Testing device for accelerating chloride ion erosion of reinforced concrete and testing method thereof

Abstract

The invention provides a test device and method for accelerating chloride ion erosion of reinforced concrete, the test device is used for testing a concrete test piece, the test device comprises: a clamp including a first clamp and a second clamp on the left and right sides, the first clamp and the second clamp are respectively provided with corresponding bolt holes, and the first clamp and the second clamp are connected through a screw penetrating the bolt holes, notches are respectively formed in the tops of the first clamp and the second clamp; the solution tanks comprise the first solution tank and the second solution tank, the first solution tank and the second solution tank are arranged on the side faces of the first clamp and the second clamp respectively and communicated with the notches in the tops of the first clamp and the second clamp, and the first solution tank on the first clamp is opposite to the second solution tank on the second clamp in position; the electrode plates comprise a first electrode plate and a second electrode plate, the first electrode plate and the second electrode plate penetrate through the notches and are inserted into the first solution tank and the second solution tank respectively, and the electrode plates are connected with a voltage-stabilized direct-current power supply through wires.

Description

Technical Field

[0001] The invention relates to the technical field of reinforced concrete durability testing, and in particular to a testing device and method for accelerating chloride ion corrosion of reinforced concrete. Background Art

[0002] At the beginning of the 21st century, with the rapid development of the economy, my country entered a peak period of infrastructure construction, and a large number of reinforced concrete structures (buildings) were built. At this stage and for a long time in the future, relevant practitioners will mainly carry out work around the maintenance, upkeep and renovation of existing structures (buildings). The durability problem of reinforced concrete structures has become increasingly prominent. Chemical erosion is an important factor affecting the durability of reinforced concrete structures. Among them, chloride ions enter the concrete through absorption, penetration and diffusion, and produce electrochemical reactions with steel bars to cause steel corrosion. Cracks are generated in the concrete under the action of steel corrosion expansion products. As the cracks develop, the protective layer eventually falls off and the structure fails, causing huge economic losses and safety risks. Therefore, it is particularly important to study the deterioration and damage mechanism of reinforced concrete under chloride ion erosion.

[0003] At present, there are many test methods for the durability of concrete under chemical erosion at home and abroad, mainly including sulfate erosion resistance test, chloride ion penetration resistance test, and carbonation test. Most of these test methods have the problem of too long test cycle. Among them, the chloride ion penetration resistance test measures the concrete's resistance to chloride ion penetration by using the fast chloride ion migration coefficient method or the electric flux method. Although the test cycle of these two methods is not long, the test parameters are single and can only detect the migration ability of chloride ions in concrete. It is impossible to study the mechanism of steel corrosion expansion caused by chloride ion erosion, the generation and development process of concrete cracks, and the influence of chloride ion permeability coefficient after cracks develop. It is an indirect characterization of the durability of reinforced concrete under chloride ion erosion.

[0004] In practice, the impact of chloride ions on the durability of reinforced concrete structures involves a series of factors, such as the migration of chloride ions to the surface of steel bars, the corrosion and expansion of steel bars after depassivation, the generation and expansion of concrete cracks, and the influence of cracks on the diffusion coefficient of chloride ions.

[0005] Therefore, the urgent problem to be solved is how to conveniently and efficiently study the durability of reinforced concrete structures under chloride ion corrosion. Summary of the invention

[0006] The present invention is made to solve the above-mentioned problem, and its purpose is to provide a test device and a test method for accelerating chloride ion corrosion of reinforced concrete.

[0007] The invention provides a test device for accelerating chloride ion corrosion of reinforced concrete, which has the following characteristics and comprises: a clamp, comprising a first clamp and a second clamp on left and right sides, the first clamp and the second clamp are respectively provided with corresponding bolt holes, the first clamp and the second clamp are connected by screws penetrating the bolt holes, the first clamp and the second clamp can adjust relative positions, clamp concrete test pieces, so that a solution tank can become a closed space, and the tops of the first clamp and the second clamp are respectively provided with notches; a solution tank, comprising a first solution tank and a second solution tank, the first solution tank and the second solution tank are respectively arranged on the sides of the first clamp and the second clamp, and are communicated with the notches on the tops of the first clamp and the second clamp, the first solution tank on the first clamp and the second solution tank on the second clamp are opposite in position; and an electrode plate, comprising a first electrode plate and a second electrode plate, the first electrode plate and the second electrode plate are respectively inserted into the first solution tank and the second solution tank through the notches, and the electrode plate is connected to a regulated DC power supply through a wire.

