efd induction

EFD Induction

Terac – straightening with induction

Presentation by: Mark Wells

Product & Application Manager (Europe)

Presented by: Tom Brown

Regional Sales Manager (USA)

Distortion through welding

• Welding and other manufacturing processes where heat is introduced will leave stresses in the metal during subsequent cooling, causing distortion or warping

• Distortion can be unsightly, prevent correct fit and even add weakness to the assembly

References

1. THE MANAGEMENT OF THIN PLATE DISTORTIONN.A. McPHERSONBAE Systems – Surface Fleet Solutions(With reference to: Prediction and Prevention of Excessive Unfairness in Arleigh Burke (DDG-51) Class Deckhouse fabrication, Kirk, M., Conrardy, C., DeBiccari, A. and Michaleris, P)

2. INDUCTION HEAT STRAIGHTENING – A DISTORTION REWORK REDUCTION TOOL FOR THIN PLATE

N.A.McPherson & A.CoyleBAE Systems, Surface Fleet SolutionsM. A. Wells, EFD Induction a.s.

Overview – Ship Building• Despite improvements in

manufacturing techniques the ship-building industry is hugely affected by distortion

“Typically figures of 25,000-30,000 man-hours have been quoted for the heat straightening cost for frigates and offshore patrol vessels…” ¹

Overview – Ship Building

“..it has been estimated that the total could be up to ten times the heat straightening figures, once factors such as schedule interruptions, stripping down equipment, repainting etc are taken into consideration.” ¹

Improvements in rework requirement

Thermal forming / straightening

• Strategically heating metals with or without mechanical force is used to bend plates, beams, pipes etc

• Straightening (by heat) is mainly done by shortening (shrinking) of the long areas / surfaces (Picture shows straightening by flame)

Thermal straightening – by flame• The traditional method of straightening plates in ship-building

is to use a flame on the convex surfaces of distorted areas• The heated zone is quite shallow and on cooling, the heated

side of the plate contracts more than the “cold” side• Shrinkage of the surface causes excess material to expand

vertically• Typically used on >5mm plate

Thermal straightening – by flame

By heating a number of areas the plate can be flattened

Thermal straightening – by flame

Shrinking of surface to straighten the bulge

• Adds stress to (and shrinks) the treated surface

• Requires skilled operators• Risk of overheating of the

surface– Hydrogen ingress

• Noisy• Heating-up of the local

environment• Toxic fumes

Flame straightening can only be achieved when heating from the convex side

Alternative “traditional” method

• Using a “straight edge”


• Mechanical force to pull the sheet against the straight edge


• 25 – 50mm stitch welds to keep the plate “straight”


• Apply heat (by flame) to keep the plate straight before removing the straight edge using grinders

Alternative “traditional” method 2

• Weld bolts to the affected area

Alternative “traditional” methods

• Requires skilled operators

• Very hard work• Time consuming• Sacrificial materials• Noisy• Unsightly results

There is a better way….

With straight edgeWith straight edge

With inductionWith induction

Thermal straightening – by induction

• The inductor generates an eddy current in the steel plate, which generates a rapid heat increase to a concentrated heating zone.

• The Terac equipment is tuned not to exceed Curie temperature therefore magnetic steel cannot overheat

Video – through heating


Heating Times

010203040506070

4 6 8 10 12 14 16 18 20

Thickness (mm)

Tim

e (S

econ

ds)

Surface heated toCurieThrough Heated

Chart shows times to achieve Curie temperature (Approx. 740°C) at the surface and through the steel plate

Thermal straightening – by induction• The straightening effect occurs when the heated material

expands and contracts• A rapid, through - heating, forces the heated area to

expand vertically • Deformation is permanent• During cooling down, the material around the heated

zone will shrink equally in all directions and due to this, the plate becomes shorter


• Permanent vertical expansion evidence


• Shrinking close to the welds is shrinking at the weld-affected points and is sufficient in most situations


• Shrinking close to the welds from one side decreases the convex AND concave bulges

Typical heating pattern – first pass

Typical heating pattern – second pass

Typical heating pattern – third pass

Typical heating pattern – first pass

Operational Trial at BAE Systems – Surface Fleet

“This section covers work carried out in a shipyard involved in the construction of naval vessels with a high proportion of thin plate in the structure.” ²

“A number of areas were induction heat straightened following a laid down sequence. Deflections on areas were measured before, during and after the induction heat straightening process.” ²


“The induction heating process was compared against a standard, but well controlled , flame heating procedure. This procedure followed the laid down sequence used for the induction heating.” ²

