THE BASICS: THERMOSET LAMINATES - ARE THEY FOR YOU?

Written by Jack Haley, Vice President of Sales, Oliner Fibre Co., Inc., a Master Distributor of vulcanized laminates and one of the largest US distributors for canvas and fine weave canvas laminates. Mr. Haley has over 35 years in the electrical and electronic insulation field. He can be reached at Oliner Fibre Co., Inc., 1409 Clive Circle, Wilmington, DE 19803, 800-294-2025, 302-764-6858, Fax: 302-764-6859.

Laminated thermosetting products consist essentially of fibrous sheet materials such as cellulose paper, cotton fabric, glass fabric etc. which are impregnated or coated with a thermosetting resin binder and consolidated under high temperature and pressure into hard, solid products of high mechanic strength.

The term "Thermosetting" has been adopted to provide a broad basis for the inclusion of thermosetting resins such as phenolic, melamine, silicone, polyester and epoxy.

After impregnation and drying, the material is cut into sheets which are stacked together between metal pressing plates and pressed under high temperatures and pressures to form laminated thermosetting sheets. Tempera tures in the neighborhood of 270° to 350°F are commonly employed.

Thermosetting laminates properties range from hard materials used for machining to softer plasticized grades for punch press fabrication.

Mechanical applications for thermosetting laminates benefit from properties such as dimensional stability, rigidity, resistance to elevated temperatures, a high strength to weight ratio, and moisture resistance. Thermosetting laminates have superior electrical properties, high electrical strength and excellent electrical insulation resistance. The degree of electrical resistance is dependent on the combination of material used.

Representative Grades

• Paper Base Grade X

• Primarily intended for mechanical applications where electrical properties are secondary. A machining material.

• Paper Base Grade XP-XPC

• Grade XP can be hot punched. Moderate moisture resistance and electrical properties. XPC can be cold punched and sheared sheets up to 1/8" thickness, can be punched cold.

• Paper Base Grade XX

• Good electrical properties. Good machinability.

• Fabric Base Grades C and CE and CEF Grades

• C is a strong tough grade suitable for gears, pulleys etc. Grade CE possesses electrical properties greater than Grade C.

• Glass base grade G-7 (Silicone Resin)

• Extremely good dielectric loss. excellent heat and arc resistance. Flame resistance.

• Glass Base G-9 (Melamine Resin)

• High. mechanical strength. Good flame resistance.

• Glass Base G-10, G-11 (Epoxy Resin)

• Good mechanical strength of room temperature. Good dielectrical loss and electrical strength properties. G-11 similar to G-10, but higher flexural strength.

Applications for Thermoset Laminates

• End Laminates
• Switchboard Panels
• Starter, Generator Insulation
• Terminal Boards
• High Voltage Television Insulation
• Rotor Vanes
• Insulating Washers .
• Gaskets
• Gears

These laminates conform to NEMA and MIL-SPEC MIL-1-24768.

The following chart outlines mechanical, electrical and physical properties for common thermoset materials.

Machining Thermosets

Laminated Plastics can be readily fabricated with standard wood or metal working machinery and tools. Because of the free-cutting characteristics of these plastics high cutting speeds and feeds are possible.

Laminated Plastics can be sheared on metal squaring shears of the guillotine type. Laminates can be sheared up to about 1/8" thick depending on the grade. Laminate grades up to 1/16" and most fabric grade up to 1/8" may be sheared at room temperature. Heat harder stocks to 200-280°F before shearing.

Laminates can be slit to about 5/32" depending on the grade. Harder grades must be heated to 200°F before slitting.

Standard band saws can be used for sawing. Saws should be carbon steel or hardened steel. Teeth from 5 top points per inch. Speed should be up to 8000 surface feet per minute with the work fed as fast as it will cut without forcing.

As far as lathe operations, all standard types of lathes can be used. Tools can be high-speed steel carbide or diamond tipped and should be ground with zero to slightly positive rake.

Progressive dies result in high-speed production but compound dies are most satisfactory for intricate pieces. In general, dies are the same as for metal, except less clearance is used. Allowance must be made for yield and shrinkage. Punching grades up to 1/16" can be punched cold but other grades must be heated prior to punching.

Most fabricated parts require a finishing operation in order to remove burrs etc. Finishing methods include burring, tumbling, cleaning and buffing.

	X	XX	C	CE	L	G-7	G-11	FR4
MECHANICAL
Density GM/CC	1.38	1.37	1.35	1.34	1.34	1.80	1.80	1.82
Tensile Strength	22,000 16,000	19,000 13,000	11,200 9,500	12,000 9,000	14,000 10,000	22,000 18,000	43,000 37,000	40,000 35,000
Compressive Strength	35,000	35,000	36,000	37,000	38,000	40,000	64,000	60,000
Flexural Strength	32,000	20,000 18,000	22,000 18,000	18,000 16,000	24,000 18,000	24,000 19,000	80,000 72,000	55,000 45,000
Impact Strength ILOD	0.9 0.6	0.75 0.6	2.2 1.8	1.6 1.4	1.7 1.8	10.0 9.4	12.0 9.5	7.0 5.5
Rockwell Hardness M Scale	115	115		105	105	100	112	110
Bond Strength	950	1,500	2,000	2,000	1,800	800	1,700	2,500
ELECTRICAL
Arc Resistance	NA	NA	NA	135	NA	220	185	110
Dielectric Strength, Perpendicular	600	700	500	550	525	400	850	800
Dielectric Strength, Parallel	40	50	55	55	45	50	75	65
Dissipation Factor 10 6 cycles	-	.032	-	-	-	.003	.019	.016
Dielectric Constant	-	4.69	-	-	-	3.90	5.20	4.80
PHYSICAL
Heat Resistance, Short Time	275	275	275	300	275	500	400	350
Heat Resistance, Continuous	250	250	225	250	225	400	300
Moisture Absorption	3.6	.25	1.70	1.22	1.80	.09	.10	.11

For more information, contact the author at the contact information listed above.