Preface
* To share my investigations and results covering; material properties, type of heat instrument to use, and best practices to stay safely below high temperature limits.
Equipment
* Table 1 describes the equipment used in this report (other makes and models of equipment offering similar performance can be used).
Table 1. Description of equipment used in this report.
Materials and Temperature Ratings
* Table 2 lists some of the temperature ratings of Mylar (diaphragm material) and Polystyrene (panel frame material).
Table 2. Critical temperature ratings of Mylar and Polystyrene.
Figure 1. Sample of mylar film showing permanent damage from melting.
* As there are serious risks of damage if these materials are exposed to elevated temperatures, temperature monitoring was implemented for the diaphragm heat shrink process.
Method
Figure 2. Portable heat gun, model HAKO FV-300 with optional spatula nozzle fitted.
Figure 3. Example showing thermocouple tip carefully placed inside the panel.
* First, the setup was checked to be working properly before applying heat to the diaphragm (Fig. 4).
Figure 4. Test of setup at room temperature before applying heat.
* Throughout the heat-shrinking process the temperature was carefully monitored, keeping the measured temperature in a range between 60 Deg C (Fig. 5) and maximum 70 Deg C. My objective was to ensure the maximum temperature stayed well below the Vical softening temperature of 90 Deg C for polystyrene.
Figure 5. Example of temperature monitoring during heat shrinking.
Observations and Precautions
Heat Gun vs. Hair Dryer?
* On the diyAudio page "Acoustat Answer Man is here" some members have commented they achieved acceptable heat shrinking results with just a hair dryer, although others have commented proper results could only be achieved using a heat gun. While I respect both comments, I thought it would be interesting to see what our home hair dryer (Fig 6.) was capable of.
Figure 6. Home hair dryer, Panasonic model nanocare.
Final Notes
- This report is a supplement to the reports previously posted to the diyAudio site:
- "Acoustat Magne-Kinetic Interface MK-121-2 A Successful Restoration". https://www.diyaudio.com/community/...ace-mk-121-2-a-successful-restoration.404764/
- "Acoustat Stator Wire Repair: Hints and Lessons Learned". https://www.diyaudio.com/community/...ints-and-lessons-learned.404881/#post-7492750
- As documented in the last page of report, "Acoustat Stator Wire Repair: Hints and Lessons Learned", "Although huge progress was made with all panels, one panel in speaker 104333 continues to make random clicking noises.." While I could not detect any looseness or wrinkles in the mylar diaphragms, with the random clicking noises in this panel still happening after thorough cleaning and extensive repairs to the stator wires, I proceeded cautiously to see if applying heat shrinkage to the mylar diaphragm could resolve this issue.
* To share my investigations and results covering; material properties, type of heat instrument to use, and best practices to stay safely below high temperature limits.
Equipment
* Table 1 describes the equipment used in this report (other makes and models of equipment offering similar performance can be used).
Table 1. Description of equipment used in this report.
Materials and Temperature Ratings
* Table 2 lists some of the temperature ratings of Mylar (diaphragm material) and Polystyrene (panel frame material).
Table 2. Critical temperature ratings of Mylar and Polystyrene.
- Well below the melting points of mylar and polystyrene are the more critical thermal properties of polystyrene. At the Vical softening temperature of 90 Deg C polystyrene becomes soft, and at the glass transition temperature of 100 deg C polystyrene begins to flow.
- To validate these published ratings, I conducted a temperature experiment on test samples of mylar film and polystyrene material. Indeed, at around +250 Deg C the mylar film sample started to melt (Fig. 1), and at around 100 Deg C the polystyrene sample began to deform, although it could be restored back to its original shape.
Figure 1. Sample of mylar film showing permanent damage from melting.
* As there are serious risks of damage if these materials are exposed to elevated temperatures, temperature monitoring was implemented for the diaphragm heat shrink process.
Method
- As documented in the related reports, the following heat shrinking method was performed after all repairs had been made to the MK-121-2 interface and stator wires.
- Safety. Ensure speaker power is disconnected and the panels have fully discharged before performing the heat shrinking.
- As extensively described and posted on the diyAudio page "Acoustat Answer Man is here", there are numerous excellent guidance and helpful hints to follow when performing a mylar diaphragm heat shrinking. Examples include keeping the heat gun at 6-inches distance, keeping the heat gun always moving, never stopping in one place etc.
- The HAKO portable heat gun (Fig. 2) temperature output described in Table 1 is adjustable up to +400 Deg C, indeed this is way more than ever needed, and if used without temperature control and monitoring could seriously damage the speaker panel.
