Heat exchanging roll

Details Heat exchanging roll Heat exchanging roll

1999-03-30

2001-06-26

Lazarus, Ira S. (Department: 3743)

Heat exchange

Movable heating or cooling surface

Rotary drum

C165S089000, C492S046000, C034S124000

Reexamination Certificate

active

06250376

ABSTRACT:

CROSS REFERENCE TO RELATED APPLICATIONS
The present application claims priority under 35 U.S.C. § 119 of German Patent Application No. 198 14 597.7, filed Apr. 1, 1998, the disclosure of which is expressly incorporated by reference herein in its entirety.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention is directed to a roll with a heat exchanger. More specifically, the present invention is directed to a roll having a heat exchanger disposed inside the roll jacket. The heat exchanger connects with a supply mechanism for inflow and outflow of an external heat transfer fluid to its primary side. A secondary side of the heat exchanger and an inner surface of the roll jacket support an internal heat transfer fluid.
2. Discussion of the Background Information
DD 225 767 A1 discloses rolls used in calenders to process paper webs or other material webs. Rolls cooperate with adjacent rolls to form nips therebetween. It is known in such arrangements that it is often preferable to heat or cool the material web, either at a nip or away from such a nip.
The need to cool the roll is not limited to situations in which only the material web needs to be cooled, but includes the roll itself; for example, when the roll has an elastic coating, heat builds up during fulling of the elastic coating, and must be dissipated to prevent damage to the coating and/or web. In other applications, the roll may need to be heated when the material web is to be exposed to an elevated pressure and/or an elevated temperature. In such cases, it is known to introduce a heat transfer fluid, for example, cooling water or heating steam, into the roll using a heat exchanger.
The above noted DD 225 767 A1 discloses a fluid path for an internal heat transfer fluid. The heat transfer fluid is present in a gas phase and in a liquid phase. It condenses on the heat exchanger and is then thrown against the inside wall of the roll jacket, where it evaporates. The resultant steam condenses when it arrives at the heat exchanger, whereupon the process repeats itself.
A drawback of such a heat exchanger is that it operates only with certain temperature differentials, and only for cooling the roll. It can also be controlled only to a limited extent.
SUMMARY OF THE INVENTION
Accordingly, the present invention is intended to overcome the drawbacks of the prior art. To meet that intention, the present invention provides a roll with a heat exchanger that provides more versatility in temperature control, and can be used for both heating and cooling a roll.
According to various features of the invention, a pump is provided inside the roll, which at least partially circulates fluid from an inner surface of the roll to the heat exchanger. Consequently, controlling the circulation of the internal heat transfer fluid using the pump is possible. Temperature control is not dependent on the presence of the heat transfer fluid in a specific form (e.g., whether it can evaporate under operating conditions). The flow of heat from the roll jacket to the heat exchanger, or in the opposite direction, is controllable over relatively large areas.
Centrifugal force partially circulates the internal heat transfer fluid, while only a feed path for the external heat transfer fluid is necessary. Since the external heat transfer fluid flows only through the heat exchanger, but not through the roll jacket, lower demands are made on the external heat transfer fluid.
Unlike the prior art, the present invention roll may also be used as a heating roll. The roll can also be operated with lower temperatures, at which the steam condenses, since the steam has to be guided only through the heat exchanger. Older rolls can also be retrofit with this new design.
Preferably, the pump mechanism is mounted on the roll and rotates therewith. Accordingly, no moving connections are necessary in the path of the internal heat transfer fluid, with a corresponding reduced chance of leaks. Mounting the pump mechanism is also simplified, as movable mounts are unnecessary.
In an exemplary embodiment, the pump mechanism is disposed on one end of the roll for maintenance purposes. However, adequate space is still available on the end of the roll for other purposes.
Also in the exemplary embodiment, the pump mechanism surrounds a roll journal in a ring shape. This uniformly distributes the weight of the pump mechanism around the circumference of the roll, minimizing any imbalance.
In an exemplary embodiment, the pump mechanism arrangement has at least one pump disposed as far from the radial center of the roll as possible. The pump will thus not have to overcome centrifugal force to circulate the internal heating transfer fluid. In most cases, centrifugal force will return the internal heat transfer fluid to the pump. In any case, with this design, the internal heat transfer fluid is always present at the pump intake.
Preferably, the pump has a working element actuatable from outside the roll jacket. Depending on the design of the pump, the working element can be a piston that moves back and forth, or a rotary element (e.g., an impeller) which rotates. Other types of pumps can also be used, e.g., gear-type pumps or centrifugal pumps. The working element must be driven in some manner in all pumps. If the drive is handled externally, i.e., from outside the roll, the roll does not have to be supplied with any additional energy to drive the pump.
The working element preferably cooperates with a stationary drive mechanism during rotation of the roll. Consequently, rotation of the roll provides relative movement between the pump and the drive arrangement. This relative movement drives the working element of the pump. For example, with a rotary pump in which the working element rotates, it is possible to have a drive wheel (which is in torque transferring connection with the working element) roll on a friction surface or a toothed surface surrounding the pump arrangement. The drive wheel rotates proportionally with the speed of the roll. Thus, the pump output increases at higher rotational speeds, which is often necessary, since higher rotational speeds have a correspondingly higher amount of material web to be treated per time unit.
When the pump has a different design, such as (for example) a piston pump, the piston or a plunger connected thereto may be guided along a cam. If the plunger or the piston is loaded with a reset force (for example, a reset spring) it suffices for the cam to act on the plunger from one direction. The plunger may also be actuated in that the pump mechanism is in contact with a rotating drive wheel when the roll rotates. Whenever the plunger comes under the drive wheel, it is forced inward. It is possible to achieve the same effect, for example, by surrounding the pump mechanism with a circulating belt, which is raised from the pump mechanism in at least one position. There, the plunger can be forced back out of the pump. For more details, reference is made to the subsequently published German patent applications 197 56 152 and 198 09 080.
Preferably, the external heat transfer fluid is fed centrally to the heat exchanger, and the outflow takes place radially farther out. This has the advantage that centrifugal force provides at least part of the energy needed to circulate the fluid.
In an exemplary embodiment, the secondary side of the heat changer has a plurality of tubes in parallel with an axis of the roll, disposed in a heat exchanger chamber and which connect with a feed connection. This provides a relatively large surface for the heat transfer from the external to the internal heat transfer fluid, or vice versa. With a heated roll, the arrangement has the advantage that steam (the preferable external heat transfer fluid) condenses on the outside of the tubes to deliver heat to the internal heat transfer fluid flowing through the tubes. Because of the rotation of the roll, any condensate is immediately thrown off the tubes, such that it does not interfere with the heat transfer. Consequently, the heat transfer surfaces are “self-cle

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