Fuel mixer device for high efficiency natural gas engines

Abstract

The utility model relates to a kind of fuel mixer device for efficient natural gas engine, including natural gas control valve and mixer component, and the mixer component includes mixer body, venturi bushing, natural gas cavity and flow cone, natural gas control valve is fixed on the natural gas inlet of mixer component by bolt, venturi bushing is installed in the inside of mixer body, and venturi bushing clearance fit inserts the inside of mixer body, and venturi bushing and mixer body are fixed together by set screw, venturi bushing and mixer body form natural gas cavity, and flow cone is connected at the air side entrance of venturi bushing. Fuel mixer device for efficient natural gas engine using the utility model, using electric control natural gas control valve, can realize airtightness, natural gas can be cut off when fault or shutdown, accurately control natural gas flow to realize natural gas accurate supply under the various working conditions of engine, maintenance is convenient, and cost is low.

Description

Technical Field

[0001] This utility model relates to the industrial field, and more particularly to the field of natural gas engines, specifically referring to a high-efficiency fuel mixer device for natural gas engines. Background Technology

[0002] Natural gas is affordable, has a high calorific value, and is easy to store and transport. Therefore, industrial generator sets generally use natural gas as fuel for power generation or for driving vehicles and ships. For large-displacement natural gas engines, in order to control the optimal air-fuel ratio for combustion according to the engine operating conditions and improve power economy, it is necessary to ensure that natural gas and air are fully mixed at the required air-fuel ratio before entering the engine for combustion.

[0003] The existing technical solution involves initial mixing of natural gas and air before the turbocharger, followed by secondary mixing via the turbocharger compressor to ensure uniform mixing. The initial mixing occurs at the air mixer. Existing natural gas mixers use the Venturi principle and employ a throttle valve to regulate the natural gas intake. Different sizes of mixers need to be designed to match different engine displacements, which is obviously not economical for applications with low market demand.

[0004] Natural gas industrial units are large-scale, complete sets of equipment with relatively low annual demand. They require high product reliability, safe and reliable gas circuits, and convenient maintenance to avoid losses due to downtime. On the other hand, increasingly stringent emission regulations require engine control units to precisely control the air-fuel ratio based on engine operating conditions to ensure engine power output, emission control, and fuel economy. Current natural gas mixers have the following main drawbacks in application:

[0005] 1. Insufficient air intake adjustment accuracy of natural gas mixers. Since most natural gas mixers currently on the market use rotary piston valves or rail valves, the air intake adjustment accuracy is not high. In addition, due to the difference in the accuracy of the valve's own moving mechanism, the overall air intake control accuracy is not ideal. Furthermore, the Venturi bushing is not completely sealed with the mixer body, which will cause some natural gas to leak into the intake air and also cause changes in the air-fuel ratio.

[0006] 2. The natural gas mixer control valve cannot shut off the natural gas path. Due to the structural factors of the mixer's natural gas valve, the natural gas control valve of currently available products does not have the ability to shut off when the engine is off. If there is pressurized natural gas in the natural gas pipeline or the upstream natural gas pipeline is not shut off, it will leak out and cause an accident risk.

[0007] 3. High pressure loss in the mixer: Due to structural design issues with the natural gas mixer, the pressure loss in the mixer is large, which affects the pumping efficiency of the engine.

[0008] 4. High cost and non-modular design. When dealing with different engine displacements, the mixer assembly needs to be redesigned, resulting in high mold investment costs, high product prices, and uneconomical pricing.

[0009] After-sales maintenance is inconvenient. Some natural gas mixers on the market have the natural gas control valve integrated inside the mixer. If a malfunction occurs, the actuator needs to be removed to replace the control valve or the entire mixer needs to be replaced, resulting in high after-sales costs and long maintenance cycles. Utility Model Content

[0010] The purpose of this invention is to overcome the shortcomings of the prior art and provide a high-efficiency fuel mixer device for natural gas engines that is low in cost, easy to operate, and has a wide range of applications.

