Proper machine installation is critical in maximizing reliability and minimizing life cycle costs. Conversely, improper installation is a chronic source of downtime, poor product quality, reduced capacity and high operating costs. While installation requirements vary depending on the type of machine and its function, there are basic best practices that must be followed.
Determine whether the support structure (foundation) has sufficient mass and stiffness to permit the machine to operate in or near a state of equilibrium. Lack of mass and/or stiffness causes normal operating forces to generate abnormal vibration levels that reduce useful life and increase the frequency of maintenance.
The foundation must be capable of carrying the applied load without settlement, flexing or crushing. Foundations for heavy machinery are usually concrete or structural steel structures. For these installations, an independent concrete pad is poured that has sufficient mass and stiffness to support the machine-train and absorb the forces generated by normal operations. The total foundation mass and its related support structures should be at least five times the total rotating or moving mass of the machine-train.
Some machines must be mounted on a mezzanine. In general, these machines do not have an adequate support structure. Also, direct mounting on concrete or deck plate floors introduces a resonance problem. Normal operating forces are transmitted directly into the floor, which acts as a soundboard and amplifies these energies. In the best case, these amplified energies only result in higher than normal noise levels. In many cases, they coincide with one or more natural frequencies of the machine or foundation and can result in serious, chronic problems.
Anchor bolts secure the machine to its foundation. The use of proper methods ensures a rigid, permanent mating of parts. When machines are anchored to a concrete foundation, J-bolts are fixed into the concrete as it is poured. Size bolts to ensure adequate holding torque and to prevent them from loosening over time. Exercise care when selecting the grade of bolt, and determine if the mounting pattern will be rigid enough to lock mounting plates to the foundation. The use of hydraulic concrete and straight mounting bolts is not recommended because these bolts tend to loosen with time.
For machines mounted on mezzanines or upper floors, anchor bolt selection and configuration is even more critical. In this case, the anchor bolts must perform two critical functions: they must fix the machine in place so it cannot flex, bend or deflect; and they must isolate the machine from the foundation to prevent transmission of generated energies into the foundation.
Machinery generates energy (vibration) that must be either absorbed by the foundation or trapped within the machine. Cross talk, in which energy generated by one machine is transmitted into another machine, is a chronic source of reliability problems. This is especially true in plants having multiple continuous process lines such as paper machines, high-speed printing and metal processing lines.
When a machine is mounted on a concrete pad, the pad should be independent from the surrounding floor. Normally, the pad is formed and poured directly on bedrock and has a ?-in. to 1-in. separation between it and the surrounding floor to ensure isolation. This allows energies generated by the machine to be absorbed and prevents outside sources of vibration from entering the machine.
When a machine must be mounted directly on the floor, isolation must be accomplished by using springs or elastomeric pads specifically designed to absorb or stop transmission of generated energy. Exercise care when selecting them. Isolators are designed for specific, relatively narrow bands of frequencies (e.g.,18 to 21 Hz) and will not isolate frequencies outside their functional bandwidths. When properly sized and installed, they do a good job of protecting machines from both generated and outside energies sources. Improperly sized or installed, they are absolutely worthless.
With few exceptions, machinery is designed to operate on a true horizontal plane.
Normally, a liquid level is sufficient to level a machine properly, but new techniques such as laser alignment devices can also be used. The entire machine-train must be level and in the proper horizontal plane.
The most common failure is the method used to shim mounting feet. Too many plants fail to use shim packs that provide full footprint support. Shim packs provide a rigid connection between the mounting feet and the foundation. The surfaces must be flat and parallel to ensure there are no voids or flexing in the final bolted joints.
The final requirement is proper alignment of the machine's driver and driven units. Whereas leveling ensures that the entire machine-train is level to the earth, alignment ensures that the common shaft between the outboard driver bearing and the driven unit are in exactly the same vertical and horizontal planes. Generally, reverse-dial indicators or laser alignment instruments are used to provide the required alignment adjustments.
Alignment specifications vary depending on machine type. But normally, the shafts must be parallel and in the same plane within a maximum of 0.001 in to 0.002 in.
Actual installation requirements are provided for new machinery. The information can be found in the vendor's installation, operation and maintenance manuals. Follow the recommendations to ensure proper, trouble-free operation. Short cuts or omissions during installation process will guarantee that a machine becomes a chronic maintenance headache.
One final word,check existing machine installations periodically. Foundations settle, bolts corrode or become loose, shim packs deteriorate and alignment changes. Periodical inspections will help prevent many of the problems that result in lost production time, poor product quality and elevated costs.
Contributing Editor Keith Mobley can be reached via email atb [email protected].