Grinding, hard chrome plating • Serbian Roll Service Company doo

GRINDING

Process

Grinding represents a process that is done on the grinding machine where the roll surface is brought into an optimal condition by fine stock removal of roll material measured in micrones (value of roughness and stock removal).

Grinding operations prevent later splashing and popping of chrome layer from the roll surface which can result as a chrome peeling. After rolling operation, rolls have to be re-ground to remove metallurgically damaged stock to limit costs where stock removal has to be sufficient to ensure roll surface quality in next rolling.

Equipment

SRSC is equipped with state of the art grinder model WS 450 x 5500 mm CNC MonolithTM made by German machine manufacturer HERKULES Maschinenfabrik Siegen, and this model is dedicated for Rolling Mills work rolls by using brand new sophisticated computer systems:

Integrated fully flexible computer controlled continuous path crowning system (profile measurement system)
Integrated in-process roll measuring system also for adaptive control for “on the fly” correction grinding (grinding to tolerance, matching of roll diameters, etc.)
Eddy current crack detection system
Ultrasonic roll sub-surface inspection system
Automatic adjusting system of roll steadies for holding the rolls
Roll history data storage system (capacity 600 rolls)
Consistent repeatable roughness (Ra)

Technical characteristics

Technical characteristics of SRSC Herkules grinder:

Production capacity ……………………. up to 600 rolls/month (if stock removal not exceeding 0,25 mm per roll)
Roll dim. …………………………………… Dmin.= ∅300 mm Dmax= ∅900–1080 mm, Lmax = 5500 mm (min. and max. diameter of the roll barrel and overall length)
Roll neck dim. ………………………… Druk.= ∅130–500 mm (min. and max. diameter of the roll neck that can accept steady rest)
Max. carrying capacity ……………….. Tmax= 12 tonne (max. weight of the work roll that can be treated on CNC grinder)
Stock removal range…………………… 0,1 – 5 mm (0,1–0,25 mm for CRM rolls, and 0,3–5 mm for HSM rolls)
Roughness range ………………………. Ra= 0,5 – 2,2 µm

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ROLL TEXTURING

Roll texturing

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HARD CHROME PLATING

Process

Hard chrome plating represents an electrochemical process where the surface of roll material is covered by a layer of hard chromium (Cr2O3 or Cr6+) at an effect of direct current (DC), in order to improve the main characteristics of rolls – hardness, wear resistance, abrasion, corrosion resistance and lubricity with general low coefficient of friction.

The limited usable life of work rolls in Rolling Mills is an universal and expensive issue. The cost of supplying work rolls, mill down-time and product quality are costs related to work roll life. Many approaches have been used to extend the campaign life by alternative roll materials, but chrome plating has proven to be the most effective and universally accepted method.

Development

Develloped by CHL network in Canada in 1965 the technology has been improved and is used world-wide by the majority of the major steel and aluminium Rolling Mills. Today, CHL has a network of over 34 plants chrome plating thousands of rolls every day by using this technology, as SRSC is doing in Serbia.

The proprietary CHL chrome bath technology operates at high speed and with high efficiency to produce chrome deposits that are 25% harder than achieved by traditional chrome plating. The use of CHL chrome plating has been proven to increase the wear resistance of work rolls by 2-3 times while also providing quality, productivity and cost benefits.

SRSC production line for hard chrome plating is designed to enable continuous moving of the working material (rolls) forward through the certain elements of the production system, with a possibility of a reverse moving if that is neccessary.

Technical characteristics

Technical characteristics of SRSC chrome plating production line:

Production capacity …………………….up to 1500 rolls/month (by working 24/7 days/week and 365 days/year)
Roll max.dim. …………………………… Dmax=∅1000 mm, Lmax=5000 mm (maximim body diameter and overall length)
Max. carrying capacity …………………. Tmax= 20 tonne
Chrome layer thickness ……………….. od 2,5 – 250 µm (aver. 6-10 µm, for special requirements 250 µm)
Chrome layer hardness ……………….. 68–72 HRc (aprox. 850 – 1000 HV)
Rectifier technical characteristics ………….. 0–20 V / ±15.000 A / Tiristor Bipolar / Water cooling
Scrubber technical characteristics …………..11.500 m3/h (air flow) / Water horizontal

Roll value calculator benefits of chrome plating

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NONE DESTRUCTIVE TESTING

Process

SRSC in daily practice of processing rolls apply special NDT testing, so-called “None Destructive Testing” testing and by the methods of penetrant testing and magnetic particle testing, which are applied by the certified engineers who owns appropriate licenses.

Dye penetrant testing

Dye penetrant testing – on previously cleaned and degreased surface penetrant is applied (usually red). After penetrating the eventual crack (during penetration is about 10-15 min.), it removes the penetrant in an appropriate manner (water, dry cloth). At penetrants that need to be removed by water have to be careful and to direct water jet parallel to the metal surface, in order to not displacing penetrant from the cracks. After drying the metal surface with a dry cloth, it applies a developer who is usually a white color that brings out the penetrant from the cracks, so that on the white metal surface it is easily visible penetrant red line from the cracks. If there is a crack in the tested metal resepctively roll barrel, then the developer will draw penetrant on its side, which will be disclosed as easy to see the red line of penetrant from the cracks in the white (from the developer) the metal surface.<.p>

Magnetic particle testing

Magnetic particle testing – ferromagnetic material to be exposed to the functioning of the magnetic field, and then to the metal surface apply the iron particles (dry or in liquid suspension). Errors on the surface or right below the metal surface (up to 6 mm deep) produce magnetic poles or distort the magnetic field so that these particles are grouped in places such mistakes and give a visible indication of faults on the surface of the material.

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GRINDING

ROLL TEXTURING

HARD CHROME PLATING

NONE DESTRUCTIVE TESTING

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