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What is the difference? Silicone coated fabrics and silica fabrics for protection of surfaces during hot works

 


 

Introduction

Many high temperature resistant fabrics exist and some are particularly well-suited for welding operations and what is more generally defined as ‘’hot works’’. Such welding fabrics have been thoroughly tested by the U.S. Navy (NAVAL SEA SYSTEMS COMMAND), since welding operations take place at sea. Potential fire would have dire consequences for equipment, personnel and mission operability.

From these testings, specification MIL-C-24576A was established. Three products were specified :

TABLE II

Type I / Class I : Heavy silica cloth (36 oz)

Type I / Class II : Light silica cloth (18 oz)

Type III : E-glass silicone coated fabric : 30-36 oz/sq.yd. / 0.035'' to 0.043'' thick

Comments

For horizontal protection where molten metal will slowly cool down, Robco 188CH (MIL-C-24576A TABLE II - Type I / Class I) remains the material of choice.

For vertical protection, a lighter silica fabric like Robco 84CH (TABLE II - Type I / Class II) is a product with a proven track-record. Most welding fabrics used in the nuclear industry are silica-based fabrics, using as reference MIL-C-24576A.


Recommendations for silicone coated fabrics

6.1.2 Type III material is a glass fabric that has been silicone coated to improve abrasion resistance,

durability, and strength. This silicone coating tends to repel molten metal rather than retain the slag, and is meant to be used in less severe welding and cutting applications than type I. The MIL-C-24576A specification recommends that Type III (silicone coated glass fabric) is for welder’s curtains, and is limited to use in vertical positions. The silicone coating provides the added advantage of repelling liquids, some potentially dangerous.

Silicone coating on welding fabrics typically equates to an amount of approximately 6 oz (total both sides). As per MIL-C-24576A, this means a glass fabric of about 24 to 30 oz. Robco 7320-R fabric falls in that category.

Independent testing at the Alberta Research Council demonstrated that Robco 7171 (red or silver coloured) an 18oz fabric can also perform properly. A report is available upon request.

Can a lighter / more economical fabric be used on vertical applications, even if it means to put multiple layers at a time? From decades of experience, the thinnest/lightest glass fabric ever being used in petrochemical is 17.5 oz (no silicone coating). Thus, depending on the level of activity, the criticality of the area and type of welding operations taking place, the best ratio of safety/cost-performance must be considered.

Conclusion

It all comes down to the best ratio of safety/cost-performance. Robco 84CH silica fabric, silicone coated E-glass fabrics like Robco 7320-R (meeting MIL-C-24576A TABLE II - Type III ) or Robco 7171-R represent good choices of silicone coated E-glass fabrics for the protection of vertical surfaces during hot works. Robco 188CH heavy silica fabric remains the safest material for horizontal protection.

 

Note : Robco products were used as examples as they represent the benchmark for heat resistant fabrics with an excellent track record.

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