GB1589105A

GB1589105A - Continuous injection moulding

Info

Publication number: GB1589105A
Application number: GB1868878A
Authority: GB
Original assignee: Textron Inc
Current assignee: Textron Inc
Priority date: 1977-08-22
Filing date: 1978-05-10
Publication date: 1981-05-07
Also published as: JPS5434948A; DE2820179C2; AU3604478A; DE2820179A1; CH630286A5; CA1108814A; AU514646B2; BE869875A

Abstract

In the process, an endless, flexible metal strip (12), which encircles a casting mould wheel (10) and rotates therewith, engages in the casting mould wheel. The casting mould cavities, closing between the metal strip (12) and the casting mould wheel (10) at an engaging location (14) and opening at a releasing location (20), are filled with plastic via an injection shoe (16) through openings in the metal strip (12). After the releasing location (20), the components are removed from the casting mould cavities, the metal strip at the same time engages in the casting mould wheel (10) along an arc having a central angle (22) of less than 180 DEG , for example 110 DEG , and a large radius of curvature. This permits the use of a metal strip in which casting mould cavities are likewise formed, and which has a thickness which is many times greater than 0.001 times the casting mould wheel, without the metal strip (12) suffering from fatigue and breaking. The process is suitable in particular for producing slide fastener strips. For this purpose, carrier strips (28, 30) are introduced into corresponding recesses, for example in the casting mould wheel, are encapsulated and drawn off with the slide fastener elements from the casting mould wheel (10). <IMAGE>

Description

(54) CONTINUOUS INJECTION MOLDING (71) We, TEXTRON INC., of 40 Westminster Street, Providence, Rhode Island, United States of America, a corporation organised under the laws df the State of Delaware, United States of America, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement:- The invention relates to continuous moulding of elements of a thermoplastic resin material, herein referred to as polymer articles, and is particularly, though not exclusively, for molding slide fastener elements.

The invention utilises injection molding apparatus of the class (herein referred to as the class specified) comprising a wheel having in its periphery, circumferentiallyspaced molding cavities, and a cdntinuous flexible metal band which is pressed into contact with a part of the wheel circhm- ference to close the cavities during molding, is driven with the wheel, and allows thermoplastic resin material to be injected into and to solidify in the covered cavities.

Hitherto, the bands have been of a flexible strong metal, such as a certain stainless steel. However the bands have in practice been limited to having a maximum thick ness generally not greater than 0.001 times the diameter of the wheel since bands of greater thickness have been found to be subject to fatigue and breakage after a relatively short period of use.

Also when using apparatus of the class specified to mold symmetrical fastener elements directly on to carrier tapes, it is necessary to fdrm mold cavities in the band which must be thicker than the cavity depth.

A typical depth of cavity is 0.15 centimeter in a band of 0.2 centimeter. Therefore to avoid fatigue failures as above mentioned the wheel has been of very large diameter, e.g. two metres in diameter.

According to the invention, in apparatus of the class specified a portion of each molding cavity is formed in the inner surface of the band and has a maximum depth less than the band thickness, the band having a thickness greater than 0.001 times the wheel diameter, and the band having such length and contacting the wheel over such arcuate portion of its periphery that the band has at each point an inward radius of curvature equal to or greater than the wheel radius.

Adoption of the invention can lead to improved and less costly continuous molding of polymer articles utilizing a metal band having a thickness several times greater than 0.001 times the wheel diameter without fatigue failure of bands after only short use.

Also the invention leads to the advantage that cavities with sufficient depth can be formed in a band engaging a molding wheel to mold fastening elements without the necessity of the molding wheel having a large diameter and the band having a long length.

Since the band has an inward radius of curvature at all points, it does not assume a flat state or outwardly concave state at any point so that bending and fatigue and resultant failure of the band are reduced.

Other objects, advantages, and features of the invention will be apparent from the description of the preferred embodiment taken in conjunction with the accompanying drawings.

