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FAQ

FAQ


QWhat exactly is instrumentation?

A
Instrumentation is used to detect, measure, observe, calculate a variety of physical quantities, material composition, physical parameters and other instruments or equipment. Pressure gauges, length measuring instruments, microscopes, multipliers, etc. are all instruments and meters. Broadly speaking, instrumentation can also have automatic control, alarm, signal transmission and data processing and other functions, such as for industrial production process in the automatic control of pneumatic regulating instruments, and electric regulating instruments, as well as distributed instrument control systems are also instruments.
Radar is an instrument. Radar, the original meaning is radio detection and ranging. Radar has the characteristics of finding the target far away, measuring the target coordinates fast, and being able to use all-weather. Therefore, it has been widely used in alert, guidance, weapon control, reconnaissance, navigation support, meteorological observation, and identification of the enemy and the enemy, and has become an important electronic technology and equipment in modern warfare.
The radars used for weapons control are:
① Gun aiming radar. Real-time data for continuous determination of target coordinates, through the firing director to control the artillery aiming and firing. There are ground type and carrier type.
Missile guidance radar. Used to guide and control the flight of various tactical missiles. There are ground type and carrier type.
③ Torpedo attack radar. Installed on torpedo boats and submarines, used to determine the coordinates of the target, through the director to control the torpedo attack.
④ Airborne bombing radar. It is installed on a bomber to search for and identify ground or sea targets and determine the location of the drop.
⑤ Airborne interception radar. Installed on the fighter, used to search, intercept and track air targets, and control the shooting of artillery, rockets and missiles.
The terminal guidance radar. It is installed on the missile and automatically controls the missile to fly to the target at the end of the missile's flight.
Ballistic missile tracking radar. In anti-missile weapon systems and missile range measurements, it is used to continuously determine the coordinates and speed of ballistic missiles in flight, and accurately predict their future positions.

QCauses and preventive measures of pitting on the surface of precision castings

A

1. Causes of formation
(1) Metal oxide inclusions brought in by poor deoxidation of molten steel;
(2) The conditions for complete deoxidation are as follows: dry and clean furnace materials are selected, after melting, ferromanganese is added first, ferrosilicon is added for deoxidation, silicon calcium is added for deoxidation, then power is cut off and allowed to stand for 2min, aluminum is added for final deoxidation, and then heat preservation pouring is carried out. Immediately after pouring, add sawdust or waste wax and then cover the box for sealing and cooling.
In the case of incomplete deoxidation, if the cover box is sealed and cooled, due to the long cooling time, a large amount of oxygen existing in the molten steel has sufficient reaction time, and the formation of a large number of pitting is inevitable. In the case of complete deoxidation, the cover box cooling ensures that no external oxygen is adsorbed into the molten steel, avoiding the secondary oxidation of the molten steel and preventing the generation of pitting.
① When the shell is not baked through, a small amount of gas will be generated at the high temperature of the shell during pouring, which will promote the occurrence of interface reactions and form pitting.
The increase of impurities in the refractory material, especially the high content of Fe2O3, will directly lead to its participation in the interface reaction between the shell and the molten steel, so that oxygen enters the molten steel to cause secondary oxidation, thus increasing the tendency of pitting formation.
2. Preventions
(1) The most important factor affecting the production of pitting is the quality of molten steel; (I. e., whether deoxidation and scum are complete)
① The operation shall be carried out in strict accordance with the smelting process.
That is, according to the bottom slag → covering in melting → pre-deoxidization after melting → slag removal after power failure and standing → final deoxidization before pouring, this process is carried out.
The choice of deoxidizer should not only make the molten steel fully deoxidized, but also make the oxide formed after deoxidation have a low melting point and are easy to gather and float. The final deoxidizer aluminum addition must be strictly controlled, too much aluminum will promote the formation of pitting. (The residual amount of aluminum should be controlled between 0.015 and 0.02, which is the most ideal. If it is too low, it is easy to produce pores and pitting points, and if it is too high, it has white spots and black spots.)
③ The steel material should be very clean, and it is not advisable to use too much return material to increase the primary inclusions of the steel material. The melting process should try to prevent the exposed time of the molten steel surface and prevent the oxidation of Cr, Fe and Si elements.
(2) Since the temperature of the mold shell during pouring is above 800 ℃-900 ℃ and the temperature of molten steel is about 1600 ℃, the temperature contacting the surface of the casting is extremely high at this time, and the metal will not solidify instantly, especially the thick-walled parts. At this time, oxygen in the atmosphere is easy to react with the metal surface through the mold shell to form oxides and gather with inclusions in the molten steel to form pitting. Therefore, add sawdust (or charcoal) into the insulation, and immediately add waste wax block to cover the box for insulation after pouring the module, which is an important measure to prevent pitting.
(3) The roasting temperature of the shell shall not be lower than 1180 ℃, and the holding time shall not be less than 45min. The mold shell that is not completely burned through will have a small amount of gas during pouring, and will participate in the interfacial reaction between the molten steel and the mold shell, bringing oxygen into the molten steel, causing secondary oxidation. Carbon steel is high in C content and does not contain Cr, so when cooled in air, the interface reaction can only form a decarburized layer without causing pitting. If there are pitting, the shell is not well burned.
(4) Refractory materials, especially surface refractory materials, in addition to the main component should meet the requirements, the impurity content of Fe2O3 must be low. An excessively high Fe2O3 content will aggravate the oxidizing atmosphere of the interfacial reaction to cause the generation of pitting.
3. Summary
(1) Pitting is the aggregation of complex oxide inclusions of iron, chromium, silicon and aluminum in molten steel on the surface of castings.
(2) The main measure to prevent pitting is to deoxidize fully and completely during melting, and to make the deoxidization product easy to float; in the mold cooling process to prevent the secondary oxidation of the casting surface.
(3) Strictly implement the roasting process of the shell.
(4) Effective measures to prevent pitting of castings: purchase graphite sand (petroleum coke particles) as transition layer shell.
For more than ten years, we have been improving the quality of the casting surface (surface pitting), adding graphite powder to the back layer coating, adding about 0.3-0.5%, the effect is OK. I also through long-term practical experience, the use of the shell in the transition layer of sand to join the graphite electrode (carburant) approach is also very significant.

