1. Potting of Electromagnets in
Steel Mills with Silicone
Elastomers
Prepared by:
Project Sales Corporation
28 Founta Plaza, Suryabagh
Visakhapatnam 530020, AP
Phones: 0891 2564393, 6666482
Project Sales Corp, Visakhapatnam

2. Important Considerations in
choosing a potting material
Viscosity of the material
Specific gravity
Thermal conductivity
Reversion Resistance
Shore hardness
Curing schedule
Pot life-Working Time
Electrical properties
Temperature Stability
Project Sales Corp, Visakhapatnam

3. Viscosity
• The viscosity of the material defines
the ease with which large quantity
of material can be poured into the
magnet. If the viscosity is too high,
the pourability becomes difficult and
air pockets may d evelop in the pot.
Lower viscosity self-leveling
material gradually spread when
poured from one corner releasing
air pockets which may be in the
coils. Measured in poise. 1
poise=100cps=100mpa.s.
• The viscosity con tinues to increase
with the pot life until it cures to a
solid elastomer in 8-24 hours.
Project Sales Corp, Visakhapatnam

4. Specific Gravity
• The spec ific gravity is expres sed in terms of “as supplied”
and “as cured”. The “as supplied” specific gravity
determines the weight of the compound you buy against an
unit of volume. Higher specific gravity materials fill less
space with more volume, hence are not cost-economical for
large volume applications like potting applic ations in lifting
magnets.
• The ideal specific gravity should be in the range of 1.1 to 1.3
as supplied.
• The higher the specific gravit y, the higher quantity of the
material required.
Project Sales Corp, Visakhapatnam

5. Thermal Conductivity
• The thermal conductivity of th e material is expressed as
its ability to conduct heat. Fo r potting applications where
the material is subjected to a high amount of heat in
confined conditions, the heat has to be dissipated quickly.
This ensures too much t hermal stresses is not
encountered by the material or the coil.
• Poor thermal conductive materials require additional filler
materials to improve the condu ctivity as the potting time.
Else, when heated under conf ined conditions or deep
sections the materials may de polymerize and revert to a
more liquid stage.
Project Sales Corp, Visakhapatnam

6. Reversion Resistance
• Many types of potting materials when heated under
confined conditions or in deep sections, will
depolymerize o r r evert to a more liquid sta te. This
degradation process is referred to as reversion.
• For potting applications, this is an important
consideration if instances of depolymerization have
occurred.
• The curing mechanism and cross-linking of the product
decides its ability to be re version resistant. Reversion
resistant products cure by an “addition reaction” process
which produces no cure by-product.
Project Sales Corp, Visakhapatnam

7. Shore Hardness
• The shore hardness of a silicone material should
be such as it allows for the material to provide
stability and relief from mechanical shocks and
thermal cycling stresses.
• It should cure to a flexible material allowing for
easy reparability and removal without damage to
the coils.
• The ideal shore hardness for potting application
should be in the range of 45-50 Shore A.
Project Sales Corp, Visakhapatnam

8. Curing Schedule
• A potting material designed for deep
section cure in confined conditions should
cure within 8-24 hours with the addition of
the catalyst irrespective of thickness o r
depth.
• It is advantageous to have flexible curing
schedule with different catalyst (slow
curing, fast curing, normal curing).
• Two part materials that require 1:1 mixing
without catalyst are easier to process
• Exposure to humidity and heat decreases
curing time.
Project Sales Corp, Visakhapatnam

9. Pot Life- Working Time
• The material after mixed with a catalyst gradually
increases in its viscosity to cure to a solid elastomer.
• For large applications like lifting magnet the material
should have a pot life of anywhere above 15 minutes at
25 deg C.
• Where base/catalyst mixing ratio is above 20:1 or 10:1,
catalyst prices can escalate the cost of potting larger
sections.
• Higher pot life but not affecting the curing schedule
allows for larger packs to be bought bringing cost
savings in material costs. This allows for mixing of
larger quantity of materials per single pour cycle.
• The application time (or the time till which the material
is in a liquid state ) is normally half the pot life.
Project Sales Corp, Visakhapatnam

