My red 304

[Doug Rose]

Hey Paul...what about soft plastic 302 sets?....Doug

[paul-f]

Hey Doug...What about them?

[Doug Rose]

Hey Doug...What about them?

"Thermoplastic 300-series colors reported are summarized here:"

On your comprehensive listing of phones, I didn't see any Soft Plastic 302s listed.... only thermoplastic 302s. I was wondering if you had any documentation of them....thanks...Doug

[paul-f]

I don't recall seeing the words "soft plastic" in any Bell System documentation.

Of the BSPs I've seen, C32.502, Issue 8, October 1955 is the one I'd expect to find it.  However, it states (in part):

1.04 This section covers mountings with both metal and thermoplastic housings.

Perhaps someone has other BSPs from the mid-50s that have more info.

Or perhaps the Bell System didn't differentiate and called all plastic formulations thermoplastic.

[unbeldi]

Don't mean to revive this old thread, only link it to a more recent topic that explains the history of these sets:

http://www.classicrotaryphones.com/forum/index.php?topic=14045.msg146749#msg146749


Paul-F was quite right in his comment about the plastic types.

The term "soft plastic" is really non-sense and no one in the plastics industry knows what that means.
The 500 sets and these newly molded 302/304 housings used a plastic commonly called CAB, an abbreviation for cellulose acetate butyrate. The trade name by Tennessee Eastman was "Tenite II" at the time. This is documented in Bell System accounts.

''Thermoplastic'' is a characterization for all plastics that become soft and eventually liquify upon heating, that includes all versions of Tenite, and ABS.  It is the property that makes injection molding possible.

[Alex G. Bell]

''Thermoplastic'' is a characterization for all plastics that become soft and eventually liquify upon heating, that includes all versions of Tenite, and ABS.  It is the property that makes injection molding possible.

I concur with the definition you stated for thermoplastic and the second statement as far as it goes, but isn't Bakelite, which is a thermosetting plastic (it does not liquefy with reheating) also injection molded, or is there some other name for the process used for thermosetting materials?

[unbeldi]

I concur with the definition you stated for thermoplastic and the second statement as far as it goes, but isn't Bakelite, which is a thermosetting plastic (it does not liquefy with reheating) also injection molded, or is there some other name for the process used for thermosetting materials?

Bakelite and similar thermosets are formed by presses that press pucks, or otherwise suitably shaped lumps of resin into the desired shape dictated by the mold. The resin is a pre-reacted mixture of the components, which completely polymerizes only under high pressure (several hundred tons) and heat within a few minutes.  Other thermosets can be polymerized permanently in low-pressure processes.

But today, forms of injection molding can be used for certain thermosets, indeed, but they are not thermoplastic, and discussing this is way out of scope here. I did not want to prolong this topic.

[Alex G. Bell]

But today, forms of injection molding can be used for certain thermosets, indeed, but they are not thermoplastic, and discussing this is way out of scope here. I did not want to prolong this topic.

Thanks.  Understood.  I just wanted to clarify whether or not "injection molding" was also used for non-thermoplastic materials too.