GB2308824A

GB2308824A - Multi-cavity injection moulding

Info

Publication number: GB2308824A
Application number: GB9526638A
Authority: GB
Inventors: Soren Christian Sorensen; Jens Ole Sorensen
Original assignee: GB Electrical Inc
Current assignee: GB Electrical Inc
Priority date: 1995-12-29
Filing date: 1995-12-29
Publication date: 1997-07-09
Anticipated expiration: 2015-12-29
Also published as: DE19600304C2; FR2743328A1; DE19600304A1; GB2308824B; GB9526638D0; FR2743328B1

Description

2308824 BALANCED MULTI-CAMY INJECTION MOLDING OF CABLE TIES

BACKGROUND OF THE INVENTION

The present invention generally pertains to injection molding of ties that are useful for forming a loop fbr retain% a bundle of elongated articles, such as cables and is particularly directed to an improvement in multi-cavity injection molding of such tiesSuch a tie is commonly known as a cable tie One type of tie includes an elongated tongue with two ends and two broad sides, a locking head at one end of the tongue, a tip at the other end of the tongue, a first set of ratchet teeth extending along one broad side of the tongue and a second set of ratchet teeth exterging along the other broad side of the tongue, wherein the locking head has sides defining an opening for receiving the tip of the tongue. Referring to FIG. 1, the sides include a movable pawl 10 that is hinged at one side of the opening and an abutment surface-12 that is across the opening from the pawl. The pawl 10 has pawl teeth 14 disposed for engaging the first set of ratchet teeth 16 when the tip of the tongue 18 has is boon inserted through the opening with the first set of ratchet teeth facing 16 facing the pawl 10. When at 1 one tooth 14 is so "aged, the pawl 10 is movable toward the abutment surface 12 in response to a pulling force applied to the tongue 18 in a direction opposite to the direction of inserlion 20 in order to force the second set of ratchet teeth 22 against the abutment surface 12. Teeth 24 are disposed on the abutment surface 12 for =g the second set of ratchet teeth 22 when the tip of the tongue 18 has been inserted through the opening with the second set of ratchet teeth 22 facing the abutment surface 12 and the side of the tongue including the second set of ratchet teeth 22 is forced a the abutment surface 12 by movement of the paw) 10. Such a tie is described in U.S. Patent No. 4,473.524 to Paradis. Another type of tie differs from the tie 1 described above in that it includes a set of ratchet teeth on only the broad side of the tongue that faces the pawl when the tongue is inserted through the locking head opening.

For efficient manufacture, it is preferred to injection mold ties simultaneously with a multi-cavity mold. A problem incident to multicavity injection molding of ties is that all of the cavities of the inold in which the ties are formed are not always completely filled simultaneously with the injected plastic material. Referring to FIG. 2, which illustrates a plurality of injection molded ties 26 formed in the cavities 28 of one mold piece 30 after the mold pieces defining the cavities have been separated, it is seen that failure to completely fill all of the mold cavities simultaneously results in some of the cavities 28a bring incompletely filled, such that the ties 26a therein are not completely formed, and other cavities 28b being overfilled, such that a flashing of excess plastic 32 is attached to some & the ties 26b formed therein. The gates through which the plastic material is injected into the mold cavities 28 are located at the ends of the cavities 28 at which the locking heads 34 of the ties 26 are formed.

is SUMMARY OF THE EqWNTION

The present invention provides a method of balanced injection molding of a plurality of ties in a multi-cavity mold such that a plurality of mold cavities are completely filled approximately simultaneously with the injected plastic material. For injection molding a plurafity of ties in a multi-cavity mold, wherein each of at least two mold cavities defines a tie comprising an elongated tongue with two ends and two broad sides, a locking head at one end of the tongue, a tip at the other end of the tongue, a first set of ratchet teeth extending along one broad side of the tongue and a second set of ratchet teeth extending along the other broad side of the tongue, wherein the locking head has sides defining an opening for receiving the tip of the tongue, the sides including a movable 1 pawl that is hinged at one side of said opening and an abutment surface that is across the opening from the pawl, wherein the pawl has at least one pawl tooth disposed for Jocidng engagement with the first act of ratchet teeth when the tip of the tongue has been inserted through said opening with the first set of ratchet teeth facing the pawl and wherein the abutment surface includes at 1 one tooth for locking engagement vAth the second set of ratchet teeth when the tongue has been inserted through the opening in such a direction that the second m of ratchet teeth face the abutment surface and the side of the tongue including the second set of ratchet teeth is forced against the abutment surface by movement of the pawl, the method comprising the steps of is (a) providing maid pieces defining therebetween said at least two cavities for forming said ties having a uniform maximum thickness between the two broad sides of the ties, wherein at least one of the maid pieces includes projections for forming the ratchet teeth, and (b) injecting plastic material approximately simultaneously into at least both of said at least two maid cavities to fbrm the ticsg.

