NOZZLE FOR INJECTION MOLDING

Abstract: A nozzle for so called hot runner molds and intended for injection molding of plastic comprises two body members (2 respectively 3) which are connected to each other while constituting an annular space (4) encapsuled between the members, in which a heating element (5) or the like is located. In the interior of the nozzle there is provided a heat transferring means (7) which in a manner known per se is in contact with the rest of the nozzle by means of ribs or the like (8). Said ribs are axially located intermediate and inside the end surfaces of the heating element (5) and the heat will consequently be concentrated to the zone (8). The body member (2) has a tubular portion (12) with a bevelled end surface (13) which by means of grinding compound is ground against a corresponding conical portion (20) of the body member (3) by turning the body members relative to each other. The ribs of the heat transferring means (7) as well as the channel (6) of the nozzle is slightly conical for the sake of fastening the former by pressing and a securing is preferably obtained by means of a pin (32) which penetrates the heat transferring means (7) and extends into the tubular portion (12) of the body member (2).

Description: NOZZLE FOR INJECTION MOLDING This invention refers to a nozzle for injection molding and more parti¬ cularly refers to a heated nozzle, suitable for so called hot runner molds. In the field of injection molding so called hot runner molds have re¬ ceived an extensive use. For a successful use of this technique it is neccesary that the nozzles have the capability of transferring in an effective manner the heat to the plastic material flowing through the nozzle and that the nozzles will be reliable, sturdy and may be pro- duced at reasonable costs. To achieve this and other objects the invention has the characteristics according to the claims. In the accompanying drawing an exemplary embodiment of the invention is illustrated, wherein Fig. 1 is a longitudinal section through the new nozzle while Fig. 2 is a transverse section along l ine ll-ll with certain parts cut away. The nozzle, illustrated in the drawing which has been given the general designation numeral 1, comprises two body members 2 respectively 3, whic are mutually connected while constituting therebetween an annular space <•-. enclosed between said body members and intended to receive a heating means, for instance a heating coil 5 and further a channel 6 which pene¬ trates the nozzle axial ly. The nozzle further includes a heat transferrin means, general ly designated as 7, which in a zone 8 in a manner to be described is in contact with wall surfaces which limit the channel 6 of the member 2 and the ends of said zone 8 are located intermediate the end surfaces 9a, 9b of the heat transferring means 5- The body member 2 has in the illustrated embodiment a head 10, which preferably has a turned down end portion 11 and from the head extends a considerably thinner, cylindrical portion 12, which in the free end thereof has a bevelled end surface 13- For constituting the channel 6 the body member 2 is provided with a bore, extending from the right end thereof in the drawing which means that the cylindrical portion 12 will be tubular and the bore continues, preferably via a rounded portion in a narrower bore 15. The bores are made with high surface quality such that an even and non-porous, preferably high polished channel 6 is obtained. In the head 10 of the body member 2 and adjacent the cy- lindrical portion 12 there is provided a recess 16 in which a turned- down portion 17 of the head 18 of the second body member 3 fits and said second body member just like the ffrst body member has a bore 19. which however extends from the head 17 and in the opposite end thereof con¬ tinues in a conical bore 20, which via a rounded transition 21 continue in the nozzle outlet orifice 22. The body member 2 further has openings (not shown) through which cables 23 for supply of electrical energy to the heating coil respectively a c 2k for a sensing means, located in a groove 25 in the body member 2 extend. The heat transferring means 7 is-as entioned-substantial ly torpedo- shaped with a front pointed part 26 which extends into and a short leng beyond the outlet orifice 22 and a rear, pointed part 27 and as appears from the drawing those walls of the heat transferring means which are in contact with the body member.2 have a streamline design with the rear portion 28 more sloping than the front portion 29. As appears from fig. 2 the passage through the zone 8 of the nozzle is constituted by milled off portions 8 * of the means 7- The two body member 1,2 heads have holes 30 for bolts by means of which they are tightened together and in order to reduce the heat losses a glass fibre reinforced sealing 31 is provided. When the body members are pressed against each other the bevelled end portion 13 of the body member 2 is to sealingly engage that wall portion of the body member 1, which limits the conical bore 20. This is achieved by the illustrated embodiment therein that the body members have such a fit in each O other that they can be turned relative to each other for grinding the sealing portions 13,20 by means of grinding compound or the like. By means of the design now described it is achieved that the heating coil 5, which of course is pressed in contact with the tubular part 12, will transfer heat to the molten plastic resin passing through the nozzl in a very efficient way. Since the zone 8, in which heat is transferred from the heating means 5 to the heat transferring means 7, Is situated intermediate and within the ends of the heating means it is obvious that heat will be concentrated to this particular zone. The heat transfer to the head of the nozzle as well as to the front portion thereof is minor, which is just the kind of heat flow which is desired. The new nozzle is easy to manufacture and the design makes it possible to obtain by simple means the high surface accuracy which is needed as wel l as the sealing 13,20 just described. It is of decisive importance that the molten plactic resin can pass through the nozzle without any obstacles and to achieve this it is necessary that all surfaces have a very high surface finish and that there are no shoulders or the like which can retard the flow or retain parts of the plastic mass. This is of particular importance when mate- rials such as acetal or polyvinyle chloride plastics are to be processed. In order to make such a design possible the heat transferring means is secured in the manner that the channel is sl ightly conical (about 1:100) and the portion 8 of the heat transfer means 7 has a corresponding slope such that the means 7 can be pressed to a seat. In order to secure the means in this position one or several pins 32 are arranged (fig.2) to penetrate the heat transferring means 7 and extend into the tubular por¬ tion 12. Due to the effective heat transfer to the interior of the nozzle, mate¬ rial with high melting index such as polycarbonate can be successfully processed with the new nozzle.

Claims: A Claims: 1. Nozzle for injection molding, preferably with so called hot runner, comprising in combination two body members, connected to each other under constituting firstly an annular space enclosed between said body members and provided to receive a heating element and secondly a central channel extending axial ly through both body members, said body members being so connected to each other adjacent the outlet end of the nozzle that the heat transfer between said body members will be very small in this area a preferably torpedo shaped heat transfer element being pro¬ vided in said channel and held in contact with the surface surrounding said channel by means of axial ly extending wall portions within a zone, which axial ly is located substantially intermediate the end surfaces of the heating element to obtain an effective heat transfer from one of said body members to the other one and to the interior of said channel Nozzle as claimed in claim 1 wherein said heat transfer element with a preferably tapered end extends substantially to the outlet of the nozzle. 3. Nozzle as claimed in claim 1, wherein one of the body members has a tubular portion, the free end of which being in the shape of a thin- walled portion having a bevelled end surface provided to sealing engage a corresponding substantially conical inner surface of said second body member to constitute the connection between said body members adjacent the outlet opening of the nozzle. -*.. Nozzle as claimed in claims 1-3 inclusive, wherein the first body member has a head from which said tubular portion extends, the second body member also having a head from which extends a narrower part which is tubular by means of a bore extending axial ly form said head, said bor having such a shape and dimension that it together with the tuburlar por tion of said first body member constitutes the annular space for the hea ing element said bore further being limited by a conical wall which con¬ stitutes the portion against which the bevelled end of said first body member seal ingly rests. 5. Nozzle as claimed in claims I--*., wherein the body members are fitted i each other in a manner permitting the members to be turned to grind the seal ing surfaces -^tJH_ϊ O PI

Inventors: MUELLER HANS, MUELLER, HANS
Applicants: MUELLER HANS, MUELLER, HANS
Application year: 1984
Main classification: B29C45
IPC codes: B29C45