FR2748395A1 - PLASTIC CASTER CLAMP FOR INTRAVENOUS ADMINISTRATION - Google Patents

Abstract

The present invention relates to a roller-type clamp for intravenous administration, comprising a housing (50) of molded plastic material having at least a bottom wall (60), side walls (57, 58) and a top wall (52). , 51), characterized in that the ratio of the cross-sectional thickness of the top wall to the cross-sectional thickness of the side wall (57, 58) is within a range of 1.5 to 4.0 .

Description

The present invention relates to cylinder collets for

  intravenous administration sets and more specifically a forceps

  advanced roller for administration sets

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

good quality performance.

  During the period between the 1940s and the 1950s, IV administration sets evolved from reusable to disposable. In the past, a technique has been developed for producing and storing medical grade fluids for human infusion, for example, water, as well as dilute saline solutions, dilute dextrose solutions and the like. fluid nutrients as well as certain 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 pinching of the rubber tube. We have developed various collets

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, we

  introduced disposable administration sets.

  This made it possible to resolve the contamination problem, but introduced a new one: that of flow rates varying over time, that is to say variations in time compared to the initial setting of the desired flow rate. The pinched plastic tube raised the problem of cold flow during its pinching and this was at the origin of the variation of the flow over time; generally this variation was

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  significant (around 40 percent in the first ten minutes, then increasing) and further

  often the flow resulted in a decrease.

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

  the flow rate, which should change little over time.

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

life, even being mortal.

  Manufacturing costs were general-

  an underlying factor as is the case with most consumer products. Typical factors for cost reduction were: (1) making small parts to save materials, (2) using lower cost materials, and (3) making parts easy to

  assemble to reduce labor costs.

  Injection molded plastics are the common solution to making pliers. Economic pressures to reduce the cost of health care materials, the huge volume of infusion sets and the ever-increasing cost of plastic resins combine to greatly increase the interest in development

  pliers satisfying the requirements set out above

  above: (1) facilitate use, (2) reduce flow rates varying over time and (3) ensure firmer grip of the tube, as well as allow manufacturing at a cost always lower than that obtained by following the obvious steps making smaller parts, increasing the number of cavities in production and / or using a low-cost resin. Roller forceps for intravenous infusion sets which are sometimes referred to as IV sets and which are generally discarded together with the IV set, after one use, are well known and are primarily designed to regulate the flow rate of the liquid passing through a soft, pliable and deformable plastic tube, generally 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 intravenously the fluid having of interest. These clamps are also used as an on / off device, that is to say either to allow the flow or to stop it. It goes without saying that the clamp must, once in place, precisely control the flow over time and also be able to stop completely

flow when desired.

  Typical clamps of the prior art are those of the applicant's previous patents: United States patents No. 4,047,694 from 1977; 4,013,263 from 1977; 3,685,787 from 1972; 5,014,962 from 1991; 4,725,037 from 1988 and Re 31,584

  from 1984, descriptions of which are incorporated here

reference.

  In general, there are two basic types of roller clamps for IV sets, one being the "inclined ramp" clamp and the other called "acting in parallel" clamp or clamp whose wheel moves in generally parallel relationship with what is called a clamping surface. In each

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  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 and cylinder.

  Whatever the type of clamp, in an extreme position of the cylinder, there is a "full flow", that is to say a flow not regulated at the full capacity of the assembly IV In another position of the cylinder , generally distant from the position of full flow, there is a position without flow in which no fluid passes through the tube. It is typically a stop position. In some clamps, there is another stop position, more correctly a blocking position in which the movement of the cylinder is prevented, as will be described, and there is no flow in the tube. Between the position of full flow and the position without flow, there is generally a zone of displacement of the cylinder in which the flow can be controlled, that is to say the zone called "flow control". The length of this area can be shorter, in the axial direction, than the maximum distance in which the cylinder moves, especially if there is a locking position. In the case of pliers with an inclined ramp, the flow control is obtained by the principle of the "inclined ramp" in which the cylinder is caused, by the thumb of the operator, to climb a slope, which causes a decrease in clearance between the cylinder and the opposite surface of the housing on which the tube rests, creating the desired degree of nipping and therefore controlling the flow. 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 clamp flow settings, the orifice of the

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  tube is completely flattened in the large central area (where the radius of curvature of the tube is large), while a pair of openings are formed on each side, where the radius of curvature of the pinched tube is 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 collapse and cause the flow to decrease, after the cylinder has been brought into 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 a section at the location of the flow control area of the housing, a section guiding the wheel so that there is a clearance of the tube having the effect of forming at least one, and generally two, orifices at one of the outer edges or at both edges, to be completely closed in the pinched state. A fine control of the flow is obtained by varying the ratio between the fully closed part of the pinched tube and the other part which remains open, because there is a clearance part in the base, the housing or the wheel in which no pinching , or even a slight pinch is applied. The action or stroke of the roller need not be perfectly parallel, or even almost parallel, to the opposite gripping surface of the housing. The criterion for a clamp acting in parallel consists in having a clearance between the roller and the housing which causes the total closure by pinching of the local part of the tube and, in having the rest of the surface of the housing which is in contact with the tube , or is close to it, in order to have a clearance part which allows and / or encourages the formation of a

opening in the tube.

