• Use of the ZVAC high vacuum technique commenced January 1991, at a leading UK die-casting foundry; where it was urgently designed, developed and applied to eliminate a serious cissing problem of powder paint occurring high temperature stoving. Scrappage rates for cissing, blisters and gas porosity were often in excess of 40%.

  • This new and unique high vacuum diecasting technique was designed to avoid the weaknesses of commercially available valve based systems, and to be ruggedly reliable and effective:

  • The technique's simplicity enabled rapid application to benefit other technically challenging products, in both zinc and aluminium casting shops.

    • It could spectacularly maximise quality, productivity.

    • It was the single most effective process enhancement for eliminating gas porosity ever experienced during my then 20 years in the industry as a professional manufacturing engineer.

    • The method used simple practical proven methods of applying vacuum, which did not require expensive problematic poppet type valves like Hodler-Optivac's or Fonderex's, or clog-prone corrugated chill vents, bolted on or embedded in the die, and it worked first time spectacularly well, and continued doing so.

    • In-house QC rejections of unpainted castings fell from over 40% to less than 1%, and complaints and rejection of painted parts from the client ceased.

    • Since 2001, the method has been globalised by its designer and developer, Chris Hoskyns, who branded it 'ZVAC®' in 2004.

    • The first export of the revolutionary ZVAC vacuum diecasting technique was commissioned in December 2001, at a large advanced and highly automated zinc alloy (Zamak) die casting foundry near Shanghai, where it also worked first time, and then became implemented on nearly every die and machine.

    • The first use of ZVAC for magnesium parts was in 2004, in Canada, for the GM Corvette Z06 Engine Cradle.

    • The latest applications of ZVAC vacuum diecasting technique were in 2015, at a large ultra modern foundry in Eastern China, and a medium sized family owned company in Greece, for aesthetic domestic products in polished and plated Zamak alloy.


    Because this vacuum technology could be used to enhance the properties and manufacturability of military hardware, projects may be subject to terms of an export licence issued by the UK Government.

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    The quality benefits of using the vacuum technique were so great that the company kept it secret.

    Eventually, the company published the benefits of my vacuum method were in their brochures and websites.

    If you want to solve a similar diabolical porosity problem, then contact the technique's designer and developer Chris Hoskyns.

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    See examples comparing quality with and without vacuum from the prototype application in 1991, and from more powerful installations at other companies:

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    • Try ZVAC on an old problematic multi-slide die casting mould, which has always produced parts with bad porosity or blisters etc. Then, after seeing the excellent results, you'll want ZVAC vacuum or its ZZVs included in new dies at the design stage.

    • Upgrading old dies to ZVAC vacuum can sometimes be challenging, but with assiduous attention to detail and a deep understanding of the dynamics of the high pressure diecasting process, it has always been possible, with results that delighted the die's owner.

    • ZVAC uses a total sealing strategy, maximum possible vacuum vent and flow areas and a peripheral vacuum channel that exhausts the air from vacuum vents on the parting face and sliding core recesses.

      ZVAC's peripheral vacuum channel takes advantage of shut-out imperfections to draw die lubricant residues and air away from the die cavity in every direction, which enhances the achieved vacuum in the die.

    • Often, ZVAC's exclusive innovative massive venting method can be added to the feed gate runners to enhance rate of extraction, to maximise cavity vacuum pressure before injection commences.

    To implement ZVAC, use enquiry form or email address linked below:

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    The basic ZVAC die casting method was designed for an IBM product, and from mid 1991 began to be widely used for functional, structural and high quality aesthetic products, such as those listed below:

    POWER GENERATION: Structural Components

    • Stator yoke casings and engine coupling frames for three phase power generators, made by Newage International Ltd., of Stamford, UK.


    • Pressure tight components for medical and safety critical equipment for:
      Knorr-Bremse, Fiat, Volvo and Metso Automation.

    • Pneumatic hand tools for Desoutter

    • Pneumatic valves, pressure regulators and filter bodies for IMI Norgren

    • Heatsinks for electronics and motor drive controllers for:
      Sanyo Denki , Emerson Industrial Automation - Control Techniques, Seimens and others Examples


    • Hi-Fi amplifier and media player electronics enclosures for:
      QUAD Electroacoustics Ltd. (formerly, The Acoustical Manufacturing Co Ltd.) and Linn Products Limited.
    • Examples
    • Bases for food blenders and mixers for Kenwood Chef..

    • Radio communication handset and frames Motorola.

    • Hydraulic disc brake components for Sram Corporation.


    • Gas burner venturi and flame jet discs for kitchen cooker hobs, Colombia.

    • Aesthetic domestic and office Lighting enclosures for Concord Sylvania Lighting.