wherein step (a) comprises providing maid pieces in which the relative dimensions of the projections for forming the first set of ratchet teeth andlor the second set of ratchet teeth in said at least two maid cavities are noorm such that when plastic material is injected in accordance with step (b) injected plastic material flows through said at least two mold cavities at respective flow rates that cause at least both of said at least two maid cavities to he completely filled approximately simultaneously with the injected plastic material.

The present invention also Provides a multi-cavity maid for injection molding a plurality of ties. wherein each of at least two maid cavities deffies a tie comprising an elongated tongue with two ends and two broad sides, a locking head at one end of the tongue, a tip at the other end of the tongue, a first set of ratchet teeth extending along one 3 broad side of the tongue and a second set of ratchet teeth extending along the other broad side of the tongue, wherein the locking head has sides defining an opening for receiving the tip of the tongue, the sides including a movable pawl that is hinged at one side of said opening and an abutment surface that is across the opening from the pawl, wherein the pawl has at least one pawl tooth disposed for locking engagement with the first set of ratchet teeth when the tip of the tongue has been inserted through said opening with the first set of ratchet teeth facing the pawl and wherein the abutment surface includk!S at least one tooth for locking engagement with the second set of ratchet teeth when the tongue has been inserted through the opening in such a direction that the second set of ratchet teeth face the abutment surface and the side of the tongue including the second set of ratchet teeth is forced against the abutment surface by movement of the pawl, the mold comprising mold pieces defining therebetween said at least two cavities for forming said ties having a uniform maximum thickness between the two broad sides of the ties, wherein at least one of the mold pieces includes projections for forming the ratchet teeth; wherein the relative dimensions of the projections for forming the first set of ratchet teeth andlor the second set of ratchet teeth in said at least two mold cavities are non-uniform such that when plastic material is injected approximately simultaneously into at low both of said at least two mold cavities the injected plastic material flows through said at least two cavities at respective flow rates that cause at least both of said at least two mold cavities to be completely filled approximately simultaneously with the injected plastic material.

The present invention further provides a method of making a multi-cavity mold for injection molding a plurality of ties, wherein each of at least two mold cavities defines a tie comprising an elongated tongue with two ends and two broad sides, a locking head at one end of the tongue, a tip at the other end of the tongue, a first set of ratchet teeth extending along one broad side of the tongue and a second set of ratchet teeth extending along the other broad side of the tongue, wherein the locking head has sides defining an opening for 4 receiving the tip of the tongue, the sides including a movable paw] that is hinged at one side of said opening and an abutment surface that is across the opening from the pawl, wherein the pawl has at least one pawl tooth disposed for locking engagement with the first set of ratchet teeth when the tip of the tongue has been inserted through said opening with the first set of ratchet teeth facing the pawl and wherein the abutment surface includes at least one tooth for locking engagement with the second set of ratchet teeth when the tongue has been inserted through the opening in such a direction that the second set of ratchet teeth face the abutment surface and the side of the tongue including the second set of ratchet teeth is forced against the abutment surface by movement of the pawl, the method comprising the steps of (a) providing mold pieces defining therebetween said at least two cavities for forming said ties having a uniform maximum thickness between the two broad sides of the ties, wherein at least one of the mold pieces includes projections for fbmiing the ratchet teeth, with said projections being uniform for at least both of said at least two mold cavitiesy.

