Spring devices – Vehicle – Compound
Patent
1996-07-09
1998-04-28
Poon, Peter M.
Spring devices
Vehicle
Compound
267140, B60G 1134
Patent
active
057435162
DESCRIPTION:
BRIEF SUMMARY
The invention relates to a shock absorber for running trolleys for film stretching plants.
U.S. Pat. No. 5,072,493 has disclosed a simultaneous film stretching plant, in which the individual running or tenterhook trolleys can be moved freely without the use of otherwise conventional chain levers. In this case, the drive takes place by means of a linear motor.
By means of the tenterhooks located on the running trolley, the film edge is grasped on the left and right in each case and the film is then stretched in the transverse and longitudinal directions according to the geometry of the running rails. The distance between the running trolleys thereby becomes increasingly greater. In a runout zone, the distance can become slightly smaller again, in order to carry out some shrinkage of the film web here in a predefined ratio.
Transport systems with tenterhooks not connected by chain levers, that is to say tenterhooks or running trolleys, have regions, in which the adjacent running or tenterhook trolleys are not in contact with one another. The requirements demanded of these transport systems are: introduction of the film (in this region--the so-called stack--the tenterhook trolleys are moved together in abutment; and drive and for the advancing movement of the individual running or tenterhook trolleys (the propulsive and restraining forces should not change the distance between the tenterhooks until the commencement of the stretching zone).
These requirements are satisfied in the prior art by fixed stops in the tenterhook structure. Furthermore, constructions having an elastomeric shock absorber with a small working stroke and with low energy absorption have also become known. After the damping stroke of the elastomer is spent, these tenterhooks likewise butt on one another by means of their stops formed fixedly by the tenterhook structure. In the so-called stack upstream of the actual stretching zone, the shock absorbers then always have to be compressed as far as the stop, in order, when the film is grasped, to ensure a predetermined distance from tenterhook to tenterhook which is to be maintained exactly.
However, the above-described simultaneous stretching plants, using tenterhook or running trolleys not connected by chain levers, cause considerable loads on the transport system as a whole: slight differential speed, for example during the so-called stack formation (upstream of the stretching zone). At the same time, the hard metallic shocks between the tenterhooks exert a load not only on the running rollers of the tenterhook trolleys, but also on the rails themselves. On account of the ever-present disproportion between the drive force and the different friction losses, even tenterhooks with large elastomeric shock absorbers cannot avoid hard shocks entirely. tenterhooks during the return varies nonuniformly with the service life, collisions may occur at sometimes extreme differential speeds, said collisions leading to considerable damage to running rollers, rails and the tenterhook structure itself. At the very least, the fixed stop part is consecruently subjected to plastic deformation, with the result that the tenterhook spacing (that is to say, the exact distance from tenterhook to tenterhook in the so-called stack upstream of the stretching zone) is lost. However, a distance between the tenterhooks which is brought about thereby and which changes even only slightly, in the so-called collecting region (stack region) upstream of the stretching zone, then leads, on account of the undesirable changing stretching ratio caused thereby, to a corresponding adverse impairment in the plastic film web to be produced by stretching.
Furthermore, a constant tendency for the plant speed, that is to say the running speed of the running or tenterhook trolleys, always to increase even further is to be noted. However, the dynamic loads consequently become inadmissibly high.
Nevertheless, in some known shock absorber devices, an increase in energy absorption is not possible, even with other constructional elements from
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patent: 4675582 (1987-06-01), Hommes et al.
patent: 4825111 (1989-04-01), Hommes et al.
patent: 4853602 (1989-08-01), Hommes et al.
patent: 5051225 (1991-09-01), Hommes et al.
Lindner Paul
Ruhlemann Ulrich
Bruckner Maschinenbau GmbH
Poon Peter M.
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