    • High quality door handles and escutcheon plates in zinc alloy coated with TiN, ZrN by PDV, or Chrome and Gold plated for Behrizan and TOTO.

    • Polished and chromed aluminium hand drier cases for Airdri.

    ZVAC is very beneficial for thin and polished diecastings, particularly those which are gold plated, or coated with zirconium nitride (ZrN), titanium nitride (TiN) or chromium nitride (CrN), by physical vapour phase deposition (PVD) processes.

    ZVAC is economical to use, and the small increases in die tool cost is quickly recovered by improved quality, reduction of scrap and higher productivity.

    ZVAC has enabled companies to successfully produce die cast parts, for which the customer has specified that vacuum must be used.

    (The brand names mentioned above, have been publicised by the foundries producing the referred parts.)

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    • Vacuum diecasting techniques enable porosity and surface appearance standards to exceed those possible by the ordinary high pressure die casting process.

    • Vacuum reduces porosity.

    • Vacuum produces cleaner looking castings with less lube stains.

    • Vacuum eliminates blister and out-gassing cissing defects in painted and polished diecastings.

    • Vacuum enables organic coatings to be cured by stoving at 200°C for 20 minutes, without surface corruption by out-gassing and cissing. Dry coating methods such as epoxy and polyester powder, and wet methods like spraying or E-coating (electrophoretic), give much higher yields when the castings are made with this strong vacuum technique.

    • Vacuum can reduce occurrence of cold laps.

    • Vacuum reduces need for overflow pockets.

    • Vacuum reduces need for high pressures, and so enables larger parts or more impressions per given machine size.

    • Vacuum enables the die designer to sidestep gating conundrums.

    • Vacuum increases process yield.

    • Higher yields means less scrap and the dies produce more useable parts before needing replacing.

    • Vacuum lifts quality so much that the load on inspection personnel is reduced, releasing staff to concentrate on added value activities, instead of loss making activities like 100% viewing and scrapping defective parts.

    • Vacuum can enable parts to be made thinner.

    • Castings made with vacuum are stronger.

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    • The main advantage of ZVAC over traditional vacuum die casting methods is its reliability and ease of maintenance.

    • You don't need to buy expensive stand-by vacuum valves.

    • You don't need to buy or make expensive chillvents, which frequently get blocked by impacted flash and are difficult to clean.

    • You won't have to cut big pockets in the outer peripheries of your holder blocks to accommodate chillvents or valves, so holders retain their stiffness.

    • There is no need to have long deep runners to connect chill vents or vacuum valves placed at the edge of the die.

    • The ZVAC method uses a new vent design called ZigZagVents (ZZVs). These are deeper than conventional flat vents and enable rapid high volume flow of exhaust of air and fume from the die cavity to peripheral vacuum channel.

    • In operation, the vacuum gallery around the die in conjunction with the ZZVs, draws residual lubricants on the parting faces, away from the mould cavity, so reducing porosity caused by lubricant liquids.

    • Overflow volumes can be reduced or eliminated, so reducing remelt energy cost.

    • Economical implementation costs, allow ZVAC vacuum technique to be used simultaneously on every die and machine in a foundry.

    • ZVAC®  uses standard stock vacuum equipment, which means you can buy valves and pumps from your local high vacuum equipment suppliers.

    • The ZVAC method can show you the vacuum pressure actually in the die cavity before each shot, not just at some remote point on the supply pipe or tank.

    • Very rapid vacuum pull down is achieved by using standard large high flow vacuum valves, customised filters and large bore connecting to large vacuum reservoirs (receivers/accumulators)pipes.

    • Most existing dies can be easily and successfully converted to ZVAC venting and vacuum, even those with many hydraulic and angle-pin actuated sliding cores.

    • Groups of Zig Zag Vents can even be cut onto curved undulating parting faces, so extending the technique's versatility.

    • Zig Zag Vents can start right at the edge of the casting, so enabling dies to be kept small.

    • Zig Zag Vents can connect the feed runner from biscuit or sprue directly to the vacuum channel, so enabling rapid exhausting of shot tube air and lubricant fume.

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     Vacuum Pressures:

    • The lower the air pressure in the die before injecting metal, the smaller will be the porosity in the cast part.

    • For example:
      • Reducing the air pressure in the mould by vacuum to 1/10 of an atmosphere before injecting metal, could reduce gas porosity diameters to less than 1/2 of what they would be without vacuum.

      • Reducing the air pressure in the mould by vacuum to 1/100 of an atmosphere before injecting metal, could reduce gas porosity diameters to less than 1/4 of what they would be without vacuum.

    Those theoretical ratios might seem like small gains, but the effect of vacuum on porosity often appears to be greater than expected; most probably due to the rapid extraction of volatised residual liquid components of mould release agents (water or hydrocarbon solvents) and fumes from oil and grease lubricant carbonisation.