[0008] The test device for accelerating chloride ion corrosion of reinforced concrete provided by the present invention may also have the following features: wherein the screw is a threaded screw, and the solution notch portion is provided with a circle of grooves, and the grooves are used to place silicone gaskets.

[0009] The test device for accelerating chloride ion corrosion of reinforced concrete provided by the present invention may also have the following features: butterfly nuts are respectively provided at both ends of the full-thread screw, the butterfly nuts are located on the outside of the clamp, and a flat gasket is provided between the butterfly nut and the clamp, so that the first clamp and the second clamp can be clamped by rotating the butterfly nut.

[0010] The test device for accelerating chloride ion corrosion of reinforced concrete provided by the present invention may also have the following characteristics: the first clamp and the second clamp are made of acrylic, and the first electrode plate and the second electrode plate are made of inert titanium, stainless steel, copper or zinc.

[0011] The test device for accelerating chloride ion corrosion of reinforced concrete provided by the present invention may also have the following characteristics: wherein the first electrode plate is connected to the positive electrode of the power supply, and the second electrode plate is connected to the negative electrode of the power supply.

[0012] The test device for accelerating chloride ion corrosion of reinforced concrete provided by the present invention may also have the following characteristics: sodium hydroxide solution is added into the first solution tank, and sodium chloride solution is added into the second solution tank.

[0013] The test device for accelerating chloride ion corrosion of reinforced concrete provided by the present invention may also have the following characteristics: water is added to the first solution tank, and sodium chloride solution is added to the second solution tank.

[0014] The present invention also provides a test method for a test device for accelerating chloride ion corrosion of reinforced concrete, which has the following characteristics and specifically includes the following test steps: S1: preparing parts of the test device for accelerating chloride ion corrosion of reinforced concrete and a reinforced concrete test piece; S2: aligning the first clamp and the second clamp and aligning the bolt holes, passing the full-thread screw through the bolt holes of the clamps on both sides for preliminary connection, putting flat washers on the exposed parts on both sides of the full-thread screw, and screwing on butterfly nuts; S3: laying the first clamp flat, holding up the second clamp, and then placing the reinforced concrete test piece between the first clamp and the second clamp, adjusting the relative positions of the first clamp and the second clamp to ensure that the test piece and the solution tank of the clamp are tightly sealed, and the test piece will not loosen during the test; S4: aligning the clamp, filling the solution tank with water through the notch, and standing and observing for 10 minutes after filling. If there is no leakage at the connection between the clamp and the reinforced concrete test piece, the seal is good, and then pouring out the water; S5 : Place the first electrode plate and the second electrode plate in the first fixture and the second fixture respectively through the slot, add sodium hydroxide solution to the first solution tank, add sodium chloride solution to the second solution tank, connect the first electrode plate to the positive pole of the regulated DC power supply through a wire, and connect the second electrode plate to the negative pole of the regulated DC power supply through a wire; S6: After the installation is completed, in a ventilated environment, turn on the power to energize the electrode plate, that is, complete the test purpose of accelerating the chloride ion corrosion of the threaded steel bars in the concrete specimen, and record the current size, the degree of steel bar corrosion, and the generation and cracking of concrete cracks at regular intervals; S7: After powering on for a period of time, replace the solutions in the first solution tank and the second solution tank to eliminate the influence of ion concentration in the test; S8: After the test is completed, turn off the regulated DC power supply, take out the electrode plate, pour out the solution in the solution tank, adjust the relative positions of the first fixture and the second fixture, remove the reinforced concrete specimen, and then disassemble and clean the device.

[0015] The test method of the test device for accelerating chloride ion corrosion of reinforced concrete provided by the present invention may also have the following characteristics: an ammeter is connected in the circuit to detect the current size in real time.

[0016] The test method of the test device for accelerating chloride ion corrosion of reinforced concrete provided by the present invention may also have the following feature: wherein, the relative position of the first clamp and the second clamp is adjusted by screwing the butterfly nut.