“In this specific area of the ship the maximum allowable deflection was 6mm. The evaluation consisted of establishing the percentage of the structure brought within tolerance. It should be noted that the intention was not produce a perfectly flat structure, but one that was within the required tolerances.” ²


“In this instance the induction heating system achieved between 93 and 95% within tolerance, and the flame heating achieved between 51 and 56%. This consisted of both low and high deflections.” ²

“the time savings were estimated at about 75%. Other cost savings which could be incorporated into this were material costs (studs), strongbacks, and process costs such as grinding off the stud scars and rewelding and grinding any undercut.” ²

Metallurgical Results at BAE Systems – Surface Fleet

“Plate material was treated in the same manner as the actual structure. Testing was carried out in these areas to determine material properties such as strength, toughness and hardness. In addition, an evaluation was made of the steel microstructure in the treated areas and in reference areas of the plates.” ²

“For comparison purposes, a carefully controlled flame heating procedure was used on 5mm thick DH 36 plate, following a similar pattern to that used for the induction heating.” ²

Metallurgical Results BAE Systems – Surface Fleet

“The comparison of strength and toughness revealed very little significant difference among the induction heated samples. There was a very slight drop in toughness in the heated areas, and a similar drop in yield strength (~ 7%). However in the flame heated areas there was a reduction in toughness of almost 45% and a 7% reduction in yield strength.” ²

Metallurgical Results at BAE Systems – Surface Fleet

“The hardness of the material did show some differences, as the localised cooling and heating of the area was inevitably going to change the steel microstructure in the area.” ²

“there is between 6% and 15% increase in hardness of the induction heated areas compared to the parent plate material. For the flame heated material the increase was 16%.” ²

Performance Results ²

Test Flame InductionStraightening Performance

56% 95%

Time Saving 0 75% (Not including rework to clean up welds etc)

Yield Strength (reduction)

7% 7%

Toughness (Reduction)

45% 7%

Hardness(Increase)

16% 6 to 15%

With Terac….

Terac System

Fits very well into the shipyard environment

Terac operation

Turnkey systems – just add power

Terac System

The latest Terac is the result of almost 30 years experience gained working in the shipyard environment

Terac Inductor Unit

• Heavy Duty/Lightweight Construction

• Integrated HHT (Transformer)

• Electro-Magnets to ensure fixed position during heating

• Weight 10 kg• Cable Length 15m

Terac operation

• Simple, robust operator controls

Terac – working range

Hand Held Unit II• “Beck Special”

New development in October 2009For use with balancer unit160mm coil lengthMagnets help to keep the coil in place whilst heating(Panel condition means that magnets cannot be guaranteed to take the whole weight of the unit)

Hand Held Unit II• 2 x Buttons

• 2 x LED’s

• 90° suspension points

• Timer selection Switch

Heat Generator

State-of-the-art induction equipment for today’s industry

3 x 400 V mains supply,

25/40 kW output power

Terac Capacitor Unit

• Integrated cooling circuit and feed to inductor

• Integrated Twin Timers for programming of the heating time

• Lockable Cover• 30m cable length from Heat

Generator

Terac Inductor Unit

• Heavy Duty/Lightweight Construction

• Integrated HHT (Transformer)

• Electro-Magnets to ensure fixed position during heating

• Weight 10 kg• Cable Length 15m

Terac Inductor Unit

Terac Extension Unit

• Available as an option• Same construction as

Capacitor Unit• Adds 15m to working

radius

Hand Held Attachment for Terac

• Supply another Capacitor Unit and Head to be swappable with the deck heating Capacitor Unit and Head

–Example layout shows which items would be changed over

Hand Held Attachment for Terac

Hand Held Unit• Various coil types can be

offered i.e.–Steel–Aluminium 2 – 3mm–Aluminium 3 – 5mm

Terac operation

Features and benefits using Terac

Thermal straightening – by TeracQuality benefits over flame

straightening:

• Repeatable• Controllable• Rapid through heating up

to 20 mm• Failsafe operation –

cannot overheat (magnetic steel)

Thermal straightening – by Terac

Environmental & operator benefits over flame straightening:

• No toxic gases developed from the heating source

• Reduced smoke in case of painting or priming

• Surrounding materials at less risk from burning

• No acoustic noise• All straightening work is done

from one side• Magnetic coils provides

“clamping” of inductor during heating


Financial benefits over flame straightening:

• Ease of use–Less reliance on expensive, skilled labour–More potential operators

• Decreased risk of occupational health problems


Financial benefits over flame straightening:

• Significantly faster & more efficient process, means:

–Less man hours required for straightening, up to 80 %–Less interruption of other trades–Less overall fitting costs

• Substantial reduction in energy consumption

• Comparison Tool

EFD Induction

Terac – straightening with induction

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