Shumar developed its first Double Roll crusher in 1964 and since then its unique design has been used in mines to improve efficiency and profitability by decreasing the overall fines production (pulverized coal that is of no use) from 55 down to 22 percent.
Shumar Double Roll crushers reduce power consumption and wear, while maximizing the tonnage of useful coal during production.
- All Shumar crushers have two machined rolls to which the crushers segments are bolted.
- Each roll is fitted with six crusher segments.
- Mn. steel segments are used in primary and secondary applications, while white iron is used for some secondary washed coal applications. All segments are hand ground for proper seating.
- One roll is fixed while the loose roll is spring-loaded to enable foreign matter to pass through the crusher without causing damage. The loose roll position can also be adjusted for various product output sizes via two adjusting spindles.
- The loose roll bearings slide on the main frame and are guided at the bottom by a wearing strip fixed to the main frame and at the top by a separate top guide frame.
- Phosphor bronze and steel wearing strips are provided for all the sliding surfaces.
- The bearing are spherical roller bearings. To protect seals, the loose bearing housings are designed to pivot in the event of the roll kicking out.
- The hood is a permanent part of the frame. The outlet shoot is fitted to this section of the hood. The crusher is thus totally sealed.
- The crusher is supplied with a V-pulley drive, guard and drive stand with a pair of geared motors driving each roll separately. The drives are both situated on the same side of the machine to make it more compact.
- The segments fitted to each crusher are carefully chosen to suit the customers needs. Special segments are designed if stock segments are not suitable.
Advantages of Efficient Crushing:
Reduced Fines Production
- As sized products generally attract a higher sales price than fines, reduced fines production means additional higher profitability or makes the product more competitive in the market.
- Less wind loss and environmental dust problems.
- Large savings in washing costs as larger size coal is cheaper to wash than fines.
- Saving in capital cost of washing plant as fines plants are generally more expensive to build. Less water used in coarse plants and therefore less water pollution problems will occur.
- Less fines means lower external moisture content in the product.
Reduction in Power Consumption
- Regardless of the product sizes produced, power is required to break coal.
- Unnecessary fines production causes excess power consumption.
- Direct cost saving of motor installations, switch gear, cable and power consumption.
Reduction of Wear of Crusher Segments
- Crusher segments last longer when crushing is done efficiently, i.e. when the correct crushing ratio, roll speed and roll diameters are used.
- Direct saving in less frequent replacement costs plus down time.
Maximizing Desirable Product Size Distribution
- This means producing the maximum quantity of the desired product that the market requires, i.e getting the maximum useful tonnage of all coal mined at an optimal price.
How to Achieve Efficient Crushing:
- Never crush coal that is already product size. Screen out under-size before crushing. Each time sized coal goes through a crusher, fines are produced, even if the incoming coal is smaller than the crusher setting. This is valid even when primary crushing.
- Choose the right type of crusher. Double roll crushers have proved themselves to be the most efficient type of machines in the coal industry.
- Use the correct crushing ratio. Crushing ratio is defined as the ratio of input size to output size. The ideal ratio is 2 : 1.3 : 1 which is possible but anything above that ratio causes a serious decrease in crushing efficiency.
- Use a crusher with the right roll diameter with respect to the desired input and output size. Large pieces of coal fed to small diameter rolls produce a rolling effect of the coal as the teeth battles to grip the coal, thereby reducing throughput tonnage and increasing fines and segment wear. The nip angle, the angle from the horizontal where the rolls grip the coal, must always be as small as possible. Reduce the crushing ratio nip if the angle is too large or use larger diameter rolls.
- One of the most important aspects of the crusher design is the correct segment tooth profile. Let your crusher manufacturer know what product you desire and we will give you the correct profiles. If your product changes, contact us and we will advise you whether your present profile can still be used or if the profile should be changed. Power consumption is very largely influenced by the correct selection of the tooth profile.
- The roll speed is also important. Always contact your crusher manufacturer before altering the roll speed with respect to the input size and crushing ratio. Too high a speed can result in slippage with a resultant increase in fines and segment wear.
- When doing cost cutting exercises, do not try and reduce capital outlay on your crushing circuit to the detriment of the crushing efficiency. The capital you save initially will be lost later on a continuous basis as you create extra fines and lower profit products.