241results about How to "Reduce the effects of friction" patented technology

PCT No. PCT / US95 / 13325 Sec. 371 Date Sep. 28, 1997 Sec. 102(e) Date Sep. 28, 1997 PCT Filed Oct. 10, 1995 PCT Pub. No. WO96 / 12316 PCT Pub. Date Apr. 25, 1996Fuel cell stacks comprising stacked separator / membrane electrode assembly fuel cells in which the separators comprise a series of thin sheet platelets, having individually configured serpentine micro-channel reactant gas humidification active areas and cooling fields therein. The individual platelets are stacked with coordinate features aligned in contact with adjacent platelets and bonded to form a monolithic separator. Post-bonding processing includes passivation, such as nitriding. Preferred platelet material is 4-25 mil Ti, in which the features, serpentine channels, tabs, lands, vias, manifolds and holes, are formed by chemical and laser etching, cutting, pressing or embossing, with combinations of depth and through etching preferred. The platelet manufacturing process is continuous and fast. By employing CAD based platelet design and photolithography, rapid change in feature design can accommodate a wide range of thermal management and humidification techniques. One hundred H2-O2 / PEM fuel cell stacks of this IFMT platelet design will exhibit outputs on the order of 0.75 kW / kg, some 3-6 times greater than the current graphite plate PEM stacks.

A mitral valve annulus reshaping device includes at least a portion that is formed of a biocompatible shape memory alloy SMA having a characteristic temperature, Af, that is preferably below body temperature. The device is constrained in an unstable martensite (UM) state while being introduced through a catheter that passes through the venous system and into the coronary sinus of the heart. The reshaping device is deployed adjacent to the mitral valve annulus of the heart as it is forced from the catheter. When released from the constraint of the catheter, the SMA of the device at least partially converts from the UM state to an austenitic state and attempts to change to a programmed shape that exerts a force on the adjacent tissue and modifies the shape of the annulus. The strain of the SMA can be varied when the device is within the coronary sinus.

An ejector system comprises a lobed, supersonic primary nozzle and a convergent / divergent ejector shroud. The lobed nozzle is just upstream from the ejector shroud, such that there is an annular space between the nozzle and shroud for admitting a secondary flow. In operation, a primary flow of high-pressure steam or air is directed through the primary nozzle, where it is accelerated to supersonic speed. The primary flow then exits the primary nozzle, where it entrains and is mixed with the secondary flow, creating a low pressure region or vacuum. The ejector shroud subsequently decelerates the combined flow while increasing the flow pressure, which increases suction performance and reduces energy loss. Because the primary nozzle mixes the two flows, the ejector shroud is able to have a length-to-entrance-diameter ratio significantly smaller than typical shrouds / diffusers, which decreases the system's size and increases performance.

An apparatus, a method and a control system for controlling an industrial robot with at least one axis of rotation and / or translation. The robot includes at least one actuator or motor at each of the axes for driving a movement of an arm of the robot and at least one sensor at each of the rotatable shafts. A dither-signal generator for generation of a periodic signal is used to provide a varying dither signal to a servo of the actuator. Automatic adaption of the dither signal is provided. A computer program for carrying out the method and a graphical user interface.

The invention discloses a component combined torsion experimental device comprising two counter-force frames which are fixed on a foundation terrace, a counter-force beam with two ends which are fixed at the upper ends of the counter-force frames and a counter-force wall fixed at the left side of the counter-force beam, wherein a component is fixed on the foundation terrace. The component combined torsion experimental device is characterized by further comprising a vertical force loading system for applying a vertical force to the component, a horizontal force loading system for applying a horizontal force to the component, a component top linear displacement guide system for meeting requirements of axial deformation, bending deformation and shearing deformation of the component, and a foundation displacement limiting system for fixing the position of the component. According to the experimental device and the method disclosed by the invention, the disadvantages of the existing similar experimental devices and methods are overcome; an experimental principle is scientific and an experimental process is simple to operate and control; the experimental device is convenient to assemble and can be used while being installed; and the experimental device can be circularly used and an experimental result meets a combined torsion performance of the structural component under the horizontal earthquake action, so as to provide experimental guarantees for disclosing a combined torsion mechanism and an anti-seismic property of the structural component.

