Adhesive Metering subsystems
Table of Contents
Over the years, many metering systems have been developed for dispensing low and high viscosity material to meet the different customer needs.
These systems have specific advantages and limitations which characterize their designs. Some offer flexibility and speed over precision and accuracy while others offer micro-precision and accuracy at the expense of speed and flexibility. Due to its higher repeatability and accuracy, the piston meter is one of the most common used metering systems, at least in the automotive industry.
Looking at the industry in general, there are many types of metering systems in use. GLUDITEC classifies them according to their accuracy and methods of regulation related to their different operating principles.
Pressure Regulator
Pressure regulators are the simplest way of metering and dispensing material. Using pressure from the pump system they maintain the pre-set pressure and thus offer a continuous flow of material throughout the application.
This type of meter is mainly used for simple, continuous applications. The selection of such a metering system is based on material viscosity and required meter filling pressure. Regulators of this type offer pressure accuracy across the entire range from 25 to 300 bar, thanks to the linear flow characteristics for high and low flow levels.
Manual system
Here the pressure regulator is located between the material supply system and the applicator. This smooths out the effect of pressure peaks from the displacement pump and results in a consistent application pattern.
Automated systems
The pressure regulator is usually located between the material supply system and the next level of metering. This allows a consistent filling pressure to be maintained and reduces stress on the sealings of the metering device.
Gear meter
Gear meters are the next level of metering after pressure regulators. They also offer a continuous flow throughout the application of the material by maintaining either the pressure or the flow at a constant preset level.
Gear meters employ rotating gears which transport the dispensing material at the desired pressure or flow rate. They are particularly suitable for continuous dispensing of either high or very low viscosity materials without abrasive properties or vulnerability to shearing.
Gear meters are commonly used for continuous metering of PU, silicones or butyl. They are usually found in processes where the accuracy of an electric tandem meter is not required.
Micro gear ring meters
For metering very low viscosity materials, such as activator and primer fluids, micro gear ring meters are available which enable highly accurate dispensing of low volumes. This kind of meter is electrically driven.
Flow meter
In general flow meters are instruments for measuring, monitoring or recording the flow rate, pressure, or discharge of liquids or gases. Functioning together with a controller and pressure regulator, the flow meter represents the next level of metering.]
Flow meters are an excellent choice for continuous metering of low viscosity, single component materials such as PVC in sealing applications. They provide accurate metering by constantly regulating the volume flow, independent of viscosity or temperature effects. This type of meter must be controlled by a dispensing system controller to ensure its functionality.
The illustration below shows a flow meter in an automated system
Piston meter
Piston meters are the most accurate way of metering and dispensing the material and achieving the desired application characteristics. They have a fixed volume material chamber which is emptied by a piston, thus providing defined volumetric dispensing. The application volume is defined depending on the working principle of the piston meter.
They are available in different materials and heating variants to cover a wide range of applications. The various working principles, variations and types of piston meters can be described as follows:
LIFO
Last-in, First-out. Available in all meters
Used when large material volumes are dispensed and the meter is fully emptied in the process.
FIFO
First-in, First-out. Available only in electric meters
Commonly used for materials with a short pot time and when only a fraction of the total meter volume is dispensed at a time.
Piston meter variations
Piston meters vary according to the requirements of the overall production process and the final application. Below are the most common variations:
Single Component (1C)
Single-component materials such as silicone sealants, UV curable acrylates, urethanes and epoxies, are primarily chosen for their ease of use, but the curing process is long unless energy is used.
Tandem
In some applications, it is necessary to process large quantities of sealing and insulating material with high precision. In order to avoid cycle interruption during filling, tandem units are used. The tandem metering unit consists of two single metering units. An Intelligent swap logic ensures that material is applied in a constant flow
Two Component (2C)
Typically selected for their fast-curing characteristics, two component materials require meter, mix and dispense machines.
GLUDITEC provides fully automated dispensing machines that are integrated with production lines or robots.
Types of piston meters and their differences
The piston or displacer can be driven pneumatically, hydraulically or electrically, enabling dispensing regardless of material viscosity. The pros and cons of these three types are shown below:
Pneumatic
Advantages
– Reliable under different conditions
– Lower initial costs
Disadvantages
– Lower pressures
– Lower accuracy
– Size and weight
– Higher running costs
Hydraulic
Advantages
– High pressure (up to 400 bar)
– Fast filling time
– Lower initial cost
Disadvantages
– Hydraulic oil
– Higher installation costs
– Higher maintenance costs
Electric
Advantages
– Accurate
– Reliable
– Simple installation
– Cleaner and quieter environment
– High pressures (up to 300 bar)
– Lower running costs
Disadvantages
– Initial investment
How to choose the right piston meter?
In the case of an glazing application for car windscreens, we usually talk about a triangular shaped application. For powertrain we speak about round bead application and for seam sealing we talk about flatstream application.
Due to safety factors we consider using piston meters only up to 80-90% of their possible meter volume, which we call effective volume. Therefore a 400 cm³ piston meter would be the ideal choice in the glazing case. For the powertrain a 20 cm³ would be enough, and in the case of seam sealing the industry tends to use a continuous application technology due to the much higher material volume used. The most common choice in this case are the 80 cm³ and 160 cm³ tandem piston meters as they are still compact and not too big and heavy for the robots used.
The volume size of the meter may also be bigger if lower cycle times are required or if it is necessary to apply twice within a one meter filling cycle. Here the weight of bigger metering units must be taken into consideration since robots that are able to support these heavy meters may be more expensive (as in the seam sealing application). Also, if the meter is too heavy to mount on the robot, long hoses may be required, which may have a negative impact on accuracy.
For more information, please contact GLUDITEC:
Hotline: (+84) 969 469 089
Email: info@gluditec.com