1. Overview of nozzle material
In 1870, the great forerunner of the gunshot, Benjamin Chew Tilghman, the granddaddy of the shot-blasting, used a spray shot to clean out the nozzle that was inserted into the hose, and the nozzle was used for about 15 minutes. In the early 1900s, cast iron was available for up to six hours. For a long time after that, the nozzle life didn't improve much. Until the late 1930s, the first nozzles were made with hard alloy (tungsten carbide) lining, which can last up to 300 hours. With the development of abrasive jet technology and material science, the nozzle material has also changed greatly. At present, the domestic and foreign production nozzle materials have metal, hard alloy and ceramic. In general, under the same conditions, cast-iron and steel nozzle life is not as good as the hard alloy nozzle, and the life of the carbide nozzle is inferior to the ceramic nozzle.
1. Metal nozzle
Metal materials have good processing technology and toughness, and the method of heat treatment can further improve its performance, such as improving its hardness and strength. Metal materials are commonly used in early nozzles. The hardness of metal materials is relatively low, and the erosion rate is high in the low erosion Angle. Therefore, the nozzle used to make it has a serious erosion wear and short service life. Metal nozzle manufacturing process is simple and low cost, not suitable for large operation. Common metal nozzles are: cast iron, hardened steel, stainless steel, etc. It can also be made into a nozzle with seamless steel tube, that is, the nozzle is a seamless steel tube, which has two functions of spray gun and nozzle, simple structure and short life span.
2. Hard alloy nozzle
The manufacturing process of hard alloy nozzle is much more complicated than that of metal nozzle, with relatively high cost, but with long service life, it has a higher life than metal nozzle under the same conditions. The hard alloy material has high strength and toughness, good thermal conductivity and higher hardness than metal materials; The abrasion wear rate of the carbide nozzle is much smaller than that of the metal nozzle, and its anti-erosion performance is higher than that of the metal nozzle. But hard alloy has high hardness, low toughness and poor processing technology, so it is not suitable for the production of complicated nozzle. In practical application, the hardness alloy is usually made into a ring or block inlaid on some of the badly worn parts of the nozzle. The y-type used in countries such as the United States and Canada and the multi-stage nozzles in our country are inlaid hard alloys in the nozzle vulnerable parts.
Cobalt tungsten carbide according to the main ingredients are divided into: class (YG) titanium, tungsten cobalt classes (YT) and adding rare carbide (YW) three categories, each with advantages and disadvantages, the main ingredients for tungsten carbide (WC), titanium carbide (TIC), niobium carbide (NBC), such as common metal binder phase is CO. The commonly used brand of YG hard alloy is YG3/YG3X/YG6/YG6X and YG8, etc. There are YT5, YT14, YT15, YT30 etc. YW hard alloy is commonly used in YW1 and YW2.
3. Ceramic nozzle
The ceramic materials have been widely used in the engineering field due to its high hardness, high wear resistance and excellent heat resistance. For the production of cutting tools, engine parts, bearing parts, metallurgy, coal mines, chemicals and other industries such as wear-resistant and corrosion-resistant parts. These advantages of ceramic materials are also ideal materials for preparing nozzles. The life of ceramic nozzles is significantly higher than that of metals and hard alloys.
Ceramic nozzle manufacture process is complex, the manufacturing cost is metal and tungsten carbide nozzle is much higher, but has a better wear resistance performance, for example, when using quartz sand, slag and metal abrasive, ceramic nozzle anti-wear ability than high several times of hard, but it belongs to the typical brittle material, easy to generate crack under the flake material, thus not suitable for use in strong shock situation. The ceramic materials of the nozzle are Al2O3 ceramics, B4C ceramics and SIC, etc. The price of Al2O3 ceramic nozzle is low, but due to low hardness and poor wear resistance, it is often used in small amount of sand blasting. The service life of SIC ceramic nozzle is highest than that of Al2O3, which is used for the replacement of hard alloy. B4C ceramic nozzles are the best wear-resistant properties of commercial nozzle materials, and the manufacturing cost is the highest because of the complex fabrication process. B4C ceramic nozzle has the very high hardness and wear resistance, but the intensity of the B4C ceramic nozzle and fracture is low, low reliability, low degree of densification and B4C ceramic materials, you need to use the ultra high temperature sintering furnace, B4C ceramic nozzle prices high.
2. Overview of nozzle structure type
Different nozzle structure will result in different processing efficiency and service life. The reasonable nozzle structure enables the abrasive to obtain high speed, thus improving machining efficiency and reducing the necessary conditions for cost. In the long period after the introduction of the nozzle, the cylindrical nozzle structure was adopted, then the conical nozzle was introduced and the venturi nozzle structure appeared in the mid-1950s. So far, there are various types of nozzle structures developed at home and abroad, and the types and characteristics of nozzle structures are as follows:
1. Cylindrical straight hole nozzle structure
It combines the function of spray gun and nozzle, the structure is simple. It can be replaced by seamless steel tube or by drilling holes in the material. However, the nozzle life is shorter, and it is used in the situation where the sand blasting treatment is not high.
2. Taper nozzle structure
The nozzle structure has a cone-shaped inlet and a straight segment of the cluster. It is relatively easy to get the abrasive into the nozzle, and the abrasive is more evenly distributed in the nozzle section than the cylindrical nozzle.
