BACKGROUND OF THE INVENTION In a plastic molding apparatus it is extremely important to provide cooling of mold blocks of a moving mold tunnel as the mold blocks are in the product forming stage. The cooling of the mold blocks provides substantial benefits to the product itself.

One example of a molding apparatus using a moving mold tunnel is a, plastic pipe mold. It is known with existing pipe molds to provide internal cooling of the mold blocks as they move through the mold tunnel. In some cases, this internal cooling is provided by chilled water. Controlling the flow of the water to prevent drippage from the molding apparatus can be quite difficult.

Internal cooling of mold blocks is also provided by means of a chilled gas. This necessitates specific internal machining of the mold blocks. This is expensive and makes it extremely difficult to retrofit the mold blocks to include cooling capacity.

Some attempts have been made to provide external cooling of the mold blocks while they are in the mold tunnel. These attempts involve the flowing of cooling air lengthwise of the mold tunnel to the outside of the mold blocks. However, according to conventional practice

there is no way of ensuring that the cooling air is maintained in contact with the mold blocks. It is simply free to flow outwardly away from the mold blocks rather than being contained at the surface of the mold blocks.

SUMMARY OF THE PRESENT INVENTION The present invention relates to a method of providing cooling to the exterior surface of a mold block and more specifically to a mold block adapted for the exterior cooling. The cooling method of the present invention does not necessitate internal mold block machining and does allow retrofitting of existing mold blocks with the cooling features of the present invention.

More specifically, according to the present invention a mold block for use with other mold blocks in forming a moving mold tunnel of a plastic molding apparatus has front and rear surfaces which face direction of travel for the mold block. The mold block further has a side surface between the front and rear surfaces of the mold block. The mold block includes a closed sided open ended channel which extends at least substantially across the side surface of the mold block.

The channel provides a controlled flow passage for a cooling medium, preferably a cooling gas to be fed to and remain in intimate contact with the mold block.

In one embodiment of the invention the channel extends vertically of the mold block. In another embodiment of the invention the channel extends horizontally of the mold block.

By providing the channel along the side surface of the mold block each mold block can be cooled individually

of every other mold block or the mold blocks can be cooled as a group along the mold tunnel. In all cases the cooling medium is contained in a manner to maximize the cooling benefits of the cooling medium. Furthermore, existing mold blocks without the cooling features of the present invention can be retrofitted to include a side mounted cooling channel.

BRIEF DESCRIPTION OF THE DRAWINGS The above as well as other advantages and features of the present invention will be described in greater detail according to the preferred embodiments of the present invention in which; Figure 1 is a schematic view of a pipe molding apparatus including mold blocks provided with cooling features according to a preferred embodiment of the present invention; Figure 2 is an enlarged schematic view through the moving mold tunnel of the molding apparatus of Figure 1; Figure 3 is a front view of one of the mold blocks from the moving mold tunnel of Figure 2; Figure 4 is a front view of a further mold block modified from the mold block of Figure 3 according to another preferred embodiment of the present invention; and Figure 5 is a front view of a mold block according to still a further preferred embodiment of the present invention.

DETAILED DESCRIPTION ACCORDING TO THE PREFERRED EMBODIMENTS OF THE PRESENT INVENTION IN WHICH: Figure 1 shows a pipe molding apparatus generally indicated at 1. This apparatus includes an extruder 3 which delivers molten plastic through a die 5 to a plastic corrugator generally indicated at 7. The plastic corrugator comprises an upper endless train 11 of mold block sections and a lower endless train 13 of mold block sections. The mold block sections on the upper and lower trains come together along a moving mold tunnel 14 which receives the molten plastic to shape a plastic pipe 9 which comes out the downstream end of the mold tunnel.

Figure 2 shows the mold block sections 17 mounted by mold block carriers 15 to the upper train 11 of the mold blocks. Mold block sections 21 are mounted by carriers 19 to the lower train 13 of the corrugator. The mold block sections from the upper and lower trains or loops move in the direction of arrow A through the mold tunnel 14. Each of the mold block sections as indicated by mold block sections 17 in Figure 2 has a front face F and a rear face R both of which face in the direction of travel of the mold blocks through the mold tunnel.

An air plenum 23 extends along the length of the mold tunnel. The purpose of this air plenum will be described later in detail.

Figure 3 of the drawings shows the front face of one of the mold blocks formed from upper mold block section 17 and lower mold block section 21. The upper mold block section has a parting face 18 which joins with the parting face 22 of the lower mold block section to form a completely closed mold block. The two mold block sections define an interior pipe forming mold region 24.

The pipe formed in this molding region can be shaped by either vacuum drawn through small slits in the mold block section or by blow molding which introduces positive air pressure to the pipe formed in the molding region 24.

Figure 3 shows that the mold block has first and second side surfaces S to its opposite sides between the front and rear surfaces of the mold block. A cooling system generally indicated at 31 is fitted to each of the side surfaces of the mold block.

In the Figure 3 embodiment cooling system 31 comprises a labyrinth channel comprising a primary channel part 43 and secondary channel parts 47 and 51.

As can be seen in Figure 3 channel part 47 reverses in direction relative to channel part 43 at the mouth 45 between the two channel parts. Channel 51 reverses in direction relative to channel part 47 at the mouth 49 between the two channel parts.

The primary channel part 43 has an open mouth 41 which enters between the closed sides of channel part 43.

