Repairing Polyporpylene

ASM109,
Excellent idea for heating and pushing the new insert into the plastic. I was thinking of all sorts of ways to check the temp of the insert, IR temp gun, oven, trial and error, etc. all with lots of room to screw things up even more. I thought of making a new insert but was stuck on how to melt it into the air box. I never thought of what you suggested. Seems pretty fool-proof.
I'm going to try this Loctite glue and if that doesn't work I'm sure making a new insert like you suggest will be the answer.
Thanks
 
Asm109 said:
I would make a knurled insert with a larger diameter and melt it into the air box. The trick is to heat the insert by placing it on the tip of an electric soldering iron and hold it on the hole. Push down gently and as the insert heats up it will sink in. Stop pushing when it gets flush.
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I have used 10AWG wire for soldering gun tips for many years. It has probably been 40 years since I used a store bought tip. The length of wire will control the ultimate temperature. 5" works fairly well for soldering but you may want to use 7 or 8 to control the temperature better for plastic welding.
I think that your idea will work. I would make a brass or copper threaded shaft to fill the insert so plastic won't fill the threads and to condict heat to the insert and finally to hold it in position until the plastic solidifies after the repair. Polypropylene is a fairly common plastic and you should be able to find filler material. Look for the triangle sign with a 5 or PP. I had read that many of the caps on food products are polypropylene. Miracle Whip is one for sure. If you look hard enough you may even find some black PP.
Good luck with the repair!
 
I got plastic filler rod at Horrible Freight that includes GREEN polypropylene. Ugh. I saw that they had the plastic welder (the one that needs an air compressor but has temp control - my air is plenty good) so I bought that just because. Then I needed something to practice on so now all of my black shop vac accessories (PP plastic) have green trim!
Put the old insert back in the airbox using the Loctite plastic bond stuff. Not sure how it will hold the plastic but I still have 2 fingers that I can't get apart. I will let it set up overnight and then fill in the beveled area with GREEN plastic using my new plastic welder. That heat will probably ruin the bond of the Loctite so I bet I'll be making a new insert anyway.
Didn't think about controlling the temp of a soldering gun tip via the length of the wire. Makes sense though.
 
Can you cut any scrap material from the box to use as a filler rod? You could melt the material into the hole and mix it with the sides or f the hole and push the insert into the soft plastic.
 
RJSakowski said:
I think that your idea will work.
Good luck with the repair!
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I know it will. This is how we install ultrasonic inserts into machined or 3d printed (FDM) prototypes. Low volumes its not worth the time it takes to set up the ultrasonic inserter so you bust out the Weller soldering station and insert them. Just don't use the EE's soldering station or there will be He)) to pay.
 
Might I suggest that you grab a Teenut of suitable size* and hot-melt glue it in place (with the flange inside the air box). You might want to partially or completely grind off the spurs and/or bend them flush with the flange. The hot melt will hold the tee nut in place until you insert the threaded fastener.

* You mentioned that the original fasteners were M5. I've never seen tee nuts in metric sizes. But a 10-32 tee nut and screw should be close enough to work. If you absolutely want to stay with M5, you might be able to run an M5 tap through the nut. Tee nuts are cheap enough that you can afford to experiment.
Screen Shot 2018-03-25 at 9.44.48 PM.jpg

PS - regarding the markings on the plastic ... The two "clock faces" are some kind of date and/or time code. The "PP H" indicates it's a polypropylene homopolymer. Don't know what the 25 means. Don't know what the squares indicate.
 
In a pinch, I've always used a soldering iron and a black Tyrap or wire tie as a filler rod. Works more often than not. Your mileage may vary. It's a pretty redneck type of fix. Git-r-dun!!!
 
Toxguy - thanks. I thought a rivnut was just like an insert. I didn't realize they were like a pop rivet. Maybe that's where the "Riv" comes from, huh. Doh:blowup:
 
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