At a given moment, only one streamline can pass through a space point. General streamlines cannot intersect and branch. Otherwise, there will be several different flow directions at the same space point. Streamlines can only intersect at those points in the flow field where the velocity is zero or infinite, because there is no problem that the same point flows in different directions at these points. The point with zero velocity is called stagnation point, and the point with infinite velocity is called singularity.
Streamlines cannot turn suddenly, but are smooth and continuous curves; Where streamline is dense, the flow velocity in the flow field is large, and where streamline is sparse, the flow velocity is small.
What is a self-leveling coating? What are its characteristics? This is a weak dust absorption material. At present, it has been accepted and used by many domestic manufacturers and users, especially in the pharmaceutical industry. A basic hardware level is to produce clean floors. Self-leveling coating is made of epoxy resin as film-forming material, adding various additives, pigments, fillers and so on. It has the following characteristics.
① The coating has good self-leveling, and the film can be formed at one time 1mm or more, and the construction is simple.
② The coating has the characteristics of good toughness, good wear resistance, non-toxicity and non-flame-retardant.
③ The surface is smooth and bright, with good decoration, which can meet the cleanliness requirement of 100.
Electrophoretic coatings can be divided into anodic electrophoretic coatings and cathodic electrophoretic coatings according to the workpiece motor, and anionic electrophoretic coatings and cationic electrophoretic coatings according to the ionic form of film-forming substances in water. Cathodic electrophoretic coatings can be divided into one-component electrophoretic coatings and two-component electrophoretic coatings according to the water dispersion state. According to the film thickness, it can also be divided into thin film type, medium thick film type and thick film type cathodic electrophoretic coatings.
Electrophoretic coating, as a new type of coating with low pollution, energy saving, resource saving, protection and corrosion resistance, has the characteristics of flat coating, water resistance and chemical resistance, and is easy to realize mechanization and automation of coating industry. It is suitable for coating workpieces with complex shapes, edges and holes, and is widely used for coating hardware such as automobiles, automobiles, electromechanical appliances, etc.
What is the raw material of HIPS? What are the characteristics of buttocks? HIPS plastic
Opaque opacified particles. The density is 1.05g/cm 3. The melting temperature is 150~ 180℃. The thermal decomposition temperature is 300℃. They are soluble in aromatic hydrocarbons, chlorinated hydrocarbons, ketones (except ketones) and esters. They are resistant to many mineral oils, organic acids, alkalis, salts, lower alcohols and their derivatives. The gloss and comprehensive properties of the material are poor. The modification of HIPS is to add butadiene, because the impact strength of PS is very low, the product is very brittle, and the toughness of butadiene is very good. After adding butadiene, the impact strength of PS can be increased by 2~3 times. Although the impact strength of HIPS is much higher than that of PS, its comprehensive performance is still not as good as ABS, PC/ABS and so on. The impact property of HIPS is relatively low in engineering plastics.
buttock
It is an impact-resistant polystyrene product made by adding polybutadiene rubber particles into polystyrene. This polystyrene product will add micron-sized rubber particles, and the polystyrene and rubber particles will be connected together by grafting.
When impacted, the stress at the tip of the crack propagation sleeve will be released by the relatively soft rubber particles. Therefore, the crack propagation is hindered and the impact resistance is improved.
What is carbon fiber? What are the characteristics? Carbon fiber is a new fiber material with high strength and high modulus, and its carbon content is as high as 95%. It is a microcrystalline graphite material made of organic fibers such as flaky graphite microcrystals piled up along the fiber axis and carbonized and graphitized. Carbon fiber is "soft outside and rigid inside", which is lighter than aluminum, but stronger than steel, and has the characteristics of corrosion resistance and high modulus. It is an important material for national defense, military industry and civil use. It not only has the inherent characteristics of carbon materials, but also has the softness and machinability of textile fibers, and is a new generation of reinforced fibers.
Carbon fiber has many excellent properties, such as high axial strength and modulus, low density, high specific efficiency, no creep, ultra-high temperature resistance in non-oxidizing environment, good fatigue resistance, small thermal expansion coefficient and anisotropy, good corrosion resistance and good X-ray permeability. Good electrical and thermal conductivity, good electromagnetic shielding, etc.
