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Process Guide
Keeping a Sealant Bead Consistent
The four variables that change bead size when nothing on the machine has changed
Introduction
A dispensing machine holds its program exactly. The bead still changes size, and the cause is almost never the machine. Four variables account for most of it, and three of them live outside the equipment entirely.
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Material temperature
Viscosity falls as material warms, and at constant delivery pressure a thinner material flows faster. The same program produces a larger bead on a warm afternoon than on a cold morning.
Conditioning the material to a stable temperature is usually the single most effective change a plant can make to bead consistency, and it costs less than any machine adjustment.
Path speed through corners
On a straight run, delivery and speed are matched. At a corner the axes decelerate, and if delivery does not decelerate with them, the bead grows at exactly the place where a seal is most likely to fail.
Coordinated delivery is what prevents this. When checking a new program, look at the corners first - the straights will look fine either way.
The applicator tip
A partially blocked or damaged tip changes the bead section while the machine reports a perfectly normal cycle. This is the most common cause of a bead that is wrong but not obviously wrong.
Tip inspection belongs in the shift routine, not in the monthly maintenance schedule.
The first bead after a stop
Material settles and pressure equalises during a stop, so the first bead afterwards is the one most likely to be short or inconsistent.
Purging and checking before committing a component is a small habit that prevents a scrapped panel.
What to check when the bead changes
In order: tip condition, material temperature, delivery pressure, then the program. The program is last because it is the thing that did not change.
Keeping a simple log of bead checks at batch start makes a gradual drift visible before it becomes a reject.
Takeaways
The Short Version
- Material temperature changes viscosity and therefore bead size at constant delivery
- Corners reveal a delivery and speed mismatch before straights do
- Tip condition is the most common cause of a bead that is quietly wrong
- Check tip, temperature and pressure before suspecting the program
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Equipment Discussed
Questions
Questions About This Article
What is the short answer?
Material temperature changes viscosity and therefore bead size at constant delivery.
Does this apply to equipment we already own?
Most of it does. The engineering described here is not specific to Delkotech machines, although where our equipment is relevant we link to it.
Who should read this?
Engineering, maintenance and production people who have to specify, buy or live with the equipment. It is written to be useful on the floor rather than in a brochure.
Can Delkotech advise on our specific case?
Yes. Email [email protected] with the part, the operation and what is going wrong, and you will get an engineer's answer rather than a sales response.
Talk to an engineer
Ask About Your Own Application
Send the part and the problem. You will get an engineer's answer, including when the answer is that automation is not the right call.