Browsing by Author "Apps, R. L."
Now showing 1 - 15 of 15
Results Per Page
Sort Options
Item Open Access Assessment of blasted surfaces progress report no. 3(College of Aeronautics, 1964-09) Apps, R. L.Introduction This report covers work carried out from January - August, 1964. The work has largely consisted of further tests with the Cranfield reflectivity equipment and associated measurements of pull-off strength, but a brief assessment has also been made of an instrument for measuring reflectivity developed by the Paint Research Station. A number of miscellaneous tests are also reported. The final months of the period covered by the report have been spent in the design and construction of a new reflectivity instrument which incorporates features that the previous instruments have shown to be desirable'. Particular topics reported cover the effect of grit size and blasting time, and also a determination of the effect of using light sources of specific colours instead of white light. Much of this work has been done at laboratories and works away from Cranfield to allow external assessment of the reflectivity equipment. A number of miscellaneous tests have also been made covering the use of non-metallic grits and 'Jasonl type hammers for surface preparation, the assessment of sprayed coatings by a simple bend test and the examination of the variation of strength with time of two adhesives to determine whether an adhesive could be used for practical site testing of sprayed coatings.Item Open Access Assessment of blasted surfaces: progress report no. 2(College of Aeronautics, 1964-02) Pamdeth, N. M.; Apps, R. L.Introduction Previous work had shown that the conditions of grit blasting markedly affected the reflectivity of a mild steel surface and that measurement of reflectivity thus offered a method for the assessment of blasted surfaces. The increase in reflectivity of a series of blasted specimens was found to relate to decreasing surface quality and, after metal spraying, to decreasing bond strength between the base and the sprayed metal. However, one series of specimens did not show any correlation between reflectivity and surface quality and it was decided that an examination of a considerable number of specimens prepared under more carefully controlled conditions was necessary for the next stage of the work. The present report gives the results of reflectivity and bond strength measurements on some 300 specimens of mild steel blasted under a number of different conditions by three suppliers. Reflectivity measurements again showed 'that specimens prepared by any one supplier could be placed in a series of increasing reflectivity, although some difficulties were still encountered in relating the result of different suppliers. These difficulties were most marked with specimens blasted with worn grit. However, correlation between reflectivity, pull-off strength and blasting conditions was good with the series of specimens provided by two suppliers. The series from a third supplier has not been fully tested yet, but very little difference in reflectivity readings has been found.Item Open Access The Characteristics and Structure of High Pressure (1-42 bars) Gas Tungsten Arcs(Cranfield University, 1982) Allum, C. J.; Apps, R. L.The last decade has seen a considerable growth in the exploitation of deep sea mineral reserves. Accompanying these developments has come the need for suitable underwater repair and uainten-nce techniques. one such technique involves the use of fusion welding processes in localised dry high pressure environments created around weldments. Pressure chambers at Cranfield have been employed to simulate this sitiu. ation. These have been used to investigate the influence of ambient pressure (1 to 45 bars) on gas-tungsten arcs. The study has been of a basic nature with emphasis on arc characteristics and arc structure. Special attention is given to the argon TIG arc although helium TIG arcs and constricted argon-tungsten arcs have also been examined. Arc characteristics are reported in terms of arc appearance and modes, electrical characteristics and weld bead studies. The investigation of arc structure is concerned with gaining an understanding of observed characteristics. This has involved experimental and theoretical developments. Experimental techniques used include, electrostatic probes, calorimetry and the measurement of total power radiated from an arc. Models developed here have successfully explained many of the experimental findings and special emphasis has been directed at understanding gas flow in the column and arc stability. Much of the work included in this thesis has implications for the development of underwater welding procedures. Results presented should also contribute to gaining a better understanding of arcs operating under normal ambient conditions. However, these aspects are not discussed in any detail as the main emphasis has been placed on documenting and explaining the influence of pressure on gas-tungsten arcs.Item Open Access Chevron cracking in steel weld metals(Cranfield University, 1979-05) Mota, J. M. F.; Apps, R. L.A less well known form of transverse cracking in carbon manganese and low alloy steel weld metals, generally referred to as chevron cracking, has been found in a large number of industrial welds. These cracks are characterized by their macroscopic orientation, which is approximately transverse to the welding direction and at 45 with the plane of the plates (in a butt joint), and by the staircase morphology, which is easily recognized under microscopical examination. A special test was designed to reproduce these cracks under laboratory controlled conditions and a large number of welds was carried out. Chevron cracks were found in the tests with medium strength weld metals deposited by submerged arc with a basic agglomerated flux and by manual metal arc with basic and cellulosic electrodes. No chevron cracks were observed in the welds with rutile electrodes. High temperature baking of the submerged arc flux and the basic electrodes eliminated or reduced