QTechnical requirements for precision casting

A

For example, sand precision casting, mass production plants should create conditions for the use of technologically advanced modeling, core-making methods. The productivity of the old-fashioned shock or shock molding machine production line is not high enough, the labor intensity of workers is large, the noise is large, and it is not suitable for the requirements of mass production, so it should be gradually transformed. For small castings, a box-free high-pressure molding machine production line with horizontal or vertical parting can be adopted, with high production efficiency and less floor space for real molding. For medium parts, various box high-pressure molding machine production lines and air punching molding lines can be selected to meet the requirements of fast and high-precision molding production lines. Core-making methods can be selected: cold core box, hot core box, shell core and other high-efficiency core-making methods.
For large castings in medium batches, resin self-hardening sand can be considered for molding and coring.
For heavy castings produced in small batches, manual molding is still an important method. Manual molding can adapt to various complex requirements and is relatively flexible, and does not require a lot of process equipment. Can be applied to water glass sand, VRH method water glass sand, organic ester water glass self-hardening sand, clay dry type, resin self-hardening sand and cement sand, etc.
Mass production or long-term production of stereotyped products using multi-box modeling, split box modeling method is more appropriate, although the mold, sand box, etc. began to invest high, but can be compensated for saving modeling man-hours, improve product quality. Casting methods such as low pressure casting, die casting and centrifugal casting are only suitable for mass production because of the high price of equipment and molds. The condition method should be suitable for, for example, the same production of large machine tool bed and other castings, generally using the core modeling method, not making the pattern and sand box, in the pit core; while the other factory is the use of sand box modeling method, production pattern.
Different enterprises have different production conditions (including equipment, venues, staff quality, etc.), production habits and accumulated experience. According to these conditions, we should consider what products are suitable for and what products are not suitable for (or can not). Accuracy requirements and costs The accuracy of castings obtained by various casting methods is different, the initial investment and productivity are also inconsistent, and the final economic benefits are also different. Therefore, in order to be more, faster, better and less, we should take into account all aspects. A preliminary cost estimate should be made for the selected casting method to determine the casting method that is economically efficient and can guarantee the casting requirements.

