Chapter 13 - Thick Barrier Linings Flashcards
What is natural rubber?
Derived from latex obtained from hevea trees and is coagulated with acetic or formic acid
Unsaturated hydrocarbon known as polyisoprene
What is synthetic rubber?
Any one of a group of manmade elastomers with one or more of the properties of natural rubber.
What is vulcanization?
It is a physicochemical ( physical and chemical) change resulting from the cross-linking of the unsaturated hydrocarbon chain of natural rubber (polyisoprene) with sulfur, and the application of heat.
What are the three factors that affect the properties of the vulcanizate (vulcanized product)?
Percentage of sulfur and accelerator used
Temperature of the curing process
Time of cure
What methods are used to cure (vulcanized) rubber?
Autoclave (vulcanized) cure Internal steam cure Atmospheric steam cure (also called exhaust steam cure) Hot-water cure Chemical cure
What are the three categories of natural rubber?
Soft
Semi-hard
Hard
In lining constructions which rubber is used to form a “tri-ply” sandwich?
Semi-hard or hard rubber between two layers of soft rubber.
What are some various types of synthetic rubber?
Butyl rubber Neoprene rubber Nitrile rubber Chlorobutyl rubber Hypalon types
What are the typical surface preparation requirements for rubber?
1) steel shall be new, full-weight steel, free from structural defects
2) steel plate shall be flat with no appreciable warp or buckle
3) steel plate should have a minimum thickness and weight as specified
4) vessel must be braced to avoid bulging
5) all welds to be continuous, peened, and ground to remove sharp edges and high spots
6) edges and corners should be ground to a minimum radius as specified
7) all weld spatter should be removed
8) blast cleaned to NACE 1/ SP 5 white metal with a surface profile of 1.5 to 2.5 mils.
What are some of the causes of failure with rubber linings?
Incorrect product selected for the intended service
Using rubber after the shelf life has expired
Using rubber lining that was not properly stored. Rubber must be kept cool in storage because, with heat it can vulcanize on the roll. If this occurs, the material should be discarded.
Incorrect application process
Inadequate cure.
What are the three methods for applying polyethylene?
Melting the resin and extruding it onto the surface of the article
Heating the work piece and then immersing it into a fluidized bed
Flame spraying
What are the two major classes or rubber?
Natural and synthetic
