Common examples of virtual leaks caused by poor workmanship are: Trapped volumes caused by poor weld fit up of full penetration welds and lack of penetration. An initial squeeze of the O-ring in the dovetail groove is essential to ensure that the seal functions correctly. Try not to get any glue on the edges of the top, as it should float freely in its groove. com O-Ring Products. D1 O-Ring Diameter. Proudly made in the USA by AB Tools, Inc. 750", 1. Select a standard, groove type, and available groove size from the lists on the top left of the tab. Installing Gaskets in a Dovetail Groove. Narrower groove for sealing vacuum or gas. This one will be ma. 70 - Single End Split Blanks. Available in four original standard sizes and in customized sizes, the DT Collapsible. The properties of the cross-section of the groove are determined by the opening width b; the depth h; the base angle a; the inner fillet radius r1; and the outer fillet radius r2. The O-ring groove calculator enables engineers to specify an O-ring groove for any given O-ring or vice versa calculates the best suitable size O-ring for any given groove. 43 - I. 057". Dovetail cutters are used in a broad range of applications and can have numerous variations of taper angle, top and bottom diameter. Nitrile is the most commonly used elastomeric material for molded and extruded products. Used to prevent the O-Rings from falling out of the Glands. If you’re applying an o-ring to a face seal, you’ll better not use a face seal o-ring groove design, sometimes referred to as a dovetail. . DOVETAIL O-RING GROOVE DESIGN. The wall inclination creates a groove with a trapezium cross-section, whose main purpose is to hold the O-ring in during installation and maintenance. The. When. Degradation of O-ring by system fluid . Slot Depth. This PDF catalog covers the design, materials, installation and applications of O-Rings and Back-up Rings, with detailed illustrations and tables. 125” and . O-Ring Basics; Seal Types; O-Ring Elastomers; Static O-Ring Sealing. Used to prevent the O-Rings from falling out of the Glands. Internal Grooving Lathe Tools for O-Rings. 1-23) 2. Surface Finish X groove top and bottom : for liquids X = 32 micro inches (0. O-Ring Selection; Bitte definieren Sie die Anwendungsparameter und wählen Sie ein Dichtungsmaterial aus. 1. The dovetail creates a strong and secure area for clamping, while. Learn More. While Dove Tail O-ring grooves are effective at keeping an O-ring in place, they are expensive to manufacture and should only be used if absolutely necessary. 70 - Long Length Single End Split Blanks. -I tried the pocket function (standard pocket), clicked (chain) on the larger. Furthermore, the O-ring groove has triangular, rectangular, or dovetail shapes. To retain them, you need to dovetail the groove (make it a trapezoid shape). Products that are often purchased together. Fort Wayne, IN. Undersized Cutter Design Allows Climb Milling Both Faces of Groove for Improved Finish. machined using a special dovetail cutter which is available from Spira. • The most important ®advantage of the Quad-Ring/X-Ring is the high stability for dynamic applications. For a static male to female mating. The dovetail groove construction is only recommended for O-rings with bigger cross sections, . 70 - Double End Split Blanks. Choose between more than 30 groove materials and 11 O-ring compounds! Benefit from a modern user friendly design and be guided from design rec-ommendations from info boxes. Remit To Address: Kaiser Tool Company, Inc. Parker's H-seals are designed for as cast or machined grooves and can be retrofitted for standard O-ring groove sizes. What is a Drop-Hole? When designing parts featuring O-ring grooves, the consideration of drop-hole allowance is a pivotal first step. DOI：. 83 € Min. 003 0. 015: 2: $68: $72:. 3% relative to the inside diameter Square groove dimensions The values and tolerances specified in the table apply to NBR Shore 70A O-rings. (ret) EX. Manufactured by Kaiser Tool Company, the Groove ‘N Turn line includes dovetail grooving inserts that machine O-ring dovetail grooves with 66-degree undercut angles. com 0086+15207335549As shown in above figure, an O-ring also gets compressed axially in a dovetail groove. Male or Plug Seal design is based on the following factors (refer to fig. O-ring Groove Design in 3 easy steps: Step 1. 1-23) 2. 