QDevelopment Prospect of Precision Casting

A

The metal materials of precision casting enterprises mainly come from purchased materials, waste castings and sprue of the enterprise. The purchased metal materials are often in bulk, rarely pressed into a cylindrical shape, and materials of different materials are easily confused together, such as 316 materials mixed with 304 or 430 materials. Therefore, precision casting enterprises should choose to purchase materials that are pressed into the cylinder as much as possible. The chemical composition of each batch of purchased materials is analyzed by optical spectrum analyzer. If possible, the supplier shall conduct on-site inspection to evaluate whether the materials are identified, protected and stored in isolation.
The scrap steel (waste castings, pouring risers) of the enterprise shall be subject to rust removal, oil stain removal, sand removal and cleaning and drying treatment to control S and P components. In addition, scrap steel of different materials should be marked, protected and stored separately, and should not be confused.

QPrecision casting-factors affecting the dimensional accuracy of precision castings

A

Factors affecting the dimensional accuracy of precision castings:
Under normal circumstances, the dimensional accuracy of precision castings is affected by many factors, such as casting structure, casting material, molding, shell making, roasting, pouring and so on. Any link setting and unreasonable operation will change the shrinkage rate of castings, resulting in deviation between the dimensional accuracy and requirements of castings. The following factors can cause defects in the dimensional accuracy of precision castings:
(1) The influence of the casting structure: a. The casting wall thickness, the shrinkage rate is large, the casting wall is thin, and the shrinkage rate is small. B. The free shrinkage rate is large, and the hindrance shrinkage rate is small.
(2) the influence of casting material: a. the higher the carbon content in the material, the smaller the linear shrinkage rate, the lower the carbon content, the greater the linear shrinkage rate. B the casting shrinkage of common materials is as follows: casting shrinkage K =(LM-LJ)/LJ× 100%,LM is the cavity size, and LJ is the casting size. K is affected by the following factors: wax mold K1, casting structure K2, alloy type K3, pouring temperature K4.
(3) The influence of molding on the linear shrinkage of castings: a. The influence of wax injection temperature, wax injection pressure and holding time on the size of the investment mold is the most obvious, followed by wax injection pressure. The holding time has little influence on the final size of the investment mold after ensuring the molding of the investment mold. B. The linear shrinkage of the wax (mold) compound is about 0.9-1.1%. C. investment storage, there will be further shrinkage, the shrinkage value of about 10% of the total shrinkage, but when stored for 12 hours, the investment size is basically stable. D the radial shrinkage rate of wax mold is only 30-40% of the shrinkage rate in the length direction, and the influence of wax injection temperature on free shrinkage rate is far greater than that on hindered shrinkage rate (the best wax injection temperature is 57-59 ℃, the higher the temperature, the greater the shrinkage).
(4) The influence of shell materials: the use of zircon sand, zircon powder, Shangdian sand, Shangdian powder, because of its small expansion coefficient, only 4.6 × 10-6/℃, so it can be ignored.
(5) the influence of shell roasting: because the expansion coefficient of shell is small, when the shell temperature is 1150 ℃, it is only 0.053, so it can be ignored.
(6) The influence of casting temperature: the higher the casting temperature, the greater the shrinkage rate, and the lower the casting temperature, the smaller the shrinkage rate, so the casting temperature should be appropriate.

QThe contrast characteristics of the form of precision casting

A

Precision casting is to take what method, this is a very major problem, in addition we can understand is for special processing methods and relatively more concerned about the characteristics of precision casting in some of the detailed form, this is our detailed decomposition and casting of some of the main way, for the construction of this form and the discovery that the relative coating form produced by ourselves can make us have a series of product development methods at a certain level, we have to take a certain complementary way to carry out the special performance of the rational form of the corresponding strategy, for the general level of complex advantage principle in uninterrupted processing can take the characteristics of the development of casting form and characteristics in an alternative way, then we have to use a new method and specific ideas to explain the corresponding explanation, explain some common state of the casting program, the marketing means that can be adopted in a certain execution process is not the detailed variety possessed by the general precision processing characteristics. For such changes in our casting type, there is still a certain expansibility and excavation. Such painting should reach some detailed characteristics that we have in a certain recommendation. Our production scale also has a certain harmony in a certain expansion, to a large extent, the feature classification we need is a non-definitional extension and general follow-up mining is the basic of a class of features we have.
The key adjustment method of precision casting is the focus of our decentralized measurement, and it is also the superior nature of our problem. For the precision level, we should pay attention to the corresponding support punching according to different product structure types. Such products are the kind that our customers need.

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