Rosta Tensioner Devices
Since 1944 ROSTA has been one of the industries most used manufactures of tensioning devices as well as damping systems of various types. Since then, they have continually made various improvements and breakthroughs with their tensioning devices to where the SE style arm tensioners have become the top choice for many facilities around the world!
Rosta Tensioner Types
Standard Tensioner Devices
NOTE: ** tensioning elements without idler hardware/ other sizes available upon request.
SE-R Reinforced Arm Tensioners
SE-I Stainless Steel Tensioners
SE-B Boomerang Tensioners
SE-F Front Mount Tensioners
NOTE: SEF-15, SEF-18, and SEF-27 metric holes are also available.
SE-FE Front Mount Tensioners
ROSTA Tensioner Technology
At the core, what really makes ROSTA tensioners different from the rest is the specially designed high-quality rubber element. The only wear component on arm style tensioners is the rubber material insert (excluding sprocket or pulley), this basically means that the tensioner is only as good as the element inside of it. Over the years ROSTA has developed a special compound that shows superior wear performance, tension force, and overall durability versus "look-alikes".
Function
The rubber suspension element is primarily designed for applications as torsional spring devices offering operation angles of +/- 30°. Depending on the particular function, not only torsional moments are generated by pivoting the spring device. According to the specific application additional radial Fr, axal Fa and or cardanic Mk forces have usually been taken into consideration.
Spring Characteristic
By pivoting the unique ROSTA torsional spring device a virtually linear spring characteristic occurs with a slightly progressive upper end, when load is applied in the high pivoting range, close at 30° element rotation. If purely linear or even degressive spring characteristics are required, the design of the leverage has to be altered and/or a cam-disc has to be used as arm guidance in order to obtain a function adapted spring characteristic. Furthermore, please note that elastomeric bonds are incompressible, i.e. of constant volume.
Internal Element Damping
The occurring energy damping in the ROSTA element is addicted to the resulting energy loss work in the rubber inserts during the pivoting activity of the spring device.
In the process of the element actuation, a part of the resulting energy is transformed into frictional work generating heat. The shaded surface between load and relieve headline indicates effective energy loss. At element actuation out of the zero position up to 30°, the resulting average energy loss is at 15 to 20%. At the actuation of a pre-tensioned element, the resulting ± working angle is usually only a few degrees, therefore the energy loss reduces within a limit (see graph: “Energy loss per oscillation”).
Uniquely animated element oscillations fade within a short term, due to the occurring energy loss at each following post-pulse oscillation. (Very important at the use of
ROSTA screen mountings – during the operation procedure of the screen the resulting power loss in the ROSTA mountings is negligible; during the running down phase, close to the resonance frequency of the suspensions, an important amplitude exaggeration occurs. The high
energy loss in the ROSTA screen mountings dampens and absorbs these exaggerations within only a few post-pulse oscillations.)
Natural Frequency of a ROSTA Suspension
The determination of the natural frequency of a ROSTA suspension has to be carried out by spreading the tangent at the loading point “A” on the parabolic arc of the load-deflection curve. The resulting distance s1 on the axis of abscissa comes up to the arithmetical spring deflection in mm, required for the determination of the natural frequency
Cold Flow and Settling of the Rubber Suspensions
If over a certain period of time, the load is permanently applied on an elastic component (e.g. rubber suspension) consistent deformation occurs (cold flow). Cold flow or settling appears during a linear logarithmic sequence. According to the respective diagram, more than 50% of this overall settling or cold flow of a ROSTA element under load occurs after only one day of service. After approx. one year of operation the total cold flow deformation will be compensated (depending on environmental temperatures and applied frequencies). The empirical settling factor of a ROSTA rubber suspension lies within 3° to 5°, i.e. the inner core does not totally move back to the neutral 0° position of the element. In applications with series or parallel con durations of several elements (e.g. AB screen mountings), the effective cold flow factor lies at approx. +10% of the nominal deflection curve. This fact has to be taken into consideration while designing axle bearings or screen mountings with ROSTA elements.
Temperature Influence
The ROSTA rubber suspension elements equipped with the standard rubber quality “Rubmix 10” are designed to be applied in the temperature range of –40 °C to +80 °C (–40 °F to +180 °F). With rising temperatures the mechanical stiffness of the rubber inserts and consequently the resulting element torque decrease within acceptable tolerances (at +180 °F approx. –5%). At lower temperatures (below the freezing point) the torsional element stiffness rises up to max. +15% at –40 °F. Furthermore, the internal damping factor (hysteresis) of the ROSTA rubber suspensions increases at lower temperatures and declines again at rising conditions. Due to the internal molecular friction through element torsion, the rubber inserts warm up in a continuous manner. Thus, the effective occurring element temperature can vary in relation to the environmental temperature.
Service Life
Provided the rubber suspension elements are selected according to our technical specifications, i.e. are operating within the given frequencies and oscillation angles and under the mentioned surrounding conditions, no loss of performance and functionality can be expected for many years. Extremely low or high permanent surrounding temperatures considerably shorten the lifetime expectancy of the rubber suspension elements. The opposite service life curve indicates the relevant life deduction at extreme ±temperatures from factor 1 at room temperature of +71.6 °F.
Quality Control and Tolerances
Since December 1992 ROSTA AG has been an ISO 9001 standard certified development, manufacture, and distribution company. All products are submitted to a periodical function and quality control. On the test machines of the in-house laboratory the rubber inserts are continuously tested and controlled with regard to Shore A hardness, compression set, abrasive wear, rebound resilience, tensile strength, breaking elongation and aging behavior. The dimensional tolerance of the rubber inserts are hardened according to DIN 7715 standard and the Shore A hardness according to DIN 53505 standard. The housings and the inner-core proles of the rubber suspensions are subjected to the tolerance guidelines of the relevant production process and respective supplier (e.g. cast, extruded, edge rolled) and the individual material consistency (e.g. light metal casting, steel tube, nodular cast iron part, etc.). The resulting torsional moments and spring deflections of the ROSTA rubber suspension elements are residing in a tolerance range of ±15% at most, but lie usually in an essentially narrower range!
Rubber Qualities
Nearly 80% of all ROSTA rubber suspension elements are equipped with rubber inserts of standard quality “Rubmix 10”. This rubber quality based on a high content of natural rubber (caoutchouc) offers a good shape-memory, small settling factors (cold flow), high mechanical load capacities and moderate aging behaviors (little hardening of the inserts). Where high oil-consistency, heat-resistance or higher torque is required, other qualities of elastomeric inserts can be applied in the
ROSTA rubber suspension elements.
Chemical Consistency
The standardized ROSTA rubber suspension elements are equipped with elastic inserts of quality type “Rubmix 10”. This rubber quality is based on a high content of natural rubber. It offers against large media a high chemical consistency. In some specific applications, however, some additional protective barrier or the application of elements with synthetical elastomeric inserts (qualities “Rubmix 20”, “Rubmix 40” or “Rubmix 50”) is required. Applying these alternative inserts, the general element characteristics slightly differ (see chapter 10 “rubber qualities”). The below indicated consistency table is merely a guideline and is incomplete. For specific applications please contact ROSTA and inform us about the environmental conditions and about the detailed concentration of liquid or aerial media being in contact with the rubber suspension elements.
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