What Is Hot Melt Open Time and Why Does It Matter?
Hot melt open time is the time interval, which can reliably bond with the second piece after the adhesive is applied on the surface. This time is not only a number in the product catalog; the line speed is a process window, which should be evaluated with the part size, ambient temperature and operator movement.
The setting time with open time is not the same
On the open time, the remaining time for the merger of two surfaces; the setting time tells the speed of winning sufficient first strength to carry the combined parts or switch to the next station. Long open time does not always mean slow adjustment, but formulation and application conditions affect these two behavior together. Pressing or holding time should be described separately when the choice is done.
What variables do the actual open time?
The value given by the manufacturer is the result of a specific test method. A cold metal surface can shorten the practical open time by rapidly pulling heat from hot adhesive. Porous material can absorb adhesive; thick bead can warm for longer time. The ambient airflow, application temperature, adhesive quantity and waiting time between parts can not be accurately diagnosed without being recorded.
Signs of very short and very long open time
When the adhesive surface is short, it does not freeze enough; the bond can be neatly separated from the surface and the fiber break may not be seen. A long-term product from the truth can lead to the cross-fixing of the part in fast lines, slipping or longer fixture time. Break mode, line rhythm and temperature profile should be examined together, instead of looking at alone pull force in both cases.
Verification method on line
Do the trial with a single sample, not waiting time steps. Combine parts with the same surface preparation and the same glue quantity, for example, short waiting and the longest waiting time targeted. Wait for samples in real service conditions; then save the type of break up to bond resistance. Thus, the safe process window meets the production variable is determined.
Application control list
- Measure the shortest and longest waiting time of the assembly.
- Save surface and ambient temperature.
- Fix beads diameter or application grammage.
- Confirm setting time separately from open time.
- Report crushing mode and reprocessing rate.
Conclusion
The right open time allows the operator or automation to be fixed without delaying the line while providing enough assembly time. The decision should be based on the reading of the actual line trial with the TDS value.
Manstechnic approach
Manstechnic creates the product proposal not only according to the open time in the catalog; by evaluating the surface temperature, mounting distance, line speed and application equipment together.