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Using Asphalt Based Potting Compound

Pulished:2019-08-27Number:loading...Source:Shanghai Spark Technology Industrial Inc.

Using Asphalt Based Potting Compound

 

The Potting process is to cover an electronic or electrical device with a sealant material to protect it from the surrounding environment.  Most of the time it is for protection from water or moisture and /or to electrically insulate it so that it will operate as designed. This process is called potting.  Many names have been used interchangeably so there is some confusion of the terms. The most commonly used term is encapsulation or potting.

 

Potting/Encapsulation

The potting method uses a "pot" or case or shell to put the device in and then pour the liquid potting compound to the top of the case covering the device and completely encasing it. The  case becomes part of the finished unit. This is the most common method used, especially for high speed and many-units-per-hour production-line conditions.

Planning Process for a Successful Design

The major purpose of potting or encapsulation of a unit is for environmental protection.  This could be for moisture protection, protection from chemicals, insulate from electric interference and so on. Also potting is used to provide heat dissipation, flame retardance and cushioning from shock.   Normally, hot melt potting method is not the first choice because it is viewed as a messy process that has many problems associated with it.  Much of this perception is due to lack of knowledge of what is available and poor design of the manufacturing process. 

Hot melt compound such as asphalt based potting compound has been around for over 30 years.  It has been applied in electronic ballasts, HID ballasts, industrial capacitors, power supplies and LED drivers in recent years.

The advantage to asphalt based potting compound is price and heat dissipation.  Usually it is fraction the cost as other compounds such as resins or epoxy materials.  Also, it expands during warm temperature and it is ideal for component protection and effective heat dissipation.


 

Below is a stepwise planning process that will help you understand what is needed for a successful design.

Phase 1 - Part Design:

The design of the part includes three steps. The first step in your planning is the design of the unit or part to be potted or not. The second step is to make the device friendly to potting. The third is to determine an estimated cost. In this design phase, you design the unit so that it can be manufactured quickly, minimum bubbles entrapped, easy to pour and with a minimum of rejected parts. 

The first decision is whether to pot or encapsulate the part. The most popular method of protection is potting a unit in a shell or case.  The unit is placed in the potting shell, and the resin system poured around it.  When it hardens the shell becomes part of the finished unit.  The shell material is a consideration because you are balancing of the ability to bond to it vs. the cost of the shell.  To lengthen the life cycle of the device, potting is always the method used.

Design the part to be friendly to potting includes easy air release, little shrinkage, and proper use of plastics.

Phase 2 – Operating Parameters 

The conditions that the part will experience in use are defined so the potting compound can be selected.  These include; high and low operating temperature; other environmental conditions such as humidity, chemicals and pressure or vacuum; physical requirements such as compressive strength (for bolt holes) and other requirements such as thermal conductivity, flame retardant, Underwriters Laboratories requirements and the color of the hardened potting compound.

Phase 3 – Processing Parameters

Manufacturing of the unit is a large part of the plan scheme.  Usually with very minimal investment in an asphalt potting machine placed towards the end of the assembly line, one can start to produce thousands of electronic units every day.  The number of units to be made per hour depends on the output rate of the potting machine. 

Another advantage with hot melt potting compound is that it will harden/cure in minutes, not hours.  It is not unusual to see operators enclosing the units for testing minutes after the potting process.

Phase 4 – Testing of Potted Unit

After potting or encapsulating the device, testing will determine if the potting compound selection is acceptable.  Temperature cycling testing is the most telling test. The usual temperature range for thermal cycle is between 0C to 80C for hot melt potting compound.  The recommended thermal cycle would be from the lowest temperature to the highest temperature the device will see in use.  Run the cycle 20 times with a one-hour dwell time at the lowest and highest temperatures.  The faster the rate of change from the high to the low and back, the more severe the test. We suggest that at least 10 units are tested in the temperature cycle to determine a failure rate.

After the temperature cycle, test the unit for its intended use to determine if its performance is affected.  If no effect, then the potting compound is suitable. 

Phase 5 – Set-up

For mass production, asphalt potting machine is recommended.  In order to allow adequate time to set up in factory, ordering equipment early is recommended.  Always allow 4-6 weeks of assembly and shipping time.  The largest asphalt dispensing machine can dispense over 1 metric ton per day on average.

Phase 6 – Plant Trial

The last step is the plant trial on production equipment. Fine-tuning of the asphalt potting machine equipment sometimes takes considerable time on startup.  It is recommended that the asphalt potting machine supplier to ship the machine along with the potting compound to your plant so you can work out any problems before the production.  It is also recommended that both the suppliers of the potting compound and the asphalt potting machine supplier to be the same so you can rule out any compatibility issues. During installation of the asphalt potting machine, the machine supplier needs to be present during the trial so any problems can be resolved on location during real time. 

Shanghai Spark Technology Industrial is the leading supplier of asphalt based potting compound and it also manufactures potting machines for assembly lines.  Its products are RoHS and REACH compliant and it registered under UL.  For more information, please visit www.ssti93.com for more information.

 

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