A laser assisted machining method and device comprise a tool mount on which a laser head is disposed. A digital thermometer is disposed in a machining tool or on the tool mount for feeding data to a system controller. A laser is used to enable the blade of the machining tool to heat and soften a workpiece instantaneously. As the machining process is in progress, the chip is rapidly removed. The temperature of the tool tip is monitored by the digital thermometer for automatic control of the temperature of heating the workpiece by the laser, thereby keeping the temperature of the tool tip in a specific allowable range. The efficiency of the machining process and the surface precision are thus enhanced.

The invention discloses an apparatus for testing rock drillability under a stratum condition, which comprises a clamping mechanism, a pressure balancing mechanism and a power mechanism, wherein the clamping mechanism is arranged at the lower end of the pressure balancing mechanism; the power mechanism is arranged in the pressure balancing mechanism and the clamping mechanism; the clamping mechanism consists of a clamp holder kettle body, a taper sleeve, a rubber sleeve, an upper plunger and a lower plunger; the pressure balancing mechanism consists of a wellhole pressure kettle body, a bit pressure kettle body and a bit pressure piston; and the power mechanism consists of a motor, a speed reducer, a canine impacter and a drill stem. The testing apparatus, which adopts the structure of mechanical-electrical integration, can test the rock drillability really and accurately by simulating the temperature, confining pressure, pore pressure and wellhole slurry pressure under the stratum condition, particularly the overlying confining pressure, pore pressure and wellhole slurry pressure of over 90 MPa of strata, and therefore has a more practical instruction significance for well drilling construction.

The invention relates to the technical field of medical equipment and particularly relates to a measurement device and method for thrombus elasticity. The measurement device for thrombus elasticity comprises a driving module, an adjustable constant-temperature module, a testing cup, a testing needle, a reflection mirror and a moving device, wherein the adjustable constant-temperature module is arranged on the driving module and is connected with the driving module; the testing cup is arranged in the adjustable constant-temperature module; the testing needle is arranged on the testing cup; the reflection mirror is fixed on the testing needle; the moving device is connected with the reflection mirror; the adjustable constant-temperature module is used for heating or cooling the testing cup. The measurement device for thrombus elasticity further comprises a laser device, a PSD (Position Sensitive Detector) position sensor, a data processing module which is electrically connected with the PSD position sensor, and a man-machine interaction module which is electrically connected with the data processing module. According to the measurement device and the measurement method provided by the invention, an optical lever principle is used for measuring thrombus elasticity and the influences caused by the measurement with an electromagnetic sensor are eliminated, so that the measurement precision is improved. The adjustable constant-temperature module is used for adjusting and controlling the temperatures of experiment samples, so that the influences of an environmental temperature during blood clotting can be really simulated, and the accuracy of measured data is improved.

The invention discloses a throttle valve port performance test device which comprises a visualized flow field, a hydraulic test loop and a data acquisition control system, wherein the hydraulic test loop comprises a main oil circuit, a pilot control oil circuit and a cooling oil circuit; the visualized flow field comprises a valve cavity made of transparent material, a valve core provided with a throttle valve port of which the performance is to be tested, a laser, a CCD camera and a synchronous control device; movement of the valve core is controlled through reset springs at two ends and controlled oil together; the data acquisition control system comprises pressure sensors placed near the throttle valve port in the visualized flow field and in control oil cavities at two ends of the valve core, a flow sensor, a displacement sensor, a sound-level meter and a temperature meter in an oil tank. The device can directly observe cavitation form and flow phenomenon in the visualized flow field, and completes measurement of various parameters such as valve port noise, steady flow force of the valve core, pressure distribution of the flow field, flow and displacement of the valve core at the same time.

The invention discloses a buckling-restrained shearing steel plate energy dissipation device with clamping plates. The energy dissipation device comprises a core energy dissipation component, a buckling-restrained device, a top plate and a bottom plate, the core energy dissipation component is a rectangular energy dissipation steel plate, the top plate and the bottom plate are fixedly connected at the upper end and the lower end of the rectangular energy dissipation steel plate respectively, the buckling-restrained device comprises two clamping plates, four guide trough plates and stiffening ribs, the two clamping plates are arranged on the front side and the rear side of the rectangular energy dissipation steel plate respectively, the upper ends of the two clamping plates are fixed with the top plate, the four guide trough plates are fixed on the bottom plate and limit movement of the lower ends of the two clamping plates respectively, and the stiffening ribs are arranged on one lateral surface, departing from the rectangular energy dissipation steel plate, of each clamping plate. By the buckling-restrained shearing steel plate energy dissipation device with the clamping plates, slotting or punching of the core energy dissipation component can be avoided, and the stiffening ribs can be prevented from being directly welded on the core energy dissipation component. By the aid of the buckling-restrained device, out-of-plane deformation of the core energy dissipation component can be limited effectively, bearing capacity is enhanced, and hysteretic behavior is improved.