(b) injecting plastic material at a minimal injection pressure approximately simultaneously into at least both of said at least two mold cavities in order to form the ties and completely fill one of the cavities with the injected plastic material; (c) measuring the relative extent to which said at least two mold cavities are fined with the injected plastic material,- and (d) when at least both of said at least two mold cavities are not completely filled approximately simultaneously, adjusting the relative dimensions of the projections for forming the first set of ratchet teeth andlor the second set of ratchet teeth in at least both of said at least two mold cavities to be such that when plastic material is injected in accordance with step (b) injected plastic mat flows through said at least two cavities at respective flow rates that cause at least both of said at least two mold cavities to be completely fined approximately simultaneously with the injected plastic material- The forgoing aspects of the present invention also are applicable to multi-cavity injection molding of a plurality of cable ties in which ratchet teeth are provided on only one side of the tongue for engagement with the pawl.

Additional katuros of the present invention are described with reference to the detailed description of the preferred embodiments.

BREEF DESCREMON OF THE DRAWING FIG. 1 is a sectional view showing preferred engagement of the ratchet teeth of a prior art fie with the pawl and the abutment surface within the locking head of the tie.

FIG. 2 illustrates a in a prior art multi-cavity injection molding method wherein a plurality of injection molded ties are in the cavities of one mold piece after the mold pieces defining the tie-forming cavities have been separated.

FIG. 3 is a sectional view of one portion of a mold defining a portion of one mold cavity fbr forming the ratchet teeth of one tie in a multicavity mold in accordance with the present invention.

FIG. 3A is a sectional view showing the engagement of the pawl and the abutment surface with the ratchet-teeth portion of one tie formed with the portion of the mold shown in FIG, 3.

6 FIG. 4 is a sectional view of another portion of a mold defining a portion of another mold cavity for forming the ratchet teeth of another tie in a multi-cavity mold in accordance with the present invention.

FIG. 4A is a sectional view showing the engagement of the pawl and the abutment surface with the ratchet-teeth portion of anothex tie formed with the portion of the mold shown in FIG. 4.

DETAILED DESCRIEPTION Referring to FIGS, 3, 3A, 4 and 4A, a preferred embodiment of the mold of the present invention includes at least two mold pieces 40, 42 defining therebetween at leam two c"ffics 44, 46 for respectively forming ties 48, 50 having a un6rm maximum thicImess T between the two broad sides of the ties 48, 50. One of the mold pieces 40 includes projections 52 for forming the first set of ratchet teeth 16 that engage the pawl teeth 14,' Another of the mold pieces 42 includes projections 54 for forming the second set of ratchet teeth 22 that engage the abutment surface teeth 24, The relative dimensions is of the projections 52 for fbm-dng the first set of mtchet teeth 16 in the two mold cavities 44, 46 are non-uniform andlor the relative dimensions of the projections 54 for forming the second set of ratchet teeth 22 in the two mold cavities 44, 46 are non-uniffirm such that when plastic material is irdected approximately simultaneously into both of the two mold cavities 44, 46 the injected plastic material flows through the two cavities 44, 46 at respective flow rates that cause both of the two mold cavities 44, 46 to be completely filled apprely simultaneously with the injected plastic material.

Referring to FIG. 1, it is seen that the first set of ratchet teeth 16 have a prefrred depth Ap and the second set of ratchet teeth 22 have a preferred depth Bp. In the portion 7 of the mold shown in FIG. 3, the projections 52 of the one mold piece 40 have a depth dimension AL that is larger than required for forming a first set of ratchet teeth 16 having the preferred depth Ap, and the projections 54 of the other mold piece 42 have a depth dimension BL that is larger than required for fornmg a second set of ratchet teeth 22 having the preferred depth Bp. whereby the first set of ratchet teeth 16 have a depth AL that is larger than the preferred depth Ap and the second set of ratchet tooth 22 have a depth BL that is larger than the preferred depth Bp, as shown in FIG. 3A.

4A.

In the portion of the mold shown in FIG. 4, the projections 52 of the one Mold piece 40 have a depth dimension AS that is smaller than required for forming a first set of ratchet teeth 16 having the preferred depth Ap, and the prqiections 54 of the other mold piece 42 have a depth dimension BS that is smaller than required for forming a second set of ratchet teeth 22 having the preferred depth Bp; whereby the first set of ratchet teeth 16 have a depth AS that is smaller than the preferred depth Ap and the second set of ratchet teeth 22 have a depth BS that is smaller than the preferred depth Bp, as shown in FIG.

