely the original heat treatment. 4 - Cleaning Filler Metals All welding processes need clean materials and consumables, especially those that run unattended for long stretches of time during which small amounts of oil or dirt may build up objectionable chunks likely to interfere with acceptable results. Special cleaning pads are available, designed to clean welding wires for GMAW (Mig) if a setup for manual discontinuous operation is satisfactory. If more thorough and continuous cleaning is needed, readers are referred to a recent article published at page 26 of the September 2008 issue of the Welding Journal. The article describes the workings of a special machine designed for wire surface preparation. The wire to be treated is advanced at high speed and tension, while a length of it has, wrapped all around and in frictional contact with it, constantly renewed moving cords, either braided or flat. The operating friction force between the two, results from the difference of speed, high for the wire, low for the cord. A number of parameters influence the friction force that must be kept in an optimum range for best results. The following data are reported for the application of a commercial product called Helicord, of different shapes and materials depending on the surface preparation required. The cord speed is adjustable between 4 and 120 cm per minute. The controlled cord tension can vary between 2 and 30 N (newton). The range of the friction force is from 6 to 100 N. For cleaning operations cord and wrapped wire run in opposite directions. Cord pre-tension is established by controlling the release speed from the supply spool and the collection speed of the take-up spool. The cleaning operation can be combined with abrasive powders absorbed in the cord, or with high boiling solvent dispensed by a metering pump. If heavy drawing compounds need to be removed from the wire, two such machines can be mounted in series for obtaining acceptable cleaning results. During the development work different analysis methods were screened to find in each case the most reliable one, capable of verifying the amount of residual compound still present on the wire after treatment, at the required level of detection and accuracy. Discussion of the characteristics of experimental testing methods and of some results conclude the article. Interested readers are urged to seek the original paper whose reference is reported above. 5 - Online Press: recent Welding related Articles How Peripherals can maximize your Robotic Welding Performance What's involved in Abrasive Waterjet Maintenance? Welding and Cutting - get two no cost issues of the Ten Tips for Improving Plasma Cutting Quality How Shock Absorbers are made (Video)
6 - Terms and Definitions Reminder Block Sequence in a multipass weld is a combined sequence of separate weld beads that are laid down one upon the other for the whole block, filling the whole thickness of the joint, before going on to weld another block. Chain Intermittent Weld is a non continuous weld done on both sides of a joint by depositing opposite short separate beads while leaving unwelded intervals on both sides between successive welds. Gap is a non standard term used to describe root opening or joint clearance. Gas Regulator is a device used to supply gas from a higher pressure container at nominally constant pressure. Joint Type is one of the five typical configurations described as butt, corner, edge, lap and T, based on the relative position of flat elements in the joint. Multiport Nozzle is a constricting nozzle of the plasma arc torch with a few holes placed to provide some control on the arc shape. Oxygen Lance Cutting process uses a consumable lance supplying oxygen, while preheat for starting is provided by other means. Process is any one of basic technologies (operational elements) used for joining or for cutting materials, grouped according to some common characteristics. 7 - Article - How to weld Clad Steel Clad Steel plates are useful products that are made of a layer of corrosion resistant material like Nickel Alloy or Stainless Steel, metallurgically bonded on top of carbon or low alloy steel. This kind of composite base metal permits to place the expensive protective material in contact with the aggressive chemical medium (usually inside some sort of container or vessel) while the outside of it (facing a milder environment) is made of a less expensive steel of suitable properties to meet the structural requirements. By using clad steel instead of solid alloy plate, substantial economic savings of about half the cost of the material can be realized. One method used to produce clad steel is outlined in the new website page on Explosion Welding, announced hereafter in the following section. When planning the fabrication of engineering structures that use clad steel, welding procedures by conventional processes can be applied, taking care not to compromise the corrosion resistance properties of the weld by dilution of iron within the nickel material. This occurrence must be avoided as it will drastically reduce corrosion resistance and mechanical properties of the cladding at the weld location. Preferably both sides of the plates should be equally accessible for welding. Butt joints should be selected for welding in flat position. A suitable filler material should be selected for the clad metal. For plates of total thickness less than about 10 mm (3/8"), the first pass is done on the clad side, caring that the molten metal will not reach the steel, to avoid dilution with iron. The use of over alloyed filler metal is recommended. The plates are turned over and the joint is back gauged just up to the root of the first alloy pass. The weld is then completed from the back side with the same alloy filler metal. For thicker plates, the joint edges should be prepared by beveling or contour milling from the steel side, leaving a small steel land (straight thickness near the clad side) on top of the cladding. Welding is performed from the steel side with steel filler metal, avoiding to reach the cladding. Upon overturning the plates and back gouging or machining the root, welding is completed by two or more passes (again to avoid iron dilution as much as possible) with nickel base alloy or stainless as appropriate. The joints of thick plates are possibly prepared with double V, double U or double J shape, to reduce the amount of deposited metal and to control distortion. Part of the joint may be filled with steel and only the top layers on the cladding side will be welded with nickel alloy, controlling iron dilution at the working face with a sufficient number of layers. If the plates cannot be overturned, welding has to be performed entirely from one side, upon preparing the joint shape as needed. If only the steel side is accessible the whole joint should be welded with nickel alloy metal, and then some iron dilution is inevitable with consequent reduction of corrosion resistance properties. Sometimes the strip back method is used for thick joints. To apply this technique, a certain distance from the joint edge is stripped of all the clad layer. The steel plate is then welded normally, without fear of dilution. Upon its completion, the protective layer is restored where it had been removed, by usual surfacing methods with suitable alloy. Although it requires more welding, this technique avoids any risks of cracking because of penetration of steel welding into the cladding. The selected procedure should be tested on a small test piece and approved (qualified) before starting important fabrications. 