preface
Heroes are made by the times, and technology drives change. Going back to the 1830s, Scottish inventor Robert Anderson created the first non-rechargeable electric carriage. However, due to limitations in battery life and motor control technology, the engine was switched to a steam piston principle. Similarly，based on the steam piston principle, piston pump technology emerged and gave rise to industry leaders such as Scheugenpflug，Huebers from Germany, and NLC from Japan. These companies have established a leading position in the market by leveraging piston pump technology.
As time progressed and technology rapidly advanced, motor technology evolved from the AC motor in 1873, through the stepper motor in 1970, to modern servo motors. Each technological update and transformation brought new possibilities for pump control methods. Entering the 20th century, the rise of high-precision screw pump metering technology brought unprecedented efficiency and accuracy to industrial production and quality control. In this new era, a number of companies specializing in high-precision screw pumps have emerged both domestically and internationally. Notable examples include Germany's ViscoTec (founded in 1997, primarily focusing on pumps for the food, pharmaceutical, and chemical industries), Bdtronic, and American companies PVA and Nordson, as well as China's XETAR.
Next, we will delve into the working principles, structures, performance, and characteristics of piston pumps and screw pumps. We will also examine their performance in handling high-viscosity adhesives containing solid particles. Through the analysis of specific industrial cases, we will reveal the excellent performance of screw pumps in the new era and their significant effects in practical applications.
Ⅰ. piston pump
1.1 Working principle of piston pump
The working principle of a piston pump is to compress and transport liquid or gas through the movement of a piston. Its working principle is as follows:
Metering Process: Feeding → Metering → Retracting → Cycling
The piston moves back and forth through a fixed cylinder liner and seals, with the seals installed on the cylinder body.
The plunger performs a reciprocating motion within the pump cylinder liner, causing a change in the volume between the plunger and the cylinder liner. This results in periodic changes in the working volume of the pump chamber, allowing for the repeated suction and discharge of liquid while increasing its pressure.
A reciprocating piston pump relies on the back-and-forth motion of the piston within the pump cylinder to cyclically expand and contract the working volume of the pump cylinder, thereby sucking in and discharging liquid. It has self-priming capabilities and can maintain nearly constant flow even under significant pressure changes. This makes it particularly suitable for transporting highly viscous liquids in scenarios with small flow rates and high heads. However, when transporting high-viscosity liquids or adhesives containing solid fillers, the adhesive can easily precipitate and stratify within the piston chamber. Solid fillers tend to deposit at the bottom of the piston chamber, leading to pump jamming and other malfunctions.
1.2 Performance of piston pump
The piston pump's principle is simple, making it primarily suitable for high-pressure applications where accurate metering of low-viscosity fluids is required. However, its structure is relatively complex and has certain inherent drawbacks. It requires complementary inlet and outlet directional valves, leading to higher maintenance and repair costs. The piston seals and directional diaphragms are prone to wear and need frequent replacement. There are metering defects, such as discontinuous metering processes and limited single extrusion volumes. Because the piston and cylinder volume is fixed, adjusting the ratio and discharge volume is inconvenient, and it is less compatible with transporting high-viscosity fluids containing solid particles.
Structural Diagram of Piston Pump
1.3 The piston pump delivers high viscosity or solid particle containing adhesive
When a piston pump is used to transport high-viscosity liquids or media containing solid particles, several components are prone to wear. The piston seals, directional diaphragms (made of rubber or plastic), and the piston directional chamber (metal) are especially susceptible. The directional diaphragm seals against the chamber's protrusion through compression. With repeated impacts over time, the solid particles in the medium cause significant wear on both the diaphragm and the chamber protrusion. This wear often necessitates replacing the diaphragm once or even multiple times a month, resulting in time-consuming and labor-intensive maintenance.
Wear Phenomenon of Piston Pump Directional Diaphragm
Ⅱ. Screw pumps
Compared to piston pumps, screw pumps emerged later. In 1930, aviation pioneer René Moineau, while inventing the jet engine compressor, discovered that this principle could also work as a pump system. His groundbreaking paper laid the foundation for the single-screw pump. This type of pump, also known as the Moineau pump, is classified as a rotary positive displacement pump.
