Home > Getting miles out of your mill: Should you buy a refurbished grinding mill?

Getting miles out of your mill: Should you buy a refurbished grinding mill?

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During the pre-GFC mining boom a new grinding mill was one of the longest lead items for a processing plant. 

As a result many, mostly junior, miners rushed into the purchase of refurbished mills in order to quickly capitalise on the boom. 

Their purchases were driven primarily by delivery time above price and quality.

Then the GFC struck and mill delivery times fell quickly, returning the market to a scenario where price and quality were the leading drivers.

As the mining sector heats up again delivery times are likely to lengthen, and the question of whether to purchase a new or refurbished mill is a timely one.

Outotec mechanical engineer Daniel Braithwaite told Australian Mining it was not uncommon for miners to be making the wrong choice when choosing between a new or refurbished mill.

"Normally this error is not seen as the wrong decision until the benefit of hindsight makes it clear," he said.

According to Braithwaite there are two main factors to consider when purchasing a new mill.

The first factors are quantifiable costs, or costs that outline a definable capital expenditure or opportunity cost, and the second are unquantifiable costs, or costs that cannot be defined due to unknowns.

On top of these costs, a mill's ability to adhere to safety guidelines is important.

"Meeting modern safety standards should be a large consideration in any mill purchaser's 'most wanted' list," said Braithwaite.

In terms of quantifiable costs, the price of equipment for a refurbished mill will typically appear as a cheaper option, but there are additional considerations such as costs for inspections and audits of components.

With refurbished equipment a complete design review is necessary to make sure the mill is suitable for its new role and its components meet current standards.

Along with this analysis thorough inspections are required to determine existing flaws such as cracks, dents, and casting defects.

"Basically you should be looking with the same rigour that a new designed mill would undergo," he said.

"What is bought is what you get, and the owner has to live with this."

Braithwaite said if these reviews weren't completed properly they left buyers open to a number of serious problems.

"The consequences of failing to consider all factors in a review can be dramatic - both from an equipment and OH&S perspective," he said.

Braithwaite said cracking of critical components through overloading, inadequate lubrication causing bearing failures, and vibration problems are some of the many risks of a poor review.

"Such factors can end up costing a site millions in lost production," he said.

Another major quantifiable cost is the design of the mill's electrical equipment and its bearings. 

Braithwaite said bearing selection was often overlooked by buyers, and while impossible to quantify on a generic basis, the energy lost through friction in old bearings could be significant.

In terms of delivery time, a new mill will generally have a longer delivery but installation and commissioning are usually shorter than for a reconditioned mill.

Reconditioned mills could often present unexpected surprises hidden until the commissioning stage, Braithwaite added.

"This is where it pays to have a thorough mill audit beforehand and also a comprehensive knowledge of the mill history," he said.

Braithwaite said the need for maintenance tasks no longer possible due to modern safety standards, and unserviceable parts that are no longer available were two examples of these surprises.

"In the worst case scenario, and it has happened on many occasions, a second hand mill will take as long or longer to become operational with no cost benefit, and with lower availability and higher maintenance costs." 

He went on to say that buyers could also be surprised by mill designs that did not take into account the conditions of the new location, such as heavy rain, dust, or high temperatures.

While new mills were specifically designed for each site, it was often hard to find a good site match for second hand mills.

"Sometimes a close fit can be found," he said.

"But as the difference between ideal size and installed size increases, the further the milling circuit moves away from being optimal.

"As the deviation from optimal grows, liner life decreases, leading to increased shutdowns and energy consumption."

The terms of warranty and amount of ongoing support your seller is willing to give you are also important factors.

"For a new mill owner the most important aspect of warranty is the support provided by the mill supplier in the event issues occur," Braithwaite said.

"This is invaluable to limiting down time."

If all factors have been considered and a thorough analysis undertaken buyers should ultimately be able to make a well informed decision.
Braithwaite's final advice is to play it safe.

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