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Understand Coating Production Processes and Equipment at a Glance – Save and Share Now!
Jinzong Enterprise has been engaged in the research, development, and manufacturing of coating production equipment for over 20 years. With a deep focus on the development of intelligent coating production lines, we provide one-stop solutions encompassing design, manufacturing, and engineering installation. Continuously improving product quality and service standards, we have earned a strong reputation and a stable market both domestically and internationally. Today, we would like to share with you the processes and equipment involved in coating production, helping you gain a comprehensive understanding of related manufacturing information.
I. Basic Components of Coatings
Resin | Pigment | Solvent | Additives
II. Manufacturing Process:
Pre-dispersion → Grinding → Mixing & Adjustment → Color Tinting → Testing → Filtering & Filling
III. Manufacturing Process Flowchart
Note: QC1 refers to Raw Material Inspection; QC2 refers to In-Process Quality Control; QC3 refers to Finished Product Inspection.
Coating Production Equipment
The production process for colored paint is as follows:
Pre-dispersion → Grinding → Color Tinting & Formulation → Filtering & Packaging
The production equipment is now introduced according to the colored paint manufacturing process.
Pre-dispersion Equipment
Pre-dispersion mixes the pigment with a portion of the paint vehicle to form a semi-finished pigment paste. It is the first step in paste production. Its purposes are: ① To achieve uniform mixing of pigments; ② To partially wet the pigments; ③ To initially break down large pigment agglomerates. This step focuses primarily on mixing, playing a partial dispersing role, and prepares the material for the subsequent grinding stage. The effectiveness of pre-dispersion directly impacts the quality and efficiency of the grinding and dispersion process. The primary equipment used is the high-speed disperser.
In addition to its use as a dispersing unit, the high-speed disperser can also serve as the main production equipment for colored paint. For instance, when the pigments used are easily dispersible or when the fineness requirements for the paint are not stringent, the high-speed disperser can be directly employed to produce the finished colored paint.
Its structure is shown in Figure 2-1 (a floor-standing high-speed disperser). It consists of a main body, a transmission device, a main shaft, and an impeller.
Floor-mounted High-speed Disperser External View Diagram
The machine body is equipped with a hydraulic lifting and swiveling mechanism. The hydraulic lifting system uses a gear oil pump to supply pressurized oil for raising the machine head, while lowering relies on its own weight, with the descent speed controlled by a stroke throttle valve. The swiveling mechanism allows the machine head to rotate 360°, and it can be locked in position with a handle after rotation. The transmission device is driven by a motor via a V-belt drive. The motor can be three-speed, dual-speed, or equipped with stepless speed regulation (such as belt-type) or frequency conversion speed regulation. The rotational speed ranges from several hundred to over ten thousand revolutions per minute, with power varying from dozens to hundreds of kilowatts.
The key component of the high-speed disperser is the serrated disc impeller.
The diameter of the mixing tank has a direct relationship with the selection of the impeller size. Empirical data indicate that when the tank diameter is in the range of φ = 2.8–4.0D (where D is the impeller diameter), the dispersion effect is optimal.
The high-speed rotation of the impeller causes the paint slurry to exhibit a rolling circulation flow, generating a large vortex. A turbulent zone forms approximately 2.5–5 cm from the edge of the impeller, where pigment particles are subjected to strong shear and impact forces, allowing them to disperse quickly into the slurry.
The rotational speed of the impeller should achieve a peripheral speed of about 20 m/s to obtain satisfactory dispersion results. Excessive speed can cause splashing of the slurry and increase power consumption. The recommended maximum peripheral speed is Vmax = 20–30 m/s.
Dispersers can be installed in two ways: floor-mounted, suitable for portable tank operations, and platform-mounted, where one disperser can serve several fixed tanks.
Grinding and Dispersion Equipment
Grinding equipment is a primary apparatus in paint production and can be categorized into two basic types: one type uses grinding media, such as sand mills and ball mills, while the other type operates without grinding media, relying on shear forces for dispersion, such as triple-roll mills and single-roll mills.
Equipment with grinding media relies on the impact and shearing forces generated by the grinding media (e.g., glass beads, steel beads, pebbles) during collisions and mutual rolling or sliding to achieve grinding and dispersion. This type is typically used for the production of low to medium viscosity paint slurries with good fluidity, offering high output and dispersion efficiency. Grinding and dispersion equipment without grinding media can be used for highly viscous or even paste-like materials. The vertical sand mill and triple-roll mill are introduced below.
Vertical Sand Mill
Its external structure is shown in Figure 2-4 and consists of the machine body, main motor, transmission components, cylinder, disperser, feeding system, and electrical control system.
