Prior to purchasing any equipment, it is necessary to consider carefully its technical characteristics and cost-effectiveness.
Constant pursuit to solve the question in the cheapest way is dictated by lack of financial means. This is understandable. But on the other hand, such a decisions on capital expenditures lead to long-term financial load on the enterprise. Therefore, the decision made should be based on the optimal factors.
Further information should help in making decisions regarding the capital expenditures.
Corrosion protection of various construction objects is an important issue especially when industrial sphere is developing in a quick pace.
It is necessary not only to preserve the currently constructed objects, but also to maintain in an appropriate condition the existing constructions, for example, architectural monuments or city infrastructure objects.
One of the truths about the anticorrosion treatment is a high quality cleaning. When laying the protective painting coat on the object it is necessary to clean up the surface out from old coating, cinder, and rust. The surface must be good enough to provide the sufficient adhesion with the protective coating. This is defined by the surface profile which, in turn, depends on the selection of material, which will be used for processing.
For surface cleaning both sand and abrasive powder are used. Many enterprises does not see substantial differences between them. They choose sand due to its low cost. As one says, if there is no difference, why pay more?
Sand is a traditional, available and a quite inexpensive material for surface cleaning. Same as the abrasive powder, this material is mistakenly given the various properties. It is worth to study out, what is myth and what is a reality to make a right decision when selecting the material for surface cleaning.
FIRST MYTH: Sand does not require specific storage conditions.
Despite the prevailing opinion, that sand can be stored in any conditions (same as it is stored in the nature), it is necessary to follow all the requirements on drying, transportation and storage of the sand! If requirements are not followed, then sand easily changes its properties, which worsens the effectiveness and quality of works.
SECOND MYTH: Sand cleans out the surface as good as abrasive powder.
One thinks than sand cleans out the surface as good as abrasive powder. However, it is not true. Even when all conditions are satisfied, the sand poorly profiles the surface. The maximum grade of sand cleaning is only Sa 2.
Moreover, the dust subsides on the cleaned surface and decreases its adhesion with the protective coating. Considering these features of the sand, the paint spread on the surface starts to «bubble». The process of corrosion goes more intensively in such conditions, which results in the quick destruction of the painted object.
THIRD MYTH: Sand blasting is safe for people and environment since it is a natural material.
The methods of sand extraction is dangerous for humans and environment - quartz sand is obtained by explosion of the quartz vein and its further screening and processing. Accordingly, we can see an increased dust formation in the process of extraction. Result is quite negative: the dust pollutes the air and leads to origination of lung trouble.
The fact is that sand contains more than 1% of pure quartz. When extracting the sand or sand blasting, the silicon dioxide is contained in the air in a dust form. When breathing the silicon dioxide subsides on the lungs of the people. The worker of abrasive blasting has a risk of silicosis, the lung trouble, which often leads to cancer and death.
It can be surprising, that most of the developed countries has prohibited the process of surface cleaning by materials containing quartz in a free form. The law exists since 1950-1960th. Despite of the same prohibition in Russia which came into force in 2003, the sand is still actively used by the industrial enterprises for surface cleaning even in the big cities like Saint-Petersburg or Moscow, where, sometimes, water is used for decreasing the dust formation.
It is well known, that abrasive powder is made of waste products of metallurgic industry. Since this material appeared relatively recently, many people doubt that surface cleaning with usage of abrasive is reliable and safe indeed. They find reasons to use sand instead of powder.
FOURTH MYTH: Abrasive powder is obtained from the waste products of metallurgic industry, that means, it contains hazardous substances and pollutes the environment.
Abrasive powder is produced artificially by processing the slag of copper melting (copperslag) and nickel (nickelslag) production. Despite of the common belief in the harm, such abrasive is safe and environmentally friendly due to low dust formation and lack of quartz in a free form. Any abrasive powder goes through certification process and compliant with standards.
Also, when producing the abrasive powder, the slag dump of metallurgic production is used, which needs utilization. As a result, the product of secondary market of copper and nickel is formed.
The waste products after abrasive cleaning is utilized as a constructional. Also, it can be used as a filling compound for concrete constructions or in road construction.
FIFTH MYTH: After abrasive cleaning, the dirty footprints remain.
Indeed, abrasive powder has a black color. Despite of this, the remains of abrasive powder after cleaning does not require special treatment for removing from the surface. While sand must be removed from the surface by water dust elimination.
SIXTH MYTH: Abrasive is not cost-effective compared to sand.
