Easy and Affordable Spare Parts

by Marco Radukic Labtimes 05/2016

Moulding is a very old production technique, already applied by the ancient Greeks and Romans to fabricate bronze statues of their gods and heroes. But it is also a very modern and smart method to reproduce hard-to-find spare parts of lab apparatuses.

In laboratory work, sooner or later, small plastic spare parts are needed, many of which are sold (if at all) exclusively by the manufacturer. Prices for these spares can be ridiculously high. A set of two spacers for the manufacturing of polyacrylamide gels, for example, can cost up to 50 euros. We investigated universally applicable alternatives and came up with the classic moulding technique.

Two simple steps

In the first step, a negative form of the part is produced by moulding with silicone. Broken work pieces need to be repaired before moulding, so that the original form is maintained. To save silicone, the moulding container should not much exceed the dimensions of the work piece. We attached our spacers to the bottom of a small plastic box with two percent agarose. Agarose can also be used to level uneven container bottoms before attachment of the work piece.

Spacers to be reproduced are attached to the bottom of the moulding container with agarose. Photo: Marco Radukic

For the moulding itself, we used a two-component silicone. Silicone for moulding purposes can be bought online with various properties and in small quantities. Our silicone needed eight hours curing time, then the piece was demoulded. The finished mould can be used many times when stored away from light.

The second step is the casting of the copied pieces with resin. The most common resins are epoxy, polyester and polyurethane resins, of which epoxy resin most likely offers the best chemical resistance. However, not every resin is directly compatible with every silicone. Some may require a release agent, which might limit the accuracy of the pour (always refer to the manufacturer’s specifications). We, therefore, decided to use a polyurethane resin (available from composite vendors or online shops) that can be used without a release agent together with our silicone.

Resin and hardener are mixed in accordance with the manufacturer’s instructions and quickly poured into the mould. The resin can be vented in a vacuum bell jar before pouring to make sure that no air bubbles are embedded into the cast. Air bubbles can also be removed with a slim metal spatula. For our application, however, this was not necessary, since the used resin is of very low viscosity and it worked right away without venting. We added a drop of white colour to the resin before the pour, since the new spacers would otherwise be crystal clear.

The copied spacers are identical to the original parts, down to the finest detail. Photo: Marco Radukic

Five percent of retail price

After four hours curing time, our brand new spacers were finished. Identical to the original, down to the finest detail (which would be impossible with the alternative 3D printing), high in strength and UV resistant thanks to the used resin. Hardening polyacrylamide and even a 24-hour storage in isopropanol could not damage our spacers.

Incredibly, the cost per piece was only five percent of the retail price.

(Marco Radukic is a master student in Kristian Müller’s Cellular and Molecular Biotechnology Group at the University of Bielefeld)

Last Changed: 05.10.2016