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

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  used to create the desired degree of pinch or partial closure of the tube. While the term "parallel" is used, it is not intended to describe a geometric parallelism or an arrangement in which the stroke of the cylinder takes place in a perfectly parallel fashion over the entire stroke; and such "parallel" action is only necessary in the range of the cylinder stroke for flow control. In fact, a clamp with parallel action can form, and this is generally the case, a small relative angle between the stroke of the cylinder and the opposite surface on which the tube rests and is tightened, 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 a primary control or a variation of the flow rate because the change in the clearance between the cylinder and the surface on which the tube is clamped is insufficient to directly vary the cross-sectional area of the flow, in contrast to an inclined ramp clamp. There is also the case where, in the area of the housing before the flow control and after the closed or no flow position, as opposed to the blocking position, the tightening action can also be non parallel in its structure. Since there are areas other than those where flow control is performed, the need for even approximate parallel action, as described here, is neither appropriate nor

necessary.

  Although the production of a cylinder clamp acting in parallel, in which only one cheek of the tube is fully clamped at closure, may constitute an improvement for clamps designed to give good performance with regard to the variable flow rates with the time, by completely pinching an opening which would otherwise be formed and would tend to exhibit a reduction in cold flow, more pointed constructions proceed to the total pinching at the closing of the two

  cheeks of the soft plastic tube.

  The characteristic which distinguishes a cylinder clamp acting in parallel (double action) from an inclined ramp clamp concerns the way of obtaining the flow control. Cylinder clamps acting in parallel obtain the flow control by pinching a cheek completely at closure, and generally the two cheeks of the tube over the entire range of flow control, and vary the ratio between the part completely pinched at closure and part not pinched depending on the position of the cylinder in the flow control area. It appears that a complete pinch closure of one or both cheeks, but not of the adjacent section of the tube, is only necessary in this range of the stroke of the cylinder which

  effectively constitutes the flow control range.

  In the case of pliers with an inclined ramp, the flow control is obtained by varying the clearance between the cylinder and the opposite gripping surface. It thus appears that, even if a true parallelism may not exist in a clamp with "action in parallel", the amount of non-parallelism is insufficient to vary the play by any amount which appreciably affects the change of the debit. This is particularly true if one or both cheeks are fully pinched when closing within the range of the cylinder stroke in the control area

flow.

  A typical arrangement for ensuring that one or both cheeks of the tube are fully pinched on closure is to provide a clearance between the bottom of the cylinder and the opposite surface of the housing against which the tube is pinched, which is generally not not more than double the thickness of the wall of the pinched tube and, in some cases, less than double this thickness. In general, a lower clearance

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  double the thickness of the wall is satisfactory for ensuring that one or both cheeks are completely pinched on closing. Again, it will be understood that this need for a defined clearance exists only in the flow control area. In fact, the clearance is greater at the entry side of the housing and may be somewhat smaller near the exit side of the housing, especially if there is a lock

separate when closed.

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

and the loose part.

  In the realization of the inclined ramp clamp, as the cylinder advances, the central section of the pinched tube may bend and be completely crushed when closed, but the clearance between the cylinder and the opposite surface of the housing: (1) is sufficient large to allow the formation of openings, and in general, to 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 pliers acting in parallel, the clearance is in the surface of the cylinder. A general characteristic of these types of pliers is that the open area of the cross section of the tube varies as the cylinder progresses in its course, the amount of surface

  open being linked to the configuration of the clearance.

  As is known, the clearance may take a wide variety of forms and may be on the outside of one side of the housing, or above the tube or at any other location. Its function is to vary the area

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  open presented to flow in response to movement

of the cylinder.

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

the desired degree of pinching.

  In the grippers to which the present invention relates, 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 upper surface of the housing must be designed to resist bending when subjected to an upwardly directed force such as that caused by the axis of the pinch wheel. (3) The side walls of the housing must be designed to withstand stresses. (4) The lower surface of the housing must be designed to resist bending as well as to function in compression, provide a release action with variable width as well as an ideal location for special elements in elevation. The elements in elevation, if they exist, have varying heights, widths and spacings. (5) The housing must be made of a plastic material which can be injection molded, must have a cross section designed to facilitate the flow of the injection molded plastic material in order to fill all the

steel mold cavity.