8 - Site Updating: Welding Ductile Iron, Explosion Welding The Pages of this Month deal with two interesting subjects. The first one explains the procedures needed to weld an important class of Cast Irons. The second page, reachable by clicking on Explosion Welding, provides essential information on a widely employed process. It is true that clad material is made mainly by specialized industries. But the clad plates can solve many problems to regular welding shops. It is important to know how to use such products if facing specific fabrication problems. Transition parts (say half of aluminum and half of steel), made by any suitable process, including Explosion Welding, are easily welded to components by traditional means. The only attention is to connect properly the materials to the correct side of the transition part (i.e. aluminum to aluminum and steel to steel). Additional precautions must be applied for bimetallic plates to be welded to themselves. An example of such a welding is presented above in section (7). To stay up to date with the ever expanding Content of the website you may subscribe to one of the RSS readers by taking the actions explained under the NavBar in any page. When looking for specific information and links, Readers are urged to use the Google Search window that appears in almost every page of our Website. Another method to find one's way in the maze of this Website is to look at the Site Map and/or to visit periodically the Site Blog. In case that everything else fails and if you still do not find the information on welding and related subjects that you need, please Contact Us and we will try to find the answer for you. 9 - Short Items 9.1 - Castability represents the relative ease with which a molten metal flows through and fills a mold or casting die. 9.2 - Cathodic Protection of a metal consists in the reduction of corrosion rate by shifting the corrosion potential of the electrode toward a less oxidizing potential. This is achieved by applying an external electromotive force or by galvanically coupling it to a more anodic metal. 9.3 - Cleavage Fracture appears when most of the grains of a polycrystalline metal have failed by cleavage, resulting in bright reflecting facets. This failure is associated with low-energy brittle fracture. 9.4 - Electroless Plating is the deposition of conductive material from an autocatalytic plating solution without the application of electrical current. 9.5 - Fines are the portion of a powder composed of particles smaller than a specified size, too small to be further graded. 9.6 - Friction is the resisting force opposing relative movement between two bodies. It is generated by attrition, tangentially to the common boundary under the action of an external force, when one body moves or tends to move relative to the surface of the other. 10 - Explorations: beyond the Welder Science Friction: An X-Ray Machine Energized by Adhesive Tape Sticky Tape X-Rays (Video) Hubble unveils Colourful Star Birth Region Global Warming Currency of Compassion halts Global Food Crisis 11 - Contributions: Ceramic Coatings Ceramic Coatings are used as Thermal Barriers to protect substrates in high temperature applications. The purpose is to introduce an insulating layer, thereby preserving the properties of the structure at a temperature lower than that of direct exposure. Additionally if the ceramic layer is impervious to oxygen, the integrity of the substrate can be assured by avoiding destructive oxidation. If the substrate is metallic, thermal spray processes have been successfully used in certain applications by carefully selecting the intermediate materials for limiting the stresses, due to differential thermal expansion, that may cause spalling of the coatings. A recent article in the October 2008 issue of Advanced Materials and Processes at page 30, reviews studies for the development of new ceramic coatings intended for ultra high temperatures, as needed for protecting carbon-carbon composite materials for aerospace structures. During the re-entry phase through the atmosphere such vehicles must be capable of withstanding extreme aerothermal heating. The article reports that two ceramic materials were studied, silicon carbide (SiC) and zirconium diboride (ZrB2). It is planned to use the combination of the two materials, that will provide adequate protection, as it was determined that no single ceramic alone is sufficiently protective. Adherence and resistance to spalling are primary requirements, while preventing oxygen passage through the layers is essential. Sufficient erosion resistance is also required. The techniques explored, singly or in combination, include sputter deposition, electroplating, electron beam irradiation, liquid precursor methods, slurry coating, pack cementation and chemical vapor deposition. The article reviews the problems, the variants and the methods used to control the results. Although the potential of this approach seems to have been clearly determined, the practical application of the selected methods needs further work. Interested readers are urged to seek the above mentioned source. 12 - Testimonials From: Lyn Evans Hi Elia, [...] Thanks a lot, Lyn
From: Vinayak Manoj
Thanks Mr. Elia Levi for the suggestion. Regards
13 - Correspondence: a few Comments 13.1 - A recurring, somewhat disturbing problem, is that of readers that throw up a question without adequate details. As I mean to provide significant answers and I cannot guess the missing information, I ask for additional input, sometimes dedicating quite a bit of attention to the problem. To my surprise I find that the original question has no follow-up, no answer, nothing. I cannot understand such a behavior that leaves me baffled and mystified. 13.2 - From time to time I receive requests of quotes for specific hardware or consumables that readers imagine we should be able to supply. Sorry, we are not. 14 - Bulletin Board 14.1 - Symposium on Thermal Spray 14.2 - Joining Dissimilar Metals Conference
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