ELASTOSIL® RT 628 A/B is a flowable, addition-curing, 2-part silicone rubber for potting, encapsulation and casting applications. The product vulcanizes at room temperature or under heat to yield a permanently flexible silicone rubber with very good mechanical properties.


Cured ELASTOSIL® RT 628 A/B shows long term stability against weathering, moisture and UV radiation. The silicone elastomer may continously be exposed to constantly changing climatic conditions, UV radiation and temperatures as high as 180 °C (356 °F) without damage.




  • 9 : 1 mixing ratio
  • High extrusion rate
  • Self-levelling
  • Rapid heat cure possible



  • Medium hardness
  • High tear resistance
  • Recommended service temperature range: -50 °C to +180 °C

Spezifische Merkmale von ELASTOSIL® RT 628 A/B

  • Additionsvernetzend
  • elektrisch isolierend
  • Fließfähig
  • hitzebeständig
  • niedrige Viskosität
  • UV- & verwitterungsbeständig
  • zweikomponentig
  • General purpose grade for casting applications
  • Encapsulation of electrical componentes
  • Elastic fixation of generator windings


Only A and B components with the same batch number should be processed together! In order to homogeneously redisperse fillers that might have settled during transport and storage, both component A and component B should be stirred well before use.


Surface preparation:

All surfaces must be clean and free of contaminants that will inhibit the cure of ELASTOSIL® RT 628 A/B. Examples of inhibiting contaminants are sulfur containing materials, plasticizers, urethanes, amine containing materials and organometallic compounds – especially organotin compounds. If a substrate’s ability to inhibit cure is unknown, a small scale test should be run to determine compatibility.



Caution ! Component A of ELASTOSIL® RT 628 A/B contains the crosslinker, component B comprises the platinum catalyst. Since even traces of platinum catalyst may cause gelling of component A, all tools (e. g. spatula, stirrers, mixing cups etc.) used for handling either component B or the A/B mix must not come into contact with component A by mistake.


The two components should be thoroughly mixed at a 9 : 1 ratio by weight, either manually or preferably by automatic metering lines equipped with static or dynamic mixing devices.


Material application:

If applicable, a vacuum encapsulation is recommended in order to eliminate any air introduced during mixing and dispensing, or trapped under components and devices. Alternatively, component A and B can be deaerated individually prior use to remove absorbed air; to evacuate the air from the A/B mix is also possible. For this purpose applying a vacuum of 25-50 mbar for 10-15 min proved useful.



Though curing by heat is possible, ELASTOSIL® RT 628 A/B is processed typically at room temperature. The level of Sh hardness usually reaches 75 % of the final value within 8 to 10 hours of curing. It is therefore possible to demould casted articles earlier than indicated by the curing time value given in the table "Catalyzed".


When cured under heat, the vulcanization time is highly dependent on temperature, size and heat sink properties of the respective substrates or of the assembly parts to be encapsulated, respectively. Typical curing temperatures and resulting curing times are given in adjacent table.


Furthermore the reactivity of ELASTOSIL® RT 628 A/B can be adjusted within wide limits by adding WACKER® Catalyst EP or WACKER® Inhibitor PT 88 to suit the processing requirements of the particular application. WACKER® Catalyst EP increases reactivity, i. e. pot life and curing time are reduced. WACKER® Inhibitor PT 88 is a pot life extender and thus prolongs pot life and curing time.


Detailed information about processing 2-part addition-curing silicones is given in our brochure “ROOM TEMPERATURE VULCANIZING (RTV) SILICONES - MATERIAL AND PROCESSING GUIDELINES”. We recommend running preliminary tests to optimize conditions for the particular application.



If removal of the silicone from machines or dispensing equipment is necessary, white spirit or similar nonpolar solvents are recommended. However, cleaning ideally should take place before the silicone is fully vulcanized. Cured silicone rubber needs to be rubbed off or removed mechanically, if necessary in combination with a swelling agent (solvent) or a chemical silicone remover



Store in a dry and cool place.


The 'Best use before end' date of each batch is shown on the product label.


Storage beyond the date specified on the label does not necessarily mean that the product is no longer usable. In this case however, the properties required for the intended use must be checked for quality assurance reasons.

Vertrieb & Support

Wacker Chemie AG
Heilbronner Strasse 74
70191 Stuttgart
+49  711  61942-0 (Phone)
+49 711 61942-61  (Fax)

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