Patent Description:
Prefabricated concrete elements, such as hollow-core slabs and solid concrete slabs, are conventionally cast by slipform casting or extrusion casting on long casting beds as a continuous casting process. The length of said continuous casting process is defined either on the basis of the total length of the elements to be cast, or on the basis of the maximum length of the casting bed. The length of casting beds used in casting can be from <NUM>-<NUM> up to <NUM>-<NUM>, depending on the size of the element plant. When a casting equipment has cast a continuous slab on a casting bed, the cast concrete slab is allowed to be cured on the casting bed. After the concrete mass has cured, the uniform cast element is cut, generally by sawing, into pieces with predetermined lengths on the basis of the design characteristics of the ready-made elements, and the cut concrete elements are lifted off the casting bed to storage, to wait for transportation to their appointed targets of usage.

Generally concrete elements cast by slipform or extrusion casting are prestressed, i.e. they are provided with prestressed reinforcement strands. These reinforcements strands are prestressed by pulling the strands to a predefined stress before starting of the actual casting with a suitable casting machine.

The stressing of reinforcement strands may be carried out strand by strand, or in a bundle, where all of the required reinforcement strands are connected to a single strand pulling plate or beam after which the plate is moved a predetermined distance with a bundle stressing device in order to achieve the required stressing of the reinforcement strands.

After the strand pulling beam is moved the predetermined distance with the bundle stressing device to stress the reinforcement strand bundle, the beam is typically locked at the pulled position with wedges. This allows the detachment of the bundle stressing device from the beam so that the same bundle stressing device can be used to service a plurality of adjacent casting beds.

Setting of the wedges in the locking of the strand pulling beam during the strand stressing process is manual work, which requires the operator of the bundle stressing machine to leave the cover of the machine and move to the casting bed area, which creates possible work hazards if any of the stressed reinforcement strands happen to break. Further, the area where the wedges are set is also typically uneven and dirty and often oily, which causes additional hazards.

Publication <CIT> discloses a solution comprising a device for operating locking means of a strand pulling beam. In this solution the device comprises nut tightening means for automatically rotating and fastening a fastening nut screwed to a fastening rod.

Other locking solutions for the strand pulling beam are disclosed in publications <CIT>, <CIT>, <CIT> and <CIT>. <CIT> discloses an apparatus for prestressing reinforcement strands in the prefabrication of prestressed concrete products on a casting bed in accordance with the preamble of claim <NUM>.

The present invention removes the need for the operator to leave the cover of the bundle stressing device for the locking of the strand pulling beam, as well as other related actions, which significantly increases the work safety. Further, the present invention also allow certification that the locking process, as well as other related actions, are done properly.

The apparatus of the invention for prestressing reinforcement strands in the prefabrication of prestressed concrete products on a casting bed comprises at least one device for moving a strand pulling beam in relation to the casting bed, and at least one device for operating locking means of the strand pulling beam for locking and releasing the position of the strand pulling beam relation to the casting bed. By operating locking means of the strand pulling beam via the device, the operator can release and lock the strand pulling beam from safe location without need to enter in the area of the casting bed.

The at least one device for moving the strand pulling beam is preferably a hydraulic cylinder. Further, the apparatus preferably comprises two of these devices connected to the strand pulling beam on both ends of the beam.

The apparatus of the invention comprises a device for operating the locking means comprise means for gripping and moving a wedge locking the strand pulling beam in relation to the casting bed. These means allow detachable attachment of the wedge to the device and vertical moving of the wedge for raising it from the locking position to released position, and vice versa. Further, there are preferably separate means for each wedge locking the strand pulling beam in relation to the casting bed. In the apparatus of the invention the apparatus is mounted movably on rails for moving the apparatus between adjacent casting beds.

In the apparatus of the invention the at least one device for moving the strand pulling beam is detachably connected to the strand pulling beam, and the apparatus comprises at least one device for detaching the strand pulling beam from the apparatus. According to an embodiment, the device for detaching the strand pulling beam preferably comprises means for gripping and moving at least one locking pin connecting the device for moving the strand pulling beam to the strand pulling beam. These means allow detachable attachment of the locking pin to the detachment device and vertical moving of the locking pin for raising it from the locking position to released position, and vice versa. Further, there are preferably separate means for each locking pin connecting the devices for moving the strand pulling beam to the strand pulling beam.

