KWS Manufacturing

Screw Conveyor Surface Finishes

The surface finish of the interior and exterior of a screw conveyor can be very important to the success of the overall bulk material process. Certain bulk materials such as chemicals or food products require special finishes to maintain the integrity of the bulk material and prevent contamination. Understanding the bulk material process is very important to determining the proper surface finish of a screw conveyor.

Most industrial applications such as conveying limestone, biosolids or offal require no special polishing of the welds, flights or pipe on the interior of a screw conveyor. Likewise, the exterior of a screw conveyor requires no special polishing of the welds or surfaces of the troughs, trough ends or covers. Pits and crevices are allowed at welded joints because the bulk material will not contaminate or corrode.

Special industrial applications such as conveying food ingredients or specialty chemicals require special polishing of the welds, flights and pipe on the interior of a screw conveyor. Continuous welding of the flights to both sides of the center pipe is typically required to eliminate any pits or crevices. The surfaces of the flights, welds and pipe are then polished to a specific grit finish to meet the requirements of the application. The exterior of a screw conveyor may require special welding and polishing of the troughs, trough ends and covers. No pits or crevices are allowed at welded joints because the bulk material could be contaminated or cause corrosion.

The KWS screw conveyor surface finishes shown below address the needs of almost every bulk material application. Surface finishes are called out for the interior and exterior of a screw conveyor including the welds, flights, pipe, troughs, trough ends and covers.

The KWS screw conveyor surface finishes are much more comprehensive when compared to the CEMA surface finishes. KWS addresses the surface finish requirements of the welds, flights, pipe, troughs, trough ends and covers while CEMA only addresses the surface finish of the welds on a screw conveyor. The CEMA surface finish call outs are incomplete and can be confusing to the Customer, possibly creating a problem.

Our goal at KWS is to exceed the expectations of our Customers by providing screw conveyors with the proper surface finish for the application and process.

Screw Assembly

KWS Industrial Finish 1S

Weld: Weld spatter and slag removed, 40 to 50 grit finish, pits and crevices permissible (CEMA II)
Flight Surface: Mill finish, no grinding or polishing on steel surfaces
Pipe: Mill finish, no grinding or polishing on steel surfaces

KWS Industrial Finish 2S

Weld: Weld spatter and slag removed, 80 to 100 grit finish, pits and crevices permissible (CEMA III)
Flight Surface: Mill finish, no grinding or polishing on steel surfaces
Pipe: Mill finish, no grinding or polishing on steel surfaces

KWS Industrial Finish 3S

Weld: Weld spatter and slag removed, welds as laid, no pits or crevices permissible (No CEMA equivalent)
Flight Surface: Mill finish, no grinding or polishing on steel surfaces
Pipe: Mill finish, no grinding or polishing on steel surfaces

KWS Industrial Finish 1SP

Weld, Flight Surface and Pipe: 150 grit finish on all surfaces, no pits or crevices permissible (No CEMA Equivalent)

Trough Assembly (Including Trough Ends and Covers)

KWS Industrial Finish 1T – Interior and/or Exterior

Weld: Weld splatter and slag removed, 40 to 50 grit finish, pits and crevices permissible (CEMA II)
Trough Surface: Mill finish, no grinding or polishing on steel surfaces

KWS Industrial Finish 2T – Interior and/or Exterior

Weld: Weld spatter and slag removed, 80 to 100 grit finish, pits and crevices permissible (CEMA III)
Trough Surface: Mill finish, no grinding or polishing on steel surfaces

KWS Industrial Finish 3T – Interior and/or Exterior

Weld: Weld spatter and slag removed, welds as laid, no pits or crevices permissible (No CEMA equivalent)
Trough Surface: Mill finish, no grinding or polishing on steel surfaces

KWS Industrial Finish 1TP – Interior Only

Weld: 150 grit finish, no pits or crevices permissible (CEMA IV)
Trough Surface: Mill finish, no grinding or polishing on 2B surfaces, plate surfaces to be polished to 150 grit finish

KWS Industrial Finish 2TP – Interior Only

Weld and Trough Surface: 150 grit finish on all surfaces, no pits or crevices permissible (No CEMA Equivalent)

Standard Exterior Paint Finish for Carbon Steel Components and Assemblies

(Up to 220-Degrees F)
Surface Preparation: Hand tool clean per SSPC-SP2
Paint: One shop coat of KWS gray enamel, 2 to 3 mils minimum DFT

Standard Exterior Paint Finish for Carbon Steel Components and Assemblies

(Between 220 and 600-Degrees F)
Surface Preparation: Near white blast per SSPC-SP10
Paint: One shop coat of KWS high temperature paint, 2 to 3 mils minimum DFT