  When parallel action pliers were introduced to the market in commercial volumes around 1975, the dwellings were approximately 50mm in length. The sloped ramp housings were approximately 35mm long. Parallel action pliers have gained a significant share of the market thanks to their best

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  performance compared to inclined ramp pliers and, in 1978, involved almost all of the sales from one (Abbott Labs) of the two largest companies (Baxter Travenol is the other company) in the United States of America involved in products requiring pliers for use in IV sets Around 1986, Baxter began using longer patented pliers. Then other companies such as Cutter (which actually started at an earlier date), McGaw, IVAC and Borla, introduced pliers with 50mm slots and the trend started

found thus established.

  With the more widespread use of longer clamps, manufacturing costs have increased significantly for a large part of the market, although many longer clamps do not offer the better performance of the patented clamp acting in parallel. Most of these companies have simply followed the trend of having a longer length of housing. In the case of pliers acting in parallel with Abbott, there was a functional reason for the length, in addition to providing a flow not varying over time, and a firmer grip of the tube, the longer stroke long cylinder allows adjustment

  finer the degree of the pinch and therefore the flow.

  Therefore, in an effort to conform to the trend towards a longer length, the market has introduced heavier tongs, seemingly not caring, about the resulting increase in the manufacturing costs of these relatively heavier tongs , or by giving a lower priority at this point. These cost increases represent a significant sum given the number

pliers used annually.

  Recently, the costs of manufacturing a cylinder clamp, and many other plastic items, have increased significantly from a plastic resin part representing it 2,748,395 percent of manufacturing costs to the common 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 increasing. Thus, if the moldable part which can be used can be redesigned to provide at least as good a function but using a relatively smaller quantity of plastic resin, it is possible to produce

  great savings in manufacturing costs.

  Most types of pliers have a housing with a generally uniform cross-section of wall thickness. Such a study parameter is simple to specify when creating the clamp by first focusing on a few important surface configurations: clamping surface of the housing, guide of the wheel axis, width of the wheel slot, etc. and then completing the study by simply specifying a thickness

uniform for the wall.

  The new clamp form of the present invention not only provides the desired type of clamping (side walls of the tube fully clamped at closure, etc.) but, moreover, incorporates mechanical resistance (flexural modulus, etc.) and the mold design (injected plastic which completely fills the passages) and has a structure allowing a significant reduction to be obtained

  materials needed for each clamp.

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

  and generally three times the thickness of the non-wall

  deformation of the soft plastic tube, and

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  (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 adjustment takes place (flow control zone). An obvious solution to reduce weight

  parts is to reduce the length of the housing.

  However, this is undesirable since part of the length of the housing, generally at its largest end, must facilitate the introduction of the wheel so as to make the combination operational. The remaining part is mainly used to provide a reasonable stroke for the wheel so as to gradually pinch the tube at any position of the section

  for clearing or controlling the accommodation.

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

  given from the soft plastic tube.

  Current clamp clamp housings have a uniform wall thickness in the range of 0.3 to 0.5 times the outside diameter of the tube than the clamp

must tighten.

  There is a minimum practical length for the accommodation. For a tube of the current size with 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 outside diameter of the tube.

  The wall thickness of the clamp housing is generally 1.2 mm to 1.7 mm or about 0.2 to 0.5 times the outside diameter of the tube. Most importantly, the clamp housing generally has a uniform cross section. This is apparently done (uniform wall thickness) for the following reasons:

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1. This is simple to specify.

  2. This is a standard study 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 gripper designs pay little or no consideration to variations in the expected mechanical deflection of the plastic housing when it is

  subject to the stresses associated with tightening the tube.

  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 implementation will minimize the deflections when subjected to a load, or allow a nominal deflection but such a deflection must be included in the elastic limit, or, if the elastic limit is exceeded, will minimize the amount of deflection or the degree of

  exceeding the elastic limit.

  When a clamp housing is put into use, i.e. assembled with a clamped tube and the other constituents of an IV assembly, the expected deflection occurs, and its value depends, in part, on the type ( tension, bending, etc.) of the stress that is applied. The side walls of the clamp housing are mainly subjected to tension while the upper edge or upper wall is mainly subjected to bending or bending, with a secondary component of 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 it is used to pinch the tube, will be due: 1. First of all, to bending or bending

  from the upper edge or wall of the housing.

  2. Second, at the wall tension

side of the housing.

  4. To a lesser degree, the local compression force exerted directly by the wheel axle 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 surface of the housing, through the double thickness of the wall of the

pinched plastic tube.