[0011] To achieve the above objectives, the present invention provides a high-efficiency fuel mixer device for a natural gas engine as follows:

[0012] The main features of this high-efficiency natural gas engine fuel mixer device are that the device includes a natural gas control valve 1 and a mixer component 2. The mixer component 2 includes a mixer body 3, a venturi bushing 7, a natural gas chamber 9, and a guide cone. The natural gas control valve 1 is fixed to the natural gas inlet of the mixer component 2 by bolts. The venturi bushing 7 is installed inside the mixer body 3 and is inserted into the mixer body 3 with a clearance fit. The venturi bushing 7 is fixed to the mixer body 3 by a set screw 6. A natural gas chamber 9 is formed between the venturi bushing 7 and the mixer body 3. The guide cone is connected to the air-side inlet of the venturi bushing 7.

[0013] Preferably, the natural gas control valve 1 includes a valve plate and a valve seat. When the natural gas control valve 1 is in the closed position, the valve plate sits on the valve seat, and the valve plate contacts the valve seat and generates compression. The valve plate is a metal part, and the valve seat is a rubber part.

[0014] Preferably, the mixer component 2 further includes a flange structure, with two flange structures respectively disposed at both ends of the mixer body 3. The flange structure has threaded holes on its flange thickness surface and set screw holes on its flange thickness surface.

[0015] Preferably, the Venturi bushing 7 includes a contraction section, a natural gas nozzle assembly, a throat, a fillet, and a diffuser section. The air inlet end of the Venturi bushing 7 is provided with a contraction section, a throat, and a diffuser section from the outside to the inside. The fillet is located at the connection between the throat and the diffuser section. The natural gas nozzle assembly is located at the junction of the throat and the contraction section, and near the intersection line of the contraction section and the throat.

[0016] Preferably, the contraction section is a conical hole, the throat is a cylindrical straight hole, and the diffusion section is a conical hole. The taper of the conical hole in the contraction section is greater than the taper of the diffusion section, and the length of the diffusion section is greater than the length of the contraction section.

[0017] Preferably, the outlet section of the mixer body 3 has an outlet section cone surface, and the diffusion section has the same taper as the outlet section cone surface and is located on the same cone surface.

[0018] Preferably, the guide cone includes an outer diameter, a mounting claw, and a windward surface. The outer diameter is connected to the windward surface, which is located on one side of the air intake end of the venturi bushing 7. The mounting claw is mounted on the windward surface.

[0019] Preferably, the outer diameter of the guide cone is cylindrical, the windward surface is spherical cone, and the interior is hollow.

[0020] Preferably, the device further includes a first sealing ring 4, which is disposed at the mounting joint surface of the natural gas control valve 1 and the mixer assembly 2.

[0021] Preferably, the device further includes a second sealing ring 5 and a third sealing ring 8, both of which are disposed at the junction of the venturi bushing 7 and the mixer body 3.

[0022] Preferably, the venturi bushing 7 is provided with a plurality of mounting threaded holes, and the guide cone is fixed to the threaded holes of the venturi bushing 7 by screws.

[0023] This invention relates to a high-efficiency fuel mixer for natural gas engines. It employs an electronically controlled natural gas control valve with a unique valve plate and seat design that ensures airtightness. In case of malfunction or shutdown, the natural gas supply can be cut off to prevent leaks and potential hazards. Furthermore, the natural gas control valve offers high angle control precision, accurately controlling the natural gas flow to ensure precise supply under various engine operating conditions. Sealing rings are installed on both sides of the mixer chamber to prevent natural gas leakage from the gap between the venturi bushing and the mixer body during operation, thus preventing inaccurate gas metering. The natural gas control valve is independently installed on the natural gas mixer, facilitating convenient maintenance and reducing costs. Attached Figure Description

[0024] Figure 1 This is an external view of the high-efficiency natural gas engine fuel mixer device of this utility model.

[0025] Figure 2 This is a cross-sectional view of the high-efficiency fuel mixer device for a natural gas engine according to the present invention.

[0026] Figure 3 This is a schematic diagram of the mixer assembly of the high-efficiency natural gas engine fuel mixer device of this utility model.

[0027] Figure 4 This is a cross-sectional view of the mixer assembly of the high-efficiency natural gas engine fuel mixer device of this utility model.

[0028] Figure 5 This is a schematic diagram of the guide cone of the high-efficiency natural gas engine fuel mixer device of this utility model.

