We have already discussed the Basics of Lubricants. We have discussed the Lubricating Oil & Lubricating grease and the basic difference between Lubricating Oil & grease; we also discussed what viscosity & what NLGI grade is. Here we are trying to discuss the Grease Lubrication system used in different types of stone crushers. Before understanding which lubrication system is good for crusher bearing lubrication, we need to understand the application & crusher working principle.What is crusher & crusher working principle.
Stone Crushers or Rock Crushers are mainly used in the mining industry to reduce the size of stones into smaller rocks, gravel, sand, or rock dust. In some industries, crushers are also used to reduce the size of waste material into smaller ones to recycle or dispose of the waste material. Additionally, rock breakers are normally installed next to a crusher to reduce oversize material, which is normally too large for a crusher. Finally, crushers reduce particle size enough to be processed into finer particles in a SAG Mill followed by a Ball Mill.
Different types of Crushers
Mainly crushers can be classified in two main groups as per their working principle.
- Compressive crushers that compress or press the material until it breaks into parts.
- Impact crushers using the principle of quick & high impacts to crush the material into parts.
Different types of Compressive crushers:- JAW Crusher, Gyratory crushers, cone crushers
You can say that this is the first stage primary crusher used to break big stones into a size that rocks can be transported through conveyors to the next crushing stage. As the name suggests itself, jaw crushers break stones, and other materials need to break between a fixed and a moving jaw. The jaw, which is mounted on a pitman, is moving, and it has a reciprocating motion, and the other jaw is fixed & stays as it is. When the material runs between the two jaws, the jaws compress larger rocks into smaller pieces. Like JAW crushers, Gyratory crushers are also used mostly in the primary stage to break big stones into smaller pieces. Cone crushers resemble gyratory crushers from a technological point of view, but cone crushers are popular in the secondary stage and quaternary stages of cursing stones.
Impact crushers (Hammer Crusher)
Impact crushers are also crushing machines like compressive crushers, but this type of crushers use sudden high impact on stones to reduce their size instead of pressing the material until it breaks into parts. This type of impact crusher can be used in any stage of the crushing process.
As per the working principle of Impact / Hammer crushers, they can be classified into two main types.
- Horizontal shaft impact (HSI) crushers.
- Vertical shaft impact (VSI) crushers.
Now we have discussed the basics of different types of crushers. As per the working principle of different types of crushers, we need to think from a Lubrication point of view.
So, As per the working principles of different types of crushers, there are some criticalities as per lubrication point of view.
Lubrication Criticality of Crushers Bearing
- Very high & shock load on bearings.
- Very high chances of metal-to-metal point contact on bearings due to shock load.
- Very dusty environment.
- Grease should have good sealing property also to reduce contamination from foreign particles.
Crusher Bearing failure reasons
Poor or inadequate lubrication is one of the major reasons for bearing failure in all types of crushers. Normally, the Original Equipment Manufacturer (OEM) collaborates with the bearing & lubricants manufacturer to develop a recommended re-lubrication schedule. Operators and maintenance people should follow the OEM provided re-lubrication recommendation chart, normally written in the product catalogue book or product maintenance book, to maximize the bearing life.
In addition, it should be taken care, not to over lubricate the bearings. In grease lubrication systems, if bearings are over lubricated, then due to lubricant churning, excessive heat can generate inside the bearing & breaks down the lubricants film, and this can cause premature bearing failure. In addition, it should be noted that mixing of different greases or other lubricants should also be avoided, as this can result in breakdowns and may cause premature failure.
In addition to that, Damage to crusher bearing is a result of Grease contamination & improper lubrication result to metal-to-metal contact & wear.
Common reasons of Metal-to-Metal contact & wear is as include
- Abrasive wear and debris denting inside of the bearing caused by contamination of lubricants.
- Excessive shock loads or vibrations in the application or use of a wrong viscosity grease or grease viscosity reduction due to excessive temperature inside the bearing or all of these reasons can result in metal-to-metal contact & wear in the bearing.
- Fretting or fretting corrosion, which typically results from a loose fit of bearing inside hosing or in the shaft, leading to relative motion between the bearing and the shaft or housing.
Recommended Grease Lubrication for different types of stone crusher
To help to protect crusher bearings from failure, it is critical to use the right lubricant products. Original Equipment Manufacturers (OEM) of different types of crushers should recommend, or maintenance peoples should check for lithium or calcium based greases that have a min base oil viscosity of ISO 220 to 460 centistokes (CST) at 40 degrees centigrade and that grease should contain extreme pressure (EP) additives. In some cases, operators can also look for greases containing a molybdenum disulfide (Mos2) to protect against adhesive wear inside the bearing. In addition, it is highly recommended that crusher bearings be frequently re-lubricated to ensure proper lubrication or use high viscosity oil-based grease to increase re lubrication interval so that the film thickness of grease can withstand the shock load coming in the bearing during operation.
Oil Lubrication system for different types of crusher
Normally, operating an oil-lubricated crusher with contaminated lubricating oil (old, dirty oil) is a common mistake followed by maintenance people. As a thumb rule, operators should use gear lubricants added with extreme pressure additive with a minimum oil viscosity of 22 CST at the bearing operating temperature. This typically demands an AGMA 3 EP or 4 EP gear oil which Exhibit high Timken OK loads and excellent results on the FZG and Four-Ball Wear Test addition to that; gear oil should meet or exceeds DIN 51517 Part 3, U.S. Steel 224, AGMA 9005-E02, ISO 12925-1 CKC/CKD, David Brown S1.53.101, GM LS-2 EP Gear Oil. OEM should also recommend a routine oil-sampling checkup program to monitor oil and crusher conditions effectively.
You can also read below articles to get more information
What is Tribology, Tribosystem & Lubrication
Basics of Industrial Lubricants.
Lubricating Oils Vs Lubricating Greases | What to Choose & Why?