  If we now examine the prior art patents relating to the clamps, most of them only indicate that the side walls are thinner than the upper or lower walls of the housing. Furthermore, the drawings of some of the patents for cylinder clamps tend to describe various configurations, but do not teach anything about how the dimensions of the walls are illustrated. For example, United States Patent Nos. 1,411,731; 1,959,074; 2,595,511; 3,135,259; 3,189,038 and 3,289,999 seem to indicate uniform structures for the walls. U.S. Patents No. 3,099,429; 3,215,394; 3,215,395; 3,297,558 and 4,340,201 include drawings which may be interpreted as

  representing a structure with thin walls. Among them-

  ci, U.S. Patent No. 3,099,429 to

  Broman's name deserves special comments.

  Broman illustrates a clamp with a thinner side wall and the clamping surface seems to be thicker than the side walls. However, to be homogeneous with the present invention, as will be discussed, the guide surface of the wheel axle at Broman must be thicker than the clamping surface as well as the side wall. 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 weight savings, mechanical strength considerations (bending, tension, etc.). No mention is made of why the wall thickness is as shown and it would appear that the thickness of the cross section is in various places just a

arbitrary illustration.

  Thus, an object of the present invention is an improved collet structure which will have the same performance characteristics as the best pliers, such as those discussed in the applicants' patents and which have a similar appearance, which will be suitable for injection molding and which, however, in the present invention, will allow

  to obtain lower manufacturing costs.

  It is also an object to provide such pliers using a significantly smaller amount

of materials.

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

  using shorter molding cycle times.

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

  varying over time 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 the

objectives set out above.

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

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  improved cylinder pliers for IV sets and more particularly an improved cylinder clamp for IV sets having the unique advantages of reducing manufacturing costs and unexpectedly maintaining excellent performance and having a structure for obtaining the relative dimensions indicated above 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 parts of the cross section of the housing. An improvement concerning the present invention consists in further varying the cross section depending on its location on the longitudinal axis of the housing. For example, the cross section at the location of the part of the housing designed to allow the insertion of the wheel, has reduced requirements in terms of mechanical strength. In this zone, the axis of the wheel does not press completely against the opposite surface of the housing during a clamping action on the tube. In addition, there is generally 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, the so-called flow control area, the structure must expect high forces which result from

  the interaction of the wheel, the housing and the tight tube.

  Consequently, taking into account all the factors discussed in connection with constraints and deviations, etc., in a new and unique design of the clamp housing and a new and improved cylinder clamp for use with assemblies IV, according to the present invention, the housing must have for the flow control part: a. a thick upper edge of the section

  transverse or wall for housing.

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  b. A housing with a thin side wall. vs. A thick bottom wall (but not as thick as the top edge wall) of the housing. An important point is the relationship of the ratio between the thickness of the cross section of the top wall and the thickness of the cross section of the side wall, which is according to the

  present invention in the range of 1.5 to 4.0.

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

  wheel applies a relatively high local force.

  Point (b) above is used to reduce the weight of the material and to take advantage of the fact that there is a relatively small deflection during tensioning, and also of the fact that thin plastic walls are able to resist forces of

relatively intense traction.

  Point (c) above is used to reduce (but not more than is necessary) the bottom wall

  so as to minimize bending and bending.

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

soft plastic.

  The greatest bending occurs when the wheel is placed in the center between, and therefore approximately the same distance from, the extreme supports of the housing. Thus, the axially centered part of the upper wall must be thicker with the endorsement than at one or the other end. However, this is not practical for injection molded parts because an "undercut angle" of the part will not be present to allow removal of the newly molded part which, when it is injection molded. in the conventional way, will shrink to securely hang on the core of the mold. However, a practical compromise consists in having an embodiment in which the wall thickness of the housing is reduced near the small end of the housing, but is not

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

  Creep or cold flow may occur in the impeller and the collet housing (usually occurs in a larger

  measurement in the tight tube of soft plastic).

  To exist, the applied load must ensure that the part exceeds its elastic limit. If there is creep or cold flow, the dimensions of the part can vary over time, without changing the load and this will contribute to a flow varying over time 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 large enough (and strong enough) to avoid exceeding the elastic limit or minimizing the stress. On the other hand, we must expect deviations because a deformation generally accompanies a constraint. It is generally best to operate within the limit

elastic.

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

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  correct injection molding, a "fill" cross section or tunnel is required in the part to ensure that the molten plastic resin, usually at a temperature in the range of 175 to 250 C, will flow easily so as to fill the cavity quickly and completely. If the tunnel is too small, the molten plastic will cool too quickly and "freeze" before it is completely filled. At low temperatures, the viscosity of the injected plastic resin, which is very dependent on temperature, will be so high that partial filling will occur. Too large a tunnel, or cross-section of filling, will eliminate the problem of partial filling, but will result in a part using too much plastic resin (expensive) and will also and unnecessarily increase the time (and therefore the manufacturing costs) necessary for the cooling of the plastic material injected to a temperature allowing the part formed to be ejected from the mold cavity while remaining capable of retaining its newly obtained shape (no warping). A long residence time in the mold increases the costs of molding, generally in a linear fashion. More specifically, if the cycle time to produce the part molded by the molding machine is

  doubled, the cost of molding is also doubled.

