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Amar Elastomers Private Limited: Optimisation of Runnability and Selection of Suction Roll Shell in Wet End

Over the last 35 years, Amar Elastomers, through diligence and persistence, has built itself a brand and acquired a reputation for service universally benchmarked against the best, by innovating the preferred and required rubber roll solutions for paper machines for the Indian paper mills and for overseas mills also.

Mr. Rajiv Kumar Agarwal, CEO,
Amar Elastomers Private Limited

Amar Elastomers has been a one stop destination for engineered rubber roll coverings and complete roll shells. Just to introduce and throw a lime light on the journey since the inception in 1996, AMAR ELASTOMERS has been continuously fighting with the odds of the industry for better sustainability of new and advanced roll coverings. To be precise the company is an integrated rubber roll manufacturing unit, engaged from shell manufacturing in its steel melting shop followed with shell machining and assembly in huge mechanical shops and then rubber coverings of these manufactured shells as per the applications in the rubber division shop. This fleet of equipment is then balanced in the final ultramodern facility for grinding on CNC grinders and then drilling of press rolls on CNC multi spindle drilling machines.

It should be understood on first priority that suction rolls are subject to various corrosion related mechanisms, which includes intergranular corrosions, pitting and surface roughening, corrosion fatigue and corrosion due to the erosion on surface of the shell. Failures arising due to corrosion of shell, what we call as Corrosion Fatigue is the main and greatest concern, in the selection of stainless-steel shell nomenclature.

Initiation of crack and growing or expansion of the same under the imposition of cyclic stresses mainly generate corrosion fatigue. Wet end rolls of a paper machine experience a stress reversal cycle during each rotation of roll, as the stresses are developed in the nip of the roll and thus giving the way to corrosion fatigue.

A SN-Curve (sometimes written S-N Curve) would be the best way to understand the subject. And S-N Curve is a plot of the magnitude of an alternating stress versus the number of cycles to failure for a given material. Since these suction rolls experience lot may cycles a in a year, thus the magnitude of cyclic stresses that can be imposed on a suction roll are quite low.

Amar Elastomer’s historical experience and approach in the metallurgical sector have given birth to centrifugally casted suction roll shells for the paper industry for the first time in India. Steel manufactured from Virgin Ferro-Alloys in ladle melting and refining system, results to best micro bonded structure. This enables and helps in better refined and uniformly distributed molecular pattern of the alloying elements. Often the neglected elements like Nitrogen and Copper has added the strength in our shell steel composition in ultimate binding of the molecular granular structure and had resulted to higher tensile strength of the produce. The fine selection of hardness and Young’ Modulus keeps the deflection of the material in the required limits.

In earlier days, mills generally used shell material to be of bronze and which were gradually replaced by austenitic steel e.g., CF-8M and martensitic steel e.g., CF-15, which provided better strength and corrosion improvements over bronze. These have single phase microstructure consisting grains of either ferritic, austenitic or martensitic stainless steel.

Later, this metallurgy was taken up by Duplex Steel with variant nomenclatures of different shell manufacturers and suppliers. To be precise Duplex Stainless Steel is an Austenitic – ferritic Stainless Steel. They are called “duplex” because they have a two-phase microstructure consisting grains of ferritic (body centred cubic lattice) and austenitic (face-centred cubic lattice) stainless steel in roughly equal proportions and which can be more deeply studied from the iron-carbon diagram. They are designed to provide better corrosion resistance, particularly chloride stress corrosion and chloride pitting corrosion.

All these studies and further based on the pitting corrosion resistance (PREN), we had designed a much superior alloy for higher nip loaded rolls and faster speed machine rolls called AMAR NICHRO-SUC ANS-40, which satisfies our PREN≥40 theory (≈Cr% + 3.3Mo% + 16N%).

Often the neglected elements like Nitrogen and Copper has added the strength in our shell steel composition in ultimate binding of the molecular granular structure and had resulted to higher tensile strength of the produce. The fine selection of hardness and Young’ Modulus keeps the deflection of the material in the required limits.

Interestingly, AMAR NICHRO-SUC shell is drilled by gun drilling process on high speed CNC programmed multi-spindle drilling SPM. That’s not to say the sophisticated SPM delivers a wide range of drilling patterns, satisfying the paper machine and mills requirements as far as the nip loads and drainage are concerned.

Figure: Typical S-N fatigue failure curve

Amar Elastomer also provides comprehensive services through its network of technicians by closely following the customers and rendering them the latest know-how and technology on suction roll advancements. Regular inspections and scheduled maintenance of manufactured and delivered complete suction rolls with internal vacuum units happen to be a key feature of the company’s intensive drive for suction rolls. Talking of scheduled maintenance would mean emphasizing more on periodic inspections, grinding and sealing strip changing of the rolls to improve the performance of the rolls.

As far as the overall design parameters are concerned, our design engineers are quite particular in selection of bearing type and size as far as the dynamics of the roll is concerned. Based on the experiences on the machine and the speed and nip load, we design and allocate the most appropriate bearings to the complete roll. Basically, these rolls have now been a complete subject of understanding right from the shell selection to the internal unit manufacturing. Even the position and selection of the showering system (slushing and lubricating) plays a vital role in maintaining the stable health of suction roll during operation.

Also, the use of premium sealing accessories like sealing strips and end deckles adds more to the value to our roll.

We urge the paper mill community to experience our services and products for better economic and technical viability and as a solution for better performance of the rolls in such a competitive world.

– This article has been written by Mr. Rajiv Kumar Agarwal, CEO, Amar Elastomers Private Limited.

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