CASE & PARTS GP-PLANETARY 9P6238 - Caterpillar

air through the nozzle transports the stream of molten droplets onto the bore wall. The high kinetic energy causes the particles to flatten when they impinge on the surface of the substrate. The heat transfer between the flattened particles and the substrate causes a rapid solidification. Thus the coating is made up of these solidified droplets stacked one on top of another along the surface.
Illustration 3 g02723951
Typical coating cross section illustrates lamellar structure (At 500X magnification).
Since multiple particles are required to create a coating, several passes of the gun applying material are required to produce the desired coating thickness. The formed coating is used for "surface" type applications and will not provide any strength to a part. The only function of the coating is to add some desirable characteristics to the surface that is lacking in the worn piece part. Desirable thermal spray characteristics include:
Better wear characteristics
Dimension restoration
Corrosion protection
Electrically conductive or electrically resistiveBecause of the nature and structure of metal spray coatings, they should not be used when the coating will be subjected to line or point-to-point contact and severe, sharp, and repeated type of impact.Surface Finishing and Post-Coating Treatment
Surface Finishing
Finishing techniques for PTWA sprayed deposits differ from practices followed for standard machined surfaces and for solid materials. Since PTWA sprayed deposited coatings consist mainly of mechanical bonds, excessive tool pressure or high feed rate results in premature and excessive tool wear and causes the coating to spall, crack, or pit.Finishing techniques used for a PTWA sprayed coating depend on the type of material applied, coating hardness, and desired surface finish.Machine finishes can be achieved with carbide inset type tools. Follow the recommended parameters for RPM, depth of cut and surface feet per minute requirements. Recommended inserts include:
ISCAR DNMG 432 TF IC507
Carboloy DNMG 432 MF CP200
Kennametal DNMS 432 KD100CPD
Sandvik DNMG 432 PF G4015 or G4025Wet type grinding is recommended when the coating is to be finished by grinding.Post-Coating Treatment
All sprayed coatings are considered to besomewhat porous. Porosity is the measurement of the density of a coating when compared to the same type of material in solid or cast from. Generally, the porosity of a coating will be found to be beneficial for bearing type applications since the coatings will retain lubrication. When a lubrication function is not desired or where the coating will be exposed to a corrosive type of environment or where fluid leakage is not desired, the coating should be treated with a sealer. The recommended sealers are: Loctite 290, a wick type air drying sealer, or Metco 185 crystalline wax sealer. Both types of sealers are easy and simple to apply.Support Equipment and Operations
Masking Aids
Masking is required to protect critical surfaces and holes from the effects of thermal spraying. Any type of material that can withstand these effects is considered a suitable masking material.The mask can be permanent sheet metal or a temporary material. Temporary-type masking materials are:
Hard Rubber
High temperature silicon rubber
High temperature fiber type materials
Several layers of duct or masking tape
Cloths
LiquidsSpray Booths and Rooms
Any thermal