Carbide Coatings

Case Study 1

Equipment: Vertical Raymond Mill

Name of the wear part: Carbide coating on vertical Raymond Mill body liner

Vertical Raymond Mill

Vertical Raymond Mill

Problem: Wear debris contaminates products and is re-assumed to be one cause of reduced brightness of the product.

Cause of the problem: Air transports (conveys) the powdered product ground inside vertical mill. This causes severe erosion on the body liner. The resulted wear debris are conveyed along with the product.

Our solution: Carbide coating on the wear liners that were selected with following MOC.

  •  Boiler quality base plate of 6mm overlaid with chromium carbide containing weld alloy of 4mm thickness. Weld alloy was Eutectic OA 4601 teromatic wire and was welded using robot on a water-submerged plate. The deposited alloy had 56 HRC hardness.Though harder and more wear resistance carbides deposits were available; their use was restricted by the subsequent bending of wear liners to the fit the body. The inside geometry of the vertical mill body and the location of retaining holes were non-standard and varied on a mill-to-mill basis causing fitting delays.
  • Packing material failure due to sleeve surface roughness.
  • Mild steel plate of 10mm thickness was coated with Ni-Cr-B-Si alloy containing tungsten carbide to a concentration of around 50%. The deposit thickness was 0.4mm and hardness was around 60 HRC for the matrix and 850 Vickers for the carbide particles. Deposits were applied by the spray and fuse process and powder used was SF 15211/SF 10112 of Eutectic. Equipment by which spray had been done is Castodyn 8000 of Eutectic + Castolin Switzerland. The process is fast and plates can be bend to one desired shape without many efforts. Fitment is also relatively easy. The cost of providing the needed 0.8mm thick coating may be high.

Provide a long lasting wear resistant surface of ceramic oxides or metallic carbides. We have a robotic Plasma transferred arc system (PTA) and flame spray equipment to apply coatings of tungsten carbide in a nickel chrome boron matrix and chromium oxides. The coating thickness is selected based on application wear potential and varies from 0.5mm to 1.5mm in thickness. For severe wear applications PTA coated sleeves last longer.

Industries: Thermal power plants, Sugar industries, Oil and gas sector and chemical process plants are major consumers.

Case Study 2

Equipment: Atomiser

Name of the wear part: Wear part of wheel disc

Atomiser_Disc1

Atomiser Disc

Atomiser_Disc2

Atomiser Disc

Problem: Wear part is made out of Boron Carbide material, which is a kind of ceramic material and is brittle in nature. The raw material impinges at a very high velocity on a rotating disc. The resultant erosion thins the Boron Carbide till it suddenly break in to the pieces. The disc is rotating at 24,000 RPM and the sudden breakage causes heavy damage to other parts.

Cause of the problem: Main cause of wear is erosion at a temperature of 540 C along with centrifugal force due to high rotational speed. The impinging material is hard and has a tendency of caking. This reduces some wear but increases imbalance that may cause vibration and subsequent failure due to variance in centrifugal forces.

Our solution: Boron Carbide was replaced by wear part made of machinable and harden able Titanium Carbide. This material can be processed more easily to manufacture this rather complex profile. TiC isn’t brittle, has high erosion resistance and retains hardness at an elevated temperature of 540 C. The low density doesn’t induce stress on the bearings of the wheel disc that is rotating at 24000 RPM. This application has now been standardized. The wear part is inspected every month during the routine maintenance schedule to study the thinning and to decide on replacement period. The end user managed to save a huge amount of money because of avoidance of sudden break down and unscheduled shut down.