Abrasive is consumed in the same rate as sand having a higher cost. As opposed to sand, abrasive powder can be recuperated – used second time. When hit against the surface, its particles are split into smaller parts, but can be used again to obtain high-profiled surface. The sand particles gets split into dust with a diameter of 15-30 micron which pollutes the work zone and clogs between peaks of the machined surface covered on 70-85 % by the particles if quartz sand. To remove these particles from the surface, the labor-intensive operation of dedusting is needed (washing out with a high pressured water). This requires additional time and financial resources.
In such a way, to process one square meter of the surface 50 -70 kg of sand is needed, compared to only 15- 35 kg of abrasive. This tells us about more cost-effective consumption of abrasive powder.
Enterprises, which use abrasive, are able to select between various fractions depending on the desired profile. Abrasive is widely used for cleaning metal, brick, concrete, stone surfaces. It can be used for polishing and smoothing the glass or wood surfaces.
Moreover, well-known manufacturers of paint materials - Tikkurila, Hempel, Jotun, etc. give 10 – 20 years guarantee for the painted surfaces provided the work zone was machined using abrasive. That means, abrasive powder really receive positive feedback from professionals.
Think: pollution of the environment or reprocessing the industrial waste? Sa 2 or Sa 3? Cost or health? Dispose or use again? Corrosion and destruction or an excellent adhesion of the coating and surface? – and decide, which material for surface machining you will choose next time. We hope that you will make a right selection.
Source: Industrial portal 1akz.ru
Spot blasting can be applied in a various way depending on the used abrasive.
Compressor is not a component part of the device for spot blasting. However, its technical characteristics has a significant influence on the quality and cleaning productivity. Lets discuss three main parameters of the compressor:
Compressor capacity is the main parameter which defines the cleaning capacity. For example, compressor rated 0.75 and 75 kW in power has an equal pressure 7 bars of the compressed air. At the same time, first one has a capacity of 0,11 – 0,12 m3/min, and the second one 11,3 – 12,7 m3/min. Only the second compressor will provide the necessary conditions for spot blasting.
Example: At pressure 7 bar through the nozzle of 9.5 mm goes 5.3 m3 of compressed air per a minute. If capacity of the compressor is only 4,2 m3/min, then pressure of 7 bar in the nozzle will never be reached, only 4.9 bar. Decrease of the working pressure on 0.07 bar leads to 1% lowering of the cleaning quality. In our case, the loss of cleaning capacity will be 45%.
Work pressure when cleaning with steel shot must be around 6,3 – 7 bars. Application of the pressure higher than 7 bar is inappropriate, as it leads to a rapid fragmentation of the abrasive material without noticeable increase of the cleaning capacity.
Compressed air quality is determined by the content of water and oil. Dehumidification is carried out in the specific equipment - moisture separator. The amount of oil inside the compressed air depends on the type of compressor and its technical condition. Modern compressors can supply compressed air without oil additions.
Compressed air quality is essentially important when closed loop circulation of the metallic abrasive material. Oil contents in the compressed air leads to pollution of the abrasive material and transformation of the oil on the cleaned surface. Water may lead to humidification of the abrasive material, faults in operation of pistons of abrasive supply. At winter, it leads to freezing of abrasive and equipment breakdown.
Working parameters of equipment operation
They depend on the technical construction. The main parameters are:
Operation convenience is an actual time of equipment operation relatively to calendar time. This is determined by operating capability of the equipment, return of the abrasive material back to work, necessary intervals for maintenance, repair operations, and breakdown rates.
Current losses of abrasive material is stagnant zones in the its transportation zones where abrasive deposits and requires periodic manual removal. This is often present in the system of mechanical supply of abrasive material.
The cleaning effectiveness influences on the amount of small shots removed from the working zone during the stripping of clogging (mostly small fractions). The important fact is whether there is a possibility to regulate the characteristics of the separator.
The installed power influences on the cost of cleaning. Ventilation effectiveness of the working zone of the chamber affects the working conditions of the operators and their productivity and, in turn, affects the cost of abrasive cleaning. The cost of surface machining includes all the expenses on equipment operation including the amortization expenses.
Method and time of capital expenditures realization
Here is a question of equipment commissioning from the moment of making decision of its purchase or its making under own steam. The method of realization may play a major role if equipment buyer has an opportunity to manufacture the part of the equipment on his own enterprise with available industrial capacities. The problem is only in complexity of manufacturing of some parts and their working efficiency.
