I. Type and characteristics of regulating valve Regulating valve in accordance with the different power source can be divided into pneumatic control valve, electric control valve, hydraulic control valve and self-regulating valve. In accordance with the different action switch, can be divided into straight-stroke regulator, rotary regulator and so on. In the gas, hydraulic control valve, according to different implementing agencies, there are pneumatic diaphragm control valve, cylinder adjustment or shut-off valve. In accordance with the applicable temperature is different, there are room temperature, temperature, high temperature or low temperature control valve. In accordance with the applicable pressure is different, there are atmospheric type, high pressure type. In accordance with the different movements of the valve, there are adjustable, cut off and so on. There are a wide range of control valve features a wide range of applications, each with its own application features such as ball valve has the advantages of fast cutting, self-cleaning, small leakage, large flow, small pressure loss, but its regulation is poor, although V Ball valve can be used to adjust. Butterfly valve for large-caliber, large flow, low pressure occasion, but its large amount of leakage, the action of a low degree of jumping phenomenon. Single-seat valve to regulate the characteristics of good, small amount of leakage, but not resistant to pressure, poor anti-imbalance, easy to wear spool defects are more common. Thus, a good key factor to adjust the system characteristics, a key factor is how to choose a suitable control valve, improper selection, easily lead to deterioration of the quality of the regulation system, or even can not be properly adjusted. Second, the basic principles of control valve selection Valve selection is a comprehensive judgment, taking into account the local and overall, to achieve the best quality system to adjust the quality of the most important work, it is necessary to consider the working conditions of the environment, the type of valve structure, Flow characteristics, financial and other factors, but also consider as much as possible the entire control system in the best state of control. In practice, the general principles of selection are as follows: (A) caliber and CV value calculation This is the premise and basis of selection of control valve, the nominal diameter of the choice, the main consideration is the maximum CV, rated CV, adjustable range, Adjust margin and several other factors. The general principle is to make as much as possible to adjust the valve opening in the normal range of 30 to 80%, better regulation. When calculating the CV value, consider the maximum percentage of CV value equal to 90-95% as the maximum CV value. The minimum CV value is recommended to be determined at 10-20% opening. (B) the flow characteristics and the choice of spool 1. The choice of flow characteristics The basic principle is to make the flow characteristics of the characteristics of the regulator and the characteristics of the regulator to reverse, in order to facilitate the overall adjustment of the overall characteristics of the system close to linear. There are two general: linear characteristics and equal percentage characteristics. The former applies to: 1. Most of the system pressure loss is distributed on the valve 2. Small pressure changes 3. Adjustable range of small occasions The latter applies to: 1. Adjustable range of large occasions 2. Pipe pressure loss large 3 Valve pressure changes in most cases can choose to wait for the percentage of features. 2. The choice of spool generally have: plunger-shaped, sleeve-shaped, V-shaped, rotating shape, quick opening and so on. Plunger-shaped adjustment characteristics of a good, sleeve-shaped valve can reduce noise, anti-imbalance ability, and quick opening should not have too much pressure. These aspects should be comprehensive consideration of process media conditions, environmental conditions and other factors. (C) the choice of pipe connections generally follow the process of pipe connection standards. Such as: 1 "Most of the following pipe for the threaded connection, the general use of medium and low pressure flat flange, high pressure, high temperature generally concave or convex flange or trapezoidal groove flange, but also special welding, welding flange, etc. ( Fourth, the selection of the valve cover mainly based on temperature and sealing requirements, there are room temperature, temperature, high and low temperature and bellows seal, multiple seal type, etc. (e) filler selection according to high sealing, low coefficient of friction Requirements such as large vacuum conditions, you can reverse the V-PTFE packing, in order to avoid inhalation of air, low temperature or flammable gas conditions, the general combination of a variety of filler is better. Valve Material Selection 1. The material of the valve is decided by considering the influence of the fluid on erosion, cavitation and cavitation of the valve body, as well as the material selection of high temperature and low temperature, etc. Under high temperature conditions, it is generally required that the selected material contain chromium , Nickel, molybdenum and other elements.Low temperature conditions, the general selection of Austrian body stainless steel and other materials. 2. Valve components to prevent cavitation, cavitation, particle erosion, etc., generally to be hardened. Corrosion, should consider the choice of anti-corrosion materials or lining (VII) the choice of implementing agencies in any case the choice of implementing agencies should consider the following requirements: 1. Sufficient output torque to overcome axial imbalance 2. Meet the needs of the trip 3. Sufficient valve seat sealing pressure 4. Operating time to meet the technical requirements (8) The choice of valve attachment may be based on specific circumstances, such as with valve positioner, electrical converter, solenoid valve, travel switch, Third, the control valve maintenance Valve maintenance is often overlooked by people, due to improper maintenance or not in place or not maintenance, resulting in the failure of the entire control system have occurred, in fact, the control valve is also a kind of instrument, we must attach importance to it Of the maintenance work in order to ensure the normal operation of the control system, reliable and effective operation, the following maintenance precautions. Currently, we generally have the following three maintenance methods: 1. Passive Maintenance - to maintain after the accident, in fact Is maintenance; 2. Preventive maintenance - regularly scheduled maintenance according to experience or plan; 3. Predictive maintenance - mining Non-invasive diagnostic testing and evaluation devices with advanced technology components or intelligent instruments such as the maintenance of intelligent diagnostic techniques used by some foreign manufacturers of locators. Maintenance should focus on the following parts: 1. Stem packing section Should always check for leaks, damage, deformation, etc., if found should be promptly replaced. 2. Itinerary. Check the itinerary is in place or whether there is a dead zone, with or without internal leakage or surge, etc. 3. The implementing agencies are intact , No leakage, no string gas, etc. 4. Valve positioner and other accessories are intact, the input and output pressure is within the specified range, linearity, etc. In short, the automatic control valve as an important part of the entire control system, The working status of a direct impact on the quality of the regulatory system.Selected, good, good management of each of the automatic control department, an important part of staff.
Proper clamping is critical to efficiency. This is especially true for metallographic cutting of large workpieces.
If the clamping tool used is not appropriate, the time required to clamp large workpiece will be greatly increased, affecting the subsequent cutting process, the loss is not worth the gain. Worse, large artifacts are more likely to move if they are not clamped. This means extra holding time for cutting or, worse, damage to the sample.
Solution: Use a better or customized gripper tool
If you work with large artifacts frequently, make sure you have a good range of gripper tools to choose from, because having the right tools on hand can save a lot of time.
If you often work with similar-shaped artifacts, custom clamping tools are by far the most efficient choice. Custom clamping tools not only save you time, but also ensure consistency between the sample and the cutting wheel, reducing the risk of cutting wheel deflection, thus ensuring an easily reproducible process.
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