The relative differences between the depth dimensions Ap, AL and AS and the relative diffierences between the depth dimensions Bp, BL and BS are greatly exaggerated in the drawing. The actual differences in these depth dimensions is such that the strength of loeldng engagement between the ratchet teeth 16, 22 and the respective pawl teeth 14 and abutment surface teeth 24 is not significantly affected even though the pawl teeth 14 do not extend to the full depth AL of the first set of ratchet teeth 16 when the depth AL of the first set of ratchet teeth 16 is larger than the preferred depth Ap and the abutment surface teeth 24 do not extend to the full depth BL of the second set of ratchet teeth 22 when the depth BL of the second set of ratchet teeth 22 is larger than the preferred depth Bp, as shown in FIG. 3A andlor the first set of ratchet teeth 16 do not extend to the full 8 depth of pawl teeth 14 when the depth AS of the first set of ratchet teeth 16 is smaller than, the preferred depth Ap and the second set of ratchet teeth 22 do not extend to the 1WI depth of the abutment surface teeth 24 when the depth B S of the second set of ratchet teeth 22 is smaller than the preferred depth Bp, as shown in FIG. 4A.

In the preferred method of making the molds, the mold pieces that are provided initially define therebetween at least two cavities 44, 46 for forming ties 48, 50 having a uniform maximum thickness T between the two broad sides of the ties 48, 50, wherein each of the mold pieces 40, 42 includes projections 52, 54 for forming the ratchet teeth 16, 22, with the projections 52 for forming the first set of ratchet teeth 16 being uniform for at least both of the at least two mold cavities 44, 46 and with the projections 54 for forming the second set of ratchet teeth 22 being uniffirm for at least both of the at least two mold cavities 44, 46. Preferably, the projections 52, 54 have depth dimensions AL, BL, as shown in FIG. 3, that are larger than required for forming ratchet teeth 16, 22 of the preferred dimensions Ap, Bp shown in FIG. 1.

Plastic material is then injected at a minimal injection pressure approximately simultaneously into at least both of the at least two mold cavities 44, 46 in order to form the ties 48, 50 and completely fill one of the cavities 44, 46 with the injected plastic material.

The relative extent to which the at least two mold cavities 44, 46 are filled with the injected plastic material is measured; and when at least both of the at least two mold cavities 44, 46 are not completely filled approximately simultaneously, the relative depth dimensions A, B of the projections 52, 54 for at least both of the at least two mold cavities 44, 46 are adjusted to be such that when plastic material is injected at a minimal injection pressure approximately simultaneously into at least both of the at least two mold cavities 9 "9 46, the injected plastic material flows through the at 1 two cavities 44, 46 at respective flow rates that cause at least both of the at least two mold cavities 44, 46 to be completely filled approximately simultaneously with the injected plastic material.

The depth dimensions A. B of the projections 52, 54 are adjusted by reducing the extensions of the tips 56, 58 of the respective projections 52, 54, with the tips 56 of all of the projections 52 for forming a first set of ratchet teeth 16 being reduced by a first uniform dcptt4 and with extensions of the tips 58 of all of the projections 54 for forming a second set of ratchet teeth 22 being reduced by a second uniform depth, which may or is may not be the same as the first uniform depth by which the tips 56 of the projections 54 are reduced. Alternatively the depths of only some of tips 56 and/or 58 of the projections 52 and/or 54 for forming one or more ties 49, 50 are reduced andlor such reduction is not necessarily unifbrm for all of the tips 56, 58 as to which the depth is reduced.

In alternative preferred embodiments, the depth of only either the tips 56 of the projections 52 that form the first set of ratchet teeth 16 or the tips 58 of the projections 54 that form the second set of ratchet teeth 22 are reduced.

Prefrably, the dimensions of the projections 52 for forming the first set of ratchet teeth 16 andlor the dimensions of the projections 54 for forming the second set of ratchet teeth 22 are adjusted so that the projections 52 andlor 54 for at least one of the at least two mold cavities 44, 46 are of the dimensions required for forming ratchet teeth 16 and/or 22 of the preferred dimensions Ap andlor Bp.

