Form in place
Form-in-place gasket technology is becoming widely available.
Every time an engine builder has to lay a silicon bead on a head gasket, he finds himself muttering, “There has to be a better way to do this!”, as he wipes the goo off his fingers. Excess silicone sealant inevitably squeezes out at the joint, creating a freestanding bead of material that is held in place solely by a very thin film at the seal joint, creating the perfect opportunity for it to fatigue off
and find its way into the return oil flow, eventually blocking a screen at the oil pickup.
The advent of ‘bench top’ CNC routers and similar equipment has allowed the development of inexpensive, precisely controlled dispensing systems. Now a well-established technology, simple, two and three-axis CNC stepper motor gantry machines can be retrofitted with lead screw-controlled syringe injectors in order to create custom programmed gasket and adhesive patterns. Or, one can simply purchase a form-in-place gasket machine, which is essentially an already assembled package exactly as described above. Nor does one have to be an expert to refit a gantry router; a number of companies offer kits for this purpose. The price of these systems has come down to the point where moderate-to-large-volume race engine builders can reasonably consider one of these machines for their shop.
Form-in-place gasket technology is the controlled application of a bead of material onto the desired surface. Virtually 100% of the gasketting material is used, since it is dispensed directly in a specific pattern onto a given component: hence, there is far less material waste than with a conventional die-cut gasket. While the majority of applications are planar 2D patterns, complex 3D joint sealing is readily accomplished. Applying the bead into an already machined O-ring groove results in a permanent seal that can be reassembled several times, ideal for race engine applications. Even better, this technique allows for metal-to-metal contact on the remainder of the surface, as the O-ring needs very little cross-section to accomplish its sealing function. Programming the bead ‘toolpath’ is a relatively simple conversion of DXF drawings, something that the most rudimentary cadcam system can accomplish with ease. The cross sectional area of the bead can be adjusted to account for local features as it is dispensed by simply changing the syringe lead screw feed rate relative to the combined XYZ feed rate.
Turnaround is rapid; no custom tooling, moulds, fixturing, silk-screening, or involved setups are required, and chemical companies offer a tremendous range of dispensable materials, including silicones, natural rubbers, foams, and epoxies. Some of these materials can be UV cured for near-immediate assembly. In some cases, such as a silicon bead on a head gasket, assembly can be with the material still ‘wet’, or a small bead can be allowed to dry, and ‘cold flow’ when assembled.
For smaller shops not interested in doing this work themselves, there are now many finishing and coating companies that provide this service. The low cost of the equipment allows them to do this at a reasonable price, and this could become feasible for multiple applications on major gaskets for the engines that a given builder specialises in.
Written by John Stowe.