Cutting – By endless band or chain knife – With means to guard the tension
Patent
1989-05-22
1990-05-22
Schran, Donald R.
Cutting
By endless band or chain knife
With means to guard the tension
83 58, 83621, 83818, 83 62, B23D 5510, B27B 1308
Patent
active
049267337
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to an arrangement which is intended for tensioning the cutting blades of band saws and like machines and which comprises a hydraulic piston-cylinder device the piston of which is intended to activate blade tension control means, such that the tension in the blade is governed by the hydraulic pressure in the cylinder of the piston-cylinder device.
In band saws which are equipped with blade tensioning facilities, e.g. the band saw described and illustrated in No. SE-7312757-3 the blade is tensioned with the aid of an hydraulically operated piston which is urged upwards by means of pump pressure, this pressure being held constant with the aid of a pressure-compensated pump and diverse pressure regulators. This in combination with a solid steel piston results in a rigid, inelastic tensioning system with no resilience or ability to absorb shock.
With the growing demand for sawing machines of higher performance levels, it has been found desirable to introduce resiliency in blade tension in order, inter alia, to be able to compensate for those changes in blade length which result from heating and cooling of the blade. No. SE-7317517-6 describes a completely gas-sprung system, which nevertheless is encumbered with certain drawbacks.
The main object of the present invention is to provide a blade tensioning arrangement which incorporates a hydraulic piston-cylinder device and with which at least the aforesaid disadvantage inherent with known hydraulic devices is eliminated.
This object is achieved in accordance with the invention by controlling the hydraulic pressure pneumatically, thereby introducing resiliency and shock absorbing facility into the system and enabling the blade tension to be regulated or controlled in a particularly simple manner.
Accordingly, this invention consists in a blade tensioning arrangement of the kind described in the introduction which is characterized in that the arrangement includes means for regulating the hydraulic pressure pneumatically; in that the regulating means include a pneumatically operated pressure booster or amplifier; and in that means are provided for activating the pressure booster at the end of a working stroke of the piston, such as to achieve the desired working tension in the saw blade.
The inventive arrangement is thus controlled solely by the pneumatics incorporated in the arrangement, therewith enabling the blade tension to be controlled and regulated in a very simple fashion, as beforementioned. Furthermore, since the hydraulic pump found in prior art blade tensioning systems has been replaced with, inter alia, a pneumatically operated pressure booster, it is possible to create a desired degree of resilience or spring in the system. It is essential that a facility is provided which will enable the blade tension of a band saw to be regulated readily and simply, since the correct blade tension is directly proportional to the blade width, which changes each time the blade is ground. Consequently, a pneumatic pressure regulator is preferably connected to the pressure booster, so as to enable the blade to be tensioned to a desired working tension and maintained at this level of tension. The use of such a pneumatic pressure regulator can be highly beneficial, among other things because it is simple to control.
In order to achieve the requisite amount of spring, or shock absorbency, in the system, an additional volume of air can be made available between the pressure booster and the pressure regulator. In accordance with a preferred embodiment of the agreement, the hydraulic piston-cylinder device has connected thereto a pressure sensor which initiates activation of the pneumatic pressure booster when the hydraulic pressure reaches a preset value.
In accordance with a particularly preferred embodiment of the invention, which provides a very compact construction of the whole blade tensioning arrangement, the hydraulic piston is hollow and the pressure booster is located within the piston and is carried by the piston during piston movement.
REFERENCES:
patent: 3905266 (1975-09-01), Weavell et al.
Aktiebolaget A.K. Eriksson
Schran Donald R.
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