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THERMEX Quenched & Tempered Rebars

Relevance of THERMEX Quenching & Tempering Technology

SECTION 1: Steel 2020
Basic Global Norms
Comparison: India & China
THE YEARS AHEAD: 2005 - 2020
SECTION 2: Relevance of Thermex Rebars
Global Trends in Rebars
Relevance of THERMEX Quenching & Tempering Technology
H&K India Thermex References and Photos of Installations

 

FLASH NEWS

 

RA  RAMSARUP BARS & RODS becomes first secondary mill

 

        to start Thermex 500 in thicker sizes - 20 to 40mm rebars

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H&K introduced 'Stop-Start Shears' in India. Today over 30 such shears installed.

THERMEX RELEVANCE TO INDIA

The Thermex Quenching & Tempering Technology was developed and patented in the early 1980s. This was one of the two quenching technologies that received world patents and global acceptance amongst the civil engineers because it met all their requirements. Germany adopted this technology immediately and reaped great cost savings on account of use of Grade 500 rebars. See Chart 5.

 

It is estimated that India could have saved about Rs 8,000 crores (80,000 million) in the 15 year period from 1985 to 2000 if it had changed over to use of Grade 500 rebars as was happening in developed countries. This estimate is based on rebar prices of Rs 12,500 per tonne. The savings today can be imagined if one considers the current price of Rs 25,000 per T. This is the price we paid for the ‘closed market’ policies of the past. The cost in terms of safety cannot be quantified.

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Chart 5: Changing Trend in Germany

Another reason why this change to products superior to CTD bars was the delay in amendment to the Code IS 13920. Rebars are governed by the Code IS 1786:1985 which is apparently based merely on the values obtainable by the CTD process. This needs urgent revision in light of the superior technology now available in the country. Alternatively, a separate Code should be evolved for “Quenched & Tempered” rebars (incorrectly referred to as TMT rebars in India). IS 1786 lays down the properties of the different grade rebars allowed in India. On comparison with actual properties and internal norms followed by Thermex Licensees in the country the difference is very stark. See Table 1.

 

 Table 1: Comparison - IS:1786 and Properties of Thermex rebars.

 

 

Properties

IS 1786 Grade Fe415

Grade Thermex 400

Thermex 400

Typical Values

IS 1786

Grade Fe500

Grade Thermex 500

Thermex 500

Typical Values

Yield Strength, N/mm2 min.

415

415

430 – 460

500

500

520 – 560

Min. Stress Ratio, (UTS:YS)

1.10

1.13

1.15 – 1.25

1.08

1.12

1.15 – 1.24

UTS,

N/mm2 min.

485

485

500 – 570

545

560

590 – 630

A5 Elongation, min %

14.5

18

20 - 25

12

16

18 - 22

 

The typical values of Thermex Grades 400 and 500 rebars mentioned in the Table-1 above do not include samples from the Durgapur and Bhilai Steel Plants of SAIL. Instead they are test results obtained in the period from August 2000 to April 2003 of 934 samples in the small mills of Thermex Licensees. Special importance is given in checking the Stress Ratio as this is a very significant factor when considering rebars for earthquake zones. Many Licensees get UTS / YS values in the range of 1.20 to 1.35 even for Grade 500 against the IS standard of only 1.08.

 

It must unfortunately be stated that all matters move rather slowly in our system. Even though a company of the stature of S.A.I.L. introduced Thermex rebars over 10 years ago, the Bureau of Indian Standards did not deem it urgent to amend the IS 13920. This Code did not permit use of Grade Fe 500 rebars in seismic zones because the elongation value specified in IS 1786 for Grade 500 was a low 12% - the value obtainable in CTD. Rather than improving the Code, BIS banned the use of Grade Fe500. It was only in March 2002 that an amendment was issued which permitted the use of Fe 500 and Fe 550 in seismic zones 3, 4 & 5 if the Elongation value was 14.5 % or more. One expected that with 55 % of the country under these seismic categories greater urgency to be shown. This delay only helped extend the life of CTD bars in India while the country lost crores of Rupees as it could not benefit from the introduction of superior quality rebars of higher strength and greater safety than CTD bars.

 

The Thermex process is a very defined and exact technology. Every Thermex system supplied is designed specifically for each rolling mill depending upon its parameters. Further, the collaborators and Licensors, HSE of Germany, insist up on each system being designed for Grade Thermex 500 – that was the original intent for developing this unique technology. Thus, every Licensee is able to produce Thermex 500 routinely without any special effort of its personnel. It is a simple-to-operate system and because all the equipment is supplied to the customer, there is no chance of failure. Unlike in other quenching & tempering technologies where the client does the engineering and selects and makes equipment on his own, the Thermex Licence is issued to only those rolling mills that obtain Thermex equipment from the Licensor, H&K in the case of mills in the Indian Region. In every such installation in India and other countries, the desired bar structure of peripheral tempered martensite structure with a fine grained ferrite-pearlite core is obtained in the very first bar rolled. No ‘trial and error’ is involved in this Thermex Technology.

 

It is heartening to note that quantity of Thermex rebars produced has grown phenomenally. The Thermex rebar capacity has crossed 2 million tonnes in India and with the orders currently under execution this will reach 3 million tonnes easily. Many municipal corporations and organisations now specifically specify Thermex rebars in their tenders. Thermex will undoubtedly play a major role in the years ahead. It is the only branded rebar in the country.

 

THERMEX is a registered trademark of H&K Rolling Mill Engineers Pvt. Ltd. in India and is owned by HSE, Germany in other Countries