Museum of Plugs and Sockets logo, small Bakelite molding marks
used by MPAD and DMAW
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2-pin
plugs
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Schuko
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appliance
connect.

 

MPAD mark - Praegemark



MPAD molding marks  (Pressmassen Prägemarken)

The German Technical Association of Manufacturers of Standardized Molded and Compression Molded Materials introduced in 1924 an industry standard for Bakelite and comparable resins. Molding marks were issued by MPAD, the Staatliche Materialprüfungsamt zu Berlin-Dahlem (State Materials Testing Institute in Berlin-Dahlem). Testing of Bakelite products by MPAD ended early 1960s1.

In general, testing was not compulsory, but in the 1930s-'50s it was mandatory for products that could be delivered to German Rail, Post and Army.

 

Examples of MPAD marks on plugs

Examples of MPAD marks found on plugs, with codes that identify the press work2 (top) and the pressed material (bottom).

a
34
Siemens-Schuckertwerke, Berlin
S3
Phenol-formaldehyde resin (Bakelite) reinforced with sawdust
b 39 Dr. Deisting, Kierspe
1 Phenol-formaldehyde resin with anorganic (mineral) filling agent (not specified)
c vF Hugo Burgmaler, Schmiechen
31 Phenol- or cresol-formaldehyde resin reinforced with sawdust
d F2 Franz Stauch, Unterrodach
1  313
not listed by Oburg4; could be a 1 and 31 'dual code'
e 95 Erich Jäger, Homburg
131 Urea-formaldehyde reinforced with cellulose
f 67 ABL-BEZEG, Lauf bei Nürnberg
131 31
Code that may indicate that a mold is used for 31 or 131, depending on batch
g MU Maehler & Kaege, Ingelheim-Rhein
51 Urea-formadehyde reinforced with cellulose

23 Busch-Jaeger, Lüdenscheid
31

24 Gebrüber Merten, Gummersbach
1  31

Notes

1 Although MPAD ended testing of Bakelite products early 1960s, molding mark can also be found on plugs and socket made in the 1970s. Making molds was expensive and have often been used as long as possible, also for modern thermosetting polymers that were used from the 1960s, see image below of an appliance connector made in the 1970s-'80s.

Merten switched appliance connector



2 Most manufacturers had their own press work facility, but production of casts could have been contracted out. In such cases the MPAD code corresponds to the company that made the casts.

3 S is the most commonly used code on plugs and sockets made in the 1930s. Code 1 is rarely used; 31 only occasionally.
Bakelite plugs and sockets made from 1950s have nearly always a 1 in combination with a 90 degrees rotated 31 code


4 Wilhelm Oburger, Die Isolierstoffe der Elektrotechnik. Springer Verlag, 1957. Page 256, table 10-9.

Links to lists with MPAD codes: 1938 list, 1954 list, and a not dated list with some more codes.

 


DAMW Ueberwachungszeichen
DAMW molding marks



DDR quality marks
TLG quality marks

Q = top quality
S = very good quality *
1 = good quality
2 = acceptable quality **
 * : used until 1960, then S merged with Q
** : abolished in 1970

Marks on plugs made in the German Democratic Republic
 
In the German Democratic Republic (DDR) product tests were introduced in 1950 by the German Organization for testing of materials and goods (Deutsches Amt für Material und Warenprüfung, DAMW). In 1973 it became the Organization for standards, measure and testing of materials (Amt für Standardisierung, Messwesen und Warenprüfung, ASMW). In 1990 ASMW became a part of the Deutsche  Institut für Normung (DIN).
Two types of marks can be found on Eastern German products:

DAMW molding marks (Überwachungszeichen für Formmassen).
Molding marks were used for casts made of Phenoplast (phenol based resins) and Aminoplast (urea based resins). The name Bakelite was not used in the DDR.

Left code identifies the press work. For example:
  N04 = VEB Elektroinstallation Sonderhausen (Thüringen).
  N06 = VEB Elektroinstallation Ruhla (Thüringen).
  N25 = VEB Elektroinstallation Kranichfeld (Thüringen).
Right code indicates the resin used. No. 31 = phenol-formaldehyde resin, reinforced with sawdust filler. Designs 'b' and 'c' were most often used.
Links for full list of DAMW company codes and types of material used.

TGL quality marks (Gütezeichen der DDR).
The quality of products was tested according to the Technical instructions on quality and terms of delivery (Technische Güte- und Lieferbedingungen, TGL), comparable to DIN standards. The quality was among others normative for the price level. Top quality was mainly used for export to western countries; a source of hard currency.

 


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