Metso Insights Blog Mining and metals blog Extended warranties for grinding mills
Oct 9, 2023

Failure is not an option – Extended warranties for grinding mills

Jean Bernard Demers
Jean Bernard Demers
Product Director, Grinding Digital, Field Service and Repairs
Grinding mill’s largest components are critical assets where the impact of failure is high. When failure is not an option, extended warranties from the grinding mill OEM can ensure longevity of the part’s lifecycle. Read on about the common causes of failure and how extended warranties can be valuable assurances of product longevity and performance.
34’ SAG Mill gear at teeth cutting
34’ SAG Mill gear at teeth cutting

Historically, recorded equipment failures often lead to emergency repairs and expedited delivery of replacement parts, both of which result in costly operational expenditures and lost production revenue due to unforeseen downtime. Very often, a proper root cause analysis is not conducted, let alone recorded, to provide the necessary information and awareness to prevent reoccurrence of the same issues and the required repairs. In the rare cases that a proper investigation is carried out by either the equipment owner or a third party, this information is rarely shared publicly to benefit others operating the same equipment with the exact same reliability issues. This is especially true with grinding mills where some of the equipment’s largest components are critical assets where the impact of failures is high. When failure is not an option, extended warranties from the grinding mill OEM can ensure longevity of the part’s lifecycle.

Causes of failure

In grinding mills, as with any engineered fixed plant equipment, causes of failure can be narrowed down to six main stages in the product’s lifecycle: design, manufacturing, installation, operation, maintenance and storage. A good understanding of these stages can allow the equipment owner to better predict and prevent unplanned outages by leveraging the OEM’s continuous knowledge and expertise.


The success of an extended warranty begins with selecting an appropriate design for the intended application. Engineering teams need to evaluate loads, calculate stresses and anticipate challenges the product will need to sustain during its lifecycle to define the proper design criteria. For instance, a mill rotating body is submitted to a finite element analysis (FEA) to ensure it is designed for theoretical indefinite life. Likewise, a gearset is designed to AGMA 6014, the industry’s most stringent standard for open gears, to ensure a 25-year life. Hence, with a blend of knowledge and experience to define an intelligent design and select robust materials, the foundation is laid for a well-conceived product that can endure and achieve its expected operating life without risks of premature failures.

Man sitting in front of an old computer.
Finite Element Analysis of a grinding mill in early 1990s


A product's design means little without proper manufacturing. Quality control processes must be rigorous, ensuring that each unit is produced to the design’s exact specifications. Attention to detail during manufacturing reduces the likelihood of defects that could trigger premature failures. High-quality manufacturing translates to a product that not only performs reliably but also garners trust among customers. For instance, as specified in AGMA 6014, ring gears’ metallurgical characteristics shall be as per Grade M2 material requirements. Also as outlined in AGMA 2000-A88, ring gears require quality levels based on the power they could transmit when measuring final pitch, profile, lead and runout. Inspection and Test Plans (ITP) allow the definition of proper specifications, acceptance criteria, and documentation for quality assurance to evaluate whether the components have the right fit, form, and function. Hence, manufacturing is a crucial step in ensuring a quality product is delivered free of defects that may cause failures that could otherwise have been prevented.

Dominion’s equipment performance track record circa 1970s
Dominion’s equipment performance track record circa 1970s


Grinding mills are a complex assembly of different components, so the success of the product relies heavily on proper installation. Clear and comprehensive installation instructions, along with professional installation services when needed, help avoid mistakes that could compromise the product's performance or longevity. Far too often the installation and commissioning of the component is dismissed as a simple and straightforward process. In many cases, the work is executed without the required precision, as the component is considered to be heavy and robust  to be able to sustain the toughest beatings. The reality is quite the opposite. The heavier the equipment or component, the more spectacular the failure. A correct installation with tolerances as low as 0.001” per foot is required to ensure the product operates as intended from day one to decrease potential early failures.

Two men working around a grinding mill gear.
Assembling split gear on a grinding mill.


Educating customers on how to use the product correctly can significantly extend its lifespan. Many failures have been correlated with misuse or improper operation. Providing user manuals, online resources and customer support helps users make the most of their purchase while avoiding unintentional damage. Proper operation minimizes wear and tear, reducing the likelihood of failures. For grinding mills, ensuring components such as bearings are properly lubricated with a functional mill lube system and avoiding contamination from foreign matter such as dust particles or slurry ingress, can minimize failures and significantly prolong equipment operating life.

Excessive wash from slurry ingress in a trunnion causes a catastrophic failure.
Excessive wash from slurry ingress in a trunnion causes a catastrophic failure.
Extended warranties
Read more about extended warranties in our brochure.


Routine maintenance is the cornerstone of product longevity. Clear guidelines on maintenance intervals, tasks, and procedures empower users to keep their product in optimal condition. Regular maintenance not only prevents potential issues but also identifies minor problems before they escalate. Indeed, replacing seals or filters periodically is a simple task that could protect contamination of major components such as trunnion bearings. Likewise, cleaning the gear once or twice a year for an inspection and relubrication also removes contamination and ensures that no indications have appeared over time. By fostering a culture of maintenance, customers are more likely to enjoy trouble-free performance.

Man doing digital gear inspection of a grinding mill ring gear.
Digital Gear Inspection of a grinding mill ring gear.


It may seem trivial to discuss storage when referring to equipment reliability. However, proper storage of replacement components is critical to maintain fit, form, and function with proper protection against corrosion and other potential damages. On several occasions, metallic components made of either steel or iron are shipped to a customer site and left outside under changing weather conditions only to spend the winter under snowbanks, resulting in heavy rusting discovered in the springtime when the snow melts. Therefore, long term indoor storage protection including rust inhibitors and wood crating are mandatory to maintain components in good condition.

Basic OEM warranties cover design and manufacturing for up to 12 months. However, without any proactive involvement from the OEM beyond supplying the part, the potential for issues and component failure can increase drastically as a result of improper or neglected installation, operation, or maintenance practices. By providing extended warranties to include these processes, Metso now provides extended warranties on ring gears, trunnions, heads and shells for coverage periods up to 120 months.

Long term storage packaging.
Long term storage packaging.

Why added protection?

Grinding mills have significantly increased in size since the 1990s. As a result, this has drastically changed the layout in grinding circuits. Many modern sites now operate fewer large mills and rather have several parallel lines of smaller-sized mills. Hence, production interruptions are significantly more costly, and failure risks are greater than ever. However, this doesn’t mean the equipment will fail, but it must be kept in check by doing the right things by partnering with your OEM for the appropriate protection coverage, which includes complete guidelines for best practices and coverage requirements, yearly inspections, technical support and complete replacement of the component if failure occurs.

An extended warranty’s success is a result of a harmonious symphony among design, manufacturing, installation, operation, and maintenance. A well-designed product that undergoes meticulous manufacturing, is properly installed, operated with care, and regularly maintained, is bound to stand the test of time. Such a product is less likely to experience premature failures or unexpected issues, leading to maximized equipment operating life. When considering an extended warranty, customers should assess the commitment of the manufacturer and how it invests in creating durable, reliable, and well-supported products and how it shows its dedication to achieving customer satisfaction. Metso’s holistic approach transforms extended warranties from mere insurance policies into valuable assurances of product longevity and performance.