Injection molding distribution manifold having improved uniformity of manifold block temperatures

Auxiliary end heating devices on an elongated, heated hot melt distribution manifold body assist in maintaining uniform temperatures throughout all portions and passageways of the manifold body. The heating devices preferably take the form of thick film electrical resistive heaters of plate-like construction. The end heaters are on their own control circuit separate and apart from the circuit for other heaters for remaining portions of the manifold body. Special isolating slots are formed in lower corners of the manifold body between supporting standoffs and overhead melt passageways in the manifold body.

TECHNICAL FIELD

This invention relates to injection molding manifolds and, more particularly, to ways of managing heat distribution throughout the manifold in an effort to achieve uniform temperatures of all melt channels or passages, even those near the ends of the manifold.

BACKGROUND AND SUMMARY

Elongated manifold blocks typically have a central inlet passage that delivers hot melt from an extruder or other source into the center of the block and then splits it into a main runner that delivers the melt to a series of injection nozzles spaced along the length of the manifold body. While various means are typically utilized to keep the body hot so that the melt flows properly at all times, the opposite ends of the manifold are typically exposed to ambient air. Consequently, passages associated with the endmost nozzles are difficult to maintain at the same high temperatures as other passages in the body. Moreover, structures utilized to support the manifold often function as heat sinks to draw off disproportionate amounts of heat in end portions of the body and compound the problem.

The present invention addresses this problem by providing a way of supplying auxiliary heat specifically to opposite end portions of the manifold body in addition to that which is supplied to the body as a whole. Furthermore, the temperature in at least one of the end portions is sensed separately from the rest of the body to control the auxiliary supply of heat separately from the main supply, with a view to establishing a uniform temperature throughout the entire body if at all possible.

In a preferred form of the invention, each auxiliary source of heat is a generally flat electrical resistance type heater applied to each end surface of the manifold body. Preferably, the heater covers the entire exposed surface of the end of the body. In addition, in order to reduce the amount of heat drawn off by supports at the corners of the body, a pair of isolating slots extend transversely through the entire body and are located generally between each support and the melt passages in the upper and inboard regions of the body. In a preferred form, each isolating slot is generally L-shaped, having a vertical leg that is shorter than the horizontal leg and with the horizontal leg extending inwardly toward the center of the body from the bottom of the vertical leg.

DETAILED DESCRIPTION

The present invention is susceptible of embodiment in many different forms. While the drawings illustrate and the specification describes certain preferred embodiments of the invention, it is to be understood that such disclosure is by way of example only. There is no intent to limit the principles of the present invention to the particular disclosed embodiments.

The distribution manifold assembly10includes an elongated parallelepiped metallic manifold body12preferably constructed from 4140 alloy steel. Body12is supported by a pair of end supports or standoffs14and16and by a center support18, all of which are preferably constructed from a low thermal conductivity material such as 304 stainless steel. Underlying the supports14,16and18is a horizontal support plate20that is preferably constructed of a high carbon alloy steel.

Secured to the front face of body12is a sprue bushing22that is adapted to be connected to the outlet of an extruder or other source of hot melt for the purpose of supplying such molten plastic material to manifold assembly10. Sprue bushing22has a through passage24that delivers melt to an upwardly inclined inlet passage26in body12. Inlet passage26, in turn, intersects with a main, longitudinally extending runner passage28that extends essentially the full length of body12in opposite directions from central inlet passage26. Main runner28is capped at its opposite ends by a pair of plugs30and32. A series of branch passages34intersect with main runner28along the length thereof and lead to corresponding injection nozzles36. Preferably, nozzles36may take the form of the nozzles disclosed and claimed in co-pending application Ser. No. 10/272,974, filed Oct. 16, 2002 in the name of Brian R. Lefebure titled “Injection Molding Nozzle.” Said application is hereby incorporated by reference into the present specification.

Manifold body12is provided with heating mechanism broadly denoted by the numeral38for keeping body12at a high enough temperature that plastic material within the various internal passages of body12remains molten at all times. In part such heating mechanism38takes the form of four electrical resistance type heating rods or elements40that extend along the length of body12and are situated at each of the four corners thereof as viewed from the end or in transverse cross-section. Elements40may, for example, take the form of rods available from Watlow Electric Manufacturing Company of St. Louis, Mo. and are secured in place in a well-known manner. Opposite ends of elements40project outwardly beyond manifold body12and into corresponding upright receivers42and44wherein elements40are electrically connected with various circuitry and the like. A sensor in the nature of a thermocouple46received within body12generally near the mid-portion thereof above main runner28is connected in the same electrical circuit as heating elements40for the purpose of controlling operation of elements40. Thermocouple46is operable to sense when the temperature within the surrounding region of manifold body12drops to a predetermined level so as to cause heating elements40to be activated as necessary to maintain the predetermined temperature. Although a wide variety of sensors may be utilized for carrying out this function, one acceptable sensor is a standard thermocouple available from Watlow Electric Manufacturing Company of St. Louis, Mo.

