Category Archives: Shims

Product Spotlight: Polyimide Shims

At Shimco, we have over 25 years of experience producing many different kinds of shims for a range of industries and applications. We are truly experts in shims.

One of the many types of shims we produce—used mainly for the aerospace industry, but certainly not limited to this—are polyimide shims, made out of a polyimide polymer such as Dupont’s Kapton®.  The concept of these types of shims is the same as others, but there are certain qualities of the material that make it advantageous for particular needs and applications.

Polyimide shims begin in foil form, just like our metal laminates, but get glued with a unique and proprietary glue compound developed by Shimco. The end product can be peeled just like any other shims but can also be pressed back together by hand if the incorrect number of lawyers are removed.

These polyimide shims are often used between metallic and non-metallic parts. Since polyimide is an electrical insulator, it aids in the electrical isolation of the adjacent parts. This electrical insulation property is important as it helps to stop the transmission of electricity, such as is the case during in-flight lightning strikes.

What’s another benefit? Polyimide is thermally stable over a wide temperature range, as are carbon fiber parts. However, metallic parts expand and contract more readily under temperature fluctuations.  Placing Polyimide between metallic and carbon fiber parts provides a buffer for this thermal expansion and contraction, helping to alleviate some of the stress and pressure on the assembled parts when temperatures fluctuate.

Polyimide is also resistant to reaction with many chemicals.  Placing it between chemically dissimilar parts helps to prevent undesirable reactions between those parts, reducing the need for frequent inspection, maintenance and possible repairs.

Check out an example of these shims that were produced for a client of ours, and feel free to contact us with any questions or for more information.

Understanding Different Types of Shims

Shims are integral for many various parts, serving a range of industries and applications. However, not all shims are created equal, and different shims serve different purposes. Below is a description of four different types of shims, and what they are used for:

Traditional Shims: Shims are thin pieces of material used to fill in small spaces or gaps. Typically a solid piece of metal, this can be a spacer, washer, or filler. Traditional shims are designed into the assembly as pre-planned parts. They are not adjustable, and are designed with specific thicknesses, lengths, widths, etc.

Edge Bond (Adjustable) Shims: These are shims measured for inaccuracies. Technicians using them will pull off one or three layers to compensate for machining errors, whereas other products are designed into the assembly, and then they remove layers.  Shims are designed to fit into certain spaces, which are designed for adjustment, but are part of the assembly package. These are for very fine adjustments between parts being assembled. Machined out of foil, 20-80 layers are cut out using CNC machining, edm wire cutting, and other processes. The foil layers are then put into jogs, and the edges are glued with specific aerospace-quality glue. After that, the layers are peeled off to make the length of the assembly to the exact specifications.

 tapered_shims_bannerTapered Shims: When surfaces have a taper on them, tapered shims are used to fit in between the other parts. They can make the assembly tight by pushing apart the pieces, and sometimes they will push into the assembly, with the rest of the shim designed into the assembly.

Peelable (Adjustable) Shims: These shims have flat, three-dimensional layers that are glued together so that the technician can peel away layers not needed to get to the exact right thickness.  Typically they are 2,000th-3,000th of an inch thick.