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BASicS of ElAStoMEr injEction MoulDing

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DESMA MAnuAl

BASicS of ElAStoMEr injEction MoulDing

2. Print run, March 2014 | En

DESMA MAnuAl | PrEfAcE | 5

1. ProjEct EnginEEring

2. MAtEriAl 2.1 Vulcanization2.2 compound test

3. ProDuction MEthoDS3.1 Vulca-presses (cM)3.2 transfer presses (tM)3.3 injection moulding (iM)3.4 injection compressing moulding (icM)3.5 itM-Procedure

4. injEction MoulD4.1 Vacuum4.2 inserts4.3 Bumping

5. injEction MoulDing MAchinES5.1 temperature control5.2 injection unit 5.2.1 Material feeding 5.2.2 general designs 5.2.3 current DESMA designs 5.2.4 non-return value 5.2.5 cleaning / compound change

DESMA realizes turnkey machines and systems for the production of rubber and sili-cone moulded parts. Simultaneously we also open up access to valuable knowledge for you as a user and for elastomer processing companies.

How to have injection moulding machines and processes under control – successfully! the DESMA manual about the basics of injection moulding provides you with an overall picture. this is comprehensive know-how available for direct use in your work: up-to-date, compact and especially clear with many graphics and dia-grams.

A smooth and safe production. Even with the latest technologies. You can get informed about the basic knowledge of project engineering and materials, production and moulds, but also about all DESMA machines and innovations and their successful use in the optimized injection moulding process. contents from practice for practice that not only industry newcomers and trainees can take advantage of, but experi-enced specialist as well who can update and selectively expand their skills.

We provide you with further support for your work by way of DESMA training offers and the forward-looking DESMA e-training: www.e-training.desma.biz

The team DESMA wishes you good success!

tABlE of contEntS

PrEfAcE

  »There is probably no other inert substance, the properties    of which excite in the human mind an equal amount of curiosity, surprise, and admiration than those of gum elastic.«

Charles Goodyear5.3 clamping unit 5.3.1 clamping 5.3.2 current DESMA designs 5.3.3 Protective closing function/ Mould protection

6. ProcESS control 6.1 influencing variables6.2 typical article defects, causes and countermeasures 6.2.1 insufficient fillling (insufficient inner cavity pressure) 6.2.2 overmoulding/ flash 6.2.3 insufficient cross-linking 6.2.4 inclusion of foreign particles 6.2.5 Scorch (premature start of cross-linking) 6.2.6 gas entrapping 6.2.7 Mould contamination 6.2.8 Demoulding fault

7. ADjuStMEnt StrAtEgY/ PArAMEtEr oPtiMizAtion

8. ProjEct PArtnErS

06

080810

121212131415

16181919

202224

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363641

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DESMA MAnuAl | ProjEct EnginEEring | 76 | ProjEct EnginEEring | DESMA MAnuAl

111. ProjEct EnginEEring

Planning a mould part production typically begins with the con-sideration which manufacturing concept or automation level would be ideally suited in the specific case. the type of article, the envisaged production quantity as well as raw material costs (elastomer compound) are decisive fac-tors when taking one’s choice. it is always the objective to achieve optimal article quality at minimum manufacturing costs. the comparative calculation must therefore not lack the costs for energy, maintenance, waste and the like.

Quick answer with DESMA CoolAppWhether and when the usage of a cold runner system is profi-table can be swiftly determined with DESMA CoolApp. this CoolApp application developed by DESMA and free available allows for waste savings to be easily calculated when using a cold runner system. these savings are calculated automatedly by selecting the adequate cold runner and amortization period

is exactly defined. A comprehensive program for article calculation and cavity layout is also made available and thus completes its efficiency.

Almost simultaneously the precise compound recipe is being determined. Above all, the material has to ensure technical product requirements, but also must be easily to process and affordable. it is important that the processing properties of the individual material batches do not strongly fluctuate.

As soon as an appropriate manufacturing concept and an appropriate compound recipe are found, the injection mould and the required machine can be elaborated respectively de-signed as second step.

After having completed all components, the exact (optimum) process control is established by way of injection tests in the course of which the fine-tuning of the injection mould is also carried out – e.g. optimization of the material distribution onto the individual mould cavities, of injection and/or venting.

compound, mould, machine and process control eventually determine product quality, manufacturing costs and hence profitability of production. only when these factors are opti-mally synchronized, a perfect result can be expected.

BASE polyMEr (ruBBEr TypE) MnE-Monic SpEciAl propErTiES

natural rubber nr heavy mechanical loads possible

Ethylene-propylene-diene rubber EPDM Water- and weather-resistant

nitrile-butadiene rubber nBr oil-resistant

Butyl rubber iir gas-tight

fluorine rubber fPM gas-tight, high general resistance

Silicone rubber VMQ Weather-, water-, oil and heat-resistant

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

Processingproperties?Batch variations?

