With the ever increasing advancement in automation, spray painting facilities have become the main equipment in industries such as furniture manufacturing, home appliance production, auto parts, electronic products, hardware products, plastic products, and glass decoration. For modern manufacturing companies, a spray painting production line that is not only high-efficiency, high-performance, stable, and quality but also a production line that greatly affects the product appearance quality, production efficiency, manufacturing cost, and company's market competitiveness can only be a success.
From initial pretreatment to spraying and leveling to finally reaching curing, each step of the whole spraying process plays a significant role to the final surface quality. One of the most pivotal processes in this entire system is UV drying.
Until recently, many spray painting production lines relied on conventional hot air drying technique to cure their paint films. Although this method is reliable, it normally leads to a lengthy period of setting, consumes a huge amount of power, has a big space requirement, and is highly sensitive to temperature changes caused by the surroundings. However, lately with the steady growth in the UV coatings and UV curing technologies, a number of firms have shifted to employing UV dryer machines instead of traditional drying machines. By using ultraviolet light to cure paint films within seconds or even less, UV dryers outperform traditional methods in significantly speeding up the production cycle of spray painting lines. At the same time, they enhance product surface quality and reduce the incidence of rework, thereby becoming indispensable components of modern automatic spray painting systems.
What then, is exactly the UV drying process in a spray painting production line? What is the contribution of the UV dryer machine to the entire production? In what ways should companies optimize the design of UV drying equipment in order to be efficient and economical when setting up spray painting production line? We hope this article helps you figure out these issues and learn firsthand the value of practical application of UV drying technology in modern spray painting production lines.
What is UV drying? Why is the use of UV dryers in spray painting production lines increasing?
UV drying or UV curing refers to a process in which UV light radiation is used to activate the photoinitiator of the UV coating, a reaction that leads to a rapid polymerization of the coating causing the coating to change from a liquid to a solid phase quickly. Unlike conventional drying methods in which solvent evaporation by heating is the main principle, UV drying is fundamentally a photochemical process.
The essential idea is not to heat but activate the resin system using UV energy, making the coating cross-link and harden at once creating a strong and tight protective film. Due to their entirely different curing mechanisms, UV dryer machines in spray painting lines are a lot faster than conventional drying equipment.
Typically, the conventional method can take up to several hours to achieve a dried film, while the UV curing process often takes just between a few seconds up to tens of seconds, which leads to an overall improvement in production performance.
Industry data and manufacturer testimonials available on the internet show that under equal capacity conditions, spray painting lines that utilize UV drying technology have been able to shorten cycle time of work by more than 50% in general, and with continuous production projects being implemented, the improvement may even reach 3 to 10fold.
Growing use of UV dryer machines is not just limited to higher production rates but also to other benefits such as space saving, reduction of intermediate inventory, improvement of surface quality, and lower cost of operation. As a trend, manufacturers of furniture spray painting, plastic spray painting, hardware spray painting and electronic products spray painting production lines are starting to integrate the full use of UVDrying systems and are working on turning their facilities into automated and smart production lines.
So what is the step-by-step UV drying process at a spray painting line?
A modern painting production system usually includes pretreatment system, conveying system, spraying system, leveling zone, UV dryer machine, cooling system, inspection station, and packing area. Though different industries may implement minor adjustments to processes due to specific requirements, they are basically the same in flow. UV drying, however, has a deciding effect after painting stage on a product quality.
1. Pretreatment Stage
Painting of workpieces will only be good on the pretreated surfaces. Hence, without proper pretreatment that includes removal of grease, moisture, dust, oxide layer from workpieces surface, a good film by the most perfect drying technology will never develop.
For different products materials and characteristics, painting lines usually apply one of, many, and perhaps all: degreasing, rust removal, water washing, pure water washing, drying, electrostatic dust collection, plasma treatment, or flame treatment.
Data obtained from different industries indicate that over 60% of spray quality issues are related in fact with the inadequate state of pretreatment but not with the UV drying device at all. Therefore, building a spray painting production line, the company needs foremost be sure of steady operation of the pretreatment department.
2. Spray Coating Stage
After pretreatment the pieces will be directed by a conveying system from one stage to another. Most of the paint application facilities today feature robots, automated sprayers or multi-axis arms. Computer programs dictate the position of the spray gun, size of spray pattern, air pressure, and speed of conveyors, so as to deliver the most even paint coverage.
In UV systems, paint application typically requires dedicated UV coatings that are thinner and the final coat thickness of such coatings is usually measured in micrometers. It's quite common to see such figures as 20-80 micrometers. If the painting is done with less material, one should expect inferior hiding and lack of smoothness, if the painting is done with excess material, however, one risks getting a surface which dries faster internally but not necessarily surface which also leads to insufficient curing and cracking. Consequently the spray painting process must be controlled at the highest level since this determines the quality of the paint job which then has great bearing on the results from UVDrying.
