FR2751231A1 - METHOD OF MANUFACTURING A ROULETTE TYPE CLAMPING PLIERS FOR INTRAVENOUS DELIVERY - Google Patents

Abstract

The present invention relates to a method of modifying a mold consisting of two halves (70, 75) of cavity (76) and a core for the production of housings for a plastic roller type clamp for intravenous administration, said housings comprising a cylindrical roller axle bearing surface (31a, 32a) and a tube clamping surface, comprising treating each of the cavity halves (70, 75) to bring them closer together in a proportion of 25 to 60% of the original thickness of the side walls of the molded part in order to reduce the weight of the molded part. This process allows the weight of the molded parts in the housing to be reduced while producing a housing structure that still meets the strength and more of the high speed molding requirements.

Description

The present invention relates to cylinder clamps for

administration sets

  intravenous and more particularly a clamp.

  rolled out for sets of administrators

  intravenous treatment with the unique advantages of low manufacturing cost and unexpected maintenance

good quality performance.

  During the period between the 1940s and 1950s, intravenous sets evolved from reusable to disposable. In the past, a technique has been developed to produce and store medical grade fluids for human infusion of, for example, water, as well as dilute salt solutions, dilute dextrose solutions and others. fluid nutrients as well as some medications. These fluids were stored in sealed glass containers and were administered using a sterile rubber surgical tube. The tube and other administration components were generally re-sterilized and reused. The flow rate of the administered fluid was adjusted by varying the degree of nip of the rubber tube. Various clamps have been developed

for this type of application.

  With the increase in use, the arrival of medical grade polyvinyl chloride tubes and the need to reduce or eliminate the serious problem of patient / hospital contamination,

  introduced disposable administration sets.

  This has solved the problem of contamination, but has introduced a new one: that of flow rates varying over time, that is to say

  variations in time compared to the initial setting-

  the desired flow rate. The pinched plastic tube raised the problem of cold flow when it was pinched and this caused the change in flow rate over time; generally, this variation was significant (in the order of 40 per cent in the first ten minutes, then increased) and more

  often the flow translated into a decrease.

  The first collet (which did not act in parallel) was described in the years 1967 to deal with the problem of flow variation over time, and in the following years a series of advanced pliers was introduced. parallel as well as a number of important improvements. The main feature of these newly developed clamps was, prior to 1967, the ease of adjustment and, in the following years, the combination of ease of use and / or the ability to adjust

  the flow, which should change little in time.

  Another category of improvements was that of a forceps providing better grip of the tube because, if the clamp was released accidentally, the resulting increase in flow, or, in extreme cases, leakage could be a risk for the

life, even being deadly.

  The manufacturing costs were generally

  an underlying factor, as is the case with most high-use products. Typical factors in reducing costs were: (1) the manufacture of small parts to save materials, (2) the use of materials at lower cost, and (3) the production of easy-to-use parts.

  assemble to reduce labor costs.

  Injection-molded plastics are the common solution for making a clamp. Economic pressures to reduce health equipment costs, the huge volume of infusion set use and cost

  ever-growing plastic resins combine

  to greatly increase the interest of the focus

  pliers satisfying the requirements set out below.

  above: (1) to facilitate the use, (2) to reduce the time varying flow rates and (3) to ensure a firmer gripping of the tube, as well as to allow the manufacture at a cost always lower than that obtained by following the steps obvious realization of smaller parts, increasing the number of cavities in manufacture and / or the use of a low cost resin. The roller clamps for intravenous infusion sets sometimes referred to as IV sets, which are generally discarded together with set IV, after a single use, are well known and are designed primarily to regulate the flow rate of the liquid passing through a soft plastic tube, foldable and deformable, usually made of polyvinyl chloride. The degree of pinching of the tube is normally used to decrease, and therefore regulate, the flow rate to the desired value, which is generally measured in drops per minute, which represents the prescribed flow rate at which it is desired to administer the fluid presenting the fluid intravenously. of interest. These collets are also used as an on / off device, that is to say either to allow flow or to stop it. It goes without saying that the clamp must, once set up, accurately control the flow over time and also be able to stop completely

the flow rate when desired.

  Typical prior art clips are those of the Applicant's prior patents: U.S. Patents 4,047,694, 1977; 4,013,263 of 1977; 3,685,787 in 1972; 5,014,962 of 1991; 4,725,037 from 1988 and Re 31,584

  of 1984, the descriptions of which are incorporated here

reference.

  In general, there are two basic types of

  roller clamps for IV assemblies, one

  being the "inclined ramp" gripper and the other so-called "parallel action" gripper or gripper whose wheel moves in a generally parallel relationship with what is designated by clamping surface. In each case, the clamp basically comprises a housing in which is placed a wheel (cylinder or roller) generally supported by the housing, the plastic tube being received in the housing and located between a base surface or clamping surface of the housing.

housing and the cylinder.