    The theoretical relationships between porosity volume, pore diameter and vacuum, and leaks and vacuum, are shown by graphs.

    In the die-casting foundry, ZVAC enables very low pressures to be reliably achieved, by using a comprehensive sealing strategy together with large area vents, large pipes, large filters and large valves.

     Sealing the die:

    • Primary sealing is on the holder block (bolster) parting face, and is accomplished by a very practical method, with precision made high temperature silicone rubber cord. The most frequently asked question is, "Does it survive die flashing?" The answer is, "Yes"; but dies should not be allowed to flash-out repeatedly.

    • Secondary sealing is internal, by two alternative ways:
      (a): injecting special non-corrosive liquid RTV silicone rubber,
      (b): fitting silicone foam or solid cord. or strategically placed silicone, PU or PTFE O_rings.

    • The sealing method is tolerant of gross die face contamination, corrosion and distortion of the die and slide abutments; and, has proven to be reliable and durable on hundreds of dies since 1990.

     Evacuating the die:

    • The cavity and slide ways are entirely surrounded by a large vacuum channel, which has large bore ports to large bore pipes and valves (25 to 50 mm ID).

    • The peripheral vacuum channel draws lubricant residues away from the die-mold cavity and intercepts any inward air leakage.

    • Vacuum is directly connected to the mould cavity by multiple deep ZigZag Vents (ZZVs, Z_Vents or ZVs).

    • In 1991, ZZVs were a completely new and revolutionary type of high flow die vent; and totally different to the orthodox block-style inserts with their convoluted chillvent surfaces.

    • When the metal enters the ZZVs from the die cavity, the characteristic flow pattern cause it to freeze close to the cavity, so blocking pressure from the injection before the vent channel has fully filled.
      Examples of flow in ZZVs (PopUp Window)
      Examples of flow in ZZVs (New Window).

    • Operational clearances and shut-out imperfections in sliding cores actually enhance vacuum level by providing additional venting from the mould cavity to the peripheral vacuum channel.

    • To maximise evacuation rate, groups of ZZVs can also be connected to main metal feed runners.

    • Total vent area can be much more than that possible with poppet valves and chill vents, so enabling maximum vacuum to be realised very quickly.

    • The plan and cross section profile of ZZVs was designed to keep them clear and not block up like corrugated chill vents or poppet valves, which are very difficult to clean.

    • As well as maximising vacuum in diecasting, ZZVs were found to be very effective when used in non-vacuum dies.

    • When the mould has filled, metal flows into the ZZVs and starts to freeze as its flow is repeatedly reversed upon itself, which progressively chokes the path of the metal.
      More about ZZVs...

     Process Notes:

    • Vacuum within the die cavity can be directly measured before and throughout each shot, which gives more accurate data than measuring it on the supply side of the valve, as in commercial systems.

    • In the ZVAC method, air and fumes are extracted at maximum rates during the plunger slow and fast injection plunger strokes, up to complete filling of the die cavity.

     Robust Simplicity:

    • All features use robust fundamental engineering methods and equipment, and are fully explained in the notes that are provided during the training for a project.

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    • The first experiments with Zig Zag Vents were performed in March and April 1991 on three dies for a large Mazak-3 (zamak-3) zinc alloy product for IBM. The trials proved that air could be drawn directly from the feed runners as well as from casting die cavity rim and overflows, through vents cut directly into the die parting faces 0.020" deep by 0.563" wide (0.5 x 14mm).

    • In July 1991, I issued a design standard for various vent configurations ranging from 0.5 to 0.8 mm deep, up to 20mm wide, arranged as single or multiple close grouped channels. Those trials were made in a very busy production environment, and recorded as photocopies of sketches and of actual castings with zigzag vents attached.

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    To get ZVAC, send an email to Chris Hoskyns, a UK registered Chartered Engineer (CEng) with over 43 years of practical experience of developing diecasting foundry processes and improving quality and productivity.


    Depending on size and amount of advanced preparation, ZVAC vacuum projects can be done over one or several on_site stages:

    • STAGE 1
      • Company design, toolshop and foundry teams instructed in the details of the method.
      • Die design prepared for modifying an existing or new die.
      • Equipment specified and ordered.

    • STAGE 2
      • Install pump, receivers, vacuum network.
      • Add vacuum control to machines.
      • Complete modification of an existing die for vacuum and test die sealing.

    • STAGE 3
      • Commission system and test die on machine.
      • Do a short production run with vacuum to prove benefits.
      • Put vacuum die tool into full production.
      • Verify benefits and scrap reduction.
    Fees for the consultancy service are agreed with the client before instruction commences.

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    ZVAC guru promises that ZVAC®  will bring bags of benefits to your die casting quality, and you'll bag bigger profits.


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