Herwever, if such an adjustment doesn't result in the injected plastic material flowing through the at least two cavities 44, 46 at respective flow rates that cause the at lout two mold cavities 44, 46 to be completely filled approximately simultaneously with the injected plastic material, the dimensions of the projections 52 for forming the first set of ratchet teeth 16 andlor the dimensions of the projections 54 for forming the second set of ratchet teeth 22 are adjusted so that the projections 52 and/or 54 for at least one of the at least two mold cavities 44, 46 are of a dimension AL andlor BL larger than required for forming ratchet teeth 16 and/or 22 of the preferred dimension Ap andlor Bp and so that the projections 52 andlor 54 for at least another of the at least two mold cavities 44, 46 are of a dimension As andlor BS smaller than required for forming ratchet teeth 16 and/or 22 of the preferred dimension Ap andlor Bp.

When such adjustments result in the injected plastic material flowing through the at least two cavities 44, 46 at respective flow rates that cause the at least two mold cavities 44, 46 to be completely filled approximately simultaneously with the injected plastic material, the multi-cavity mold is provided for balanced hjection molding of a plurality of ties and plastic material is injected approximately simultaneously into at least both of the at least two mold cavities 44, 46 to form the ties 48, 50.

is The advantages specifically stated herein do not necessarily apply to every conceivable embodiment of the present invention. Further, such stated advantages-of the present invention are only examples and should not be construed as the only advantages of the present invention.

While the above description contains many specificities, these should not be construed as limitations on the scope of the present invention, but rather as exemplifications of the preferred embodiments described herein. Other variations are possible and the scope of the present invention should be determined not by the embodiments described herein but rather by the claims and their legal equivalents.

CLAWS 2 4 6 8 12 14 16 18 22 1. A method of injection molding a plurality of ties in a multi-cavity mold, wherein each of at least two mold cavities (44, 46) defines a tie (48, 50) comprising an elongated tongue (18) with two ends and two broad sides, a locking head at one end of the tongue, a tip at the other end of the tongue, a first set of ratchet teeth (16) extending along one broad side of the tongue and a second set of ratchet teeth (22) extending along the other broad side of the tongue, wherein the loffing head has sides defining an opening for receiving the tip of the tongue, the sides including a movable pawl (10) that is hinged at one side of said opening and an abutment surface (12) that is across the opening from the pawl, wherein the pawl has at least one pawl tooth (14) disposed for locking engagement with the first set of ratchet teeth when the tip of the tongue has been inserted through said opening with the first set of ratchet teeth facing the pawl and wherein the abutment surface includes at least one tooth (24) for locking engagement with the second set of ratchet teeth when the tongue has been inserted through the opening in such a direction that the second set of ratchet teeth face the abutment surface and the side of the tongue including the second set of ratchet teeth is forced against the abutment surface by movement of the pawl, the method comprising the steps of (a) providing mold pieces (40, 42) defining therehetween said at least two cavities (44, 46) for forming said ties (48, 50) having a uniform maximum thickness (T) between the two broad sides of the ties, wherein at least one of the mold pieces includes projections (52, 54) for forming the ratchet teeth; and (b) injecting plastic material approximately simultaneously into at least both of said at least two mold cavities to form the ties; wherein step (a) comprises providing mold pieces in which the relative dimensions 24 (A, B) of the projections for forming the first set of ratchet teeth andlor the second set of ratchet teeth in said at least two mold cavities are non-uniform such that when plastic 12 26 material is injected in accordance with step (b) injected plastic material flows through said at least two mold cavities at respective flow rates that cause at least both of said at least 28 two mold cavities to be completely filled approximately simultaneously with the injected plastic material.

2 6 8 12 14 16 18 22 2. A method of injection molding a plurality of ties in a multi-cavity mold, wherein each of at least two mold cavities (44, 46) defines a tie (48, 50) comprising an elongated tongue (18) with two ends and two broad sides, a locking head at one end of the tongue, a tip at the other end of the tongue, and a set of ratchet teeth (16) extending along one broad side of the tongue, wherein the locking head has sides defining an opening for receiving the tip of the tongue, the sides including a movable pawl (10) that is hinged at one side of said opening and an abruttnent surface that is across the opening from the pawl, wherein the pawl has at least one pawl tooth (14) disposed for locking engagement with the set of ratchet teeth when the tip of the tongue has been inserted through said opening with the set of ratchet teeth facing the pawl, the method comprising the steps of.