markedly the incidence of cracking in all cases indicating that hydrogen was the main factor controlling the cracking occurrence. Cont/d.Item Open Access Final report of grit blasting and metal spraying trials carried out at H. M. Dockyard, Devonport(College of Aeronautics, 1966-03) Apps, R. L.Mild steel surfaces that are to be protected by aluminium or zinc spray coatings are generally prepared by blasting with chilled iron angular grit. Previous work1had shown that a relationship exists between the grit blasting conditions (at least in terms of blasting angle and grit condition), the reflectivity of the blasted surface and the bond strength of a spray coating of aluminium on the blasted surface. An instrument has been developed that assesses the suitability of a blasted surface for subsequent spraying by measuring the reflectivity and has proved reasonably successful under laboratory conditions. The present need is to ascertain the performance of this reflectivity meter under shop and site conditions. The opportunity to carry out such tests at H.M. Dockyard, Devonport, was offered by the Ministry of Defence and a series of tests was made on 16th June, 1965.Item Open Access Fusion characteristics in P-GMAW of mild steel(1986-04) Quintino, Luisa; Apps, R. L.The influence of process parameters on deposition and fusion characteristics of mild steel with Pulsed Gas Metal Arc Welding has been investigated using a transistorized power supply. A simple model of melting behaviour has been developed which allows the prediction of dilution behaviour and explains the interplay between mass and heat in P-GMAW. In order to predict heat affected zone area, a model driven from the former one has also been developed. Deposition characteristics were studied taking the care of studying the influence of each welding parameter at each time, whenever it was possible. Emphasis was given to shielding gas mixture which was found to significantly influence metal transfer mode and arc stability. A systematic approach to choose process parameters in Pulsed Gas Metal Arc Welding with a constant current power supply is proposed. It was found that mean current and welding speed play the most important role in determining fusion characteristics, thus, based on a simple model, methods of controlling these aspects are suggested. Emphasis was placed on understanding dilution behaviour. It was found possibility to develop.procedures allowing the independent choice of deposition rate and dilution behaviour and to give an account of many observations with simple models of melting phenomena. The developed model is combined with calorimetric heat transfer measurements to investigate the result that only a small fraction of the total process power is required to melt the observed fusion areas. A "dual Heat" source fusion model is suggested where plate melting is largely in response to direct arc heating, providing means of optimising plate dilution and thereby reducing the risk of fusion defects. A generalized representation of fusion characteristics is given which allows independent selection of required fusion characteristics to be assessed.Item Open Access Measurement of thermal cycles in the weld heat affected zone of mild steel(College of Aeronautics, 1967-09) Coward, M. D.; Apps, R. L.The thermal cycles in the mild steel parent plate adjacent to a bead on plate weld have been measured for heat inputs of 108, 54 and 42 kJ/inch, by means of embedded thermocouples connected to high response automatic recorders. The results show that decreasing the heat input increases the cooling rate and decreases the width of the heat affected zone. For thermal cycles in which the peak temperatures reached 900°C or above, two points of inflection have been noted in the temperature ranges 400° - 600°C and 950° - 1200°C. The inflection in the lower temperature range, which has been observed by other workers, has been attributed to latent heat from the exothermic transformation of austenite to ferrite. The higher inflection point, not previously reported, has been tentatively related to the solidification in the weld pool and the release of the latent heat of fusion.Item Open Access Metal transfer in MIG welding(1982-10) Ma, Jilong; Apps, R. L.The metal transfer process in MIG welding has been investigated. The heat balance of the melting process, forces acting on the wire tip and droplets, and droplet movement were examined quantitatively both under steady current and pulsed current conditions. A novel transistorised power source was employed for precision current adjustment which with the use of high speed cinephotography and careful metallographic techniques has allowed a re-assessment of current theories to be made. A new metal transfer mode designated as ’Drop Spray* has been discovered. This transfer mode is located between the well known globular and spray transfer modes and only occurs in a very narrow current range of 20A, but it has several important features. The relationship between metal transfer mode and the welding variables has been established quantitatively for the first time. It was found that the extension resistance and heat content of droplets are determined by current and hence metal transfer modes. The amount of spatter and fume was also found to be determined by transfer mode. Metal transfer under pulsed current was also investigated. It was found that the metal transfer modes under pulsed current are the same as that of steady current. It was also found that the first drop of every pulse is of drop spray mode and the subsequent droplets will be stream spray. Careful observations and measurements have been made at various stages of the current pulse to enable greater understanding of the influence of the pulse parameters. Based on the results mentioned above, a concept of controlled MIG welding was proposed, based on the control of metal transfer mode. By this concept any predetermined feature of conventional MIG welding can be achieved consistently and repeatedly. As an application of the proposed concept, drop spray transfer was reproduced