Roll Crushers are compression-type crushers used to reduce large lumps of many different materials into smaller sizes suitable for sale or for easier handling downstream.
They consist of one (Single Roll) or two (Double Roll) rotating roll shafts equipped with teeth. Feed material is either crushed between the roll and a curved crushing plate in a Single Roll configuration or between the teeth and the roll bodies in a Double Roll configuration. The product size is determined by the space between the roll bodies or the roll body and the crushing plate.
Two-stage Roll Crushers, such as Triple Roll and Quad Roll Crushers, feature both primary and secondary crushing in a single machine. Triple Roll Crushers consist of a single roll configuration in the top stage and a double roll configuration in the bottom stage. Quad Roll Crushers consist of a double roll configuration in both the top and bottom stages.
The bottom stage of a Triple Roll Crusher.
Crusher rolls are available in two designs:
- Roll shell configuration
- Segmented roll configuration
The roll shell design is a solid roll shell comprised of high strength steel pressed and keyed to the roll shaft or bolted between two flange shafts.
The segmented roll design typically features two end hubs pressed onto a roll shaft. Roll segments attach to the hubs with high-strength bolts. An alternative design features segments secured with high-strength bolts to a solid roll barrel.
A benefit to the segmented design is that individual segments can be replaced as necessary without having to replace the entire roll.
Regularly scheduled maintenance will help you to identify when roll shells or segments need to be replaced, but in addition to the visual clues, there are some operational/physical signs it’s time to change out your roll segments.
Signs of roll segment wear
1. Visible wear
The first sign you may need to change your roll segments is visible wear to the crushing elements, including the teeth and the roll base, or uneven wear to the point an adjustment in crusher setting cannot compensate for it.
Tooth and segment wear may be recognised during routine preventative maintenance checks or by a change in product size when no adjustment to the body-to-body setting has been made. At a minimum, the teeth and segments should be inspected every 1,800 working hours, or once a month, for wear or damage.
At some point, the teeth on the roll shells or segments will become worn or break. If the teeth are found to be excessively worn, they must be repaired or replaced. Tooth templates will typically be provided by the manufacturer to aid in determining levels of wear.
Before replacing the whole segment, however, decide if the issue can be remedied by rebuilding or replacing the worn teeth. These procedures can be found in the machine’s operation and maintenance manual.
If replacement is required, the procedure can also be found in the manual.
Be sure to follow all appropriate safety precautions when preforming any maintenance or repairs to your crusher.
2. Oversized product
As mentioned above, a change in product size without a change in the crusher setting can indicate tooth wear.
With Roll Crushers, the product size is determined by the distance between the two roll bodies, or between the roll body and the crushing plate in Single Roll Crushers and the top stage of Triple Roll Crushers. A larger product size can be made by increasing the distance between the two roll bodies, while a smaller product size can be achieved by decreasing the distance between the two roll bodies.
If you haven’t changed the crusher setting but are noticing a larger-than-desired product size coming out of the crusher, it may be time to take a look at the roll teeth.
3. Reduced throughput
Throughput can tell you a lot about the condition of the crusher and/or the feed. If you notice a change in throughput, first determine if there has been a change to the feed material. Higher percentages of larger material in the feed can cause the material to bounce around on top of the rolls, preventing other feed material from reaching the rolls and thereby reducing throughput.
Another factor that affects throughput is the crusher setting. A larger body-to-body setting equals higher throughput, since larger material can pass through at a faster rate. A smaller body-to-body setting equals less throughput.
If the crusher setting is the same and the feed material remains unchanged, you may want to inspect the teeth for wear or damage. When the crushing elements are worn or damaged, it takes longer for the teeth to grab the feed material, which reduces throughput.
4. Excessive fines
Roll Crushers are designed to create a cubical product with minimal fines generation. If you start to see an excessive amount of fines coming out of the crusher, you should check the rolls for signs of wear. Worn or damaged teeth can grind at the material rather than breaking it cleanly, creating more fines in the product stream.
Roll teeth are designed to draw the material in to crush to the desired size. Worn or damaged teeth are not able to effectively grab at the material or pull it between the crushing rolls. This can lead to larger lumps of feed material to remain in the hopper, which prohibits incoming feed material from reaching the rolls, effectively plugging the machine and creating a stall situation.
If you notice your Roll Crusher is plugging or stalling, you may want to check the roll segments for wear or damage and determine the best course of action for remedying the situation, whether it be repair or replacement.
Roll Crusher spare parts
In reality, you shouldn’t be waiting until you see the above signs to order spare parts. You should have a stock of certain items available at your facility at all times.
Having spare parts readily available when you need them can make the difference between being down for a few hours and being down for a few days. Your machine’s operation and maintenance manual should indicate which spare parts should be kept on hand and how many of each are ideal.
Once a spare part is used, it is good practice to immediately order a replacement to ensure minimal downtime the next time a changeout or repair is necessary.