[0017] Functions and Effects of the Invention

[0018] According to the test device and test method for accelerating chloride ion corrosion of reinforced concrete involved in the present invention, under the action of potential difference, the chloride ions in the sodium chloride solution will be accelerated to migrate from one side of the reinforced concrete specimen to the other side, thereby efficiently simulating the situation in which chloride ions indiscriminately corrode the reinforced concrete structure from all directions in real scenes. The damage and deterioration laws of the reinforced concrete structure under corrosion of different chloride ion concentrations are studied through the ammeter readings, the degree of steel bar corrosion and the concrete crack detection. In addition, the test device is simple and easy to operate, and real-time observation can be achieved by only tightening the butterfly nut and turning on the power. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 It is a three-dimensional structural schematic diagram of the overall structure of the test device for accelerating chloride ion corrosion of reinforced concrete in an embodiment of the present invention;

[0020] Figure 2 It is a schematic diagram of the planar structure of a full-thread screw, a flat washer and a butterfly nut of the overall structure of the test device for accelerating chloride ion corrosion of reinforced concrete in an embodiment of the present invention;

[0021] Figure 3 It is a schematic diagram of the three-dimensional structure of a reinforced concrete test piece of the overall structure of the test device for accelerating chloride ion corrosion of reinforced concrete in an embodiment of the present invention;

[0022] Figure 4 It is a three-dimensional structural schematic diagram of a local structure of a fixture of the overall structure of a test device for accelerating chloride ion corrosion of reinforced concrete in an embodiment of the present invention;

[0023] Figure 5 It is a schematic diagram of the three-dimensional structure of the fixture without the electrode inserted in the overall structure of the test device for accelerating chloride ion corrosion of reinforced concrete in an embodiment of the present invention;

[0024] Figure 6 A schematic diagram of the planar structure of a silicone gasket of the overall structure of a test device for accelerating chloride ion corrosion of reinforced concrete in an embodiment of the present invention; and

[0025] Figure 7 It is a schematic diagram of the planar structure of the electrode plates and conductors of the overall structure of the test device for accelerating chloride ion corrosion of reinforced concrete in an embodiment of the present invention. DETAILED DESCRIPTION

[0026] In the description of this application, it should be noted that, unless otherwise clearly specified and limited, the terms "installed", "connected", and "connected" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection, an electrical connection, or mutual communication; it can be a direct connection, or an indirect connection through an intermediate medium, it can be the internal connection of two elements or the interaction relationship between two elements. For ordinary technicians in this field, the specific meanings of the above terms in this application can be understood according to specific circumstances.

[0027] In order to make the technical means, creative features, objectives and effects achieved by the present invention easy to understand, the following embodiments are combined with the accompanying drawings to specifically describe the test device and test method for accelerating chloride ion corrosion of reinforced concrete of the present invention.

[0028] Figure 1 It is a schematic structural diagram of a test device for accelerating chloride ion corrosion of reinforced concrete in an embodiment of the present invention. Figure 2 It is a schematic plan view of the structure of a fully threaded screw, a flat washer and a butterfly nut of the overall structure of the test device for accelerating chloride ion corrosion of reinforced concrete in an embodiment of the present invention. Figure 3 It is a schematic diagram of the three-dimensional structure of a reinforced concrete specimen of the overall structure of a test device for accelerating chloride ion corrosion of reinforced concrete in an embodiment of the present invention.

[0029] like Figure 1-3 As shown, the test device for accelerating chloride ion corrosion of reinforced concrete in this embodiment includes a fixture, a solution tank and an electrode plate, which is used to test the corrosion of concrete blocks. The concrete specimen is a cube with a side length of 100 mm. The concrete specimen contains a threaded steel bar, which is a herringbone threaded steel bar with a nominal diameter of 20 mm.

[0030] Figure 4 It is a three-dimensional structural schematic diagram of the local structure of the fixture of the overall structure of the test device for accelerating chloride ion corrosion of reinforced concrete in an embodiment of the present invention. Figure 5 It is a three-dimensional structural schematic diagram of the fixture of the overall structure of the test device for accelerating chloride ion corrosion of reinforced concrete in an embodiment of the present invention without inserting electrodes.

[0031] like Figure 4-5 As shown, the fixture includes a first fixture and a second fixture on the left and right sides. The first fixture and the second fixture are made of acrylic, and the size of the fixture is 140mm×65mm×140mm.

