AND SOLUTIONS RATED A+
✔✔What are the four distinct stages powders pass through when a heat source is
applied? - ✔✔The flow stage- which occurs when the particles of powder begin to flow,
but are not fully liquid
Wetting stage- which occurs when the particles of powder absorb more heat, fully
liquefy, and wet the surface
Gel stage- which occurs when the particles of the powder begin to gel, converting into a
solid
Curing stage- allows for further changes to take place, permitting the powder to cure
properly
✔✔Advantages and disadvantages of plural component airless spray over single piston
airless spray systems - ✔✔Advantages:
Accurate mixing of materials without human element
Ability to spray very thick solvent free materials without thinner
The ability to spray materials with very short pot life
Disadvantages:
Cost is much higher than cost of single piston pump
Higher education requirement for the Mechanic
High voltage electricity is required for the heaters
Applicators job more difficult with multiple hoses
✔✔2 major classes of rubber - ✔✔Natural- derived from latex obtained from Hevea
trees and is coagulated with acetic or formic acid.
Unsaturated hydrocarbon known as polyisoprene
Synthetic- any one of a group of man made elastomers with one or more of the
properties of natural rubber.
✔✔Vulcanization - ✔✔Vulcanization 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.
✔✔Three factors that affect the properties of the vulcanizate (vulcanized product) -
✔✔Percentage of sulphur and accelerator used
Temperature of the curing process
Time of cure
✔✔Methods used to cure (vulcanize) rubber are - ✔✔Autoclave (vulcanizer) cure
Internal steam cure
Atmospheric steam cure (also called exhaust steam cure)
Hot water cure
Chemical cure
, ✔✔The three categories of natural rubber are - ✔✔Soft, semi hard, hard
✔✔What is a tri-ply lining - ✔✔Lining construction used to form a sandwich which is
semi-hard, or hard, rubber between two layers of soft rubber
✔✔Some various types of synthetic rubber are - ✔✔Butyl rubber
Neoprene rubber
Nitrile rubber
Chlorobutyl rubber
Hypalon types
✔✔Typical surface preparation requirements (rubbers) - ✔✔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 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 with surface profile of 1.5-2.5 mils
✔✔Some of the causes of failure with rubber linings may be - ✔✔Incorrect product
selected for the intended service
Using rubber after the shelf life has expired
Using rubber lining that wasn't stored properly. Rubber must be kept in cool storage
because with heat it can vulcanize on the roll.
Incorrect application process
Inadequate cure
✔✔Three methods for applying polyethylene are - ✔✔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
✔✔The standards engineering society (SES) describes a standard as - ✔✔A document
that applies collectively to codes, specifications, recommended practices,
classifications, test methods, and guides, which have been prepared by a standards
developing organization or group, and published in accordance with established
procedures.
✔✔Voluntary standards - ✔✔Are standards established generally by private sector
bodies that are available for use by any person or organization, private or government.