10. Electrical Properties
The potting material for lifting magnets should have:
•good dielectric strength
•as high a volume resistivity as possible
Project Sales Corp, Visakhapatnam

11. Temperature Stability
• Materials designed for deep sect ion cure working in confined
conditions should not melt or appreciably soften even at elevated
temperatures >200 deg C.
• Aging tests conducted on the material should show little or no effect
on the basic electrical or elastomeric physical properties.
• The overall cured material s hould handle the thermal cycling
experienced in a lifting magnet in a quick time.
• Higher quality materials des igned fo r very high temperatures work
even at elevated temperatures >300 deg C for a few hours despite
confined conditions and are used fo r critical applic ations where
reliability is extremely critical.
Project Sales Corp, Visakhapatnam

12. Introducing
Sylgard 170 A&B
The highest temperature and reversion
resistant potting material for lifting
magnets working at elevated
temperatures in steel mills
1st trial worldwide by Project Sales Corp
at Vizag Steel, India and a major success
Project Sales Corp, Visakhapatnam

13. Sylgard 170 A&B
Brief Description
• Type Two-part Silicone Elastomer
• Colour Part A: Black/ Part B: White
• Physical Form
– As supplied Low viscosity liquid
– As cured Flexible rubber
• Cure At room temperatures
• Special Properties Reversion resistant; will not depolymerize
even at elevated temperatures; improved flame
resistance; high mechanical shock handling
capacity; UL tested; Proven in steel mills; 1:1
mixing, requires no catalyst
• Benefits Easy processing; reparability; better
components life after potting
Project Sales Corp, Visakhapatnam

14. Sylgard 170 A& B
Technical Advantages
• Reversion Resistance: Unique “addition reaction 1:1” curing
process which produces no cure by-product. Excellent reversion
resistance at very elevated temperatures.
• Low Toxicity : No special precautions required for normal
industrial handling
• No solvents or cure by-product : Requires no special venting;
cure can be easily heat accelerated; will not cause corrosion
• One to one mix ratio : Part A and Part B components do not
require lot matching; provides more accurate and simplified
handling and processing. Coloured white and black for easy
identification.
• Excellent fire resistant properties: Provides fire protection an d
maintains UL fire rating classifi cations of 94 V-0. Passed large
scale functional fire tests in accordance with ASTM E-119-73 as
a fire stop material.
Project Sales Corp, Visakhapatnam

15. Sylgard 170 A& B
Technical Advantages
• No exotherm : Will not damage sensitive components during
cure.
• Cures to a flexible elastomer: Provides stability and relief from
mechanical shock and thermal cycling stresses; easy
reparability
• Excellent dielectric properties: Maintains and protects existing
electrical insulation requirements.
• Stability over a wide temperature range: Maintains elastomeric
flexibility and provides functional stability at high temperatures
>250 deg C.
• Cost Savings: Excellent life. No catalysts costs. Easy
processing. Improves potted co mponent life resulting in costs
savings.
Project Sales Corp, Visakhapatnam

16. For Further details
• For further details, contact the
Dow Corning distributors for
Silicone Elastomers in this
region:
Global leaders in silicone
Project Sales Corp technology for the electrical
28 Founta Plaza, Suryabagh, and electronic markets
Visakhapatnam 530020, AP India Operations
Phones: 0891 2564393; Dow Corning India Pvt. Limited
6666482 Wockhardt Towers, East Wing
Level 2, Bandra-Kurla Complex
Fax: 0891 2590482 Bandra East, Mumbai 400 051
mailto: Tel: 022 - 6694 6868
satish@projectsalescorp.com Fax: 022 – 6694 6848
Project Sales Corp, Visakhapatnam