Runner system?No. of mould cavities?Layout?

Output?Repeat accuracy?Equipment?

Is correct machine operating point set?Variations in operating time or temperature?

Elastomer Mould

Machine Process control

Manufacturing costsMechanical propertiesService Life

Productquality

CoolApp

Apart from the web application, an especially developed Apple iPad version can be found at www.desma.biz. or simply scan the Qr code on the left!

i

222. MAtEriAl

2.1 VulcAnizATion

Various additions have to be added to the rubber base material (base polymer) in order to be able to produce an elastic and long-life end product. only the addition of a cross-linking agent (sulfur, peroxide, etc.) makes the processing to the elas-tic end product (vulcanisate) possible. other substances improve resistance to wear and aging stability. the processing properties as well can be optimized by way of suitable addi-tions. the workable material is therefore called „elastomer compound“. if not being cross-linked and at ambient tempera-ture, consistency of this compound varies between viscous (lSr silicone), plasticine-like (solid silicone) and solid (rubber).

With increasing temperature, the flowability of the compound improves almost proportionally. however, the heat input also reduces the latent period after which the chemical cross-lin-king (vulcanization) starts. in this process, solid compounds (cross-linking points) between the individual macro molecules of the base polymer gradually develop. this drastically reduces the flowability of the mass, and the material response gradu-ally changes from plastic to elastic. this reaction starts earlier and develops faster at higher temperatures. Stopping the heat input permits the cross-linking reaction to be aborted prema-turely. the maximum possible cross-linking density (= 100 % cross-linking degree) is limited by the compound recipes / the cross-linking agent in the compound.

to avoid cross-linking before or during cavity filling, „retar-ders“ are added to the compound. After the mould has been filled, however, the reaction shall start and progress as fast as possible. „Accelerators“, that take effect with the cross-linking reaction, help here. the required vulcanization or cure time

thus depends on the compound recipe, the mass temperature curve, and the required degree of vulcanization. With thick-walled products, in particular, you must bear in mind that the cross-linking process continues after demoulding for a short while (while the product is cooling down), since a lot of heat is still stored in the product. With a medium wall thickness, this „postvulcanization“ is approximately 10%. to achieve the requi-red final quality, the products can also be post-vulcanized or fully cured in a curing oven. Due to the lower machine hour rate, this frequently results in lower costs. the vacuum oven also permits specific degassing.

37 % Naturalrubber (NR)

35 % Filler (e.g. soot, determines product hardness)Source: Fa. Bayer

1 % Flow promoter(e.g. mineral oil, lowers viscositiy during processing)

1 % Retarding agent/accelerator(control start and speed of vulcanization)

7 % Protective agent (increases resistance/service life)

7 % Cross-lin-king agent(e.g. sulphur, enables vulcanization)

12 % Styrene-Butadie-ne Rubber (SBR)

5min 90min 8h Time

Mass temperature

Flowable compound,not cross-linked

180 °C

120 °C

60 °C

Compound not cross-linked, but not flowable (too cold)

Over-vulcanized(risk of reversion!)

Requested state of vulcanization90 – 100 %

Scorched1 – 90 %

20 °Cnot cross-linked

~ 80 °Cnot cross-linked

scorched

fully cured

over-vulcanized(reversion)

1min

70 % 100 %

Compression set

Hardness

State of vulcanization

Tear resistance

Test

feat

ure

(qua

lity)

Dynamicmodule

Static module

Tear propagation resistance

DESMA MAnuAl | MAtEriAl | 98 | MAtEriAl | DESMA MAnuAl

unstressed

unstressed after stress

NON-CROSS-LINKED COMPOUND:mainly plastic

VULCANIZED PRODUCT:almost purely elastic

stressed

after stressstressed

2.2 coMpounD TEST

Vulcameter Test (MDr)Standard test procedure for production release after the com-pound has been produced.

• rheological and precuring behaviour at constant temperature

• the small amplitude and low frequency produce only minimum shearing / friction

• corresponds to the process flow in the cM process (vulca-presses)

Since the mass temperature development in injection moul-ding is not constant, and the shear rate is much higher, the determined data cannot be used directly for setting the injec-tion moulding machine.

however, the torque curve and a little experience permit at least the approximate processing properties of a compound to be assessed. Such a statement is possible for the following points:

a) flowability during injection (necessary pressure)b) Processing time (max. injection time)c) Vulcanization rate (necessary cure time)

the known cure time optimization systems / cure time calcula-tors also use (among other things) cure-meter data to maintain the article quality at a constant level, even at changing produc-tion conditions.