In this embodiment of the at least one device for detaching the strand pulling beam is preferably at least partially movably connected to the apparatus for changing the distance between the means for gripping the locking pin and the apparatus. This allows the locking and release of the strand pulling beam to and from the device(s) for moving the strand pulling beam at different positions in relation to the casting bed.

In an embodiment of the apparatus of the invention the apparatus comprises a cover for an operator operating the apparatus.

More precisely the features defining an apparatus in accordance with the present invention are presented in claim <NUM>. Dependent claims present advantageous features and embodiments of the invention.

Exemplifying embodiment of the invention is explained in greater detail below in the sense of example and with reference to accompanying drawings, where.

<FIG> shows schematically an embodiment of the apparatus of the invention, which apparatus is a bundle stressing machine <NUM>.

When prestressing reinforcement strands <NUM> in a bundle in the production of prefabricated concrete products, the strands are first connected to a strand pulling beam <NUM>, which is then pulled backwards with the bundle stressing machine <NUM> to a predetermined distance to achieve the required prestressing of the reinforcement strands before the concrete casting phase is started.

Since the forces acting of the reinforcement strands <NUM> during the prestressing can be up to <NUM> kN, there is always a possibility that one or more reinforcement strands break during the prestressing, which would cause a significant danger to the personnel of the prefabrication site. Thus, when the reinforcement strands <NUM> are prestressed, personnel are evacuated from the area of the casting bed, and the operator of the bundle stressing machine <NUM> is behind the cover <NUM> of the machine. The bundle stressing machine <NUM> also typically gives sound and light alarms when the strand pulling is about to start and when it is ongoing.

When the strand pulling is done, i.e. the bundle stressing machine <NUM> has pulled the strand pulling beam <NUM> the predetermined distance, the strand pulling beam is locked at this position with wedges <NUM>, which are inserted in the slots <NUM> formed in the abutment section <NUM> of the end of the casting bed. After the wedges <NUM> are at their locking places, the pull on the strand pulling beam <NUM> is slowly released and the strand pulling beam will rest against the wedges, after which the bundle stressing machine <NUM> can be detached from the strand pulling beam <NUM> and moved to another adjacent casting bed via rails <NUM> for a new reinforcement strand prestressing process.

The bundle stressing machine <NUM> is equipped with devices <NUM>, <NUM>' for operating locking means of the strand pulling beam, which devices comprise arms <NUM>, <NUM>' with gripping portions <NUM>, <NUM>'for gripping the wedges <NUM>. The operation of these devices <NUM>, <NUM>' are discussed in more detail later with reference to <FIG>.

The bundle stressing machine <NUM> is also equipped with devices <NUM>, <NUM>' for detaching the strand pulling beam from the bundle stressing machine, which devices comprise arms <NUM>, <NUM>' with gripping portions <NUM>, <NUM>' for gripping locking pins <NUM>. The operation of these devices <NUM>, <NUM>' are discussed in more detail later with reference to <FIG>.

<FIG> illustrates the operation of the devices <NUM>, <NUM>' for operating the locking means, i.e. the wedges <NUM>, of the strand pulling beam <NUM> with the bundle stressing machine <NUM> of <FIG>. In <FIG> the machine <NUM> is shown both as a side view and as a top view.

During the prestressing process of the reinforcement strands <NUM>, i.e. when the strand pulling beam <NUM> is being pulled, the wedges <NUM> are in lifted position, as shown in <FIG>. In this lifted position the wedges <NUM> are supported with the gripping portions <NUM>, <NUM>' of the devices <NUM>, <NUM>', which gripping portions in this embodiment are formed as forks opening towards the sides of the abutment section <NUM> of the casting bed, wherein the prongs of the forks set themselves on both sides of the wedges <NUM> in grooves formed in the wedges.

When locking the strand pulling beam <NUM> at its pulled position the wedges <NUM> are lowered with vertical downward movement of the arms <NUM>, <NUM>', which inserts the wedges into the slots (<NUM> in <FIG>) formed in the abutment section <NUM> of the casting bed, as shown in <FIG>.

