Mill Liner

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When striving to achieve better grinding profitability, there are a few things about mill liners that are worth considering. importance of mill liner weight, number of parts and optimized grinding media charge. All these aspects affect each other, but they will be covered one by one.
1. Mill liner design in relation to total mill weight:
Weight has a great impact on the process, so it needs to be considered in utilizing the maximum capacity of the grinding mill. The theoretical capacity is mainly based on volume of the mill, installed power and structural strength of the mill. The mill structure and bearings can handle a certain maximum weight, consisting of the weight of the mill itself, the weight of the grinding charge (media and ore/slurry) and the weight of the liners.

Mill weight is something that we can’t really change. To maximize capacity and utilize the installed power, many mill operators try to maximize the charge weight. This means that the maximum allowed weight limits the capacity. So, what is left to work with is the mill lining.

In order to reach maximum capacity, we need to analyze the mill’s total weight and consider various mill liner design options. In many cases, the lining can be optimized to occupy as little volume as possible; and if the material is used where it does the most good, it is often possible to minimize the weight.

Mill Liner

LINER WEIGHT VS WEAR LIFE

1.There is often a trade-off between liner weight and wear life. A lighter lining is generally thinner and, unless the design is highly optimized, it will have a shorter wear life. However, liner weight and long wear life don’t always have to be contradicting. By mixing and blending different types of liners – metallic, Poly-Met and rubber – in the same design, and by using each type where it performs best, it is possible to minimize the weight and still maintain or even increase the wear life.

A light liner in itself does not save energy. It does somewhat reduce the load on the bearings etc., but the real benefit of a lighter lining is that the mill can carry a higher charge without exceeding the maximum weight. While it isn’t possible to add media directly equivalent to the weight saved, it is also impossible to add enough to increase the mill utilization.

There are many old mills out there that are worn and torn by operation, and it is not unusual that the mill structure and bearings cannot take the same load as they used to. By minimizing the weight, it can be possible to prolong the life of such equipment.

2. Maximizing mill liner size and minimizing mill liner parts
Back in the day, mill liners were carried and installed manually, which required a lot of man-hours – and muscles. Thus, the liners couldn’t be very heavy and there were many parts to be installed. However, downtime wasn’t much of an issue, because there were many small mills on site.

Nowadays, things are different. Higher production means a much higher wear rate as well. Considering the high throughput of big mills, every hour of downtime represents lost production.

The first thing to look at is maximizing the liner size and weight. It is possible to make double liners and optimize the design layout so that the liners that are replaced most frequently are as big as possible. The logical next step is to look at alternative materials and designs. By using lighter materials, it is often possible to increase the liner size significantly without increasing the weight and thereby reducing the number of liners.

3. Optimized grinding media charge
The media charge affects grinding efficiency and throughput. Properly selected and sized media charge of good quality is one way to ensure that the total cost of grinding is kept at a minimum.

If the lining is transmitting the energy from the rotating mill to the charge, the grinding media is doing the actual grinding work. Breaking rock of a certain size and with certain properties requires a certain energy – and that determines the top media size. To get the final finer product, smaller sizes of media are required. As the actual grinding takes place between the media in the charge, it is important to have as many contact points as possible between grinding surfaces and with the right energy. This means that the charge must comprise a mix of sizes in the right proportions, hardness and quality.

4. Optimized grinding mill liner design
A mill lining should be optimized by design in order to minimize problems, utilize the mill’s capacity and keep a good liner profile throughout the wear life. This can be done by maximizing the efficiency of the grinding process.

It is important to control the charge motion to ensure that as much of the impact, attribution and abrasion takes place on top of and inside the charge. If there’s too little charge motion, there won’t be enough energy to grind the ore; and if there’s too much charge motion, there’s a risk that a lot of energy turns into liner and media wear, heat and noise. If the liners are subject to direct impact, there is also a big risk of liner breakage.

As a mill liner wears, it typically becomes less profiled and at some point, it loses its capability to provide enough lift to create the correct charge motion. By optimizing the design, it is possible to minimize these effects.

Our EBcastworld liner concept retains an efficient profile, similarly to metallic mill linings, as different types of wear-resistant inserts are used in combination with impact-resistant rubber.

MILL LINER DESIGN TRENDS

The current trend is to go for a wide-space design to prevent packing and to utilize the mill volume to the highest extent possible. It is really important to make a design that promotes the optimum charge motion to prevent the liners from being impacted by the media and ore, and at the same time to make sure that the efficiency is as high as possible in order to save energy.

A high-low design is one way to improve the performance in a mill with a tight-spaced drilling pattern. However, that does require more frequent maintenance, as you need to replace every second row twice as often. A more modern design is the wide spaced, one-shot design, where everything can be replaced at the same time, minimizing the number of maintenance stops.

5. Well-organized maintenance of mill linings to finish up efforts towards better profitability

Every mill stop, no matter how short, causes costs, so the number of stops should be minimized. Often, the mill has to be at least partially ground out, water might have to be pumped out and the mill properly washed out to ensure that all the trapped ore or other particles are removed so that the mill can be entered safely. Some mills are quite hot or the process can contain gas or fumes that must be vented out, and the pH value in some mills makes the environment less friendly. Finally, relining takes time; and even after everything is done, it takes a little while before the mill is running at full capacity again.

One way to avoid extra maintenance stops is to ensure that the liner wear life is in balance, i.e. as many parts as possible should have the same wear life. If the plan is to have two major maintenance stops every year, the liners should last 6, 12, 18 or 24 months to minimize the need for intermediate stops.

THE CORRECT LINING REDUCES MAINTENANCE TIME
It is crucial to carefully study the wear pattern inside the mill. It is a good idea, especially with a new design, to measure the liners more frequently to determine if the wear is linear or if it accelerates in certain positions or at some particular state of wear. Once the wear pattern is known, the design can be changed accordingly.

Changes in feed size, ore properties, throughput, mill speed etc. can have a big impact on liner life. It is important to keep track of these parameters as well, and to match changes with the wear trends that are seen when analyzing the wear pattern. When the correlation between wear trend and operation are known, it is easy to plan and avoid surprises.

The ability to mix and blend different types of liners and materials in the same mill really gives you unique possibilities to balance the wear life. For example, you can minimize the weight and the number of components and maximize the liner size.
All these are important factors in reducing the maintenance time.

I sell products, but I am more willing to help you achieve a win-win situation. EBcastworld welcomes your orders with 21 years of production experience

 

Eternal Bliss Alloy Casting & Forging Co, Ltd.

E-mail: sales@ebcastworld.com

Our What’s app: 0086-130 930 23772

www.ebcastworld.com

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