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Connect - September/October 1998

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The Internet is already making a real impact on TWI's communications with its Members and other contacts worldwide. The corporate site has seen 600% expansion in the last three years and now logs some 2700 hits per day from sites all over the world. The corporate site is already impressive containing details of products, activities and publications, which support TWI's, core business of Member and professional services. The real challenge of the Internet for TWI is the distribution of knowledge and the possibility of selling information at prices which are far below those currently possible with conventional communication.

Developing knowledge trading is complicated. It involves building and maintaining websites which are at the leading edge of Internet technology while simultaneously equipping those sites with products and services which go some way to copy the experience of dealing with a human expert.

For the last two years, TWI has been developing an experimental knowledge trading platform in association with BT Research at Martlesham. By pooling the resources of two 'best of breed' organisations the aim is to keep developments at the leading edge of site and content development.

During this period, TWI has operated with support from the DTI to develop an entirely new range of information, to convert over 10% of staff into a 'content factory' and to pilot the new services with a limited number of external organisations. We have also secured European Community funding for the launch of pilot services in French, Italian and Spanish. The next phase of this development has just started with the transfer of the site to a server at Abington. The pilot service will continue for the next three months, following which the service is scheduled to expand to a wider circle of Members.

Watch this space! In the interim, if you would like further details, please contact David Kilpatrick at TWI. E-mail: djkilpatrick@twi-global.com



 

Fracture behaviour of transition weldments
TWI partners in half million ECU collaboration

Connect, September/October 1998

A series of collaborative projects in the Age cluster of research work on nuclear fission and reactor safety began in 1997. TWI is contributing to a 500 000 ECU project on Structural Integrity of Bi-Metallic Components (BIMET) together with Electricité de France, Framatome, GKSS, CEA, VTT, JRC and AEA Technology.

The work includes:

  • manufacture of representative transition welds
  • large scale testing of pipework specimens
  • analysis of fracture behaviour using advanced fracture mechanics concepts

The work will contribute to the development and validation of analysis methods for surface flaws in tubular ferritic to austenitic stainless steel transition welds. The project is due to be completed by the end of 1999.



 

Inching onward - friction stir steels the lead

Connect, September/October 1998

Successful friction stir welds in steel plate of 1" (25mm) thickness have now been achieved at TWI.

In recent years friction stir welding (FSW) has shown its credentials in joining non-ferrous materials including aluminium, lead, magnesium, zinc and even copper. So far, little has been reported about joining ferrous materials but now the feasibility of joining relatively thick plate by FSW has come under the spotlight at TWI and trials have produced positive results.

Friction stir is a thermomechanical hot shear process in which a non-consumable tool is inserted and rotated within a joint. The heat generated causes intense plastic deformation.

A plasticised 'third-body' is formed that surrounds the probe and the contacting region of the rotating tool (Fig. 1). The local temperature rises and the yield strength of the material at the interface between the rotating tool and the workpiece falls to below the applied shear stress. In so doing, it generates suitable 'third-body' conditions to allow passage of the FSW tool through materials such as steel.

Fig. 1 Schematic diagram of friction stir process
Fig. 1 Schematic diagram of friction stir process
Fig. 1 Schematic diagram of friction stir process

Hydrostatic pressure is maintained enabling plastic flow of material from the leading side to the trailing side of the tool and the formation of a solid-phase joint.

A specially shaped rotating tool is used which travels at speeds between 1.7 and 4mm/sec (100-240mm/min), comparable with arc welding. Figs. 2 and 3 show typical welds.

Fig. 2 Test weld showing 1" (25mm) carbon steel double sided FWS butt weld
Fig. 2 Test weld showing 1" (25mm) carbon steel double sided FWS butt weld
Fig. 3 One metre long 12mm thick low carbon 12% chrome steel, double sided test weld
Fig. 3 One metre long 12mm thick low carbon 12% chrome steel, double sided test weld
Fig. 4 Cross-weld tensile test samples in low carbon 12% chrome steel. The weld surfaces are machines to uniform thickness before testing
Fig. 4 Cross-weld tensile test samples in low carbon 12% chrome steel. The weld surfaces are machines to uniform thickness before testing

Mechanical properties of the welds look promising (Fig. 4) encouraging further development by way of a Group Sponsored Project.

To find out more, call Wayne Thomas, Keith Johnson, Dave Nicholas or Phil Threadgill. E-mail: efp@twi-global.com



 

New project to exploit FSW of steels

Connect, September/October 1998

A Group Sponsored Project has recently been launched to provide the expertise for industry to exploit the new breakthrough in friction welding of steels. The programme will optimise tool design, process parameters and establish the service performance of welds and tools.

