Flame retardant compound

[Grump]

Hi

Need a basic formulation for above mentioned compound .

Cost is the major factor here , so am looking at what the cheapest option would be to reduce the flammability of exsisting offspec compounds .

Article to be molded is a rubber impact for conveyor rolls .

TIA

 

[GrahamBennett]

Grump, what hardness do you require?

 

[Compositepro]

You give very little information, but alumina trihydrate (ATH) would be one option.

 

[Grump]

Only realised after posting how vague the query was .

At present we are using offcut rubberlining rubber , predominantly 45 - 50 shore hardness . To this we add Aluminium Trioxide , Zinc Borax and paraffine wax .

The spec given is that a 2mm thick strip sample needs to extinguish itself within 5-7 seconds after being lit . The above chemicals achieve the result required but add quite a cost to the compound ,and also the amounts needed affect the hardness drastically .

Hardness required is between 65 and 70 shore .

 

[GrahamBennett]

First of all, flame/fire resistant compounds are almost all contain very expensive ingredients. A halogen-containing polymer is essential. These burn but are self-extinguishing. Phosphate esters (e.g. tricresyl phosphate) are good softeners or plasticisers. Another softener is liquid chlorinated paraffin wax. Mineral fillers are preferred for flame resistance so carbon black levels must be kept to a minimum. Flame retarders are antimony trioxide (care – toxic), zinc borate, and alumina trihydrate. In halogenated polymers antimony trioxide reacts to form antimony trihalide, which is the flame extinguisher. Zinc borate decomposes to form a hard crust on the surface of the material. Alumina trihydrate releases it’s water of crystallisation as steam at elevated temperatures, causing the flames to extinguish by cooling the flame front down. Recent developments include a new family of flame and fire retardants based on chloroethyl phosphate. The heat resistance of NR can be impaired by blending with PVC and the use of tricresyl phosphate as a plasticiser.

You should replace the paraffin wax and replace it with 5 or 6phr of either chlorinated paraffin wax or tricresyl phosphate.

I would not want to guess what else is in your base compound but you should remove anything that is flammable such as mineral oils. Since your desired hardness of 60 - 65 is above what you are finding now, do not replace any oil removed. If the hardness is still on the low side, add ground or precipitated whiting, or hard clay.