Controlling Machine Vibration And Shock

Dynamic loads, and the resulting vibration or shock, are a fact of life with rotating and oscillating machinery. Both shock and vibration can damage equipment, increase operating costs, reduce quality and productivity, and generate objectionable noise levels. Manufacturers have long recognized the need to isolate and dampen machine-generated vibration and shock. As a result, machine mounts of various designs and materials have been developed to solve the problem. However, determining the proper mount for a given application requires a basic understanding of the forces and motions that cause vibration and shock.

Identifying The Problem

Vibration is a dynamic force that results in a continuous sine-wave type of motion. Any mass with elasticity can vibrate; elasticity is the tendency of the mass to return to its original size, shape or position after the force that has been applied to it has been removed. In the manufacturing world, vibration forces are generated by rotating and oscillating motions of the type found in lathes, conveyors and similar equipment.

Shock differs from vibration in that it results from an impact, usually sudden, as opposed to the application of a periodic force. A plane landing on the deck of an aircraft carrier and a hammer striking a nail are examples.

Shock is non-repetitive and of limited duration, with the pulses decaying prior to the advent of another impact. In manufacturing, typical sources of shock include presses and sheet metal punching machines. Mount design and selection to control shock in machines such as these require an analysis of maximum deflection and acceleration of the disturbing force and the resulting wave shape. The mount must be able to disperse the shock energy and handle the deflection created by the impact force without the equipment swaying or the mounts straining beyond safe limits.

Choosing The Right Mount

How do you choose which mount-type is best for your application? Vibration and shock are distinct conditions and have differing effects on mounting pads. Today, most machines engaged in manufacturing or assembly are installed on mounts, which provide at least some degree of isolation from the factory floor. The mounts often provide the added benefit of leveling the equipment. In so doing, these mounts not only improve productivity, but they also increase the life of the machinery.

Choosing the right mount for the application is seldom as simple as ordering an off-the-shelf product. It requires not only an understanding of the causes of vibration and shock but also an understanding of the characteristics of the available mount options.

Rubber has proven to be an effective vibration- and shock-dampening material. It is classified as an elastomer and can be of different materials with a variety of properties. Such materials include silicone, isoprene, neoprene and nitrile. Parameters used to identify the appropriate materials in a given mount include tensile and compression strength, density, hardness, permeability to gases, elasticity and tear resistance.

Two specific mount designs have come to fill the role of the vibration and shock/leveling machine mount. An economical solution for precision leveling and noise dampening is a mount with built-in leveling bolts, such as the MHD-Series from Sunnex, Natick, Massachusetts (shown). The built-in leveling bolt fits through the body of this machine mount, eliminating horizontal sway. The mount absorbs shock in high speed, dynamic production machinery, where dampening is critical. It also features precision leveling to within 0.01 mm.

Even more precise leveling is available from wedge style mounts, such as Sunnex’s WM-Series. These mounts are designed for applications requiring high load capacities. They feature a high-precision, adjustable leveling system and dampening pads that effectively reduce noise and shock. Applications for the wedge style mount include transfer lines, presses and machine tools.

Many machine bedding systems have also been designed to dampen shock and vibration, the most common of these being machine pads. Made from special nitrile rubber, the pads absorb shock and vibration. They are available in a range of widths and hardnesses, with different patterns on the underside suited for different types of flooring.

Stainless steel mounts can come into play when applications require strict hygiene standards or where corrosive materials are being used. Stainless steel and zinc plated machine mounts are resistant to corrosive gases and liquids, while standing up to abrasive cleaning agents used in clean rooms. They are an apt choice for food and beverage packaging machinery, chemical and pharmaceutical processing systems, and medical manufacturing equipment.

Choosing the right mount requires a basic understanding of both the problem (vibration or shock) and the solutions. However, that does not mean that you are on your own when it comes to picking the right product. Mount manufacturers are more than willing to offer advice on those standard products available on the market that are best suited to your particular application. They will even design and produce a product that adequately controls vibration and shock for your specific requirements. When the mount is completely in sync with the application, the result is much more likely to be reduced downtime, increased productivity and improved profits.