In the drawings: Fig. 1 is a side elevation view of an apparatus for molding coupling elements on the edge of a continuous tape in accordance with the invention.

Fig. 2 is a cross section view of a portion of the apparatus of Fig. 1 taken at line 2-2 in Fig. 1.

Fig. 3 is a bottom view of a portion of a band of the apparatus of Fig. 1 Fig. 4 is an enlarged side view of a portion of the band matching with the cavity wheel 6f Fig. 1.

Fig. 5 is a bottom view of a portion of a modified band in accordance with the invention.

Fig. 6 is a cross section view of the modified band of Fig. 5 with a corresponding modified portion of a cavity wheel.

Fig. 7 is a bottom view of still another modified band portion in accordance with the invention.

Fig. 8 is a cross section view of the modified band portion of Fig. 7 together with another corresponding modified cavity wheel portion in accordance with the invention.

A molding apparatus, illustrated in Fig.

1 and employed in accordance with the invention, includes a molding or cavity wheel 10 and an annular band or flexible member 12 encircling the wheel 10. Both the wheel 10 and the band 12 are rotated in a counter clockwise direction as viewed in Fig. 1. The band 12 is forced against the cavity wheel at a stationary engaging point 14 by an injection shoe 16 of a thermoplastic injection apparatus biased against the outside of the band 12. A band drive wheel 18 engages the outside of the band at a stationary disengaging point 20 to hold the band 12 continually against the wheel 10 during rotation from point 14 to point 20 through an angle 22 of engagement. After the disengaging point 20 the band 12 is maintained spaced from the periphery of the wheel 10 until rotated back to the engaging point 14.

As shown in Fig. 2, the cavity wheel 10 has a pair of annular channels 24 and 26 formed around the periphery of the wheel 10 for receiving respective carrier tapes 28 and 30. A plurality of cavity means includes a pair of rows of cavity portions 32 and 34 formed in the periphery of the cavity wheel 10 and spaced along the inner edges of the channels 24 and 26 together with corresponding rows of cavity portions 36 and 38, see also Fig. 3, formed in the inside of band 12 for mating with the cavity portions 32 and 34 to form cavities having the shape of slide fastener elements to be molded on the inner edges of the tapes 28 and 30. The wheel 10 also has a plurality of runner channels 40 spaced around the periphery of the wheel 10 and extending between the cavity portions 32 and 34 with narrow neck or gate portions 42 and 44 opening into the cavity portions 32 and 34.

Holes or openings 46 are formed through the central portion of the band 12 spaced along its length for communicating between the center portions of the respective channels 40 and the injection shoe 16 to permit passage of pressurized molten thermoplastic material into the channels 40 and hence into the cavities 32, 34, 36 and 38.

The wheel 10 has an annular rim 48 at one side thereof forming an edge guide for one edge of the band 12. At the other side of the wheel 10, as shown in Fig. 4, there are a plurality of undulations or projections 50, forming teeth for mating or meshing with similar undulations or depressions 52 formed in the band 12. The projections 50 and depressions 52 have the same spacing as the cavities 32, 34, 36 and 38 around the respective wheel 10 and band 12 so as to bring about and maintain registration of the cavities 36 and 38 of the band 12 with cavities 32 and 34 in the wheel 10. The wheel 10 is formed by conventional machining techniques from a suitable metal such as normally employed in molding dies.

The band 12 is formed from a commercially available flexible resilient sheet or strip of metal such as a stainless steel including 17% chromium, 4% nickel, 4% copper and 75% iron with other possible constituents, or a stainless steel including 17% chromium, 7% nickel and 76% iron with other possible constituents. One suitable material is ARMCO speciality steel 17-4 ph from Armco Steel Corporation and identified as melting specifications ASTM A693 and AMS 5604. The band material has a thickness suitable to accomodate the cavities 36 and 38 and is formed by conventional techniques into the band 12. The band material thickness is selected substantially greater than 0.001 times the diameter of the wheel 10 and preferably several times the diameter of wheel 10 so that the diameter of the wheel and the length of the band 12 can be kept to a minimum.