3. Leveling Stage
To be perfectly honest, the product just cannot be subjected to curing by means of UV drying technology right after being sprayed and passing through the UV dryer machine. This is a misconception which leads to serious mistakes.
So, in fact, one must leave the freshly deposited paint film to level itself out. It is here that the paint film has time to settle and make itself into a relatively smooth and flat surface.
The stage normally lasts for two to ten minutes. Its primary function is to remove paint marks left by the spray gun, to smooth out paint surface that is raised in little spots (orange peel), to allow paint film air bubbles to go away and hence to equalize the whole layer of the coating in the form of a paint film.
If an inadequately leveled film gets subjected to UV drying, then the textures and other defects in the film will be permanently set after the drying, leading to bad quality of the product. Therefore, leveling is not only a preparatory stage for drying but a very important stage in production that ensures getting a fine finish product from the entire painting process.
4. UV Drying stage
Beneath the leveling stage, the UV Drying machine is where the major change takes place through a chemical reaction triggered by the UV radiation. The UV dryer machine is where the most significant part of the paint finishing occurs.
At this stage, UV light emitted from the machine hits the surface of the film that has just been painted, the photoinitiators in the paint start rapidly absorbing the energy of UV light, the photo reaction is triggered, resulting in polymerization. The whole painting layer is being rapidly cross-linked, a very hard, compact and tightly protected film can be instantly produced. After this drying phase, the workpiece can be put into storage without having to wait any more for the surface to dry naturally.
UV dryers in modern spray painting production lines have become more efficient devices, as such, their components not only include traditional components such as UV light bulbs, reflector, conveyor track but also such advanced devices as computerized control systems, safety protection equipment, exhaust fan system that help to ensure proper drying. For products such as high-gloss furniture panels, high-performance parts of electronic products casings, and automotive interior parts requiring thick coating and with high surface quality requirements, the paint films on such parts are not only thick but also require a long time to dry due to the complex workpiece.
Some production lines, therefore, adopt a multi-stage curing technique by setting up multiple dryers. For example, the first dryer uses low-power UV light to carry out pre-curing that prevents a rapid shrinkage of the paint film; the second dryer employs medium power UV light for further curing, and at the end of the third drying step, the high power UV dryer machine completes the crosslinked network, thereby effectively relieving stress and resulting in high gloss and resistance against abrasive particles, as expected, it also produces an end product with excellent surface appearance.
5. Cooling and Inspection Stage
Although UV dryer machine is not the heating up device, yet UV light bulbs still emit heat so that after getting UV drying, the products usually go into a cooling area where the temperature of a part can decrease by air, water or circulating cold air in preparation for the next inspection.
Then products will be conveyed to the quality testing workstation to inspect the product from different aspects that are mainly: gloss, adhesion, hardness, film thickness, rubbing resistance, alcohol resistance, coloring difference and surface defects. Products coming out of UV dryer machines normally present a high degree of hardness of coating film such that high-performance UV systems may even reach pencil hardness levels up to 4H-6H while the cross-cut adhesion would be as good as grade 0.
Thus, the coating film will meet the surface performance requirements of most industrial products. After passing the tests, since the film is completely hardened, products no longer have to be put in storage for a long period and instead may be going directly to the packing and storing operations, consequently significantly reducing the cycle time of the spray painting line as a whole.
The Essential Role of UV Dryers in Spray Painting Production Line – Did You Know?
As a vital component of modern spray painting production lines, UV dryer machines are mainly responsible for the curing of paint films. Moreover, they directly influence the overall production efficiency and product quality. The reasons are as follows: first, they help achieve instant curing so the products can be directly moved to the next process without waiting for natural drying. As a result, the entire production cycle is shortened by the large degree of time saved. The second reason lies in the effect of the UV dryer machines on the improvements of the painting film. They result in hard surfaces, wear and scratch resistance besides increasing the gloss and volume of the painting films. Third, dust particles are less likely to get stuck in the surface of the painting film due to the extremely short UV curing time, thereby significantly enhancing product surface consistency.
In addition, UV dryer machines can help companies reorganize their layout of the whole spray painting production line. Since a traditional heated air drying tunnel requires a minimum length of dozens of meters whereas ultraviolet drying systems only require a few meters to complete a drying process. So, this space saving would certainly be a plus for companies that are working with limited factory area as it also makes equipment layout more flexible.
The Core Parameters that are Responsible for Effective UV Drying
In spite of the fact that UV dryer machines, apart from the rapid curing speed, have such high-efficiency, the improper setting of process parameters may still lead to a bad quality after the curing stage.
Paint layer thickness
Rapid conveyor moving speed results in a very short time for UV dryer machine to reach.
It’s hard for the UV dryer machine to work smoothly if the conveyor is not adjusted according to the requirements of the actual work in progress at the shop floor (e.g. by increasing/decreasing the number of parts being dried per unit time).
