DESMA MAnuAl COlD runnEr tEChnOlOgy | intrODuCtiOn | 1

BASiCS Of COlD runnEr tEChnOlOgy

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DESMA MAnuAl COlD runnEr tEChnOlOgy

BASiCS Of COlD runnEr tEChnOlOgy

1. Print run, October 2014 | En

DESMA MAnuAl COlD runnEr tEChnOlOgy | EDitOriAl | 5

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1. intrODuCtiOn1.1 recycling problems1.2 Production costs1.3 Production method 1.3.1 Overflow grooves and article flash 1.3.2 Sprue waste

2. tEMPErAturE COntrOl2.1 liquid temperature control 2.2 flow and temperature control performance 2.3 heat transfer medium2.4 temperature control devices

3. COlD runnEr tyPES3.1 nozzle systems 3.1.1 nozzle without temperature control 3.1.2 nozzle without temperature control with spring-loaded sliding nozzle 3.1.3 liquid-temperature-controlled nozzle 3.1.4 liquid-temperature-controlled nozzle with spring-loaded sliding nozzle 3.1.5 nozzle with needle valve3.2 Cold runner distributor block systems 3.2.1 Split cold runner block 3.2.2 Split cold runner block with inserted tubes 3.2.3 Partly closed cold runner block 3.2.4 Closed cold runner block3.3 Contamination problems

4. DESMA COlD runnEr tEChnOlOgy4.1 Standard cold runner 4.1.1 nozzle area 4.1.2 Bloc area 4.1.3 temperature control 4.1.4 Electrical installation 4.2 Vario cold runner 4.3 flowControl cold runner 4.3.1 CrBControl

5. DESMA itM tEChnOlOgy5.1 itM pots without temperature control (hot pot)5.2 itM pots with temperature control (cold pot)5.3 ZeroWaste itM

6. lAyOut AnD CAlCulAtiOn tOOlS6.1 DESMA cold runner layout tool “CrB Calc”6.2 DESMA production cost calculator “Article Calc”

7. ExAMPlE Of PrOjECt EnginEEring7.1 rubber-to-metal bushing7.2 Sealing ring 7.3 O-ring 7.3.1 Production with hot runner 7.3.2 Production with cold runner 7.3.3 Production with central cold runner (2 decks) 7.3.4 Summary7.4 Valve bonnet seal7.5 further examples of application (2-deck production)

8. PrOjECt PArtnErS

tABlE Of COntEntSDESMA realises turnkey machines and systems as well as moulds and cold runners for the production of sophisticated rubber and silicone moulded products. At the same time, we also provide companies that are processing elastomers and you as user with access to valuable expert knowledge.

More performance, productivity and profitability in elastomer processing. Cold runner technology as basis for automation makes it possible! in this DESMA manual you will learn how cold runners help you to reduce the share of waste or even achieve a waste-free production, a more flexible mould design and shorter cycle times as well as an increased product quality with low reject rates.

A lead in knowledge for planning and application. Obtain information about cur-rent cold runner technology and get to know the different systems and models: from the established standard cold runners to the innovative ZeroWaste itM technology. rounded off by layout and calculation tools, novices in this branch of industry, trai-nees and experienced experts receive a complete range of knowledge. Practical, com- pact and easy to understand because of the many diagrams.

the DESMA range of training courses and the trend-setting DESMA E-learning platform offer you further support for your work: www.desma.biz/en

With best wishes for your success – your DESMA team!

EDitOriAl

»Thebasicprinciplesofcoldrunnertechnologyanditspracticalapplicationduringtheinjectionmouldingofelastomers. Herealltheinformationisavailableataglance.«

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11. intrODuCtiOn

In average, just the material costs are 60 % of the production costs of elastomer products!

Merely a total of 40 % of the costs are thus attributed to energy, labour, machines, and the like. Since automation sys-tems, energy-saving drives, etc. have already exhausted the potential savings in these sections, below we chiefly want to discuss potential savings in the field of material costs.

With elastomers, the compound price depends very much on the employed basis polymer. Depending on the requirements the compound must satisfy, there are extreme price differ-ences for fluorocaoutchouc and silicone rubber compounds.

Since the required properties can usually not (yet) be achieved with low-price material, reducing the waste content in produc-tion as far as possible is the obvious thing to do.