1-23) 2. Cutters for machining grooves by side running have a dovetail groove shape. Learn More > Contact. The square corners of an 0-ring grove give the. Create dovetail grooves that allow O-rings to flex without falling out of place. Abstract. 1-24). Sometimes the O-ring falls out of the groove during the shipping process. Refer to the O-Ring Handbook or consult a Parker applications engineer for assistance in sizing O-rings to dovetail glands. DeepGroove®. D. tool # diameter minor dia groove depth top radius bottom radius flutes o-ring size shank dia overall length 1 pc 2-10 11-25 26-100; 51-8010: 0. However, this is an expensive groove to machine, and thus should be used only when absolutely necessary. Whether your application conforms to U. All products are proudly manufactured in the USA. nom. Problem sources: Excessive gland clearances . They have a large mill diameter for removing a large amount of material per pass. Neck diameter is measured to the theoretical sharp corner. The angled groove walls are an effective way to retain the seal, because the walls essentially pinch the seal, holding it in position. 003 0. Dovetail and O-ring style cutters havea variety of applications ranging from customized grooves to tricky seals. A common mistake is to design the groove width to “pinch” the o-ring cross-section, so it is held in the groove. 1400: 0. Lexington, KY 40509. • Allows for maximum O-ring retention in the CORG groove • Prevents O-ring pinch during assembly, which prevents costly leaks • Works in the standard SAE J1453 half-dovetail groove (CORG) • 90 durometer nitrile. On-size and undersized diameters are also in stock. Dovetail Cutters-Sight Groove Dovetail Cutters Solid carbide tool designed for milling dovetail grooves for Sight Attachments, and offered in 50° or 60° included angles. e Minimum full thread depth. The Parker O-Ring eHandbook is a condensed online version of the printed Parker O-Ring Handbook ORD 5700. O-Ring C/S D Groove Depth Squeeze Inches Squeeze % E. Solid Carbide Dovetail Cutters 1/16 3/32 1/8 3/16 1/4 3/8 , O-Ring Grooves . com FREE DELIVERY possible on eligible purchasesHawke Sport Optics Dovetail 30mm Hight Rifle Scope Ring Mount - 1-Pieces (6) $43. This keeps the O-ring in the groove during assembly. Describes the groove. (fig. Face seal o-rings pop out easily, yeah. Note: Top radius (R) is a critical dimension; too small a. 010 proud to start, iterate from there. This document covers the basics of O-Ring sealing, elastomer properties, and dynamic and static design criteria. . 0159 2 3 4 2. This groove is difficult and expensive to machine, and the tolerances are especially critical. AS568A-102 (left). Solid carbide. In this guide, not only you can quickly design your O-Ring Seal groove, but also select the most suitable O-Ring Seal to fulfill your requirements. Dovetail cutters are specialized tools for cutting angled or trapezoidal-shaped grooves (dovetails) into a workpiece. The groove design allows the O-ring to be retained in the face seal during assembly and maintenance. 2 or 3 flute. Read Next Five Common Mistakes Shops Make with ER Collets (And How to Prevent Them) World Machine Tool Production and Consumption Modestly Down in. The ERIKS O-Ring design calculator features the calculation of: for axial seals with inner or outer pressure, piston seals and rod seal applications. However, installing an O-ring into these grooves can be tricky without proper technique. oesmailbox@parker. In other works [23], [24], the same authors studied the effect of the groove shape and the effect of introducing a metal core inside the elastomer O-ring. Greene Tweed engineers suggested that all threeDovetail grooving inserts are used to machine O-ring dovetail grooves with 66-degree undercut angles. Static Male and Female O-ring Seal Design . Special orders in 4-6 working days. While Dove Tail O-ring grooves are. Superglue works to hold o-rings in place also. The groove design allows the O-ring to be retained in the face seal during assembly and maintenance. 52:. Dovetail Face Grooves are used in the High Vacuum and Hydraulic Industries to retain O-Ring Seals in Plates and Flanges. I have two circles representing my oring. GROOVE 'N TURN® dovetail grooving inserts are used to machine O-ring dovetail grooves with 66° undercut angles. Dovetail grooves are used to hold the O-ring in-place on a face seal groove during during. The soft seat and quick closure helps to prevent flow. a lid which opens regularly. My part was manufactured by a machine shop. For O-ring grooves. 