Magazine: "Professional Painting" (2)2003
Main information about abrasive materials based on nickel slag
There are three main types of abrasive materials:
The natural abrasives are mineral – sand, silicium, garnet, zirconium, and other minerals. Produced abrasives are made specifically for spot blasting. Among them small shots (including lump), plastic, glass balls, aluminum oxide, silicone carbide, etc. Abrasive materials made of waste products are obtained during the industrial processes. Among them is a slag, which is a waste product of metal smelting or power generation.
Nickelslag is a product produced from granulated slags of nickel production. Content of dustlike fraction), then more accurate is processing. The fractional content of nickelslag granula is about 0.1 – 3.5 mm.
Hardness is property of the material to resist the penetration of other solid body into it. It is the property of more solid body to penetrate inside other materials. The hardness is defined as the amount of load needed to start the damaging the mineral.
The influence of the abrasive material on the machined surface is determined by its hardness. If abrasive is harder than substrate, then it will leave a profile on the surface. If it is softer than surface, but harder than coating, then it will remove the coating.
The hardness of the abrasive material is measured using Moos scale (except for steel abrasives). At this scale, the hardness properties are measured from 1 to 10. So that, 1 means that material is soft, like talc, and 10 means that material is hard as diamond.
The hard abrasives are more effective in a complex cases: when removing the corrosion and rolling scale. The soft ones are suitable for fine purification.
The granules of nickelslag has a high hardness (6-7 on Mohs scale) which allows to reach cleaning extent of Sa 3 (pure metal without corrosion and old coatings). Nickelslag has a good ability to profile the surface (notch 60 – 120 mkm), which is favourable for adhesion. Abrasive powder made of nickelslag is good material for removing an old coating, coke dross and corrosion from the metallic, brick, concrete, stone surfaces prior to laying the protective coating.
Durability is a property of the material to resist against the destruction caused by internal tensions originated from external forces. Durability can be divided into various types, among them static (under the constant load), dynamical, and fatigue (endurance) resulted from the cyclic variable loads.
According to the methodic of determining the dynamical durability of the abrasive powder (presented in TC 3989-002-82101794-2008), the nickelslag has this coefficient equal not less than 10 units. The durability of granules of abrasive material made of nickelslag provides low level of the dust content in the process of cleaning. An additional dedusting is not required, which simplifies the technology of spot blasting.
The coefficient of abrasive ability.
Abrasive ability is an ability of one material to process another one or a group of materials. Abrasive ability is defined by the amount of grinded material in a period of time.
To define the abrasive ability, the tested material is placed between two metallic and glass disks, which rotate in an opposite direction. Depending on the amount of removed metal or glass in a single amount of time, the abrasive ability of the tested material is defined.
Abrasive ability depends on the type of the grinding material, work mode, viscosity and durability of the grains. The less the content of admixtures in the abrasive material, the higher its abrasive ability.
For comparison, the coefficient of abrasive ability of abrasive powder made from nickelslag is 4.4 – 4.6 mg, and copper slag – 4.0-4.2 mg.
This property of abrasive shows how long the particle can stay not destroyed by, when hit against the surface. Impact viscosity directly depends on the hardness of the particles (nickelslag is 7.0, copperslag – 5.5 – 6.0 on Moos scale).
When processing with abrasive powder with low impact viscosity, on the machined surface, there is a big amount of fine dust formed with diameter of 15 – 30 micron. This dust pollutes the work zone and clogs between peaks of the machined surface, which is covered on 70-85 % by the small particles in the form of film not visible to human eyes. For removal of these particles, the time-consuming operation of dedusting is needed (water flushing under the high pressure), which requires additional financial and time resources.
The usage of abrasive powder made of nickelslag due to its high specific viscosity significantly lowers the above mentioned expenses for object cleaning.
Chemical composition is a combination of chemical elements and their compounds.
Optimal chemical composition of nickelslag is its advantage compared to other abrasive materials available on the market. For example, copperslag contains 40% of ferrum oxides, which leads to active spark formation in the process of blast cleaning of metallic surfaces. Nickelslag does not form sparks and is non-explosive and non-combustible. Abrasive powder produced from nickelslag stays undistracted for a long time when hit against the cleaned surface due to its high dynamical durability (more than 10 units). It significantly decreases the consumption rate of abrasive material and increases the effectiveness of the cleaning process.
The hardness of the granules of abrasive powder produced from nickleslag (7 Moos) provides low level of dust content during the surface preparation. This leads to higher convenience, safety and eco-friendliness of abrasive blasting. The modern technology of fractionation allows to reach an optimal granulometric content of the powder. Balanced range of grain sizes and high abrasive ability of nickelslag provides uniform structure and asperity of the cleaned surface. This guarantees reliable bonding of the protective coatings with the surface (adhesion).