[0029] Figure label:

[0030] 1. Natural gas control valve

[0031] 2 Mixer Components

[0032] 3. Mixer body

[0033] 4 First sealing ring

[0034] 5 Second sealing ring

[0035] 6 Set screws

[0036] 7 Venturi bushings

[0037] 8 Third sealing ring

[0038] 9 cavity

[0039] 10 guide cones

[0040] 11 Screws

[0041] 12 Air ventilation section

[0042] 1.1 Valve Plate

[0043] 1.2 Rubber valve seat

[0044] 3.1 Flange Structure

[0045] 3.2 Threaded Hole

[0046] 3.3 Set screw hole

[0047] 3.4 Exit Section Conical Surface

[0048] 7.1 Contraction segment

[0049] 7.2 Natural Gas Nozzle Assembly

[0050] 7.3 Throat

[0051] 7.4 Rounded corners

[0052] 7.5 Diffusion Section

[0053] 10.1 Outer diameter of the guide cone

[0054] 10.2 Installing the claw

[0055] 10.3 Windward side Detailed Implementation

[0056] To more clearly describe the technical content of this utility model, the following description is provided in conjunction with specific embodiments.

[0057] This utility model discloses a high-efficiency fuel mixer device for a natural gas engine, which includes a natural gas control valve 1 and a mixer component 2. The mixer component 2 includes a mixer body 3, a venturi bushing 7, a natural gas chamber 9, and a guide cone 10. The natural gas control valve 1 is fixed to the natural gas inlet of the mixer component 2 by bolts. The venturi bushing 7 is installed inside the mixer body 3 and is inserted into the mixer body 3 with a clearance fit. The venturi bushing 7 is fixed to the mixer body 3 by a set screw 6. A natural gas chamber 9 is formed between the venturi bushing 7 and the mixer body 3. The guide cone 10 is connected to the air-side inlet of the venturi bushing 7.

[0058] In a preferred embodiment of the present invention, the natural gas control valve 1 includes a valve plate 1.1 and a valve seat 1.2. When the natural gas control valve 1 is in the closed position, the valve plate 1.1 sits on the valve seat 1.2, and the valve plate 1.1 contacts the valve seat 1.2 and generates compression. The valve plate 1.1 is a metal part, and the valve seat 1.2 is a rubber part.

[0059] In a preferred embodiment of the present invention, the mixer component 2 further includes a flange structure 3.1. The two flange structures 3.1 are respectively disposed at both ends of the mixer body 3. The flange structure 3.1 has a threaded hole 3.2 on the flange thickness direction surface and a set screw hole 3.3 on the flange thickness surface.

[0060] In a preferred embodiment of this utility model, the Venturi bushing 7 includes a contraction section 7.1, a natural gas nozzle group 7.2, a throat 7.3, a rounded corner 7.4, and a diffuser section 7.5. The air inlet end of the Venturi bushing 7 is provided with the contraction section 7.1, the throat 7.3, and the diffuser section 7.5 from the outside to the inside. The rounded corner 7.4 is located at the connection between the throat 7.3 and the diffuser section 7.5. The natural gas nozzle group 7.2 is located at the junction of the throat 7.3 and the contraction section 7.1, and is close to the intersection line of the contraction section 7.1 and the throat 7.3.

[0061] In a preferred embodiment of the present invention, the contraction section 7.1 is a conical hole, the throat 7.3 is a cylindrical straight hole, and the diffusion section 7.5 is a conical hole. The taper of the conical hole in the contraction section 7.1 is greater than the taper of the diffusion section 7.5, and the length of the diffusion section 7.5 is greater than the length of the contraction section 7.1.

[0062] In a preferred embodiment of the present invention, the outlet section of the mixer body 3 has an outlet section conical surface 3.4, and the diffusion section 7.5 has the same taper as the outlet section conical surface 3.4 and is located on the same conical surface.

[0063] In a preferred embodiment of the present invention, the guide cone 10 includes an outer diameter 10.1, a mounting claw 10.2, and a windward surface 10.3. The outer diameter 10.1 of the guide cone is connected to the windward surface 10.3. The windward surface 10.3 is located on one side of the air intake end of the Venturi bushing 7, and the mounting claw 10.2 is mounted on the windward surface 10.3.

