Wednesday 20th Nov, 2019

Beware of the Wearwolf

Grant Wellwood, General Manager of bulk materials engineering firm Jenike & Johanson answers readers’ questions about how to explain the issue of wear to decision makers.

Grant Wellwood, General Manager of bulk materials engineering firm Jenike & Johanson answers readers’ questions about how to explain the issue of wear to decision makers.

Q. Premature failure of rotable spares occur so regularly in our bulk solids handling operations that the impact is just considered a price of doing business. The problem is that when you drill down, this “price” of doing business is far beyond the cost of the spares. Wear is actually the root cause of significant productivity loss in our value chain. However, with the growing excitement around automation and digital operations, it is hard to get focus on this boring, low-tech aspect of our operations, which have been long since normalised by our industry. Do you have any suggestions regarding how I can raise awareness internally and then get some science into the formulation of long-term solutions?

Thanks in advance, “Almost Worn Out”

A. Thanks for sharing your frustration Almost Worn Out (AWO). Wherever there is bulk solids movement, there is wear. As a consequence of the second law of thermodynamics, wear can’t be eliminated, only managed through a strategy of rotable spares and scheduled shutdowns. As you correctly point out, when a rotable spare fails before its scheduled replacement, the whole operation can be affected.

The long-term solution to wear-related surprises is a combination of both awareness and science. Wear is low-tech, ugly and value destroying – almost the polar opposite to the high-tech things that are considered exciting today. The pathway to success therefore involves changing the way people think about their business, which means we need to use some soft skills. Technologists often feel uncomfortable in this area, which perhaps explains why value destruction due to issues like wear have been normalised. But if we want to achieve genuine improvements in productivity (as you do AWO), we have to adopt a different mindset.

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Anyone who is at or has been close to the front line of a bulk solids handling (BSH) operation will be acutely aware of the impact of wear on their business. Unfortunately, in businesses where wear has been normalised, those with the power to make a difference and commission long-term solutions are often located off-site and may not have experienced wear first hand leading to an iceberg of ignorance. The science of wear is not covered in detail in most engineering undergraduate courses, so the process of raising awareness generally comes off a very low base. Put simply, most people simply don’t want to know about this ugly and value-destroying part of their business. So, how can this be changed? First of all, framing is important.

Reframing the issue: If your value chain involves material transformation (chemical and/or physical), at the highest level you are really in the business of designing and operating money-making machines. The revenue from your “machine” is directly proportional to the sustainable flow rate through it, which is something that most operations need to maximise. A useful way to reframe things is to forget about your business specifics and focus on it as a money-making system.

In the food sector, they think about their value chains in terms of Critical Control Points (CCP). These are physical locations in the process line where failure could cause harm to people, the environment or the business and where preventative control measures can be applied. This is useful framework that can be applied to BSH value chains, which are only as strong as their weakest link. The implications of failure in any one link, can manifest across, or even bring down, the entire value chain.

So, thinking in terms of CCPs is a great way to consider maximising flow and revenue as it puts the focus on controllable risks, like wear.

In the context of a BSH value chain, CCPs can be defined as physical locations in our value chain where there is a unique combination of our controllable parameters, namely, materials – both flowing and fixed – geometry and throughput.

According to this definition, there are usually many CCPs within every operation, but each one involves conscious decisions that affect phenomenon, like wear. Having established the physical points on which to focus, it’s now time to address the issue of wear awareness.

Awearness

There is a body of science to describe the specific type of abrasive wear we see in BSH called open three body (O3B) abrasion. What is typically missing is an understanding of the benefits of applying this science and for senior decision makers in order to get support for long term solutions.

As the decision makers often don’t have an appreciation for wear, there is work to do to bridge the iceberg of ignorance. While your own iceberg can be expansive, bridging it is absolutely vital for success, but how?

One consistently successful approach when dealing with laypeople and lapsed-technologists is to use analogies. Subjects like wear are difficult to communicate because they often aren’t anchored to anything in the practical experience of the decision makers, but analogies can mentally moor them to something familiar. Applied well, analogies are a very effective tool, but they do take some effort to get right. So, what makes a compelling analogy?

A good analogy:

  is a compromise between two conflicting goals: familiarity and representativeness

  is an abstract idea in terms of something you already know

  matches at least some of the features of the complexity you’re trying to explain. The more similarities or connections your analogy has, the more intuitively powerful, and less “gimmicky” it is

A familiar and well-fitting analogy also has another important purpose. It helps your decision maker communicate the essence of your story within their network and “up the line”. In fact, a good analogy can be the difference between success and failure when you can’t be there to recount it yourself.