(&) providing mold pieces (40, 42) defining therebetween said at least two cavities (44, 46) for forming said ties (48, 50) having a uniform maximum thickness (T) between the two broad sides of the ties, wherein at 1 one of the mold pieces (40) includes projections (52) for forming the ratchet teeth, and (b) injecting plastic material approximately simultaneously into at least both of said at least two mold cavities to form the ties., wherein step (a) comprises providing mold pieces in which the relative dimensions (A) of the projections for said at lean two mold cavities are non-uniform such that when plastic material is injected in accordance with step (b) Oected plasde material flows through said at least two mold cavities at respective flow rates that cause at least both of said at least two mold cavities to he completely filled approximately simultaneously with the injected plastic material.

13 2 4 6 8 12 14 16 18 22 24 26 3. A multi-cavity mold for injection molding a plurality of ties, wherein each of at leut two mold cavities (44, 46) defines a tie comprising an elongated tongue (18) with two ends and two broad sides, a locking head at one end of the tongue, a tip at the other end of the tongue, a first set of ratchet teeth (16) extending along one broad side of the tongue and a second set of ratchet teeth (22) extending along the other broad side of the tongue, wherein the locking head has sides defining an opening for receiving the tip of the tongue, the sides including a movable pawl (10) that is hinged at one side of said opening and an abutment mrftce (12) that is across the opening froin the pawl, wherein the pawl has at least one pawl tooth (14) disposed for locking engagement with the first set of ratchet teeth when the tip of the tongue has been inserted through said opening with the first set of ratchet teeth facing the pawl and wherein the abutment surface includes at least one tooth (24) for locking engagement with the second set of ratchet teeth when the tongue has been inserted through the opening in such a direction that the second set of ratchet teeth face the abutment surface and the side of the tongue including the second set of ratchet teeth is forced against the abutment surface by movement of the pawl, the mold comprisi;ng mold pieces (40, 42) defining therebetween said at least two cavities (44. 46) for forming said ties (48, 50) having a uniform maximum thickness (T) between the two broad sides of the ties, wherein al least one of the mold pieces includes projections (52, 54) for forming the ratchet teeth, wherein the relative dimensions (A B) of the projections for forming the first set of ratchet teeth andlor the second set of ratchet teeth in said at least two mold cavities are non-unifbrm such that when plastic material is injected approxhuately simultaneously into at least both of said at least two mold cavities the 4ected plastic material flows through said at 1 two cavities at respective flow rates that cause at least both of said at least two mold cavities to be completely filled approximately simultaneously with the injected plastic material.

14 4 6 8 12 14 16 18 2 6 4. A multi-cavity mold fbr injection molding a plurality of ties, wherein each of at least two mold cavities (44, 46) defines a tie (48, 50) comprising an elongated tongue (18) with two ends and two broad sides, a locking head at one end of the tongue, a tip at the other end of the tongue, and a set of ratchet teeth (16) extending along one broad side of the tongue, wherein the locking head has sides definingan opening for receiving the tip of the tongue, the sides including a movable pawl (10) that is hinged at one side of said opening and an abutment surface that is across the opening from the paa, wherein the pawl has at least one pawl tooth (14) disposed for locking engagement with the set of ratchet teeth when the tip of the tongue has been inserted through said opening with the set of ratchet teeth facing the pawl, the mold comprising mold pieces (40, 42) defining therebetween said at least two cavities (44, 46) for forming said ties (48, 50) having a uniform maximum thickness (T) between the two broad sides of the ties, wherein at least one of the mold pieces (40) includes projections (52) for forming the ratchet teeth, wherein the relative dimensions (A) of the projections for said at least two mold cavities are non-unifonn such that when plasfic material is injected approximately simultaneously into at least both of said at least two mold cavities the injected plastic material flows through said at least two cavities at respective flow rates that cause at least both of said at least two mold cavities to be completely filled approximately simultaneously with the injected plastic material.

