Corrugated mold block

Abstract: A corrugated mold block (10) for a vacuum machine for molding corrugated tubes is formed of a plurality of sub-blocks (16) rigidly secured end to end. Each sub-block has an arcuate face which is corrugated (18) with not more than one complete wavelength of circumferential grooves and lands, and two longitudinally spaced end surfaces. A vacuum channel (40) is provided about one of the end surfaces of each sub-block, and openings in each sub-block connect the channel and the face. When the sub-blocks are secured together into a mold block (and when mold blocks abut during molding), the vacuum channels and openings together define vacuum passages for each of the corrugation grooves, which passages are all connected to a vacuum source for drawing a vacuum during molding.

Description: The present invention relates to mould blocks, and more particularly to mould blocks which circulate about an endless path to form vacuum corrugated tubes. A well known method for manufacturing corrugated pipes is to extrude a tube of thermoplastic from a head and then conform that tube to the interior of a corrugated mould tunnel formed by mould blocks. The mould blocks typically come in pairs and mate together to form a portion of the mould tunnel, and the thermoplastic is either blown into its shape (by pressure created within the mould tunnel) or by vacuum (where vacuum draws the air from around the mould tunnel). Structures which have been used in the vacuum method of manufacture are illustrated in US-A-4318872, US-A-4439130 and US-A-4718844. These patents all address the problem of drawing a uniform, strong vacuum around the entirety of the mould blocks which are continually moving during the moulding process. As can be seen from these structures, it is difficult to form inexpensively any such mould block. It is an object of the present invention to provide a mould block adapted to draw a strong and uniform vacuum about the mould tunnel in order properly to conform the thermoplastic to the desired corrugated tubular shape, while at the same time minimizing the complexity and cost of the mould block. In accordance with one aspect of the invention as claimed, this object is accomplished by the provision of a corrugated mould block for a vacuum machine for moulding corrugated tubes, the mould block being movable about an endless path and cooperating with other mould blocks to define a mould tunnel with a vacuum source along a portion of said path, the mould block comprising a plurality of sub-blocks secured end to end; each subblock having a face substantially arcuate about a longitudinal axis and corrugated with not more than one complete wavelength of circumferential grooves and lands for defining a portion of the mould tunnel, two longitudinally spaced end surfaces wherein additional sub-blocks may be adjoined so as to extend the tunnel in a longitudinal direction, a vacuum channel about one of the end surfaces and spaced from the face, and means for defining openings between the face and the channel, whereby the vacuum channels and defined openings of abutting sub-blocks together define a vacuum passage; and the mould block further comprising means for connecting the vacuum passage to the vacuum source when the mould block passes along the mould tunnel. According to another aspect of the present invention as claimed there is provided a method of manufacturing a corrugated mould block, comprising the steps of forming a plurality of sub-blocks each having a face substantially arcuate about a longitudinal axis and corrugated with not more than one complete wavelength of circumferential grooves and lands, two longitudinally spaced end surfaces, a vacuum channel about one of the end surfaces, the channel being open to the outside of the sub-block, and openings between the face and the channel; aligning the formed sub-blocks longitudinally with their end surfaces abutting and their faces forming a semicircular, longitudinally disposed continuous corrugation; and rigidly securing the aligned sub-blocks together. In order that the present invention may be well understood there will now be described an embodiment thereof, given by way of example, reference being made to the accompanying drawings, in which: Fig. 1 is a perspective view of a pair of mould blocks embodying the present invention; Fig. 2 is a top view of one such mould block embodying the present invention; Fig. 3 is a sectional view of the same mould block; Fig. 4 is an exploded sectional view of two sub-blocks employed in the same mould block; and Fig. 5 is a side view of the same mould block. A pair of mating mould blocks 10 is shown in perspective in Fig. 1. When together as shown in Fig. 1, each mould block forms a portion of a mould tunnel 12 about a longitudinal axis 14. With the embodiment illustrated in Fig. 1, two mould blocks would be circulated about an endless track or path with the mould blocks 10 separated as the blocks pass an extruder head (which