  Whatever the type of clamp, in an extreme position of the cylinder, there is a "complete flow", ie an unregulated flow at the full capacity of the assembly IV In another position of the cylinder , generally distant from the full flow position, there is a non-flow position in which no fluid passes through the tube. This is typically a stop position. In some clamps, there is another stop position, more properly a locking position in which the motion of the cylinder is prevented, as will be described, and there is no flow in the tube. Between the full flow position and the no flow position, there is generally a cylinder displacement zone in which the flow rate can be controlled, that is, the so-called "flow control" zone. The length of this zone may be smaller in the axial direction than the maximum distance in which the cylinder moves, particularly if there is a blocking position. In the case of an inclined ramp clamp, the flow control is obtained by the principle of the "inclined ramp" in which the cylinder is brought, by the thumb of the operator, to climb a slope, which causes a reduced clearance between the cylinder and the opposite surface of the housing on which the tube rests, hence the creation of the desired degree of pinching and therefore the

  flow control. As the cylinder or wheel advances, -

  the clearance between the cylinder and the surface of the housing on which the tube rests decreases and, in the extreme position, creates a complete stop (pinched tube). For typical tweezer flow settings, the tube orifice is completely crushed in the large central area (where the radius of curvature of the tube is high), while a pair of openings are formed at each side, where o The radius of curvature of the pinched tube is the smallest and therefore offers greater resistance to pinching. The phenomenon of cold flow in the plastic tube explains why the newly formed openings continue to crash and cause the flow to decrease, after the cylinder has been moved to its new position and remains there. In a clamp acting in parallel (double action), the effects of cold flow are reduced or ideally eliminated by having at a location in the housing flow control area a section guiding the wheel so that there is obtained a clearance of the tube having the effect of forming at least one, and usually two holes at one of the outer edges or both edges, to be completely closed in the pinched state. Fine flow control is achieved by varying the ratio between the fully closed portion of the pinched tube and the other portion that remains open, as there is a clearance portion in the base, housing or wheel in which no pinch or even a slight pinch is applied. The action or stroke of the roller does not need to be perfectly parallel, or almost parallel, to the opposite pinching surface of the housing. The criterion for a clamp acting in parallel is to have a clearance between the roller and the housing which causes the total closure by pinching the local part of the tube and, to have the rest of the surface of the housing which is in contact with the tube , or is close to it, in order to have some of

  release that allows and / or encourages the formation of-

opening in the tube.

  In the type of clamp acting in parallel, the cylinder clamps completely to the closure part of the tube, and generally a clearance in the housing

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  serves to create the desired degree of nip or partial closure of the tube. While the term "parallel" is used, it is not intended to describe a geometrical parallelism or an arrangement in which the stroke of the cylinder is effected in a perfectly parallel manner over the entire stroke; and such "parallel" action is only necessary in the range of the cylinder stroke for flow control. In fact, a parallel action clamp can form, and this is usually the case, a small relative angle between the cylinder stroke and the opposite surface on which the tube rests and is clamped, for example, as a consequence of a "draft" used in the production of the injection mold, as will be discussed. However, this relatively small angle is, in itself, insufficient and is not intended to effect primary control or flow variation since the change in clearance between the cylinder and the surface on which the tube is clamped is insufficient to vary directly the area of the cross section of the flow, in contrast with a clamp at the inclined ramp. There is also the case where, in the area of the housing preceding the flow control and after the closed or no flow position, as opposed to the locking position, the clamping action may also be parallel in its structure. Since there are zones other than those where flow control is performed, the need for parallel action even as approximate, as described here, is neither appropriate nor

necessary.

  Although the realization of a cylinder clamp acting in parallel, in which only one cheek of the tube is fully pinched at closing,

  can be an improvement for pliers-

  designed to perform well in terms of variable flow rates over time, by fully pinching an opening that would otherwise be formed and would tend to have a reduction in cold flow, more advanced realizations result in a total pinch at the closing of both

  cheeks of the tube made of soft plastic material.

  The distinguishing feature of a parallel cylinder clamp (dual action) of an inclined boom clamp is how to achieve flow control. Clamps. cylinder acting in parallel get control of flow by pinching completely at closure a cheek, and generally both cheeks of the tube over the entire range of flow control and vary the ratio between part fully pinched at closure and part not pinched depending on the position of the cylinder in the flow control area. It appears that a full pinch closure of one or both of the cheeks, but not of the adjacent section of the tube, is only necessary in this range of the cylinder stroke.

  actually constitutes the flow control range.

  In the case of an inclined ramp clamp, the flow control is achieved by varying the clearance between the cylinder and the opposing clamping surface. It thus appears that, even though a true parallelism may not exist in a "parallel action" forceps, the quantity of the non-parallelism is insufficient to vary the game of any quantity which appreciably affects the change of the debit. This is especially true if one of the cheeks or both cheeks are fully pinched at closing in the range of the cylinder stroke in the control zone

flow.

  A typical arrangement for ensuring that a cheek or both cheeks of the tube are fully pinched at closure is to provide a game between the game.

  bottom of the cylinder and the opposite surface of the housing-

  against which the tube is pinched, which is generally not greater than twice the thickness of the wall of the unclamped tube and in some cases less than twice that thickness. In general, a lower game

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  Double the thickness of the wall is satisfactory to ensure that one cheek or both cheeks are fully pinched at closing. Again, it will be appreciated that this need for a defined set exists only in the rate control area. In fact, the game is larger at the entrance side of the housing and may be somewhat smaller near the exit side of the housing, particularly if there is a lock

separated at closing.

  In the "parallel action" clamp, the clearance between the cylinder and the opposite housing clamping surface may or may not vary with the position of the cylinder, but this variation of the clearance practically does not control the size of the formed opening. The control is obtained, in this case, by varying the ratio between the wall portion tightened on closing

and the untightened part.

  In the realization of the inclined ramp gripper, while the cylinder is advancing, the central section of the pinched tube can flex and be totally crushed upon closing, but the clearance between the cylinder and the opposite surface of the housing: (1) is sufficiently large to allow the formation of openings, and in general, at one or both cheeks of the tube, and (2) varies to create the desired size of the openings and the corresponding flow rate. In a less common version of a clamp acting in parallel, the clearance is in the surface of the cylinder. A general characteristic of these types of clamps is that the open area of the cross-section of the tube varies as the cylinder progresses in its stroke, the amount of the surface

  open being related to the configuration of the release.