Figure 2. Portable heat gun, model HAKO FV-300 with optional spatula nozzle fitted.
- For the HAKO heat gun settings, I used a temperature position of "3", where minimum position "0" is the lowest temperature setting, with maximum position "10" being the highest temperature setting.
- Together with the spatula nozzle fitted to disperse the heat gun's airflow, keeping the nozzle at distance from the diaphragm, and keeping the heat gun moving at all times worked well.
- Utilizing the Fluke DVM temperature measuring function with the thermocouple tip carefully placed between the stator wires and diaphragm (Fig. 3), allowed for monitoring of the panel's temperature in real time. Then, for the next area where heat shrinking was conducted the thermocouple tip was moved to the next area accordingly.
Figure 3. Example showing thermocouple tip carefully placed inside the panel.
* First, the setup was checked to be working properly before applying heat to the diaphragm (Fig. 4).
Figure 4. Test of setup at room temperature before applying heat.
* Throughout the heat-shrinking process the temperature was carefully monitored, keeping the measured temperature in a range between 60 Deg C (Fig. 5) and maximum 70 Deg C. My objective was to ensure the maximum temperature stayed well below the Vical softening temperature of 90 Deg C for polystyrene.
Figure 5. Example of temperature monitoring during heat shrinking.
Observations and Precautions
- As described on the diyAudio page "Acoustat Answer Man is here", the precautions of keeping the heat gun at 6-inches distance, keeping the heat gun always moving, never stopping in one place etc. proved to be very sound advice.
- For example, I observed that just taking your eyes off the heat gun for a few seconds or pausing movement of the heat gun for a few seconds could cause the monitored temperature to easily jump up +5 deg C.
- After completion of the heat shrinking process, significant heat is retained within the panel, and this will take considerable time to cool down and reach rest state. Suggest keeping the temperature monitoring circuitry intact until it is confirmed the panel has returned to normal room temperature (Fig. 4), before power can be connected to the speakers.
Heat Gun vs. Hair Dryer?
* On the diyAudio page "Acoustat Answer Man is here" some members have commented they achieved acceptable heat shrinking results with just a hair dryer, although others have commented proper results could only be achieved using a heat gun. While I respect both comments, I thought it would be interesting to see what our home hair dryer (Fig 6.) was capable of.
Figure 6. Home hair dryer, Panasonic model nanocare.
- Looking at the manufacturer's product specifications, my wife's hair dryer is rated 1200 W, whereas my heat gun is rated a little less at 1000 W. To comply with health and safety regulations a commercial hair dryer has temperature limiting to prevent burning of scalp/skin, nevertheless I was intrigued to find out what a 1200 W hair dryer could do.
- With this hair dryer set to maximum heat setting and repeating the setup including temperature monitoring, a brief test showed that I was able to achieve +60 Deg C on the panel surface. Although it might take longer time, it would seem this model of hair dryer could successfully be used (with your wife's permission!) to safely perform the diaphragm heat shrinking.
Final Notes
- I cannot say if the temperature band of 60 deg C to maximum 70 deg C that I chose was optimum, but it did no harm and it maintained an important safety margin below the Vical softening temperature of 90 Deg C for polystyrene. Of course, there may be other methods of performing diaphragm heat shrinking, this report is intended to share amongst our members what worked for me.
- As mentioned in the Preface, the objective was to try heat shrinking the mylar diaphragm as a last resort to see if the remaining random clicking noises in one of the panels could be minimized. But as there was nothing initially wrong with the diaphragms, i.e. no noticeable looseness or wrinkles, it's hard to say in this case the heat shrinking process made any difference to the random clicking noises.
- However, this exercise proved that when using a heat gun the heat shrinking process can be done safely in a controlled manner, and with a suitable high output hair dryer it may be possible to achieve successful heat shrinking having little risk of overheating damage.
Nice report!
I have used both hair drier and heat guns as well. Both works fine. And to achieve higher temp on the hair dryer i put small pieces of tape on the inlet reducing the airflow. This gives a higher temp on the output. Start just with a small piece of tape... do not destroy someone's dearest item, fixing your dearest item.
I have used both hair drier and heat guns as well. Both works fine. And to achieve higher temp on the hair dryer i put small pieces of tape on the inlet reducing the airflow. This gives a higher temp on the output. Start just with a small piece of tape... do not destroy someone's dearest item, fixing your dearest item.