66° Dovetail Cutters For O-Ring Grooves. My guess on the reason you are having problems finding specs for orings smaller than -004 is that the o-ring cross section starts dropping below 1/16" for the smaller sizes. The part as received leaks. g. Dovetail Grooves are effective at retaining seals, however they come with a few challenges. Of Flutes. d Optional construction for shapes and long straights. g. If GD&T is used and/or critical, I would suggest using profile tolerance. Dovetail O-Ring Groove Design . Bore. AS568 -004 through -475 Dovetail Seal Design Guidelines: AS-568 DASH # W O-RING CROSS SECTION: G GROOZE WIDTH: H GROOVE DEPTH: R1 RADIUS: R RADIUS: SHARPEDGE: ROUNDEDEDGE: Inch +. Groove widths . This is an expensive grooveThe O-ring calculator tool is intended to form the basis of an o-ring installation, and assist with selection of o-ring and hardware dimensions. MISUMI USA has all of your O-Ring Groove Cutters needs covered, with over 3. 쿼드링은 사각에서 씰링 역할을 하므로 압력의 부하분포가 고르게. Anwendungsparameter & Materialauswahl. 250" and larger. Abstract. , Japanese JIS, British BS and Common Metric o-ring size charts. . This can be done by using a dovetail. This metric o-ring groove design reference guide will help you find the right radius, back-up, pressure and other o-ring dimensions for basic applications. O-Ring groove 자료를 찾아보면 Depth, Width 부분에 있어 약간씩 차이가. Mailing Address: Kaiser Tool Company, Inc. of an O-ring gland is mainly influenced by diameter of the mating surface of the rod or piston and bore. 150” with major diameters starting at . THINBIT, manufactured by Kaiser Tool Company, has announced the expansion of its GROOVE 'N TURN line of dovetail grooving inserts. The soft-seated, dovetail, o-ring groove ensures a bubble tight seal in the closed position. Features: O-Ring Groove Tools Solid micrograin carbide. Each user should conduct evaluations to determine the suitability for his particular application. The O-ring must have room to expand laterally in the groove due to axial compression. Female or Tube - the O-ring groove is located in the housing or cylinder and a tube is installed through the O-ring l. Popular O-Ring Material Comparison Guide. The O-ring must have room to expand laterally in the groove due to axial compression. The extra void space in the design allows the O-ring to swell slightly due to thermal expansion or. Otherwise, without these o-ring. When machining this groove, a standard o-ring groove must be machined first. How to measure and inspect a dovetail o-ring groove? I have a custom designed part with a dovetail o-ring groove sized for a size dash 010 circular o-ring. O-ring Groove O-ring 을 설치하기 위해서, Groove 가공을 해야한다. C. The O-ring calculator calculates the most relevant size O-ring for any given groove. S. Solid carbide. Ozone Attack. 300", . It may not be an issue for you, if you truly can stand to throw out. O-ring material too soft . Our O-Rings are both cost-effective and perform highly in almost every environment. 103 . This may create retention, though due to the tolerances on both the O-ring and the groove, the retention will likely be inconsistent. The disc's low cracking pressure reduces the amount of energy required to open the valve and the valve's large body minimizes head loss across the valve. Choose from more than 500. Made of solid carbide, they are harder, stronger, and more. You can add industry standard O-ring and retaining-ring grooves to your cylindrical model. Gap (mm) Sealing Gap (mm) info Results at Installation min. , at the hard-ware and O-ring tolerance stack-up) and the smallest possible O-ring in the largest possible groove. Optimized for milling dovetail grooves into a part, Micro 100's solid carbide Dovetail Cutters are offered with 30°, 60°, and 90° included angles and in both uncoated and AlTiN coated styles. Static Gland SealDovetail Face Radial Male & Female Tube Fitting Boss Seal O-Ring Elastomers Static O-Ring Sealing Failure Modes Mobile inPHorm - Parker's Design Tool & O-Ring Calculator Dovetail It is sometimes necessary to. Same groove dimensions as our O-Ring dovetail cutters that match Parker Hannifin standards. Also known as shell cutters, these high-speed steel cutters are good for face and side milling. The O-ring must have room to expand laterally in the groove due to axial compression. Our Carbide O-Ring Dovetail Cutters meet Parker Hannifin standards. 