The invention relates to a systematic detection method for an anti-cracking performance of concrete and in particular relates to a systematic detection method for comprehensively judging the anti-cracking performance of the concrete by detecting an anti-cracking safety coefficient, a shrinkage strain amount, a strength and elastic modulus development curve, a strain concentration point and the restriction degree. The detection method comprises the following steps of detecting a temperature strain parameter of the concrete to judge the anti-cracking safety coefficient of the concrete; detecting a shrinkage strain value of the concrete to judge the shrinkage strain amount of the concrete; detecting the maturity of the concrete to construct the strength and the elastic modulus development curve; simulating and calculating the strain concentration point of the concrete through a central processing unit; detecting a friction coefficient of a concrete entity model to judge the restriction degree of the concrete; comprehensively evaluating the anti-cracking performance of the concrete according to the steps. According to the systematic detection method, the anti-cracking performance of the concrete can be effectively detected, and the manufacturing quality of the concrete is improved, so that the concrete can meet a requirement of a high-standard submarine construction environment.

The invention discloses a bidirectional layered sample pressing device for preparing a consolidation test sample and a sample pressing method thereof. The device is formed in the following manner: the inner wall of a guide cylinder is sleeved with a pressurization piston, the bottom surface of the flange of the pressurization piston is joined with the top of the guide cylinder, a cutting ring groove is formed in a position below the pressurization piston on the inner wall of the guide cylinder, the top of a cutting ring is embedded in the cutting ring groove of the guide cylinder, and the diameter of the cutting ring is equal to that of the pressurization piston; the cutting edge of the cutting ring is embedded in the hollow cavity of a circular ring-shaped projection on the top of a base; one or two disk-shaped cushion blocks are embedded in the inner cavity of the cutting ring; the distance between the bottom surface of the flange of the pressurization piston and the lower end face of the pressurization piston, the height of the inner wall above the cutting ring groove of the guide cylinder and the height of the cushion block are equal to 1 / n of the height of the cutting ring, and n is layering time in a test sample pressing process and is equal to 3 or 4. The pressing density of the test sample pressed by the device is more uniform, and interference caused by friction force of the ring wall in a sample loading process is small, so that the test data error of a consolidation test is small, and the test result is more accurate and reliable.

The invention provides a soil consolidation detector of using weight and air pressure combined loading and a detection method. The soil consolidation detector is suitable for the technical field of property detection of soil and especially suitable for remolded soil consolidation process testing and consolidation process testing of natural soil with relatively high moisture content. The soil consolidation detector comprises a reaction frame, a weight loading device, a weight and air pressure loading conversion device, a sensing measurement device, a consolidation container and an air source pressure controller; after weight loading and forming of a certain settlement amount, upper counter-force is formed through an adjusting nut and a conversion accessory; an air pressure loading device is started to push the consolidation container to ascend to gradually replace a weight load; air pressure is applied to pre-determined consolidation pressure; and the deformations of soil samples in the weight loading process and the air pressure loading process are automatically switched and observed and the soil consolidation quality is recorded and controlled through two groups of sensors on the sensing measurement device. The soil consolidation detector is relatively high in accuracy and convenient to operate; and soil which is uniform in property and high in strength and has different soil consolidation degrees can consolidated under a high load condition.

The invention discloses an active paying-off machine apparatus, which comprises a frame, wherein, rotational fast pulleys are fixed at the upper part of the frame; brackets, which are fixedly connected with the frame, are respectively arranged on two sides of the fast pulleys; cable clamps are fixed on the brackets; a rotating shaft is connected with an end part of a rocker arm, the rotating shaft is rotationally matched with bearings arranged on the frame; driving wheels, which are connected with the fast pulleys through an inner core of a wire cable, are rotationally fixed at one end of the rocker arm away from the rotating shaft; and the rotating shaft is connected with the twist spindle of a sensor used for sensing the rotation angle. The active paying-off machine is used for controlling the paying-off speed of the active paying-off machine, thereby balancing the tension of the inner cores of the wire cable arranged between the active paying-off machine and a plastic extruder within a certain range, improving the paying-off speed, and reducing the fault rate of the inner core of the wire cable.