  As is known, the clearance can take a wide variety of shapes and can be outside one side of the housing, or above the pipe or at any other location. Its function is to vary the open area presented to the flow in response to the motion

of the cylinder.

  In virtually all models and types of collets that use a cylinder and a housing, the axis of the cylinder bears against a guide surface while the position of the wheel or cylinder is changed as well as when it is in position. place, creating

the desired degree of pinching.

  In the clamps of the present invention, there are special requirements, and some of these important requirements are as follows: (1) The upper surfaces of the housing must be designed to withstand the pressure exerted by the cylinder axis. (2) The top surface of the housing shall be designed to withstand bending when subjected to an upward force such as that caused by the axis of the pinch wheel. (3) The side walls of the housing shall be designed to withstand voltages. (4) The bottom surface of the housing shall be designed to withstand bending and to operate in compression, provide a variable width clearing action and an ideal location for special raised elements. The raised elements, where they exist, have varying heights, widths and spacings. (5) The housing shall be made of a plastics material that may be injection molded, shall have a cross section designed to facilitate the flow of the injection-molded plastic material to fill the entire

cavity of the steel mold.

  When parallel-action clamps were introduced to the market in commercial volumes around 1975, the units were about 50 mm in length. Sloped dwellings were approximately 35 mm long. Parallel Action Pliers have taken a significant share of the market with their best

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  performance compared to the inclined boom clamps and, in 1978, accounted for almost all of the sales of one (Abbott Labs) of the two largest companies (Baxter Travenol is the other company> from the United States of America involved). In 1986, Baxter began using a longer patented clip, and then other companies such as Cutter (which actually started on an earlier date), McGaw, IVAC and Borla, introduced pliers with 50 mm housing and the trend was

found so established.

  With the more widespread use of longer clamps, manufacturing costs increased substantially for a large part of the market, although many longer clamps did not provide the best performance of the patented parallel clamp. Most of these companies simply followed the trend of having greater length of housing. In the case of Abbott's parallel clamps, there was a functional reason for the length, in addition to the provision of a non-time varying flow rate, and a firmer grip of the tube, the longer stroke. long cylinder allowed adjustment

  25.most end of the degree of pinching and therefore of the flow.

  Therefore, in an effort to comply with the trend towards greater length, the market has introduced heavier tongs, apparently seemingly uninterested, from the resulting increased manufacturing costs of these relatively heavier tongs. , or giving a lower priority to this point. These cost increases represent a significant amount given the number of

tongs used annually.

  Recently, the manufacturing costs of one cylinder clamp, and many other plastic articles, have increased significantly from a plastic resin portion representing one hundred percent of manufacturing costs to the current case where the cost of plastic resin is a great

  part or a dominant part of the manufacturing costs.

  Generally, the fraction relating to the cost of molding is relatively small, and the fraction relating to the cost of raw materials is relatively large and is increasing. Thus, if the usable moldable part can be redesigned to provide a function at least as good but using a relatively smaller amount of plastic resin, it is possible to realize

  big savings in manufacturing costs.

  Most types of pliers have a housing whose cross-section of the wall thickness is fairly uniform throughout. Such a study parameter is simple to specify when creating the clamp by focusing first on some important configurations of the surface: housing pinch surface, wheel axle guide, width of the slot of the wheel, etc. , then completing the study by simply specifying a thickness

uniform for the wall.

  The new form of clamp of the present invention not only provides the desired type of nip (side walls of the tube fully clamped to the closure, etc.) but, in addition, incorporates the mechanical strength (flexural modulus, etc.) and the design of the mold (injected plastic material that completely fills the passages) and has a structure to achieve a significant reduction

  materials needed for each clamp.

  Currently, typical cylinder clamps have dimensions in the following ranges: (1) main diameter of the wheel: 1.3 to 1.8 times the outer nominal diameter of the tube, and (2) the thickness of the housing wall: two

  and usually three times the thickness of the non-wall

  deformed the soft plastic tube, and (3) uniform thickness of the wall over the entire cross-section, such a cross-section being the same over the entire operational length of the housing where the flow control (control zone of the housing) occurs. debit). An obvious solution to reduce weight

  parts consists in reducing the length of the housing.

  However, this is not desirable because part of the length of the housing, generally at its largest end, should facilitate the introduction of the wheel so as to make the combination operational. The remaining portion serves primarily to provide a reasonable stroke for the wheel so as to progressively pinch the tube at any position in the section

  release or control of housing.

  It is not practical to reduce the overall or principal width or height of the cross-section of the clamp housing because, if it is done, it will be difficult to surround and pinch a diameter

  given tube of soft plastic material.

  The current housings of the collets have a uniform wall thickness in the range of 0.3 to 0.5 times the outer diameter of the tube as the clamp

must tighten.

  There is a minimum practical length for housing. For a tube of the current size having an outside diameter of 3.25 to 4.5 mm, the minimum length of the housing is in the range of 23 mm to 55 mm. ,

  or about 7 to 25 times the outer diameter of the tube.

  The wall thickness of the clamp housing is generally from 1.2 mm to 1.7 mm or from about 0.2 to 0.5 times the outer diameter of the tube. Most importantly, the housing of the clamp usually has a

  uniform cross section. This is apparently-

  performed (uniform thickness of the wall) for the following reasons:

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1. This is simple to specify.

  2. This is a typical design parameter for injection molded parts. A uniform thickness of the wall facilitates the filling of the steel mold with the injected plastic material. 3. Most embodiments of clamps bears little or no consideration to variations in the expected mechanical sag of the plastic housing when it is

  subject to the constraints associated with tightening the tube.