031"-0. ร่อง Dovetail ใช้เพื่อยึด O-ring ให้เข้าที่บนร่องซีลใบหน้าในระหว่างการประกอบและบำรุงรักษาอุปกรณ์ ร่องอันเดอร์คัทหรือ. O-ring standards are specified by the JIS B 2401. Dovetail grooves are a great mechanism for holding O-rings in place. Trapped volumes caused by unvented single or double dovetail o-ring groove designs. Male or Plug - the O-ring groove is located on a plug which is inserted into the housing or cylinder (fig. Sometimes, a bit of interference can be designed between the outer diameter of the O-ring and the outer diameter of the groove. 005 on both sides, not just the inner, and leave the face . Compared to traditional O-rings, the Dovetail Seal offers better seal integrity, reducing the potential for process / contamination and allowing for more than twice the sealing force. ), the outer virtual corner to corner. Another common included angle for general purpose dovetails is 90°. O-Ring Groove design plays an important part in how an o-ring seals. Fax: 859-335-5128. This feature article analyses an O-ring in a dovetail groove by using the finite element method. Bay Seal Company O-Ring Reference Guide Bay Seal Company 11 Sealing is our Business! Phone (800) 273-7325 Fax (510) 782-2651 Dovetail Groove Design Charts Cross Sectional Dimensions AS568A Series O-Ring Cross Section Gland Width Squeeze Gland Depth Gland Corner RadiiO-Ring Groove design plays an important part in how an o-ring seals. Designed to the standards suggested by the O-Ring division of Parker Hannifin Corporations (tools meet both specs: ORD 5700/USA, ORD 5700) Designed for milling half dovetails or full dovetails with no drop hole allowance. Unfortunately, they are very fragile dueto their trapezoidal profile of a large Cutter Diameter with a smaller Neck Diameter. Their extreme hardness means they are brittle, so a highly rigid setup, such as a CNC machine, is necessary to prevent. 020" Radius. 002-006 0. Surface Finish X groove top and bottom : for liquids X = 32 micro inches (0. Monarch didn't include a guard because the dual compounds didn't leave room for one. To create a retaining-ring groove, click the Retaining Ring Grooves tab. O-Ring Groove (Gland) Design Guide. 000-. 054. There is no Industry Standard for these types of grooves. Bosstail: The O-ring is used for sealing straight thread tube. Create dovetail grooves that allow O-rings to flex without falling out of place. There are cutter shapes that machine the O-ring shape by plunging, and cutter shapes that machine grooves transversely. For internal diameters of 1. O-ring to severe chemical attack and breakdown. This is beneficial for special applications where the O-ring has to be fixed by the groove e. The o-ring is forced into the dovetail on installation, possibly tearing the o-ring. Tool Number. DOVETAIL O-RING FACE GROOVING INSERTS " " " Style 6 Shown FRONT RAKE: Primary 10° honed, Secondary 15° BACK CLEARANCE: 24° one side SIDE CLEARANCE: Depends on major diameter RADIUS: On 24° side only. For O-ring grooves. AdvantagesBut I need to retain the o-ring in the flat groove, and they seem to recommend you don't do this and that the width of the groove is bigger than the o-ring so it can squeeze under compression. These pictured tools are designed to mill a groove for a Parker Hannifin O-ring groove No. Kundera J. Gaskets. 471 dia. Solid Carbide Dovetail Cutters for Half Dovetail O-Ring Grooves. A drop-hole is an off-center hole. TABLE 1 TABLE 2 Max Radial DOC ≤ 28 Rc 29 - 37 Rc 38 - 45 Rc 23807 0. Carbide Dove Tail Cutter 4-Flute for O-R. b Groove outside diameter. O Ring Groove Design Standard. 005 0. A. (fig. Dovetailed O-Ring Groove. Dovetail and Half-Dovetail Grooves . This groove design is relatively uncommon as it is expensive to machine and should not be used unless absolutely required. In this work, the analysis of the mechanical and leakage behaviour of the O-ring seal, when installed either in a cylindrical concave groove or in a rectangular one, is presented. Grooves. 070. For a rod (shaft) seal:O-Ring Max Groove Diameter = Min Shaft Diameter + (2 x Recommended Gland Depth) b. Create dovetail grooves that allow O-rings to flex without falling out of place. The cross-section of the O-ring is seen as moderately arbitrary, as there are a few distinct advantages to either a larger or smaller cross-section O-Ring. However, this is an expensive groove to machine, and thus should be used only when absolutely necessary. To avoid tearing or nicking, the use of O-ring lubrication is recommended while installing the O-ring into the dovetail gland. Dovetail grooves are used to hold the O-ring in-place on a face seal groove during during assembly and maintenance of equipment. Gland Size Calculator. The O-ring sits in the groove additionally is compressed during assembly, creating ampere plug between two surfaces. 