3. Venturi nozzle structure
Its structure is a venturi type of mouthpiece, the nozzle outlet is a microconical section, the outlet diameter is slightly larger. Air flow in the throat part of the speed of sound, compared in nozzle exit can reach above 355 m/s of supersonic (general cylindrical line straight hole abrasive nozzle exit velocity is low, only about 97 m/s), the nozzle is mainly used to get a high rate of abrasive, it than ordinary nozzle cleaning efficiency increased by 15% - 50%. In order to prevent the nozzle from wearing too fast, the lining of the nozzle can be used with hard alloy or ceramic nozzle material. In order to prevent blockage, the nozzle diameter should be 3 to 4 times the size of abrasive.
4. Special nozzle structure
Its structure is a double mouth special sandblasting nozzle, the structure is complex, the general application is in special occasions, such as the sandblasting treatment in the pipeline.
5. Composite nozzle structure
In the inlet, outlet and middle part of the nozzle, the materials with different properties are designed and assembled into the nozzle in a mechanical way. The combination nozzle inlet and outlet part are designed for high hardness ceramic or other wear-resisting materials; The middle section of nozzle can be designed as a metal or other material with high toughness. The combined nozzle can meet the requirements of the nozzle inlet, outlet and middle part to resist wear and tear, and improve the abrasion resistance of the nozzle to some extent. But compared with the overall structure nozzle, two or more materials need to be prepared, and the related processes such as assembly are added.
Under the condition of constant work pressure, the diameter of nozzle is enlarged, and the machining efficiency is improved accordingly. At this time, the flow of gas also increases, so the corresponding compressed air must be improved for the nozzle of different diameters to ensure sufficient working pressure.
The nozzle is very wear-resistant during the use of the nozzle. It is very important to use the nozzle properly. Generally before the sandblasting to monitor the wear and tear of the blast nozzle, badly worn to cause a decline in job stress, pressure drop of 0.01 mpa, can make the machining efficiency dropped to about 2%, site operation standard is the most commonly used of the nozzle abrasion working pressure drop for indicators. Normally, the diameter of the nozzle is better than the original 20%.
Nozzle with high speed and long distance type nozzle structure size and the relationship between the air consumption, high speed type is mainly used in the communication industry, chemical industry and the surface of the water conservancy electric power industry and other large equipment sandblasting and corrupt derusting processing, rust removal efficiency of 30 m3 / h. The long-range jet nozzle is mainly used for the surface derusting treatment of the equipment such as bridge vehicles and chemical pipes, and the rust removal efficiency is 18-20m2/ h.
3. Overview of the selection of the nozzle
The general principle of selecting type of nozzle
1. Material selection: according to the composition and temperature of the process medium
2. Metal nozzles series selection: according to the distribution shape, distribution density and atomization degree
3. Selection of nozzle specifications: according to flow, pressure and spray Angle
(part I) - (part I) - (part iii) - (part iv)
Part I: two to three capital letters, which represent the series of nozzles
The second part: the number of Numbers, the standard number of the nozzle
Part 3: spray Angle of nozzle
Part four: the material of the nozzle
Example:
1. SV - 1.10-600-316 l
SV spiral nozzles (spiral flow type virtual conical nozzles), the nozzles standard number is 1.10, the spray Angle is 600, and the nozzle material is 316L
2. WP - 47.0-1200 - PVC
WP vortex flow plastic solid taper nozzle, nozzles standard number 47.0, spraying Angle of 1200, nozzle material PVC (PVC plastic)
Selection of nozzle material
All materials that can be machined, cast or moulded by mechanical or manual methods can be used to make nozzles, such as steel, ceramics, wood, plastics, graphite and all metal materials. Selecting the material of the nozzle, the strength, corrosion resistance, temperature resistance and heat resistance, wear resistance and machinability of the material should be considered according to different usage situations.
The main factors affecting the performance of the nozzle are
Because the operation pressure and flow of the medium, temperature, viscosity, specific gravity and surface tension, etc all can affect the operation of the nozzle performance, so the nozzle to standard no. General with certain pressure water as standard to finalize the design.
1, the pressure,
(1) the most obvious effect of pressure on the nozzle performance is to change the flow of the nozzle. Generally speaking, under the operating range of the nozzle, pressure and flow have the following approximate relationship:
P2 over P1 is equal to Q2 over Q1
Where: P1 and Q1 are the pressure and flow in the first state
P2 and Q2 are the pressure and flow of the second state
(2) diameter of pressure and droplets of the nozzle: when the pressure increases, the droplet diameter will decrease
(3) pressure and spray Angle: when the pressure increases, the spray Angle will change slightly
2, the proportion of
The proportion of the medium also directly affects the flow. Under the same pressure, the small medium flow is large, and the following approximate relationship is generally:
QW/Q1= (R1 / RW) 1/2 (same pressure)
Where: the flow capacity of QW is M3/H when water is medium
Q1 operating medium flow M3/H
The proportion of RW water in R1 operating medium
3, viscosity
The influence of viscosity on the nozzle performance is very complicated, which affects the external characteristics of all nozzles, such as spray Angle, spray volume, distribution density, diameter of droplet and atomization. Therefore, the nozzle of a low-viscosity fluid similar to water is generally not considered for its influence; However, the nozzle of high viscosity fluid which differs from water is required to be tested and simulated.
4, temperature,
The temperature mainly affects the performance of the nozzle by changing the viscosity and surface tension of the fluid.
5. Surface tension
The influence of surface tension on the nozzle performance is obvious, especially affecting the diameter and spray Angle of the nozzle.