One of those sides in defined by a pair of mounting plates 33 and 34 secured directly to the side surface of the mold block. The other side is defined by plate 35 which runs downwardly to the mouth 45 between the primary channel part 43 and the secondary channel part 47.

The secondary channel part 47 is defined by plate 35 on its one side and plate 37 on its other side. Plate 37 terminates short of the channel mouth 49 so that the other secondary channel part 51 is defined by plate 37 on its one side and plate 39 on its other or outer side.

The outside secondary channel part 51 in the embodiment shown in Figure 3 turns inwardly to a short

horizontally extending channel part 53 terminating with a channel outlet mouth 55. This channel mouth opens to the inside of the mold block and connects with vacuum lines 57 and 59 which are in turn connected with a main vacuum line 61.

As will be seen from the description above the labyrinth of channel parts as described comprises a plurality of close sided open ended channel parts which extend vertically to opposite sides of the mold block.

As earlier noted, an air plenum 23 runs along the length of the mold block tunnel. As each of the mold blocks moves through the tunnel it is fed with cooled air from the plenum 23 with that cooled air being fed into the channel labyrinth through the open mouth 41 of the primary channel 43. This channel which is the closest channel part to the side surface of the mold block receives the coldest air. This is where the air has the greatest cooling effect on the mold block.

The air although somewhat slightly warmed by the initial cooling while moving through channel part 43 is then reversed in direction up through channel part 47 and further reversed in direction downwardly through channel part 51. The air at this point although warmer than when it initially entered channel part 43 is still cooler than the outside air around the mold block and still has a cooling effect on the mold block.

In the embodiment shown in Figure 3 the cooling air is drawn by vacuum into the cooling labyrinth. This vacuum is one which is used to control other functions of the mold blocks such as vacuum forming of the product and/or internal vacuum cooling of the mold block. The vacuum as earlier noted is drawn from the main vacuum

line 61 through the channels 57 and 59 which connect directly to the outlet end 55 of the channel labyrinth 31.

It is to be noted from Figure 3 that the channel labyrinth 31 is easily adapted for retrofitting to an existing mold block not having the exterior mold cooling features. The two plate parts 33 and 34 secured directly to the outside side surface of the mold block. These plate parts separate from one another for opening and closing of the two mold block sections.

From the description above, it should be seen how individual mold block continues to receive cooling air which is trapped at the opposite side surfaces of the mold block as the mold block moves through the mold tunnel.

Figure 4 of the drawings shows a mold block formed by an upper mold block section 65 and a lower mold block section 67. A channel labyrinth generally indicated at 71 is mounted to each of the side surfaces of the mold block formed by sections 65 and 67.

In this embodiment the entrance to the labyrinth is through a mouth 75 leading to primary channel part 77.

The outlet from the labyrinth is through a channel mouth 79 from a secondary channel part 81. An internal mouth 80 is provided between the channel parts 75 and 79. The flow of cooling air into the labyrinth therefore enters through the mouth 75, runs along primary channel part 77 and reverses through internal channel mouth along channel part 81. The air then exits the labyrinth at mouth 79.

In the embodiment shown in Figure 4 the air movement through the cooling passage is provided by an

outside source of positive air pressure as opposed to the vacuum draw shown in the Figure 3 embodiment.

Figure 3 of the drawings shows a cooling channel having three cooling channel parts. Figure 4 of the drawings shows a cooling channel having two cooling channel parts. It is to be understood that more channel parts can be added to either of the labyrinths or either of the labyrinths shown in Figures 3 and 4 can be replaced with a cooling channel having a single channel part. Furthermore, a single channel part can be operated through vacuum or through positive air pressure. In any event, the channel is provided directly along the side surface of the mold block where the cooling medium e. g., preferably a cooling gas is trapped to provide contact cooling of the mold block.

In the embodiments described thus far the cooling channel including all parts of the cooling channel extends vertically along each side face of each mold block. This cooling channel can be closed at each of its three sides and opened only at the ends of the cooling channel. In this arrangement, the cooling air is individual to each mold block.

In another aspect of the invention the cooling channel to each side of each mold block is closed radially of each mold block as shown in the drawings but open to the front and back sides of each mold block.

This arrangement enables a transfer of the cooling air from mold block to mold block along the mold tunnel.

However, in keeping with the key concept of the present invention the air is still trapped from escaping radially outwardly of the mold blocks..

Figure 5 of the drawings shows another preferred

feature of the present invention. More specifically, Figure 5 shows a mold block formed by upper mold block section 91 and lower mold block section 93. The front face of the mold block formed by the sections is facing outwardly in Figure 5.

Provided to the opposite sides of the mold block are a plurality of fluid medium receiving channels 95.

These channels are bordered along their inside surfaces by a wall 96 extending vertically of each mold block section. Wall 96 provides a common mounting wall for each of the channels 95.

The channels 95 are capped outwardly by a second wall 97.

In this embodiment the channels 95 extend <BR> horizontally i. e. , from front to back of each of the mold blocks. They are not necessarily connected with one another but rather each of the channels receives its own flow of cooling air. This air is provided through an open mouth 99 which feeds to all of the channels. The open mouth 99 is again fed from a plenum of air extending along the length of the mold tunnel.

What is consistent between the Figure 5 embodiment and the earlier described embodiments is the feature that the cooling air is trapped along the side surface of the molds blocks and is not allowed to flow outwardly away from the mold blocks.

Although various preferred embodiments of the present invention have been described in detail, it will be appreciated by those skilled in the art that variations may be made without departing from the spirit of the invention or the scope of the appended claims.