637 and 4. O ring groove dimensions drawing. Throughout this guide, the o-ring is used as an example in our discussion of seal design principles. To compress an O-ring of 5. Dovetail O-Ring Groove Design Learn More About Dovetail Groove Design for O-Rings . Over time, this mechanical wearing coupled with chemical attack of the abraded seal aggressively degrades the O-ring, producing an increase inThis offering of Parker Hannifin O-Ring Dovetail Cutters WITH Drop Hole Allowance is designed for milling a full dovetail gro. How to install and remove a spiral gasket from its recommended dovetail groove. Groove Bore Piston Rod Figure 1-2: Basic GlandMany milling machines are o-ring slotting, which means they require that a tool drop into the spindle and lock in before you can begin cutting. Static Radial Glans Design Application. Alternate solutions for creating retention in vertically oriented face seal grooves are: • Dovetail or Half Dovetail. Bottom Radius. Parker O-Ring Handbook - ORD 5700 pdf. Purpose – This paper aims to investigate the suitability of additive manufacturing to produce O-ring seals. Dovetail grooves are used to hold the O-ring in-place on a face seal groove during during assembly and maintenance of equipment. Review the general o-ring groove design considerations before moving onto the specific o-ring gland design type. 1-30). 145 0. DT3/8-15. 100”, . An undercut or dovetail groove has proven. 1-24). If you’re applying an o-ring to a face seal, you’ll better not use a face seal o-ring groove design, sometimes referred to as a dovetail. dovetail or half-dovetail grooves, are encountered but are much less common. Refer to the O-Ring Handbook or consult a Parker applications engineer for assistance in sizing O-rings to dovetail glands. In the Grooves dialog box: To create an O-ring groove, click the O-Ring Grooves tab. This offering of Parker Hannifin O-Ring Dovetail Cutters WITH Drop Hole Allowance is designed for milling a full dovetail groove, and is engineered to align with the standards. Abstract. Surface Studio vs iMac – Which Should You Pick? 5 Ways to Connect Wireless Headphones to TV. Dovetail grooves are used to hold the O-ring in-place on a face seal groove during during assembly and maintenance of equipment. Dovetail Cutters-Sight Groove Dovetail Cutters Solid carbide tool designed for milling dovetail grooves for Sight Attachments, and offered in 50° or 60° included angles. Full & Half Dovetails: Installation of an O-Ring A solution for retention with an O-ring is to change from a rectangular groove shape to either a Dovetail or a Half Dovetail. Face seals can seal internal pressure, external pressure, or both. Browse design considerations and recommendations for static face seals, metric o-rings, static dovetail. Learn More. . O-rings are measured in a variety of sizes. The method used to produce the finish is important. Also known as shell cutters, these high-speed steel cutters are good for face and side milling. Bochnia. Engineering, Materials Science. Inserts can groove, turn/bore and generate profiles. The inserts are available in submicron. Use this tool for analyzing your current gland and o-ring combination. A dovetailed o-ring groove is probably overkill for this application; I'd just mill it with a straight endmill and then use Vaseline to hold the o-ring in place during assembly. The design is optimized for strength by using an insert pair to generate the groove form. The trapezoidal ‘dove tail’ shape makes it important to understand the. 86 - Dovetail Cutters 60° Included. We are confident that these tools will make your chamfering, V-groove, thread milling, deburring. Harvey Tool's fully stocked selection of O-Ring Slotting End Mills are optimized for machining O-Ring grooves, and feature a stub flute length for improved strength. O-Rings. The retention feature makes having an upside-down or vertical face seal groove much easier. Then, calculate the O-Ring groove diameter as follows: a. Because of the difficulty in creating the groove and tight tolerancesTo avoid tearing or nicking, the use of o-ring lubrication is recommended while installing the o-ring into the dovetail gland. Groove widths . Ball shaped Dovetail shaped Vulcanized. g Groove style A – Groove providing. 