Force-Controlled Feed Speed

Drilling with face grinding can be carried out with tool-path-controlled or force-controlled feed speed. The machine used plays a decisive role in... 

An extraction plant should operate at steady state in accordance with the flow-sheet design for the process. However, fluctuation in feed streams can cause changes in product quaUty unless a sophisticated system of feed-forward control is used (103). Upsets of operation caused by flooding in the column always force shutdowns. Therefore, interface control could be of utmost importance. The plant design should be based on (/) process control (qv) decisions made by trained technical personnel, (2) off-line analysis or limited on-line automatic analysis, and (J) control panels equipped with manual and automatic control for motor speed, flow, interface level, pressure, temperature, etc. 

The American version of the dynamic filter, known as the Artisan continuous filter (Fig. 30), uses such nonfiltering rotors in the form of turbine-type elements. The cylindrical vessel is divided into a series of disk-type compartments, each housing one rotor, and the stationary surfaces are covered with filter cloth. The feed is pumped in at one end of the vessel, forced to pass through the compartments in series, and discharged as a thick paste at the other end. At low rotor speeds the cake thickness is controlled by the clearance between the scraper and the filter medium on the stationary plate, while at higher speeds part of the cake is swept away and only a thin layer remains and acts as the actual medium. 

The compaction system consists of two, counter-rotating rolls at equivalent speeds. One roll is normally fixed while the other is allowed to float. The floating roll was implemented to control the roll gap. The roll force is applied to the floating roll by hydraulic pressure, which is counteracted by the normal force of the fixed rolls. This force is subsequently applied to the blend in the gap. A schematic of three typical roller compaction system arrangements with a feed screw can be found in Fig. 6.1. 

The hopper is usually made of stainless steel and has the shape of a funnel to contain and deliver the product to be compressed. It may be provided with a window for the observation of the product level and may also be provided with low-level sensors that signal an alarm, shut off the engine, or activate the feeding mechanism to deliver the product when it falls below this level. The feeder system usually consists of three sections (in the case of force feeders) and is ideal for press performance at high speed. The first section of a force feeder system is where the hopper is connected and is responsible for the flow of the product from the hopper to the next sections. The second section is where the die cavities are filled to their maximum capacities, and the third section is where the weight control adjustment takes place. These sections contain paddle systems which prevent packing of the product. The... 

The passage of hot melt between the rolls creates a pressure forcing them apart and the calculation of tolerances using a statistical model has been described (417). There is a rolling bank of feed material created in the gap or nip set between the first pair and also the second pair of rolls. Passage of the material is controlled by roll temperature, surface finish and the ratio of the roll speeds at the nip. The final calender nip controls film thickness. 

Monitoring and controlling the roll speed and force and the feed screw speed and torque are adjusted through PLC for process controls. Prebreaker and flake crushers are attached sizing features. CIP capability exists. 

Since, within practical limits, it can be assumed that the roll force necessary to produce a good product and, therefore, the gap at constant separation force are independent of roller speed, this control system can be applied to automatically adjust the feed rate to varying roll speeds and press capacities. Consequently, it can also be used in connection with level controls in the feed hopper which automatically change the production rate (roller speed) according to the level of available raw material in the bin. 

The screw-crammer system uses a conical hopper with a screw that is driven by a separate gear reducer and variable-speed drive motor. The output and effectiveness of the crammer are determined by the screw configuration and the available speed. The ram-type system, on the other hand, uses a pneumatic ram to stuff material into the screw. The ram is a piston-driven unit with the stroke timing adjustable by setting a series of timers located in the control panel. The feed section used by the ram system has an opening that is 12-14 times larger than that of a standard screw extruder. This allows low-bulk-density material to flow freely into the feed throat where the ram can compress it into the screw. Depending on the extruder size, the ram can compact materials with a force of 2000-9000 psi. 

One method of feeding material into an entry loop is by simply driving the payoff mandrel with an electric motor (see Fig. 11). Normally, this is accomplished with a DC motor, but on slow speed lines, an AC motor with an on-off -type operation may be adequate. When a DC motor is utilized, the loop position is usually automatically controlled with a set of photocells and flood lights or an ultrasonic sensor. This method of paying off material from the master coil is quite acceptable provided there are no stickers from the annealing furnace or any dents or damage to the sides of the coil. These defects would cause the material to stick to itself and not pay off with the force of gravity as it is uncoiled. 

For the size reduction of smaller particles, hammer mills are often employed. In these machines, free-swinging, hammers are rotated at high speed so that they are thrown out by the centrifugal force, hit the feed, and break it down by the force of impact. In many cases the discharge from this mill is through a sieve or screen to control the output particle size. 

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