What does a good analogy for wear look like? The wear mechanism map looks a lot like the classification of living things, so an analogy based on anthropomorphism (human characteristics to an object) works well. In particular, one proven analogy is based on werewolves. In addition to the useful play on words there are many helpful connections and parallels, including being:

  fierce and powerful

  cunning yet merciless

  shape-shifting and irreversible

  steeped in superstition and myth

  impossible to eliminate but conceivably manageable

Thanks to pop culture and Halloween most managers will be aware of these characteristics, so the iconology is robust.

To bring it all together, a powerful analogy to heighten awareness of wear in the minds of decision makers on top of the iceberg might be: “beware the wear-wolf” that lurks within every critical control point in our value chain.

Sometimes, people actually question the importance of wear to the business. This is when you confront them with their own production run chart, which can look something noisy like Figure 1.

Here we see production on a day-by-day basis in a high volume, low-margin business, like mining. A perfect production day gap of 39 per cent like this one is typical. It is also a measure of latent capacity, which helps them take notice, especially since wear is one of the main root causes of this value destruction.

Having created the wear-wolf, it is time to put it to work.

Beware

Each wear-wolf is unique in terms of its nature and destructive powers. Its potential is baked-in during the design stage, meaning that:

  they lurk within every design decision

  it is possible to limit their destructive potential at these CCPs.

The second message was that, once created, wear-wolves are immortal, but they can be managed if you understand their nature.

If a werewolf actually appeared today, the first thing we would do is to study and understand it with a suite of thorough medical tests. By inference, we need to treat our CCP wear-wolves in the same manner, by applying science.

As those of us who have experienced wear first-hand know, it can’t be engineered away, and we depend on a rotable spares or a scheduled-shutdown strategy to manage it. In this operating context, our collective goal is to control wear and ensure we don’t have any surprises that interfere with our plans. The critical bit of information we need to know is the wear rate (WR) at each control point.

In terms of the analogy, this can be considered the essence or DNA of each and every wear-wolf. At this point many decision makers (like those in procurement) may tell you that they are way ahead of you, and are already using science to inform their wear-related decisions, citing standards like the American Society for Testing and Materials (ASTM) G65-rubber sand wheel test, or pointing to wear surfaces’ composition prescriptions.

These measures equate to fingerprinting, in that they capture something of the beasts involved, but not what you need to know to control them. In this case, this is the wear rate.

ASTM G65 is conducted using sand and was designed to produce a ranking of loss, so in terms of actionable insights, it is actually worthless. Additionally, chemistry says nothing of the crystalline structure that is the attribute determining wear resistance. These facts are quite intuitive so once they are pointed out, the folly is recognised. However, if G65 or chemical composition of the rotable spares can’t do the job, how can the wear be controlled in a science-informed manner?

To do so, a device that can accelerate abrasive wear in a realistic fashion is needed. In terms of our analogy, this is equivalent to conducting a medical stress test on our wear-wolves and would involve emulating the O3B abrasive wear mechanism for all the variables involved, including:

  normal pressure

  distance travelled

  material properties like hardness

  the as-supplied shape and size distribution of the abrasive particles

Once a CCP WR is known, the wear-wolf can be domesticated into an aware wear-wolf, that can be helpful.

By being aware of wear, designers can explore and optimise geometry or wear material combinations in the virtual world using tools like discrete element method modelling.

Secondly, it enables procurement functions to create value instead of being based around the price of rotable spares. It is also possible to learn about the accumulated wear damage at each critical control point and therefore predict its tonnes or time-to-failure value.

There is even a factor that can transform the topic of wear into something more attractive in today’s high-tech environment. There is a lot of talk about digital twins and dynamic optimisation, but they can often ignore wear or treat it as invariant. Ideally, you need to know the remaining life of all your CCPs, and how they will be incorporated as a result of your proposed process change.

Finally, aware wear-wolves can learn. For example, conducting post mortems on spent rotables and using machine learning to process data collected during the parts service life, creates a feedback loop that would see accelerated wear test estimates get better over time.

In conclusion, if your business involves the high-volume movement of bulk solids, you are really in the business of sustaining flow in defiance of the second law of thermodynamics. While wear can’t be eliminated, it can be controlled if the wear rate of each CCP is known.

The wear-wolf analogy is a strong one that can help increase awareness and improve messaging to the key decision makers who have the power to realise the opportunities.

Remember, wherever you can create aware wear-wolves, you create opportunities.