Definition
An automatic squeegee machine is an automated device that mechanically or pneumatically drives a squeegee to evenly apply adhesives, sealants, or similar fluids on flat or curved substrates. Its core function is to control the thickness, width, and uniformity of the adhesive layer, and it is often used in industrial scenarios such as electronic assembly, packaging processing, woodworking products, and building components. Equipment typically includes a scraper assembly, feed mechanism, substrate holding platform, and control unit to replace manual operations to improve coating consistency and reduce material waste.
Rationale
The working principle of an automatic squeegee machine is based on the relative movement between the squeegee and the substrate. The adhesive is delivered to the front of the scraper by pumping or gravity feeding system, which presses against the surface of the substrate with a set gap. As the substrate (or scraper) moves in the direction of coating, the adhesive is sheared and spread into a uniform thin layer under the action of the scraper. The coating thickness is primarily determined by the gap between the scraper and the substrate, which can be adjusted by a precision adjustment mechanism such as a micrometer or a servo motor-driven lead screw. Some equipment uses scraper elastic deformation to compensate for small unevenness of the substrate to ensure that the adhesive layer is flat.
During the coating process, the fluid behavior is affected by viscosity, surface tension and shear rate. For non-Newtonian fluids, scraper speed and pressure need to be adjusted according to rheological characteristics. The basic coating thickness d can be expressed as:
d = h × (F / (η × v))
where d is the thickness of the adhesive layer, h is the scraper gap, F is the positive pressure of the scraper on the substrate, η is the apparent viscosity of the glue, and v is the relative motion speed. In practical application, the parameters need to be calibrated through experiments.
Measurement method
The performance verification of automatic scrapers mainly relies on the measurement of coating quality. Common methods include offline measurement and in-line inspection. Offline measurement takes samples from the finished coating product, uses a micrometer or optical thickness gauge to determine the thickness of the adhesive layer, and detects defects such as bubbles and scratches visually or with a magnifying glass. Online inspection integrates laser displacement sensors or vision systems to monitor the thickness fluctuations of continuous sections of the adhesive layer in real time. For high-precision scenes, 3D topography data is obtained using white light interferometers or confocal microscopy. The sensor zero point should be calibrated before measurement, and the effect of the thickness of the substrate itself should be considered. Adhesive layer uniformity is typically assessed as the ratio of standard deviation to average thickness (coefficient of variation), with lower values indicating better coating consistency.
Influencing factors
The coating quality is affected by a combination of factors. The material and morphology of the scraper directly affect the surface state of the adhesive layer, such as the metal scraper has high rigidity and slow wear, but it needs to be matched with a flexible substrate; Polyurethane scrapers have good elasticity and are suitable for rough surfaces. The angle of the scraper (front angle and back angle) determines the flow channel of the glue, and too large an angle will lead to the accumulation of glue, and too small will easily scrape too much. The viscosity of the glue changes significantly with temperature, and too low viscosity causes sagging, and too high will cause drawing or nodules. Substrate surface energy is equally important, and low surface energy materials need to be pretreated (e.g., corona) to improve wettability. The feed rate needs to be matched to the glue supply rate, otherwise intermittent coating may occur.
Applications:
Automatic squeegees play a pivotal role in several industrial links. In electronics manufacturing, sealant coating for mobile phone screens, battery modules, or photovoltaic modules requires adhesive layer thickness to be accurate to the micron level to avoid seal failure or extrusion deformation. The packaging industry uses it to complete the uniform application of carton hemming adhesive or label adhesive to improve sealing strength and control costs. In the field of wood products, the squeegee is responsible for the quantitative coating of glue during the splicing of the board, reducing the later trimming process. In the production of building components, it is used in the preparation of sealant layers for fire doors and insulation boards. In addition, the lamination process of film or paper also relies on a squeegee to achieve uniform adhesive thickness.
Key points of selection
Choosing an automatic scraper needs to be combined with the process requirements. First, determine the scraper material and gap adjustment range according to the properties of the glue. Adhesives with high viscosity or fillers should be made with carbide scrapers and a large clearance range (e.g., 0.1 to 5 mm). Secondly, the width and running speed of the substrate are evaluated, and the narrow substrate is suitable for compact desktops, and the wide substrate needs to be gantry structure and equipped with tension control system. In terms of control accuracy, servo-driven equipment is suitable for micron-level coating, while pneumatic models are more economical and reliable. The feeding method needs to be suitable for the packaging form of glue, such as pressure plate pumping is suitable for high-viscosity barrel glue, and gravity hopper is suitable for low-viscosity glue. In addition, considering the cleanliness level and maintenance convenience, the equipment for dust-free workshops should be equipped with closed dust covers, and the scraper wearing parts should support rapid replacement.