[0064] In a preferred embodiment of this utility model, the outer diameter 10.1 of the guide cone is a cylindrical structure, and the windward surface 10.3 is a spherical cone structure with a hollow interior.

[0065] In a preferred embodiment of the present invention, the device further includes a first sealing ring 4, which is disposed at the mounting joint surface of the natural gas control valve 1 and the mixer assembly 2.

[0066] In a preferred embodiment of the present invention, the device further includes a second sealing ring 5 and a third sealing ring 8, both of which are disposed at the junction of the venturi bushing 7 and the mixer body 3.

[0067] In a preferred embodiment of the present invention, the Venturi bushing 7 is provided with a plurality of mounting threaded holes, and the guide cone 10 is fixed to the threaded holes of the Venturi bushing 7 by screws 11.

[0068] In a specific embodiment of this utility model, the high-efficiency natural gas mixer assembly consists of a natural gas control valve 1, a mixer assembly 2, and a guide cone 10.

[0069] The natural gas control valve 1 is bolted to the natural gas inlet of the mixer assembly 2, and the guide cone 10 is bolted to the air-side inlet of the venturi bushing 7.

[0070] A first sealing ring 4 is provided at the joint surface of the natural gas control valve 1 and the mixer assembly 2 to ensure the airtightness between the control valve 1 and the mixer assembly 2 and prevent natural gas from leaking out.

[0071] Natural gas control valve 1 is an airtight valve. The valve plate 1.1 is a metal part, and the valve seat 1.2 is a rubber part. When the valve is fully closed, the valve plate 1.1 contacts the valve seat 1.2 and is squeezed to achieve zero leakage and airtightness. When natural gas control valve 1 is in the closed position, the valve plate 1.1 sits on the rubber valve seat 1.2 and has an airtight function under pressure.

[0072] The mixer assembly 2 consists of a mixer body 3, a second sealing ring 5, a set screw 6, a venturi bushing 7, a third sealing ring 8, a natural gas chamber 9, a guide cone 10, and a guide cone 11.

[0073] The mixer body 3 is provided with a double flange structure 3.1, and threaded holes 3.2 are provided on the flange thickness surface for customers to install and fix the mixer position. At the same time, set screw holes 3.3 are provided on the flange thickness surface.

[0074] The Venturi bushing 7 and the mixer body 3 are fitted with a clearance at the joint, and a second sealing ring 5 and a third sealing ring 8 are provided at the joint. The Venturi bushing 7 and the mixer body are fixed together by set screws 6.

[0075] The Venturi bushing 7 is inserted into the mixer body 3 with a clearance fit, and the Venturi bushing 7 is fixed to the mixer body 3 by the set screw 6. A second sealing ring 5 and a third sealing ring 8 are provided at the joint between the Venturi bushing 7 and the mixer body 3 to prevent natural gas from leaking from the joint.

[0076] The venturi bushing 7 is provided at the air inlet end with a contraction section 7.1, a throat 7.3, and a diffuser section 7.5. A fillet 7.4 is provided at the connection between the throat 7.3 and the diffuser section 7.5. A natural gas nozzle group 7.2 is provided near the junction of the throat 7.3 and the contraction section 7.1.

[0077] The venturi bushing 7 has a concave section 7.1 with a conical bore, a throat 7.3 with a cylindrical straight bore, and a diffuser section 7.5 with a conical bore. The taper of the conical bore in the concave section 7.1 is greater than the taper of the diffuser section 7.5, and the length of the diffuser section 7.5 is greater than that of the concave section 7.1.

[0078] The natural gas nozzle 7.2 is located near the intersection of the contraction section 7.1 and the throat 7.3.

[0079] The Venturi bushing diffuser section 7.5 has the same taper as the outlet section cone surface 3.4 of the mixer body 3, and they are on the same cone surface with no discontinuity.

[0080] A natural gas chamber 9 is formed between the Venturi bushing 7 and the mixer body 3. The volume of the natural gas chamber 9 needs to reach a certain value to stabilize the natural gas supply pressure and ensure the uniformity of the flow rate of all natural gas nozzles 7.2.

[0081] Multiple mounting threaded holes can be provided on the Venturi bushing 7, and the guide cone 10 is fixed to the Venturi bushing 7 by screws 11.