Compared with traditional glass fiber, the Young's modulus of carbon fiber is more than three times that of traditional glass fiber. Compared with Kevlar fiber, its Young's modulus is about twice that of Kevlar fiber. It is insoluble and swollen in organic solvents, acids and alkalis, and has outstanding corrosion resistance.
What is PBT? What are his characteristics? 1, Introduction
According to Global Plastic Network, PBT (polybutylene terephthalate) is a kind of crystalline linear saturated polyester. PBT resin is widely used in electronic appliances, automobile industry and machinery, instruments and meters, household appliances and other fields because of its excellent mechanical efficiency, electrical efficiency, heat resistance and processing efficiency, especially its good comprehensive performance.
2. Features
Mechanical efficiency: high strength, fatigue resistance, dimensional stability, small creep (small change at high temperature)
Thermal aging resistance: the enhanced UL temperature index reaches 120~ 140℃ (outdoor long-term aging resistance is also very good).
Solvent resistance: no stress cracking.
Stability to water: PBT is easy to decompose in water (be careful when used in high temperature and high humidity environment);
Electrical efficiency:
(1) Insulation efficiency: excellent (it can keep the electrical efficiency stable even in humidity and high temperature, and is an ideal material for manufacturing electronic and electrical parts).
(2) Dielectric coefficient: 3.0-3.2
(3) Arc resistance: 120s.
Molding processability: injection molding or extrusion with ordinary equipment. Because of its fast crystallization speed and good fluidity, the mold temperature is lower than other engineering plastics. It only takes a few seconds to process thin-walled parts and 40-60s for large parts.
3. Brief introduction of injection molding process of 3.PBT material
(1) drying treatment
PBT material is easy to hydrolyze at high temperature and must be dried before processing. It is suggested that the drying conditions in air are 120℃ for 6-8 hours, or 150℃ for 2-4 hours. The humidity of PBT material must be less than 0.03%.
(2) Melting temperature
225~275℃, suggested temperature: 250℃.
(3) Injection pressure
Medium (up to 1500 bar). Injection speed: the injection speed should be as fast as possible (because PBT solidifies quickly).
(4) mold temperature
The unreinforced material is 40~60℃. The cooling cavity of the mold should be well designed to reduce the bending of plastic parts. Heat loss must be rapid and uniform. It is suggested that the diameter of die cooling cavity is12 mm.
(5) Runner
It is suggested that the circular channel be used to increase the pressure transmission (empirical formula: channel diameter = plastic thickness+1.5mm).
(6) Gate
Various types of doors can be used. Hot runner can also be used, but attention should be paid to prevent leakage and material degradation. The gate diameter should be between 0.8t and 1.0t (t refers to the thickness of plastic parts). If underwater gates are used, the recommended minimum diameter is 0.75mm..
What is white noise? What are the characteristics? Definition: White noise refers to noise whose power spectral density is evenly distributed in the whole frequency domain.
White noise or white noise is a random signal or process with constant power spectral density. In other words, the power of the signal is the same in all frequency bands. Because white light is a mixture of monochromatic lights with various frequencies (colors), this property of a signal with a flat power spectrum is called "white", and this signal is also called white noise. In contrast, other noise signals that do not have this property are called colored noise.
The ideal white noise has infinite bandwidth, so its energy is infinite, which is impossible in the real world. In fact, we often regard the flat signal with limited bandwidth as white noise, because it makes our mathematical analysis more convenient. White noise is a powerful tool for system analysis because it is convenient in mathematical processing. Generally speaking, as long as the spectral width of a noise process is much larger than that of the system it acts on, and its spectral density can be regarded as a constant within this bandwidth, it can be treated as white noise. For example, thermal noise and shot noise have uniform power spectral density in a wide frequency range, and they can usually be considered as white noise.
What is separable? What are the characteristics of some numbers? Divisibility is the relationship between two natural numbers (excluding 0) in mathematics. The natural number A can be divisible by the natural number B, which means that A is an integer multiple of B, which means that there is no remainder when A is divided by B, which means that B is a factor of A ... For example, 15 can be divisible by 5, and 20 cannot be divisible by 6 (because the remainder is 2). [Edit this paragraph] divisible rule
Rule 1 (1): Any number can be divisible by 1.