  The mechanical deflection (deformation) depends on many parameters and for a given plastic resin, for example ABS (acrylonitrile butadiene styrene), depends, in part, on the stress and the type of stress (tension, bending, compression, torsion, etc.). A good achievement will minimize sagging when subjected to a load, or allow nominal sagging, but such sag must be within the yield point, or, if the yield strength is exceeded, will minimize the amount of sagging or degree of sagging. of

  exceeding the yield point.

  When a clamp housing is put into use, i.e. assembled with a pinched tube and the other components of a set IV, the expected sag occurs, and its value depends, in part, on the type ( tension, bending, etc.) of the stress that is applied. The side walls of the housing of the clamp are mainly subjected to tension while the upper edge or upper wall is subjected mainly to a bending or bending, with a secondary component of the local compression, due to the pressure applied by the axis of the cylinder wheel, where it is in contact with this upper surface. The mechanical deformation of the housing, when used to pinch the tube, will be due:

  1. First of all, bending or bending.

  from the upper edge or wall of the housing.

  2. Second, at the tension of the wall

side of housing.

  > -4. To a lesser degree, the local compression force exerted directly by the wheel axis on the upper edge of the housing where the contact

takes place.

  4. At the pressure applied by the main circumference of the wheel against the lower part of the housing surface, through the double thickness of the wall of the

plastic tube pinched.

  Turning now to prior art patents for forceps, most of them only indicate that the side walls are thinner than the top or bottom walls of the housing. In addition, the drawings of some of the cylinder clip patents tend to describe various configurations, but do not teach how the wall dimensions are illustrated. For example, U.S. Patents No. 1,411,731; 1,959,074; 2,595,511; 3,135,259; 3,189,038 and 3,289,999 appear to indicate uniform structures for the walls. The United States of America No. 3,099,429; 3,215,394; 3,215,395; 3,297,558 and 4,340,201 include drawings that can be interpreted as

  representing a thin-walled structure. Among them-

  Here, U.S. Patent No. 3,099,429 to

  Broman's name deserves special comment.

  Broman illustrates a clamp with a thinner sidewall and the clamping surface appears to be thicker than the sidewalls. However, to be consistent with the present invention, as will be discussed, the steering surface of the wheel axis at Broman must be thicker than the clamping surface as well as the sidewall. In the Broman patent, the guide surface has the same thickness as the thin side wall and is much thinner than the clamping surface. Broman makes no mention of savings in weight, considerations of mechanical strength (bending, tension, etc.). No mention is made of why the thickness of the wall * is as illustrated and it would appear that the thickness of the cross-section is at various points simply a

arbitrary illustration.

  Thus, an object of the present invention is an improved clamp structure which will have the same performance characteristics as the best clamps, such as those discussed in the Applicant's patents and which have a similar appearance, which injection molding and which, nevertheless, in the present invention, will allow

  to obtain lower manufacturing costs.

  An object is also to provide such a clamp using a substantially smaller amount

of materials.

  An object of the present invention is also to provide improved pliers of this kind in

  using shorter times of the molding cycle.

  In the case of clamps acting in parallel, an object is also to provide an improved clamp, as described, with flow rates

  time-variant reduced or minimized.

  Another object of the present invention is to provide an improved clamp in which there is

  a firm grip on the tight tube.

  An object of the present invention is also to provide a unique and inexpensive method for modifying an existing housing mold in order to achieve

objectives outlined above.

  These objects and other objects according to the present invention are achieved by providing

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  improved IV cylinder clamps for IV assemblies and more particularly an improved IV cylinder for IV assemblies having the unique advantages of reducing manufacturing costs and unexpected maintenance of excellent performance and having a structure for obtaining the relative dimensions indicated below. afterwards in order to maintain good performance and at the same time significantly reduce

manufacturing costs.

  Thus, the preferred and practical solution of the present invention is to selectively specify the portions of the housing cross-section. An improvement over the present invention is to further vary the cross-section according to its location on the longitudinal axis of the housing. For example, the cross-section at the location of the portion of the housing designed to allow insertion of the wheel, has reduced requirements for strength. In this zone, the axis of the wheel does not fully press against the opposite surface of the housing during a clamping action of the tube. In addition, there is usually a very weak action, or, very often, no clamping action on the tube in this area. On the other hand, in the generally longer operational section of the housing, so-called flow control area, the structure must expect high forces that result from

  the interaction of wheel, housing and tight tube.

  Consequently, taking into account all the factors discussed in relation to stresses and deviations, etc., in a new and unique design of the housing of the clamp and a new cylinder clamp and improved for use with

  sets I.V., according to the present invention,

  housing must have for the flow control part. at. an upper edge or cutting wall

thick for housing.

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  b. A housing with a small side wall. c. A thick bottom wall (but not as thick as the wall of the upper edge) of the housing. An important point is the relation of the ratio of the thickness of the cross-section of the upper wall to the cross-sectional thickness of the side wall, which is according to the

  present invention in the range of 1.5 to 4.0.

  It should be noted that a thick upper edge of the following cross section per se (a) is used to minimize the degree of bending or bending because such deformation may be high and a thick cross-section will make it minimal. A second justification for (a) above is to minimize the degree of local deviation or notch of the housing surface just where the axle of the

  wheel applies a relatively high local force.

  The point (b) above serves to reduce the weight of the material and to take advantage of the fact that there is a relatively small deflection at power up, and also because thin plastic walls are able to withstand the forces of

relatively intense traction.

  The point (c) above serves to reduce (but not more than is necessary) the bottom wall

  in order to minimize bending and bending.

  The parameter (a) above causes the housing to be subjected to a relatively high force which causes bending and bending, a force which is applied by the axle of the wheel. The purpose of the parameter (c) is to respond to a similar opposing force, also causing bending and bending, but this force is more evenly distributed because it is transmitted and applied by the clamping action of the tube.

soft plastic.

