In PU high pressure foaming equipment, the metering pump is the core component to ensure that the A/B two-component raw materials are accurately fed in the set ratio. Its performance directly determines the density, structural uniformity and product yield of the foamed product. Unlike ordinary delivery pumps, the metering pumps dedicated to high-pressure foaming machines need to meet complex working conditions of high pressure, high viscosity and high precision , and the selection should be cautious. This article will comprehensively analyze the scientific selection strategy of metering pumps from multiple dimensions such as performance parameters, structural type, compatible materials and drive mode.
Working principle of metering pump (taking high pressure foaming application as an example)
Polyurethane high pressure foaming machines often use high precision gear pumps or plunger pumps for metering. The basic principle is: the motor drives the coupling to drive the pump shaft to rotate, and the raw materials are stably sucked from the storage tank and output to the mixing head at a constant rate through the physical displacement of the internal and external meshing gears or reciprocating pistons. The metering pump is usually equipped with a high-pressure sensor (pressure range: 10~25 MPa) to feedback data to the PLC in real time to ensure that the proportional error is controlled within ±0.5%.
Data source: “China Polyurethane Industry Yearbook 2023”, KraussMaffei Technology White Paper
Key selection parameters of metering pumps
1）Working Pressure
The rated pressure of the high pressure foaming metering pump must be 10~20% higher than the maximum working pressure of the system to ensure the stability and safety margin of continuous operation.
- Actual demand : The typical operating pressure of the high-pressure foaming system is 12~18 MPa
- Recommended selection pressure range : 15~22 MPa
Reference standard: ISO 19879-2020 “Pressure requirements for hydraulic systems”
2） Flow Rate
The flow rate should match the daily or minute foaming production volume. It is advisable to select 70~90% of the rated flow rate as the working flow range to ensure the working efficiency and accuracy of the pump.
- For example, if the daily production of 30 cubic meters of PU foam is required, a single device needs to supply about 12~15 L/min
- Recommended pump specifications: rated flow rate is 16~18 L/min
Data source: BASF Technical Manual “PU Continuous Foaming System Design Parameter Table”
3） Pump Head Material
A/B materials are highly active and corrosive. The selection of pump materials must meet the following requirements:
Material | Applicable media | characteristic |
Stainless steel 316L | Polyether polyols, polyisocyanates | Corrosion resistant and high pressure resistant |
Cemented Carbide (WC Coating) | High hardness foaming agent, flame retardant | Strong wear resistance |
Polytetrafluoroethylene (PTFE) | Small dose auxiliary agent channel | Good anti-adhesion |
Selection suggestions: If the catalyst/foaming agent formula is highly corrosive, be sure to consult the manufacturer for customization of the anti-corrosion layer.
4）Viscosity & Medium Compatibility
The viscosity change of high pressure foaming raw materials has a great influence on the metering pump:
- Viscosity of polyether at room temperature: 200~1200 mPa·s (large fluctuation under temperature control)
- Isocyanate: 80~350 mPa·s
- The pump is required to have the ability to adapt to a wide viscosity range (50~1500 mPa·s)
If winter materials (high viscosity formula) are used, it is recommended to use a high viscosity dedicated pump head or a heated pump body structure design .
Data source: Huntsman Polyurethane Product Technical Specification
5） Structure and drive mode
● Structural type recommendation
type | Features | Application Scenario |
Gear Type | Continuous conveying, small pulsation | Continuous foaming, high-speed production line |
Plunger type | High pressure, high precision | Intermittent foaming, point pouring |
Hydraulic diaphragm | Corrosion resistant and capable of conveying granular materials | Special additives or insoluble filler systems |
● Drive mode
- Motor drive: General use in industry, adaptable to frequency converter to adjust flow
- Servo motor: excellent precision control (≤±0.1%), used for high-end technology
Other technical requirements
1）Metering Accuracy
It is recommended to select a pump body with a control accuracy better than ±1%. For precision process requirements (such as car seats and refrigerator foaming), products with an accuracy within ±0.5% should be selected.
2）Temperature control
- Normal working temperature: 20～50℃
- Extreme environment (winter): minimum 10°C, pump body needs heating and insulation (with PTC or oil circulation)
- The viscosity of some isocyanates increases significantly below 35°C and cannot be metered smoothly without heating.
Common Problems and Solutions
question | Possible causes | Suggested Actions |
Proportional deviation abnormality | Pump wear and unstable back pressure | Check pump cavity and calibrate sensor |
Large discharge pulsation | Pump head seal leakage | Replace the O-ring or spring |
Insufficient flow | Viscosity is too high or pump size is too small | Heat the raw material or replace the pump with a larger size |
Summarize
When selecting a metering pump suitable for a high pressure PU foaming machine, it is necessary to comprehensively consider aspects such as pressure level, flow matching, pump head material, viscosity adaptability and drive structure , and make a comprehensive assessment in combination with the formula process, production scale and operating environment.
Recommended actions:
- Conventional medium capacity system : gear motor driven metering pump + stainless steel pump body + hydraulic constant pressure system
- High-precision application scenarios (such as refrigerator liner, track insulation): servo motor + plunger metering pump
- Corrosive or flame retardant material system : hydraulic diaphragm + fluororubber seal + carbide flow parts
If you are unsure of parameters or need customized pump selection suggestions, please contact Pioneer technical engineers for selection support and testing services.
