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A coarse screen is a device that is used to remove large floating and suspended solids from water. The screen is placed in the wastewater treatment system to protect the pumps and downstream equipment from clogging and damage. There are two types of coarse screens: the manually cleaned coarse screen and the mechanically cleaned coarse screen.
The manually cleaned coarse screen is the most common type of screen used in wastewater treatment facilities. The screen is made of parallel bars, wire, or perforated plates that are spaced at regular intervals. The bars are typically made of steel, stainless steel, or aluminum and have openings that range from 6 mm to 150 mm. The bars are fixed in a frame and placed horizontally across a channel or tank. The wastewater flows through the openings and removes the large solids. The screen needs to be cleaned manually with a rake or brush when the solids build up on the surface.
The mechanically cleaned coarse screen is an automatic screen that is cleaned by a motorized rake or brush. The screen has the same structure as the manually cleaned screen. The only difference is that it has a traveling carriage that moves along the surface of the screen. The carriage is driven by an electric motor and moves back and forth. When the screen needs to be cleaned, the carriage is turned on and moves along the screen. The carriage pushes the solids off the surface and into a collection trough. Mechanically cleaned screens are more expensive than manually cleaned screens, but they are more efficient and reduce the labor costs of cleaning the screens.
Coarse screens are available in various specifications and sizes to meet different industrial needs. The most common mesh size is around 2 to 10 mm. Coarse screens with a 2-mm mesh can remove stones, hair, bones, and other large objects, while those with a 5-mm mesh can be used to remove rice, wheat, and other grains. Coarse screens with a 10-mm mesh are typically used for fruits and vegetables.
The power requirement of the coarse screen is another important specification. It is generally indicated as a horsepower (HP) range. The power requirement depends on the size and design of the screen and the material being screened. For example, the power requirement of a coarse screen for grading nuts is around 1.5 HP, while the power requirement of an industrial coarse screen for grading grains is around 3 to 5 HP.
Coarse screens can be made of different materials, such as plastic, stainless steel, and galvanized steel. In the food processing industry, stainless steel is the most common material. It is durable, corrosion-resistant, and easy to clean. Galvanized steel is a cost-effective option. It is suitable for applications in a dry or non-corrosive environment. Plastic coarse screens are used for light-duty filtering tasks.
Coarse screens can be square or round. The square shape is more common than the round shape. Round coarse screens work well in traditional industrial machines. They are easy to replace and install. The square shape provides more screening area and is more effective for high-capacity screening.
Proper maintenance can extend the service life of the coarse screen. Here are some common maintenance tips:
Regular inspection is necessary to find and repair any damage or wear in time. If the screen is damaged, it may allow impurities to pass through, which can affect the product quality. For example, a damaged coarse screen in a food processing machine may allow insects to pass, leading to food contamination.
Cleaning the coarse screen is essential. Over time, impurities will build up on the screen, which will block the mesh holes and reduce the screening efficiency. The cleaning method depends on the specific material and application of the coarse screen. For example, stainless steel coarse screens can be cleaned with water, detergent, or a high-pressure washer.
Proper storage is also important. If the coarse screen is not used for a long time, it needs to be stored in a dry and clean place. It should be kept away from direct sunlight and any corrosive or moisture substances.
Coarse screens are widely used in various industries and applications to perform the important function of pre-treatment, as well as the removal of large and unwanted solid particles from the water and wastewater streams.
At the beginning of the treatment process, a bar screen often serves as the first line of defense to filter out large debris and foreign matter, which ensures that downstream equipment and processes function efficiently. Besides, it protects delicate and expensive equipment from damage caused by abrasives contained in the water.
Coarse screens can remove the large contaminants from the influent wastewater. This prevents clogging and damage to pumps, pipelines, and treatment equipment in the plant. Meanwhile, it also improves the overall water quality of the treatment process.
Coarse screens help to control product quality by filtering out oversized particles, debris, and contaminants from ingredients and processing water. Here, they can prevent equipment damage and ensure food safety.
Coarse screens play a vital role in ensuring product quality and protecting production equipment by removing large particles, impurities, and agglomerates from raw materials and process liquids.
Coarse screens help to separate oversized materials, such as wood chips and bark, at various stages of the pulping and papermaking process. This can ensure the smooth operation and longevity of production machinery and equipment.
Coarse screens can pre-screen feed materials to crushers and processing plants, removing oversized rocks and debris. This not only protects downstream equipment but also optimizes the efficiency of the crushing and processing operations.
When choosing the appropriate coarse screen, there are several factors to consider.
It is important to consider the specific intended use of the coarse screen. Different industries and processes have unique screening requirements. For example, the mining industry may require heavy-duty screens, while the food processing industry may need sanitary screens. Select a coarse screen that is designed for the application to ensure optimal performance and compliance with relevant industry standards.
Coarse screens are available in various mesh sizes and opening shapes. It is important to choose the right screen size and opening to achieve the desired separation and flow rate. Consider the materials being screened and the required particle size. Select a coarse screen with an appropriate mesh size and opening to ensure effective screening while avoiding clogging and excessive material retention.
Coarse screens can have single or multiple screen decks, as well as different frame configurations. When choosing a coarse screen, consider the specific screening task and the characteristics of the material being screened. Select the appropriate screen deck and frame design to achieve the desired separation efficiency and material flow. In addition, consider the durability and support requirements of the coarse screen. Choose a well-constructed frame that can withstand the operational load and provide adequate support for the screen decks.
If choosing a vibrating coarse screen, consider its vibration type and amplitude. Linear and circular are two common vibration types. Linear vibration is suitable for loose and layered materials, while circular vibration is suitable for viscous and high-humidity materials. The amplitude determines the energy transfer to the screen surface. Choose the appropriate vibration type and amplitude to ensure effective material movement and screening performance.
When choosing a coarse screen, consider its quality and brand. Choose a well-constructed and durable coarse screen from a reputable manufacturer. Quality screens can achieve optimal performance and have a longer service life, thereby reducing maintenance and replacement costs.
Q1: What are the differences between fine screens and coarse screens?
A1: The main difference is the size of the mesh opening. A fine screen will have a finer mesh opening than a coarse one, as the name implies. This allows smaller, lighter materials to pass through, while retaining larger particles. The opposite is true for coarse screens.
Q2: What are the applications of coarse screens?
A2: Coarse screens have many uses in various industries, such as mining, construction, agriculture, and food processing. In the mining industry, they are used to separate ore before crushing it. Screens with large openings allow small, high-value nuggets to pass through, while retaining larger rocks in the slurry. In the construction industry, they are used to separate gravel, sand, and stone. In the agriculture industry, they are used to separate solid and liquid manure. In the food processing industry, coarse screens are used to separate large particles of rice and wheat from small chaff.
Q3: How do manufacturers determine the size of the openings in coarse screens?
A3: The size of the openings in a coarse screen is determined by the size of the material that needs to be separated. Manufacturers may use a standard size set by an independent organization or create custom sizes for clients.