  The greatest bending occurs when the wheel is placed centrally between, and therefore at approximately the same distance, the extreme supports of the housing. Thus, the axially centered portion of the upper wall must be thicker at the end than at one end or the other end. However, this is not practical for injection molded parts because a "draft angle" of the workpiece will not be present to allow removal of the newly molded part which, when molded by. injection in the conventional way, will shrink to hook securely to the mold core. However, a practical compromise is to have an embodiment in which the wall thickness of the housing is decreased near the small end of the housing, but is not

  not diminished as much at the open end of the housing.

  A creep or cold flow can occur in the wheel and the housing of the collet (it usually takes place in a larger

  measured in the tight tube made of soft plastic material).

  To exist, the applied load must make the piece exceed its elastic limit. If there is creep or cold flow, the dimensions of the part may vary over time, without changing the load, and this will contribute to a time varying flow rate for the fluid passing through the pinched tube. To avoid this undesirable phenomenon, the load must be limited, or the cross sections of the walls must be sufficiently large (and strong enough) to avoid the exceeding of the elastic limit or the minimization of the stress. On the other hand, one must expect deviations because deformation usually accompanies a constraint. The best is usually to operate within the limit

elastic.

  Since the part described in the present invention is made of a plastic material and is preferably molded, to obtain a

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  Proper injection molding, a "fill" or tunnel cross-section is required in the workpiece to ensure that the molten plastic resin, generally at a temperature in the range of 175 to 250 C, will flow easily to fill the cavity quickly and completely. If the tunnel is too small, the molten plastic will cool too quickly and "freeze" before full filling. At low temperatures, the viscosity of the highly temperature-dependent plastic resin injected will be so high that partial filling will occur. A tunnel that is too large, or a filling cross-section, will eliminate the problem of partial filling, but will result in a part using too much (expensive) plastic resin and will also unnecessarily increase the time (and consequently the manufacturing costs) required for cooling the injected plastic material to a temperature allowing ejection of the formed piece from the mold cavity while remaining able to retain its newly obtained shape (no warpage). Long residence time in the mold increases molding costs, generally in a linear fashion. Specifically, if the cycle time to produce the molded part by the molding machine is

  doubled, the cost of molding is also doubled.

  With respect to the molding operation and the making of the mold, it is important in the present invention to select and properly combine the dimensions and location of the filling cross-section, or filling tunnel, so as to have the necessary mechanical resistance when the piece is then brought to

  be sufficiently rigid or strong

  in the bending, flexing or tensioning mode, as well as to provide a totally formed part. Thus, the preferred form of the mold for proper molding has an inner cavity and outer surfaces of the core

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  dimensioned, positioned and capable of satisfying the following independent conditions: (1) Filling tunnel, or filling cross-section, appropriately dimensioned, but not too large to result in unnecessary increase in the weight of the part and / or for

slow down the manufacturing cycle.

  (2) Properly sized cross-section conferring rigidity or flexion

  desired, being just adequate but not too high.

  (3) Walls having a fine cross-section satisfying other requirements for tensile strength and part integrity, while using a minimum of plastic material so that the total weight remains low and also to facilitate obtaining a cooling time of

  short time for faster manufacturing time.

  A faster manufacturing time makes it possible to obtain higher manufacturing volumes for a given time interval; generally, the doubling of the cross-section increases the cooling time of the molded part and the corresponding cost of molding the mold.

four times.

  As explained above, the upper wall of the housing is made thicker so as to have the necessary mechanical strength to obtain the required bending stiffness and to avoid excessive penetration (notch) caused

  by the local force of the axle of the wheel.

  However, a thick-walled section generally requires a longer cooling time, a necessary step in injection molding. This longer cooling time has the effect of increasing the cost of manufacture because the mold cycling time is longer. All of the above is correct and true, even for a one-dimensional cooling, as is the case of a room having a

  low thickness compared to its other two.

  dimensions. However, in the case where another dimension, perpendicular to the thickness dimension, is comparable to the thickness, the cooling is effectively a two-dimensional cooling and therefore requires a shorter time. Thus, in order to avoid excessive cooling times, the upper side of the thick wall must have a thickness comparable to its width. This serves the dual function of providing faster two-dimensional cooling and providing a generous passage for the melt-injected plastic material, facilitating complete filling of the contiguous thin sidewall.

housing.

  Another aspect of the present invention is the relative ease with which existing molds can be modified to take advantage of the present invention. One feature includes a relatively simple change of the injection molding cavity by bringing the two halves of this cavity closer together to provide thinner sidewalls (which must withstand tensile forces during their use). Another feature includes (1) shifting the mold core relative to the cavity so as to (a) increase the thickness of the axle guiding portion of the wheel in the housing (to provide resistance to necessary bending and impingement resistance of the wheel axle), (b) placing the casting action in such a way as to ensure a good distribution of the molten plastic material, (c) substantially reducing the wall thickness of the housing clamping surface (due to the inherently larger cross-sectional area of its wall), (d) introducing or maintaining a two-dimensional heat transfer (cooling) where the axle guide of the wheel in the housing has a larger cross section of the wall (so as to reduce the cycle time of the

molding in manufacture).

  In the case of the housing, in the range of the flow control, the cross section of the housing according to the present invention is such that: 1. The thickness of the side wall is less than or equal to twice, or more generally in the range from 1.2 to 2.2 times the thickness of the wall of the tube

  soft plastic deformed (nominal thickness), not 2.2 to 3 times.

  2. The thickness of the upper wall (guide of the caster axle) is 2 to 3.5 times that of the wall of the non-deformed soft plastic tube (this value is

  in the typical range or is larger).

