Powder Coating – Masking.

Powder Coatings Ltd are able to offer comprehensive advice on any masking requirements you may have, we source products from all the major masking suppliers as well as commissioning bespoke masking solutions for components that cannot be masked using off the shelf materials.

There will often be occasions when the parts that you make require certain areas to be kept free from Powder Coating.

This can be for a variety of reasons;

  • Parts that need to fit together and have tight tolerances such as two tubes that form an assembly. Any Powder Coating on the mating surfaces would impede them fitting correctly and result in wasted time/effort cleaning the mating surfaces.
  • Holes or recesses that have bearings fitted into them; Bearings are usually a ‘press fit’ and the inside diameter of the part that accepts the bearing must be the correct dimension.  A build-up of Powder Coating can interfere with the fit and residues of powder that are removed/loosened during the fitting process can block the bearings and stop them running freely.
  • Internal or external threads; if a thread is coated with powder this will cause problems during the assembly process. Removing powder coating from tapped holes or threaded surfaces is extremely difficult and can waste a huge amount of time and slow down the assembly process after coating.
  • Gasket surfaces; many machined components that have to be fitted together have surfaces that require gaskets or seals between the two components. The mating surfaces have to be kept free of Powder Coating to ensure that no leaks occur and that the components fit together precisely.
  • Electrical Earthing;  All metal electrical components or enclosures require an ‘earthing point’ This is an area of the component surface that has no coating applied so that an earth tag or connection can be fixed to the surface  of the part ensuring the part can be used safely.

The range of masking materials and parts that are available is huge. Long gone are the days when a worker with a roll of paper masking tape would attempt to mask areas accurately or roll up little wads of tape and push them into threaded holes, all of which was never very successful and left sticky residues on the surface of the parts as the glue on the tape melted in the oven during the curing process.

Masking Tapes; these are made of a polyester material that is usually 2 mil thick and able to withstand temperatures 200 + degrees centigrade. It is available in a wide variety of widths ranging from 1/8” up to 9”. The adhesive type is silicon based so it can withstand the heat and leaves no sticky residues when removed.

Die Cut Discs or rectangles; supplied on a roll these are small die cut discs/rectangles of polyester masking material that can be easily peeled off the roll and applied accurately to components where required.

Tapered Plugs; used to insert into holes the taper ensures a tight fit; they are able to withstand up to 200 + degrees centigrade so the parts can withstand the heat of the oven with them in situ and be removed after curing.

Caps; these are used to fit over external threaded parts or machined spigots while they are being coated. They are sometimes used to fit over threads and spigots after finishing so that the parts do not get damaged in transit.

Die Cut Shapes; in cases where specific areas of a component require masking and off the shelf die cut discs or rectangles are not suitable it is now possible to produce die cut shapes that exactly match the relevant area. Using Computer Aided Drawing technology the masking material producer makes a bespoke tool that exactly cuts the required shape using adhesive backed polyester sheet. The bespoke shapes are then applied to a roll of base material so that they can be peeled off as and when required and applied accurately to the relevant area that needs masking.

Bespoke Silicon Tubing; this is useful when a specific internal diameter needs to be free of powder coating and a stock item cannot be found. As long as the precise internal dimension is known an extruded bespoke silicon tube can be produced with the outside diameter of the tube exactly matching the inside diameter of the part that requires masking. The tube can be cut to the specific length required and fitted inside the component prior to coating.  

Bespoke masking pieces; Certain parts have irregular shapes or multiple angles that need masking. We can commission bespoke masking pieces. A multi impression tool is produced that matches the exact shape of the area to be masked. Molten silicon rubber is injected into the tool and after cooling the bespoke masks are trimmed and ready for use. 

Liquid Mask; An air drying masking film that can be applied by spray, brush or roller. After coating the mask can be peeled off and disposed of. This is an ideal way to mask irregular shaped surfaces and prototypes prior to bespoke masking pieces being produced.

Another important issue to remember is the information supplied by the customer to the powder coater. Very often masking requirements are an ‘after thought’. The coater will be supplied the drawing or sample component and generally informally told that a particular thread or holes need masking.  This is not very efficient and if not fully understood can result in parts that are not masked to customers’ requirements causing delays and un-necessary rejects. The best way to inform a coater exactly what parts or areas need masking is to produce a bespoke Masking Drawing and add it to the drawing register for the part.  With Computer Aided Drawing Systems it is relatively easy to highlight in a different colour the specific areas, threads or spigots that do not require coating. The coater can attach this drawing to his Route Card so that all works personnel are fully informed about the specific masking requirements.

Contact roger@powder-coatings.co.uk with any questions or requests for more information.