US2358624A - Means for heating thermoplastic materials for molding - Google Patents

Description

A. A. BU RRY Sept. 19, 1944.

MEANS FOR HEATING THERMOPLASTIC MATERIALS FOR MOLDING Filed April 23, 1943 5 Sheets-Sheet l Z? mm &

Wi M n 6 v 4 A. A. BURRY Sept. 19, 1944.

MEANS FOR HEATING THERMOPLASTIC MATERIALS FOR MOLDING Filed April 23, 1943 5 Sheets-Sheet 2 [rm/enter. Ari/var BMW 1% P 1944- A. A. BURRY 2,358,624

MEANS FOR HEATING THERMOPLASTIC MATERIALS FOR MOLDING Patented Sept. 19, 1944 MEANS FOR HEATING THERMOPLASTIC MATERIALS FQR MOLDING Arthur A. Burry, Toronto, Ontario, Canada Application All!" 23, I943, Serial N0. 484,297

6 Claims. an. 18-30) the bottom of the cylinder, said jacket contain- This invention relates to devices for heating thermo-plastlcs as they are fed to the molds or dies and particularly to that type of machine where the pressure cylinder is vertically arranged and in which a heated hollow core is arranged within the cylinder in order that heat may be applied uniformly to a comparatively thin body of the thermo-plastic material.

The principal object of the invention is to provide means for effecting a direct circulation ofthe heating means through the interior of the hollow core and for directing condensate back to the steam generator so that the heat transfer surfaces will be maintained in constant direct contact with live steam maintained at a predetermined temperature.

The principal feature of the invention consists in the novel construction and arrangement of a hollow core to be supported within an upright cylinder through which the 'thermo-plastic material is forced and which is surrounded by a steam jacket provided with an immersion electric heating unit arranged in a sump below the level of the bottom of the cylinder to generate steam and effect the continuous flow around the WV cylinder, whereby communication between the steam jacket surrounding the cylinder and the interior of the core is maintained through ducts ing a body of water surrounding the heater a whereby steam was generated to maintain a continuous flow around the periphery of the cylinder to create and maintain a substantially uniform temperature surrounding the cylinder to plastify the contents thereof.

r The plastic injection molding of numerous articles of commerce is being very rapidly developed and certain types of molding machines are in operation in which the cylinders are preferably arranged in an upright position, and the particular purpose of the present invention is to apply an improved form of my invention to such type of machine and to provide the cylinder with a core which will be heated uniformly from end-to-end and which will be so constructed that leakage of either the plastic material or the heating medium will be avoided.

formed in the cylinder registering with ducts formed in the core, and tubular extensions of said ducts extend upwardly within the interior of the core to points adjacent to the top thereof and other ducts are arranged in said core extending outwardly from the bottom thereof and communicating with discharge ducts formed in the cylinder and communicating with the surrounding jacket to complete the circulating of the heating medium.

In the accompanying drawings Figure 1 a vertical mid-sectional view of a plastic extrusion cylinder constructed in accordance with this invention taken through the ducts which conduct steam from the cylinder heating jacket to the upper end of the interior of the'core.

Figure 2 is a vertical sectional view through the cylinder shown in Figure 1, the section being made at right angles to that of Figure 1 and taken through the line 2-2 of Figure 1 and also showing the arrangement of the heating element in a sump forming part of the cylinder jacket.

Figure 3 is a horizontal sectional view taken through the line 3-'-3 of Figure 2.

In my United States Patent 2,115,940, dated May 3, 1938, I disclosed a plastic injection device in the form of a cylinder having a discharge orifice and provided with pressure means for ejecting thecylinder contents with the cylinder surrounded by a steam jacket spaced therefrom :and in which an immersion electric heating unit was arranged at the bottom of the jacket below In my co-pending application filed concurrently herewith I have disclosed a structure for securing the heated core within a plastic heating cylinder with compression seals for sealing the juncture of the ducts leading to the interior of the core with the ducts leading from the heating jacket, and the structure defined in this present application for this purpose is practically the same as that shown in the concurrent application.

In the structure illustrated herein the cylinder l is arranged in an upright or vertical position and surrounding this cylinder is a steam jacket 2 which is provided with end flanges 3 and 4 which are a driving fit on the periphery of the cylinder, and the jacket and cylinder being constructed of metal with a similar co-emcient of expansion, will remain steam-tight under extraordinarily high temperatures and pressures. The jacket 2 is formed with an integral transversely disposed chamber 5 which is open to the interior of the steam jacket and extends below the bottom end of the jacket so that this chamber forms a sump which contains a small body of water. i

An electric heating element 6 is supported longitudinally within this chamber 5 and heats the water contained therein to form steam which circulates around the exterior of the cylinder within the jacket at a very high temperature, and as its heat is absorbed by the cylinder and the steam loses its thermal efliciency it drops to the bottom of the jacket and returns to the sump to be elevated to a higher temperature.

A dome I is arranged in the wall of the steam jacket in a suitable position and to it is secured a tubular connection 8 to support a suitable gauge.