  With regard to the molding operation and the production of the mold, it is important in the present invention to correctly choose and combine the dimensions and the location of the filling cross section, or filling tunnel, so as to have the mechanical strength necessary when the part is then caused to behave in a sufficiently rigid or strong manner in the bending, bending or tensioning mode, as well as to provide a fully formed part. Thus, the preferred form of the mold for correct molding has an internal cavity and external surfaces of the core sized, positioned and fulfilling the following independent conditions: (1) Filling tunnel, or filling cross section, with suitable dimensions suitable but not too large to result in an unnecessary increase in part weight and / or

slow down the manufacturing cycle.

  (2) Correctly dimensioned cross section giving rigidity or bending

  desired, being just adequate but not too high.

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

  short duration for faster manufacturing time.

  Faster manufacturing time results in higher manufacturing volumes for a given time interval; generally, doubling the cross section increases the cooling time of the molded part and the corresponding cost of molding

four times.

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

  by the local force of the wheel axle.

  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 manufacturing since the time for mold cycling is longer. All of the above is correct and true, even for one-dimensional cooling, as is the case with a part having a

  thin 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 generous passage for the injected plastic in the molten state, which facilitates complete filling of the adjoining thin side wall.

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 together to obtain thinner side walls (which must withstand tensile forces during use). Another feature includes (1) shifting the mold core from the cavity so as to (a) increase the thickness of the guide portion of the wheel axle in the housing (to provide resistance to the necessary bending as well as the resistance to penetration by the axle of the wheel), (b) to place the etching attack so as to ensure a good distribution of the molten plastic, (c) to substantially reduce the thickness of the wall of the housing clamping surface (due to the larger cross-sectional area by inherence of its wall), (d) to introduce or maintain a two-dimensional heat transfer (cooling) there o the wheel axle guide in the housing has a

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  larger wall cross section (so as to reduce the cycle time of the

molding in manufacturing).

  In the case of the housing, in the range of 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 1.2 to 2.2 times the thickness of the wall of the material tube

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

  2. The thickness of the upper wall (guide of the roller axis) is 2 to 3.5 times that of the wall of the tube made of soft, non-deformed plastic material (this value is

  o0 in the typical range or is greater).

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

  higher (as opposed to the fact that they are generally equal).

  4. The thickness of the side wall is 0.3 to 0.6 times that of the upper wall (as opposed to the fact that they are generally identical), and may be i5 less than half that of the wall lower or upper section of

roulette axis 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 set out below. In this way, the objectives mentioned

above are achieved.

  The present invention will be clearly understood from the following description given in

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

FR9705546 - 08/22/97

  Figure 3 is a sectional view of a clamp housing according to the present invention; Figure 4 is a schematic view of the mold of the prior art; Figure 4A is a view similar to that of Figure 4, showing a mold according to the present invention; and Figure 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 classic cross section (A)

for comparison).

  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 a clamp with an inclined ramp. The clamp 10 comprises a housing 12, a wheel in the form of a cylinder 14 having an axle 16 received in grooves made 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 illustration purposes, the space 19 formed between the lower part of the cylinder and the surface 17 receiving a tube in which a fluid circulates in a controlled manner as a function of the position of the cylinder. The tubing material is generally plasticized polyvinyl chloride of the type previously used in I.V. sets, although medical grade plastic tubing can also be used. In general, the tubes have an inner diameter of about 2.3 mm to 3.0 mm, an outer 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.

24 2748395

  For this illustration of the clamp acting in parallel, the wheel functions to tighten completely on closing the side walls of the tube for the reasons discussed above and the groove with the variable cross section is used to vary the open part of the tube 'in order to control fluid flow. In the form shown, the flow control zone extends approximately between zone 22 and zone 23, the lower surface comprising a perpendicular element 25 in elevation which functions as a lock to ensure complete closure, even if the zone of closure is immediately upstream of element 25. In fact, there is also no flow with the cylinder placed in the zone located 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 fundamentally in almost parallel, or even exactly parallel, relation to the surface 17 in this flow control zone. The stroke of the wheel on the element 25 is not parallel, but there is no control of the

  flow 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 impeller in the flow control zone can vary from one type of clamp to another in order to maintain a tightening complete on each side of the tube. There are also clamp structures, not shown, in which only one side of the tube is fully pinched at closure because, in such an embodiment, the flow orifice is closed on one side.