The invention discloses a hub burr self-adjusting type grinding machine which comprises a bottom linear motion mechanism, a top horizontal linear motion mechanism and a top vertical linear motion mechanism, wherein the bottom linear motion mechanism is fixed on a base; brackets are symmetrically arranged on opposite sides of the base; the top horizontal linear motion mechanism is arranged between upper ends of the two brackets; the top vertical linear motion mechanism is arranged on the top horizontal linear motion mechanism in a sliding manner; a self-adjusting grinding mechanism is arranged on the top vertical linear motion mechanism; a support frame is arranged on the bottom linear motion mechanism; a square frame with an opening in the middle is arranged on the support frame; rotation mechanisms and positioning mechanisms for the rotation mechanisms are symmetrically arranged on two opposite sides of the square frame. The grinding mechanism provided by the invention is reasonable in design, adopts a floating spindle to realize a mode of automatic adjusting on all sides, solves a problem that products are easy to hurt or the grinding is not in place at the time of grinding in an ordinary computer numerical control machining center, significantly improves grinding efficiency and effect, and doubles the grinding efficiency.

The invention relates to a full-automatic powder hydraulic forming machine which comprises a stander, a lower die, an upper die and a core die, and is characterized in that a die frame is arranged ona movable die frame rack and positioned between the upper and the lower dies; the movable die frame rack is driven to move up and down by a mold stripping oil cylinder; and an automatic material distribution mechanism is installed on the movable die frame rack and set to move up and down along with the movable die frame rack. The pressing technique adopts the way of pressurizing and exhausting fora plurality of times to lead powder to be gradually exhausted and compacted and simultaneously utilizes die frame floating technology to realize bidirectional pressurization of a green body in the processes of low pressure pressing, medium-pressure pressing and high pressure pressing, so that the frictional influence of the powder for the wall of the die frame can be reduced, the compactness at the upper and the lower parts of the green body can be consistent, and the quality of the green body is greatly improved.

The invention discloses a heat backward extrusion molding process of a large-sized cup-shaped piece, relating to a backward extrusion molding method. By using the invention, the forming force for the heat backward extrusion of the large-sized cup-shaped piece can be reduced and the problem in the prior art that the production efficiency is low is solved. The heat backward extrusion molding process comprises the following concrete steps of: (1) placing a heat blank in a material accommodating cavity; (2) downwards pressing a pressure head to enable a backward extrusion punch head to be contacted with the blank; (3) downwards pressing the pressure head and allowing a backward extrusion cylinder to downwards slide along an inner cavity of a base and compress a spring until the spring contacts with the bottom plane of the inner cavity of the base; (4) downwards pressing the pressure head to enable all blanks to be reduced and extruded to a backward extrusion cavity to be attached to an ejector rod; (5) downwards pressing the pressure head and starting the backward extrusion molding process until the process is finished; (6) backward lifting the pressure head, lifting the backward extrusion cylinder, limiting a stamped part by a stripper plate to separate from the backward extrusion punch head, allowing the ejector rod to upwards eject and then taking out the stamped part after the stamped part is separated from the backward extrusion cylinder; (7) retracting the ejector rod and allowing an ejecting material to fall off and ensuring that a die restores the initial state; and (8) repeating the process steps from (1) to (7) and continuously finishing the heat backward extrusion molding of the large-sized cup-shaped piece.

The invention relates to a test bench for fretting abrasion of a double-strand aluminum lead, and the test bench comprises a base plate, wherein a first lead frame and a second lead frame are arranged on the base plate in pair; a third lead frame and a fourth lead frame are arranged on the base plate in pair; a sliding slot is arranged at one sides of the third and fourth lead frames; one end of a sliding block in the sliding slot is connected to a holding device while the other end is connected to a connecting rod; and the connecting rod is connected to an eccentric block. The test bench canbe used for truly simulating the fretting abrasion between external aluminum leads of an overhead transmission line under various working conditions (such as fretting amplitude, frequency, load, leadincluded angle, wrap angle, and the like), thereby analyzing the fretting characteristics of the lead under the conditions, supplying a method for improving the fretting abrasion, reducing the abrasion between the leads and prolonging the service life of the overhead transmission line. The test bench provided by the invention plays an important role in researching the fretting abrasion between the leads.