  3. The thickness of the bottom wall is less than or equal to that of the wall

  superior (as opposed to being generally equal).

  4. The thickness of the side wall is 0.3 to 0.6 times that of the top wall (as opposed to being generally the same), and may be less than half that of the bottom wall or the upper section of

wheel axle guide.

  As previously indicated, the ratio between the thickness of the cross section of the top wall and the thickness of the cross section of the wall

  lateral is in the range of 2 to 5.

  Further details will be presented below. In this way, the objectives mentioned

above are achieved.

  The present invention will be well understood in the following description made in

  connection with the accompanying drawings, in which: Figure 1 is a perspective view of a typical forceps of the prior art; Figure 2 is a sectional view of the common form of collets as used in the prior art;

23 2751231

  Figure 3 is a sectional view of a.

  gripper housing according to the present invention; Figure 4 is a schematic view of the prior art mold; Figure 4A is a view similar to that of Figure 4 showing a mold according to the present invention; and Fig. 5 is a schematic view which compares a modification form (left side) of the new part (N) to illustrate its effects (the right side represents a conventional cross-section (A)

for comparison purposes).

  In connection with FIGS. 1 and 2, a clamp 10 acting in parallel with the prior art is shown, although the present invention can also be applied to an inclined ramp clamp. The clamp 10 comprises a housing 12, a wheel in the form of a cylinder 14 having an axle 16 received in grooves formed in the upper part of the housing. In this embodiment given by way of explanation, the housing comprises a lower surface 17, the latter having a rib 18, a V-shaped rib being shown for purposes of illustration, the space 19 formed between the lower part of the cylinder and the surface 17 receiving a tube in which circulates a fluid in a controlled manner according to the position of the cylinder. The tube material is generally plasticized polyvinyl chloride of the type previously used in I.V. assemblies, although plastic tubes of medical grade may also be employed. In general, the tubes have an inner diameter of about 2.3 mm to 3.0 mm, an outside diameter of 3.5 mm to 4.5 mm and a Shore D hardness greater than about 68 and generally less than 80. The groove has a variable cross section along its length so as to change the cross-sectional area of the tube in

which the fluid circulates.

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  For this illustration of the clamp acting in parallel, the wheel operates to fully tighten the closure of the side walls of the tube for the reasons discussed above and the groove to the variable cross section serves to vary the open portion of the tube 'to control the flow of the fluid. In the form shown, the flow control area extends approximately between zone 22 and zone 23, the lower surface having a raised elevation element 25 which functions as a lock to ensure complete closure, even if the closure is immediately upstream of the element 25. In fact, there is also no flow with the cylinder placed in the area at the end of the groove and before the bump. Thus, the stroke of the wheel in its path is generally close, but not necessarily precisely, to a parallel relationship in the flow control area by providing grooves for the axle on the outer periphery, as shown , which are basically in almost parallel, or even exactly parallel, relation to the surface 17 in this flow control area. The run of the wheel on the element 25 is not parallel, but there is no control of the

  25debit in this area, as discussed.

  Generally, the clearance between the lower part of the wheel and the surface 17 is not greater than twice the nominal thickness of the wall of the tube 20 used with the clamp. Since tubes of various sizes can be used, the clearance between the surface 17 and the lower part of the wheel in the flow control area can vary from one type of clamp to another in order to maintain a clamping force. complete on each side of the tube. There are also clip structures, not shown, in which only one side of the tube is fully pinched to the closure because, in such an embodiment, the flow port is closed on one side.

  In Figure 2, it can be seen that the housing 12.

  has a substantially uniform cross-sectional area of about 0.3-0.5 times the outer diameter of the tube, typically 1.2 mm to 1.7 mm, the length of the housing being between 20 mm and about 55 mm. The uniform cross-section can be seen from the cross section of the bottom wall 17a which constitutes the surface 17 and the wall 18a in the portion with the groove 18. The side walls 27 and 28 of the housing have essentially the same thickness in section that the lower wall 17a and the wall 18a of the groove. There is a transition zone 29 between the walls 27 and 28 which comprises a portion having the cross-section of the walls 27 and 28 and the wall portions 31 and 32 which constitute the walls of the trunnions in which the axle 16 of the wheel moves. This transition zone is formed of the lower shoulders 31a and 32a of the trunnions in which the axle 16 of the wheel moves. Above the shoulders 31a and 32a there are the upper edges or upper walls 36 and 37 of the housing, the latter constituting the upper part of the trunnions. As can be seen, these upper edges or walls have a cross-sectional thickness substantially equal to that of the walls

lateral 27 and 28.

  FIG. 3 shows the preferred embodiment of the present invention, again in the form of a clamp acting in parallel, comprising the parts, the housing, the V groove, the tube, etc.

  already described. However, for descriptive purposes,

  will discuss only the single housing 50. The cross section of the housing of the clamp can be divided into three zones, each satisfying conditions

  individual and special according to the present invention.

  The upper zone which comprises the region having the upper edges or walls 51 and 52, the portion lying above the shoulders 53 and 54 and having the walls 61 and 62 must be capable of

  withstand a bending load due to the tightening of the tube.

  and imposed by the axle of the wheel whose position varies along the length of the housing. The trunnion of the wheel bears against the lower side 51a and 52a of the upper edges or walls during a clamping operation. The lower sides must be able to withstand the penetration of the axle of the wheel or the trunnion as a consequence of the clamping action penetration imposed by the axle of the wheel whose radius of curvature is relatively small. This penetration is usually in the form of a local cut. A less obvious condition is that during molding, a fluid passage must be provided for the injection of molten plastic material so that it can pass through a large part, or ideally, the entire axial length of the piece without have a large zone of contact, a zone that causes cooling and, if it is too large, causes premature solidification. There is also lateral flow to form the walls 57 and 58. In addition, to facilitate flow, the cross section of the upper edges 51 and 52 will be close to a circular section, as illustrated. The second zone is the lateral zone which basically comprises the side walls 57 and 58 and the wall part comprising the shoulders 53 and 54 and the walls of the groove or sections 61 and 62 of the wheel axle guide wall. . This lateral zone must have sufficient mechanical strength to withstand the tensile forces due to the clamping action and produced within the housing of the clamp. The lateral area should have a smaller, but nevertheless sufficient, cross-section so that the injected molded plastic material flows along the vertical distance to properly fill the lateral area of the housing without undergoing premature cooling and thus solidifying

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  before filling this area. Depending on the location.

