Three Tips for Designing Hardface Weld and Spray and Fuse Parts
The benefits of hardface welding or spray and fuse coatings are many and amazing. They are impact and abrasion resistant and can stand up to some of the toughest wear environments. As with any industrial wear solution, there are benefits and things to consider when deciding if it’s the solution for you. Due to the heat involved in creating these coatings there are three things you will want to weigh when considering a hardface weld or spray & fuse coating; base material compatibility, when and how to do the final machining, and how to prep the coated area for application.
1. Pick Compatible Base Materials
Base materials will react differently to the heating cycles of welded coatings as well as spray and fuse coatings. These coatings are hardened materials; so, if the base metal moves too much while coating it can result in hairline cracks in the coating or even failure due to cracking. For example, Nitronic 50 and 17-4 PH stainless steels are not recommended for spray and fuse coatings because the coating will usually crack and can even come off when fusing. These parts can sometimes be processed but if you have an option to use 300 series stainless steel or Inconel 625, etc. your costs will be lower, and the process will be easier. Once you have the right base material, you need to know how to machine it prior to coating.
2. Leave the Dimensions Oversized and Wait for Final Machining
No matter what material you choose, the base material will move during hardfacing or applying spray and fuse coatings. This means all final machining on areas other than the coating area should be left oversized. When heat is applied, everything will suck in. Inside diameters will go smaller, lengths will get smaller. The part needs to be designed beforehand to account for this. For example, if applying the coating to the outside diameter of a sleeve, the inside diameter will get smaller and the length will shorten. Everything will “move in.” To ensure enough material is present you will want to leave stock on these dimensions. This also affects any holes or threading on the parts. You must wait until all coating is done to machine these details into your part. The one area you don’t want to leave extra material is the coating location.
3. Leave Room for the Coating
Welded coatings, especially, tend to be thicker than other coatings such as thermal spray coatings. If your part has tight tolerances, you must account for the coating thickness. Most of the time the section to be coated should be undercut to the depth of the desired finish thickness of the coating. This dimension will also move but is mitigated by the addition of the welded material. The weld will be built up past the final dimension and machined to the proper dimension after coating.
Don't Be Afraid to Ask for Help
Hardface weld and spray and fuse coatings are very great solutions when they are incorporated into the initial design of the part. Since they cause dimensional changes, they often can’t be added on as an afterthought to a part the way that thermal spray coatings can be. You must be careful to select the best base material and design the part dimensions to account for coating thickness and dimensional changes due to heat. A company that applies hardface coatings and spray and fuse coatings should be able to suggest dimensions or base materials that would be compatible with the coatings you are interested in to aid in the design of the part.
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