Cartridge Heaters versus Oil Heaters

[dozer67]

I am looking for data on the pro's and con's of both. Thermal imagery of a cartridge heater compared to oil heated tools? I am not a fan of cartridge heaters and i am trying to convey a message that oil heaters offer a more uniform controlled heat across the the tool compared to cartridge heaters. Any help is appreciated..

 

[patprimmer]

Oil transfers heat better, but it really depends on how well it is designed and built.

Oil does have associated costs, mess and OH&S issues.

Regards
Pat
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[btrueblood]

Oil can catch fire, which I think pat alludes to with the OH&S comment.

Know of at least one rubber molding shop that junked all their cartride-heated mold tooling, and converted to steam heat, for a net savings (mainly due to faster cycle times, but also no more repair of broken heaters, and lower scrap rates due to inconsistent heat). Dunno if that can be applied to a plastic molding machine?

 

[Pud]

offer a more uniform controlled heat across the the tool

Not so. It depends where and how many oil channels/cartridge heaters there are and their positioning relative to the cavity surfaces, along with the thermal mass of the tool.

We use both, and the real problem with cartridges is keeping the tool cool - especially if fast cycling or substantial mass of the the parts.

btrueblood: The problem with oil is if a pipe bursts - hot oil @ 150°C or so spraying everywhere is a bit of a problem. It's always a very high flash point oil. It's also messy to clean up.

Cheers
H

http://www.tynevalleyplastics.co.uk

It seems to me you have confused a safe drinking limit with what I like to call "lunch"

 

[ornerynorsk]

What molding process? As BTB mentioned, steam is great for compression and transfer molding. Glycol works nice for injection molding.

I really dislike cartridge and strip heaters for the fact that one can rarely place them optimally. Hot spots can be more than a nuisance, they can ruin the processing parameters of an otherwise good tool.

Do you have mainly heat input, or do you need to regulate both a heat and cool cycle?

It is better to have enough ideas for some of them to be wrong, than to be always right by having no ideas at all.

 

[Compositepro]

The primary fundamental difference is that something that is heated by hot oil can never exceed the temperature of the oil. This is the main reason to use oil. It protects temperature sensitive materials.
Both types of heating can be poorly designed or well designed. A poorly designed oil system will result in cold spots. A poorly designed cartridge system will result in hot spots and, perhaps, cold spots.
One important point that many overlook is that it is not possible to have high heat fluxes and very uniform temperature. Where there is heat flow there must be temperature gradients.

 

[patprimmer]

bt

Hot oil under pressure does not evaporate when released so it travels further and soaks through clothing and retains heat to transfer to the body more than steam does.

Small leaks and spillage when changing moulds also causes a slip hazard.

I have seen both cartridge and oil used successfully and unsuccessfully on thermoplastic GF PET where a mould surface temperature on ejection should be at least 130 deg C (I think from memory) to obtain optimum crystallization and properties and consistent and predictable shrinkage/warpage is dependent on that level of crystallization at all points within the moulding.

Temperature gradients always exist and change continually throughout the cycle. Keeping the material cooling rate optimum is the art or skill in placing mould cooling/heating media.

For thermoplastics, so called mould heating is actually controlled mould cooling so it does not cool to fast. If ambient air cools the mould to fast, cartridge heaters reduce the cooling rate by offsetting air cooling. Thermoplastic in it's molten or mouldable state is always hotter than when ejected, so heat is always removed while in the mould. Controlled rate of heat removal from exactly where you want it removed is the secret to success.

Oil generally gives you more scope for better control, but it still has to be done right.

Regards
Pat
See FAQ731-376 for tips on use of eng-tips by professional engineers &

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for site rules

 

[btrueblood]

Should point out, steam burns are no fun either, and a steam leak can be nearly invisible, depending on conditions.

Hmmm...perhaps plutonium molds?

 

[ornerynorsk]

Material producers are making advances in thermal properties. Hastelloy might be your more practical plutonium substitute, thermally speaking. Doubt you could pump enough coolant through it once it warmed up, though.

It is better to have enough ideas for some of them to be wrong, than to be always right by having no ideas at all.