2.1 Overview of screw pump principles
Screw pumps are divided into single-screw, twin-screw, and multi-screw types, with single-screw pumps being the most commonly used. The single-screw eccentric pump evolved from several sealed piston chambers, combining the sealing capability of a piston pump and the continuity of a gear pump. The eccentric rotation addresses the metering and transportation of high-viscosity fluids containing solid particles. As precision components, the manufacturing process and accuracy of the stator and rotor are essential to ensuring the high performance of the screw pump.
Infinite Piston Principle Diagram
2.2 Kinematic characteristics of screw pumps
(1) The stator and rotor profiles of a single-head single-screw pump essentially use the external equidistant line of a standard hypocycloid as the stator profile, while the conjugate curve to this profile forms the rotor profile, creating a spatial conjugate surface.
(2) The rotor can be visualized as the trajectory formed by a disc with a radius R continuously moving along a helical path with a pitch t and an eccentricity e.
a) The single-screw pump belongs to the category of rotary positive displacement pumps. It operates on the principle of an infinitely cycling piston, based on precise volumetric distribution.
b) Precise control of fluid flow is achieved by controlling the rotor's rotation angle and speed via a servo motor and control system.
c) The pump relies on the volumetric changes and movement created by the meshing space between the rotor and the stator to transport or pressurize the liquid.
d) When the servo motor rotates, it drives the rotor to rotate with it. The meshing space volume at the suction end of the pump gradually increases, causing a pressure drop. Under the influence of this pressure difference, the liquid enters the meshing space.
e) As the volume increases to its maximum, forming a sealed chamber, the liquid continuously moves axially within these sealed chambers until it reaches the discharge end. At this point, the meshing space volume at the discharge end gradually decreases, thereby expelling the liquid.
Animation Demonstration of Screw Pump Principle
2.3 Screw pump structure
The structural characteristic of the screw pump is its infinitely cycling small chambers, which prevent pump jamming when handling high-viscosity liquids or media containing solid particles.
Structural Diagram of XETAR Screw Pump
2.4 Performance of screw pumps
1. Simple structure, easy disassembly, maintenance-free, stable pressure without pulsation, and high metering accuracy.
2. Due to the special structure of the screw pump, it has self-sealing properties, and the inlet and outlet do not require valves.
3. Can measure indefinitely without single extrusion volume limitations.
4. Capable of transporting fluids containing solid particles.
5. Wide viscosity range adaptability, suitable for both low and high viscosity fluids.
6. Combines the high precision and long service life of a piston pump with the simple structure and stable, pulsation-free flow and pressure of a gear pump.
Schematic Diagram of the Internal Structure of XETAR Screw Pump
2.5 Screw pump delivers high viscosity or solid particle containing adhesive
The structural characteristics of screw pumps make them particularly suitable for handling high-viscosity liquids or media containing solid particles. Our company uses high-precision machine tools to manufacture screw pumps with ceramic rotors and wear-resistant rubber stators. This ensures that the screw pumps meet the CMK accuracy standards for adhesive dispensing. For applications involving high-viscosity adhesives with solid particles, our screw pumps can achieve a maintenance-free lifespan of up to three years.
To meet the demands of different adhesive applications, we offer a variety of materials for screw pump rotors and stators. This ensures excellent performance and long service life under various working conditions.
Materials of XETAR Screw Pump Stators and Rotors
Ⅲ. Advantages of screw pumps
XETAR was born in the new era of the 21st century, keeping pace with technological advancements. With 25 years of research and development experience, we continuously apply cutting-edge technologies to our screw pumps. We fully utilize the high-performance drive and control technology of servo motors, bringing high flexibility and precision to pump applications. Thanks to its excellent performance and reliability, XETAR has gained widespread market recognition.