[0082] The outer diameter of the guide cone 10.1 is a cylindrical structure with multiple mounting claws 10.2 evenly distributed. The windward side 10.3 is a spherical cone structure with a hollow interior.

[0083] The mixer assembly 2 adopts a modular design, which is backward compatible with small displacement engines. Based on the engine displacement requirements and natural gas demand, the Venturi bushing can be backward compatible with smaller displacement engines by machining different diameters and numbers of natural gas nozzles 7.2 without changing the mold. A guide cone 10 is installed at the air inlet of the Venturi bushing. The size of the air passage section 12 is adjusted by adjusting the outer diameter 10.1 of the guide cone, thereby adjusting the intake volume and ensuring a good Venturi effect. The guide cone 10 is installed into the threaded hole of the Venturi bushing 7 by screws 11.

[0084] The Venturi gas inlet of this utility model is achieved by using multiple sets of evenly distributed gas nozzles. The nozzle positions are optimized, and the Venturi effect is strongest at these positions. By adjusting the size and number of gas nozzles, it can be adapted to different engine displacements and gas requirements. The gas chamber pressure distribution is uniform, the fuel passing through each nozzle is consistent, the gas mixing is more uniform, and the mixing efficiency is higher.

[0085] The technical solution of this utility model has a stronger Venturi effect and a function to adjust the gas flow according to the engine load, resulting in better mixing efficiency and lean combustion control.

[0086] To address the issues of low accuracy in natural gas flow regulation and poor air-fuel ratio control in current mixers, this invention employs an electronic throttle valve for the natural gas control valve. This valve offers high position control accuracy and can respond quickly and in real-time to the controller's flow control requirements. Furthermore, the connection between the venturi bushing and the mixer body is sealed with an O-ring to prevent natural gas leakage and air ingress, thus meeting the fuel matching requirements for lean combustion and high-power output in engines.

[0087] The mixer control valve of this invention has zero leakage airtightness in the fully closed position. When the engine stops, the valve plate closes to the fully closed position, cutting off the natural gas path and reducing the danger caused by gas leakage. It can meet the requirements of fuel mixing uniformity. In addition, the control valve has excellent external zero leakage capability, preventing natural gas from leaking out from the bearing end of the control valve. Furthermore, this mixer control valve has a fail-safe default position. In the event of a failure of the control valve or other engine control devices, the control valve will return to the fully closed position under the action of the spring return torque to cut off the natural gas, avoiding the risk of natural gas leakage in the event of device failure.

[0088] The air path structure of the natural gas mixer of this utility model, through theoretical calculation, AI-aided design analysis, and CFD simulation, has greatly reduced the back pressure of the air path, reduced engine pumping losses, improved engine efficiency, and reduced power loss after size and structural optimization.

[0089] This utility model's natural gas mixer adopts a modular design. By adding a guide cone, it can adapt to the intake air requirements of engines with different displacements and the negative pressure requirements of natural gas intake in Venturi mixers. It has low replacement costs, reduces customer selection costs, reduces product expenses, and improves economic advantages.

[0090] The control valve of this utility model is a separate design from the mixer body. The control valve is installed on the mixer body by bolts. When the control valve fails or is adapted to different displacement engines, only one control valve needs to be replaced to quickly complete maintenance and upgrade.

[0091] The mixer of this invention is designed according to the engine displacement distribution, with the largest displacement in that displacement range. For engines with smaller displacements, the mixer only needs to adjust the diameter and number of natural gas nozzles on the venturi bushing and machine guide cone mounting threaded holes on the venturi bushing. By installing guide cones of different diameters, it can be compatible with gas engines with even smaller displacements.

[0092] For the specific implementation scheme of this embodiment, please refer to the relevant descriptions in the above embodiments, which will not be repeated here.

[0093] It is understood that the same or similar parts in the above embodiments can be referred to each other, and the contents not described in detail in some embodiments can be referred to the same or similar contents in other embodiments.

[0094] It should be noted that in the description of this utility model, the terms "first," "second," etc., are used for descriptive purposes only and should not be construed as indicating or implying relative importance. Furthermore, in the description of this utility model, unless otherwise stated, "a plurality of" means at least two.

[0095] In the description of this specification, the references to terms such as "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the present invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.