The band 12 is maintained with a continuous inward radius of curvature which is equal to or greater at all points to the radius 53 of the wheel 10 without any portions thereof becoming straight and without any outward radius of curvature. Additionally the band 12 must have a length greater than the circumference of the wheel 10 to produce a space 54 between the band 12 and wheel 10 during rotation from point 20 to point 14; this space 54 must be sufficient to permit the insertion of the tapes 28 and 30 and the laying of the tapes 28 and 30 by roller means 56 in the channels 24 and 26 as well as to permit the removal of stringers 58 and 60 consisting of the tapes 28 and 30 with the molded coupling elements thereon from the cavity wheel 10 and band 12. For such band lengths the angle 22 of engagement between points 14 and 20 generally must be substantially less than 1800, is preferably less than 1600, and is especilly preferably less than 1200; otherwise the band 12 would have straight portions and possibly portions with outward radii of curvature. Further the angle 22 of engagement must be sufficient to permit injection and solidification of the polymer in the cavities 32, 34, 36 and 38 while the band 12 engages the wheel 10. Generally the band 12 should have a length in the range from 5% to 30% longer than the circumference of the wheel 10. Shorter lengths of band 12 relative to the circumference of wheel 10 permit larger angles 22 of engagement while longer lengths of band 12 relative to the circumference of wheel 10 require smaller angles 22 of engagement.

Thus it is preferred to have the length of the band 22 less than 25to larger than the circumference of the wheel 10 to permit a larger angle 22 of engagement allowing employment of a relatively small wheel 10 and short band 12. Also bands 12 having relatively lesser thicknesses permit longer bands and/or greater angles 22 of engagement; but the minimum thickness of the band is determined by the required depth for the cavities 36 and 38 plus an allowance necessary for proper machining and normal variation during forming of the cavities.

In an example of a cavity wheel and band in accordance with the invention, the cavity wheel 10 has a diameter of 40.64 centimeters (16 inches) the band 12 has a thickness of 0.198 centimeters (0.078 inches), the cavities 36 and 38 are machined to a depth of 0.146 centimeter (0.0575 inches), the angle 22 between points 14 and 20 is 1100, and the length of the band 12 is selected to produce a spacing 54 of 4.445 centimeter (1.75 inches) between the wheel 10 and band 12 on the side where spaced apart.

In use or operation of the apparatus shown in Figs. 1-4 the wheel 10 and band 12 are simultaneously rotated counter clockwise.

The band 12 is forced against the outer periphery of the wheel 10 at point 14 and is maintained against the periphery of the wheel 10 from point 14 to point 20 by the force of the band drive wheel 18. The tapes 28 and 30 are fed into the respective channels 28 and 30 in the wheel 10 prior to the engagement of the band 12 with the wheel 10 at point 14. Molten thermoplastic polymer is injected from the thermoplastic injection means via injection shoe 16 through the openings 46 in the band 12 into the channels 40 and hence into cavities 32, 34, 36 and 38 formed between the band 12 and the wheel 10 and around the inner edges of the tapes 28 and 30. After injection adjacent to the engaging point 14 the molten polymer is solidified within the cavities to form solid coupling elements secured on the inner edges of the tapes 28 and 30. After solidification of the polymer to form solid coupling elements, the band 12 is disengaged from the wheel 10 at point 20. Thereafter the stringers 58 and 60 including the tapes 28 and 30 with the molded coupling elements on the inner edges thereof are removed from the injection molding apparatus and passed on for further proces sing, such as severing of the runners, connecting the elements and pull-up of the stringers 58 and 60 to form a slide fastener chain.

It has been discovered that the maintenance of an inward radius of curvature at all points in the band 12 equal to or greater than the radius of the wheel 10 throughout all points thereof, permits the employment of a metal band 12 having a thickness substantially greater than 0.001 times the diameter of the wheel 10 without failure due to fatigue and stress on the band 12. Previously it had been believed that metal bands having a thickness greater than 0.001 times the diameter of the wheel would be subject to fatigue and failure due to stress on the band. Also by adopting these features a substantial reduction in the size and cost of a cavity wheel and a band used for continuous molding is made possible.