  In Figure 2, we can see that the housing 12-

  has a substantially uniform cross section equal to about 0.3 - 0.5 times the outside diameter of the tube, typically from 1.2 mm to 1.7 mm, the length of the housing being between 20 mm and about 55 mm. We can see the uniform cross section from the cross section of the bottom wall 17a which constitutes the surface 17 and of the wall 18a in the part having the groove 18. The side walls 27 and 28 of the housing have essentially the same thickness in cuts only the bottom wall 17a and the wall 18a of the groove. There is a transition zone 29 between the walls 27 and 28 which comprises a part having the cross section of the walls 27 and 28 and the wall parts 31 and 32 which constitute the walls of the trunnions in which the axle 16 moves. wheel. This transition zone is formed of the lower shoulders 31a and 32a of the pins 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 pins. As can be seen, these upper edges or walls have a thickness in cross section fundamentally equal to that of the walls

side 27 and 28.

  In FIG. 3, the preferred embodiment of the present invention is represented, 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 description purposes,

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

  individual and special according to the present invention.

  The upper zone which comprises the region comprising the upper edges or walls 51 and 52, the portion lying above the shoulders 53 and 54 and comprising 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 over the length of the housing. The pin of the wheel presses against the lower side 51a and 52a of the upper edges or walls during a tightening operation. The lower sides must be able to withstand the penetration of the wheel axle or journal as a consequence of the clamping action, penetration imposed by the wheel axle whose radius of curvature is relatively small. This penetration generally takes the form of a local notch. A less obvious condition is that during molding, a fluid passage must be provided for the injection of the molten plastic material so that it can pass through a large part, or ideally, the entire axial length of the part without have a large contact area, an area which causes cooling and which, if too large, causes premature solidification. There is also a lateral flow to form the walls 57 and 58. In addition, to facilitate the 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 lateral 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 guide wall of the wheel axle. . This lateral zone must have sufficient mechanical resistance to withstand the tensile forces due to the clamping action and produced inside the housing of the clamp. The lateral zone must have a smaller cross section, but nevertheless sufficient, so that the injected molded plastic material flows along the vertical distance to correctly fill the lateral zone of the housing without undergoing premature cooling and therefore solidify before filling. this zone. Depending on the location of the "pouring attacks" which admit the 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 lower wall 60 and the wall part 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 bent along the main diameter of the wheel which in turn compresses the double layer of the soft plastic tube, the need to resist 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 burdens must also be borne and other imperatives must also be satisfied. However, this is generally taken into account (with a reasonable safety margin) if the

  above conditions are met.

  These conditions can be satisfied with dimensions of housing expressed in relationships

  various within the approximate ranges shown.

  (1) The thickness of the side walls is 0.8 to 2.5 times the thickness of the wall of the tube in non-deformed soft plastic (nominal thickness); (2) The thickness of the upper wall is 2 to 3.5 times the thickness of the wall of the tube in soft, non-deformed plastic; (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 upper wall; (5) The ratio between the weight and the length of the clamp housing is less than 1.6 grams per centimeter and the mechanical strength makes it possible to completely close a PVC tube having an internal diameter of 2.3 to 3.0 mm and an outer 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 a 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 wall of the tube (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 clamp housing where the tube is controlled; and (11) The upper wall is so dimensioned that the ratio between its thickness and its width, in cross section, is in the range of

0.5 to 1.0.

  The clamp housing can also have a wheel guide section in the upper wall, the cross section of which has a

  width to height ratio less than 2.0.

29 2748395

  From the above, it appears that the present invention relates to a clamp housing whose thickness of the upper, side and / or lower walls is reduced in the area not carrying out the command (inlet section and at right of full closure) when these thicknesses are compared to that of a corresponding part of the zone where the tube can be pinched to obtain control or stop of the flow. Another aspect of the present invention is the possibility of modernizing an existing mold and implementing the present invention with a mold which produces housings for a cylinder type collet which can now be modified to include most of the features. of the present invention. The approach described is applicable either to an inclined cylinder clamp or to a clamp

acting in parallel.

  In Figure 2 there is shown a typical sectional section of a housingfor pliers. Figure 3 shows a preferred embodiment. It will be noted that, by comparing the structure of FIG. 2 to that of FIG. 3, in the structure of the present invention, the upper guide surface of the wheel (51, 52) is an enlarged cross-section, the lower surface of clamping 60 is essentially unchanged or slightly thinner, and the thickness of the side walls (57, 58) is greatly reduced. FIG. 5 is an illustration which facilitates the comparison, the part on the left (N) representing the new realization and the part on the right (A) the realization of the prior art. The lower clamping surface can and should be thinner than the upper surface. This is due to the fact that its width is larger than that of

  the upper guide surface of the wheel axle.

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

2748395

  flexural strength is, the other dimensions being identical, nominally proportional to the cross-sectional area. Therefore, a thinner section is preferred for the lower clamping surface to achieve a balanced structural realization. The upper guide surface of the wheel has, because of the opening allowing the travel of the wheel, a smaller width than that of the lower surface and, to ensure a suitable resistance to bending and also a resistance to notch 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 side walls is greatly reduced by using a thin wall. This is due to the fact that 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 conducting a proper study of the application, one can benefit

  a significant saving in terms of weight.