  "casting attacks" which admit molten plastic into the cavity, the side must also have a cross section allowing the filling of the contiguous zone, not served by its own "attack". The lower zone which basically comprises the bottom wall 60 and the wall portion formed by the clearance groove 65 must be able to withstand bending loads similar to those of the upper zone. The bending load of the lower zone is similar to that of the upper zone; however, since the bending applied to the lower zone is in accordance with the main diameter of the wheel which in turn compresses the double layer of the soft plastic tube, the need to withstand a penetration load is greatly reduced. In addition, since the cross-section of the lower zone has a width greater than the combined widths of the upper left and right zones, the depth dimension of this lower zone must be smaller to obtain the cross-sectional area to support load

bending.

  Other charges must also be borne and other requirements must also be met. However, it is generally considered (with a reasonable margin of safety) if

  conditions set out above are satisfied.

  These conditions can be satisfied with housing dimensions expressed in relationships

  various in the approximate ranges indicated.

  (1) The thickness of the side walls is 0.8 to 2.5 times the wall thickness of the non-deformed soft plastic tube (nominal thickness);

  (2) The thickness of the upper wall is.

  from 2 to 3.5 times the thickness of the wall of the non-deformed soft plastic tube; (3) The thickness of the bottom wall is 0.4 to 1.0 times that of the top wall; (4) The thickness of the side walls is 0.3 to 0.8 times that of the top wall; (5) The ratio between the weight and the length of the housing of the clamp is less than 1.6 grams per centimeter and the mechanical strength allows to completely close a PVC tube having an internal diameter of 2.3 to 3.0 mm and an outside diameter of 3.5 mm to 4.5 mm with a Shore D hardness greater than 68 and not greater than about 80; (6) The thickness of the side walls is less than two-thirds of that of the wall in the upper guide section of the wheel in the area of the housing constituting the flow control area; (7) The thickness of the side walls is less than that of the bottom wall; (8) The thickness of the side walls is less than one quarter of the width of the main diameter of the wheel; (9) The thickness of the side walls is less than 2.5 times that of the tube wall (tight) when this tube is in the non-deformed state; (10) The ratio between the thickness of the side walls and the thickness of the top wall is less than 0.7 over the entire length of the housing of the clamp where the tube is controlled; and (11) The top wall is so dimensioned that the ratio of its thickness to its width, in cross-section, is in the range of

0.5 to 1.0.

  The housing of the clamp may also have a wheel guide section in the upper wall whose cross section has a

* ratio between width and height less than 2.0.

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  From the foregoing, it appears that the present invention relates to a gripper housing whose thickness of the upper, side and / or lower walls is reduced in the area not performing the control (inlet section and to the right). of the full closure) when comparing these thicknesses to that of a corresponding part of the area where the tube can be pinched to achieve control or stopping of the flow. Another aspect of the present invention is the ability to retrofit an existing mold and to implement the present invention with a mold that produces housings for a cylinder type chuck that can now be modified to include most of the features. desirable of the present invention. The approach described is applicable to either an inclined cylinder clamp or a clamp

acting in parallel.

  In Figure 2 there is shown a typical sectional section of a housing for clamp. Figure 3 shows a preferred embodiment. It will be noted that, by comparing the structure of FIG. 2 with that of FIG. 3, in the structure of the present invention, the upper wheel guide surface (51, 52) is an enlarged cross section, the lower surface of Tightening 60 is essentially unchanged or slightly thinner, and the thickness of the sidewalls (57, 58) is greatly reduced. FIG. 5 is an illustration which facilitates the comparison, the left-hand part (N) representing the new embodiment and the right-hand part (A) the embodiment of the prior art. The lower clamping surface can and

  must be thinner than the top surface. That is-

  due to the fact that its width is larger than that of

  the upper axle guide surface of the wheel.

  Both the upper and lower surfaces are subjected to substantially equal bending forces. The

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  flexural strength is, the other dimensions being identical, nominally proportional to the area of the cross-section. Therefore, a thinner section is preferred for the lower clamping surface to achieve a balanced structural realization. The upper wheel guide surface has, because of the wheel-opening, a smaller width than the lower surface, and to provide adequate bending resistance and resistance to bending. cut by the axle of the wheel, this thickness of the upper guide of the wheel and the cross section must be increased. The cross sectional area of the sidewalls is greatly diminished by using a thin wall. This is because the main load, when using the clamp, is a tensile load. For ABS, polystyrene and other commonly used thermoplastics, the tensile strength is high, and their modulus of elongation is low. Therefore, by carrying out a correct study of the application, one can benefit

  a significant saving in weight.