over a wide current range by means of metal transfer control. A new controlled MIG process designated as ’controlled drop spray MIG' has been developed which features high efficiency, all positional ability, freedom from spatter, low fume generation and good bead appearance. The preliminary bead on plate trial shows that all the expected results have been achieved although many more trials are necessary to fully prove the process.Item Open Access Process modelling to establish control algorithms for automated GMAW(Cranfield University, 1991-09) Scotti, A.; Norrish, J.; Apps, R. L.The feasibility of fully automatic GMAW processes may rely on the development of sophisticated equipment to emulate the manual welding torch oscillation pattern or on the development of high level methods of control to prevent the appearance of defects, especially the lack of sidewall fusion. An intermediate solution is to optimise the weaving parameters of a conventional pattern oscillator in such a way as to minimise the level of rejection. A prototype of a computerised system to work with Pulsed-GMAW equipment, in the vertical-up position, was proposed to produce a minimal level of rejection for welds in plates up to 25 mm thick. The system basically consists of optimised mode control algorithms, based on theoretical and experimental models of weld pool behaviour. Three tasks are performed by the system; the selection of parameters for an optimum working point, an off-line simulation of the operation and real-time error monitoring of the process. Statistical experimental modelling was applied in order to build most of the optimised models, because of the large number of variables to be treated and their complex inter-correlation. The welding variables were correlated with single responses. Partial and Correlation Analysis techniques were used to discover the relationship between the variables and the responses. Regression Analysis was then applied as a means of obtaining the 'weight' of the most significant variables. Finally, since some variables were found to be collinear, a corrective technique for biased variables was employed. Acceptance criteria for bead shapes were proposed and assessed. The effect of the oscillation parameters and other welding variables on the bead formation was analyzed and an operational 'envelope' for the parameters determined. A theoretical approach to predict the occurrence of poorly shaped beads, due to the lack of metal bridge between the joint walls, was successfully developed and applied in parallel with the statistical experimental methods. Equations for optimising the bead shape and for determining the operational envelope contours were subsequently generated and evaluated. An extension of the system to an actual adaptive control scheme was discussed and sensors and signals to be used were evaluated. Finally, a process instability phenomenon in long test plates was identified and investigated. This instability may prevent the use of GMA W in some conditions in the vertical-up position.Item Open Access Progress report to sponsors in the surfacing division, The Welding Institute(College of Aeronautics, 19) Apps, R. L.Since the last report to sponsors circulated in mid-1967, considerable concern has been felt over the wide scatter of results. The scatter in results between specimens produced in a single batch was generally comparatively small, in the order of 15%, but occasional results occurred which ehow6d much greater differences from the average. Identical experiments carried out in different batches exhibited rather more scatter than with in single batches. Similar scatter was noted in the results of other workers" 2 . Additionally, many blasting variables which had previously been considered important by metal sprayers appeared to have very little effect on the bond strength of flame sprayed aluminium coatings on mild steel. Consideration of scatter in results suggested four possible reasons for this scatter.Item Open Access Statistical modelling of the narrow gap gas metal arc welding process(Cranfield University, 1990-04) Modenesi, P. J.; Apps, R. L.The J-laying technique for the construction of offshore pipelines requires a fast welding process that can produce sound welds in the horizontal-vertical position. The suitability of narrow gap gas metal arc welding (NG-GMA W) process for this application was previously demonstrated. The present programme studied the influence of process parameters on the fusion characteristics of NG-GMA welding in a range of different shielding gas compositions and welding positions. Statistical techniques were employed for both designing the experimental programme and to process the data generated. A partial factorial design scheme was used to investigate the influence of input variables and their interaction in determining weld bead shape. Modelling equations were developed by multiple linear regression to represent different characteristics of the weld bead. Transformation of the response variable based on the Cox-Box method was commonly used to simplify the model format. Modelling results were analysed by graphical techniques including surface plots and a multiplot approach was developed in order to graphically assess the influence of up to four input variables on the bead shape. Conditions for acceptable bead formation were determined and the process sensitivity to minor changes in input parameters assessed. Asymmetrical base metal fusion in horizontalvertical welding is discussed and techniques to improve fusion presented. At the same time, the interaction between the power supply output characteristic and the bead geometry was studied for narrow gap joints and the effect of shielding gas composition on both process stability and fusion of the base metal was assessed. An arc instability mode that is strongly influenced by arc length, power supply characteristic and shielding gas composition was demonstrated and its properties investigated. An optimized shielding gas composition for narrow gap process was suggested.Item Open Access A study of coarse