[0032] The first clamp and the second clamp are respectively provided with four corresponding groups of bolt holes, and the diameter of the holes is 8.2mm. The first clamp and the second clamp are connected by four groups of threaded screws passing through the bolt holes. The screws are selected from M8 full-threaded screws with a length of 270mm, and their maximum diameter is 8mm to ensure that they can pass through the bolt holes. Butterfly nuts are respectively provided at both ends of the threaded screws. The butterfly nuts are located on the outside of the clamps. A flat gasket is provided between the butterfly nuts and the clamps, so that the relative position of the first clamp and the second clamp can be adjusted by rotating the butterfly nuts to clamp the concrete specimen so that the solution tank can become a closed space to ensure that there will be no leakage after the solution tank is filled with solution. The matching butterfly nuts and flat gaskets are also selected in M8 size. The tops of the first clamp and the second clamp are respectively provided with notches passing through the solution tank. The notches are composed of two rectangular openings. The slender opening size is 70mm×4mm, which is used to take and place the electrode plates, and the wide opening size is 30mm×26mm, which is used to add and pour out the solution.

[0033] The solution tank comprises a first solution tank and a second solution tank. Sodium hydroxide solution or water is added into the first solution tank, and sodium chloride solution is added into the second solution tank. The size of the solution tank is 90mm×90mm and the depth is 55mm.

[0034] Figure 6 It is a schematic diagram of the planar structure of the silicone gasket of the overall structure of the test device for accelerating chloride ion corrosion of reinforced concrete in an embodiment of the present invention.

[0035] The first solution tank and the second solution tank are respectively arranged on the sides of the first fixture and the second fixture, and are connected with the notches on the tops of the first fixture and the second fixture. The first solution tank on the first fixture is opposite to the second solution tank on the second fixture. Figure 6 As shown, a circle of grooves is provided at the mouth of the solution tank, and the grooves are used to place the silicone gaskets. The dimensions of the grooves and the silicone gaskets are 100 mm×100 mm and 2 mm deep.

[0036] Figure 7 It is a schematic diagram of the planar structure of the electrode plates and conductors of the overall structure of the test device for accelerating chloride ion corrosion of reinforced concrete in an embodiment of the present invention.

[0037] like Figure 7 As shown, the electrode plates include a first electrode plate and a second electrode plate, and the materials of the first electrode plate and the second electrode plate are inert titanium, stainless steel, copper or zinc.

[0038] The first electrode plate and the second electrode plate are respectively inserted into the first solution tank and the second solution tank through the slot, and the electrode plates are connected to the regulated DC power supply through wires, wherein the first electrode plate is connected to the positive pole of the power supply, and the second electrode plate is connected to the negative pole of the power supply. The long ear part of the electrode plate is connected to the wire. In order to facilitate the electrode plate to enter and exit the solution tank and connect the wire, its width must be less than 70mm and its length must be greater than 120mm.

[0039] The test method of the test device for accelerating chloride ion corrosion of reinforced concrete specifically includes the following test steps:

[0040] S1: Prepare the parts of the test apparatus for accelerated chloride ion corrosion of reinforced concrete and reinforced concrete specimens.

[0041] S2: Install two silicone washers into the grooves of the first clamp and the second clamp respectively, ensure that they are tightly fixed, put the first clamp and the second clamp straight and align the bolt holes, pass the full-thread screw through the bolt holes of the clamps on both sides for preliminary connection, put flat washers on the exposed parts on both sides of the full-thread screw, screw on the butterfly nuts, but do not screw them deep, and reserve sufficient space for the insertion of the reinforced concrete specimen.

[0042] S3: Lay the first clamp flat, lift the second clamp, then place the reinforced concrete specimen between the first clamp and the second clamp, tighten the butterfly nut, adjust the relative position of the first clamp and the second clamp, ensure that the specimen and the solution tank of the clamp are tightly sealed, and the specimen will not loosen during the test.

[0043] S4: Align the first and second clamps, and fill the solution tank with water through the slot. After filling, let it stand and observe for 10 minutes. If there is no leakage at the connection between the clamp and the reinforced concrete specimen, the seal is good, and then pour out the water.