Also, a decrease in output can arise from light source degradation, the cleaning condition of a reflector surface, or a decline in the performance of a cooling system. Therefore it is highly recommended for the companies to regularly perform inspections of and maintenance on their UV drying units in order to keep them functioning in a stable manner. That the UV dryer machines are working continuously and properly not only helps in saving energy but also contributes greatly toward environmental protection through reduced waste.
The Various Applications of UV Dryers for Spray Painting Production Lines Across Different Industries
In the furniture manufacturing sector, UV spray painting machines mostly deal with wooden doors, cabinets, wardrobes, office furniture and decorative panels. Usually, primer, topcoat plus several layers of coat are sprayed together with UV dryer machines in between in order to make the surfaces high-gloss, matte, skin-like etc.
We all know that when it comes to surface quality, products like mobile phone shells, computer shells, smart home appliance panels in the electronics industry have extremely high demands. UV drying technologies ensure consistent manufacturing of the products and also significantly increase productivity.
The plastics and parts industry has also made wide application of UV dryer machines particularly in manufacturing and repairing of plastic decorative parts, dashboards, and interior parts. An automated UV drying spray painting production line allows companies to achieve stable and high-efficiency mass production.
In addition, UV drying is also continuously being utilized into glass, hardware, packaging and printing, medical device, cosmetic packaging, and new energy supporting products industries.
How can a company decide which UV dryer to purchase to build its spray painting production line?
When planning a spray painting production line, a company should consider various factors such as the type of product, required capacity, workpiece size, and anticipated expansion before making the final decision about choosing a UV dryer machine. It should not rely only on the cost of the equipment. The main criteria for the selection would probably be equipment width, even illumination, number of lamp sets, light source, method of cooling, range of conveyor speed, automatic control system and degree of ease in maintenance.
In case a product has a complicated shape or paint layer is comparatively thicker, multiple UV dryer machines can be used for the sequential curing of the film in order to attain a higher quality and more stable end product. If a company has a great focus on environmental impact and energy saving, LED UV technology can be considered for inclusion during the planning stage.
In addition to the main production line design at that first stage, it is wise to have reserved expansion interfaces and thus make the future addition of UV drying equipment based on order increases easier and cheaper as compared to if the modifications had been made afterwards.
FAQ
Can UV dryer machines be applied to all kinds of spray painting production lines?
The fact is, not every spray painting production line can benefit from an application of UV dryer machines. UV curing will only take place if the paint film can react to UV rays, i.e. it can either be the special UV coatings or the special system of coatings able to be cured by UV. So, for ordinary thermosetting coatings or normally drying coatings, conventional hot air drying is still needed.
What is the typical UV drying time in a spray painting production line?
The exact timing varies according to the product and the process. Usually, UV dryer machines are capable of finishing the curing within 2-20 seconds. Thick films, high glosses, or special products could involve a multi-step UV curing process, which adds up to a few tens of seconds. Anyway, comparing it with the traditional methods, this time reduction alone is a major efficiency gain.
Will UV dryer machines change the temperature of a product during the drying process?
As a rule, UV drying only relies on the curing effect, so the light source is the one that produces heat in a UV dryer machine if its light source is a regular tungsten lamp. Due to that reason, most of the spray painting production lines are equipped with a cooling system in the dryer. On the other hand, the recently developed LED UV dryer machines do not heat as much at all and are quite well-suited to be used on heat-sensitive materials. Thus the use of LED UV dryer machines for the drying of plastic parts, printed circuit boards, electronic products, etc.is particularly recommended.
What are the main methods to enhance the painting film curing level of the UV dryer in a painting line?
The factors to improve the curing quality of the paint film with the UV dryer machine are multiple; to name a few: selecting appropriate type of paint that can be cured by UV, controlling the amount of spraying so that the film thickness is properly controlled, and the spreading of paint is done correctly. Moreover, the time the conveying belts keep the products in the dryer as a function of belt speed has to be just right too. On top of that, the amount of UV light hitting the paint film is also monitored by the machine on a regular basis. In addition to that the equipment should also undergo periodic overhaul in order to keep the dryers working efficiently and to minimize the risk of any technical failures. When a combination of right equipment, well-designed procedure, and appropriate type of paint is present together, that is when a well-planned spray painting line achieves its peak performance.
Why are LED UV dryer machines preferred to the traditional ones?
LED UV dryer machines not only use the energy efficiently, have a longer lamp life, but also can work with much higher precision and have more control. The LED UV lamp can also start up faster and require no pre-heating. These features can be very helpful for a modern spray painting line that relies a lot on automated systems for production, such as the ones that are controlled robotically. At the same time, these dryers can also help in lowering environmental emissions and are considered to be eco-friendly in comparison to the traditional UV drying methods. Nevertheless, when it comes to buying a drying unit for a particular product, the right choice has a number of factors - the most important being a good compromise between the production process, the formulation of the paint and the budget of the company - in fact, the one that will give the best cost-benefit ratio. It is for these reasons that an all-round consideration is necessary before making the final decision on the choice of a UV dryer machine.