  In manufacturing, almost all embodiments of cylinder clamps for infusion sets (and screws) is provided for injection molding. Their inner and outer surfaces are chamfered (have a draft) to facilitate the ejection of the mold, can be made with simple two-plate molds, etc. In the case of a clamp acting in parallel, this chamfer provides a small angle for what is called the clamping surface;

  however, this small angle (for example from the order of

  0.5 degree) does not play any role in controlling the flow as already discussed. The function envisaged; utilisation facility; the ease of adjustment, a narrow grip of the tube, etc. are all determined by

  mold core design. It is the core that.

  shape the interior configuration and dimensions of the housing. The dimensions of the core, its shape, the dimensional tolerances, etc., determine the characteristics of the molded part. It is therefore probable that, for almost all of the clamps, the function of the part studied is focused on the core; and the shape of the cavity, its dimensions, etc., are generally obtained by simply specifying a uniform wall thickness for the part that is

  typically in the range of 1.1 to 1.5 mm.

  In contrast, according to the present invention, the key elements constituting the improvement have almost nothing to do with the realization of the cavity and can see, if anything, with the realization of the core. To transform an existing mold, the halves of the cavity are slightly leveled, as already discussed and will discuss again, then joined. The cavity is moreover slightly offset with respect to the core. The core is left essentially unchanged, but the casting attacks are relocated to allow the introduction of the plastic material injected into the core.

  guiding surface of the wheel, now thickened.

  A typical cavity for housing is constructed in a clam-like mold and often the two halves 70 and 75 are nearly symmetrical or exactly symmetrical; refer to Figure 4. As is known, a mold core is also used which is placed in the cavity 76 during the molding operation. For such a prior art mold used to make one of the prior art pliers, two relatively simple steps are required to produce a modified mold for the manufacture of the pliers.

  of the present invention.

  1. The coupling halves of the cavity shall be leveled in a relatively small amount, in the order of 40 to 80 per cent of the thickness

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  original wall. In Figure 4A this is shown.

  by leveling the surfaces 70A and 70B and 75A and 75B. In the case where the thickness of the wall of the piece already has a generally modest chamfer (slightly thinner at the small end of the housing and slightly larger at the large end of the housing, such a chamfer must then remain; will have a wall thickness that will vary by a few thousandths of a millimeter per mm of length). A draft is used to facilitate the removal of the mold part. This slight chamfer can be generally preserved by leveling the same depth of material on

  the entire contact area of half of the cavity.

  2. With the halves of the cavity separated, as shown in FIG. 4A, a small amount of the material may be removed from the portion of the mold surface that constitutes the outer portion of the wheel guide on the molded housing. In Figure 4A, these surfaces are identified by 70C and 75C. As this is done only on this special area, some important dimensions of the casting and the determining shape

  due to the core of the mold, are not altered.

  The effect of the above is to bring the halves of the cavity in an amount equal to 25 percent - 60 percent of the original thickness of the side wall of the molded part. The vertical offset of the core is typically in the range of percent to 70 percent of the original thickness of

the upper wall.

  These two steps are relatively simple to

  run and can be done quickly and inexpensively.

  As a result of this approach, it is hardly necessary to modify the generally more expensive core part of the mold. The cavity part, already less expensive, of the mold

  only has to undergo a relatively minor operation.

  All this is in contrast to the much higher cost of building a new multi-cavity mold.

  Another cost comparison will be the cost

  the manufacture of the newly modified part in relation to the cost of the original part. Weight savings of 30 percent, for example, will generally result in savings in the overall cost of manufacturing by 20 percent. This is because the cost of the raw material is a large fraction of the total cost of manufacturing. A significant additional saving in manufacturing costs will also be achieved because the new achievement must allow for a faster manufacturing cycle. This is due to the fact. that the part, given the thinner wall thickness, and also the fact that the thickened part is subjected to two-dimensional cooling and not to one-dimensional cooling, will require a shorter cooling time. All the benefits of the new achievement will be retained as the casting attacks are properly placed. A logical location will allow the plastic material to be injected into the cavity at one end of the axle guide surface (edge attack). For this location, the flow passage of the injected plastic material has a shape close to the ideal shape, that of an approximately circular and not too small cross section. This flow tunnel can then "feed" the thinner side walls and other parts of the mold cavity as needed. An alternative location for casting attacks will allow the plastic to enter one end of the lower housing clamping surface (an edge attack may also be considered). Again, the cross section is generous and allows excellent access to thin walls. To obtain a part with symmetrical properties, two attacks on opposite sides of the

  cavity or a larger attack placed in the center, a.

  such central location being generally in the center of

the lower clamping surface.

  In essence, the cost improvement requires a relatively modest change of the cavity, involving the shaving of the contact surface of the two halves and a slight enlargement of the surface for the axle of the wheel; in addition, a slight offset of the core from the cavity in the range of 25 percent to 70 percent of the original thickness of the top wall, in the direction of thickening. thin the bottom wall. The potential economic benefits of changing the mold, compared to the construction of new molds to reflect the improved performance, are relatively large. This is because companies that can obtain immediate benefits already have molds for large fabrications and have large market shares. The modification of their molds can be done at a very modest cost and with a time

  very low stop for conversion.

  The present invention is not limited to the embodiments which have just been described, it is, on the contrary, susceptible of modifications and modifications.

  variants that will occur to those skilled in the art.

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Claims (2)

  A method of modifying a mold consisting of two recess halves (70, 75) and a housing core for an intravenous plastic caster type plier, said housing comprising a cylindrical roller axle bearing surface (31a, 32a) and a tube clamping surface, characterized in that it comprises treating each of the cavity halves (70, 75) to bring them closer together; the other in a proportion of 25 to 60 percent of the original thickness of the side walls of the room   molded to reduce the weight of the molded part.   A method according to claim 1 for the manufacture of plastic caster-type clamp housings having a top wall section, characterized in that it comprises a step of shifting the core in a direction relative to the cavity (76) to thicken the upper wall of the molded housing, such offset being made in a proportion of 20 to 70 percent of the original thickness from the top wall.