If you are interested in becoming a project sponsor or would like further information on the project, contact Stuart MacLachlan. E-mail: smaclachlan@twi-global.com



 

Ceramics first

Connect, September/October 1998

Professor John Wood of Nottingham University cuts the ribbon to open TWI's new Ceramics Centre
Professor John Wood of Nottingham University cuts the ribbon to open TWI's new Ceramics Centre

A special event in TWI's calendar took place on 30 June 1998 - the first Ceramics Open Day.

The event comprised a seminar and tour and an opportunity for visitors to get advice on their ceramic problems.

Morning presentations were given by Professor John Wood (Nottingham University) on Foresight and its impact on the ceramics industry, Professor Tony Kelly (University of Cambridge) on high temperature ceramics, Dr Tony Razzell (Rolls Royce plc) on ceramics for aeroengines and Dr Wendy Hanson of TWI who gave an overview of ceramic technologies at TWI.

After lunch, Professor Wood cut the ribbon (with a pair of zirconia ceramic scissors) to open the new Ceramics Centre. Attendees were given a tour of the facility and could attend a clinic with TWI staff providing help and advice on a wide range of joining and ceramics issues.

If you would like to visit the new Centre, or if you wish to discuss a specific ceramic-related issue, please contact Wendy Hanson at TWI. E-mail: wbhanson@twi-global.com



 

Fuel cells - investing in a clean future

Connect, September/October 1998

A planar, ceramic solid oxide fuel cell stack
A planar, ceramic solid oxide fuel cell stack

Fuel cells are high-efficiency devices that convert chemical energy stored in hydrocarbon and hydrogen fuels directly into electricity without going through a combustion cycle.

There are four main fuel cell types, each suited to different applications, but they all have one thing in common. They are invariably based on a stack of individual cells that need physical and electrical joining. For high temperature ceramic fuel cells, which need to operate continuously for tens of thousands of hours, joining the ceramic and metal components presents a considerable challenge.

This is exactly the type of challenge in which TWI has developed expertise through the Core Research Programmes on high temperature ceramic joining. Research includes work on ceramic reinforced braze systems for ceramic-ceramic and ceramic-metal joints and glass-ceramic systems for improved thermal expansion matching. In addition TWI combines practical engineering experience of these systems with finite element modelling to improve joint design and minimise residual stresses.

The increasing importance of fuel cells in the future was the subject of an international symposium held in London at the end of 1997.

For more information on TWI's expertise in this area contact Wendy Hanson. E-mail: wbhanson@twi-global.com



 

News in brief

Connect, September/October 1998

New Group Sponsored Projects (GSPs)

Three GSPs have recently been launched in TWI's Materials Department:

  • Improvement of type IV creep life in welded modified 9Cr1Mo steels by optimisation of creep strength mismatch:
    Project Leader, Adrienne Barnes
  • ERW/HFI welded line pipe for sour service applications:
    Project Leader, Richard Pargeter
  • Optimising the properties of weldments in weldable martensitic and supermartensitic stainless steels:
    Project Leader, Paul Woollin

For details on any of these projects, e-mail: mat@twi-global.com


Awards threesome for TWI

This summer, staff at Abington have been awarded a trio of prizes for work on electron beam welding, corrosion control and multimedia production.

Allan Sanderson receives the 1998 IIV Yoshiaki Arata Award given annually to an individual who has realised outstanding achievements in fundamental research in welding science and technology leading to significant progress in welding engineering and related fields.

Mike Gittos and Trevor Gooch have been awarded the Guy Bengough prize of the Institute of Materials for a paper published in the preceding two years making an outstanding contribution to the subject of corrosion and corrosion control. Their joint paper was entitled Effect of iron dilution on corrosion resistance of Ni-Cr-Mo cladding.

The recently published CD-ROM Welding Fume Tutor won first prize for the best multimedia product at the 3rd European Film and Multimedia Festival. There were 47 entries in the competition.

Martin Bourton, Graham Carter, John Dadson and Brian Smith formed the team.


