Polypropylene (PP) or Polyethylene (PE) or ABS?

[robfg67]

I cracked the black plastic HVAC box (located under the dash on the passenger side) and want to repair it with an epoxy.

 

Does anyone know what type of plastic it is made from?

[Tex06]

I looked into this at one point (same issue, crack at the bottom). I ended up repairing with fiberglass as I had a hole roughly the size of a half dollar that I couldn't find the missing piece for. Has held up well for the past 8 years. 

[robfg67]

I bought the traditional JB Weld but it will not work as well if the box is PP or PE.

 

I'm guessing no one here knows, so I'll just try the JB Weld regular.

 

Thanks

[ghetdjc320]

It’s not ABS. Pretty sure it was Polyethylene when I did some plastic welding on my old unit. I used PE filler rods

[AZJeff]

If we are talking about the actual heater box proper, it’s going to be of a resin that won’t deform under the temperatures seen around the heater core, which are going to be about 200*F.

 

That rules about polypropylene or polyethylene.  It might be ABS, but it’s also mineral filled, to increase its stiffness.  Epoxy should work.   If the damage is extensive (long crack or a hole), a piece of thin aluminum laid over the damage and bonded with the epoxy would be prudent.  (A few “pop” rivets through the aluminum/plastic sandwich to help position the repair would also help.

 

I have done this on other ABS parts such as old dashboards in the past with good success.

[robfg67]

2 hours ago, AZJeff said:

If we are talking about the actual heater box proper, it’s going to be of a resin that won’t deform under the temperatures seen around the heater core, which are going to be about 200*F.

 

That rules about polypropylene or polyethylene.  It might be ABS, but it’s also mineral filled, to increase its stiffness.  Epoxy should work.   If the damage is extensive (long crack or a hole), a piece of thin aluminum laid over the damage and bonded with the epoxy would be prudent.  (A few “pop” rivets through the aluminum/plastic sandwich to help position the repair would also help.

 

I have done this on other ABS parts such as old dashboards in the past with good success.

Do you think JB Weld would work? If not, can you recommend an epoxy?

 

Thanks

[AZJeff]

2 hours ago, robfg67 said:

Do you think JB Weld would work? If not, can you recommend an epoxy?

 

Thanks

Can you send a picture of what the damage looks like?   I can make a better suggestion on how to best repair it so that it's more or less permanent.

[ghetdjc320]

5 hours ago, AZJeff said:

If we are talking about the actual heater box proper, it’s going to be of a resin that won’t deform under the temperatures seen around the heater core, which are going to be about 200*F.

 

That rules about polypropylene or polyethylene.  It might be ABS, but it’s also mineral filled, to increase its stiffness.  Epoxy should work.   If the damage is extensive (long crack or a hole), a piece of thin aluminum laid over the damage and bonded with the epoxy would be prudent.  (A few “pop” rivets through the aluminum/plastic sandwich to help position the repair would also help.

 

I have done this on other ABS parts such as old dashboards in the past with good success.

ABS starts to deform around 100c. I’m betting it’s a poly blend of some sort. There are a few home tests you can do to find out what type of plastic it is. Most plastic epoxy’s should work fine with some minor prep. Heck, you could just use some aluminum duct tape. 

[AZJeff]

5 hours ago, ghetdjc320 said:

ABS starts to deform around 100c. I’m betting it’s a poly blend of some sort. There are a few home tests you can do to find out what type of plastic it is. Most plastic epoxy’s should work fine with some minor prep. Heck, you could just use some aluminum duct tape. 

It’s actually probably “macro blend” which is a PC+ABS blend.  And like I mentioned, it’s mineral filled to enhance rigidity.   Depending on the type/length/location of the crack and/or hole, an added reinforcement of aluminum sheet about 0.025” thk. would be beneficial.

[ghetdjc320]

2 hours ago, AZJeff said:

It’s actually probably “macro blend” which is a PC+ABS blend.  And like I mentioned, it’s mineral filled to enhance rigidity.   Depending on the type/length/location of the crack and/or hole, an added reinforcement of aluminum sheet about 0.025” thk. would be beneficial.

Don’t they make hvac duct tape in that thickness? 

[AZJeff]

I have never seen duct tape that thick, but I am not an expert on that stuff.   The idea behind the aluminum is to help keep the crack or hold from expanding, and the epoxy becomes the agent to bond/seal the aluminum to the existing resin HVAC case.

[robfg67]

21 hours ago, AZJeff said:

Can you send a picture of what the damage looks like?   I can make a better suggestion on how to best repair it so that it's more or less permanent.

Pictures attached...

 

 

[AZJeff]

If anything attaches to that threaded stud, it would prudent to somehow figure out a way to distribute the forces that said stud will apply to the epoxied joint, which will mostly be in tension.  Since the area of the bonded joint is small, the epoxy has to work pretty hard to keep the joint glued.   The best solution would be a combination of adhesive both on the outside and INSIDE, but since that means disassembling the heater box, that isn't probably in the cards.

 

The attached is my suggestion on how to do the best possible bond without having to take the heater box apart and still get a good strong joint.

 

 

AAA.pdf

[robfg67]

Brilliant!

 

I'll tackle this job this weekend and post the pictures.

 

Thanks

[robfg67]

I scuffed the area up well and used the entire tube.

 

 

[AZJeff]

On 6/9/2024 at 8:36 AM, robfg67 said:

I scuffed the area up well and used the entire tube.

 

 

That looks like it will do the trick.   Let us know if that fix is permanent 

[Tex06]

Here to say JB weld is a good all around epoxy, especially on glass-reinforced or mineral- filled plastics. 

 

To test if the box was abs, you can clean a spot with alcohol real well then wipe with a paper towel damp with acetone or MEK. ABS will smear black on the paper towel and you can use ABS adhesive to repair it (found in the plumbing aisle for black pipe).

 

Not a foolproof test but does help positively ID ABS. 

[Salvagedcircuit]

Huh. Now I'm wondering what plastic the lower dash panel is made from. I was considering using ABS filament to plastic weld the crack in my lower dash.