Schematic Diagram of Vertical Sand Mill Structure
1—Discharge and Sand Outlet; 2—Cooling Water Inlet; 3—Feed Pipe; 4—Stepless Speed Changer; 5—Feed Pump; 6—Speed Control Handwheel; 7—Control Button Panel; 8—Disperser; 9—Centrifugal Clutch; 10—Bearing Housing; 11—Screen Mesh; 12—Cylinder
Working Principle, as shown in Figure 2-5. The pre-dispersed paint slurry is fed from the bottom by the feed pump, and the flow rate can be adjusted. The bottom valve (8) is a specially designed check valve that prevents glass beads from flowing backward when the pump stops. Once the paint material is fed, start the sand mill. The disperser shaft drives the dispersion disc (5) to rotate at high speed, achieving a peripheral speed of approximately 10 m/s at the outer edge of the disc (the shaft speed ranges from 600 to 1500 rpm). The paint slurry and glass beads near the dispersion disc are driven by viscous resistance, following the rotation of the disc, thrown toward the cylinder wall of the sand mill, and then returned to the center. As a result, pigment particles are subjected to shear and impact forces, dispersing into the paint material. The dispersed paint slurry overflows through the screen mesh from the outlet, while the glass beads are retained by the mesh.
1—Water Jacket; 2—Typical Flow Pattern of Paint Slurry Between Two Disperser Discs (Dual Annular Rolling Grinding Action); 3—Screen Mesh; 4—Outlet for Dispersed Paint Slurry; 5—Disperser Disc; 6—Mixture of Paint Slurry and Grinding Media; 7—Balance Wheel; 8—Bottom Valve; 9—Inlet for Pre-mixed Paint Slurry
If the paint slurry does not meet the fineness requirements after one pass, it can be ground again in the sand mill until it meets the standard. Alternatively, several sand mills (2–5 units) can be used in series. The fineness achievable with a sand mill is approximately 20 μm.
The glass beads have a diameter of 1–3 mm. Due to wear, they should be regularly cleaned, sieved, and replenished.
During operation, the sand mill generates a significant amount of heat due to friction. Therefore, the outer cylinder is designed as a jacketed structure, through which cooling water is circulated for cooling.
Laboratory sand mills generally have a capacity of <5 L, while production sand mills range from 40–80 L. These values refer to the effective volume of the cylinder. In terms of production capacity, for example, a 40 L sand mill can typically process 270–700 kg of color paste per hour.
Precautions for operating the sand mill:
(1) Never start the mill when there is no material or grinding media inside the cylinder, as this would cause severe wear to components like the disperser discs and glass beads.
(2) When starting up, first activate the feed pump, and only start the main motor after paint slurry is visible at the outlet.
(3) After prolonged shutdown, check whether the disperser disc is stuck. Do not force startup.
(4) After prolonged shutdown, inspect whether the top screen has dried and formed a skin, to prevent overflow of paint slurry from the top screen (overtopping) upon startup.
(5) When cleaning the sand mill, operate the disperser only in short bursts (jog mode) to minimize wear on the disperser discs and grinding media.
(6) When using new grinding media, sieve it first to remove impurities.
Paint Mixing Equipment
In addition to the high-speed disperser mentioned earlier, which can be used for paint mixing and color matching, large-scale production typically employs paint mixing tanks, commonly referred to as tinting tanks. These tanks are installed on elevated platforms above ground level. Their structure is relatively simple, as shown in Figure 2-10, and consists of an agitation device, a drive motor, and a mixing vessel. The mixing paddles can be installed at the bottom or on the sides, and the motor may be single-speed or multi-speed.
High-speed Direct-driven Paint Mixing Tank
Direct-driven High-speed Paint Mixing Tank
1—Drive Motor; 2—Mixing Tank; 3—Serrated Disc-Type Agitator Blades; 4—Discharge Outlet
Filtration Equipment
During the production process, paint inevitably becomes contaminated with dust, impurities, or sometimes skin formation. Therefore, filtration is necessary before final packaging. Common filtration equipment used for paints includes sieves, filter presses, vibrating screens, bag filters, cartridge filters, and self-cleaning filters.
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Sieve
A simple filtration sieve consists of a copper wire mesh or nylon fabric stretched over a frame, placed in a funnel made of sheet metal or stainless steel. -
Vibrating Screen
The screen mesh vibrates at high frequency to prevent clogging by residues. -
Filter Press Sieve
Commonly known as a multi-surface sieve. It comprises a cylindrical housing with a quick-open top cover, inside which a perforated filter basket is suspended. The basket is lined with metal mesh or fabric. Paint is pumped into the upper part of the filter, enters the basket, where impurities are trapped, and the filtered liquid exits from the bottom. -
Bag Filter
A commonly used equipment for paint filtration. Filter bags are housed in a slender cylindrical container supported by metal mesh bags. During operation, paint is pumped into the filter bags, residues are retained inside, and the qualified paint slurry flows out from the outlet.
Bag filters are generally equipped with pressure gauges. During operation, when the pressure rises and filtration resistance increases, reaching 0.4 MPa, the system should be shut down for filter bag replacement.
Filters should be cleaned promptly after each use and maintained in a tidy condition for subsequent operations.
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