The invention discloses a parking locking mechanism for an automobile speed changer. The parking locking mechanism for the automobile speed changer is characterized in that the parking locking mechanism comprises a locking mechanism body and a manual unlocking mechanism; the locking mechanism body is composed of a conical surface intermediate shaft, a friction ring, a conical surface locking ring, a lead screw, a guide rod and a motor; the shaft end of the conical surface intermediate shaft is in a conical surface shape, and the periphery of the conical surface intermediate shaft comprises multiple rows of oil discharge grooves which are connected with a through hole in the shaft center; an inner hole of the conical surface locking ring is conical and comprises multiple oil return grooves; the motor is controlled to rotate to drive the conical surface locking ring, the friction ring and the conical surface intermediate shaft for combination so as to achieve braking of the speed changer; the concentricity of three conical surfaces of the conical surface intermediate shaft, the friction ring and the conical surface locking ring can be guaranteed during mounting of the parking locking mechanism, so that braking accuracy is guaranteed and automobile sliding is avoided. Power-off self-locking and power-on unlocking are achieved; the control operation is simple; the structure is compact; comprehensive functions are achieved; the reliability and the stability of parking braking are effectively improved.

The invention relates to a throttle arrangement for an exhaust system of an internal combustion engine having a throttle valve for throttling a stream of exhaust gas flowing through a pipe and having a restoring spring which prestresses the throttle valve into a closed position. The throttle valve is pivotable about a pivot axis in the pipe between the closed position [and the open position] and the restoring spring is supported on the valve end on a lever fixedly connected to the throttle valve and is supported at the pipe end on a bearing for accommodating a shaft extending coaxially with the pivot axis. The restoring spring is adapted to support the spring forces on the pipe end in an essentially symmetrical manner with respect to a plane of symmetry that extends perpendicular to the pivot axis and is in the area of the support on the valve end.

A system (100) for positioning a working tool (21) in a wellbore (1). The positioning system (100) comprises a casing element (110) with a marker (111, 112, 113) provided on an inner surface, the marker (111, 112, 113) having a distinct diameter different from the inner diameter of the casing element (110). The system further comprises a positioning tool (120) with a latching element (121, 122) adapted to form a latch (115) with the marker (111, 112, 113), and a force detector (130) adapted to detect an axial latching force (FL) applied to a tubing string (20) from the latch (115) when the casing element (110) is located within the wellbore (1) and the force detector (130) is located at a surface (2) outside the wellbore (1).

A motor producing a rectilinear drive force can be simultaneously provided with a small size and a lightweight, high accuracy and a large drive force. In a spiral linear motor 1, a rotator 3 and stator 2 are both constituted having a spiral shape and, by joining together both spiral-shaped parts, a drive force is produced in the axial direction during rotation in a spiral shape. By affording the spiral linear motor a spiral shape, a large drive force can be obtained similarly to that of a reduction gear and a large drive force can be obtained by utilizing a large area that lies opposite in the axial direction of the rotator and stator.

The invention discloses a pressure control valve for an independent hydraulic control packer. The pressure control valve comprises a central pipe, an outer sleeve, an one-way valve, and a pressure relief device. The outer side of the central pipe is sleeved with the outer sleeve in a hollow manner, and a hydraulic control oil flow annular is formed between the outer sleeve and the central pipe; anoutwardly convex annular platform is arranged on the outer wall of the upper end of the central pipe, and the upper end of the outer sleeve is connected with the outer wall of the annular platform; the annular platform is provided with a separate axial upper hydraulic oil passage, the lower end of the outer sleeve is provided with a separate axial lower hydraulic oil passage, and the upper hydraulic oil passage and the lower hydraulic oil passage are communicated with the hydraulic control oil flow annular; and a lower port of the upper hydraulic oil passage is connected with the one-way valve through which the hydraulic oil can only flow downward, and the pressure relief device is arranged on the outer wall of the central pipe. According to the pressure control valve for the independenthydraulic control packer, by adopting a built-in hydraulic oil single-fluid design, flow direction control of the hydraulic oil in hydraulic control pipelines is achieved, by adopting a double-pistonlinkage design, the opening and closing of a double wall cavity of the pressure control valve and oil pipeline passages are achieved, and demands of downhole rapid pressure relief and unsealing of a marine hydraulic control packer are met.