dispenses heated, thermoplastic in a cylindrical fashion). The mould blocks 10 are then brought together as shown in Fig. 1 to define the mould tunnel 12 (together with adjacent pairs of mould blocks), and a vacuum draws the thermoplastic against the walls of the mould tunnel 12 to form the corrugated tube or pipe. It should be noted that the two mould blocks 10 could be carried about one track pivotally by a single carriage in a clam shell type of operation such as shown in US-A-4439130, or alternatively, the mould blocks 10 could be used in a system such as that shown in US-A-4319872, with the two mould blocks of each pair carried on opposite endless tracks, mated together along a portion of the tracks to form a mould tunnel. Reference will now be made to the detailed structure of a mould block 10 embodying the present invention. Although only one mould block 10 will be described, it should be understood that the other mould block 10 in each pair will be identical to (and turned 180 degrees from) the mould block 10 being described. As best shown in Figs. 1-3, the mould block 10 comprises a plurality of adjacent sub-blocks 16 adjoined so as to define a continuous corrugated surface 18 with alternating grooves 20 and lands 22 and substantially arcuate 180 degrees about the longitudinal axis 14 (see Fig. 1). The grooves 20 and lands 22 of each sub-block extend up to one complete wavelength (i.e., the width of one groove 20 and one land 22), so that when together, the mould block face defines a continuous corrugated surface through the mould tunnel 12. Adjacent sub-blocks 16 are mated at their front end face 24 and the rear end face 26, respectively. The sub-blocks 16 defining the mould block 10 (four such sub-blocks are shown in Fig. 3) are aligned by a dowel 28 fitted into countersunk fastener passageways 30 of each pair of adjacent sub-blocks 16. Bolts 32 run coaxially through the dowels 28 the length of the mould block 10, and secure the sub-blocks 16 together by tightening of the bolts 32 and nuts 33 (the nuts and bolt heads reside in the outer fastener passageways in the end sub-blocks 16). A plurality of slits 34 are disposed at the grooves 20 of the sub-blocks 16 and are connected to a plurality of vacuum ports 36. The ports 36 are in turn in communication with semicircular grooves 38 cast in the end faces 24, 26 of each sub-block 16 which, when the sub-blocks 16 are secured together as described above, define a continuous circular vacuum passage 40. When adjacent mould blocks 10 are closed, a similar vacuum passage 40 is created between the adjacent mould blocks 10. As will be understood by a skilled artisan, mould blocks of the present invention could also be made with semicircular grooves in only one end face of each sub-block 16. Similarly, it will be understood by a skilled artisan that the interior face slits could directly communicate with the semicircular groove in the sub-block end faces, and that the semicircular grooves could be less than 180 degrees, and in fact non-connected arcuate grooves can be used with systems where more than one vacuum source is provided. Each vacuum passage 40 is also open into a vacuum channel 42 which, together with a mating channel of the other mould block 10 of each pair, define a vacuum header 44 open at the top of the mould block pair (see Figs. 4 and 5). This arrangement of grooves 20 and lands 22 within each sub-block 16 permits the dedication of a vacuum passage 40 to each groove 20 of the corrugated surface 18, thereby inducing a strong, uniform vacuum at each groove 20 of the mould tunnel 12. As will be understood by a skilled artisan, one or more vacuum manifolds can be provided adjacent the mould tunnel 12 so as to communicate with the vacuum header 44 during moulding. Accordingly, as indicated by the arrows 46, a vacuum is drawn through the vacuum header 44, the vacuum passages 40 defined by the end face grooves 38, the vacuum ports 36, and the vacuum slits 34, thereby assuring that the thermoplastic properly conforms to the mould tunnel 12. As should also be understood by a skilled artisan, the present invention can also be practised by using sub-blocks which are arcuate through less than 180 degrees (for example, a single large mould block could also be formed by suitably rigidly connecting together sub-blocks which are not more than one complete wavelength long but have faces curving only 90 degrees). As should also be understood by a skilled artisan, the present invention could similarly be practised through the use of selected longitudinal bores through the sub-blocks in order to connect a couple of the vacuum passages so that only one vacuum channel to the header need be provided for the connected passages. The above described structure will thus draw a strong and uniform vacuum about the mould tunnel in order properly to conform the thermoplastic to the desired corrugated tubular shape, while at the same time minimizing the complexity and cost of the mould block.

