注塑模具venting 2.ppt

1、Efficient venting for mobile phone parts moulded using Zytel HTN 53G50,Roger Wilkinson Technical Manager DuPont Engineering Polymers Hemel Hempstead, UK January 2005,The information provided in this documentation corresponds to our knowledge on the subject at the date of its publication. This inform

2、ation may be subject to revision as new knowledge and experience becomes available. The data provided fall within the normal range of product properties and relate only to the specific material designated; these data may not be valid for such material used in combination with any other materials or

3、additives or in any process, unless expressly indicated otherwise. The data provided should not be used to establish specification limits nor used alone as the basis of design; they are not intended to substitute for any testing may need to conduct to determine for yourself the suitability of a spec

4、ific material for your particular purposes. Since DuPont cannot anticipate all variations in end-use conditions DuPont makes no warranties and assumes no liability in connection with any use of this information. Nothing in this publication is to be considered as a license to operate under or a recom

5、mendation to infringe any patent rights. CAUTION: Do not use this product in medical applications involving permanent implantation in the human body. For other medical applications see DuPont Medical Caution Statement, H-51459. Registered trademark of DuPont,Efficient Venting,Page 2,Whats a vent?,ga

6、p big enough to let the air out small enough to keep the plastic in some polymers are viscous, they can have deeper vents nylons have very low viscosity, they must have shallower vents this makes it more difficult to effectively vent tools designed for moulding nylon, especially when using the very

7、fast injection fill times that are needed for nylons with high levels of glass fibre reinforcement HTN53G50 has 50% by weight glass fibre reinforcement,Efficient Venting,Page 3,Why vent injection moulds?,cavity (and any cold runner) is full of air at 1 bar most diesel engines work by compressing air

8、 to about 22 bar cavity pressures in phone moulding can go up to 3000 bar fast fill speed gives best surface finish (resin-rich surface) fast fill speed gives stronger weld lines fast fill speed gives more equal pressure transfer through cavity cant sell parts with burn marks or poor surface finish

9、moulder doesnt want to ruin the tool by burning away steel,Efficient Venting,Page 4,What blocks vents?,carbonised polymer from diesel effect flash additives/pigments/volatiles in the material degraded material (molecular weight reduced during moulding) incorrect machine start-up procedures incorrect

10、 hot runner start up procedures low viscosity material, especially wet nylon,Efficient Venting,Page 5,What venting methods are there?,apply a vacuum to the cavity before injection fill make the tool (or parts of it) from porous metal recognise that venting is a priority at the tool design stage then

11、 put the maximum venting into the tool,Efficient Venting,Page 6,Vacuum venting:,most efficient method, no air left to compress and burn needs very careful tool design, plus an exhaust mechanism will increase overall cycle time by a few seconds needs a gasket surrounding the complete split line diffi

12、cult to do this with some split lines and side actions may need seals around ejector pins, moving cores etc works best with tools that have hot runner valve gates will not stop degraded material giving mould deposit,Efficient Venting,Page 7,Porous materials of mould construction?,porous = sintered s

13、intered inserts are used for venting, particularly where surface aspect is not critical various particle sizes are available to suit different polymers material used for insert must have strength, pressures involved in moulding will crush it otherwise insert must be sparked on both sides, machining

14、it will close the gaps between the particles needs to be low cost and easily replaceable, it will get blocked,Efficient Venting,Page 8,Priority venting, guiding principles:,vent land must be as short as possible vent land must be as wide as possible split line venting must cover at least the last 1/

15、2 of fill, more is better relief channels must exit to atmosphere without restriction moving cores/ejector pins must be vented fixed cores/inserts should also be vented known gas trap areas need extra venting. Additional ejector pins solely there for venting should be considered,Efficient Venting,Pa

16、ge 9,Typical split line relief channel positions:,e.g. for end-gated oblong,Efficient Venting,Page 10,Typical split line relief channel positions:,e.g. for centre gated disc,Efficient Venting,Page 11,Typical split line relief channel positions:,e.g. for oblong with cut-outs,Efficient Venting,Page 12

17、,Typical relief channel positioning,Efficient Venting,Page 13,Typical relief channel positioning,Efficient Venting,Page 14,Typical split line vent cross-section:,Efficient Venting,Page 15,Taken closer in critical areas:,Efficient Venting,Page 16,Taken closer to shut-off in critical area,Efficient Ve

18、nting,Page 17,Ejector pin venting:,Ejector pins include sleeve ejectors Working clearance already exists with all ejector pins Diameters are much easier to control to very close tolerances than other shapes Ejector pins are low cost parts of the tool They are easily replaceable The same venting principles apply, full width relief channel as close as possible to the shut-off with