Article 2 (2) of the law of divisibility: Numbers with 2, 4, 6, 8 and 0 can be divisible by 2.
Article 3, paragraph 3, of the law of divisibility: If the sum of digits of each digit can be divisible by 3, then this number can be divisible by 3.
Article 4, paragraph 4, of the law of divisibility: If the last two digits are divisible by 4, this number can be divisible by 4.
Article 5, paragraph 5, of the law of divisibility: Any number with a bit of 0 or 5 can be divisible by 5.
Article 6 (6) of the law of divisibility: A number can be divisible by 6 as long as it can be divisible by 2 and 3 at the same time.
Rule 7 (7) of the law of divisibility: Cut off the single digits, and then subtract twice the single digits from the remainder. If the difference is a multiple of 7, the original number can be divisible by 7.
Article 8, paragraph 8 of the law of divisibility: If the last three digits can be divisible by 8, this number can be divisible by 8.
Article 9 (9) of the law of divisibility: If the sum of digits of each digit can be divisible by 9, then this number can be divisible by 9.
Article 10 of the law of divisibility (10): If the last digit of an integer is 0, the number can be divisible by 10.
Article 11 of the law of divisibility (1 1): If the difference between the sum of odd digits and the sum of even digits of an integer can be divisible by 1 1, then the number can be divisible by1. 1 1 can also be processed by the "tail-cutting method" in the above inspection 7! The only difference in the process is that the multiple is 1 instead of 2!
Article 12 of the law of divisibility (12): If an integer can be divisible by 3 and 4, then this number can be divisible by 12.
Article 13 of the law of divisibility (13): If the single digit of an integer is truncated, then multiply the four digits of this single digit to the remainder. If the difference is a multiple of 13, the original number can be divisible by 13. If the difference is too big or it is difficult to see whether it is a multiple of 13 in mental arithmetic, we should continue the above-mentioned process of "truncation, multiplication, addition and difference test" until a clear judgment can be made.
Article 14 of the law of divisibility (14): a If the single digit of an integer is truncated, subtract 5 times of the single digit from the remainder. If the difference is a multiple of 17, the original number can be divisible by 17. If the difference is too large or it is difficult to see whether it is a multiple of 17 in mental arithmetic, it is necessary to continue the above-mentioned process of "rounding, multiplication, subtraction and difference test" until a clear judgment can be made. B. If the difference between the last three digits of an integer and the three times of the previous separated number is divisible by 17, then this number can be divisible by 17.
Article 15 of the law of divisibility (15): a If the single digit of an integer is truncated, and then this single digit is added twice by the remainder, if the difference is a multiple of 19, the original number can be divisible by 19. If the difference is too large or it is difficult to see whether it is a multiple of 19 in mental arithmetic, it is necessary to continue the process of "truncation, multiplication, addition and difference test" until a clear judgment can be made. B. If the difference between the last three digits of an integer and the previous partition number is 7 times divisible by 19, then this number can be divisible by 19.
Article 16 of the law of divisibility (16): If the difference between the last four digits of an integer and the first five times of the divisible number can be divisible by 23, then this number can be divisible by 23.
Article 17 of the law of divisibility (17): If the difference between the last four digits of an integer and the first five times of the divisible number can be divisible by 2, then this number can be divisible by 29.
What is blocking the door? What are the characteristics of blocking the door? Blocking the door is usually when the groom goes home to pick up the bride. At the door of the bride's room, there will be several people behind the door. The groom must give them red envelopes and guess their questions before he can go in and pick up the bride. Some people block the door and don't let others out or in. This is usually a bad behavior.
What is a two-force lever? What are the characteristics of the two sticks? Two-force rod means that two forces act on a rod to make it in a balanced state.
The two forces on the two force bars are a pair of balancing forces.
What is the church? What are the characteristics of the church? The original meaning of the church is a group of people called by God from this world.
I. Apostolic nature of the church
Second, the archduke of the church
Three. The sanctity of the church
Four. Unity of the church
Reference text: 1 Corinthians 1: 1-3
:dyjdj。 /Gospel Station/Jiaohui/2012-11-27/35301.