Thermoplastic main and by-products can be heated and thus returned to their liquid state, in analogy with metal products. the resulting melt can be used for new products (recycling). Since merely the physical aggregate state changes, the mate-rial quality does not deteriorate - provided that the material is not contaminated (homogeneity) and melted gently.

for vulcanized elastomers, however, this process cannot be used for recycling. the chemical cross-linking of the macro molecules prevents the material from softening / melting when it is warmed up. At a temperature of approximately 250 °C (depends on basis polymer and time), the elastomer is thermally disintegrated, and thus useless. its behaviour is therefore more similar to that of wood.

the material value of vulcanized by-products is – compared with thermoplastics – thus basically zero. Although chemical

recycling of rubber waste is technically possible, it requires a high technical effort and is thus at least not yet economic.the by-products are thus frequently disposed of as waste – at additional disposal costs. if you want to avoid these dispos-al costs, there are the following possibilities:

first, the waste must mechanically be reduced / shredded. the particle size depends on the future use.

Filling material substitutethe production of new rubber compounds permits up to approx-imately 5 % fine old rubber powder to be added. this requires less filling material (soot, chalk, etc.) to be purchased.

Material for less strained itemsAdding a “glue” permits a dimensionally stable connection of the rubber particles to be achieved. this method is used, for example, for producing soft floor coverings for playgrounds.

Aggregate in civil engineeringusing old rubber powder instead of sand (or similar sub- stances) permits in some cases specific desired properties to be achieved.

BASE polyMEr (ruBBEr TypE) MnEMonIc coSTS pEr kg

natural rubber nr approximately 2.50 €

Ethylene-propylene-diene rubber EPDM approximately 3.50 €

nitrile-butadiene rubber nBr approximately 3.50 €

Butyl rubber iir approximately 4 €

fluorine rubber fPM approximately 25…1,500 €

Silicone rubber VMQ approximately 5…500 €

1.1 rEcyclIng proBlEMS 1.2 proDucTIon coSTS

Thermoplast Elastomer, vulcanized

By-product (waste)

By-product (waste)

productproduct

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for the reasons discussed above, the precious raw material should be processed as efficiently as possible. On the other hand, the investment costs for new production systems should be as low as possible in order to obtain a short amortization period.

if you compare in an existing plant the ratio of used material and marketable items, there is frequently a large gap between the two values.Even if the existing waste share is assumed as being “no fur-ther optimizable”, there remain potential savings of approx-imately 12 % of the production costs from the vulcanized by-products, such as sprue, overflow grooves, and flash (20 % of the material costs are approximately 12 % of the production costs).

1.3 proDucTIon METhoD AnD WASTE conTEnT

TypIcAl AvErAgE MoulD coMponEnT proDucTIon: (injection moulding procedure without cold runner technology)

Employed Material: 1,000 kgBy-products (spurce, flash, etc.): -200 kgEject fraction: -50 kgMarketable items: 750 kg

" Total waste content 25% !

it has already been possible for some time to produce perfect articles practically without any flash waste using the itM (Injec-tion Transfer Moulding) process. today, such perfect articles can also be successfully produced using the iM (Injection Moul-ding) process along with appropriate machinery and tools, for example, in the production of seals. Whether or not there are still potential savings that can be exhausted in special cases depends very much on the individual articles. for large complex geometric structures with inserted parts, for example, this can only be achieved with very high investments. this makes profit-ability frequently questionable. you must therefore check each individual case. there is not usually a universal method (tool) that can be used to avoid flashes.

in this field “reduction of sprue waste”, there are frequently very efficient methods to save material. this is true irrespec-tive of the geometry of the specific article. We therefore ur-gently recommend that you make exact comparison calcula- tions when selecting your production method.

1.3.1 OVErflOW grOOVES AnD ArtiClE flASh

1.3.2 SPruE WAStE

IM with hotrunner

manifold

Sprue wasteInvestment costs

~17%Low

~10%Medium

~3%Medium

0%High

0%High

50 – 500%Low

50 – 500%Low

ICM ITM withhot runner

ITM with cold runner

ITM withdirect injection

(ZeroWaste© ITM)

IM withStandard cold

runner

IM with direct injection

(FlowControl® cold runner)

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Type?Price?Specialfeatures?

Type?Dimension?Inserts?

Period ofamortization?

CM, TM, IM, ITMRunner systems?No. of cavities?Layout? " Article quality

" Manufacturing costs" selling price

Compound? Article? Production quality?