3.1 The difference between piston metering pump and screw metering pump
In terms of the differences between electric vehicle motors and traditional internal combustion engines, screw pumps are maintenance-free, easy to control, and capable of real-time feedback, aligning with the future direction of flexible automation technology. For electronic industry screw metering pumps, there are currently three categories:
1. Imported brands, represented by Germany's ViscoTec and Japan's HEISHIN.
2. Domestic brands replacing imports, represented by XETAR.
3. Other domestic brands.
The differences are as follows: XETAR has over 15 years of experience in the application and research of screw pumps. It was the first domestic user of the VISCOTEC RD series screw pumps from Germany, giving it a comprehensive understanding of screw pump performance. This expertise enables XETAR to manufacture screw pumps that benchmark against VISCOTEC. In contrast, other domestic brands currently lack the capability to manufacture their own stators and rotors. Without this fundamental ability, they cannot demonstrate the performance of their screw pumps, making it challenging to provide high-performance pump bodies.
Making a high-quality screw pump involves several key dimensions:
1. Performance Metrics: Understanding the performance indicators that define a good screw pump.
2. Advanced Equipment and Techniques: Having high-performance processing equipment and techniques. （XETAR has invested over ten million in this area.）
3. Material Expertise: Being familiar with rotor and stator materials. XETAR's all-ceramic rotor with 11 series models is unique worldwide, and all stator materials are imported.
4. Application Knowledge: Fully understanding adhesives and application scenarios. With over 25 years of experience in dispensing applications, XETAR has insights that no imported pump brand can match. For instance, selecting the right pump often involves choosing a larger pump capacity to enhance reliability and extend lifespan, ensuring customer satisfaction.
XETAR emphasizes that 80% of the capability of fluid dispensing equipment comes from high-precision, high-reliability hardware, while 20% is based on process experience. Both elements complement each other and are indispensable. Currently, the situation is that Germany's VISCOTEC has excellent hardware but lacks sufficient process experience. XETAR combines both aspects. Other domestic brands often neither produce good hardware nor understand the processes, leading to overconfidence and poor performance.
XETAR screw pumps not only offer adjustable dispensing ratios, adjustable dispensing speeds, and unlimited dispensing volumes, but they also easily meet various complex industrial application requirements. Let’s delve into the advantages of XETAR screw pumps:
Self-sealing Performance: No need for valves at the inlet and outlet.
Infinite Circulating Measurement: No limitation on single extrusion volume.
Non-compressive Transport: Low shear and pulsation-free, ensuring no compression of the medium during transport.
Solid Particle Handling: Capable of transporting fluids containing solid particles.
Wide Viscosity Range: Suitable for both low and high viscosity fluids.
Reflow Capability: Prevents dripping and stringing of the medium.
Stable Flow Rate: Unaffected by changes in density and viscosity.
High Precision and Longevity: Combines the high precision and long service life of piston pumps.
These features highlight the superior performance and versatility of XETAR screw pumps in industrial applications.
XETAR screw pumps
XETAR screw pumps can achieve minimal single-component fluid dispensing. For different types of two-component liquids and pastes, they enable precise mixing based on the minimum dispensing volume. By accurately controlling the target dispensing of single-component materials, they ensure precise material mixing ratios, suitable for manual workstations as well as semi-automatic or fully automatic operations. Compared to the market share held by international brands, we are confident in confronting market challenges with our dispensing accuracy. Our micro-droplet dispensing screw valve provides consistent bead-like dispensing that adapts to any flow rate changes, unaffected by pressure, temperature, or time, with repeatability greater than 99%. Our latest micro-droplet dispensing screw valve, the VF-HDY100, features a rotor screw diameter of only 2.0mm and can dispense a minimum volume as low as 0.1mg.
Micro-Droplet Dispensing Accuracy Test
Ⅳ. conclusion
Driven by both the times and technology, pump technology has undergone a profound transformation from the steam piston era to modern high-precision screw pumps. This process not only witnesses the progress of industrial civilization, but also highlights the importance of technological innovation for production efficiency and quality control.
Through an in-depth analysis of piston pumps and screw pumps, we can easily see that while each has its strengths, screw pumps demonstrate superior performance when handling complex media such as high-viscosity adhesives containing solid particles. Screw pumps fundamentally solve common issues like oil leakage, effectively prevent pipeline clogging, and offer high-precision metering, stable pressure output, and pulsation-free fluid transfer. Additionally, their maintenance-free and wear-resistant advantages make screw pumps an indispensable key component in industrial production.