The invention discloses a dual-compression soil sample preparation device, which comprises a dual-compression mechanism and a sample preparation barrel, wherein the sample preparation barrel is vertically arranged and cuts through from top to bottom; the dual-compression mechanism comprises an upper compression device and a lower compression device; the upper compression device comprises an upperadjusting rod arranged at the upper end of the sample preparation barrel, an upper limiting part and an upper compression part, the upper compression part is movably arranged in the sample preparationbarrel in a sleeved mode, the upper limiting part is arranged above the upper compression part, and the upper limiting part and the upper compression part are arranged on the upper adjusting rod in amode that the distance between the upper limiting part and the upper compression part can be adjusted; the lower compression device comprises a lower adjusting rod, a lower limiting part and a lowercompression part, the lower compression part is tightly arranged in the sample preparation barrel in a sleeved mode, the lower limiting part is arranged under the lower compression part, the lower limiting part and the lower compression part are arranged on the lower adjusting rod in a mode that the distance between the lower limiting part and the lower compression part can be adjusted, and the lower adjusting rod is fixedly connected with a piston rod of a hydraulic device in the axial direction. By means of the structure, soil sample evenness can be improved. The invention further provides asample preparation method of the dual-compression soil sample preparation device.

The invention relates to a bimetal composite pipe machining method in particular to a magnetic pulse forming method for a lining bimetal composite pipe. The method aims at solving the problem that an existing magnetic pulse bimetal composite pipe forming method cannot combine a large-diameter pipe blank. The method includes the steps of firstly, surface purification treatment of the pipe blank to be combined, secondly, locating and clamping of the pipe blank to be combined, thirdly, machining of the first combining sub-step, fourthly, machining of the following combining sub-steps and fifthly, machining of the bimetal composite pipe. By the adoption of the forming method, an expanding and bulging manner of a thin wall pipe is used for achieving mechanical combination of an inner pipe and an outer pipe, the manufacturing process is simple, and the combined strength can reach 0.5 MPa to 13 MPa compared with similar products and higher than the combined strength of about 0.2 MPa of the similar products. The forming method is suitable for manufacturing the lining bimetal composite pipe.

A steering controller for controlling an electric power steering includes a load estimator estimating a road surface load, a pre-correction target determiner determining a pre-correction target steer torque based on the estimated road surface load, a steer angle detector detecting a steer angle, and a target corrector correcting the pre-correction target steer torque based on the steer angle, and the controller determines an assist torque instruction value based on the deviation between the target steer torque and a steer torque, thereby establishing a robust steering feel of an electric power steering system irrespective of the change of the mechanical friction of the power steering system.

The invention belongs to the related technical field of treatment of sludge slurry with ultrahigh water content. The full-automatic hydraulic permeation consolidation device comprises a water pressurecontrol assembly, a permeation consolidation assembly, a measuring assembly and a data acquisition assembly, the water pressure control assembly is connected with the permeation consolidation assembly, and the measuring assembly is arranged on the permeation consolidation assembly and connected with the data acquisition assembly; the consolidation device is used for realizing drainage consolidation of a soil body through pushing and friction dragging effects of seepage force of high-pressure water on a soil sample; the water pressure control assembly is used for controlling the seepage force,and the data acquisition assembly is used for acquiring the pore pressure at each depth of a soil sample in the seepage consolidation assembly, the displacement at each time and the drainage rate inreal time so as to obtain the seepage coefficients of different stages. According to the invention, the filter pressing benefit is improved, real-time and automatic acquisition of test data is realized, large errors caused by manual reading are avoided, and the test data is accurate and reliable.

An attachment device for tightening an adjustable resistant strap, comprising a buckle composed of a pair of superposed rings of different dimensions. The buckle is associated with a positioning shim housed around a closed first turn arranged opposite the blocking slot of the strap. The positioning shim is configured to separate the top strand and the bottom strand of said turn from one another. This results in a reduction of the friction effect when relative movement takes place between the two rings. The shim is equipped for this purpose with two guide apertures through which the bottom strand and the top strand of the closed turn attached to the buckle respectively pass.