  In manufacturing, almost all the realizations of cylinder clamps for infusion sets (as well as with screws) are 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 molds with two plates, etc. In the case of pliers acting in parallel, this chamfer provides a small angle for what is called the clamping surface; however, this small angle (for example of the order of 0.5 degrees) plays no role in controlling the flow rate as already discussed. The proposed function; utilisation facility; ease of adjustment, tight grip of the tube, etc. are all determined by the design of the mold core. It is the core that forms the configuration and the interior dimensions of the housing. The dimensions of the core, its shape, the tolerances of the dimensions, etc., determine the characteristics of the molded part. It is therefore probable that, for almost all the pliers, 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 room which is

  generally 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 production of the cavity and can see, if it is nothing, with the production of the core. To transform an existing mold, the halves of the cavity are slightly leveled, as we have already discussed and will discuss it again, then joined together. The cavity is also slightly offset from the core. The core is left essentially unchanged, but the pouring attacks are relocated to allow the introduction of the plastic material injected into the

  wheel guide surface, now thickened.

  A typical cavity for housing is constructed in a mold like a clam and often the two halves 70 and 75 are almost 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 making the pliers

  of the present invention.

  1. The coupling halves of the cavity should be leveled off in a relatively small amount, on the order of 40 to 80 percent of the original wall thickness. In FIG. 4A, this is represented by leveling the surfaces 70A and 70B and 75A and 75B. In the case where the thickness of the wall of the part 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; a typical draft will have a wall thickness which will vary by a few thousandths of a mm by a mm in length). A draft is used to facilitate removal of the part from the mold. This slight chamfer can generally be preserved by leveling the same depth of material on

  the entire contact surface of half of the cavity.

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

  due to the mold core, are not altered.

  The effect of the above is to bring the halves of the cavity together 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 generally in the range of percent to 70 percent of the original thickness of

the top wall.

  These two steps are relatively simple to

  and can be done quickly and inexpensively.

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

  only needs to undergo a relatively minor operation.

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

  Another cost comparison will be the cost-

  the manufacturing of the newly modified part compared to the cost of the original part. Weight savings of 30 percent, for example, will generally translate into overall manufacturing cost savings of 20 percent. The reason is that the cost of the raw material constitutes a large fraction of the total cost of manufacturing. A significant additional saving in manufacturing costs will also be obtained since the new realization must allow a faster manufacturing cycle. This is due to the fact that the part, given the smaller thickness of its walls, and also the fact that the thickened part is subjected to two-dimensional cooling and not to one-dimensional cooling, will require a cooling time. shorter. All the advantages of the new realization will be preserved insofar as the casting attacks are correctly placed. A logical location will allow the plastic to be injected into the cavity at one end of the guide surface of the wheel axle (attack from the edge). For this location, the flow passage of the injected plastic has a shape close to the ideal shape, that of an approximately circular cross section and not too small. This flow tunnel can then "feed" the thinner side walls and the other parts of the mold cavity as necessary. An alternative location for casting attacks will allow the plastic to enter at one end of the lower clamping surface of the housing (an edge attack can also be considered). Again, the cross section is generous and allows excellent access to thin walls. To ensure that a part with symmetrical properties is obtained, two attacks on the opposite sides of the cavity are generally used or a larger attack placed in the center, such a central location generally being in the center of

the lower clamping surface.

  In essence, improving costs requires a relatively modest change in the cavity, involving leveling of the contact surface of the two halves and a slight enlargement of the surface for the wheel axle; 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 the top wall and thin the bottom wall. The potential economic benefits obtained by changing the mold, compared to building new molds to reflect the improved realization, are relatively large. This is due to the fact that the companies which can obtain immediate benefits already have molds for large productions and have large market shares. The modification of their molds can be done at a very modest cost and with 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 subject to modifications and

  variants which will appear to those skilled in the art.

Claims (21)