Claims: A corrugated mould block for a vacuum machine for moulding corrugated tubes, the mould block (10) being movable about an endless path and cooperating with other mould blocks (10) to define a mould tunnel (12) with a vacuum source along a portion of said path, the mould block (10) comprising a plurality of sub-blocks (16) secured end to end; each sub-block (16) having a face (18) substantially arcuate about a longitudinal axis (14) and corrugated with not more than one complete wavelength of circumferential grooves (20) and lands (22) for defining a portion of the mould tunnel (12), two longitudinally spaced end surfaces (24, 26) wherein additional sub-blocks (16) may be adjoined so as to extend the tunnel (12) in a longitudinal direction, a vacuum channel (38) about one of the end surfaces (24, 26) and spaced from the face (18), and means for defining openings (34, 36) between the face (18) and the channel (38), whereby the vacuum channels (38) and defined openings (34, 36) of abutting sub-blocks (16) together define a vacuum passage (40); and the mould block (10) further comprising means for connecting (42, 44) the vacuum passage (40) to the vacuum source when the mould block (10) passes along the mould tunnel (12). A corrugated mould block as claimed in claim 1, wherein the face (18) of each sub-block (16) comprises one circumferential land (22) symmetrically flanked by two circumferential half grooves (20). A corrugated mould block as claimed in claim 1 or claim 2, wherein the sub-blocks (16) when secured together in a mould block (10) define a continuum of substantially semicircular evenly spaced circumferential grooves (20) and lands (22). A corrugated mould block as claimed in any of the preceding claims, wherein at least one vacuum channel (38) is closed by abutment of the end surfaces (24, 26) of adjacent secured sub-blocks (16). A corrugated mould block as claimed in any of the preceding claims, wherein the defined openings (34, 36) comprise vacuum ports radiating outwardly from the face (18) to the vacuum channels (38). A corrugated mould block as claimed in any of the preceding claims, further comprising a plurality of aligned longitudinal passages (30) through the sub-blocks (16) and a fastener (32) extending through the aligned passages (30) and securing a selected plurality of the sub-blocks (16) together into a mould block (10). A method of manufacturing a corrugated mould block, comprising the steps of forming a plurality of sub-blocks (16) each having a face (18) substantially arcuate about a longitudinal axis (14) and corrugated with not more than one complete wavelength of circumferential grooves (20) and lands (22), two longitudinally spaced end surfaces (24, 26), a vacuum channel (38) about one of the end surfaces (24, 26), the channel (38) being open to the outside of the sub-block (16), and openings (34, 36) between the face (18) and the channel (38); aligning the formed sub-blocks (16) longitudinally with their end surfaces (24, 26) abutting and their faces (18) forming a semicircular, longitudinally disposed continuous corrugation; and rigidly securing the aligned sub-blocks (16) together. A method as claimed in claim 7, wherein the forming method comprises casting metal.

Inventors: BERNS JOHN S, DICKHUT HEINRICH B, BERNS, JOHN S., DICKHUT, HEINRICH B.
Applicants: CULLOM MACHINE TOOL & DIE INC, CULLOM MACHINE TOOL & DIE, INC.
Application year: 1990
Main classification: B29C49
IPC codes: B29C33, B29C49