Jaw Crushers are often used as primary crushers where the main duty is to produce a material that can be transported by belt conveyor to the subsequent stages of the plant. They crush material via compression, by squeezing it between a moving piece of steel and a stationary piece of steel.
One of the main benefits of Jaw Crushers compared to other types of primary crushers has to do with the wearing components. Wear is typically limited to the jaw plates and side plates. Additionally, these plates can be reversible, allowing for double the wear life.
To further increase the wear life of these components, proper feeding practices should be followed. Properly feeding the crusher not only increases component wear life, but it also improves the efficiency of the Jaw Crusher itself.
Follow these best practices for feeding Jaw Crushers to improve maintenance and operation.
1. In line feeding
Jaw Crushers should only be fed in line with some type of Feeder or scalping screen. This means the discharge end of the feeding machine should line up with the feed opening (or gape, the opening as measured from jaw die to jaw die) of the Jaw Crusher. In-line feeding limits opportunities for the material to clog the Jaw Crusher.
2. Choke feeding
Jaw Crushers work best when the entire crushing chamber is used for material size reduction. Choke feed a Jaw Crusher to maintain a crushing chamber that is at least 80% full. This will help to draw the material down into the crushing chamber, as well as create a better material shape and improve overall efficiency.
3. Remove sizes larger than the crusher openingMaterial that exceeds the size of the feed opening can clog the Jaw Crusher and reduce efficiency. It can also sit on top of the opening and block production altogether.
Removing oversize ahead of the Jaw Crusher will help to avoid blocking and clogging of the crusher opening. A good rule of thumb is that the maximum feed size should be 80% of the crusher opening. If the crusher opening is 30”, a 24” feed top size is recommended.
4. Scalp out the fines by pre-screening the feed
Fines in the feed can limit production for several reasons. They can clog the crushing chamber, reducing the tons per hour and efficiency of the crusher. They can also prevent even distribution of particle sizes and generate an inconsistent product shape.
Fines can also create unnecessary wear on crusher components. Scalping out this material ahead of time will help to prolong the life of wear components (jaw dies and side plates), as well as help to reduce the downtime required to changeout worn components.
Vibrating Grizzly Feeders, Wobbler Feeders and scalping screens are commonly used to feed Jaw Crushers because of their ability to remove fines from the crusher feed. Vibrating Grizzly Feeders and scalping screens can feature metal comb-like bars though which fine material can fall. The larger material travels on top of the bars toward the crusher opening. Wobbler Feeders feature elliptical bars that scrub material as it moves toward the crusher opening, with fines passing through the spaces between each bar.
5. Provide a well-graded feed
Another best practice for feeding Jaw Crushers is to blend the feed material ahead of the crusher to ensure a well-graded feed. This will produce steady, consistent tons per hour out of the Jaw Crusher. It will also promote inter-particle crushing to break any flat or elongated material.
A well-graded feed for a Jaw Crusher includes material larger than the closed-side setting but no larger than 80% of the feed opening. As stated in the two previous best practices, remove oversize, fines and material equal to the product size ahead of time for optimum operation.
6. Avoid feeding lightweight or sticky material
Jaw Crushers are known for being able to handle a wide variety of materials, specifically those that are very hard, very abrasive and non-friable. They can even handle some wet materials.
Jaws are not designed for handling lightweight or sticky materials, however. Sticky materials can build up on the jaw plates and reduce efficiency. Lightweight materials don’t draw down into the crushing chamber well, which also reduces efficiency.
7. Limit steel and other metals in the feed
In aggregate or mineral processing plants, tramp metal isn’t necessarily expected to be in the feed, although it may enter in the form of a broken bucket tooth for example. In C&D recycling plants, metals such as rebar and dowel bars in reinforced concrete are actually anticipated in the feed.
While Jaw Crushers can handle metal, such as steel, in a feed, and can even pass the steel without harm to the crusher if equipped with an automatic tramp relief system, it is best to limit the amount metal that enters the crusher. If the crusher does not feature a tramp relief system, the toggle that maintains the closed-side setting can break, potentially damaging other components in the plant as it falls out of the crusher as well as causing unplanned downtime to replace the toggle.
It is always best to remove as much steel as possible via a hydraulic breaker, shear or concrete processor before feeding into the Jaw Crusher. This will reduce the potential for unwanted costly repairs and downtime.
What you feed a Jaw Crusher and how you feed a Jaw Crusher are critical to its operational efficiency. Following these best practices will ensure your Jaw Crusher is operating at optimum efficiency while reducing wear and tear, increasing your overall productivity and profitability.