5. A method of making a multi-cavity mold for injection molding a plurality of ties, wherein each of at least two mold cavities (44, 46) defines a tie (48, 50) comprising an elongated tongue (18) with two ends and two broad sides, a locking head at one end of the tongue, a tip at the other end of the tongue, a first set of ratchet teeth (16) extending along one broad side of the tongue and a second set of ratchet teeth (22) extending along the other broad side of the tongue, wherein the locking head has sides defining an opening is 8 12 14 16 18 22 24 26 28 32 for receiving the tip of the tongue, the sides including a movable pawl (10) that is hinged at one side of said opening and an abutment surface (12) that is across the opening from the pawl, wherein the pawl has at least one pawl tooth (14) disposed for locking engagement with the first set of ratchet teeth when the tip of the tongue has been inserted through said opening with the first set of ratchet teeth facing the pawl and wherein the abutment surface includes at least one tooth (24) for locking engagement with the second set of ratchet teeth when the tongue has been inserted through the opening in such a direction that the second set of ratchet teeth face the abutment surface and the side of the tongue including the second set of ratchet teeth is forced against the abutment surface by movement of the pawl, the method comprising the steps of (a) providing mold pieces (40, 42) defining therebetween said at least two cavities (44, 46) for forming said ties (48. 50) having a uniform maximum thickness (T) between the tWo broad sides of the ties, wherein at Jew one of the mold pieces includes projections (52, 54) for forming the mtchet teeth, with said projections being uniform for at least both of said at least two mold cavities; 0) injecting plastic material at a minimal injection pressure approximately simultaneously into at 1 both of said at least two mold cavities in order to form the ties and completely fill one of the cavities with the injected plastic material.

(c) measuring the relative extent to which said at least two mold cavities are filled with the injected plastic material. and (d) when at least both of said at least two mold cavities are not completely filled approximately simultaneously, adjusting the relative dimensions (A, B) of the projections for forming the first set of ratchet teeth andlor the second set of ratchet teeth in at least both of said at least two mold cavities to be such that when plastic material is injected in accordance with step (b) injected plastic material flows through said at least two cavities at respective flow rates that cause at least both of said at least two mold cavities to be completely filled approximately simultaneously with the injected plastic material.

16 4 6 8 14 16 18 22 24 26 6. A method of n a multi-cavity mold for injection molding a plurality of ties, wherein each of at least two mold cavities (44, 46) defines a tie (48, 50) comprising an elongated tongue (18) with two ends and two broad sides, a locking head at one end of the tongue, a tip at the other end of the tongue, and a set of ratchet teeth ( 16) extending along one broad side of the tongue, wherein the locking head has sides defining an opening for receiving the tip of the tongue, the sides including a movable pawl (10) that is hinged at one side of said opening and an abutment surface that is across the opening from the pawl, wherein the pawl has at least one pawl tooth (14) disposed for locking engagement with the set of ratchet teeth when the tip of the tongue has been inseTted through said opening with the set of ratchet teeth facing the pawl, the method comprising the steps of (a) providing mold pieces (40, 42) defining therebetween said at least two cavities (44, 46) for forming said ties (48, 50) having a uniform maximum thickness (T) between the two broad sides of the ties, wherein at least one of the mold pieces (40) includes projections (52) fbr forming the ratchet teeth, with said projections being uniform for at lean both of said at least two mold cavities; (b) injecting plastic material at a minimal injection pressure approximately simultaneously into at least both of said at lean two mold cavities in order to form the ties and completely fill one of the cavities with the injected plastic material., (c) measuring the relative extent to which said at least two mold cavities are filled with the injected plastic material; and (d) when at least both of said at least two mold cavities are not completely filled approximately simultaneously, adjusting the relative dimensions (A) of the projections for at least both of said at 1 two mold cavities to be such that when plastic material is injected m accordance with step (b) injected plastic material flows through said at least two cavities at respective flow rates that cause at least both of said at least two mold 17 cavities to be completely filled approximately simultaneously with the injected plastic 28 material.

Claims

7. A method according to Claim 6 or 7, wherein step (a) comprises the step

of.. (e) providing said mold pieces including said projections having dimensions (AL,

BL) that are larger than required for forming ratchet teeth of a preferred dimension (Ap, BP).

2 8. A method according to Claim 7, wherein step (d) comprises the step of (f) adjusting the dimensions of the projections so that the projections for at least one of said at least two mold cavities are of a dimension (Ap, Bp) required for forming 2 4 ratchet teeth of the preferred dimension.

9. A method according to Claim 7, wherein step (d) comprises the step of (f) adjusting the dimensions of the projections so that the projections for at least one of said at least two mold cavities are of a dimension (AL, BL) larger than required for forming ratchet teeth of the preferred dimension and the projections for at least another of said at least two mold cavities are of a dimension (AS, BS) smaller than required for 2 6 forming ratchet teeth of the preferred dimension.

is