An Ultra-Stable Combination
The filling of steel and cast structures with epoxy resin-bonded mineral casting is a well-established technique. More than that, machine bed assemblies are increasingly being designed as hybrid structures from the outset – using EPUFILL technology from RAMPF Machine Systems.
Cavities in steel or gray cast iron machine bed components have been filled with castable materials, usually epoxy resin-bonded mineral casting or cement-bound concrete, since the start of the 1980s. This technique has thus been tried and tested for more than three decades, and has been finely tuned throughout this period.
Marc Dizdarevic, CEO of RAMPF Machine Systems, confirms this:
At first, cavities were often filled in a subsequent process to improve dynamic performance. Since then, this technique has become a process in its own right that is offered on an industrial scale, i.e. machine bed assemblies are designed with a hybrid structure from the outset.
EPUFILL – outstanding damping properties guaranteed
RAMPF Machine Systems adopted this technology early on and has established a dedicated division – EPUFILL. This is where structures that are welded or cast, made of steel or comprised of a metal shell are filled with the in-house product EPUMENT® mineral casting. The key benefits include much better damping properties and more favorable thermal component behavior due to the greater thermal capacity.
“We made a conscious decision to opt for filling with epoxy resin-bonded mineral casting. The crucial advantage of this compared to filling with water-based concrete is that the filling material adopts a solid bond with the outer sheath, thereby creating a composite structure with excellent long-term stability,” explains Dizdarevic.
The text below focuses on steel composite structures filled with EPUMENT® mineral casting.
The steel sheath is filled in stages: metering, mixing, filling, compaction, curing. The raw materials must be metered and mixed with precision. Depending on the viscosity of the filler material and the fill geometry (such as wall thickness), compaction is ensured during filling by means of shaking and/or vibration.
Precision finishing: milling, drilling, grinding, and shaving can be used for precision finishing purposes. Manufacturers recommend that the filled machine bed component is processed to achieve its final precision only after it has fully cured (approximately one to two weeks after filling).
Dynamic properties: the special feature of hybrid machine bed assemblies is that the material composite contributes new – usually desirable – properties. For example, damping filler materials have a positive impact on dynamic properties such as vibration amplitudes and natural vibration, which also reduces noise emissions. The greater mass of steel composite structures generally has positive dynamic effects.
Thermal performance: steel composite structures are less sensitive to short-term temperature fluctuations due to the high specific thermal capacity and low thermal conductivity of EPUMENT mineral casting. Furthermore, cooling or heating lines can be integrated to control the temperature of machine bed components.
Static performance: the overall static performance of steel composite structures is influenced by both the steel sheath and the filling. The modulus of elasticity, strength of the filler materials, and wall thicknesses of the steel sheath are also important in this context. (Right: without EPUFILL; left: with EPUFILL).
Key parameters for the long-term stability of machine bed components with consistent properties throughout their service life include the adhesive force between the hybrid partners and the moisture absorption of the filling. This is where mineral casting differs greatly from concrete as a filler material. Given identical sand-blasted contact surfaces, concrete achieves a maximum of 50 percent of the bonding strength with steel. Due to the very high moisture absorption of concrete fillings, the pouring surface also needs to be sealed.
Marc Dizdarevic sums up the technology’s benefits:
Using EPUFILL technology to manufacture machine bed components is worthwhile first and foremost when dealing with small order quantities, such as when producing prototypes and special machines that need to accommodate high static and dynamic stresses. This technique saves the high one-off costs of the mold while still utilizing the numerous advantages of mineral casting.