Driving motor

TORQUE MEASUREMENT

180 °C

180 °C

Driving motor

180 °C

180 °C

Compound test (20 °C)

Results in torque curve(„vulcameter curve“)

180 °C

20 °CTimet 100t 90t 0

Mas

s te

mpe

ratu

re

Torq

ue

100 %

90 %

0 %

b

α

Maximum

Minimuma

c

Incubation period

a) Flowabilty b) Processing timec) Vulcanization rate

Measuring mixers (from Brabender, for example)the measuring mixer is another, less known, test method. its structure is very similar to the compounder. the mass tempe-rature can thus be measured exactly during the test. the high-er resolution permits changes to be detected that are still in the range of the measuring fluctuations of the cure-meter.

Drive with torque measurement

Contra-rotating mixer arms(~60 U/min)

Feed throat

Temperature-controlled chamber

(~130 °C)

Temperature-controlled chamber(~130 °C)

Mass temperature sensorGear

22DESMA MAnuAl | MAtEriAl | 1110 | MAtEriAl | DESMA MAnuAl

333. ProDuction MEthoDS

1. insert the cold compound into the mould cavity2. closing and pressing of the mould (cavity filling)3. Vulcanization4. open the mould, demould the article, cleaning the split lines

1. insert cold compound into the transfer pot2. closing and pressing of the mould (cavity filling)3. Vulcanization 4. open the mould, demould the article and transfer sheet, cleaning

with hot runner1. closing and pressing of the mould 2. injection process (cavity filling) 3. During vulcanization time: plasticizing and dosing of the compound4. open the mould, demould the article and runner, cleaning

with cold runner block1. closing and pressing of the mould2. injection process (cavity filling)3. During vulcanization: plasticizing and dosing the compound4. open the mould, demould the article and runner, cleaning

3.1 VulcA-prESSES (cM procEDurE)

3.2 TrAnSfEr prESSES (TM procEDurE)

3.3 injEcTion MoulDing (iM procEDurE)

1 2 3 4180 °C

BEnEfiTS DiSADVAnTAgES

low investment costs Very long cycle time

Simple technique irregular cross-linking

high number of cavities possible reworking necessary

Small compound shearing high waste proportion (flash)

Blank preparation necessary

1 2 3 4180 °C

BEnEfiTS DiSADVAnTAgES

Shorter cycle time More complex moulding techniques

More regular cross-linking higher costs

high number of cavities possible high waste proportion (transfer sheet)

low-flash articles possible

BEnEfiTS DiSADVAnTAgES

Very short cycle time high investment costs

regular cross-linking lower possible number of cavaties

Automatic intake and dosing Without crB: much waste

Articles without reworking possible,

With FlowControl cold runner block without waste!

1 2 3 4

20 °C

180 °C

1 2 3 4

180 °C

20 °C

DESMA MAnuAl | ProDuction MEthoDS | 1312 | ProDuction MEthoDS | DESMA MAnuAl

DESMA MAnuAl | ProjEct PArtnErS | 57

8

8. thiS ProjEct WAS SuPPortED BY thE folloWing coMPAniES

production locations worldwide

5 servicestations andagencies worldwide

35

Ideas and solutions in rubber compounding

Well, that´s one way of tryingto increase your success.

Or you choose KRAIBURG! This way you can be sure you’ve made the perfect decision.

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DESMA Anzeige 08-2013.indd 1 01.08.2013 14:20:47

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DESMA - B&RTechnology partnershipfor elastomer machine automation

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

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

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Balluff position measurement technology means the highest precision with different operating principles. For industrial applications. For reliable function. Contactless. Wear-free. From position detection to distance measure-ment, take advantage of high quality – both fl exible and cost-oriented.

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iMprinT BASicS of ElAStoMErinjEction MoulDing

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 Eur2. Print run, March 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 book without the writ-ten 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.

PWS develops sustainable solutions in pro-

cess and automation technology for various

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We support our customers from the fi rst

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of production. They can thus count on high

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wide. Within the SMS group PWS is part of

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leader in the heavy machinery and plant

engineering.

PUTTING THE CUSTOMER’S NEEDS FIRST: PROCESS AUTOMATION TECHNOLOGY FOR YOUR SUCCESS

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Individual confi gurations State of the art technologyIntuitive operating concepts

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klöckner DESMAElastomertechnik gmbHAn der Bära78567 fridingen, germany

Phone +49 7463 8340fax +49 7463 834159info@desma.bizwww.desma.biz

just scan it and get directly to our website!

Klöckner DESMA Elastomertechnik gmbh