The cavity wheel 10 and the band 12 described above contain two channels and two rows of mating cavities for molding two continuous stringers of a slide fastener; however, the cavity wheel and band can be constructed with only one channel and one row of cavities for forming only one stringer, or the cavity wheel and band may be constructed with more than two channels and two rows of cavities for forming more than two stringers. Additionally the above embodiment is described for molding coupling elements into inner edges of continuous tapes; however the present invention could also be used for molding other articles such as elongated elements on connecting threads as disclosed in Specifications Nos. 1 546492 and 1 546 493.

A modification of the apparatus for molding elements on the edge of the tape is illustrated in Figs. 5 and 6 and includes grooves 100 and 102 formed in the periphery of the cavity wheel together with grooves 104 and 106 formed in the inside surface of the band 12 intersecting the respective cavity portions 32, 34, 36 and 38.

The grooves 100 and 104 mate to form a channel or passageway for receiving a bead 108 of the tape 28 while the grooves 102 and 106 mate to form a passageway for receiving a bead 110 of the tape 30. The beads 108 and 110 on the inner edges of the tapes 28 and 30 provide for a stronger support of the coupling elements on the tapes.

Another modification of the apparatus for forming molded coupling elements on the edges of the tapes is illustrated in Figs.

7 and 8. In this modification, channels 124 and 126 for receiving the tapes 28 and 30 are formed on the inside surface of the band 12 in place of the channels 24 and 26 in the wheel 10 of the apparatus of Fig. 2.

Since the invention is subject to many modifications, variations, and changes in detail within the scope of the claims, it is intended that all matter in the foregoing description or shown in the accompanying drawings be interpreted as illustrative and not in a limiting sense.

WHAT WE CLAIM IS: 1. Apparatus of the class specified wherein a portion of each molding cavity is formed in the inner surface of the band and has a maximum depth less than the band thickness, the band having a thickness greater than 0.001 times the wheel diameter, and the band having such length and contacting the wheel over such arcuate portion of its periphery that the band has at each point an inward radius of curvature equal to or greater than the wheel radius.

2. Apparatus as claimed in claim 1, wherein the band contacts the wheel over less than a 1600 arcuate portion of the wheel circumference.

3. Apparatus as claimed in claim 2, wherein the band contacts the wheel over less than a 1200 arcuate portion of the wheel circumference.

/4. Apparatus as clamied in any of claims 1 to 3, wherein the band length is less than 30% greater than the wheel circumference.

5. Apparatus as claimed in claim 4, wherein the band length is within the range 5% to 25% greater than the wheel circumference.

6. Apparatus as claimed in any of claims 1 to 5 for molding slide fastener coupling elements on to a stringer tape edge, there being a channel between the band and wheel to receive the tape with one edge of the tape overlapping the cavities.

7. Apparatus of the class specified and substantially as hereinbefore described with reference to and as shown on the accompanying drawings.

8. Apparatus of the class specified wherein the wheel and band have dimensions substantially in accordance with the foregoing example.

9. A method of molding polymer elements when utilizing apparatus as claimed in any of claims 1 to 8.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. detail within the scope of the claims, it is intended that all matter in the foregoing description or shown in the accompanying drawings be interpreted as illustrative and not in a limiting sense. WHAT WE CLAIM IS:

1. Apparatus of the class specified wherein a portion of each molding cavity is formed in the inner surface of the band and has a maximum depth less than the band thickness, the band having a thickness greater than 0.001 times the wheel diameter, and the band having such length and contacting the wheel over such arcuate portion of its periphery that the band has at each point an inward radius of curvature equal to or greater than the wheel radius.

/

4. Apparatus as clamied in any of claims 1 to 3, wherein the band length is less than 30% greater than the wheel circumference.