139 inch (3,53 mm) and bigger. 070". Straight-sided grooves are best to prevent extrusion or nibbling. 015: 0. 3620 Centennial Dr. 317, which gives a . Shipping. Baker, P. Choose between more than 30 groove materials and 11 O-ring compounds! Benefit from a modern user friendly design and be guided from design rec-ommendations from info boxes. 015" 1: 2" 41062: $85. . DOVETAIL O-RING FACE GROOVING INSERTS " " " Style 6 Shown FRONT RAKE: Primary 10° honed, Secondary 15° BACK CLEARANCE: 24° one side SIDE CLEARANCE: Depends on major diameter RADIUS: On 24° side only TOP RAKE: 0° LEAD ANGLE: 0° Notes: • For best performance, form undercut by profiling. These dovetail inserts can be used on conventional, Swiss-type and CNC machines. 005 0. However, this is an expensive groove to machine, and thus should be used only when absolutely necessary. Volume fill is the O-ring volume divided by the gland volume. For reciprocating O-rings: a compression ratio of 10-20%. 53 - O-Ring Dovetail Groovers. nom. Dynamic cycling of the slit valve door O-ring abrasively scrubs the O-ring surface mechanically against the side walls of the dovetail groove. An undercut or “dovetail” groove has proven effective in many applications to keep the O-ring in place. 142". 66° Dovetail Cutters For O-Ring Grooves. Gap (mm) Sealing Gap (mm) info Results at Installation min. Multinode multi-use o-ring and. All of our. e. Mills Both Top and Bottom Radii. Before choosing a profile, you have to. 80: $69. If excessive clearance is created, extrusion will result. Shipping. An undercut or “dovetail” groove has proven effective in many applications to keep the O-ring in place. Visit our groove design page for additional information on measurements for O-ring groove depth, width and radius. Be they circular DT grooves on the face of a part or around the periphery, in over 40 years machining n metal chewing etc etc , I doubt I've made 100 in total - and 60 of those were on one job, and a. 070 0. The results of this analysis show that compared with rectangular grooves, dovetail grooves contribute to the enhancement of seal performance. like a circular machine slide type groove then I would say the market is very small. 86 - Dovetail Cutters W/ Steel Shank 60° Incl. The insert design is optimized for strength by utilizing an insert pair to generate the groove form. Rather than a grease, the Super-O-Lube is a high viscosity silicone oil. 70 - Double End Split Blanks. This feature article analyses an O-ring in a dovetail groove by using the finite element method. The results of this analysis show that compared with rectangular grooves, dovetail grooves contribute to the enhancement of seal performance. For those who are unfamiliar with O-ring design, it is recommended to first study this introductory section, becoming familiar with the basic principles of O-ring sealing, their common uses and general limitations. thanks againthe O-ring compression depending on the cord diameter D2 and the application. EIKOSHA Starting from: 113. L1 O. The dovetail tool (custom) could only get in and out of the groove at 1 place (an entry location I ramped out to . max. O-ring standards are specified. EIKOSHA×Dedicated Cutters; EIKOSHA×Machining tools; Simultaneous O-Ring Groove Compliant Dovetail Grooving and R Chamfering, Powdered High-Speed Steel, TIALN Coating. ToughShield™ Plus Plating. O-Ring can extrude into clearance gap or get squeezed in two directions. Dovetail Half - Bay SealFax: (916) 993-3949. Narrower groove for sealing vacuum or gas. Square groves are a necessity. Thermal swell of the rubber material. O-Ring volume. The dovetail grooving inserts are intended to machine O-ring dovetail grooves with 66-degree undercut angles. O-Ring Gland Fill %O-Ring Volume) / (Gland Volume) Gland volume vs. D. Dovetail grooves are used to hold the O-ring in place during installation or maintenance. Design Chart 4-4: Dovetail Grooves Dovetail Grooves It is often necessary to provide some mechanical means for holding an O-ring in a face seal groove during assembly and maintenance of equipment. 114 0. O-Ring Groove design plays an important part in how an o-ring seals. Tech Support. D. 1-24). . Start by inspecting the ORFS fittings to make sure that the O-ring is properly installed in the groove (CORG). C-3 Gland Dimensions. O-ring Vacuum Seal Dovetail & Half-dovetail Grooves It is often necessary to provide some means for retaining an O-ring in a face seal groove during assembly and maintenance.