In the position of <FIG>, wherein the wedges <NUM> are located in their locking position in the slots, the devices <NUM>, <NUM>' can be moved horizontally towards each other along the rails <NUM> in order to move the forks away from the wedges and thus detach the wedges from the gripping portions <NUM>.

Release of the locking of the strand pulling beam <NUM> is done in similar manner but in opposite order, once the concrete product cast on the casting bed is cured and the strands connected to the strand pulling beam are cut.

Figures 3A-3C illustrates the operation of the devices <NUM>, <NUM>' for detaching the strand pulling beam <NUM> from the bundle stressing machine of <FIG>. Similarly than in <FIG>, the machine <NUM> is shown both as a side view and as a top view in figures 3A-3C.

The ends of the piston rods of the hydraulic cylinders <NUM> of the bundle stressing machine <NUM> used to create the pulling force to the strand pulling beam <NUM> are connected to the beam with removable locking pins <NUM>.

When the strand pulling beam <NUM> is released, such as when the bundle stressing machine <NUM> is moved between the different casting beds along rails <NUM>, the locking pins <NUM> are in lifted position, as shown in <FIG>. In this lifted position the locking pins <NUM> are supported with the gripping portions <NUM>, <NUM>' of the devices <NUM>, <NUM>', which gripping portions in this embodiment are formed as forks opening away from the bundle stressing machine <NUM> in the longitudinal direction of the casting bed, wherein the prongs of the forks set themselves on both sides of the locking pins <NUM> in grooves formed in the locking pins.

When locking the strand pulling beam <NUM> is attached to the ends of the piston rods of the hydraulic cylinders <NUM>, the ends of the piston rods are first moved to the strand pulling beam, after which the locking pins <NUM> are lowered with vertical downward movement of the arms <NUM>, <NUM>', which inserts the locking pins into and through holes formed at the ends of the strand pulling beam and fastening lugs at the ends of the piston rods into the position shown in <FIG>.

The attachment and detachment of the gripping portions <NUM>, <NUM>' to and from the locking pins <NUM> is achieved with horizontal movement of the devices <NUM>, <NUM>' along the rails <NUM>, <NUM>'. Further, the rails <NUM>, <NUM>' also allows the devices <NUM>, <NUM>' to be moved at suitable position for detaching and attaching the ends of the piston rods of the hydraulic cylinders <NUM> from and to the strand pulling beam <NUM> when the beam is located at the opposite end of the abutment section <NUM> of the casting, as shown in figure 3C, or along any position along the abutment section. Before moving the devices <NUM>, <NUM>' in horizontal direction with the rails <NUM>, <NUM>', the devices <NUM>, <NUM>,' are moved towards each other along the rails <NUM>, with the wedges <NUM>, in order to avoid collision between these devices.

Claim 1:
Apparatus (<NUM>) for prestressing reinforcement strands (<NUM>) in the prefabrication of prestressed concrete products on a casting bed, wherein the apparatus comprises at least one device (<NUM>) for moving a strand pulling beam (<NUM>) in relation to the casting bed, which is detachably connected to the strand pulling beam, and the apparatus (<NUM>) comprises at least one device (<NUM>, <NUM>') for detaching the strand pulling beam from the apparatus (<NUM>), and at least one device (<NUM>, <NUM>') for operating locking means (<NUM>) of the strand pulling beam (<NUM>) for locking and releasing the position of the strand pulling beam in relation to the casting bed, wherein the device (<NUM>, <NUM>') for operating the locking means comprises means (<NUM>, <NUM>, <NUM>; <NUM>', <NUM>', <NUM>) for gripping and moving a wedge (<NUM>) locking the strand pulling beam (<NUM>) in relation to the casting bed, and wherein the apparatus (<NUM>) is mounted movably on rails (<NUM>) for moving the apparatus between adjacent casting beds, characterized in that said means (<NUM>, <NUM>, <NUM>; <NUM>', <NUM>', <NUM>) for gripping and moving the wedge (<NUM>) allow detachable attachment of the wedge (<NUM>) to the device (<NUM>, <NUM>') for operating the locking means and vertical moving of the wedge for raising it from the locking position to released position, and vice versa.