[0044] S5: Place the first electrode plate and the second electrode plate in the first fixture and the second fixture respectively through the slots, add sodium hydroxide solution into the first solution tank, add sodium chloride solution into the second solution tank, connect the first electrode plate to the positive pole of the regulated DC power supply through a wire, connect the second electrode plate to the negative pole of the regulated DC power supply through a wire, connect an ammeter in the circuit, and detect the current in real time.

[0045] S6: After installation, in a ventilated environment, turn on the power to energize the electrode plate. Under the action of the potential difference, the chloride ions in the sodium chloride solution will be accelerated to migrate from one side of the reinforced concrete specimen to the other side, thus completing the test purpose of accelerating the chloride ion corrosion of the threaded steel bars in the concrete specimen. At each time interval, record the current size, the degree of steel bar corrosion, and the occurrence and cracking of concrete cracks.

[0046] S7: After being powered on for a period of time, the chloride ions in the sodium chloride solution and the hydroxide ions in the sodium hydroxide solution are continuously consumed, and the solutions in the first solution tank and the second solution tank are replaced to eliminate the influence of the ion concentration in the test.

[0047] S8: After the test is completed, turn off the regulated DC power supply, take out the electrode plate, pour out the solution in the solution tank, loosen the butterfly nut, adjust the relative position of the first clamp and the second clamp, remove the reinforced concrete specimen, and then disassemble and clean the device.

[0048] By adjusting the concentration of sodium chloride solution, the corrosion of reinforced concrete with different chloride ion concentrations can be studied.

[0049] Functions and Effects of the Embodiments

[0050] According to the test device and test method for accelerating chloride ion corrosion of reinforced concrete involved in the present invention, under the action of potential difference, the chloride ions in the sodium chloride solution will be accelerated to migrate from one side of the reinforced concrete specimen to the other side, thereby efficiently simulating the situation in which chloride ions indiscriminately corrode the reinforced concrete structure from all directions in real scenes. The damage and deterioration laws of the reinforced concrete structure under corrosion of different chloride ion concentrations are studied through the ammeter readings, the degree of steel bar corrosion and the concrete crack detection. In addition, the test device is simple and easy to operate, and real-time observation can be achieved by only tightening the butterfly nut and turning on the power.

[0051] The test device of the present invention combines the characteristics of an electric flux test device, but is not used solely to determine the chloride ion penetration resistance of concrete. Instead, it can study a series of factors such as the migration of chloride ions to the surface of steel bars, the corrosion and expansion of steel bars after depassivation, the generation and expansion of concrete cracks, and the influence of cracks on the chloride ion diffusion coefficient, so as to explore the process and mechanism of damage and deterioration of reinforced concrete structures under chloride ion corrosion, and provide an efficient and convenient test device and method for solving the durability problem of reinforced concrete structures under chloride ion corrosion.

[0052] The present invention enables the first clamp and the second clamp to clamp the concrete test block by arranging the butterfly nut, the flat gasket and the silicone gasket, ensuring that the test piece and the solution tank of the clamp can be tightly sealed, and the test piece will not loosen during the test.

[0053] The present invention realizes real-time detection of current magnitude by connecting an ammeter in the circuit, thereby being able to analyze the real-time current magnitude, the degree of steel bar corrosion, and the generation and cracking of concrete cracks.

[0054] Those skilled in the art should understand that the present invention is not limited to the above embodiments, and the above embodiments and descriptions are only for explaining the principles of the present invention. Without departing from the spirit and scope of the present invention, the present invention may have various changes and improvements, and these changes and improvements fall within the scope of the present invention to be protected. The scope of protection of the present invention is defined by the attached claims and their equivalents.

Claims

1. A test device for accelerating chloride ion corrosion of reinforced concrete, used for testing concrete specimens, characterized in that: include: A clamp, comprising a first clamp and a second clamp on left and right sides, the first clamp and the second clamp are respectively provided with corresponding bolt holes, the first clamp and the second clamp are connected by screws passing through the bolt holes, the first clamp and the second clamp can adjust relative positions, clamp the concrete specimen, so that the solution tank can become a closed space, and the tops of the first clamp and the second clamp are respectively provided with notches; A solution tank, comprising a first solution tank and a second solution tank, wherein the first solution tank and the second solution tank are respectively arranged on the sides of the first fixture and the second fixture, and are connected to the notches on the tops of the first fixture and the second fixture, and the first solution tank on the first fixture is opposite to the second solution tank on the second fixture; as well as The electrode plate comprises a first electrode plate and a second electrode plate, wherein the first electrode plate and the second electrode plate are respectively inserted into the first solution tank and the second solution tank through the notch, and the electrode plate is connected to a regulated DC power supply through a wire.