  1. Clamp (10) of the roller type (14) made of molded plastic for intravenous administration, comprising a housing. (50) of molded plastic material comprising at least one bottom wall (60), side walls (57,58) and one top wall (52,51), characterized in that the ratio between the thickness in cross section of the upper wall and the cross-sectional thickness of the side wall (57.58) is in a range of 1.5 to 4.0.   2. Pliers according to claim 1, characterized in that it further comprises a cylindrical caster (14) and a plastic tube (20) which is clamped between the caster and the housing, the housing having a ratio between weight and length less than 1.6 grams per centimeter, and a mechanical strength capable of completely closing by clamping a polyvinyl chloride tube (20) having an inside diameter of 2.3 mm and an outside diameter of between 3.5 mm and 4 , 5 mm, and   having a Shore D hardness greater than 68.   3. Clamp according to claim 2, characterized in that said side walls (57,58) have a thickness comprised in a range of 0.8 to 2.5 times that of   plastic tube walls.   4. Pliers according to claim 1, characterized in that it further comprises an upper section (61,62) for guiding the axis of rotation of the caster, a cylindrical caster (14) having an axis of rotation (16), said housing comprising a section constituting a flow control zone, (17), the cross section of the side walls of the flow control zone being less than two thirds of the thickness of the section   upper guide of the caster axis.   5. Pliers according to claim 4, characterized in that it further comprises a plastic tube (20.) which is clamped between the roller and the housing, the thickness of the side walls (57,58) being less than double the thickness of the wall of the pinched tube   when the latter is in the non-deformed state.   I5 6. Clamp according to claim 4, characterized in that the thickness of the side walls (57,58) is less than half that of the wall of the section   upper roller axle guide (51,52).   7. Pliers according to claim 1, characterized in that it further comprises a cylindrical caster (14) and a plastic tube (20) which is clamped between the caster and the lower wall of the housing, the thickness of the walls lateral being less than the   half that of the bottom wall.   8. Pliers according to claim 7, characterized in that said housing comprises an upper section (51,52) for guiding the caster axis, and the thickness of the side walls is less than two thirds of that of the upper section of roulette axis guide or from the bottom wall.   9. Pliers according to claim 1, characterized in that said housing is an injection molded plastic housing (50), comprising an upper section (61,62) of the caster guide and caster guides (53,54) provided therein, a cylindrical caster (14) having an axis of rotation (16) mounted so as to move generally along the axis of the housing, the axis of rotation being received in the caster guides, said caster having dimensions making it possible to leave a space between the lower surface of the housing and the opposite section opposite said caster, a deformable plastic tube means (20) received in the housing and comprising a part located in the space separating said lower surface and said roller, the ratio between the thickness of the cross section of the top wall and the thickness of the cross section of the side wall being within a range of 1.5 to 4.0.   10. Pliers according to claim 9, characterized in that it has a wheel stroke in which the flow rate of the flow passing through the tube (20) can be adjusted, the wheel (14) moving parallel to the lower surface in the roulette race so   to adjust the flow in the tube (20).   11. Pliers according to claim 9, characterized in that said space is less than twice the thickness   of the undeformed wall of the tube (20).   12. Pliers according to claim 9, characterized in that said housing has a ratio between weight and length of less than 1.6 grams per centimeter and a mechanical strength allowing a polyvinyl chloride tube (20) to be pinched completely on closing. an internal diameter of at least 2.3 mm and an external diameter between 3.5 mm and 4.5 mm as well as Shore D hardness greater than 68.   13. Pliers according to claim 9, characterized in that said thickness of the side walls (57,58) is less than twice the thickness of the wall of the tube   (20) when the latter is in the non-deformed state.   14. Clamp according to claim 9, characterized in that said side walls (57,58) have a thickness equal to a value between 0.8 and twice that   of the wall of the plastic tube (20).   15. Clamp according to claim 9, characterized in that the cross section of the side walls (57,58) in the control zone of said flow is less than two thirds of the thickness of the upper section of roulette axle guide (61,62).   16. Pliers according to claim 14, characterized in that the thickness of the side walls (57,58) is less than half that of the upper section   for guiding the axis of the caster (61,62).   17. Clamp according to claim 9, characterized in that the thickness of said side walls (57,58) is less than half that of the bottom wall (60) 18. Pliers according to claim 9, characterized in that said thickness of the side walls (57,58) is less than two thirds of that of the upper section of the roller shaft guide or of the wall lower (60).   19. Pliers according to claim 9, characterized in that it comprises a zone comprising no flow control between an inlet section of the housing and a closed position, and in that the thickness of the upper lateral walls (57 , 58) and lower (60) has a reduced value in the zone comprising no control of the flow rate with respect to the corresponding part where the tube (20) is pinched to obtain control of the flow or stop.   20. Clamp according to claim 1, characterized in that the housing is an injection molded plastic housing (50), comprising an upper section for guiding the caster (61,62) in the upper wall (51,52), a wheel (14) having an axis of rotation mounted to move generally along the axis of the housing (50), the axis of rotation being received in the wheel guide section (61, 62), said wheel (14) having dimensions always leaving space between the lower surface (60) of the housing (50) and the opposite section opposite said caster (14), a deformable plastic tube means (20) received in said housing ( 50) and comprising a part situated in the space separating said bottom wall (60) and said caster (14), and the caster guide section (61, 62) having a cross section whose ratio   between width and height is less than 2.0.   21. Clamp according to any one of claims 1,   2, 4 and 8, characterized in that said clamp is a clamp acting in parallel.