Curious about ZVAC? :   Send your questions via form below:

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Used in England since January 1991, ZVAC is now spreading around the world for precision engineered die cast products like:

• Pneumatic, gas and hydraulic valves
• Heatsinks for electronics and motor drive controllers
• Radio communication handset chasses and frames
• Automotive components:
  • oil pumps
  • transmission transfer cases
  • engine cradles
  • body shell structural elements
  • oil filter mountings and manifolds
  • brake components
• Pressure tight components for medical equipment

• Bathroom fittings
• Door handles and furniture
• Lighting enclosures
• Consumer goods

Name and Origin of ZVAC:

The name ZVAC was given to this vacuum method in 2004, during a Canadian project. ZVAC can be pronounced zedvac, zevac or zeevac.

Designed in November 1990 and developed in 1991 by the Technical Manager of Dyson Diecastings Ltd., Chris Hoskyns, ZVAC was first used for producing zinc alloy die cast parts without porosity or blisters for an IBM Computer product.

Later, in November 1991, ZVAC was also used for aluminium diecastings on machines from 100 to 700 ton lock.

The ZVAC vacuum method is still used by the company, but they proudly refer to it as 'their own developed vacuum method'.

ZVAC is economical to use and the small increase in die tool costs are quickly recovered by a large reduction of scrap cost losses, less waste of time, reduced inspection load and more orders from satisfied customers.

ZVAC enables companies to quote for diecast parts which have vacuum in their process specification, confident that that they will be able to produce them on time.

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Patenting was rendered impossible by the Company's disclosure of technical details to third parties, and later also by publication of an application in China in 2003.

A pragmatic view is that it would be impossible for a small company or individual to enforce compliance to a patent of a technique, which can be used in secret behind closed doors.

Use of ZVAC is spreading, because when it is used, one can mount a ZVAC die on a machine, make the parts, finish the run, and then take the die down, without hassles of stoppages to clear blocked vacuum valves.

Sometimes, dies with ZVAC run for months continuously, with only occasional routine die face maintenance.

Now are you interested? :   Send your questions via form below:

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TO GET ZVAC

To get ZVAC, you invite its creator to spend some time at your plant, to show your die designers and tool makers the basics of the technique; i.e. sealing strategies, maximising evacuation flow rates and minimising leaks.

You will need to install a vacuum pump and some other standard commercial pipe mounted vacuum valves and filters, which would be specified to suit one or all of your machines.

The ZVAC vacuum method has to be 100% integrated with the die construction, but can often be retrofitted to existing dies without much modification.

Each vacuum project is different, but usually has three stages:

• STAGE 1
• Presenting the principles of the method
• Examining existing or planned new dies and machines
• Show how to adapt dies and machines to ZVAC
• Specify and order equipment


• STAGE 2
• Purchase equipment
• Vacuum system preparation
• Machine preparation
• Die design, manufacture or modification


• STAGE 3
• Commissioning
• Proving trials and production runs with vacuum

Chris Hoskyns is a UK registered Chartered Engineer (CEng) , fully qualified, highly trained and with over 37 years of hands-on diecasting process experience.

Fees for the consultancy service are agreed with the client before instruction commences.

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GUARANTEE

You are guaranteed that ZVAC^®  will give an enormous and consistent improvement to die casting quality.

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BENEFITS OF VACUUM

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

• Which ever vacuum method is used, if it works well, it will always improve quality and reduce scrap.

• Vacuum reduces porosity.

• Vacuum produces cleaner looking castings with less lube stains.

• 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 eliminates blister defects in painted and polished parts.

• Vacuum increases process yield.

• Higher yield means the die lives are longer.

• Vacuum reduces the load on inspection personnel, by producing good parts of consistent good quality.

• Vacuum can enable parts to be made thinner.

• Castings made with vacuum are stronger.

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ADVANTAGES OF ZVAC

• The main advantage of ZVAC over traditional vacuum die casting methods is reliability.

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

• 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, filters and pipes.

• Most existing dies can be easily and successfully converted to ZVAC venting and vacuum, even those with lots of sliding cores.

• ZVAC^®  uses basic engineering principles and innovations, which are very easy to apply.

• This method can be implemented by any well equipped diecasting company.

• ZVAC is a practical method which was developed in a busy subcontract diecasting foundry and maintenance tool shop, where time, money, man_power and lady_power were at a premium.

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The ZVAC technique uses a new concept of deep channel venting named Zig Zag Vents (ZZVs) combined with large bore high flow vacuum channels and sealing techniques using binary silicone rubbers.

To significantly reduce die casting porosity by using vacuum, the air pressure in the die cavity has to be reduced to better than 90% of full vacuum; i.e. lower than 100 millibar absolute before injecting metal.

The lower the pressure, the better the cast part will be. In some instances, pressures lower than 10 mbar are possible.

The 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.

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".

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

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.

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 Z_Vents (ZVs or ZZVs).

To maximise evacuation rate, ZVs 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.

ZVs are self cleaning and do not block up like corrugated chillvent block inserts or poppet valves, which are impossible to clean without removal from the machine.

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

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

Vacuum within the die cavity is 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.

All features use robust fundamental engineering. See example of basic vacuum die technique from training material on CD.

ZVAC^®  vacuum diecasting technique can be used with semi solid, rheocasting and thixotropic casting technologies, to maximise cast feature integrity.

ZVAC^®  vacuum die casting technique can be used on machines with extremely fast (7m/s) and very slow injection plunger speeds.

ZVAC^®  has used pumps, valves and filters from Balzer, Pfeiffer, Northey Technologies, BOC-Edwards, SMC Pneumatics, Huntington Mechanical Laboratories Inc., Kanglia, manufactured in Brazil, China, Germany, Japan, Russia, USA and UK.

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SIMPLIFICATION OF EJECTOR AND INSERT SEALING METHOD.
AND
ENHANCEMENT OF LEVEL OF VACUUM IN THE MOLD

To prevent air leakage into the mould via ejector pins during vacuum application, the ejector box is sealed using the same simple standard O-ring cord compression technique as for the die faces. The ejector plate in its return position contacts O-ring seals around the primary ejector bars.

The large volume of the ejector box can be evacuated separately from applying vacuum to the mold cavity, i.e. as soon as the dies are locked.

By evacuating the ejector box prior to the evacuating the die, another reservoir of vacuum is created very close to the mold, which would further enhance speed of pressure drop in the mold as soon as the shot sleeve filing hole is covered. This is achieved by having the valves for ejector box and die mould mounted adjacently on one large bore pipe.

This method also gives an advantage of pulling residual die lubricant into the ejector pin holes, which aids their lubrication. The pins can still be lubricated via a grease gallery on the rear of the moving holder if preferred (recommended).

Applying vaccum to the ejector box simultaneously or within a short time as to the mold puts greater flow demand on the vacuum system, and the transient drop of vacuum might be significant. Pump sizes need to be larger to use this technique.

With a well flow-engineered port of about 45mm bore and large 50 mm high flow vacuum valve, an ejector box with volume of 20 litres would be evacuated down to about 10 millibar in about 0.2 seconds.

Position of the ejector box vacuum port is best at bottom of the mold, where it can be on arranged on the fixed half mold so that any ingested liquids drain out when the dies open. Alternatively, the top or sides of the ejector box could be ported, and a separate drain hole taken to the die parting face, preferably within the sealed vacuum zone.

IMPORTANT: REMEMBER: This method requires larger pump capacity, but its simplification of tooling vacuum adaption justifies the extra pump cost.