In most extruders, the change in screw speed is achieve […]
In most extruders, the change in screw speed is achieved by adjusting the speed of the motor. The motor typically rotates at full speed of approximately 1750 rpm, but this is too fast for an extruder screw. If it is rotated at such a fast speed, too much frictional heat is generated and the residence time of the plastic is too short to produce a uniform, well-stirred melt. Typical deceleration ratios range from 10:1 to 20:1. The first stage can be either gear or pulley, but the second stage uses gears and the screw is positioned at the center of the last large gear.
In some slow-running machines (such as twin-screws for UPVC), there may be 3 deceleration stages and the maximum speed may be as low as 30 rpm or lower (ratio of 60:1). At the other extreme, some very long twin-screws for agitation can run at 600 rpm or faster, thus requiring a very low deceleration rate and a lot of deep cooling.
Sometimes the deceleration rate matches the task incorrectly - there will be too much energy to use - and it is possible to add a pulley block between the motor and the first deceleration phase that changes the maximum speed.
Representatives of the above-mentioned domestic steel enterprises told reporters that domestic iron and steel enterprises are "love and hate" for importing iron ore from India: domestic small and medium-sized steel companies do not have the status of negotiating with international iron ore export giants such as BHP Billiton, so they can only be from the market. Buying stock to meet the demand of iron ore, and India's iron ore types and grades are suitable for various needs of domestic small and medium-sized steel enterprises, so Indian iron ore has played a certain role in relieving the tight demand for domestic iron ore. However, the long-term price increase of Indian iron ore with the international iron ore has caused the spot iron ore price to nearly double the long-term agreement price. The high speculative spot price of Indian iron ore has made long-term agreement suppliers dissatisfied with the low-cost supply of iron ore, which further prompted them to increase the price of iron ore exported to China. This either increases the screw speed above the previous limit or lowers the maximum speed allowing the system to operate at a greater percentage of maximum speed. This will increase the available energy, reduce the amperage and avoid motor problems. In both cases, the output may increase depending on the material and its cooling needs.