Manufacturing Concepts

22. tEMPErAturE COntrOl

Cooling large areas of the spreader in order to prevent the material in there from pre-curing is the object of a cold runner system. After the cure time has expired, you need not remove this material together with the articles. it can be used with the next injection for new articles.

unfortunately, standard technology does not allow the entire spreader to be cooled – the cold nozzle tip would excessively cool down the cavity. this would result in a significantly longer cure time, or a poorly vulcanized spot on the article. the stan-dard cold runner therefore requires some vulcanized sprue. this distance to the cavity is frequently used for a subdistri-bution from one cold runner nozzle to several cavities. A 12-nozzle cold runner, for example, can thus feed 48 cavities.

nevertheless, implementing a temperature gradient from the cold area to the hot area that is as steep as possible is extreme-ly important. to obtain a clearly defined separation between “fresh” and vulcanized material, the transition distance should only be a few millimetres long. this is the only way to prevent pre-cured material from the nozzle to be flushed into the cavi-ties during the next injection (contamination with old rubber).

this requires a very powerful cooling of the nozzle, the best insulation possible between nozzle and mould, and a powerful mould heating.

180 °C

180

°C

80 °C

135

°C

80 °C

CRB insulating plate Mould

CRB distribution block CRB heating plate

“Fresh” elastomer

Vulcanised sub-distributor

Product

Tear-off point Temperature gradient180°C

80°C

CRB distribution block

A temperature control system consists of circulation pump, sensor, heater, cooler, connecting lines, and temperature- controlled component (consumer). in a DESMA system, the temperature-controlled medium is heated / cooled centrally in the “temperature control device”. the circulation pump ensu-res a continuous flow from the temperature control device to the consumer (cold runner, for example), and back. the temp-eratures of heat transfer medium and consumer adjust to each

other. the advantage over direct heating (or cooling) is the very uniform temperature distribution in the temperature-cont-rolled component. A directly installed heating or cooling ele-ment, in contrast, has only a local effect. Due to the low space requirements of the temperature-control ducts, very filigree components (such as cold runner nozzles) can very efficiently be temperature-controlled.

2.1 lIquID TEMpErATurE conTrol

Cooling water

1 2

Unit 1 temperature zone screw cylinderUnit 2 temperature zone injection cylinder and nozzle

Temperature control devices

Temperature control liquid

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the temperature control device contains circulation pump, heating / cooling, and temperature sensor. Although the tem-perature sensor sits mostly in the return line of the temper-ature control device, it may also be installed directly on the consumer if there is sufficient space.

to cool the temperature-controlled medium, a valve opens to feed cold liquid (mostly on water basis, ≈20 °C) from a sepa-rate cooling circuit through a heat exchanger.this cools down the heat transferring medium / the consumer. to increase the temperature, the valve is closed and electric heater coils (similar to an immersion heater) are activated.

A sufficiently high flow is crucial for liquid temperature control. this is the only way to reach turbulent flow and thus a good heat transfer (reynolds number > 2,300).

the flow rate is chiefly determined by the viscosity of the heat transfer medium, the installed pump, and the pressure loss of the consumer. the pressure loss depends on cross section and length of connecting lines and temperature control ducts. the connecting lines should therefore be as short as possible and of a large cross-section. Quick-acting couplings frequently cause a very large pressure drop.

With a low flow rate (due to a contaminated or kinked hose, for example), temperature control is very inaccurate and the heat up / cooling down times increase drastically. furthermore, the risk of overheating rises significantly. this leads to a chemical destruction of oil-based media (cracking). the medium darkens heavily. the subsequent formation of clots can rapidly obstruct the entire system. heat exchanger, connecting lines etc. can frequently not be cleaned any more and must completely be replaced. Consequently, check the flow rate at regular inter-vals. if the flow rate is low, find and eliminated the cause as quickly as possible!

the cooling performance, too, is determined to 100 % by the cooling water supply. Adequate supply must therefore Be ensured (even if all machines are cooling at the same time). ideally, the cooling water temperature should be at a constant level (20 °C +/-3 K) all over the year.

Fresh-water emergency coolingin the event of a power failure, this function automatically feeds cooling fresh water (~20 °C) via a bypass directly through the cold runner. the pressure in the fresh water line (~3 bars) ensures that there is sufficient flow Precuring of the compound in the cold runner is thus avoided.