The bottom end of the cylinder is formed with a suitably stepped counterbore 9 and one or more ducts III are formed in the cylinder wall leading from the space enclosed by the jacket 2 from a point above the bottom thereof to an end face of the counterbore. The duct I is particularly illustrated in Figure 1.

One or moresimilar ducts II are formed in A head I2 is machined to form a snug fit within the stepped surfaces of the counterbore 9, and

this head has formed integral therewith a core 13 which is preferably formed with a conical end H and it is provided with-an interior chamber l5 which extends from the bottom end upwardly to a point adjacent the top.

Ducts l6 are formed in the head leading from the bottom of the chamber ii in the core laterally outward and they are formed with upturned extremities which register with the ducts Ill. The meeting ends of the ducts Ill and the ducts it are preferably formed with tapered counterbores l1 and tapered ferrules l8 formed of compressible metal are fitted into these counterbores and when the head is drawn tightly into sealing contact with the counterbore .of the cylinder the ferrules l8 form compression seals for the juncture of the ducts l0 and I6 leading tothe interior of the core from the steam chamber within the jacket 2.

Tubes [9 are fitted. snugly into the inner ends of the ducts l6 entering the chamber l5 in-the core and these extend upwardly to a point close to the top of the chamber l5 and conduct the live steam from the steam jacket to the top of the core, thus applying their most intense heat directly against the conical core point, and then flowing downward the steam communicates its temperature to the interior wall of the-core, and as it travels downward and its temperature becomes reduced it flows to the bottom.

Ducts 20 extend from the bottom of the core chamber laterally outward and their extremi-' ties are turned upward and register with the ducts II. The extremities of the ducts II and the ducts are taper-counterbored to receive ferrules II similar to the ferrules l8, which also form compression seals.

The downwardly flowing steam passing through the ducts 20 and II flows into the steam jacket at the bottom and continues'on into the sump to be re-heated into higher-temperature steam to again circulate through the core as described.

Passages 22 are formed in the head I! between the radial ducts 20 and I6 and these converge around the tapered lower end 23 of the core. The head I! is secured in any desirable manner to the end of the cylinder by suitable bolts or cap screws which are not shown;

In this particular type of machine the head is embedded in a recess in a bed block 25 which is formed with a centrally arranged discharge orifice 26' which surrounds the conical bottom end 23 of the core and directs the heated thermoplastic material into a nozzle structure 21, which is here shown threaded into and welded to one side of the block.

It will be noted that'the bottom wall of the chamber 5, in which the electric heater is enclosed, is provided with diagonally placed bosses 28 inwhich are secured suitable blow-out plugs 29. A suitable thermostat control device 30 to control the heater may be placed in one end of the chamber 5.

It will be readily appreciated that a device constructed as described will provide a cylinder for feeding thermo-plastics to a molding machine which will, by having within the centre of the cylinder a core heated to the same temperature as the outside wall of the cylinder, uniformly plastify the thin tubular stratum of material forced therethrough without danger of' the material being overheated and which will ensure uniform plasticity so that the molding results produced will be of a uniform and dependable character.

It is found desirable to provide for the release of air which may be trapped within the steam chambers and I provide a pipe'8l, preferably inserted into the dome 8 and provide same with a suitable valve (not shown) to facilitate such removal. g

A tube 32. provided with a suitable valvekls connected with one or more of the passages I! to relieve any air or non-condensible fumes the steam Jacket and extending within the interior of the hollow core, and ducts leading from the bottom of the interior of the core to the lower portion of the steam jacket.

2. A means for heating thermo-plastic materials for molding comprising an upright cylinder surrounded by a steam jacket, ducts formed in the cylinder wall communicating with said steam jacket, a hollowcore arranged in said cylinder, ducts formed in the core communicating with said cylinder ducts, and tubes extend upwardly within the hollow core from certain of said core ducts and'conducting steam directly to the upper end of the interior of the core.

3. A device as claimed in claim 1, in which a sump is arranged at the bottom of the steam jacket, an electric heating element arranged in said'sump, the ducts leading from the bottom of said core being directed to discharge into said sump.

' 4. A meansfor heating thermo-plastic materials for molding comprising an upright cylinder surrounded by a steam Jacket, said cylinder having ducts formed therein communicating with the steam jacket above the bottom and ducts arranged to communicate with the steam jacketbelow the aforesaid ducts, a head closing the cylinder having a hollow core extending into the cylinder and provided with separate sets of ducts communicating respectively with the aforesaid ducts in the cylinder, compression seals arranged between said head and cylinder to seal the Junetures of said ducts; and tubes leading from the higher set of ducts in the cylinder wall and extending upwardly within the hollow core and discharging steam into the top of the cavity in the core.

5. A device as claimed in claim 1 having an air release duct leading from the upper end of the steam jacket.

6. A device as claimed in claim 1 having an air release duct leading from the interior of the hollow core.

ARTHUR A. BURRY.

Images