Correctly dosing and mixing 2K systems: Cartridges, static mixers, and mixing ratios
Two-component adhesives and potting compounds only cure completely when both components are processed in the correct ratio and mixed homogeneously. The cartridge, dispensing tool, and static mixer form a coordinated system for this purpose. This guide shows what matters regarding ratio, equipment selection, and processing.
To the point: precise dosing in six steps
- Check the mixing ratio from the data sheet (for example, 1:1, 2:1, 4:1, or 10:1).
- Select a cartridge and static mixer suitable for this ratio.
- Select the dispensing device based on quantity and frequency: manual or compressed air.
- Discard the initial output until the material exits uniformly and thoroughly mixed.
- Dispense evenly and adhere to the pot life.
- After use, leave the filled mixer as a closure or replace it in a timely manner.
Why the mixing ratio determines quality
In 2K systems, two components react with each other in a defined ratio, such as resin and hardener or base and catalyst. If the ratio is incorrect, a portion remains uncrosslinked. The result is incomplete curing and losses in strength, temperature resistance, and media resistance. Too much hardener can be just as harmful as too little. Therefore, the ratio is not a recommendation but a specification. The information on the container and in the technical data sheet is always decisive.
Common mixing ratios and what they mean
The ratio determines the cartridge geometry and the appropriate mixer. A 10:1 cartridge cannot be correctly dispensed with a 1:1 device. The following overview serves as a guide; the specific ratio is provided in the data sheet.
| Ratio | Typical use (orientation) | Note |
|---|---|---|
| 1:1 | many methacrylates, individual epoxides and PU | Simplest dosing |
| 2:1 | many epoxies | Most common ratio for epoxies |
| 4:1 | certain epoxides and PU | Match the mixer to the ratio |
| 10:1 | many silicones, individual PU | small hardener content, mixer particularly important |
Cartridge Systems: Double Cartridge, F-System, and A-System
SILITECH offers the common 2K cartridge systems. Double cartridges keep both components separate until processing; the F-system (approx. 210 ml and 400 ml) and the A-system are commonly used. The cartridge type, volume, and ratio must match the material, dispensing device, and mixer. Coordinating the system and device prevents leakage and material loss.
Hand or compressed air: the right dispensing device
- Hand tools such as the Sulzer Mixpac DM2X series (DM 200-01 for 1:1 and 2:1, DM 200-10 for 10:1) or the Mixpac DP 400 series for 400 ml cartridges: for individual pieces and small series, full control, no compressed air connection required.
- Pneumatic tools such as the pneumatic LOCTITE cartridge gun 97002: consistent dispensing at higher frequency and less fatigue, suitable for series work.
- Syringe and Pump Dosing such as the digital LOCTITE syringe dosing system 98866 or a pneumatic feed pump: for small, precisely reproducible quantities, e.g., in electronics manufacturing.
The selection depends on the ratio, cartridge volume, and quantity.
The Static Mixer: Without It, No Homogeneous Material
The static mixer is a mixing tube with fixed elements. It blends both components solely through the extrusion pressure, without moving parts. Decisive factors are the design (helix or quadro), the number of mixing elements, and the appropriate ratio. A mixer that is too short or incorrect will not deliver homogeneous material, even if the ratio is correct. The selection of the mixer is covered in a separate article.
Properly plan for lead and waste
At the beginning, the material often does not yet emerge fully mixed. This initial flow is discarded. A residue also remains in the mixer after dispensing, which hardens. Both must be included in the quantity calculation. In the event of a work interruption within the pot life, the filled mixer can seal the cartridge. Once the pot life has expired, the mixer is replaced.
Common Mistakes in Dosing and Mixing
- Mixer too short or incorrect design: the material remains partially unmixed and does not cure completely.
- Device or mixer does not match the ratio of the material.
- Purging not discarded: the initial amount is not fully mixed.
- Pot life exceeded: the material starts to cure in the mixer.
- Angled or jerky extrusion: uneven material flow.
Practical checklist
- Ratio taken from the data sheet.
- Cartridge, device, and mixer are matched to this ratio.
- Initial portion discarded, pot life monitored.
- Clean, uniform dispensing.
- Leave the mixer in place after use or replace it in a timely manner.
We will be happy to advise you on selecting the right system of cartridge, device, and mixer based on your material and quantity.