4th International Marine Corrosion Forum

Following previous very successful forums, the Nickel Development Institute and the Marine Corrosion Club are organising the fourth International Marine Corrosion Forum to be held in April 1999 in Amsterdam. Further details from David Buxton at TWI (e-mail: dcbuxton@twi-global.com ) or The Nickel Development Institute, The Holloway, Alvechurch, Birmingham B48 7QB (e-mail: NiDI_Birmingham_UK@nidi.org )



 

Closer ties down under

Connect, September/October 1998

Chris Smallbone of WTIA (right) and Bevan Braithwaite, TWI sign the Joint Industrial Membership agreement
Chris Smallbone of WTIA (right) and Bevan Braithwaite, TWI sign the Joint Industrial Membership agreement

The long history of TWI interaction with industry in Australia has taken a further step forward. Building on the success of the previous tripartite arrangement, TWI and WTIA (Welding Technology Institute of Australia) have entered into a new Joint Industrial Membership (JIM) arrangement for Australian industry.

The aim of the scheme is to meet the needs of existing and future Industrial Members in Australia by providing a local support framework plus supply of internationally renowned expertise and leading edge technology. The synergy of the arrangement will benefit Australian industry, and both TWI and WTIA, with the objective of enhancing further growth in Industrial Membership.

Industrial Members are still able to contact TWI staff direct, but can also call upon the WTIA Federal Office in Lidcombe, NSW. In addition, with support from the Federal Government, WTIA has six State Technology Managers who will provide technology transfer and support to industry in their territory. These STMs will also be responsible for developing growth in the Joint Industrial Membership scheme.

Enquiries may be directed in the first instance to WTIA Federal Office (tel 02 9748 4443 fax 02 9748 2858).



 

Sticking with TWI

Connect, September/October 1998

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Industrial Members can now take advantage of the fully equipped adhesives laboratory at Abington which is available to carry out small contract production runs.

Experienced staff can carry out pretreatment and bonding of a wide range of materials using all major types of adhesive. Laser cutting of film adhesive for complex shapes, humidity and salt spray testing services can also be undertaken.

For more information, contact Naomi Linklater with your requirements. E-mail: njlinklater@twi-global.com


 

Solar flair with Barrikade

Connect, September/October 1998

Barrikade T can be cut and adhesively bonded as easily as wood.
Barrikade T can be cut and adhesively bonded as easily as wood.

A cool idea for heat insulation - when you're hot, you're not.

A new substance has been developed at TWI which overcomes many of the heat transfer problems associated with traditional construction materials.

This cost effective barrier material, consisting of an inorganic material and binder, can be used as a coating to protect structures that may be affected by high temperatures. It can be produced in a number of thicknesses, adheres to most surfaces including metal, wood and composites and can be moulded round complicated shapes and machined using simple hand tools.

Being lightweight, this non-toxic product is ideally suited as a core material for sandwich structures. Initial trials have shown that it can withstand 1000°C on one face while the other face does not exceed 170°C after 70 minutes.

Where other barrier materials would combust, Barrikade T can withstand temperatures up to 1000�C.
Where other barrier materials would combust, Barrikade T can withstand temperatures up to 1000°C.
Butter wouldn't melt - a really effective insulating material.
Butter wouldn't melt - a really effective insulating material.

Applications for the material (patent applied for) are firewalls in building and ships and heat shields to protect from solar or other radiating heating.

Members interested in evaluating this technology for use in their present or future products or in using this idea to meet their needs, contact Paul Burling. E-mail: paul.burling@twi-global.com




 

Job knowledge for welders

Distortion - corrective techniques

 Local heating of the flange edges to produce curved beams for a bridge structure
Local heating of the flange edges to produce curved beams for a bridge structure

Every effort should be made to avoid distortion at the design stage and by using suitable fabrication procedures. As it is not always possible to avoid distortion during fabrication, several well-established corrective techniques can be employed. However, reworking to correct distortion should not be undertaken lightly as it is costly and needs considerable skill to avoid damaging the component.

In this issue, general guidelines are provided on 'best practice' for correcting distortion using mechanical or thermal techniques.

Mechanical techniques

The principal mechanical techniques are hammering and pressing. Hammering may cause surface damage and work hardening.

In cases of bowing or angular distortion, the complete component can often be straightened on a press without the disadvantages of hammering. Packing pieces are inserted between the component and the platens of the press. It is important to impose sufficient deformation to give over-correction so that the normal elastic spring-back will allow the component to assume its correct shape.

Fig. 1 Use of press to correct bowing in T butt joint
Fig. 1 Use of press to correct bowing in T butt joint
Pressing to correct bowing in a flanged plate is illustrated in Fig. 1. In long components, distortion is removed progressively in a series of incremental pressings; each one acting over a short length. In the case of the flanged plate, the load should act on the flange to prevent local damage to the web at the load points. As incremental point loading will only produce an approximately straight component, it is better to use a former to achieve a straight component or to produce a smooth curvature.