[0096] This invention relates to a high-efficiency fuel mixer for natural gas engines. It employs an electronically controlled natural gas control valve with a unique valve plate and seat design that ensures airtightness. In case of malfunction or shutdown, the natural gas supply can be cut off to prevent leaks and potential hazards. Furthermore, the natural gas control valve offers high angle control precision, accurately controlling the natural gas flow to ensure precise supply under various engine operating conditions. Sealing rings are installed on both sides of the mixer chamber to prevent natural gas leakage from the gap between the venturi bushing and the mixer body during operation, thus preventing inaccurate gas metering. The natural gas control valve is independently installed on the natural gas mixer, facilitating convenient maintenance and reducing costs.

[0097] In this specification, the present invention has been described with reference to specific embodiments thereof. However, it will be apparent that various modifications and variations can be made without departing from the spirit and scope of the present invention. Therefore, the specification and drawings should be considered illustrative rather than restrictive.

Claims

1. A high-efficiency fuel mixer device for a natural gas engine, characterized in that, The device includes a natural gas control valve and a mixer assembly. The mixer assembly includes a mixer body, a venturi bushing, a natural gas chamber, and a guide cone. The natural gas control valve is bolted to the natural gas inlet of the mixer assembly. The venturi bushing is installed inside the mixer body with a clearance fit and is fixed to the mixer body by set screws. A natural gas chamber is formed between the venturi bushing and the mixer body. The guide cone is connected to the air-side inlet of the venturi bushing.

2. The high-efficiency natural gas engine fuel mixer device according to claim 1, characterized in that, The natural gas control valve includes a valve plate and a valve seat. When the natural gas control valve is in the closed position, the valve plate sits on the valve seat, and the valve plate contacts the valve seat and generates pressure. The valve plate is a metal part, and the valve seat is a rubber part.

3. The high-efficiency natural gas engine fuel mixer device according to claim 1, characterized in that, The mixer component also includes flange structures, with two flange structures respectively disposed at both ends of the mixer body. The flange structures have threaded holes on the flange thickness direction surface and set screw holes on the flange thickness surface.

4. The high-efficiency natural gas engine fuel mixer device according to claim 1, characterized in that, The Venturi bushing includes a contraction section, a natural gas nozzle assembly, a throat, a fillet, and a diffuser section. The air inlet end of the Venturi bushing is provided with a contraction section, a throat, and a diffuser section from the outside to the inside. The fillet is located at the connection between the throat and the diffuser section. The natural gas nozzle assembly is located at the junction of the throat and the contraction section, and close to the intersection line of the contraction section and the throat.

5. The high-efficiency natural gas engine fuel mixer device according to claim 4, characterized in that, The contraction section is a conical hole, the throat is a cylindrical straight hole, and the diffusion section is a conical hole. The taper of the conical hole in the contraction section is greater than the taper of the diffusion section, and the length of the diffusion section is greater than the length of the contraction section.

6. The high-efficiency natural gas engine fuel mixer device according to claim 4, characterized in that, The outlet section of the mixer body has an outlet section cone surface, and the diffusion section has the same taper as the outlet section cone surface and is located on the same cone surface.

7. The high-efficiency natural gas engine fuel mixer device according to claim 1, characterized in that, The guide cone includes an outer diameter, a mounting claw, and a windward surface. The outer diameter of the guide cone is connected to the windward surface, which is located on one side of the air inlet end of the venturi bushing. The mounting claw is mounted on the windward surface.

8. The high-efficiency natural gas engine fuel mixer device according to claim 7, characterized in that, The outer diameter of the guide cone is cylindrical, the windward surface is spherical cone, and the interior is hollow.

9. The high-efficiency natural gas engine fuel mixer device according to claim 1, characterized in that, The device also includes a first sealing ring disposed at the mounting joint surface of the natural gas control valve and the mixer assembly.

10. The high-efficiency natural gas engine fuel mixer device according to claim 1, characterized in that, The device also includes a second sealing ring and a third sealing ring, both of which are disposed at the junction of the venturi bushing and the mixer body.

11. The high-efficiency natural gas engine fuel mixer device according to claim 1, characterized in that, The Venturi bushing is provided with multiple mounting threaded holes, and the guide cone is fixed to the threaded holes of the Venturi bushing by screws.

Images