grain heat affected zone of accelerated cooled structural steels(1990-11) Araujo, C. L. D.; Apps, R. L.Modern structural steels have significantly different (generally leaner) compositions than equivalent conventional steels developed over 20 years ago. To compensate for the lower carbon and alloy content more sophisticated thermomechanical treatments have been introduced to give very fine ferrite grain size and hence good strength, ductility and fracture toughness. Despite the fact that these changes were largely introduced to improve weldability, the modern structural steels have given problems of heat affected zone (HAZ) hydrogen induced coldcracking leading to considerable debate over the causes of this apparently increased susceptibility. The present work aimed to provide the basis for a better understanding of the metallurgical behaviour of the HAZ of these new modern steels. This was accomplished by employing three low carbon(C<0.15%) low sulphur (S<0.005%) content steels produced by the OLAC process which combines controlled rolling with accelerated cooling. A normalized low carbon (0.12%C) higher sulphur (0.031%S) steel was also included in the present project for comparison purposes. The starting point was to determine the transformation temperatures of the various microconstituents in the HAZ’s by Tn Situ’ thermal analysis. A new approach was developed in which thermal data obtained from real weld thermal cycle measurements were employed in the thermal analysis. The steels studied were analyzed in the light of the results of transformation temperatures, microstructural examinations and hardness measurements in the coarse grained region of the HAZ. This approach offers much greater accuracy and consistency than previous methods of determining thermal cycles and HAZ transformation temperatures, giving a better opportunity for studying the anomalous HAZ behaviour of modern steels. Between the OLAC steels, two steels presented very low hardness(<300HV5) within the entire range of heat inputs used (0.8-3.5kJ/mm),whereas the other gave hardnesses higher than those of the normalized steel. Higher carbon (0.13%C) and a poorly balanced alloy content was considered to be an explanation for the HAZ behaviour of this steel. An investigation on the accuracy of current carbon equivalent in predicting hardenability and hardness formulae was carried out but none of the existing formulae were completely satisfactory in indicating the trend in hardenability found in all the steels. An alternative formula for predicting the variation of hardness based on one put forward by Yurioka was developed, which proved to be suitable for three of the steels studied. However, the restricted nature of all empirical carbon equivalent formulae is demonstrated and the need to limit any such formula to a restricted range of steels is re-emphasized.Item Open Access The use of process selection exercises for the training of welding technologists(College of Aeronautics, 1967) Apps, R. L.Formal lectures and laboratory experiments do not give students sufficient experience of welding processes applied to specific fabrications. A series of designs has been evolved which ib.capable of being fabricated by several different methods and students are required to produce fabrication procedures for each design. Suggested procedures are then discussed in an open forum in which both staff and students participate. The use of these exercises has been found to be a useful method whereby course members can pass on their own experience to other students and in which students learn to make decisions based on available, but often incomplete, facts.Item Open Access Welding C-Mn steels using the pulsed current MIG welding process(Cranfield University, 1986-03) Foote, W. J.; Apps, R. L.The welding of C-Mn steels using the pulsed current MIG welding process was investigated. Following initial work on the basic fusion characteristics, the process was applied to the production of closed butt joint linepipe welding and narrow gap welding (in the flat and H-V positions). The initial stage of the work covered the determination of pulse parameters for controlled metal transfer with a variety of wires and shielding gases. Basic bead-on-plate fusion characteristics were investigated 1n all welding positions and quantified in terms of the major welding variables of current and travel speed. Welding position was shown to have no effect on fusion behaviour. Successful full penetration closed butt root welds were produced in all welding positions. Heat input was shown to be the factor controlling bead dimensions. Close control over welding parameters are needed to maintain consistent bead sizes. Complete joint simulations were also made. The vertical-up technique was shown to give superior fusion characteristics with the process producing excellent quality results in all positions. Narrow gap MIG welding was shown to be feasible without wire manipulation at gap widths below 12 mm in the flat position. A wire manipulation technique gave excellent fusion characteristics with gap widths greater than 12 mm. A computer program was devised as a guide to the selection of process parameters and possible fusion behaviour. Modelling considerations showed that H-V position narrow gap welding would be feasible only with gap widths less than 10 ... A short experimental programme validated the predictions of fusion behaviour by the model and indicated the direction for future development work.Item Open Access Welding in aircraft structures(College of Aeronautics, 1966) Apps, R. L.; Gourd, L. M.; Jubb, J. E. M.The welding processes relevant to the welding of aircraft materials are briefly reviewed, together with those materials of present or future interest for aircraft structures. The problems of design for welding are also considered. It is concluded that the prospects for welding are more premising in materials other than light alloys, which win be used for high speed aircraft. In addition, further development of automatic welding machines and large heat treatment facilities is needed.