December 1, 2008
The importance of routine inspections for impact crushers.
by Jim Schreiner
Regardless of the type of equipment used on the job site, the importance of routine inspections and proper maintenance are paramount to maximizing uptime and production output. If the plant isn’t running, it isn’t producing, and lost production is expensive or impossible to make up. Planning “maintenance time” and using it effectively is how premier producers consistently achieve higher levels of uptime availability. They anticipate maintenance and plan for predictable uptime. To say it best: More uptime translates into lower production costs.
Even though impact crushers have been around a long time, their use has expanded significantly in the last 30 years, primarily due to advances in wear parts metallurgy. On the plus side, impact crushers are capable of high throughput capacity, high reduction ratios, and are relatively forgiving to fluctuating feed materials. On the negative side, they are susceptible to high consumption of wear parts and high maintenance downtime. When crushing abrasive materials, wear parts cost and cost of downtime can become prohibitive, even with advanced wear parts technology. The first step to predictable uptime and low operating costs is applying the machine correctly.
Successful operators plan their run time and maintenance downtime and use it effectively. They make sure that when that impact crusher starts up, it is going to go the distance to the next scheduled maintenance shift. They anticipate (track and log) wear parts consumption and have spare parts available on site. They constantly inspect the machine to look for developing problems and implement corrective actions before a crisis exists.
It is a good idea to always have blow bars, apron liners, and replacement hardware on hand for that unexpected issue that can appear. If, during normal maintenance, a cracked part is discovered, replace it immediately. Waiting for a dealer to deliver parts, or being told to run the machine in its compromised condition, is too high of a price to pay. Keep critical parts on hand.
Planning for maintenance begins before purchase and installation of the crusher. Selecting crusher features that allow safe, easy, and quick maintenance means the crew is far more likely to perform maintenance and finish tasks on time. Consider the following recommendations:
1. The crusher should open easily (hydraulics) and allow for crane access and a vertical lift of heavy castings. Safe lifting points should be built into castings. Hardware should be simple and easily accessible from safe working points.
2. Look for a design that uses common castings (side liners, blow bars, apron liners) throughout the crusher. This reduces parts inventory requirements and allows interchangeable parts to be flipped or relocated to optimize utilization.
3. A crane is required for impact crusher maintenance. A jib crane built into the structure, properly located to access the crusher and new parts loading area, is recommended. This dedicated crane is relatively inexpensive and can improve safety and speed maintenance.
Checklists can help operators maintain equipment properly. It is also important to follow company rules and the pertinent Mine Safety and Health Administration (MSHA) and Occupational Safety and Health Administration (OSHA) regulations. Safety should never be compromised. The following are fundamental checklists designed to identify areas and parts needing routine inspection. Slight modifications to the checklists may be warranted, depending on the manufacturer and type of impact crusher in operation.
* Visually check to make sure the crushing chamber is empty (free of debris, rags, wire, rebar, stone, or any material that could impair startup or operation).
* Check for clearance between the blow bar and side liners.
* Check apron settings (track and log wear, and plan for next casting change).
* Check blow bar and apron liner condition; look for cracks or uneven wear. (Large, easily accessible, built-in inspection doors should be a part of the crusher design.)
* Check for loose bolts, inside and out; tighten before startup.
* Make sure all the guards and covers are secure.
* If applicable, check hydraulic fluid levels and start the hydraulic system, checking for proper operation.
* Inspect under the crusher and remove any excess stone buildup or foreign materials.
* Start the under-crusher conveyor and ensure proper operation.
* Start the crusher and note any vibration; excess vibration may indicate loose or failed rotor parts or material buildup on sheaves.
* Check and log motor amp draw, noting any change in the trend (an increase in amp draw indicates increased friction – motor bearings, crusher bearings, rotor rubbing against liners, etc.).
* Introduce feed; material should be evenly distributed across the crusher for even wear.
* Listen and feel for unusual operation; a howl could indicate worn bearings; screeches, grating, and grinding could mean something is loose.
* Again, visually inspect for loose bolts.
* Grease bearings and lubrication points as recommended by the manufacturer.
* Clean up any spillage around and under the machine.
* Check to make sure the crushing chamber is empty – free of debris, rags, wire, rebar, stone, or any material that could impair startup for the next shift.
* Check for any damage that occurred during the shift.
* After shutdown, check and log the bearing temperature noting any change in the trend. Typical bearing temperature is between 140 to 150 degrees F. Using an infrared heat gun is an easy and quick way to monitor bearing temperatures throughout the plant.
* Check all fasteners and replace those that are loose or missing.
* Check any seal arrangement on the crusher.
* Check the crusher frame for any cracks and repair as soon as possible; cracks only get worse with time.
* If using a V-belt drive, check belt tension and condition.
* Check hydraulic components, pressures, and system functions.
* Check for wear in the feed chute.
* Make sure chains or rock curtains are in good shape.
* Check under the crusher for wear on the pan, belt, and discharge chute.
* Grease the motor once a year or as recommended by the manufacturer. Be careful not to over grease.
* If the machine has a hydraulic unit, empty out the hydraulic tank and clean it, clean or replace all strainers and filters, and refill the unit with new hydraulic oil.
When it comes to wear parts, watch for uneven wear patterns. This can occur on side liners, as well as blow bars or apron liners. These parts can often be flipped or moved to a different position to maximize utilization.
Uneven wear is often caused by poor distribution of the feed entering the crusher. Material that is concentrated in the center or feeding to one side will cause concentrated wear. Check to be sure wire, rebar, or bridged material isn’t forcing material to one side. It may be necessary to modify chute work or the feeder to achieve the desired results.
Some wear is expected on the external areas of the rotor. However, excessive wear in front of the blow bar may indicate that the rotor is spinning too slowly or the feed is penetrating too quickly. Good crushing requires that material penetrate onto the face of the blow bar before impact, but if material consistently impacts the rotor before the blow bar comes around, excessive wear will occur. Consult with the dealer or the factory for recommendations if this is occurring.
Some operators choose to hard face exposed areas of the rotor for added protection from wear. Whenever welding on the rotor, remember to directly ground the rotor. Any electric current arcing through the bearings will cause premature failure of the bearing.
It is important to use the correct grease for the bearings (not general purpose grease). Refer to the operating manual for the proper grease recommendation.
When greasing the bearings, do so at the end of the day when the bearings are warm. Combined with turning the rotor, this allows for better penetration and distribution of the grease.
To sum it all up, producers need to plan their production in order to meet their sales commitments. Unplanned downtime carries a very high cost, not only in lost production, but in broken commitments to customers. Taking the time to go through the checklists, tackling the needed maintenance issues promptly, plus selecting equipment that is safe and easy to maintain are major steps toward predictable production and greater profitability – all resulting from predictable uptime.
Jim Schreiner 800-765-6601, e-mail firstname.lastname@example.org.
WWhat to Look for
* High amp draw: Any increase in amps can signal a potential problem such as the bearings needing replacement or a loose hammer or blow bar moving and dragging on the crusher wall.
* Vibration: Any vibration needs to be checked, and can indicate worn bearings, loose hammers, or rotor wear, meaning the rotor is out of balance.
* Unusual noise: The best person to notice an unusual noise is the daily operator. A howl could indicate worn bearings; screeches, grating, and grinding could mean something is loose.
* High bearing temperature: If the bearing temperature is higher than the preferred range of 140 to 150 degrees F, it may indicate over greasing or worn bearings.
* Uneven wear in the crusher: Material not feeding correctly due to a jam could create uneven wear. Check for foreign material in the crushing chamber such as rebar or wire mesh.