45 °C40 °C

20 °C

24 °C

heat exchanger (cooler)heater coils

Pump capacity curve

Flow / volume flow

Pres

sure

Rey

nold

s nu

mbe

r (R

e)

Operating point

Pressure lossTemperature control Re

230 V 33 °C

40 °C

2.2 FloW AnD TEMpErATurE conTrol pErForMAncE

15 30 45 60 75 900

20

60

100

140

Heat transfer medium

°CCooling agent20 °C – 15 l/min

kW

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Temperature control liquid on oil basis (temperature control oil)

Temperature control liquid on water basis

2.3 hEAT TrAnSFEr MEDIuM

ADvAnTAgES DISADvAnTAgES

temperatures up to approximately 300 °C possible less heating / cooling performance

long unproblematic operation of the temp. control system ensured higher viscosity than water(large duct cross-sections required)

lubrication of pump and valves Contained additives are frequently harmful

Does not attack metallic surfaces —

no problem with bacterial invasion / decomposition —

ADvAnTAgES DISADvAnTAgES

Best cooling / heating performance Special treatment required (against corrosion, lime, bacterial invasion)

good fluidity Without special temperature control devices only max. 95 °C possible

Most parts of leaked liquid evaporate With special pressurized water devices max. approximately 140 °C (danger from system pressure)

rEcoMMEnDATIon: Due to the high power demand (in particular in the narrow temperature control ducts of the cold runner nozzles), water-based temperature control media are recommended for the cold runner section.Oil-based media, in contrast, are particularly suitable for the temperature control of the injecting unit.

Devices with open temperature control circuit (pressureless)here, temperature control circuit and cooling circuit are com-pletely separate. Since there is no risk of mixing liquids, you can use a water-based or an oil-based medium as heat transfer medium. Due to the pressureless circuit, the maximum temper-ature is limited to approximately 90 °C when water-based media are used. these devices are therefore preferably used for tem-perature control of the injecting unit (with oil).

operation:1. refill opening (for temperature control medium)2. “level” indicator lamp3. Specification of the temperature-controlled component4. rating plate with performance specifications5. “Control circuit” connection6. “load circuit” connection7. Overtemperature switch8. tank overflow opening9. Drain plug (for temperature control medium)10. Cooling liquid inlet (feed)11. Cooling liquid outlet (return flow)12. temperature control medium outlet (feed)13. temperature control medium inlet (return flow)

2.4 TEMpErATurE conTrol DEvIcES

M

1. Temperature control medium inlet (return flow)2. Temperature control medium outlet (feed) 3. Cooling liquid inlet (return flow)4. Cooling liquid outlet (feed)5. Re-fill opening (for temperature controll medium)6. Cooling unit (heat exchanger)7. Cooling valve (electric)8. Heater coils9. Circulation pump10. Level switch

91

3

4

2

65

8

7

10

1

2

3

8

° 7

°

5

12

10

6

4

9

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8

8. thiS PrOjECt WAS SuPPOrtED By thE fOllOWing COMPAniES

injection moulding machines of DESMA are globally in operation

Around6,000

DESMA - B&RTechnology partnershipfor elastomer machine automation

Mono-Coat® semi-permanent release agents allow for:

Low transfer

Better rubber-to-metal bonding

Reduced mould fouling

Better rubber flow

Various slip levels

Reduced downtime

Release Agents for the Rubber Industry.

www.chemtrend.com

Trennmittel für die Gummi-Industrie.Mono-Coat® semi-permanente Trennmittel sorgen für:

Geringen Übertrag

Bessere Gummi-Metall-Verbindung

Geringere Formverkrustung

Besseren Gummifluss

Verschiedene Gleitfähigkeiten

Verringerte Stillstandzeiten

Desma - Handbuch 2013 - Final.indd 1 18.09.2013 09:50:01

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Ideas and solutions in rubber compoundingGummiwerk KRAIBURG GmbH & Co. KG

Our strengths are your advantage!

We are your experienced partner and offer personal on-site support.

Gummiwerk KRAIBURG GmbH & Co. KGwww.kraiburg-rubber-compounds.com

Cooperative RELATIONSHIP

DESMA Anzeige 08-2014_D_GB.indd 1 08.08.2014 08:25:37

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IMprInT BASiCS Of COlD runnEr tEChnOlOgy

Design / layout:monopage – strategic communications designwww.monopage.info

Author:© Klöckner DESMA Elastomertechnik gmbh www.desma.biz

publisher:© Klöckner DESMA Elastomertechnik gmbhwww.desma.biz | nominal charge 20 €1. Print run, October 2014, fridingen: 1,000 copies | En

All rights reserved, especially the right on duplication and distribution as well as the translation. it is strictly prohibited to copy or reproduce any part of this publication without the written permission of the publisher or the author. neither it’s allowed to duplicate, assimilate or distribute any part of the book with any electronic system.

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Phone +49 7463 834-0fax +49 7463 834-159info@desma.bizwww.desma.biz

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