A steel and copper roll recycling and refurbishing service that returns used or damaged chill rolls used in the plastics and lamination industries to their original finish and concentricity specifications offers potentially huge capital cost savings, production efficiency benefits and ticks all the environmental boxes for manufacturers.
It can cost up to £30,000 to replace a large steel cooling roll and £60,000 for a new copper shelled chill roll says BEP Surface Technologies whose expertise and technology enables it to refurbish rolls of all sizes up to 1500mm diameter and weighing 10 tonnes. Refurbishment charges can amount to less than 30% of the cost of purchasing a new roll from an OEM. On large copper shelled rolls refurbishment can save over 80% against new.
Precision rolls used in plastics manufacturing processes generally work in sets of three and because they can run with only microns separating them concentricity is absolutely critical. Coater rolls used in laminating processes require similarly fine tolerances. BEP’s techniques guarantee maintenance of the structural integrity of rolls and repeatability of the original chrome finish, Ra (Roughness average) and TIR (Total Indicator Reading) specifications and tolerances to ensure rolls work first time on reinstallation.
Another significant benefit is reduction in down time. Refurbishment is considerably quicker than buying new. BEP undertakes all the necessary processes in-house and can refurbish a roll in 15 working days compared with 90 days for the manufacture of a new roll. The extended lead time for new rolls being due in part to the availability of the special steels required for the manufacture of roll components.
Surface finish is a key performance factor for any roll and the company claims it can replicate any surface, having developed its skills creating ultra-high quality finishes for photographic papers.
In effect the refurbishment service offered by BEP is a sustainable, closed loop recycling system that helps to protect the environment by making good worn or damaged products and returning them for use in their original application rather than being scrapped.
Refurbishment process
Refurbishment involves several processes. Initially rolls are inspected at the company’s manufacturing facility in Radcliffe, Manchester. Reports detailing what work is required to bring them back to specification are prepared and following agreement with the customer various treatment steps, including some or all of the following, are undertaken.
To restore rollers to their original thermal efficiency internal water ways are cleaned with a specially developed temperature controlled acid solution to remove corrosion. Over time waterways on cooling and heating rolls may becoming furred up with either lime scale or rust. Providing the waterways are not completely blocked and the rust has not corroded through the roll shell they can usually be cleaned. After cleaning, any residual acidity is neutralised and the roll is thoroughly washed out with water and flushed with a rust inhibitor.
Rolls are then chromium plated to hardnesses of between 900 to 1150 HV which are retained up to 400°C. The finish also resists tarnishing above 300°C and provides low co-efficient of friction, excellent resistance to wear and abrasion plus resistance to most chemicals. However, these characteristics can only be delivered consistently if the chrome is of the highest possible purity and to achieve this BEP has developed its own custom designed high level purification plant.
At this stage the company may also recommend that any roll operating above 30°C be de-gassed. The chrome plating process introduces approximately 0.06% hydrogen into the finish and incorrectly managed during production this can cause defects in the form of tiny bubbles which can result in reject product. Although the gas disperses naturally during production manufacturers can waste production time by pre-heating rollers in their machines to minimise the effect.
Alternatively, rolls can be de-gassed to remove occluded hydrogen from the chrome deposit.The process involves heating rolls in a specially constructed temperature controlled oven to a precisely controlled thermal ramp. To eliminate the risk of distortion BEP hang rolls vertically. All temperature profile data is recorded.
Additional finishing work might also include a nickel coating under the chrome finish to provide corrosion protection to the steel or copper shell. In every case the roll can be brought back to original size with copper or nickel as required. Even rolls that have suffered indentations can be repaired.
Before the roll is re-surfaced to its original specification – impressions of the original surface will have been previously taken and analysed. In-house techniques, developed over many years, enable BEP to produce high quality mirror polished chrome plated rolls with surface finishes as fine as Ra (Roughness average) 0.005µm and with TIR and parallelity close to perfection. Paper manufacturers and laminators typically require ultra-finish chrome rolls.
A wide range of matt, silk and various textured surfaces can also be produced by shot blasting and electrolytic techniques creating finishes from fine Ra 0.1µm to rough Ra 15µm.
Finally, if required, roll bearing journals can be restored to their original size by chrome plating and precision grinding.
By extending the service life of rolls through refurbishing to the original specifications manufacturers’ can benefit from reduced costs while enhancing their sustainability and environmental credentials. |