In conventional manifold assemblies the branch passages associated with the endmost nozzles present the biggest challenge for maintaining the desired heat level because in conventional manifold assemblies opposite ends of the manifold body are exposed to ambient air. For the sake of illustration, the branch passages of manifold body12have been labeled34athrough34fwith the two endmost branches being branches34aand34f. If manifold body12were a conventional body, branches34aand34fwould be the branches most subject to heat loss.

However, in accordance with the present invention, heating mechanism38includes a pair of auxiliary end heating devices48and50applied to opposite ends of body12for the purpose of maintaining branches34aand34f, as well as their adjacent portions of main runner28, at substantially the same temperature level as all other passages within body12. In a preferred embodiment, each end heating device48,50takes the form of a generally flat electrical resistance type heater such as that available from Watlow Electric Manufacturing Company of St. Louis, Mo. as a thick film heater having a 300 or 400 series stainless steel substrate. Preferably, each heating device48,50is attached to the flat, corresponding end surface52or54of body12by suitable fasteners such as screws56. As illustrated inFIG. 3, each end heating device48,50overlies and covers virtually the entire surface area of the corresponding end surface52or54. Preferably, as illustrated with respect to heating device50inFIG. 3, each heating device48,50is designed to produce three different levels or zones of heat output from the top to the bottom of the device, namely zones A, B and C. Zone A in the top one-third of the device produces the lowest heat output, while zone B in the middle one-third produces the highest output. Zone C in the lower third produces an intermediate range of heat output.

Each heating device48,50has a pair of leads58and60connected to corresponding terminals62and64that connect electrically with heating elements of the devices. Leads58and60are connected in an electrical circuit that is separate and apart from that for heating elements40and sensor46so that devices48and50are not controlled by sensor46. Instead, devices48and50are controlled by a separate sensor66that is preferably the same type of thermocouple as sensor46. In a preferred embodiment, only one of such sensors66is utilized to control both devices48,50.

In a preferred form of the invention the sensor66is located in an end portion of manifold body12so as to be in the most advantageous position for detecting temperature variations in that critical region of the body. For purposes of the present invention, an end portion of body12is defined as that portion of the body that extends from the center line of the next-to-the-last branch passage in the body to the corresponding end surface of the body. Thus, in the present embodiment, manifold body12has two end portions12aand12b. End portion12aextends from the center line68of inboard nozzle36band branch passage34boutwardly to end surface52, and end portion12bextends from center line70of inboard nozzle36eand branch passage34eoutwardly to end surface54. In the illustrated embodiment, the sensor66is located in end portion12b,preferably slightly outboard of the central axis72of endmost nozzle36fand endmost branch passage34f.

To further control and manage heat distribution and loss within manifold body12, each end portion12aand12bis provided with its own isolating slot74or76that passes entirely transversely through body12generally between the corresponding standoff14or16and the overhead melt passageways28and34. Each slot is generally L-shaped, having a relatively short vertical leg78and a longer horizontal leg80. Horizontal leg80intersects vertical leg78at the lower end of leg78, while vertical leg78intersects horizontal leg80at the outer end of horizontal leg80. Vertical leg78is entirely disposed outboard of the axis72associated with endmost nozzle36fand endmost branch passageway34f. Horizontal leg80is spaced a short distance above the lower two heating elements40of manifold body12.

Operation

Operation and use of manifold assembly10should be apparent from the foregoing description. With the auxiliary end heaters48and50in place, the end branch passages34aand34fare no longer exposed to heat loss to the degree suffered by prior art manifolds. Instead, end portions12aand12bof manifold body12can be maintained at substantially the same temperature level as the remaining portion of the manifold body with the result that much better melt flow characteristics can be obtained. Moreover, by having end heating devices48,50under the control of their own sensor66, rather than relying upon the sensor46used for the central region of the manifold body, precise temperature control can be obtained exactly where heat loss is most likely to occur.

The isolating slots74and76immediately above each of the standoffs14,16serve as a way of breaking the drain of heat that otherwise occurs from the passageways in end regions of the body due to the standoffs14,16acting as heat sinks. Slots74,76perform their function without significantly weakening the structural integrity of the manifold body in these areas.

The inventor(s) hereby state(s) his/their intent to rely on the Doctrine of Equivalents to determine and assess the reasonably fair scope of his/their invention as pertains to any apparatus not materially departing from but outside the literal scope of the invention as set out in the following claims.