˘ˇ ˇˆ - Astro-Tex

1 Toll Free: 800/458-0456 Fax: 814/864-3452 E-mail: 2q sx yh g syxForces and motions are the elements utilized by mechanicalequipment to perform work. Unfortunately, these sameelements can produce undesirable effects, even in the mostcarefully designed equipment. The adverse effects ofvibration, shock and noise disturbances range from simpleannoyances to shortened equipment life through failure of itscomponents. They will affect comfort, safety or , shock and noise control components, properlyapplied, will improve your products. They will operate moresmoothly and quietly, and they will be less disturbing tosurrounding equipment and personnel, less susceptible todamage and less expensive to make.

2 Bonded rubber mountsprovide cost-effective solutions to problems involvingvibration, shock and structural noise theory and concepts for bonded rubber mounts arerelatively straightforward. A great many of the applicationsare uncomplicated, and the nonspecialist can handle themdirectly. However, some vibration and shock controlproblems are quite complex, making component selectionand design applications require the involvement of specialists inorder to arrive at suitable recommendations, and Lord has a technical staff available to assist you. In any event, theinformation presented in this catalog will prove useful inyour independent application solutions, as well as at thosetimes when technical assistance is necessary.

3 See applicationselection guide (page 15).This catalog has been prepared to assist the individual whodoes not frequently deal with vibration and shock problemsand to remind others of the versatility of bonded rubbermounts. It presents the important information needed toselect and use bonded rubber mounts: terms and definitions,theory, sample problems and data on standard mounts. i w 2exh2hipsxs syx There are a number of terms which should be understoodbefore entering into a discussion of vibration and shocktheory. Some of these are quite basic and may be familiar tothe users of this catalog. However, a common understandingshould exist for maximum - rate of change of velocity with along a specified axis, usually expressed in g or gravitational units.

4 It may refer to angular - the maximum displacement from its zerovalue E whenspecified as a directionfor loading - adeformation caused bysqueezing the layers of anobject in a directionperpendicular to 2@ A - the mechanism in an isolation system whichdissipates a significant amount of energy. This mechanism isimportant in controlling resonance in vibratory 2 2@ A - the number of oscillations perunit time of an external force or displacement applied to avibrating system. fd = disturbing 2@ A - an arbitrary numerical value whichmeasures the resistance to the penetration of the durometermeter indenter point; value may be taken immediately orafter a very short specified - is the highest vibration or shock level that can bewithstood without equipment failure.

5 Q 2 - an expression of the vibration shockacceleration level being imposed on a piece of equipment asa dimensionless factor times the acceleration due to - the protection of equipment from vibration and/or shock. The degree (or percentage) of isolation necessaryis a function of the fragility of the 2 2 - the measured and recorded dis-placement of a mounting plotted versus an applied 2 2@ A - the number of cycles ( Toll Free: 800/458-0456 Fax: 814/864-3452 E-mail: a mass is attached to a spring, the mass moves to itsposition of equilibrium, position 1. The differencebetween the spring s undeflected or free length and itsposition of equilibrium is called the system s staticdeflection, ds.)

6 If a force is applied to the system, position2, and then removed, the spring-mass system will vibrate,position 3. When plotted against time, the position of themass relative to its equilibrium position is a sinusoidalcurve. The maximum single amplitude is the deflection ofthe mass from its equilibrium position to its maximumdisplacement in one direction. Double amplitude displace-ment is the total deflection in both directions. The periodof vibration is the time it takes for the mass to move fromits equilibrium position to its peak in one direction, to itspeak in the other and back to its equilibrium a load is applied to our spring mass system and thenreleased, the mass will vibrate at a constant rate.

7 We callthis condition resonance, and the vibration rate is calledthe natural or resonant frequency. The natural frequencyof a system can be considered a function of mass (M) andspring rate (K). 2- when specified as adirection for loading - adeformation caused bysliding layers of an objectpast each other in adirection parallel to thelayers. %2 - a shock pulse is a transmission of kineticenergy to a system, which takes place in a relatively shortlength of time compared to the natural period of thissystem. It is followed by a natural decay of the oscillatorymotion. Shock pulses are usually displayed as plots ofacceleration vs. period of time. 2 - is the force required to induce a unitdeflection of spring.

8 A steel spring has a very linearrelationship between force and deflection. Elastomericsprings may or may not be linear depending on theamount of deflection due to the load. 2 2@ A - the deflection of the isolator underthe static or deadweight load of the mounted equipment. 2@ A - is a dimensionless unit expressingthe ratio of the response vibration output to the inputcondition. It may be measured as motion, force, velocityor acceleration. riy Vibration is an oscillatory motion. Any body with massand elasticity can vibrate. The simplest type of vibratingsystem is called a single-degree-of-freedom spring-masssystem. The spring is characterized by its spring rate, K,and a mass, Hertz or cycles per second) at which a structure willoscillate if disturbed by some force and allowed to come torest without any further outside influence.

9 2 - non-sinusoidal vibration character-ized by the excitation of a broad band of frequencies atrandom levels simultaneously. - A vibratory system is said to be operating atresonance when the frequency of the disturbance (vibrationor shock) coincides with the system natural frequency. - is the amount of deformation never recovered afterremoval of a load. It may be in shear or system is called a single-degree-of-freedom systembecause motion can occur in only one direction. Springrate defines the force required to induce a unit deflectionof a spring. A steel spring has a linear relationshipbetween force and deflection. Elastomeric springs may ormay not be linear depending on the amount and directionof the load.

10 Nonlinearity can be designed into elastomericsprings to achieve certain results. Elastomeric springs alsodiffer from steel springs in that their stiffness is sensitiveto the rate or speed of deflection. If a rubber spring isdeflected quickly, it appears stiffer than if it is Toll Free: 800/458-0456 Fax: 814/864-3452 E-mail: frequency is usually measured in hertz. Thisequation can be written in many forms:where K=spring rate, lbs/in, W=weight in pounds,M=mass in lb-sec2/in and g=acceleration of gravity, From this formula, you can see that an increase inmounting system stiffness or a decrease in weight willincrease the natural frequency. A decrease in mountingsystem stiffness or an increase in weight will decrease thenatural far we have discussed free vibration, what happenswhen a force is applied and removed from our spring masssystem.