Main Terms & Spraying Parameters of Painting Robots

The painting robot is an industrial robot that can automatically paint or spray coatings. It is mainly composed of a robot body, a computer and a corresponding control system. The hydraulically-driven painting robot also includes hydraulic oil sources such as oil pumps, fuel tanks and motors. With more than 5 or 6 degrees of freedom of joint structure, the arm has a large movement space and can do complex trajectory movement. The wrist generally has 2 to 3 degrees of freedom, being capable of making flexible movement. Therefore, what are the terms of the painting robot? Do you know the key parameters?

Ⅰ Main Terms of Painting Robots

(1) Painting Efficiency, Coatings Utilization and Effectively Painting Rate

Painting efficiency is the efficiency of spraying operation, including the effective utilization of spraying area and coatings per unit time. Coatings Utilization refers to the ratio between the coating amount on the coated material and the total amount of actual ejected coatings in the process of spraying, or the ratio between the measured thick film on the surface of the coated material and the coating thickness calculated by the amount of ejected coating, that is, the transfer efficiency of coating (TE) or coating utilization ratio. The effectively painting rate refers to the ratio between the surface area of the coating and the running area of the spray gun. In order to make the film of the edge broken part of the coating complete, the cover area of the general spray gun operation should be larger than the area of the coating.

(2) Spraying Trajectory of Spraying Robot

Spraying trajectory of spraying robot refers to the sequence and route of the spray gun in the process of spraying. The spraying robot can imitate the spraying trajectory of skilled Painting technicians.

(3) Coatings Flow Rate of Spraying Robot

The coatings flow rate of spraying robot is the amount of coatings that is delivered to each spinning cup in a unit time, also known as the amount of paint (rate). In addition to the revolving speed of spinning cup, the coatings flow rate is the second factor affecting the fineness of the atomized particles. When the other parameters are unchanged, the lower the flow rate of the coatings, the finer the atomized particles, but at the same time, the amount of solvent evaporation in the paint mist increases.  

The high flow rate of the coatings will form a corrugated coating film. At the same time, when the flow rate of the coating is too large, the coating film on the edge of the rotating cup will be thickened to a certain extent, so that the groove pattern on the rotating cup cannot divert the coatings. A layered paint film appears, which can cause undesirable phenomena such as uneven size of bubbles or paint droplets.

The maximum paint flow rate of each spray gun of the spraying robot is related to the diameter of the high-speed spinning cup and the density of the paint. The upper limit is determined by the fineness of the atomization and the effect of electrostatic coating. Practical experience has shown that the coating should be input at a constant speed, and fluctuations in a small range do not affect the quality of the coating.

In the practical spraying process, the spraying robot has different spraying areas for each spinning cup, and the flow rate of the coating is different. In addition, due to the change of the shape of the coated object, the coatings flow rate of the spinning cup also changes. Taking the automobile body as an example, when spraying a large area such as a door panel, the amount of the discharged paint should be very large. When spraying the door pillar and the window pillar, the amount of the discharged paint should be small. Therefore, the mount of discharged paint should be automatically and accurately controlled during the spraying process, and the coating quantity and the uniformity of the coating quality and the thickness of the coating film can be ensured , which is one of the important measures to improve the utilization rate of the coatings. 

(4) Revolving Speed of Spinning Cup

The revolving speed is the biggest factor affecting the atomization fineness of the high-speed spinning cup. When other process parameters are constant, the greater the revolving speed, the smaller the diameter of the coating droplet. In the slightly lower speed range, the effect of the rotational speed on the atomization fineness is significantly increased over the high speed range.

The revolving speed of the spinning cup has an effect on the film thickness. If the rotation speed is too low, the coating film will be rough; if the atomization of paint is too fine, it will cause loss of paint mist (causing over-spraying), and the thickness of the coating film will be uneven. When the atomization is ultra-fine, the airflow in the paint booth will be very sensitive. In addition to over-spraying, high revolving speed of the spinning cup can also lead to excessive wear of the turbine bearing, increase the consumption of clear compressed air and reduce the amount of solvent contained in the coating film. The optimum speed of the spinning cup can be determined according to the flow rate characteristics of the paint used. Therefore, the surface temperature of the water-based paint and the high-viscosity two-component paint have higher revolving speed than the common solvent-type paint.

In general, the revolving speed of the no-loaded spinning cup should be 6X10^4r/min, and the speed range of loaded cup should be (1.0~4.2) X10^4r/min with an error of ±500r/min.

Ⅱ Main Coating Parameters of Painting Robots

Today, electrostatic coating technology has become the mainstream in the automobile industry, and the application of electrostatic automatic spraying equipment has made automobile coating enter the era of automation. The following is a brief description of the main coating parameters of the coating robot.

(1) Painting Flow

The flow rate of the electrostatic painting robot is the amount of paint that is sent to the spinning cup per unit time, also known as the discharge amount. The size of the flow affects the thickness of the paint film. The paint covering ability of different colors is different, and the construction film thickness is also different. During the spraying process, each robot has a different spraying area and the set flow rate is different. At the same time, the flow rate is also related to the shape of the object to be sprayed. For a car, the regular five-door-one-cap type surface generally requires a large flow rate, while the column, ridge line, and corner flow  small.  

(2) Shaping Air

The gas is ejected from the small holes evenly distributed on the back side of the spinning cup, which is used to limit the swath of the paint mist, and push the atomized paint mist to the object to be coated, to place the paint mist diffusion and rebound the pollution cup and Nebulizer. For metallic paints, the spraying swath affects the final coloring effect, and the unsuitable spraying swath could cause zebra pattern or hair styling. The setting of the spraying swath is related to the separation distance between the two shots, and the number of times the paint is superimposed is three times. If the distance between the two guns is 100mm, the spraying swath is preferably controlled to 300mm, so that the same point paint can be superimposed three times. 

(3) Revolving Speed of Spinning Cup

Revolving speed of spinning cup is the key parameter of paint atomization. The centrifugal force generated when the spinning cup rotates at high speed makes the paint atomize very fine (50-100μm). The smaller the diameter of the paint drops, the better the smoothness of the paint film, and the smaller the pebbling effect, the higher the gloss. The setting of the speed is also related to the type of paint. The speed of the colored paint is relatively small, and the speed of the intermediate coat and varnish is relatively high. The speed and flow rate are also related. The flow rate is large and the rotation speed is also increased to achieve a better atomization effect. However, if the rotation speed is too high, the paint will be dry when sprayed onto the object to be coated, which may cause pebbling problems. 

(4) High Pressure

In electrostatic spraying, the object to be coated refers to the positive electrode, and the spinning cup refers to the negative electrode. When a high voltage is applied between the two electrodes, a strong electric attraction force is generated, and the atomized paint mist particles are transmitted to the surface of the object to be coated. The magnitude of the high voltage affects the electrostatic effect of electrostatic coating, the lacquering rate, and the uniformity of the paint film.

Flow rate, revolving speed, shaping air and high pressure directly affect the quality of the film and also affect the utilization of the paint. In the production, it is necessary to combine the characteristics of the paint and the parameters of the atomizer to make adjustments. The four parameters should be comprehensively considered and continuously optimized to achieve the desired spraying effect.

Post time: Oct-19-2015