Mining is a tough business, The equipment takes a beating every day. Your SAG mill is the heart of the plant. If it stops. money stops. Liners protect the mill shell. They also lift the rocks to break them. But they wear out. Replacing them is dangerous and hard work, It must be done right. This guide helps you do it safely and fast. We use our experience at SBM to help you.
First, we must know the machine. SAG stands for Semi-Autogenous Grinding. It is a big drum. It spins. Big rocks fall on other rocks. This breaks them. We also add steel balls. The balls help break the hard rocks.
The mill spins at a specific speed. We call this “Critical Speed”. If it spins too fast, rocks stick to the wall. They do not fall. Nothing breaks. If it spins too slow, rocks just slide. Energy is wasted. Usually, mills run at 70% to 75% of critical speed. Why? To get the best impact.
Key Parts:
Data from the International Journal of Mineral Processing shows correct speed saves 15% energy. It matters a lot.
You might ask: “Why do my liners break so fast” This is a big pain point. Liners are expensive. Downtime costs more. Here are the reasons.
1. Wrong Impact Angle
The rocks must land on the “toe” of the charge. If they hit the liner directly; it cracks. This is called “impacting the shell”. It is bad. The lifter angle controls this. If the angle is too steep, rocks throw too far.
2. Bad Material Choice
Some ores are very hard. We measure this with the Bond Work Index. If the ore is hard, soft steel fails. You need Chrome-Moly steel. Or high manganese steel. SBM suggests testing the ore first. Why? To pick the right metal.
3. Poor Installation
If liners are loose, they move. This movement breaks bolts. Then liners fall off. The backing material is vital. It fills gaps.
Stop. Do not rush. Liner change is heavy work. Liners weigh tons. People get hurt easily. Safety is rule number one.
Step 1: Lockout and Tagout
Cut the power. Lock the motor. Put a tag on it. No one can start it. This saves lives.
Step 2: Vent the Mill
Mills get hot. The air inside can be bad. Open the doors. Let fresh air in. Check oxygen levels. Why? To breathe safely.
Step 3: Prepare Tools
You need a Liner Handler. This is a special crane arm. It grabs the liner. Do not use ropes only. It is unsafe. Check the torque wrench. You need big torque for bolts.
Now we do the work. Follow these steps. Do not skip any.
Clean the mill first. Wash it out. Locate the bolts on the outside. Use a “thunderbolt” gun or torch. Cut the old nuts. Push the bolts in. The liner handler grabs the old plate. Pull it out gently. Watch your fingers.
This is very important. The shell surface must be clean. Remove old rubber backing. Remove rust. Use a wire brush. Why? Because dirt creates gaps. Gaps crack new liners.
Put new rubber strips on the shell. Glue them well. They act as a cushion. Steel on steel is bad. It vibrates too much. The rubber absorbs shock.
Use the handler. Lift the new SBM liner. Move it inside. Place it carefully. Align the bolt holes. It must sit flat. If it rocks, it will break.
Insert new bolts. Put on the washer and nut. Use an impact gun first. Then use a torque wrench. Tighten to the spec. Check the manual. Usually, it is over 2000 Nm. It must be tight.
Let’s look at a real job. This proves our method works.
Project Background
| Parameter | Old Competitor Liner | New SBM Liner |
|---|---|---|
| Lifter Height | 180 mm | 220 mm |
| Material | Mn13 Steel | Cr-Mo Alloy |
| Life Span | 3 Months | 6.5 Months |
| Mill Capacity | 85 tons/hour | 92 tons/hour |
The Solution
SBM engineers analyzed the wear. The old lifters were too low. The rocks slid. They did not tumble well. We changed the design. We used “High-Low” wave design. We used Cr-Mo alloy steel. It is harder than Manganese.
Client Feedback
The mine manager, Mr. Ahmed, was happy. He said: “The SBM liners fit perfectly. Installation took 2 days less. The mill runs smooth now. We save money on parts.” The energy bill dropped 8%. Why? Better grinding action.
Don’t just guess. Measure these things. It helps you decide.
How many balls are inside? Usually 10% to 15%. Too many balls break liners. Too few balls reduce tons per hour. Check this weekly.
What size rock goes in? This is F80. For SAG mills, F80 is often 100mm to 150mm. If rocks are 300mm, they break the steel. You need a crusher before the mill.
Watch the motor amps. If amps drop, liners might be worn out. Why? The load is slipping. It is not lifting.
Here are three questions users often ask us. We answer them simply.
Q1: How do I know when to change liners?
A: Measure the thickness. Use an ultrasonic gauge. If the lifter height is less than 30% of new, change it. Do not wait for cracks. Plan ahead.
Q2: Can I mix old and new liners?
A: No. This is a bad idea. It creates uneven balance. The mill will shake. It ruins the bearings. Change the whole row or the whole circle.
Q3: Steel vs. Rubber liners, which is better?
A: It depends. For SAG mills with big rocks (over 100mm), use Steel. It handles impact. For Ball mills with small rocks, Rubber is good. It lasts longer and is quiet. SBM can calculate this for you.
The job is not done after installation. You must check it.
Retighten Bolts
Run the mill for 24 hours. Then stop. Retighten all bolts. The liners settle. Bolts get loose. If you skip this, leaks happen. Slurry leaks cut the shell.
Monitor Wear Pattern
Look inside after 1 month. Where is the wear? Is it even? If only one side wears, the feed is wrong. Adjust the feed chute.
Replacing liners is science. It needs data. It needs care. Don’t buy cheap fake parts. They cost you more in the end. A good liner boosts production. It lowers power bills.
SBM provides the whole solution. We design. We cast. We install. We help you win. Your mine deserves the best armor. Keep your mill turning. Keep making profit.
Whatsapp：+8617329420102
Email: [email protected]
Address: No. 1688, Gaoke East Road, Pudong new district, Shanghai, China.
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