2. The test device for accelerating chloride ion corrosion of reinforced concrete according to claim 1, characterized in that: in, The screw is a threaded screw, and the mouths of the first solution tank and the second solution tank are respectively provided with a circle of grooves, and the grooves are used to place silicone gaskets.

3. The test device for accelerating chloride ion corrosion of reinforced concrete according to claim 2, characterized in that: in, Butterfly nuts are respectively arranged at both ends of the threaded screw, and the butterfly nuts are located on the outside of the clamp. A flat gasket is arranged between the butterfly nut and the clamp, so that the first clamp and the second clamp are clamped by rotating the butterfly nut.

4. The test device for accelerating chloride ion corrosion of reinforced concrete according to claim 1, characterized in that: in, The first clamp and the second clamp are made of acrylic, and the first electrode plate and the second electrode plate are made of inert titanium, stainless steel, copper or zinc.

5. The test device for accelerating chloride ion corrosion of reinforced concrete according to claim 1, characterized in that: in, The first electrode plate is connected to the positive electrode of the power supply, and the second electrode plate is connected to the negative electrode of the power supply.

6. The test device for accelerating chloride ion corrosion of reinforced concrete according to claim 5, characterized in that: in, Sodium hydroxide solution is added into the first solution tank, and sodium chloride solution is added into the second solution tank.

7. The test device for accelerating chloride ion corrosion of reinforced concrete according to claim 5, characterized in that: in, Water is added into the first solution tank, and sodium chloride solution is added into the second solution tank.

8. A test method for a test device for accelerating chloride ion corrosion of reinforced concrete according to any one of claims 1 to 7, characterized in that: The specific test steps include the following: S1: Prepare the parts of the test device for accelerating chloride ion corrosion of reinforced concrete and reinforced concrete specimens; S2: Align the first clamp and the second clamp and align the bolt holes, pass the screws through the bolt holes of the clamps on both sides for preliminary connection, put flat washers on the exposed parts on both sides of the screws, and screw on the butterfly nuts; S3: Lay the first fixture flat, lift the second fixture, and then place the reinforced concrete specimen between the first fixture and the second fixture, adjust the relative positions of the first fixture and the second fixture, and ensure that the specimen and the solution tank of the fixture are tightly sealed and the specimen will not loosen during the test; S4: Place the fixture upright, and pour water into the solution tank through the notch. After filling, let it stand and observe for 10 minutes. If there is no leakage at the connection between the fixture and the reinforced concrete specimen, the seal is good, and then pour out the water; S5: placing a first electrode plate and a second electrode plate in the first fixture and the second fixture respectively through the notch, adding a sodium hydroxide solution into the first solution tank, adding a sodium chloride solution into the second solution tank, connecting the first electrode plate to the positive electrode of the regulated DC power supply through a wire, and connecting the second electrode plate to the negative electrode of the regulated DC power supply through a wire; S6: After installation, in a ventilated environment, turn on the power supply to energize the electrode plate, which completes the test purpose of accelerating chloride ion corrosion of threaded steel bars in concrete specimens, and records the current size, steel bar corrosion degree, and concrete crack generation and cracking conditions at intervals; S7: After power is applied for a period of time, the solutions in the first solution tank and the second solution tank are replaced to eliminate the influence of the ion concentration in the test; S8: After the test is completed, turn off the regulated DC power supply, take out the electrode plate, pour out the solution in the solution tank, adjust the relative position of the first fixture and the second fixture, remove the reinforced concrete specimen, and then disassemble and clean the device.

9. The test method of the test device for accelerating chloride ion corrosion of reinforced concrete according to claim 8, characterized in that: in, An ammeter is connected in the circuit to detect the current magnitude in real time.

10. The test method of the test device for accelerating chloride ion corrosion of reinforced concrete according to claim 8, characterized in that: in, The relative position of the first clamp and the second clamp is adjusted by screwing the butterfly nut.

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