Best practice for mechanical straightening

The following should be adopted when using pressing techniques to remove distortion:

  • Use packing pieces which will over correct the distortion so that spring-back will return the component to the correct shape
  • Check that the component is adequately supported during pressing to prevent buckling
  • Use a former (or rolling) to achieve a straight component or produce a curvature
  • As unsecured packing pieces may fly out from the press, the following safe practice must be adopted:
    - bolt the packing pieces to the platen
    - place a metal plate of adequate thickness to intercept the 'missile'
    - clear personnel from the hazard area

Thermal techniques

The basic principle behind thermal techniques is to create sufficiently high local stresses so that, on cooling, the component is pulled back into shape. 

Fig. 2 Localised heating to correct distortion
Fig. 2 Localised heating to correct distortion

This is achieved by locally heating the material to a temperature where plastic deformation will occur as the hot, low yield strength material tries to expand against the surrounding cold, higher yield strength metal. On cooling to room temperature the heated area will attempt to shrink to a smaller size than before heating. The stresses generated thereby will pull the component into the required shape. (See Fig. 2)

Local heating is, therefore, a relatively simple but effective means of correcting welding distortion. Shrinkage level is determined by size, number, location and temperature of the heated zones. Thickness and plate size determines the area of the heated zone. Number and placement of heating zones are largely a question of experience. For new jobs, tests will often be needed to quantify the level of shrinkage.

Spot, line, or wedge-shaped heating techniques can all be used in thermal correction of distortion.

Spot heating

Fig. 3 Spot heating for correcting buckling
Fig. 3 Spot heating for correcting buckling
Spot heating (Fig. 3), is used to remove buckling, for example when a relatively thin sheet has been welded to a stiff frame. Distortion is corrected by spot heating on the convex side. If the buckling is regular, the spots can be arranged symmetrically, starting at the centre of the buckle and working outwards.

Line heating

Fig. 4 Line heating to correct angular distortion in a fillet weld
Fig. 4 Line heating to correct angular distortion in a fillet weld

Heating in straight lines is often used to correct angular distortion, for example, in fillet welds (Fig. 4). The component is heated along the line of the welded joint but on the opposite side to the weld so the induced stresses will pull the flange flat.

Wedge-shaped heating

To correct distortion in larger complex fabrications it may be necessary to heat whole areas in addition to employing line heating. The pattern aims at shrinking one part of the fabrication to pull the material back into shape. 

Fig. 5 Use of wedge shaped heating to straighten plate
Fig. 5 Use of wedge shaped heating to straighten plate

Apart from spot heating of thin panels, a wedge-shaped heating zone should be used, (Fig. 5) from base to apex and the temperature profile should be uniform through the plate thickness. For thicker section material, it may be necessary to use two torches, one on each side of the plate.

As a general guideline, to straighten a curved plate (Fig. 5) wedge dimensions should be:

  1. Length of wedge - two-thirds of the plate width
  2. Width of wedge (base) - one sixth of its length (base to apex)
The degree of straightening will typically be 5mm in a 3m length of plate.

Wedge-shaped heating can be used to correct distortion in a variety of situations, (Fig. 6):

  1. Standard rolled section which needs correction in two planes,(Fig. 6a)
  2. Buckle at edge of plate as an alternative to rolling (Fi.g 6b)
  3. Box section fabrication which is distorted out of plane (Fig. 6c)
Fig. 6 Wedge shaped heating to correct distortion a) standard rolled steel section
Fig. 6 Wedge shaped heating to correct distortion a) standard rolled steel section
b) buckled edge of plate
b) buckled edge of plate
c) box fabrication
c) box fabrication

General precautions

The dangers of using thermal straightening techniques are the risk of over-shrinking too large an area or causing metallurgical changes by heating to too high a temperature. As a general rule, when correcting distortion in steels the temperature of the area should be restricted to approximately to 60° - 650°C - dull red heat.

If the heating is interrupted, or the heat lost, the operator must allow the metal to cool and then begin again.

Best practice for distortion correction by thermal heating

The following should be adopted when using thermal techniques to remove distortion:

  • use spot heating to remove buckling in thin sheet structures
  • other than in spot heating of thin panels, use a wedge-shaped heating technique
  • use line heating to correct angular distortion in plate
  • restrict the area of heating to avoid over-shrinking the component
  • limit the temperature to 60° to 650°C (dull red heat) in steels to prevent metallurgical damage
  • in wedge heating, heat from the base to the apex of the wedge, penetrate evenly through the plate thickness and maintain an even temperature

For more information please email:


contactus@twi.co.uk