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With a current upsurge in demand for steel forgings, the production capacity of many large presses is approaching saturation point, which is reflected in full order books and lead times as long as twelve months, even 36 months for the largest forgings over 150 tonnes in weight. As a result, press uptime is becoming critical and any major overhauls must be condensed into a brief annual shutdown period, a situation that is compounded by the age of many presses still in service. There is also an ongoing need for preventative and predictive maintenance to offset the risk of column failures, broken shafts, worn-out gears and other failed press components that could bring an abrupt halt to production and profits.

 

Sheffield heavy engineering company, DavyMarkham, has unrivalled experience in remedial press repairs, especially as many forging presses throughout the world carry the original ‘Davy’ manufacturer’s plate, and is gearing up its service to meet increasing demand from this sector. Thanks to its manufacturing heritage, comprehensive inspection capability and in-depth understanding of modern engineering materials, DavyMarkham is able to provide an expert service that can return machinery to as-new or even superior condition, in considerably less time and at significantly less cost than sourcing new equipment. What’s more, through its class-leading engineering resources and equipment, the company is able to offer a ‘one stop shop’ for repairs and rebuilds, without needing to contract out specialist or very heavy work; while its manufacturing and design engineering skills enable it to apply current technology like X-ray imaging, controlled shot peening and Superbolt multi-jackbolt tensioners to extend plant operating life, particularly where fatigue is considered a problem.

 

“We can work closely with forging press companies to help them minimise production downtime, covering everything from quick-fix remedies to help keep busy plant working for the time-being, through to scheduling complete repairs and rebuilds during routine shutdowns. We can also provide the preventative maintenance and strategic spares that allow forging companies to meet their loss-of-profit insurance and employee liability commitments,” says DavyMarkham’s MD, Kevin Parkin. “Given that new presses can cost up to £10 million and lead times are now anything from two to five years, our repair service offers excellent strategic value, while our market credentials are second-to-none.”

 

Forging steel ingots, using a heavy press or hammer, results in an extremely hostile environment, particularly for sliding bearings, which are key parts in any press. This leads to deterioration and wear of faces in sliding contact and, as wear progresses, the clearance between these faces greatly increases, which can introduce harmful instability. Similarly, threaded fasteners can become loose if sufficient preload is not applied during installation and stage maintenance, leading to fatigue failure of the bolt or press columns and damage to the adjacent structures.

 

Corrosion of forging press components arising from the large volumes of water used to cool the die blocks, especially where the coolant is acidic or high in oxygen content, can additionally lead to premature failure, through corrosion cracking and a loss of fit and accurate location. A lack of timely maintenance, often due to the pressure of production schedules, can result in missing the start of small service-induced defects and cracking, then it is only a matter of time before full fatigue failure occurs. This problem is compounded for very large machines, due to the time and effort involved in stripping them down for inspection and maintenance, and for older equipment, where there is a lack of available spares and worn or damaged components sometimes have to be pressed into service.

 

DavyMarkham’s forging press repair service can mitigate such equipment failures and avoid machine downtime by employing visual inspection, NDT and FEA techniques to identify components that are subject to working stresses above their fatigue limit and ascertain whether any local environmental factors may be causing unseen damage. It can also extend this inspection service to assist customers when purchasing used presses, by checking clearances, parallelism and other key criteria.

 

Typically, DavyMarkham first undertakes a visual and dimensional site survey, which coupled with non-destructive testing examination, will help toward planning the work required to restore the machine to full working order. In-situ repairs, involving weld reclamation and machining, are often viable as quick-fix solutions, at least until the next scheduled plant shutdown, but sometimes it is necessary to strip down the equipment and return it to DavyMarkham’s purpose-equipped machine shop, exploiting its heavy lifting capabilities for handling jobs up to 350 tonnes.

 

FEA and other advanced engineering software is then used to identify those regions that have been subjected to stresses above their fatigue level and predict whether a component will eventually fail through fatigue cracking. Existing cracks can be removed by machining or arc gouging, then weld-repaired and enhanced by post-weld heat treatment. Controlled shot peening, to introduce compressive residual stress into the steel surface, and superfine polishing, to remove potential crack initiation sites, are further practical measures for enhancing and extending component fatigue life. Where necessary, DavyMarkham can also re-manufacture vital components and strategic spares, using the process of reverse engineering and 3D solid modelling where original drawings are not available.

 

For difficult re-bolting applications, particularly involving high preloads, DavyMarkham has successfully employed Superbolt tensioners in place of conventional fasteners, learning from its experience of producing the world’s largest bolted housing for Chinese steelmaker Shagang. Using traditional heat tightening, it is often difficult to achieve accurate preloads, due to the large thermal masses involved, while for very large bolted connections, conventional hydraulic tensioning schemes are often impractical. In contrast, Superbolt technology, featuring multiple jackbolt tensioners, allows precise preloads to be applied to the largest bolt with normal bolting tools and joints remaining tight even on vibrating, pulsating or reciprocating equipment, eliminating future stress failure and downtime.

 

In summary, not only can DavyMarkham’s specialised repair service maximise forging press uptime and restore machine performance to original and possibly even superior specification, it reduces excessive noise, vibrations and other safety hazards associated with operating such plant, helping employers to meet their occupational health and risk management obligations.